Scisoft

Time Travel

2009-08-30T22:42:00.005+05:30

I was surfing the net the other day when i came acroos this video. Its great! Have a glance at it.

[Video]

Now thats what i call an explaination!Especially the tricky one."Take a piece of paper , Draw two dots on it, and fold it till those two dots meet and you'll get a wormhole!"

Seems so practical, but it isn't is it?. Thats the way i like physics, you get an explaination for every mystery in it :p.

Atlantis is no mystery but a sign of human evolution?

2009-08-27T22:56:00.000+05:30

The other day, i was thinking about atlantis when something suddenly stroke my mind. is it man itself who after evolving enough in the future to make a timemachine, decided to travel back to past due to which he left some traces?. Well time is always a mysterious dimension.

I don’t know whether the theory is already proposed or not, but i just wanted to share what i thought of it for a minute.

DOOM'S DAY part II

2008-12-11T22:17:00.003+05:30

Hello friends the fact that I am going to reveal is a true one and please do read with patience. This info was collected by me on my interest and is presented to you.

This is a thread that I’m posting to tell narrate you the end of this world on the doom’s day i.e., DECEMBER, 12, 2012. I’m gonna tell you the different auricles and predictions of different people of our ancient world on this topic.

DOOM’S DAY

ANCIENT MAYAN:

Ancient Mayan civilization was one of the greatest civilizations on earth to flourish. They were experts in predicting the astronomical events and eclipses and also many more events. They always considered TIME as their factor of life. They tried to be victorious over it and devised many Techniques for that. On there observations for several or may be thousands of years, they devised a Mayan calendar for more than 6000 years which is based on the lunar and solar cycles and other heavenly bodies.

The remarkable thing about this calendar was that it even calculated the several heavenly cycles with their specific dates and also time with precision. This Mayan calendar had also one specialty, it could calculate and able to locate the doom days that were repeated every 12 years which were absolutely right like the conquest of conquistadors into Mayan, the French civil war, the two world wars etc.They were predicted by ancient Mayan priests

And last but not the least; it also predicted the end of the world on DEC 12 2012. The more astonishing explanation of them was that, on that day the earth, the sun and the black hole that lie at the centre of the Milky Way galaxy would align in a straight line by which there would be an inversion of poles i.e., the North Pole will become south and vice versa. This would occur every 25000 years as a cycle. At this moment the magnetic field will be inverted and the earth will suffer a severe catastrophic disaster.

This theory is not a false one, even the NASA has agreed with this statement and is supportive for this statement. Last time when it had occurred the earth has suffered a severe loses in its biosphere and there were many physiological changes on the earth. This is one of the predictions’ of the DOOM’S DAY.

I CHING:

I Ching is an ancient book that was written by I Ching an ancient Chinese emperor on the predictions. He was also an expert in predicting the future by his unusual method. In this method he used to toss three coins and after that he used to note down the combination of the heads and the tails and used to note them in the form of the continuous and discontinuous lines. He used to draw six lines totaling the combinations to 64.Each combination has a unique auricle and used to tell the future of a person. When modern investigators observed these combinations they noticed a unique pattern. When these combinations were graphed, taking time as a scale they were shocked to see the result. There were some ups and downs in the graph; the downs represented the global catastrophes like world wars etc. But the graph seemed to be coming to an end on an unusual date which on investigations reported to be……DEC 12 2012 the DOOMS DAY.

DOLPHIN PRISTESS:

A town in Greece called dolphin holds a very great mystery of dooms day. The priestess of Apollo God is the predictors this time. In the ancient Greek some people used to consult them for their successful prophecies. They predicted the birth of Alexander and many more historical events much earlier. They also predicted the end of world by severe global calamities. This day is imagined as doom’s day, as predicted by others.

MERLIN:

He was a very mysterious wizard of his time. He used to live in ancient England. He used to wander in forests and foresee the future. He used to give free predictions to the king of England. He predicted the fall of Charles accurately. He predicted that the London would taste the bloodshed and world would be striving in disasters. He predicted this day would be no other than the December 21.

CIVIL:

Civil is an elderly women of ancient Rome who was said to be the first Christian. She used to live in Naples of Italy in a cave and predicted many more things as other fortune tellers do. She predicted the birth of Christ and the emerging empire Constantine. She gave a prediction that the world would suffer global calamities and ultimately it would come to an end. This day was said to be December 21 2012. She predicted the fall of Roman Empire by Persians.

MOTHER SHIFTAN:

There is no strong proof that she existed in real or not. But the writer of this series of prophesies has existed in late 16^th century. He was believed to be in London. Although, he gave prophesies on the name of Mother Shift an, he predicted much real ones like world wars and the inventions of modern things. He also predicted the deadly end of the world on the doom’s day.

HOLY BIBLE:

Holy bible was also a good proof for the real auricles. In Bible, according to book of revelation there were many things in the future that changed the world. The author of this world John Chad predicted many nuclear war fares and bio-nuclear weapons using in the wars. He gave the prediction that ‘666’ would destroy the entire world. This number is believed to be the name of the person like terrorist who is trying to destroy the world. He predicted that the people cry and suffer the nature’s anger on the doom’s day.

HOPEE:

He was a tribal in American southwest. He used to perform great spiritual practices by which he could be able to predict the future. According to him, the world has been destroyed 3 times and now there is existence of 4^th one. But he said that this 4^th world will be destroyed on doom’s day an there would be the creation of 5^th world. He explained this by saying that the sun will get brighter and sea levels will rise higher.

BLACK ELB:

He was a South American in 1890. He used to get vivid dreams of the future. He predicted that there would be a global war fare by which the world gets destroyed.

WEB BOT SEQUENCE:

Unlike others, this one is a new theory. This theory is dependent on internet. The Web Bot project was started in 1998 to keep a look on different wards in the World Wide Web. In June 2001, the Web Bat project designers gathered different phrases from these wards and predicted the future as the WTC incident. This picking up the phrases has resulted has been done on several incidents such as the American war on Iraq etc.The modern observation of these phrases revealed an death blowing truth about the end of the earth on DEC 12 2012.

COMET COLLISION:

Besides all these there is a threat to our home planet from the extra terrestrial bodies like comets, meteorites etc.There are more than 1000 comets that were identified which can impact the earth with its huge mass. There is also a comet whose path has intercepted ours on DEC 12 2012.The scientists are saying that this comet is 25 times bigger than the comet that resulted in the extinction of the Dinosaurs. The preparations have already gone on the way to save its threat from us.

According to me, the time is never the same always. It has made our humans to suffer many times as well. These predictions are from all over the world and are not of same time, and not of same place and are not written by a same person as well .So we can’t neglect these predictions to be a thrash and we may not even believe them to be true .We may all underestimate our ancients on this….but the modern scientists had already agreed about the fact of earth’s end. Are these Predictions are true???…..Will the earth be destroyed on the DOOM’S DAY???….is it the end of our home planet???...is it the end of the human race on earth which has dominated the whole earth with its intellect???......Or will the man be able to escape from this DOOM’S DAY with his remarkable intelligence????.......Only the time can decide……..

….ABHIJEET

Drake's Equation

2008-10-30T20:20:00.003+05:30

The Drake equation (also sometimes called the "Green Bank equation", the "Green Bank Formula," or often erroneously labeled the "Sagan equation") is a famous result in the speculative fields of exobiology and the search for extraterrestrial intelligence (SETI).
This equation was devised by Dr. Frank Drake (now Professor Emeritus of Astronomy and Astrophysics at the University of California, Santa Cruz) in 1960, in an attempt to estimate the number of extraterrestrial civilizations in our galaxy with which we might come in contact. The main purpose of the equation is to allow scientists to quantify the uncertainty of the factors which determine the number of such extraterrestrial civilizations.

History
Frank Drake formulated his equation in 1960 in preparation for the Green Bank meeting. This meeting, held at Green Bank, West Virginia, established SETI as a scientific discipline. The historic meeting, whose participants became known as the "Order of the Dolphin," brought together leading astronomers, physicists, biologists, social scientists, and industry leaders to discuss the possibility of detecting intelligent life among the stars.
The Green Bank meeting was also remarkable because it featured the first use of the famous formula that came to be known as the "Drake Equation". This explains why the equation is also known by its other names with the "Green Bank" designation. When Drake came up with this formula, he had no notion that it would become a staple of SETI theorists for decades to come. In fact, he thought of it as an organizational tool — a way to order the different issues to be discussed at the Green Bank conference, and bring them to bear on the central question of intelligent life in the universe. Carl Sagan, a great proponent of SETI, utilized and quoted the formula often and as a result the formula is often mislabeled as "The Sagan Equation". The Green Bank Meeting was commemorated by a plaque.
The Drake equation is closely related to the Fermi paradox in that Drake suggested that a large number of extraterrestrial civilizations would form, but that the lack of evidence of such civilizations (the Fermi paradox) suggests that technological civilizations tend to destroy themselves rather quickly. This theory often stimulates an interest in identifying and publicizing ways in which humanity could destroy itself, and then countered with hopes of avoiding such destruction and eventually becoming a space-faring species. A similar argument is The Great Filter,^[1] which notes that since there are no observed extraterrestrial civilizations, despite the vast number of stars, then some step in the process must be acting as a filter to reduce the final value. According to this view, either it is very hard for intelligent life to arise, or the lifetime of such civilizations must be depressingly short.
The grand question of the number of communicating civilizations in our galaxy could, in Drake's view, be reduced to seven smaller issues with his equation.

The equation

The Drake equation states that:

where:

N is the number of civilizations in our galaxy with which communication might be possible;

and

R^* is the average rate of star formation in our galaxy

f_p is the fraction of those stars that have planets

n_e is the average number of planets that can potentially support life per star that has planets

f_ℓ is the fraction of the above that actually go on to develop life at some point

f_i is the fraction of the above that actually go on to develop intelligent life

f_c is the fraction of civilizations that develop a technology that releases detectable signs of their existence into space

L is the length of time such civilizations release detectable signals into space.

Alternative expression

The number of stars in the galaxy now, N^*, is related to the star formation rate R^* by

where T_g is the age of the galaxy. Assuming for simplicity that R^* is constant, then N^* = R^* T_g and the Drake equation can be rewritten into an alternate form phrased in terms of the more easily observable value, N^*.

R factor

One can question why the number of civilizations should be proportional to the star formation rate, though this makes technical sense. (The product of all the terms except L tells how many new communicating civilizations are born each year. Then you multiply by the lifetime to get the expected number. For example, if an average of 0.01 new civilizations are born each year, and they each last 500 years on the average, then on the average 5 will exist at any time.) The original Drake Equation can be extended to a more realistic model, where the equation uses not the number of stars that are forming now, but those that were forming several billion years ago. The alternate formulation, in terms of the number of stars in the galaxy, is easier to explain and understand, but implicitly assumes the star formation rate is constant over the life of the galaxy.

Expansions

Additional factors that have been described for the Drake equation include:

n_r or reappearance factor: The average number of times a new civilization reappears on the same planet where a previous civilization once has appeared and ended

f_m or METI factor: The fraction of communicative civilizations with clear and non-paranoid planetary consciousness (that is, those which actually engage in deliberate interstellar transmission)

With these factors in mind, the Drake equation states:

Reappearance factor

The equation may furthermore be multiplied by how many times an intelligent civilization may occur on planets where it has happened once. Even if an intelligent civilization reaches the end of its lifetime after, for example, 10.000 years, life may still prevail on the planet for billions of years, availing for the next civilization to evolve. Thus, several civilizations may come and go during the lifespan of one and the same planet. Thus, if n_r is the average number of times a new civilization reappears on the same planet where a previous civilization once has appeared and ended, then the total number of civilizations on such a planet would be (1+n_r), which is the actual factor added to the equation.
The factor depends on what generally is the cause of civilization extinction. If it is generally by temporary inhabitability, for example a nuclear winter, then n_r may be relatively high. On the other hand, if it is generally by permanent inhabitability, such as stellar evolution, then n_r may be almost zero.
In the case of total life extinction, a similar factor may be applicable for f_ℓ, that is, how many times life may appear on a planet where it has appeared once.

METI factor

Alexander Zaitsev said that to be in a communicative phase and emit dedicated messages are not the same. For example, we, although being in a communicative phase, are not a communicative civilization; we do not practice such activities as the purposeful and regular transmission of interstellar messages. For this reason, he suggested introducing the METI factor (Messaging to Extra-Terrestrial Intelligence) to the classical Drake Equation.

Historical estimates of the parameters

Considerable disagreement on the values of most of these parameters exists, but the values used by Drake and his colleagues in 1961 were:

R* = 10/year (10 stars formed per year, on the average over the life of the galaxy)
f_p = 0.5 (half of all stars formed will have planets)
n_e = 2 (stars with planets will have 2 planets capable of supporting life)
f_l = 1 (100% of these planets will develop life)
f_i = 0.01 (1% of which will be intelligent life)
f_c = 0.01 (1% of which will be able to communicate)
L = 10,000 years (which will last 10,000 years)

Drake's values give N = 10 × 0.5 × 2 × 1 × 0.01 × 0.01 × 10,000 = 10.
The value of R* is determined from considerable astronomical data, and is the least disputed term of the equation; f_p is less certain, but is still much firmer than the values following. Confidence in n_e was once higher, but the discovery of numerous gas giants in close orbit with their stars has introduced doubt that life-supporting planets commonly survive the creation of their stellar systems. In addition, most stars in our galaxy are red dwarfs, which flare violently, mostly in X-rays—a property not conducive to life as we know it (simulations also suggest that these bursts erode planetary atmospheres). The possibility of life on moons of gas giants (such as Jupiter's moon Europa, or Saturn's moon Titan) adds further uncertainty to this figure.
Geological evidence from the Earth suggests that f_l may be very high; life on Earth appears to have begun around the same time as favorable conditions arose, suggesting that abiogenesis may be relatively common once conditions are right. However, this evidence only looks at the Earth (a single model planet), and contains anthropic bias, as the planet of study was not chosen randomly, but by the living organisms that already inhabit it (ourselves). Whether this is actually a case of anthropic bias has been contested, however; it might rather merely be a limitation involving a critically small sample size, since it is argued that there is no bias involved in our asking these questions about life on Earth. Also countering this argument is that there is no evidence for abiogenesis occurring more than once on the Earth—that is, all terrestrial life stems from a common origin. If abiogenesis were more common it would be speculated to have occurred more than once on the Earth. In addition, from a classical hypothesis testing standpoint, there are zero degrees of freedom, permitting no valid estimates to be made.
One piece of data which would have major impact on f_l is the discovery of life on Mars or another planet or moon. If life were to be found on Mars which developed independently from life on Earth it would imply a higher value for f_l. While this would improve the degrees of freedom from zero to one, there would remain a great deal of uncertainty on any estimate due to the small sample size, and the chance they are not really independent.
Similar arguments of bias can be made regarding f_i and f_c by considering the Earth as a model: intelligence with the capacity of extraterrestrial communication occurs only in one species in the 4 billion year history of life on Earth. If generalized, this means only relatively old planets may have intelligent life capable of extraterrestrial communication. Again this model has a large anthropic bias and there are still zero degrees of freedom. Note that the capacity and willingness to participate in extraterrestrial communication has come relatively "quickly", with the Earth having only an estimated 100,000 year history of intelligent human life, and less than a century of technological ability.
f_i, f_c and L, like f_l, are guesses. Estimates of f_i have been affected by discoveries that the solar system's orbit is circular in the galaxy, at such a distance that it remains out of the spiral arms for hundreds of millions of years (evading radiation from novae). Also, Earth's large moon may aid the evolution of life by stabilizing the planet's axis of rotation. In addition, while it appears that life developed soon after the formation of Earth, the Cambrian explosion, in which a large variety of multicellular life forms came into being, occurred a considerable amount of time after the formation of Earth, which suggests the possibility that special conditions were necessary. Some scenarios such as the Snowball Earth or research into the extinction events have raised the possibility that life on Earth is relatively fragile. Again, the controversy over life on Mars is relevant since a discovery that life did form on Mars but ceased to exist would affect estimates of these terms.
The astronomer Carl Sagan speculated that all of the terms, except for the lifetime of a civilization, are relatively high and the determining factor in whether there are large or small numbers of civilizations in the universe is the civilization lifetime, or in other words, the ability of technological civilizations to avoid self-destruction. In Sagan's case, the Drake equation was a strong motivating factor for his interest in environmental issues and his efforts to warn against the dangers of nuclear warfare.
By plugging in apparently "plausible" values for each of the parameters above, the resultant expectant value of N is often (much) greater than 1. This has provided considerable motivation for the SETI movement. However, we have no evidence for extraterrestrial civilizations. This conflict is often called the Fermi paradox, after Enrico Fermi who first asked about our lack of observation of extraterrestrials, and motivates advocates of SETI to continually expand the volume of space in which another civilization could be observed.
Other assumptions give values of N that are (much) less than 1, but some observers believe this is still compatible with observations due to the anthropic principle: no matter how low the probability that any given galaxy will have intelligent life in it, the universe must have at least one intelligent species by definition otherwise the question would not arise.
Some computations of the Drake equation, given different assumptions:

R* = 10/year, f_p = 0.5, n_e = 2, f_l = 1, f_i = 0.01, f_c = 0.01, and L = 50,000 years

N = 10 × 0.5 × 2 × 1 × 0.01 × 0.01 × 50,000 = 50 (so 50 civilizations exist in our galaxy at any given time, on the average)

But a pessimist might equally well believe that life seldom becomes intelligent, and intelligent civilizations do not last very long:

R* = 10/year, f_p = 0.5, n_e = 2, f_l = 1, f_i = 0.001, f_c = 0.01, and L = 500 years

N = 10 × 0.5 × 2 × 1 × 0.001 × 0.01 × 500 = 0.05 (we are probably alone)

Alternatively, making some more optimistic assumptions, and assuming that 10% of civilizations become willing and able to communicate, and then spread through their local star systems for 100,000 years (a very short period in geologic time):

R* = 20/year, f_p = 0.1, n_e = 0.5, f_l = 1, f_i = 0.5, f_c = 0.1, and L = 100,000 years

N = 20 × 0.1 × 0.5 × 1 × 0.5 × 0.1 × 100,000 = 5,000

Current estimates of the parameters

This section attempts to list best current estimates for the parameters of the Drake equation.
R* = the rate of star creation in our galaxy

Estimated by Drake as 10/year. Latest calculations from NASA and the European Space Agency indicates that the current rate of star formation in our galaxy is about 7 per year.

f_p = the fraction of those stars which have planets

Estimated by Drake as 0.5. It is now known from modern planet searches that at least 30% of sunlike stars have planets, and the true proportion may be much higher, since only planets considerably larger than Earth can be detected with current technology. Infra-red surveys of dust discs around young stars imply that 20-60% of sun-like stars may form terrestrial planets.

n_e = the average number of planets (satellites may perhaps sometimes be just as good candidates) which can potentially support life per star that has planets

Estimated by Drake as 2. Marcy, et al. notes that most of the observed planets have very eccentric orbits, or orbit very close to the sun where the temperature is too high for earth-like life. However, several planetary systems that look more solar-system-like are known, such as HD 70642, HD 154345, or Gliese 849. These may well have smaller, as yet unseen, earth sized planets in their habitable zones. Also, the variety of solar systems that might have habitable zones is not just limited to solar-type stars and earth-sized planets - it is now believed that even tidally locked planets close to red dwarves might have habitable zones, and some of the large planets detected so far could potentially support life - in early 2008, two different research groups concluded that Gliese 581d may possibly be habitable.^[7] ^[8] Since about 200 planetary systems are known, this implies n_e > 0.005.

Even if planets are in the habitable zone, however, the number of planets with the right proportion of elements may be difficult to estimate. Also, the Rare Earth hypothesis, which posits that conditions for intelligent life are quite rare, has advanced a set of arguments based on the Drake equation that the number of planets or satellites that could support life is small, and quite possibly limited to Earth alone; in this case, the estimate of n_e would be infinitesimal.

f_l = the fraction of the above which actually go on to develop life

Estimated by Drake as 1.

In 2002, Charles H. Lineweaver and Tamara M. Davis (at the University of New South Wales and the Australian Centre for Astrobiology) estimated f_l as > 0.13 on planets that have existed for at least one billion years using a statistical argument based on the length of time life took to evolve on Earth. Lineweaver has also determined that about 10% of star systems in the Galaxy are hospitable to life, by having heavy elements, being far from supernovae and being stable themselves for sufficient time.

f_i = the fraction of the above which actually go on to develop intelligent life

Estimated by Drake as 0.01.

f_c = the fraction of the above which are willing and able to communicate

Estimated by Drake as 0.01.

L = the expected lifetime of such a civilization for the period that it can communicate across interstellar space

Estimated by Drake as 10,000 years.

In an article in Scientific American, Michael Shermer estimated L as 420 years, based on compiling the durations of sixty historical civilizations. Using twenty-eight civilizations more recent than the Roman Empire he calculates a figure of 304 years for "modern" civilizations. It could also be argued from Michael Shermer's results that the fall of most of these civilizations was followed by later civilizations which carried on the technologies, so it's doubtful that they are separate civilizations in the context of the Drake equation. Furthermore since none could communicate over interstellar space, the value of L here could also be argued to be zero.

The value of L can be estimated from the lifetime of our current civilization from the advent of radio astronomy in 1938 (dated from Grote Reber's parabolic dish radio telescope) to the current date. In 2008, this gives an L of 70 years. However such an assumption would be erroneous. 70 for the value of L would be an artificial minimum based on Earth's broadcasting history to date and would make unlikely the possibility of other civilizations existing. 10,000 for L is still the most popular estimate

Values based on the above estimates,

R* = 7/year, f_p = 0.5, n_e = 2, f_l = 0.33, f_i = 0.01, f_c = 0.01, and L = 10000 years

result in

N = 7 × 0.5 × 2 × 0.33 × 0.01 × 0.01 × 10000 = 2.31

Criticisms

Since there exists only one known example of a planet with life forms of any kind, several terms in the Drake equation are largely based on conjecture. However, based on Earth's experience, some scientists view intelligent life on other planets as possible and the replication of this event elsewhere is at least plausible. In a 2003 lecture at Caltech, Michael Crichton, a science fiction author, stated that, "Speaking precisely, the Drake equation is literally meaningless, and has nothing to do with science. I take the hard view that science involves the creation of testable hypotheses. The Drake equation cannot be tested and therefore SETI is not science. SETI is unquestionably a religion."
However, actual experiments by SETI scientists do not attempt to address the Drake equations for the existence of extraterrestrial civilizations anywhere in the universe, but are focused on specific, testable hypotheses (i.e., "do extraterrestrial civilizations communicating in the radio spectrum exist near sun-like stars within 50 light years of the Earth?").
Another reply to such criticism is that even though the Drake equation currently involves speculation about unmeasured parameters, it stimulates dialog on these topics. Then the focus becomes how to proceed experimentally.

Try The Drake's Equation For Yourself -

http://www.activemind.com/Mysterious/Topics/SETI/drake_equation.html

source : Wikipedia

B-2 Spirit Stealth Bomber

2008-10-25T19:31:00.003+05:30

Specifications (B-2A Block 30)

Data from Pace, Globalsecurity

General characteristics

Crew: 2
Length: 69 ft (21.0 m)
Wingspan: 172 ft (52.4 m)
Height: 17 ft (5.18 m)
Wing area: 5,140 ft² (478 m²)
Empty weight: 158,000 lb (71.7 t)
Loaded weight: 336,500 lb (152.6 t)
Max takeoff weight: 376,000 lb (170.6 t)
Powerplant: 4× General Electric F118-GE-100 turbofans, 17,300 lbf (77 kN) each

Performance

Maximum speed: Mach 0.95 (525 knots, 604 mph, 972 km/h)
Range: 6,300 nmi (11,600 km, 6,450 mi)
Service ceiling 50,000 ft (15,200 m)
Wing loading: 67.3 lb/ft² (329 kg/m²)
Thrust/weight: 0.205

Armament

2 internal bays for 50,000 lb (22,700 kg) of ordnance.
- 80× 500 lb class bombs (Mk-82) mounted on Bomb Rack Assembly (BRA)
- 36× 750 lb CBU class bombs on BRA
- 16× 2000 lb class weapons (Mk-84, JDAM-84, JDAM-102) mounted on Rotary Launcher Assembly (RLA)
- 16× B61 or B83 nuclear weapons on RLA

Later avionics and equipment improvements allow B-2A to carry JSOW and GBU-28s as well. The Spirit is also designated as a delivery aircraft for the AGM-158 JASSM when the missile enters service.

The B-2 Spirit is a multi-role bomber capable of delivering both conventional and nuclear munitions.

Along with the B-52 and B-1B, the B-2 provides the penetrating flexibility and effectiveness inherent in manned bombers. Its low-observable, or "stealth," characteristics give it the unique ability to penetrate an enemy's most sophisticated defenses and threaten its most valued, and heavily defended, targets. Its capability to penetrate air defenses and threaten effective retaliation provide an effective deterrent and combat force well into the 21st century.

The blending of low-observable technologies with high aerodynamic efficiency and large payload gives the B-2 important advantages over existing bombers. Its low-observability provides it greater freedom of action at high altitudes, thus increasing its range and a better field of view for the aircraft's sensors. Its unrefueled range is approximately 6,000 nautical miles (9,600 kilometers).

The B-2's low observability is derived from a combination of reduced infrared, acoustic, electromagnetic, visual and radar signatures. These signatures make it difficult for the sophisticated defensive systems to detect, track and engage the B-2. Many aspects of the low-observability process remain classified; however, the B-2's composite materials, special coatings and flying-wing design all contribute to its "stealthiness."

The B-2 has a crew of two pilots, an aircraft commander in the left seat and mission commander in the right, compared to the B-1B's crew of four and the B-52's crew of five.

The B-2 is intended to deliver gravity nuclear and conventional weapons, including precision-guided standoff weapons. An interim, precision-guided bomb capability called Global Positioning System (GPS) Aided Targeting System/GPS Aided Munition (GATS/GAM) is being tested and evaluated. Future configurations are planned for the B-2 to be capable of carrying and delivering the Joint Direct Attack Munition (JDAM) and Joint Air-to-Surface Standoff Missile.

B-2s, in a conventional role, staging from Whiteman AFB, MO; Diego Garcia; and Guam can cover the entire world with just one refueling. Six B-2s could execute an operation similar to the 1986 Libya raid but launch from the continental U.S. rather than Europe with a much smaller, more lethal, and more survivable force.

Background

The B-2 development program was initiated in 1981, and the Air Force was granted approval in 1987 to begin procurement of 132 operational B-2 aircraft, principally for strategic bombing missions. With the demise of the Soviet Union, the emphasis of B-2 development was changed to conventional operations and the number was reduced to 20 operational aircraft, plus 1 test aircraft that was not planned to be upgraded to an operational configuration. Production of these aircraft has been concurrent with development and testing.

The first B-2 was publicly displayed on Nov. 22, 1988, when it was rolled out of its hangar at Air Force Plant 42, Palmdale, Calif. Its first flight was July 17, 1989. The B-2 Combined Test Force, Air Force Flight Test Center, Edwards Air Force Base, Calif., is responsible for flight testing the engineering, manufacturing and development aircraft as they are produced. Three of the six developmental aircraft delivered at Edwards are continuing flight testing.

Whiteman AFB, Mo., is the B-2's only operational base. The first aircraft, Spirit of Missouri, was delivered Dec. 17, 1993. Depot maintenance responsibility for the B-2 is performed by Air Force contractor support and is managed at the Oklahoma City Air Logistics Center at Tinker AFB, Okla.

The prime contractor, responsible for overall system design and integration, is Northrop Grumman's Military Aircraft Systems Division. Boeing Military Airplanes Co., Hughes Radar Systems Group and General Electric Aircraft Engine Group are key members of the aircraft contractor team. Another major contractor, responsible for aircrew training devices (weapon system trainer and mission trainer) is Hughes Training Inc. (HTI) - Link Division, formerly known as C.A.E. - Link Flight Simulation Corp. Northrop Grumman and its major subcontractor HTI, are responsible for developing and integrating all aircrew and maintenance training programs.

The Air Force is accepting delivery of production B-2s in three configuration blocks--blocks 10, 20, and 30. Initial delivery will be 6 test aircraft, 10 aircraft in the block 10 configuration, 3 in the block 20 configuration, and 2 in the block 30 configuration.

Block 10 configured aircraft provide limited combat capability with no capability to launch conventional guided weapons. The Block 10 model carries only Mk-84 2,000-pound conventional bombs or gravity nuclear weapons. B-2s in this configuration are located at Whiteman Air Force Base and are used primarily for training. Block 20 configured aircraft have an interim capability to launch nuclear and conventional munitions, including the GAM guided munition. The Block 20 has been tested with the Mk-84, 2,000-pound, general-purpose bombs and the CBU-87/B Combined Effects Munition cluster bombs (low-altitude, full-bay release).
Block 30 configured aircraft are fully capable and meet the essential employment capabilities defined by the Air Force. The first fully configured Block 30 aircraft, AV-20 Spirit of PENNSYLVANIA, was delivered to the Air Force on 07 August 1997. Compared to the Block 20, the Block 30s have almost double the radar modes along with enhanced terrain-following capability and the ability to deliver additional weapons, including the Joint Direct Attack Munition and the Joint Stand Off Weapon. Other features include incorporation of configuration changes needed to make B-2s conform to the approved radar signature; replacement of the aft decks; installation of remaining defensive avionics functions; and installation of a contrail management system.

All block 10, 20, and test aircraft are to eventually be modified to the objective block 30 configuration. This modification process began in July 1995 and is scheduled to be completed in June 2000.

The B-2 fleet will have 16 combat-coded aircraft by the second quarter of FY00,

Upgrades

Link-16 – Providing Line-of-Sight (LOS) data for aircraft-to-aircraft, aircraft-to-C2, and aircraft-to-sensor connectivity, Link-16 is a combat force multiplier that provides U.S. and other allied military services with fully interoperable capabilities and greatly enhances tactical Command, Control, Communication, and Intelligence mission effectiveness. Link-16 provides increased survivability, develops a real-time picture of the theater battlespace, and enables the aircraft to quickly share information on short notice (target changes). Connectivity – DoD requires survivable communications media for command and control of nuclear forces. To satisfy the requirement, the Air Force plans to deploy an advanced Extremely High Frequency (EHF) satellite communications constellation. This constellation will provide a survivable, high capability communication system. Based on favorable results from a funded risk reduction study, the B-2 will integrate an EHF communication capability satisfying connectivity requirements. Digital Engine Controller - The current analog engine controllers are high failure items, and without funding, ACC will be forced to ground aircraft beginning approximately FY08. Replacement of the engine controllers will improve the B-2’s performance and increase supportability, reliability, and maintainability. Computers/Processors - With advances in computer technology and increased demands on the system, the B-2’s computers will need to be replaced with state-of-the-art processors. Although reliable, maintaining the present processors will become increasingly difficult and costly.

Signature Improvements - The B-2’s signature meets operational requirements against today’s threats. As advanced threats proliferate, it will be prudent to investigate advanced signature reduction concepts and determine if it is necessary to improve the B-2’s low observable signature. CANDIDATE LONG TERM UPGRADES BEYOND FY 15 TOTAL The basis for the useful life of the B-2 includes data from initial Developmental Test and Evaluation analysis. Data indicates the aircraft should be structurally sound to approximately 40,000 flight hours using current mission profiles. Analysis further suggests that the rudder attachment points are the first structural failure item. The B-2 has not implemented an ASIP similar to the other bombers, and this makes it difficult to predict the economic service life and attrition rate. However, a notional projection, based on the B-52, predicts one aircraft will be lost each 10 years. This attrition rate, plus attrition due to service life, will erode the B-2 force below its requirement of 19 aircraft by 2027.

Tactical delivery tactics use patterns and techniques that minimize final flight path predictability, yet allows sufficient time for accurate weapons delivery. For conventional munitions. Bomb Rack Assembly (BRA) weapons delivery accuracies depend on delivery altitude. For a weapons pass made at 5,000 ft above ground level [AGL] or below, the hit criteria is less than or equal to 300 feet. For a weapons pass made above 5,000 feetAGL, the hit criteria is less than or equal to 500 feet. Similarly, Rotary Launcher Assembly (RLA) delivery of conventional or nuclear weapons (i.e. Mk-84, B-83, B-61) is altitude dependent. For a weapons pass made at 5,000 feet AGL or below, the hit criteria is less than or equal to 300 feet. For a weapons pass made above 5,000 ft AGL, the hit criteria is less than or equal to 500 feet. The hit criteria for a weapons pass made with GAM/ JDAM munitions is less than or equal to 50 feet.

Design

A close-up of a B-2

As with the B-52 Stratofortress and B-1 Lancer, the B-2 provides the versatility inherent in manned bombers. Like other bombers, its assigned targets can be canceled or changed while in flight, the particular weapon assigned to a target can be changed, and the timing of attack, or the route to the target can be changed while in flight. In addition, its low-observable, or "stealth", characteristics give it the ability to penetrate an enemy's most sophisticated anti-aircraft defenses to attack its most heavily defended targets.

The blending of low-observable technologies with high aerodynamic efficiency and large payload gives the B-2 significant advantages over previous bombers. Its range is approximately 6,000 nautical miles (11,100 km) without refueling. Also, its low-observation ability provides the B-2 greater freedom of action at high altitudes, thus increasing its range and providing a better field of view for the aircraft's sensors. It combines GPS Aided Targeting System (GATS) with GPS-aided bombs such as Joint Direct Attack Munition (JDAM). This uses its passive electronically scanned array APQ-181 radar to correct GPS errors of targets and gain much better than laser-guided weapon accuracy when "dumb" gravity bombs are equipped with a GPS-aided "smart" guidance tail kit. It can bomb 16 targets in a single pass when equipped with 1,000 or 2,000-pound bombs, or as many as 80 when carrying 500-lb bombs.

The B-2's stealth comes from a combination of reduced acoustic, infrared, visual and radar signatures, making it difficult for opposition defenses to detect, track and engage the aircraft. Many specific aspects of the low-observability process remain classified.

B-2 during aerial refueling over the Pacific Ocean. In-flight refueling capability gives the B-2 a range limited only by maintenance and crew endurance.

The B-2 represents a further advancement of technology exploited for the F-117. Pyotr Ufimtsev, whose theoretical work made the F-117 and B-2 possible, was hired by Northrop at one time. Additionally, the B-2's composite materials, special coatings and flying wing design (which reduces the number of leading edges) contribute to its stealth abilities. The B-2 uses radar absorbent material and coatings that require climate-controlled hangars for maintenance. The engines are buried within the wing to conceal the induction fans and hide their exhaust.

The B-2 has a crew of two: a pilot in the left seat, and mission commander in the right. The B-2 has a provision for a third crew member if required in the future. For comparison, the B-1B has a crew of four and the B-52 has a crew of five. B-2 crews have been used to pioneer sleep cycle research to improve crew performance on long flights. The B-2 is highly automated, and unlike two-seat fighters, one crew member can sleep, use a flush toilet or prepare a hot meal while the other monitors the aircraft.

The USAF has funded a project to upgrade the B-2s weapon control systems so new weapons can be used, including weapons intended to hit moving targets.

CV-22 Osprey

2008-10-20T21:27:00.001+05:30

The V-22 Osprey is a tiltrotor vertical/short takeoff and landing (VSTOL), multi-mission air-craft developed to fill multi-Service combat operational requirements. The MV-22 will replace the current Marine Corps assault helicopters in the medium lift category (CH-46E and CH-53D), contributing to the dominant maneuver of the Marine landing force, as well as supporting focused logistics in the days following commencement of an amphibious operation. The Air Force variant, the CV-22, will replace the MH-53J and MH-60G and augment the MC-130 fleet in the USSOCOM Special Operations mission. The Air Force requires the CV-22 to provide a long-range VTOL insertion and extraction capability. The tiltrotor design combines the vertical flight capabilities of a helicopter with the speed and range of a turboprop airplane and permits aerial refueling and world-wide self deployment.

Two 6150 shaft horsepower turboshaft engines each drive a 38 ft diameter, 3-bladed proprotor. The proprotors are connected to each other by interconnect shafting which maintains proprotor synchronization and provides single engine power to both proprotors in the event of an engine failure. The engines and flight controls are controlled by a triply redundant digital fly-by-wire system.

The airframe is constructed primarily of graphite-reinforced epoxy composite material. The composite structure will provide improved strength to weight ratio, corrosion resistance, and damage tolerance compared to typical metal construction. Battle damage tolerance is built into the aircraft by means of composite construction and redundant and separated flight control, electrical, and hydraulic systems. An integrated electronic warfare defensive suite including a radar warning receiver, a missile warning set, and a countermeasures dispensing system, will be installed.

BACKGROUND INFORMATION

The V-22 is being developed to meet the provisions of the April 1995 Joint Multi-Mission Vertical Lift Aircraft (JMVX) Operational Requirements Document (ORD) for an advanced vertical lift aircraft. The JMVX ORD calls for an aircraft that would provide the Marine Corps and Air Force the ability to conduct assault support and long-range, high-speed missions requiring vertical takeoff and landing capabilities.

Since entry into FSD in 1986, the V-22 T&E program has concentrated principally on engineering and integration testing by the contractors. Three periods of formal development test by Naval Air Warfare Center-Aircraft Division (NAWCAD) Patuxent River, plus OTA participation in integrated test team (ITT) activities at Patuxent River, have provided some insight into the success of the development effort. After transition to EMD in 1992, an integrated contractor/government test team conducted all tests until OT-IIA in 1994. Since then, two additional periods of OT&E have been conducted.

The first operational test period (OT-IIA) was performed by COMOPTEVFOR, with assistance from AFOTEC, from May 16 to July 8, 1994, and accomplished 15 hours of actual flight test operations, within an extremely restricted flight envelope. The Navy, with Air Force support, published a joint evaluation report addressing most mission areas the V-22 is to perform.

OT-IIB was conducted from September 9, to October 18, 1995, and comprised 10 flight hours in 18 OT&E flights, plus ground evaluations. A joint Air Force/Navy OT-IIB report was published. Partly in response to DOT&E concern expressed over the severity of V-22 downwash in a hover observed during OT-IIA, the Navy conducted a limited downwash assessment concurrently with OT-IIB, from July to October 1995.

TEST & EVALUATION ACTIVITY

In accordance with the approved TEMP, OT-IIC was conducted in six phases at NAS Patuxent River and Bell-Boeing facilities in Pennsylvania and Texas, from October 1996, through May 1997.

Significant flight limitations were placed on the FSD V-22 in OT&E to date, including:

not cleared to hover over unprepared landing zones until OT-IIC

no operational internal or external loads or passengers

moderate gross weights only

not cleared to hover over water.

In addition, FSD aircraft equipment was not representative of any mission configuration. Together, these aircraft clearance and configuration limits produced an extremely artificial test environment for OT-IIC.

The OT-IIB report expressed serious concerns regarding the potential downwash effects, and recommended further investigation. While a limited assessment of downwash and workaround procedures was included in OT-IIC, complete resolution of the downwash issue will not be possible until the completion of OPEVAL, just prior to milestone III in 1999.

The Navy is conducting an aggressive LFT&E program on representative V-22 components and assemblies, in compliance with a DOT&E-approved alternative LFT&E plan. The V-22 program was granted a waiver from full-up, system-level LFT&E in April, 1997. The vulnerability testing that the program is performing is appropriate and will result in the improvement of aircraft survivability.

The V-22 program TEMP was last approved by DOT&E on September 28, 1995, and will be updated prior to each OT&E period scheduled.

TEST & EVALUATION ASSESSMENT

With DOT&E encouragement, the Navy greatly expanded the scope of OT-IIC to get better insight into the effectiveness and suitability of the EMD design. The results, while not yet conclusive regarding the potential operational effectiveness and suitability of operational aircraft, were encouraging. The six phases of the OT-IIC Assessment included: (1) shipboard assessment, (2) maintenance demonstrations, (3) tactical aircraft employment via FSD aircraft and manned flight simulator, (4) operational training plans, (5) program documentation review, and (6) software analysis.

In assessing the operational effectiveness and suitability COIs, COMOPTEVFOR and AFOTEC found that in most cases, only moderate risk exists that the COIs will not be satisfactorily resolved when development is complete. Enhancing features observed during OT-IIC included aircraft payload, range and speed characteristics better than the stated operational requirements. In addition, reliability, availability and maintainability of the EMD aircraft appeared to be significantly improved over those of the FSD aircraft.

Several areas of concern first discovered in OT-IIA or OT-IIB remain unresolved because of limitations to the EMD flight test operations. These concerns include severe proprotor downwash effects during personnel insertion and extraction via hoist or rope. In addition, concerns exist in the areas of communications, navigation , and crew field of view. New concerns arising from OT-IIC regarding the EMD schedule are being addressed by the program manager. Also, the reliability and maintainability of a few subsystems will require management attention. Despite these concerns, the V-22 design remains potentially operationally effective and suitable.

The aircraft's prime contractors include Boeing Company's helicopter division in Ridley Park, PA, and Bell Helicopter Textron of Fort Worth TX. In 1986 the cost of a single V-22 was estimated at $24 million, with 923 aircraft to be built. In 1989 the Bush administration cancelled the project, at which time the unit cost was estimated at $35 million, with 602 aircraft. The V-22 question caused friction between Secretary of Defense Richard B. Cheney and Congress throughout his tenure. DoD spent some of the money Congress appropriated to develop the aircraft, but congressional sources accused Cheney, who continued to oppose the Osprey, of violating the law by not moving ahead as Congress had directed. Cheney argued that building and testing the prototype Osprey would cost more than the amount appropriated. In the spring of 1992 several congressional supporters of the V-22 threatened to take Cheney to court over the issue. A little later, in the face of suggestions from congressional Republicans that Cheney's opposition to the Osprey was hurting President Bush's reelection campaign, especially in Texas and Pennsylvania where the aircraft would be built, Cheney relented and suggested spending $1.5 billion in fiscal years 1992 and 1993 to develop it. He made clear that he personally still opposed the Osprey and favored a less costly alternative.

The program was revived by the incoming Clinton administration, and current plans call for building 458 Ospreys for $37.3 billion, or more than $80 million apiece, with the Marines receiving 360 Ospreys, the Navy 48 and the Air Force 50. The first prototype flew in 1989. As of early 2000 three test aircraft had crashed: no one was killed in the 1991 crash, an accident in 1992 killed seven men, and the third in April 2000 killed 19 Marines.

Specifications

Early concept illustrations of V-22

Data from Boeing Integrated Defense Systems,Naval Air Systems Command, and the CV-22 Air Force Fact Sheet.

General characteristics

Crew: two pilots
Capacity: 24 troops (seated), 32 troops (floor loaded) or up to 15,000 pounds of cargo
Length: 57 ft 4 in (17.5 m)
Rotor diameter: 38 ft 0 in (11.6 m)
Wingspan: 46 ft (14 m); 84 ft 7 in (including rotors))
Height: 22 ft 1 in (overall - nacelles vertical) (17 ft 11 in 5.5 m (at top of tailfins))
Disc area: 2,268 ft² (212 m²)
Wing area: 301.4 ft² (28 m²)
Empty weight: 33,140 lb (15,032 kg)
Loaded weight: 47,500 lb (21,500 kg)
Max takeoff weight: 60,500 lb (27,400 kg)
Powerplant: 2× Rolls-Royce Allison Rolls-Royce T406 (AE 1107C-Liberty) turboshafts, 6,150 hp (4,590 kW) each

Performance

Maximum speed: 275 knots (316 mph, 509 km/h)
Cruise speed: 214 knots (246 mph, 396 km/h) at sea level
Range: 879 nmi (1,011 mi, 1,627 km) (unrefueled)
Combat radius: 370 nmi (430 mi, 690 km)
Ferry range: 2,417 nm (2,781 mi, 4,476 km)
Service ceiling 26,000 ft (7,925 m)
Rate of climb: 2,320 ft/min (11.8 m/s)
Disc loading: 20.9 lb/ft² @ 47,500 lb GW (102.23 kg/m²)
Power/mass: 0.259 hp/lb (427 W/kg)

MV-22s will be deployed to all Marine Corps medium lift active duty and reserve tactical squadrons, the medium lift training squadron (FRS), and the executive support squadron (HMX)

Messerschmitt Me 262

2008-10-18T18:56:00.002+05:30

The Messerschmitt Me 262 Schwalbe (German for Swallow) was the world's first operational turbojet fighter aircraft. It was produced in World War II and saw action starting in 1944 as a multi-role fighter/bomber/reconnaissance/interceptor warplane for the Luftwaffe. German pilots nicknamed it the Sturmvogel (Stormbird), while the Allies called it the Turbo. The Me 262 had a negligible impact on the course of the war due to its late introduction, with 509 claimed Allied kills (although higher claims are sometimes made) against the loss of more than 100 Me 262s.

Specifications (Messerschmitt Me 262 A-1a)

Data from Quest for Performance Original Messerschmitt documents

General characteristics

Crew: One
Length: 10.60 m (34 ft 9 in)
Wingspan: 12.60 m (41 ft 6 in)
Height: 3.50 m (11 ft 6 in)
Wing area: 21.7 m² (234 ft²)
Empty weight: 4,404 kg (9,709 lb)
Loaded weight: 7,130 kg (15,720 lb)
Max takeoff weight: 6977 kg (15,381 lb)
Powerplant: 2× Junkers Jumo 004B-1 turbojets, 8.8 kN (1,980 lbf) each
Aspect ratio: 7.23

Performance

Maximum speed: 900 km/h (559 mph)
Range: 1,050 km (652 mi)
Service ceiling 11,450 m (37,565 ft)
Rate of climb: 1,200 m/min (3,900 ft/min)
Thrust/weight: 0.28

Armament

Guns: 4x 30 mm MK 108 cannons (A-2a: two cannons)
Rockets: 24x 55 mm (2.2 in) R4M rockets
Bombs: 2x 250 kg (550 lb) bombs (A-2a only)

Design and development

Hans Guido Mutke's Me 262A on display at the Deutsches Museum.

The Me 262 was already being developed as Projekt P.1065 before the start of World War II. Plans were first drawn up in April 1939, and the original design was very similar to the plane that eventually entered service. The progression of the original design into service was delayed greatly by technical issues involving the new jet engines. Funding for the jet program was also initially lacking, as many high-ranking officials thought the war could easily be won with conventional aircraft. Adolf Hitler had envisioned the Me 262 not as a defensive interceptor, but as an offensive ground attack/bomber, almost as a very high speed, light payload Schnellbomber. His edict resulted in the development of the Sturmvogel (Stormbird) variant. It is debatable to what extent Hitler's interference extended the delay in bringing the Swallow into operation.

The aircraft was originally designed with a tail wheel undercarriage and the first four prototypes (Me 262 V1-V4) were built with this configuration, but it was discovered on an early test run that the engines and wings "blanked" the stabilizers, giving almost no control on the ground, as well as serious runway surface damage from the hot jet exhaust. Changing to a tricycle undercarriage arrangement, initially a fixed undercarriage on the "V5" fifth prototype, then fully retractable on the sixth (V6, with code VI+AA) and succeeding aircraft, corrected this problem.

Although it is often stated the Me 262 is a "swept wing" design, the production Me 262 had a leading edge sweep of only 18.5°. This was done primarily to properly position the center of lift relative to the centre of mass and not for the aerodynamic benefit of increasing the critical Mach number of the wing. The sweep was too slight to achieve any significant advantage. This happened after the initial design of the aircraft, when the engines proved to be heavier than originally expected. On 1 March 1940, instead of moving the wing forward on its mount, the outer wing was positioned slightly backwards to the same end. The middle section of the wing remained unswept.. Based on data from the AVA Göttingen and windtunnel results, the middle section was later swept.

The first test flights began on 18 April 1941, with the Me 262 V1 example, bearing its Stammkennzeichen radio code letters of PC+UA, but since its intended BMW 003 turbojets were not ready for fitting, a conventional Junkers Jumo 210 engine was mounted in the V1 prototype's nose, driving a propeller, to test the Me 262 V1 airframe. When the BMW 003 engines were finally installed, the Jumo was retained for safety, which proved wise as both 003s failed during the first flight and the pilot had to land using the nose mounted engine alone.

Messerschmitt Me 262 Schwalbe, the world's first jet fighter.

The V3 third prototype airframe, with the code PC+UC, became a true "jet" when it flew on 18 July 1942 in Leipheim near Günzburg, Germany, piloted by Fritz Wendel. This was almost nine months ahead of the British Gloster Meteor's first flight on 5 March 1943. The 003 engines, which were proving unreliable, were replaced by the newly available Junkers Jumo 004. Test flights continued over the next year, but the engines continued to be unreliable. Airframe modifications were complete by 1942, but hampered by the lack of engines, serial production did not begin until 1944. This delay in engine availability was in part due to the shortage of strategic materials, especially metals and alloys able to handle the extreme temperatures produced by the jet engine. Even when the engines were completed, they had an expected operational lifetime of approximately 50 hours; in fact, most 004s lasted just 12 hours. A pilot familiar with the Me 262 and its engines could expect approximately 20 to 25 hours of life from the 004s. Changing a 004 engine was intended to require three hours, but typically took eight to nine due to poorly made parts and inadequate training of ground crews.

Turbojet engines have less thrust at low speed than propellers and as a result, low-speed acceleration is relatively poor. It was more noticeable for the Me 262 as early jet engines (before the invention of afterburners) responded slowly to throttle changes. The introduction of a primitive autothrottle late in the war only helped slightly. Conversely, the higher power of jet engines at higher speeds meant the Me 262 enjoyed a much higher climb speed. Used tactically, this gave the jet fighter an even greater speed advantage in climb rate than level flight at top speed.

With one engine out, the Me 262 still flew well, with speeds of 450 to 500 km/h (280 to 310 mph), but pilots were warned never to fly slower than 300 km/h (186 mph) on one engine, as the asymmetrical thrust would cause serious problems.

Operationally, the Me 262 had an endurance of 60 to 90 minutes.

Operational history

Me 262 A-1a

In April 1944, Erprobungskommando 262 was formed at Lechfeld in Bavaria as a test unit (Jaeger Erprobungskommando Thierfelder) to introduce the 262 into service and train a core of pilots to fly it. On 26 July 1944, Lt. Alfred Schreiber with the 262 A-1a W.Nr. 130 017 downed a Mosquito reconnaissance aircraft. It was the first victory for a turbojet fighter aircraft in aviation history. Major Walter Nowotny was assigned as commander after the death of Werner Thierfelder in July 1944, and the unit redesignated Kommando Nowotny. Essentially a trials and development unit, it holds the distinction of having mounted the world's first jet fighter operations. Trials continued slowly, with initial operational missions against the Allies in August 1944 allegedly downing 19 Allied aircraft for six Me 262s lost, although these claims have never been verified by cross-checking with USAAF records. The RAF Museum holds no intelligence reports of RAF aircraft engaging in combat with Me 262s in August, although there is a report of an unarmed encounter between an Me 262 and a Mosquito. Despite orders to stay grounded, Nowotny chose to fly a mission against an enemy formation. After an engine failure, he was shot down and killed on 8 November 1944 by 1st Lt Edward “Buddy” Haydon of the 357th Fighter Group, USAAF and Capt Ernest “Feeb” Fiebelkorn of the 20th Fighter Group, USAAF. The "Kommando" was then withdrawn for further training and a revision of combat tactics to optimise the 262's strengths.

By January 1945, Jagdgeschwader 7 (JG 7) had been formed as a pure jet fighter unit, although it would be several weeks before it was operational. In the meantime, a bomber unit—I Gruppe, Kampfgeschwader 54 (KG 54)—had re-equipped with the Me 262 A-2a fighter-bomber for use in a ground attack role. However, the unit lost 12 jets in action in two weeks for minimal returns.

Jagdverband 44 (JV 44) was another Me 262 fighter unit formed in February, by Lieutenant General Adolf Galland, who had recently been dismissed as Inspector of Fighters. Galland was able to draw into the unit many of the most experienced and decorated Luftwaffe fighter pilots from other units grounded by lack of fuel.

During March, Me 262 fighter units were able, for the first time, to mount large scale attacks on Allied bomber formations. On 18 March 1945, 37 Me 262s of JG 7 intercepted a force of 1,221 bombers and 632 escorting fighters. They shot down 12 bombers and one fighter for the loss of three Me 262s. Although a four-to-one ratio was exactly what the Luftwaffe would have needed to make an impact on the war, the absolute scale of their success was minor, as it represented only one per cent of the attacking force. In 1943 and early 1944, the USAAF had been able to keep up offensive operations despite loss ratios of 5% and more, and the few available Me 262s could not inflict sufficient losses to hamper their operations.

Side view of a Me 262 night fighter, note the radar antenna on the nose and second seat for a radar operator.

Several two-seat trainer variants of the Me 262, the Me 262 B-1a, had been adapted as night fighters, complete with on-board FuG 218 Neptun radar and "stag's antlers" (Hirschgeweih) antenna, as the B-1a/U1 version. Serving with 10 Staffel, Nachtjagdgeschwader 11, Night Fighter wing, near Berlin, these few aircraft (alongside several single seat examples) accounted for most of the 13 Mosquitoes lost over Berlin in the first three months of 1945. However, actual intercepts were generally or entirely made using Wilde Sau methods, rather than AI radar-controlled interception. As the two-seat trainer was largely unavailable, many pilots had to make their first flight in a jet in a single seater without an instructor.

Despite its deficiencies, the Me 262 clearly signaled the beginning of the end of piston-engined aircraft as effective fighting machines. Once airborne, it could accelerate to speeds well over 800 km/h (500 mph), over 150 km/h (93 mph) faster than any Allied fighter operational in the European Theater of Operations.

The Me 262's top ace was probably Hauptmann Franz Schall with 17 kills which included six four-engine bombers and ten P-51 Mustang fighters, although night fighter ace Oberleutnant Kurt Welter claimed 25 Mosquitos and two four-engined bombers shot down by night and two further Mosquitos by day flying the Me 262. Most of Welter's claimed night kills were achieved in standard radar-less aircraft, even though Welter had tested a prototype Me 262 fitted with Neptun radar. Another candidate for top ace on the aircraft was Heinrich Bär, who claimed 16 enemy aircraft while flying the Me 262.

Anti-bomber tactics

The standard approach against bomber formations, which were travelling at cruise speed, called for the Me 262 to approach the bombers from the rear at a higher altitude, diving in below the bomber's flight level to get additional speed before gaining altitude again and, on reaching the bomber's level, opening fire with its four 30 mm cannon at 600 m (656 yard) range.

Allied bomber gunners found that their electric gun turrets had problems tracking the jets. Target acquisition was difficult because the jets closed into firing range quickly and had to remain in firing position only briefly using their standard attack profile.

Eventually, new combat tactics were developed to counter the Allied bombers' defences. Me 262s equipped with R4M rockets would approach from the side of a bomber formation, where their silhouettes were widest, and while still out of range of the .50 caliber guns, fire a salvo of these explosive rockets. The explosive power of only one or two of these rockets was capable of downing even the famously rugged B-17- a strike on an enemy aircraft meant its total annihilation. Although this tactic was effective, it came too late to have a real effect on the war. This method of attacking bombers became the standard until the invention and mass deployment of guided missiles. Some nicknamed this tactic the "Luftwaffe's Wolf Pack", as the fighters would often make runs in groups of two or three, fire their rockets, then return to base.

On 1 September 1944, USAAF General Carl Spaatz expressed the fear that if greater numbers of German jets appeared, they could inflict losses heavy enough to force cancellation of the Allied daylight bombing offensive.

Counter-jet tactics

Tactics against the Me 262 developed quickly despite its great speed advantage. Allied bomber escort fighters would fly high above the bombers — diving from this height gave them extra speed, thus reducing the speed difference. The Me 262 was less maneuverable than the P-51 and trained Allied pilots could catch up to a turning Me 262, though the only reliable way of dealing with the jets, as with the even faster Komet rocket fighters, was to attack them on the ground and during take off and landing. Luftwaffe airfields that were identified as jet bases were frequently bombed by medium bombers, and Allied fighters patrolled over the fields to attack jets trying to land. The Luftwaffe countered by installing flak alleys along the approach lines in order to protect the Me 262s from the ground and providing top cover with conventional fighters during takeoff and landing. Nevertheless, in March and April 1945, Allied fighter patrol patterns over Me 262 airfields resulted in numerous losses of jets and serious attrition of the force.

Another experimental tactic was installing nitrous oxide injection, much like the Germans' own GM-1 system, into Mustangs. When chasing an Me 262, the pilot could press a button injecting nitrous oxide into the engine, producing a quick burst of speed.

Other Allied fighters that encountered the Me 262 included the British Supermarine Spitfire, Hawker Tempest and the Soviet Lavochkin La-7. The first recorded Allied destruction of a Me 262, belonging to the unit known as Kommando Schenk, was on 28 August 1944, claimed as destroyed by 78th FG pilots Major Joseph Myers and 2nd Lt. Manford O. Croy flying P-47s. Oberfeldwebel Hieronymus "Ronny" Lauer of I KG(J) 51, on a landing pattern crash landed his 262 to get away from the Allied fighters, which then destroyed the Me 262 in strafing attacks. The first Me 262 shot down in combat, belonging to 3. Staffel/Kampfgeschwader 51, with unit code letters "9K+BL", was on 5 October 1944, by Spitfire IXs of 401 RCAF. The 262 pilot was H.C. Butmann in WNr 170093 of 3./KG51. The Lavochkin was the only Soviet fighter to shoot down a German jet, with La-7 ace Ivan Nikitovich Kozhedub, downing an Me 262 on 15 February 1945 over eastern Germany.

High speed research

Me 262 interior

Willy Messerschmitt regarded the Me 262 as only an interim type when it went into production.

Swept wings had been proposed as early as 1935 by Adolf Busemann, and Messerschmitt had researched the topic from 1940. In April 1941, he proposed fitting a 35° swept wing (Pfeilflügel II, literally arrow wing II) to the Me 262, the same wing sweep angle that would later be used on both the American F-86 Sabre and Soviet MiG-15 fighter jets. Though this was not implemented, he continued with the projected HG II and HG III (Hochgeschwindigkeit, high speed) derivatives in 1944, which were designed with a 35° and 45° wing sweep, respectively.

Interest in high-speed flight, which led him to initiate work on swept wings starting in 1940, is evident from the advanced developments Messerschmitt had on his drawing board in 1944. While the Me 262 HG I actually flight tested in 1944 had only small changes compared to combat aircraft, most notably a low-profile canopy (tried as the Rennkabine (literally racing cabin) on the Me 262 V9 prototype for a short time) to reduce drag, the HG II and HG III designs were far more radical. The projected HG II combined the low-drag canopy with a 35° wing sweep and a butterfly tail. The HG III had a conventional tail, but a 45° wing sweep and turbines embedded in the wingroot.

Messerschmitt also conducted a series of flight tests with the series production Me 262. In dive tests, it was determined that the Me 262 went out of control in a dive at Mach 0.86, and that higher Mach numbers would lead to a nose-down trim that could not be countered by the pilot. The resulting steepening of the dive would lead to even higher speeds and disintegration of the airframe due to excessive negative g loads.

The HG series of Me 262 derivatives was estimated to be capable of reaching transonic Mach numbers in level flight, with the top speed of the HG III being projected as Mach 0.96 at 6 km altitude. Despite the necessity to gain experience in high-speed flight for the HG II and III designs, Messerschmitt undertook no attempts to exceed the Mach 0.86 limit for the Me 262.

After the war, the Royal Aircraft Establishment, at that time one of the leading institutions in high-speed research, re-tested the Me 262 to help with British attempts at exceeding Mach 1. The RAE achieved speeds of up to Mach 0.84 and confirmed the results from the Messerschmitt dive tests. Similar tests were run by the Soviets. No attempts were made to exceed the Mach limit established by Messerschmitt.

After Willy Messerschmitt's death, the former Me 262 pilot Hans Guido Mutke claimed to be the first person to exceed Mach 1, on 9 April 1945 in a Me 262 in a "straight-down" 90° dive. This claim is disputed because it is only based on Mutke's memory of the incident, which recalls effects other Me 262 pilots observed below the speed of sound at high indicated airspeed, but with no altitude reading required to determine the actual speed. Furthermore, the pitot tube used to measure airspeed in aircraft can give falsely elevated readings as the pressure builds up inside the tube at high speeds. Finally, the Me 262 wing had only a slight sweep incorporated for trim (center of gravity) reasons and likely would have suffered structural failure due to divergence at high transonic speeds. One airframe (Me 262 HG1 V9 WNr130 004 VI+AD ) was prepared with the low-profile Rennkabine racing canopy and may have achieved an unofficial record speed of 606 mph, altitude unspecified.

Postwar history and flyable reproductions

Reproduction of a Messerschmitt Me 262 at the Berlin Air Show 2006.

After the end of the war, the Me 262 and other advanced German technologies were quickly swept up by the Americans (as part of the USAAF's Operation Lusty), British, and Soviets. Many Me 262s were found in readily-repairable condition and were confiscated.

The Me 262 was found during testing to have advantages over the early models of the Gloster Meteor. It was faster, had better cockpit visibility to the sides and rear (mostly due to the canopy frame and the discoloration caused by the plastics used in the Meteor's construction), and was a superior gun platform, as the early Meteors had a tendency to snake at high speed and exhibited "weak" aileron response. The Me 262 did have a shorter combat range than the Meteor.

The USAAF compared the P-80 Shooting Star and Me 262 concluding, "Despite a difference in gross weight of nearly 2,000 lb (907 kg), the Me 262 was superior to the P-80 in acceleration, speed and approximately the same in climb performance. The Me 262 apparently has a higher critical Mach number, from a drag standpoint, than any current Army Air Force fighter." The Army Air Force also tested an example of the Me 262A-1a/U3 (US flight evaluation serial FE-4012), an unarmed photoreconnaissance version, which was fitted with a fighter nose and given an overall smooth finish. It was used for performance comparisons against the P-80. During testing between May and August 1946, the aircraft completed eight flights, lasting four hours and 40 minutes. Testing was discontinued after four engine changes were required during the course of the tests, culminating in two single-engine landings.

These aircraft were extensively studied, aiding development of early U.S. and Soviet jet fighters. The F-86 Sabre, designed by the engineer Edgar Schmued, used the Me 262 airfoil (Messerschmitt Wing A) and a slat design similar to that of the Me 262.

The Czechoslovak aircraft industry continued to produce single-seater (designated Avia S-92) and two-seater (designated Avia CS-92) variants of the Me 262 after World War II. From August 1946, a total of nine single-seater S-92 and three two-seater CS-92 planes were completed and test flown. They were introduced in 1947 and in 1950 they were supplied to the 5th Fighter Squadron. These were kept flying as late as 1957. They were the first jet fighters to serve in the Czechoslovak Air Force. Both versions are on display at the Prague Aero museum in Kbely.

In January 2003, the American Me 262 Project completed flight testing to allow for delivery of near-exact reproductions of several versions of the Me 262 including at least two B-1c two-seater variants, one A-1c single seater and two "convertibles" that could be switched between the A-1c and B-1c configurations. All are powered by General Electric J85 engines and feature additional safety features, such as upgraded brakes and strengthened landing gear. The "c" suffix refers to the new J-85 powerplant and has been informally assigned with the approval of the Messerschmitt Foundation in Germany. Flight testing of the first newly manufactured Me 262 A-1c (single seat) variant was completed in August 2005. The first of these machines went to a private owner in the southwestern United States, while the second was delivered to the Messerschmitt Foundation at Manching, Germany. This aircraft conducted a private test flight in late April 2006, and made its public debut in May at the Berlin Air Show (ILA 2006). The new Me 262 flew during the public flight demonstrations. Me 262 Werk Number 501241 was delivered to the Collings Foundation as White 1 of JG 7. This aircraft will be offering ride-along flights starting in 2008

source : Wikipedia

P-51 Mustang

2008-10-18T18:29:00.004+05:30

The North American Aviation P-51 Mustang was an American long-range single-seat fighter aircraft that entered service with Allied air forces in the middle years of World War II.

The P-51 flew most of its wartime missions as a bomber escort in raids over Germany, helping ensure Allied air superiority from early 1944. It also saw limited service against the Japanese in the Pacific War. The Mustang began the Korean War as the United Nations' main fighter, but was relegated to a ground attack role when superseded by jet fighters early in the conflict. Nevertheless, it remained in service with some air forces until the early 1980s.

As well as being economical to produce, the Mustang was a fast, well-made, and highly durable aircraft. The definitive version, the P-51D, was powered by the Packard V-1650-7, a two-stage two-speed supercharged 12-cylinder Packard-built version of the legendary Rolls-Royce Merlin engine, and was armed with six .50 caliber (12.7 mm) Browning M2/AN machine guns, a version of the Browning adapted for use in combat aircraft.

After World War II and the Korean conflict, many Mustangs were converted for civilian use, especially air racing. The Mustang's reputation was such that, in the mid-1960s, Ford Motor Company's Designer John Najjar proposed the name for a new youth-oriented coupe after the fighter.

Specifications

P-51D Mustang

Data from The Great Book of Fighters,and Quest for Performance

General characteristics

Crew: 1
Length: 32 ft 3 in (9.83 m)
Wingspan: 37 ft 0 in (11.28 m)
Height: 13 ft 8 in (4.17 m)
Wing area: 235 ft² (21.83 m²)
Empty weight: 7,635 lb (3,465 kg)
Loaded weight: 9,200 lb (4,175 kg)
Max takeoff weight: 12,100 lb (5,490 kg)
Powerplant: 1× Packard Merlin V-1650-7 liquid-cooled supercharged V-12, 1,490 hp (1,111 kW) at 3,000 rpm;^[77] 1,720 hp (1,282 kW) at WEP
Zero-lift drag coefficient: 0.0163
Drag area: 3.80 ft² (0.35 m²)
Aspect ratio: 5.83

Performance

Maximum speed: 437 mph (703 km/h) at 25,000 ft (7,620 m)
Cruise speed: 362 mph (580 km/h)
Stall speed: 100 mph (160 km/h)
Range: 1,650 mi (2,755 km) with external tanks
Service ceiling 41,900 ft (12,770 m)
Rate of climb: 3,200 ft/min (16.3 m/s)
Wing loading: 39 lb/ft² (192 kg/m²)
Power/mass: 0.18 hp/lb (300 W/kg)
Lift-to-drag ratio: 14.6
Recommended Mach limit 0.8

Armament

6 × 0.50 in (12.7 mm) machine guns; 400 rounds per gun for the two inboard guns; 270 per outboard gun
2 hardpoints for up to 2,000 lb (907 kg)
10 × 5 in (127 mm) rockets

P-51H Mustang

Data from The Great Book of Fighters

General characteristics

Crew: 1
Length: 33 ft 4 in (10.16 m)
Wingspan: 37 ft 0 in (11.28 m)
Height: 11 ft 1 in (3.38 m)
Wing area: 235 ft² (21.83 m²)
Empty weight: 7,040 lb (3,195 kg)
Loaded weight: 9,500 lb (4,310 kg)
Max takeoff weight: 11,500 lb (5,215 kg)
Powerplant: 1× Packard Merlin V-1650-9 liquid-cooled supercharged V-12, 1,490 hp (1,111 kW) at 3,000 rpm, 2,220 hp (1,655 kW) at WEP

Performance

Maximum speed: 487 mph (784 km/h) at 25,000 ft (7,620 m)
Range: 1,160 mi (1,865 km) with external tanks
Service ceiling 41,600 ft (12,680 m)
Rate of climb: 3,300 ft/min (16.8 m/s)
Wing loading: 40.4 lb/ft² (197.4 kg/m²)
Power/mass: 0.23 hp/lb (385 W/kg)

Armament

6 × 0.50 in (12.7 mm) Browning machine guns with 1,880 total rounds (400 rounds for each on the inner pair, and 270 rounds for each of the outer two pair), or 4 of the same guns with 1,600 total rounds (400 per gun).

NA-73X: The initial prototype was designated the NA-73X by the manufacturer, North American Aviation.

Mustang I

The first production contract was awarded by the British for 320 NA-73 fighters. This aircraft was named Mustang I by the British. A second British contract for 300 more Mustang Is was assigned a model number of NA-83 by North American.
XP-51

Two aircraft of this lot delivered to the USAAF were designated XP-51.

P-51: In September 1940, 150 aircraft designated NA-91 by North American were ordered under the Lend/Lease program. These were designated by the USAAF as P-51 and initially named the Apache although this name was dropped early-on for Mustang. The British designated this model as Mustang IA. They were equipped with four long-barrelled 20 mm Hispano-Suiza Mk II cannon instead of machine guns. A number of aircraft from this lot were fitted out by the USAAF as photo reconnaissance aircraft and designated F-6A. The British would fit a number of Mustang I fighters with photographic reconnaissance equipment as well. Also, two aircraft of this lot were fitted with the Packard-built Merlin engine and were designated by North American as model NA-101 and by the USAAF initially as the XP-78, but re-designated quickly to XP-51B.

In early 1942, the USAAF ordered a lot of 500 aircraft modified as dive bombers that were designated A-36A. North American assigned the aircraft the model number NA-97. This model became the first USAAF Mustang to see combat. One aircraft was passed to the British who gave it the name Mustang I (Dive Bomber).

Following the A-36A order the USAAF ordered 310 model NA-99 fighters that were designated P-51A by the USAAF. and Mustang II by the RAF. A number of this lot of aircraft were equipped with K-24 cameras and designated F-6B. All these models of the Mustang were equipped with Allison V-1710 engines except the prototype XP-51B.

Beginning with the model NA-102 Mustang the Packard built Merlin V-1650 engine replaced the Allison. In the summer of 1943 Mustang production was begun at a new plant in Dallas, Texas as well as at the existing facility in Inglewood, California. The model NA-102 was produced as the P-51B in Inglewood while the NA-103 as the P-51C was produced at Dallas. The RAF named these models Mustang III. Again, a number of the P-51B and P-51C aircraft were fitted for photo Reconnaissance and designated F-6C.

The prototypes of the bubble canopy change were designated model NA-106 by North American and P-51D by the USAAF. The production version, while retaining the P-51D designation, was assigned a model number NA-109 by North American. The "D" became the most widely produced variant of the Mustang. A variation of the P-51D equipped with an Aeroproducts propeller in place of the Hamilton Standard propeller was designated the P-51K. The photo versions of the P-51D and P-51K were designated F-6D and F-6K respectfully. The RAF assigned the name Mustang IV to the "D" model and Mustang IVA to "K" models.

As the USAAF specifications required airframe design to a higher load factor than that used by British for their fighters, consideration was given to re-designing the Mustang to the lower British requirements in order to reduce the weight of the aircraft and thus improve performance. In 1943, North American submitted a proposal to do the re-design as model NA-105, which was accepted by the USAAF. The designation XP-51F was assigned for prototypes powered with V-1650 engines and XP-51G to those with reverse lend/lease Merlin 145M engines. Modifications included changes to the cowling, a simplified undercarriage with smaller wheels and disk brakes, and a larger canopy. A third prototype was added to the development that was powered by an Allison V-1710 engine. This aircraft was designated XP-51J. As the engine was insufficiently developed the XP-51J was loaned to Allison for engine development. A small number of XP-51Fs were passed to the British as the Mustang V.

The final production Mustang, the P-51H embodied the experience gained in the development of the lightweight XP-51F and XP-51G aircraft. This aircraft, model NA-126 and with minor differences NA-129, came too late to participate in World War II, but it brought the development of the Mustang to a peak and was one of the fastest production piston engine fighters to see service. The P-51H used the Merlin V-1659-9 engine, equipped with Simmons automatic boost control and water injection, allowing War Emergency Power as high as 2,218 horsepower (1,654 kW). Some of the weight savings inherited from the XP-51F and XP-51G were invested in lengthening the fuselage and increasing the height of the tailfin, greatly reducing the tendency to yaw, and in restoring the fuselage fuel tank. The canopy was changed back to more nearly resemble the P-51D style, over a somewhat raised pilot's position. Service access to the guns and ammunition was improved. The P-51H was designed to complement the P-47N as the primary aircraft for the invasion of Japan and 2,000 were ordered to be built at the Inglewood plant. With the solution to the problem of yaw control, the P-51H was now considered a suitable candidate for testing as an aircraft carrier based fighter; but with the end of the war, the testing was cut short, and production was halted after 555 aircraft were built. Although some P-51Hs were issued to operational units, none saw combat. One aircraft was given to the RAF for testing and evaluation. Serial number 44-64192 was re-serialled BuNo 09064 and used by the Navy to test transonic airfoil designs, then returned to the Air National Guard in 1952. The P-51H was not used for combat in the Korean War despite its improved handling characteristics, due to the lack of experience with durability of the lighter airframe under combat conditions as well as limited numbers in the USAF inventory.

With the cutback in production the variants of the P-51H with different versions of the Merlin engine were produced in either limited numbers or terminated. These included the P-51L, similar to the P-51H but utilizing the 2,270 horsepower (1,690 kW) V-1650-11 Merlin engine, which was never built; and its Dallas-built version, the P-51M or NA-124 which utilized the V-1650-9A Merlin engine lacking water injection and therefore rated for lower maximum power, of which one was built out of the original 1629 ordered, serial number 45-11743.

Design and development

The result of the MAP order was the NA-73X project (from March 1940). The design followed the best conventional practice of the era, but included two new features. One was a new NACA-designed laminar flow wing, which was associated with very low drag at high speeds. Another was the use of a new radiator design (one Curtiss had been unable to make work) that used the heated air exiting the radiator as a form of jet thrust in what is referred to as the "Meredith Effect". Because North American lacked a suitable wind tunnel, it used the GALCIT 10-foot (3.0 m) wind tunnel at Cal Tech. This led to some controversy over whether the Mustang's cooling system aerodynamics were developed by North American's engineer Edgar Schmued or by Curtiss, although historians and researchers dismiss the allegation of stolen technology; such claims are likely moot in any event, as North American had purchased Curtiss’ complete set of P-40 and XP-46 wind tunnel data and flight test reports for US$56,000.

While the United States Army Air Corps could block any sales it considered detrimental or not in the interest of the United States, the NA-73 represented a special case. In order to ensure deliveries were uninterrupted, an arrangement was eventually reached where the RAF would get its aircraft in exchange for NAA providing two free examples to the USAAC for evaluation.

The prototype NA-73X was rolled out just 117 days after the order was placed, and first flew on 26 October 1940, just 178 days after the order had been placed — an incredibly short gestation period. In general the prototype handled well and the internal arrangement allowed for an impressive fuel load. It was armed with four .30 caliber Browning (7.62 mm) and two .50 M2 Browning (12.7 mm) machineguns in the wings and two .50 M2s in the chin.

Allison-engined Mustangs

Early P-51 Mustang on a test flight. Note the 20mm cannon armament.

Mustang I/P-51/P-51A

It was quickly evident that performance, although exceptional up to 15,000 feet (4,600 m), was markedly reduced at higher altitudes. This deficiency was due largely to the single speed, single stage supercharger of the Allison V-1710 engine, where power diminished rapidly above the critical altitude rating. Prior to the Mustang project, the USAAC had Allison concentrate primarily on turbochargers in concert with General Electric; these proved to be exceptional in the P-38 Lightning and other high-altitude aircraft, in particular, the Air Corp's four-engine bombers. Most of the other uses for the Allison were for low-altitude designs, where a simpler supercharger would suffice. The turbocharger proved impractical in the Mustang, and it was forced to use the inadequate supercharger available. Still, the Mustang's advanced aerodynamics showed to advantage, as the Mustang I was about 30 mph (48 km/h) faster than contemporary Curtiss P-40 fighters, using the same powerplant (the V-1710-39 producing 1,220 hp (910 kW) at 10,500 ft (3,200 m), driving a 10-foot-6-inch (3.2 m) diameter, three-blade Curtiss-Electric propeller). The Mustang I was 30 mph (48 km/h) faster than the Spitfire Mk VC at 5,000 ft (1,500 m) and 35 mph (56 km/h) faster at 15,000 ft (4,600 m), despite the British aircraft's more powerful engine.

The first production contract was awarded by the British for 320 NA-73 fighters, named Mustang I by the British (the name being selected by an anonymous member of the Purchasing Commission). Two aircraft of this lot delivered to the USAAC for evaluation were designated XP-51. About 20 Mustang Is were delivered to the RAF, making their combat debut on 10 May 1942. With their long range and excellent low-level performance, they were employed effectively for tactical reconnaissance and ground-attack duties over the English Channel, but were thought to be of limited value as fighters due to their poor performance above 15,000 ft (4,600 m).

A second British contract called for 300 more (NA-83) Mustang I fighters. In September 1940, 150 aircraft, designated NA-91 by North American, were ordered under the Lend/Lease program. These were designated by the USAAF as P-51 and initially named Apache, although this was soon dropped and the RAF name, Mustang, adopted instead. The British designated this model as Mustang IA. The Mustang Mk IA was identical to the Mustang Mk I except that the wing-mounted machine guns were removed and replaced with four long-barrelled 20 mm Hispano Mk II cannon.

A number of aircraft from this lot were fitted out by the USAAF as F-6A photo-reconnaissance aircraft. The British would fit a number of Mustang Is with similar equipment. Also, two aircraft of this lot were fitted with Packard-built Merlin engines.^[10]^[11] These were identified as the Model NA-101 by North American and XP-78 by the USAAF, later redesignated XP-51B.

On 23 June 1942 a contract was placed for 1,200 P-51As (NA-99s), later reduced to 310 aircraft. The P-51A was the first version to be procured as a fighter by the USAAF, and used a new Allison V-1710-81 engine, a development of the -39, driving a 10-foot-9-inch (3.3 m) diameter, three bladed Curtiss-Electric propeller. The armament was changed to four wing mounted .50 calibre Browning machine guns, two in each wing, with a maximum of 350 rpg for the inboard guns and 280 rpg for the outboard. Other improvements were made in parallel with the A-36, including an improved, fixed air duct inlet replacing the moveable fitting of previous Mustang models and the fitting of wing racks able to carry either 75 gallon or 150 gallon drop tanks, increasing the maximum ferry range to 2,740 statute miles with the 150 gallon tanks. The top speed was raised to 409 mph (658 km/h) at 10,000 feet (3,000 m). Fifty aircraft were shipped to England, serving as Mustang IIs in the RAF.

A36 Apache

A-36 Apache/Invader

At the same time, the USAAC was becoming more interested in ground attack aircraft and had a new version ordered as the A-36 Apache, which included six .50 M2 Browning machine guns, dive brakes and the ability to carry two 500 lb (230 kg) bombs.

In early 1942, the USAAF ordered 500 aircraft modified as dive bombers that were designated A-36A (NA-97). This model became the first USAAF Mustang to see combat. One aircraft was passed to the British who gave it the name Mustang I (Dive Bomber).

Merlin-engined Mustangs

P-51B and P-51C

The Mustang X AM203

In April 1942, the RAF's Air Fighting Development Unit (AFDU) tested the Mustang and found its performance inadequate at higher altitudes. As such it was to be used to replace the Tomahawk in Army Cooperation Command squadrons but the commanding officer was so impressed with its manoeuvrability and low-altitude speeds that he invited Ronnie Harker from Rolls Royce's Flight Test establishment to fly it. Rolls-Royce engineers rapidly realized that equipping the Mustang with a Merlin 61 engine with its two speed, two stage supercharger would substantially improve performance and started converting five aircraft as the Mustang X. Apart from the engine installation, which utilised custom built engine bearers designed by Rolls-Royce and a standard 10 ft 9 in (3.3 m) diameter, four bladed Rotol propeller from a Spitfire Mk. IX , the Mustang X was a straight-forward adaptation of the Mustang I airframe, keeping the same radiator duct design. The Vice-Chief of the Air Staff, Air Marshal Sir Wilfrid R. Freeman, lobbied vociferously for Merlin-powered Mustangs, insisting two of the five experimental Mustang Xs be handed over to Carl Spaatz for trials and evaluation by the U.S. 8th Air Force in Britain.

P-51B in flight showing wing planform.

USAAF P-51B-10-NA

The high-altitude performance improvement was astonishing: the Mustang X (AM208) reached 433 mph (697 km/h) at 22,000 ft (6,700 m) and AL975 tested at an absolute ceiling of 40,600 ft (12,400 m).

The XP-51B prototypes were a more thorough adaptation of the airframe, with a tailor made engine installation and a complete redesign of the radiator duct. The airframe itself was strengthened, with the fuselage and engine mount area receiving more formers because of the greater weight of the Packard Merlin V-1650-3, 1,690 lb (770 kg) compared with the Allison V-1710's 1,335 lb (606 kg). The engine cowling was completely redesigned to house the Packard Merlin which, because of the intercooler radiator mounted on the supercharger casing, was 5 inches (130 mm) taller and used an updraught induction system rather than the downdraught carburetor of the Allison. The new engine drove a four bladed 11 ft 2 in (3.4 m) diameter Hamilton Standard propeller which featured cuffs of hard molded rubber. A new radiator, supercharger intercooler and oil radiator installation in a new fuselage duct was designed to cater for the increased cooling requirements of the Merlin.

It was decided that the armament of the new, P-51B (NA 102) would be the four .50 Cal Browning M2/AN machine guns (with 350 rpg for the inboard guns and 280 rpg for the outboard) of the P-51A and the bomb rack/external drop tank installation (adapted from the A-36) would also be used; the racks were rated to be able to carry up to 500 lb (230 kg) of ordnance and were also capable of carrying drop tanks. The weapons were aimed using an N-3B optical gunsight fitted with an A-1 head assembly which allowed it to be used as a gun or bomb sight through varying the angle of the reflector glass.

Pilots were also given the option of having ring and bead sights mounted on the top engine cowling formers. This option was discontinued with the later Ds.

N3B gunsight with A-1 head assembly (in this case mounted in a PBJ-1H.)

The first XP-51Bs started test flying in December 1942. After sustained lobbying at the highest level, American production was started in early 1943 with the B (NA-102) being manufactured at Inglewood, California, and the C (NA-103) at a new plant in Dallas, Texas, which was in operation by summer 1943. The RAF named these models Mustang III. In performance tests, the P-51B reached 441 mph/709.70 km/h (exactly two-thirds supersonic speed at altitude) at 25,000 ft (7.600 m) and the subsequent extended range made possible by the use of drop tanks enabled the Merlin-powered Mustang to be introduced as a bomber escort.

The range would be further increased with the introduction of an 85 gallon self-sealing fuel tank aft of the pilot's seat, starting with the B-5NA series. When this tank was full the c-g of the Mustang was moved dangerously close to the aft limit, as a result of which maneuvers were restricted until the tank was down to about 25 gallons and the external tanks had been dropped. Problems with high-speed "porpoising" of the P-51Bs and Cs with the fuselage tanks would lead to the replacement of the fabric covered elevators with metal covered surfaces and a reduction of the tailplane incidence.

Despite these modifications the P-51 Bs and Cs and the newer Ds and Ks experienced low speed handling problems that could result in an involuntary "snap-roll" under certain conditions of air speed, angle of attack, gross weight and center of gravity. Several crash reports tell of P-51Bs and Cs crashing because horizontal stabilizers were torn off during maneuvering. As a result of these problems a modification kit consisting of a dorsal fin was manufactured. One report stated:

"Unless a dorsal fin is installed on the P-51B, P-51C and P-51D airplanes, a snap roll may result when attempting a slow roll. The horizontal stabilizer will not withstand the effects of a snap roll. To prevent recurrence the stabilizer should be reinforced in accordance with T.O. 01-60J-18 dated 8 April 1944 and a dorsal fin should be installed. Dorsal fin kits are being made available to overseas activities"

These kits became available in August 1944 and were fitted to Bs and Cs and to Ds and Ks. Also incorporated was a change to the rudder trim tabs, which would help prevent the pilot over-controlling the aircraft and creating heavy loads on the tail unit.

P-51Bs and Cs started to arrive in England in August and October 1943. The P-51B/C versions were sent to 15 fighter groups that were part of the 8th and 9th Air Forces in England, and the 12th and 15th in Italy (the southern part of Italy was under Allied control by late 1943). Other deployments included the China Burma India Theater (CBI).

Allied strategists quickly exploited the long-range fighter as a bomber escort. It was largely due to the P-51 that daylight bombing raids deep into German territory became possible without prohibitive bomber losses in late 1943.

A number of the P-51B and P-51C aircraft were fitted for photo reconnaissance and designated F-6C.

P-51D and P-51K

P-51D My Girl at Iwo Jima where fighters were based to escort B-29s on bombing missions to Japan in 1945.

Miss Helen, a P-51D in its wartime markings as flown by Capt. Raymond H. Littge of the 487FS, 352FG, on aerial display in 2007. Named "Miss Nita" while the plane of Lt. Russell H. Ross, it is the last original 352FG P-51 known to exist.

One of the few remaining complaints with the Merlin-powered aircraft was a poor rearward view. This was a common problem in most fighter designs of the era, which had only been recognized by the British after the Battle of Britain proved the value of an all-around view. In order to improve the view from the Mustang at least partially, the British had field-modified some Mustangs with fishbowl-shaped sliding canopies called "Malcolm Hoods" - much like those on Spitfires. Eventually all Mk IIIs, along with some American P-51B/Cs, were equipped with Malcolm Hoods.

A better solution to the problem was the "teardrop" or "bubble" canopy. Originally developed as part of the Miles M.20 project, these newer canopies were in the process of being adapted to most British designs, eventually appearing on Typhoons, Tempests and later-built Spitfires. North American adapted several NA-106 prototypes with a bubble canopy, cutting away the decking behind the cockpit, resulting in substantially improved vision to the rear. This led to the production P-51D (NA-109), considered the definitive Mustang.

A common misconception is that the cutting down of the rear fuselage to mount the bubble canopy reduced stability requiring the addition of a dorsal fin to the forward base of the vertical tail. In fact, as described, stability problems affected the earlier Bs and Cs, as well as the subsequent D/K models; this was partly attributable to the 85 gallon fuselage fuel tank which had been installed during production of the P-51B-5-NA.

Among other modifications, armament was increased with the addition of two M2 machine guns, bringing the total to six. The inner pair of machine guns had 400 rounds each, and the others had 270 rounds, for a total of 1,880. In previous P-51s, the M2s were mounted at an extreme side angle to allow access to the feed chutes from the ammunition trays. This angled mounting had caused problems of congestion and jamming of the ammunition and spent casings and links, leading to frequent complaints of jamming during combat maneuvers. The new arrangement allowed the M2s to be mounted upright, remedying most of the jamming problems. The .50 caliber Browning machine guns, although not firing an explosive projectile, had excellent ballistics and proved adequate against the Fw 190 and Bf 109 fighters that were the main USAAF opponents at the time. The wing racks fitted to the P-51D/K series were strengthened and were able to carry up to 1,000 lb (450 kg) of ordnance. Later models had under-wing rocket pylons added to carry up to ten rockets per plane.

The gunsight was changed from the N-3B to the N-9 before the introduction in September 1944 of the K-14B gyro-computing sight.

Alterations to the undercarriage up-locks and inner-door retracting mechanisms meant that there was a change to the shape of the inner wing leading edge, which was raked forward slightly, increasing the wing area and creating a distinctive "kink" in the leading edges of the wings.

Armorers prepare to arm a P-51 with six M2 machine guns and .50 caliber ammunition

The P-51D became the most widely produced variant of the Mustang. A Dallas-built version of the P-51D, designated the P-51K, was equipped with an Aeroproducts propeller in place of the Hamilton Standard propeller, as well as a larger, differently configured canopy and other minor alterations (the vent panel was different). The hollow-bladed Aeroproducts propeller was unreliable with dangerous vibrations at full throttle due to manufacturing problems and was eventually replaced by the Hamilton Standard. By the time of the Korean war most F-51s were equipped with "uncuffed" Hamilton Standard propellers with wider, blunt tipped blades. The photo reconnaissance versions of the P-51D and P-51K were designated F-6D and F-6K respectively. The RAF assigned the name Mustang IV to the D model and Mustang IVA to K models.

The P-51D/K started arriving in Europe in mid-1944 and quickly became the primary USAAF fighter in the theater. It was produced in larger numbers than any other Mustang variant. Nevertheless, by the end of the war, roughly half of all operational Mustangs were still B or C models.

Concern over the USAAF's inability to escort B-29s all the way to mainland Japan resulted in the highly classified "Seahorse" project. In late 1944 naval aviator (and later test pilot) Bob Elder flew carrier suitability trials with a modified P-51D. The project was canceled after U.S. Marines secured the Japanese island of Iwo Jima and its airfields, making it possible for standard P-51D models to accompany B-29s all the way to the Japanese home islands and back.

During 1945–48, P-51Ds were also built under licence in Australia by the Commonwealth Aircraft Corporation.

The "lightweight" Mustangs

XP-51F, XP-51G and XP-51J

The USAAF required airframes built to their acceleration standard of 8.33 g (82 m/s²), a higher load factor than that used by the British standard of 5.33 g (52 m/s²) for their fighters. Reducing the load factor to 5.33 would allow weight to be removed, and both the USAAF and the RAF were interested in the potential performance boost.

A subtle change made in the lightweight Mustangs was the use of an improved NACA 66 series airfoil and a slightly thinner wing than that used by earlier Mustangs.

In 1943, North American submitted a proposal to re-design the P-51D as model NA-105, which was accepted by the USAAF. Modifications included changes to the cowling, a simplified undercarriage with smaller wheels and disc brakes, and a larger canopy. The designation XP-51F was assigned to prototypes powered with V-1650 engines (a small number of XP-51Fs were passed to the British as the Mustang V) and XP-51G to those with reverse lend/lease Merlin RM 14 SM engines.

A third lightweight prototype powered by an Allison V-1710-119 engine was added to the development program. This aircraft was designated XP-51J. Since the engine was insufficiently developed, the XP-51J was loaned to Allison for engine development. None of these experimental "lightweights" went into production.

P-51H

P-51H in flight

The P-51H (NA-126) was the final production Mustang, embodying the experience gained in the development of the XP-51F and XP-51G aircraft. This aircraft, with minor differences as the NA-129, came too late to participate in World War II, but it brought the development of the Mustang to a peak as one of the fastest production piston engine fighters to see service.

The P-51H used the new V-1650-9 engine, a version of the Merlin that included Simmons automatic supercharger boost control with water injection, allowing War Emergency Power as high as 2218 hp (1,500 kW). Differences between the P-51D included lengthening the fuselage and increasing the height of the tailfin, which greatly reduced the tendency to yaw. The canopy resembled the P-51D style, over a somewhat raised pilot's position. Service access to the guns and ammunition was also improved. With the new airframe several hundred pounds lighter, the extra power and a more streamlined radiator, the P-51H was among the fastest propeller fighters ever, able to reach 487 mph (784 km/h or Mach 0.74) at 25,000 ft (7,600 m).

The P-51H was designed to complement the P-47N as the primary aircraft for the invasion of Japan with 2,000 ordered to be manufactured at Inglewood. Production was just ramping up with 555 delivered when the war ended. Production serial numbers:

P-51H-1-NA 44-64160 – 44-64179
P-51H-5-NA 44-64180 – 44-64459
P-51H-10-NA 44-64460 – 44-64714

Additional orders, already on the books, were cancelled. With the cutback in production, the variants of the P-51H with different versions of the Merlin engine were produced in either limited numbers or terminated. These included the P-51L, similar to the P-51H but utilizing the 2,270 horsepower (1,690 kW) V-1650-11 Merlin engine, which was never built; and its Dallas-built version, the P-51M or NA-124 which utilized the V-1650-9A Merlin engine lacking water injection and therefore rated for lower maximum power, of which one was built out of the original 1629 ordered, serial number 45-11743.

Although some P-51Hs were issued to operational units, none saw combat in World War II, and in postwar service, most were issued to reserve units. One aircraft was provided to the RAF for testing and evaluation. Serial number 44-64192 was designated BuNo 09064 and used by the U.S. Navy to test transonic airfoil designs, then returned to the Air National Guard in 1952. The P-51H was not used for combat in the Korean War despite its improved handling characteristics, since the P-51D was available in much larger numbers and was a proven commodity.

Many of the aerodynamic advances of the P-51 (including the laminar flow wing) were carried over to North American's next generation of jet-powered fighters, the Navy FJ Fury and Air Force F-86 Sabre. The wings, empennage and canopy of the first straight-winged variant of the Fury (the FJ-1) and the unbuilt preliminary prototypes of the P-86/F-86 strongly resembled those of the Mustang before the aircraft were modified with swept-wing designs.

Post-World War II

F-51 Mustang taxis through a puddle in Korea, laden with bombs and rockets

In the aftermath of World War II, the USAAF consolidated much of its wartime combat force and selected the P-51 as a "standard" piston engine fighter while other types such as the P-38 and P-47 were withdrawn or given substantially reduced roles. However, as more advanced jet fighters (P-80 and P-84) were being introduced, the P-51 was relegated to secondary status.

In 1947, the newly-formed USAF Strategic Air Command employed Mustangs alongside F-6 Mustangs and F-82 Twin Mustangs, due to their range capabilities. In 1948, the designation P-51 (P for pursuit) was changed to F-51 (F for fighter) and the existing F designator for photographic reconnaissance aircraft was dropped because of a new designation scheme throughout the USAF. Aircraft still in service in the USAF or Air National Guard (ANG) when the system was changed included: F-51B, F-51D, F-51K, RF-51D (formerly F-6D), RF-51K (formerly F-6K), and TRF-51D (two-seat trainer conversions of F-6Ds). They remained in service from 1946 through 1951. By 1950, although Mustangs continued in service with the USAF and many other nations after the war, the majority of the USAF's Mustangs had been surplussed or transferred to the Air Force Reserve (AFRES) and the Air National Guard (ANG).

USAF F-51D dropping napalm on a target in North Korea

During the Korean War, F-51s, though obsolete as fighters, were used as close ground support aircraft and reconnaissance aircraft until the end of the war in 1953. Because of its lighter structure and less availability of spare parts, the newer, faster F-51H was not used in Korea. With the aircraft being used for ground attack, their performance was less of a concern than their ability to carry a load.

At the start of the Korean War, the Mustang once again proved its usefulness. With the availability of F-51Ds in service and in storage, a substantial number were shipped via aircraft carriers to the combat zone for use initially by both the Republic of Korea Air Force (ROKAF) and USAF. Rather than employing them as interceptors or "pure" fighters, the F-51 was given the task of ground attack, fitted with rockets and bombs. After the initial invasion from North Korea, USAF units were forced to fly from bases in Japan, and F-51Ds could hit targets in Korea that short-ranged F-80 jet fighters could not. A major concern over the vulnerability of the cooling system was realized in heavy losses due to ground fire. Mustangs continued flying with USAF and Republic of Korea Air Force (ROKAF) fighter-bomber units on close support and interdiction missions in Korea until they were largely replaced by Republic F-84 and Grumman Panther jet fighter-bombers in 1953. No. 77 Squadron Royal Australian Air Force (RAAF) operated Australian-built Mustangs as part of British Commonwealth Forces Korea, replacing them with Gloster Meteor F8s in 1951. No. 2 Squadron South African Air Force (SAAF) operated US-built Mustangs as part of the US 18th Fighter Bomber Wing, suffering heavy losses by 1953, when it converted to the F-86 Sabre.

West Virginia Air National Guard F-51D. Note: postwar "uncuffed" propeller unit.

F-51s flew in the Air Force Reserve and Air National Guard throughout the 1950s. The last American USAF Mustang was F-51D-30-NA AF Serial No. 44-74936, which was finally withdrawn from service with the West Virginia Air National Guard in 1957. This aircraft is now on display at the National Museum of the United States Air Force at Wright-Patterson AFB in Dayton, Ohio. It is, however, painted as P-51D-15-NA Ser No. 44-15174.

The final withdrawal of the Mustang from USAF dumped hundreds of P-51s out onto the civilian market. The rights to the Mustang design were purchased from North American by the Cavalier Aircraft Corporation, which attempted to market the surplus Mustang aircraft both in the U.S. and overseas. In 1967 and again in 1972, the USAF procured batches of remanufactured Mustangs from Cavalier, most of them destined for air forces in South America and Asia that were participating in the Military Assistance Program (MAP). These aircraft were remanufactured from existing original F-51D airframes but were fitted with new V-1650-7 engines, a new radio fit, tall F-51H-type vertical tails, and a stronger wing which could carry six 0.50-inch (13 mm) machine guns and a total of eight underwing hardpoints. Two 1000-pound bombs and six five-inch (127 mm) rockets could be carried. They all had an original F-51D-type canopy, but carried a second seat for an observer behind the pilot. One additional Mustang was a two-seat dual-control TF-51D (67-14866) with an enlarged canopy and only four wing guns. Although these remanufactured Mustangs were intended for sale to South American and Asian nations through the Military Assistance Program (MAP), they were delivered to the USAF with full USAF markings. They were, however, allocated new serial numbers (67-14862/14866, 67-22579/22582 and 72-1526/1541).

The last U.S. military use of the F-51 was in 1968, when the U. S. Army employed a vintage F-51D (44-72990) as a chase aircraft for the Lockheed YAH-56 Cheyenne armed helicopter project. This aircraft was so successful that the Army ordered two F-51Ds from Cavalier in 1968 for use at Fort Rucker as chase planes. They were assigned the serials 68-15795 and 65-15796. These F-51s had wingtip fuel tanks and were unarmed. Following the end of the Cheyenne program, these two chase aircraft were used for other projects. One of them (68-15795) was fitted with a 106 mm recoilless rifle for evaluation of the weapon's value in attacking fortified ground targets.

The F-51 was adopted by many foreign air forces and continued to be an effective fighter into the mid 1980s with smaller air arms. The last Mustang ever downed in battle occurred during Operation Power Pack in the Dominican Republic in 1965, with the last aircraft finally being retired by the Dominican Air Force (FAD) in 1984.

source : Wikipedia

Hughes H-4 Hercules

2008-10-18T18:14:00.002+05:30

The Hughes H-4 Hercules (registration NX37602) was a prototype heavy transport aircraft designed and built by the Hughes Aircraft company. The aircraft made its first and only flight on November 2, 1947. Built from wood due to wartime raw material restrictions on the use of aluminum, it was nicknamed the "Spruce Goose" by its critics. The Hercules is the largest flying boat ever built, and has the largest wingspan and height of any aircraft in history. It survives in good condition at the Evergreen Aviation Museum in McMinnville, Oregon.

Due to wartime restrictions on the availability of metals, the H-4 was built almost entirely of laminated birch, not spruce as its nickname suggests. The Duramold process, a form of composite technology, was used in the laminated wood construction. The aircraft was considered a technological tour de force. It married flying boats to a massive wooden airframe that required some ingenious engineering innovations to function.

Ultimately, the plane was not finished in time for use in the war and never advanced beyond the single prototype produced.

Design and development

Rearward view of the H-4's fuselage.

In 1942, the U.S. Department of War was faced with the need to transport war materiel and personnel to Britain. Allied shipping in the Atlantic Ocean was suffering heavy losses to German U-boats, so a requirement was issued for an aircraft that could cross the Atlantic with a large payload. For various reasons with regard to wartime priorities, the design was further constrained in that the aircraft could not be made of metal.

The aircraft was the brainchild of Henry J. Kaiser, who directed the Liberty ships program. He teamed with aircraft designer Howard Hughes to create what would become the largest aircraft built or even seriously contemplated at that time. When completed, it was capable of carrying 750 fully-equipped troops or one M4 Sherman tank. The original designation "HK-1" reflected the Hughes and Kaiser collaboration.

The HK-1 contract in 1942, issued as a development contract, initially called for three aircraft to be constructed under a two-year deadline in order to be available for the war effort. Seven different configurations were considered including twin-hulled and single-hulled designs with combinations of four, six and eight, wing-mounted engines. The final design chosen was a behemoth, eclipsing any large transport yet built or even envisioned. To conserve metal, it would be built mostly of wood (elevators and rudder were fabric covered); hence, the "Spruce Goose" moniker tagged on the aircraft by the media. It was also referred to as the Flying Lumberyard by critics who believed an aircraft of its size physically could not fly. Hughes himself detested the nickname "Spruce Goose".

While Kaiser had originated the "flying cargo ship" concept, he did not have an aeronautical background and deferred to Hughes and his designer, Glenn E. Odekirk.^[1] Development dragged on which frustrated Kaiser who blamed delays partly on restrictions placed for the acquisition of strategic materials such as aluminum but also placed part of the blame on Hughes' insistence on "perfection." Although construction of the first HK-1 had taken place 16 months after the receipt of the development contract, Kaiser withdrew from the project.

Size comparison between H-4 and a DC-3

Hughes continued the program on his own under the designation "H-4 Hercules" (initially identified as the HFB-1 to signify Hughes Flying Boat First Design), signing a new government contract that now limited production to one example. Work proceeded at a slow pace with the end result that the H-4 was not completed until well after the war was over.

In 1947, Howard Hughes was called to testify before the Senate War Investigating Committee over the usage of government funds for the aircraft.

During a Senate hearing on August 6, 1947 in the first of a series of appearances, Hughes said:

“

The Hercules was a monumental undertaking. It is the largest aircraft ever built. It is over five stories tall with a wingspan longer than a football field. That's more than a city block. Now, I put the sweat of my life into this thing. I have my reputation all rolled up in it and I have stated several times that if it's a failure I'll probably leave this country and never come back. And I mean it.

”

Maiden flight

Hughes H-4 Hercules on its maiden flight

During a break in the Senate hearings, Hughes returned to California to run taxi tests on the H-4. On November 2, 1947, a series of taxi tests was begun with Hughes at the controls. His crew included Dave Grant as co-pilot, and a crew of two flight engineers, 16 mechanics and two other flight crew. In addition, the H-4 carried seven invited guests from the press corps plus an additional seven industry representatives, for a total of 32 on board.

After the first two uneventful taxi runs, four reporters left to file stories but the remaining press stayed for the final test run of the day. After picking up speed on the channel facing Cabrillo Beach near Long Beach, the Hercules lifted off, remaining airborne 70 feet (21 m) off the water at a speed of 135 mph (217 km/h or 117 knots) for around a mile (1.6 km). At this altitude, the aircraft was still experiencing ground effect.

Hughes had answered his critics and the hearings ended. The aircraft never flew again. It was carefully maintained in flying condition until Hughes' death in 1976.

Postwar

Hercules at Evergreen Aviation Museum

After years of storage, in 1980, the Hercules was acquired by the California Aero Club, who successfully put the aircraft on display in a large dome adjacent to the Queen Mary exhibit in Long Beach, California. In 1988, The Walt Disney Company acquired both attractions and the associated real estate. Disney informed the California Aero club that they no longer wished to display the Hercules. After a long search for a suitable host, the California Aero Club awarded custody of the Hughes Flying Boat to Evergreen Aviation Museum. On July 9, 1990, under the direction of museum staff, the aircraft was disassembled and moved by barge to its current home in McMinnville, Oregon (about an hour southwest of Portland) where it has been on display since.

By the mid-1990s, the former Hughes Aircraft hangars including the one that held the Hercules were converted into sound stages. Scenes from movies such as Titanic, What Women Want, and End of Days have been filmed in the 315,000 square foot (29,000 m²) aircraft hangar where Howard Hughes created the flying boat. The hangar will be preserved as a structure eligible for listing in the National Register of Historic Buildings in what is today the housing development Playa Vista, Los Angeles, California.

Although the project did not move beyond the initial prototype, the H-4 Hercules, in some senses, presaged the massive transport aircraft of the late 20th century, such as the Lockheed C-5 Galaxy, the Antonov An-124 and the An-225. The Hercules demonstrated that the physical and aerodynamic principles which make flight possible are not limited by the size of the aircraft.

News story on the Hercules

Popular culture

In the film The Rocketeer (1991), hero Cliff Secord uses a large-scale model of the Hercules to escape some eager federal agents and Howard Hughes himself. After Secord glides the model to safety, Hughes expresses astonishment that the craft might actually fly.

The construction and flight of the Hercules was featured in the 2004 Hughes biopic The Aviator. Motion control and remote control models, as well as partial interiors and exteriors, of the aircraft were reproduced for this scene. The motion-control Hercules is on display at the Evergreen Aviation Museum, next to the real Hercules.

The aircraft's hold on popular imagination is demonstrated by the 1987 Hanna-Barbera animated film Yogi Bear and the Magical Flight of the Spruce Goose.

source : Wikipedia

Airbus A380

2008-10-18T17:49:00.002+05:30

The Airbus A380 is a double-deck, wide-body, four-engine airliner manufactured by the European corporation Airbus, an EADS subsidiary. The largest passenger airliner in the world, the A380 made its maiden flight on 27 April 2005 from Toulouse, France, and made its first commercial flight on 25 October 2007 from Singapore to Sydney with Singapore Airlines. The aircraft was known as the Airbus A3XX during much of its development phase, but the nickname Superjumbo has since become associated with it.

The A380's upper deck extends along almost the entire length of the fuselage, and its width is equivalent to that of a widebody aircraft. This allows for a cabin with 50% more floor space than the next-largest airliner, the Boeing 747-400. and provides seating for 525 people in standard three-class configuration or up to 853 people in all economy class configuration. The A380 is offered in passenger and freighter versions. The A380-800, the passenger model, is the largest passenger airliner in the world, but has a shorter fuselage than the Airbus A340-600 which is Airbus' next biggest passenger aeroplane. The A380-800F, the freighter model, is offered as one of the largest freight aircraft, with a listed payload capacity exceeded only by the Antonov An-225. The A380-800 has a design range of 15,200 kilometres (8,200 nmi), sufficient to fly from Boston, Massachusetts to Hong Kong for example, and a cruising speed of Mach 0.85 (about 900 km/h or 560 mph at cruising altitude). is the first commercial jet capable of using GTL-based fuel.

Development

Background

In the summer of 1988 a group of Airbus engineers, led by Jean Roeder, began working in secret on the development of a ultra-high-capacity airliner (UHCA), both to complete its own range of products and to break the dominance that Boeing had enjoyed in this market segment since the early 1970s with its 747. McDonnell Douglas unsuccessfully offered its smaller, double-deck MD-12 concept for sale. As each manufacturer looked to build a successor to the 747, they knew there was room for only one new aircraft to be profitable in the 600 to 800 seat market segment. Each knew the risk of splitting such a niche market, as had been demonstrated by the simultaneous debut of the Lockheed L-1011 and the McDonnell Douglas DC-10: both planes met the market’s needs, but the market could profitably sustain only one model, eventually resulting in Lockheed's departure from the civil airliner business.

Roeder was given approval for further evaluations of the UHCA after a formal presentation to the President and CEO in June 1990. The project was announced at the 1990 Farnborough Air Show, with the stated goal of 15 % lower operating costs than the 747-400. Airbus organized four teams of designers, one from each of its EADS partners (Aérospatiale, DaimlerChrysler Aerospace, British Aerospace, EADS CASA) to propose new technologies for its future aircraft designs. The designs would be presented in 1992 and the most competitive designs would be used.

In January 1993, Boeing and several companies in the Airbus consortium started a joint feasibility study of an aircraft known as the Very Large Commercial Transport (VLCT), aiming to form a partnership to share the limited market.

In June 1994, Airbus began developing its own very large airliner, designated the A3XX. Airbus considered several designs, including an odd side-by-side combination of two fuselages from the A340, which was Airbus’s largest jet at the time. The A3XX was pitted against the VLCT study and Boeing’s own New Large Aircraft successor to the 747, which evolved into the 747X, a stretched version of the 747 with the fore body "hump" extended rearwards to accommodate more passengers. The joint VLCT effort ended in April 1995, and Boeing suspended the 747X program in January 1997. From 1997 to 2000, as the East Asian financial crisis darkened the market outlook, Airbus refined its design, targeting a 15 to 20 percent reduction in operating costs over the existing Boeing 747-400. The A3XX design converged on a double-decker layout that provided more passenger volume than a traditional single-deck design.

Design phase

The first completed A380 at the "A380 Reveal" event in Toulouse, France.

On 19 December 2000, the supervisory board of newly restructured Airbus voted to launch a €8.8 billion program to build the A3XX, re-christened as the A380, with 55 orders from six launch customers. The A380 designation was a break from previous Airbus families, which had progressed sequentially from A300 to A340. It was chosen because the number 8 resembles the double-deck cross section, and is a lucky number in some Asian countries where the aircraft was being marketed. The aircraft’s final configuration was frozen in early 2001, and manufacturing of the first A380 wing box component started on 23 January 2002. The development cost of the A380 had grown to €11 billion when the first aircraft was completed.

Boeing, meanwhile, studied multiple 747-400 derivative designs before finally launching the Boeing 747-8 in November 2005 (with entry into service planned for 2009). Boeing chose to develop a variant for the 400 to 500 seat market, instead of matching the A380's capacity.

Production

Major structural sections of the A380 are built in France, Germany, Spain, and the United Kingdom. Due to their size, they are brought to the assembly hall in Toulouse in France by surface transportation, rather than by the A300-600ST Beluga aircraft used for other Airbus models. Components of the A380 are provided by suppliers from around the world; the five largest contributors, by value, are Rolls-Royce, SAFRAN, United Technologies, General Electric, and Goodrich.

A380 transporter ship Ville de Bordeaux

The front and rear sections of the fuselage are loaded on an Airbus Roll-on/roll-off (RORO) ship, Ville de Bordeaux, in Hamburg in northern Germany, from where they are shipped to the United Kingdom. The wings, which are manufactured at Filton in Bristol and Broughton in North Wales, are transported by barge to Mostyn docks, where the ship adds them to its cargo. In Saint-Nazaire in western France, the ship trades the fuselage sections from Hamburg for larger, assembled sections, some of which include the nose. The ship unloads in Bordeaux. Afterwards, the ship picks up the belly and tail sections by Construcciones Aeronáuticas SA in Cádiz in southern Spain, and delivers them to Bordeaux. From there, the A380 parts are transported by barge to Langon, and by oversize road convoys to the assembly hall in Toulouse. New wider roads, canal systems and barges were developed to deliver the A380 parts. After assembly, the aircraft are flown to Hamburg, XFW to be furnished and painted. It takes 3,600 litres (950 gallons) of paint to cover the 3,100 m² (33,000 ft²) exterior of an A380.

Airbus sized the production facilities and supply chain for a production rate of four A380s per month.

Testing

A380 MSN001 about to land after its maiden flight

Five A380s were built for testing and demonstration purposes.

The first A380, serial number MSN001 and registration F-WWOW, was unveiled at a ceremony in Toulouse on 18 January 2005. Its maiden flight took place at 8:29 UTC (10:29 a.m. local time) 27 April 2005. This plane, equipped with Trent 900 engines, flew from Toulouse Blagnac International Airport with a flight crew of six headed by chief test pilot Jacques Rosay. After successfully landing three hours and 54 minutes later, Rosay said flying the A380 had been “like handling a bicycle” .

On 1 December 2005 the A380 achieved its maximum design speed of Mach 0.96 (versus normal cruising speed of Mach 0.85), in a shallow dive, completing the opening of the flight envelope.

On 10 January 2006 the A380 made its first transatlantic flight to Medellín in Colombia, to test engine performance at a high altitude airport. It arrived in North America on 6 February, landing in Iqaluit, Nunavut in Canada for cold-weather testing.

A380 flying a banked turn at the ILA 2006

On 14 February 2006, during the destructive wing strength certification test on MSN5000, the test wing of the A380 failed at 145% of the limit load, short of the required 150% to meet the certification. Airbus announced modifications adding 30 kg to the wing to provide the required strength.^[20]

On 26 March 2006 the A380 underwent evacuation certification in Hamburg in Germany. With 8 of the 16 exits blocked, 853 passengers and 20 crew left the aircraft in 78 seconds, less than the 90 seconds required by certification standards.

Three days later, the A380 received European Aviation Safety Agency (EASA) and United States Federal Aviation Administration (FAA) approval to carry up to 853 passengers.

The maiden flight of the first A380 using GP7200 engines - serial number MSN009 and registration F-WWEA - took place on 25 August 2006.

Flight test engineer's station on the lower deck of A380 F-WWOW .

On 4 September 2006 the first full passenger-carrying flight test took place. The aircraft flew from Toulouse with 474 Airbus employees on board, in the first of a series of flights to test passenger facilities and comfort.

In November 2006, a further series of route proving flights took place to demonstrate the aircraft's performance for 150 flight hours under typical airline operating conditions.

Airbus obtained type certificate for the A380-841 and A380-842 model from the EASA and FAA on 12 December 2006 in a joint ceremony at the company's French headquarters.A380-861 model obtained the type certificate 14 December 2007.

As of February 2008, the five A380s in the test programme had logged over 4,565 hours during 1,364 flights, including route proving and demonstration flights.

Delivery delays

Initial production of the A380 was troubled by delays attributed to the 530 km (330 miles) of wiring in each aircraft. Airbus cited as underlying causes the complexity of the cabin wiring (100,000 wires and 40,300 connectors), its concurrent design and production, the high degree of customization for each airline, and failures of configuration management and change control. Specifically, it would appear that German and Spanish Airbus facilities continued to use CATIA version 4, while British and French sites migrated to version 5. This caused overall configuration management problems, at least in part because wiring harnesses manufactured using aluminium rather than copper conductors necessitated special design rules including non-standard dimensions and bend radii: these were not easily transferred between versions of the software.

Airbus announced the first delay in June 2005 and notified airlines that delivery would slip by six months. This reduced the number of planned deliveries by the end of 2009 from about 120 to 90–100. On 13 June 2006, Airbus announced a second delay, with the delivery schedule undergoing an additional shift of six to seven months. Although the first delivery was still planned before the end of 2006, deliveries in 2007 would drop to only 9 aircraft, and deliveries by the end of 2009 would be cut to 70–80 aircraft. The announcement caused a 26% drop in the share price of Airbus's parent, EADS, and led to the departure of EADS CEO Noël Forgeard, Airbus CEO Gustav Humbert, and A380 programme manager Charles Champion. On 3 October 2006, upon completion of a review of the A380 program, the CEO of Airbus, Christian Streiff, announced a third delay, pushing the first delivery to October 2007, to be followed by 13 deliveries in 2008, 25 in 2009, and the full production rate of 45 aircraft per year in 2010. The delay also increased the earnings shortfall projected by Airbus through 2010 to €4.8 billion.

As Airbus prioritized the work on the A380-800 over the A380-800F, freighter orders were cancelled (FedEx, UPS) or converted to A380-800 (Emirates, ILFC). Airbus suspended work on the freighter version, but said it remained on offer, albeit without a service entry date. For the passenger version Airbus negotiated a revised delivery schedule and compensation with the 13 customers, all of which retained their orders with some placing subsequent orders (Emirates, Singapore Airlines Qantas, Air France, Qatar, and Korean Air).

The first A380 with redesigned wiring harnesses achieved power-on in April 2008, with a 3 1/2 month delay. On 13 May 2008 Airbus announced reduced deliveries for the years 2008 (12) and 2009 (21).

Entry into service

Singapore Airlines Airbus A380 9V-SKA takes off from London Heathrow Airport.

The first aircraft delivered, MSN003, (registered 9V-SKA) was handed over to Singapore Airlines on 15 October 2007 and entered into service on 25 October 2007 with a commercial flight between Singapore and Sydney (flight number SQ380). Two months later Singapore Airlines CEO Chew Choong Seng said that the A380 was performing better than both the airline and Airbus had anticipated, burning 20% less fuel per passenger than the airline's existing 747-400 fleet. Singapore Airlines operated its first two aircraft, in a 471-seat configuration, between Singapore and Sydney. This was then expanded to include Singapore–London from 18 March 2008 after the third aircraft was delivered. A fourth aircraft was delivered to Singapore Airlines on the 26 April 2008 which enabled it to use the type on the Singapore-Tokyo route from 20 May. On 2 August 2008 Singapore Airlines began the temporary use of the A380 to Beijing to meet increased demand for the 2008 Summer Olympics in Beijing and on 4 August made the company's 1000th commercial flight with an A380. Singapore Airlines operates six A380 aircraft as of September 2008.

Emirates Airline was the second airline to take delivery of the A380 (registered A6-EDA) on 28 July 2008 and started flights between Dubai and New York on 1 August 2008. Emirates will begin flights between Dubai and London on 1 December 2008 and Dubai to Auckland (via Sydney) on 1 February 2009.

Qantas Airbus A380 VH-OQA at Sydney Airport.

The first aircraft for Qantas (third airline to take delivery of the A380), MSN014, (registered VH-OQA) was delivered on 19 September 2008. Qantas has announced it will use the A380, in a 450-seat configuration, on its Melbourne to Los Angeles route from 20 October 2008. Subsequent routes include Sydney to Los Angeles and London starting on the 24 October 2008.

Air France has said that its A380s will be used on its Paris to Montreal and New York routes. Lufthansa will be using the aircraft for its long-haul destinations to North America and Asia.

Design

A380 cabin cross section, showing economy class seating

The new Airbus is sold in two models. The A380-800 was originally designed to carry 555 passengers in a three-class configuration or 853 passengers (538 on the main deck and 315 on the upper deck) in a single-class economy configuration. In May 2007, Airbus began marketing the same aircraft to customers with 30 fewer passengers (now 525 passengers in three classes) traded for 370 km (200 nmi) more range, to better reflect trends in premium class accommodation. The design range for the -800 model is 15,200 km (8,200 nmi). The second model, the A380-800F freighter, will carry 150 tonnes of cargo 10,400 km (5,600 nmi). Future variants may include an A380-900 stretch seating about 656 passengers (or up to 960 passengers in an all economy configuration) and an extended range version with the same passenger capacity as the A380-800.

The A380's wing is sized for a Maximum Take-Off Weight (MTOW) over 650 tonnes in order to accommodate these future versions, albeit with some strengthening required. The stronger wing (and structure) is used on the A380-800F freighter. This common design approach sacrifices some fuel efficiency on the A380-800 passenger model, but Airbus estimates that the size of the aircraft, coupled with the advances in technology described below, will provide lower operating costs per passenger than all current variants of Boeing 747. The A380 also features wingtip fences similar to those found on the A310 and A320 to alleviate the effects of wake turbulence, increasing fuel efficiency and performance.

Flight deck

The flight deck

Airbus used similar cockpit layout, procedures and handling characteristics to those of other Airbus aircraft, to reduce crew training costs. Accordingly, the A380 features an improved glass cockpit, and fly-by-wire flight controls linked to side-sticks.^[60] The improved cockpit displays feature eight 15-by-20 cm (6-by-8-inch) liquid crystal displays, all of which are physically identical and interchangeable. These comprise two Primary Flight Displays, two navigation displays, one engine parameter display, one system display and two Multi-Function Displays. These MFDs are new with the A380, and provide an easy-to-use interface to the flight management system—replacing three multifunction control and display units. They include QWERTY keyboards and trackballs, interfacing with a graphical "point-and-click" display navigation system. or two HUD (Head Up Display) is optional.

Engines

A Rolls-Royce Trent 900 engine on the wing of an Airbus A380

The A380 can be fitted with two types of engines: A380-841, A380-842 and A380-843F with Rolls-Royce Trent 900, and the A380-861 and A380-863F with Engine Alliance GP7000 turbofans. The Trent 900 is a derivative of the Trent 800, and the GP7000 has roots from the GE90 and PW4000. The Trent 900 core is a scaled version of the Trent 500, but incorporates the swept fan technology of the stillborn Trent 8104. The GP7200 has a GE90-derived core and PW4090-derived fan and low-pressure turbo-machinery. Only two of the four engines are fitted with thrust reversers.

Noise reduction was an important requirement in the A380's design, and particularly affects engine design. Both engine types allow the aircraft to achieve QC/2 departure and QC/0.5 arrival noise limits under the Quota Count system set by London Heathrow Airport, which is expected to become a key destination for the A380.

Fuel

The A380 can run on mixed synthetic jet fuel with a natural-gas-derived component. A three hour test flight on Friday, 1 February 2008 between the Airbus company facility at Filton in the UK to the main Airbus factory in Toulouse, France, was a success. One of the A380's four engines used a mix of 60 percent standard jet kerosene and 40 percent gas to liquids (GTL) fuel supplied by Shell. The aircraft needed no modification to use the GTL fuel, which was designed to be mixed with regular jet fuel. Sebastien Remy, head of Airbus SAS's alternative fuel program, said the GTL used was no cleaner in CO₂ terms than regular fuel but it had local air quality benefits because it contains no sulphur.

Advanced materials

While most of the fuselage is aluminium, composite materials make up 25% of the A380's airframe, by weight. Carbon-fibre reinforced plastic, glass-fibre reinforced plastic and quartz-fibre reinforced plastic are used extensively in wings, fuselage sections (such as the undercarriage and rear end of fuselage), tail surfaces, and doors. The A380 is the first commercial airliner with a central wing box made of carbon fibre reinforced plastic, and it is the first to have a wing cross-section that is smoothly contoured. Other commercial airliners have wings that are partitioned span-wise in sections. The flowing, continuous cross-section allows for maximum aerodynamic efficiency. Thermoplastics are used in the leading edges of the slats. The new material GLARE (GLAss-REinforced fibre metal laminate) is used in the upper fuselage and on the stabilizers' leading edges. This aluminium-glass-fibre laminate is lighter and has better corrosion and impact resistance than conventional aluminium alloys used in aviation. Unlike earlier composite materials, it can be repaired using conventional aluminium repair techniques. Newer weldable aluminium alloys are also used. This enables the widespread use of laser beam welding manufacturing techniques — eliminating rows of rivets and resulting in a lighter, stronger structure.

Avionics architecture

The A380 employs an Integrated Modular Avionics (IMA) architecture, first used in advanced military aircraft such as the F-22 Raptor, Eurofighter Typhoon, or Dassault Rafale. It is based on a commercial off-the-shelf (COTS) design. Many previous dedicated single-purpose avionics computers are replaced by dedicated software housed in onboard processor modules and servers. This cuts the number of parts, provides increased flexibility without resorting to customised avionics, and reduces costs by using commercially available computing power.

Together with IMA, the A380 avionics are very highly networked. The data communication networks use Avionics Full-Duplex Switched Ethernet, following the ARINC 664 standard. The data networks are switched, full-duplexed, star-topology and based on 100baseTX fast-Ethernet. This reduces the amount of wiring required and minimizes latency. .

The Network Systems Server (NSS) is the heart of A380 paperless cockpit. It eliminates the bulky manuals and charts traditionally carried by the pilots. The NSS has enough inbuilt robustness to do away with onboard backup paper documents. The A380's network and server system stores data and offers electronic documentation, providing a required equipment list, navigation charts, performance calculations, and an aircraft logbook. All are accessible to the pilot from two additional 27 cm (11 inch) diagonal LCDs, each controlled by its own keyboard and control cursor device mounted in the foldable table in front of each pilot.

Systems

The A380-800 layout with 550 seats displayed

Power-by-wire flight control actuators are used for the first time in civil service, backing up the primary hydraulic flight control actuators. During certain maneuvers, they augment the primary actuators. They have self-contained hydraulic and electrical power supplies. They are used as electro-hydrostatic actuators (EHA) in the aileron and elevator, and as electrical backup hydrostatic actuators (EBHA) for the rudder and some spoilers

The aircraft's 350 bar (35 MPa or 5,000 psi) hydraulic system is an improvement over the typical 210 bar (21 MPa or 3,000 psi) system found in other commercial aircraft since the 1940s. First used in military aircraft, higher pressure hydraulics reduce the size of pipelines, actuators and other components for overall weight reduction. The 350 bar pressure is generated by eight de-clutchable hydraulic pumps. Pipelines are typically made from titanium and the system features both fuel and air-cooled heat exchangers. The hydraulics system architecture also differs significantly from other airliners. Self-contained electrically powered hydraulic power packs, instead of a secondary hydraulic system, are the backups for the primary systems. This saves weight and reduces maintenance.

The A380 uses four 150 kVA variable-frequency electrical generators eliminating the constant speed drives for better reliability. The A380 uses aluminium power cables instead of copper for greater weight savings due to the number of cables used for an aircraft of this size and complexity. The electrical power system is fully computerized and many contactors and breakers have been replaced by solid-state devices for better performance and increased reliability.

The A380 features a bulbless illumination system. LEDs are employed in the cabin, cockpit, cargo and other fuselage areas. The cabin lighting features programmable multi-spectral LEDs capable of creating a cabin ambience simulating daylight, night or shades in between. On the outside of the aircraft, HID lighting is used to give brighter, whiter and better quality illumination. These two technologies provide brightness and a service life superior to traditional incandescent light bulbs.

The A380 was initially planned without thrust reversers, as Airbus believed it to have ample braking capacity. The FAA disagreed, and Airbus elected to fit only the two inboard engines with them. The two outboard engines do not have reversers, reducing the amount of debris stirred up during landing. The A380 features electrically actuated thrust reversers, giving them better reliability than their pneumatic or hydraulic equivalents, in addition to saving weight.

Passenger provisions

Business class on the first Singapore Airlines Airbus A380 aircraft

The A380 produces 50% less cabin noise than a 747 and has higher cabin air pressure (equivalent to an altitude of 1500 metres (5000 ft) versus 2500 metres (8000 ft)); both features are expected to reduce the effects of travel fatigue.The upper and lower decks are connected by two stairways, fore and aft, wide enough to accommodate two passengers side-by-side. In a 555-passenger configuration, the A380 has 33% more seats than a 747-400 in a standard three-class configuration but 50% more cabin area and volume, resulting in more space per passenger. Its maximum certified carrying capacity is 853 passengers in an all-economy-class configuration. The two full-length decks and wide stairways allow multiple seat configurations of the Airbus A380. The announced configurations go from 450 (Qantas) up to 644 passengers (Emirates Airline two-class configuration).

Compared to a 747, the A380 has larger windows and overhead bins, and 60 cm (2 ft) of extra headroom. The wider cabin allows for up to 48 cm (19 inch) wide economy seats at a 10 abreast configuration on the main deck, while 10 abreast seating on the 747 has a seat width of only 43.7 cm (17.2 inch) (seat pitch varies by airline).

Airbus' initial publicity stressed the comfort and space of the A380's cabin, anticipating installations such as relaxation areas, bars, duty-free shops, and beauty salons. Virgin Atlantic Airways already offers a bar as part of its "Upper Class" service on its A340 and 747 aircraft, and has announced plans to include casinos, double beds, and gymnasiums on its A380s. Singapore Airlines offers twelve fully-enclosed first-class suites on its A380, each with one full and one secondary seat, full-sized bed, desk, personal storage. Four of these suites are in the form of two "double" suites featuring a double bed. Qantas Airways has shown their product which features a long flat-bed that converts from the seat but does not have privacy doors. Emirates Airline's fourteen first-class private suites have shared access to two "shower spas". First and business class passengers have shared access to a snack bar and lounge with two sofas, in addition to a first-class-only private lounge.

Integration in the infrastructure

Ground operations

The A380's 20-wheel main landing gear

Early critics claimed that the A380 would damage taxiways and other airport surfaces. However, the pressure exerted by its wheels is lower than that of a Boeing 747 or Boeing 777 because the A380 has 22 wheels, four more than the 747, and eight more than the 777. Airbus measured pavement loads using a 540-tonne (595 short tons) ballasted test rig, designed to replicate the landing gear of the A380. The rig was towed over a section of pavement at Airbus' facilities that had been instrumented with embedded load sensors.

Based on its wingspan, the U.S. FAA classifies the A380 as a Design Group VI aircraft, and originally required a width of 60 m (200 ft) for runways and 30 m (100 ft) for taxiways, compared with 45 m (150 ft) and 23 m (75 ft) for Design Group V aircraft such as the Boeing 747.The FAA also considered limiting the taxi speed of the A380 to 25 km/h (15 mph) when operating on Group V infrastructure, but issued waivers related to the speed restriction and some of the proposed runway widening requirements. Airbus claimed from the beginning that the A380 could safely operate on Group V runways and taxiways, without the need for widening. In July 2007, the FAA and EASA agreed to let the A380 operate on 45 m runways without restrictions.

A380 being serviced by three separate jetways at Frankfurt Airport; two for the main deck and one for the upper deck.

The A380 was designed to fit within an 80 × 80 m airport gate, and can land or take off on any runway that can accommodate a Boeing 747. Its large wingspan can require some taxiway and apron reconfigurations, to maintain safe separation margins when two of the aircraft pass each other. Taxiway shoulders may be required to be paved to reduce the likelihood of foreign object damage caused to (or by) the outboard engines, which overhang more than 25 m (80 ft) from the centre line of the aircraft. Any taxiway or runway bridge must be capable of supporting the A380's maximum weight. The terminal gate must be sized such that the A380's wings do not block adjacent gates, and may also provide multiple jetway bridges for simultaneous boarding on both decks. Service vehicles with lifts capable of reaching the upper deck should be obtained, as well as tractors capable of handling the A380's maximum ramp weight. The A380 test aircraft have participated in a campaign of airport compatibility testing to verify the modifications already made at several large airports, visiting a number of airports around the world.

Takeoff and landing separation

In 2005, the ICAO recommended that provisional separation criteria for the A380 on takeoff and landing be substantially greater than for the 747 because preliminary flight test data suggested a stronger wake turbulence. These criteria were in effect while the ICAO's wake vortex steering group, with representatives from the JAA, Eurocontrol, the FAA, and Airbus, refined its 3-year study of the issue with additional flight testing. In September 2006, the working group presented its first conclusions to the ICAO.

In November 2006 the ICAO issued new interim recommendations. Replacing a blanket 10 nmi separation for aircraft trailing an A380 during approach, the new distances were 6 nmi, 8 nmi and 10 nmi respectively for non-A380 "Heavy", "Medium", and "Light" ICAO aircraft categories. These compared with the 4 nmi, 5 nmi and 6 nmi spacing applicable to other "Heavy" aircraft. Another A380 following an A380 should maintain a separation of 4 nmi. On departure behind an A380, non-A380 "Heavy" aircraft are required to wait two minutes, and "Medium"/"Light" aircraft three minutes for time based operations. The ICAO also advised to use the suffix "Super" to the air traffic control to distinguish the A380 from other "Heavy" aircraft

In August 2008 the ICAO issued revised approach separations of 4 nmi for Super (another A380), 6 nmi for Heavy, 7 nmi for medium/small and 8 nmi for light.

Future variants

Airbus A380-900

Airbus top sales executive and COO John Leahy confirmed the plans for an enlarged variant, the A380-900 which is a slight stretch of the A380-800 from 73m to 79.4m in length. This version would have a seat capacity of 650 passengers in standard configuration, and around 900 passengers in economy-only configuration. The development of the A380-900 is planned to start once production of the A380-800 variant reaches 40 planes per year, expected to be in 2010. Given this timeline, the first A380-900s could be delivered to customers around 2015, about the same time as the A380-800F freighter variant. Airlines including Emirates,Virgin Atlantic, Cathay Pacific, Air France/KLM,and Lufthansa, as well as leasing company ILFC have already expressed interest in the extended model. According to an interview in Airliner World magazine's December issue, Singapore Airlines CEO Chew Choon Seng revealed at the delivery of their first A380-800 that the airline is keeping their options open with their order, by only defining their first ten A380s as -800s; the remaining nine aircraft could be switched to -900s.

Market

Parallel to the design of the A380, Airbus conducted the most extensive and thorough market analysis of commercial aviation ever undertaken. As of 2007, Airbus estimated a demand for 1,283 passenger planes in the category VLA (Very Large Aircraft, with more than 400 seats) for the next 20 years if the airport congestion remains at the current level. If the congestion increases, the demand could reach up to 1,771 VLAs. Most of this demand will be due to the urbanization and rapid economic growth in Asia.

The A380 will be used on relatively few routes, between the most saturated airports. Airbus also estimates a demand for 415 freighters in the category 120-tonne plus. Boeing, which offers the only competition in that class, the 747-8, estimates the demand for passenger VLAs at 590 and that for freighter VLAs at 370 for the period 2007-2026. In 2006 two industry analysts anticipated 400 and 880 A380 sales respectively by 2025.

As of February 2008, there were 191 orders for the A380, while there were 20 for the 747-8I (both not including VIP orders) and 81 for the 747-8F. The break-even for the A380 was initially supposed to be reached at 270 units. Due to the delays and the falling exchange rate of the US dollar, it increased to 420 units.In April 2007, Airbus CEO Louis Gallois said that break-even had risen further, but declined to give the new figure. As of April 2008, the list price of an A380 was US$ 317.2 to 337.5 million, depending on equipment installed.

Orders and deliveries

Cumulative orders for the A380.

Sixteen customers have ordered the A380, including an order from aircraft lessor ILFC and one VIP order. Total orders for the A380 stand at 198 as of 24 July 2008. A total of 27 orders originally placed for the freighter version, A380-800F, were either cancelled (20) or converted to A380-800 (7), following the production delay and the subsequent suspension of the freighter program. Airbus' new schedule is to deliver 12 A380s in 2008 and 21 in 2009.

Orders and deliveries by year

		2001	2002	2003	2004	2005	2006	2007	2008	Total
Orders	A380-800	78	0	34	10	10	24	33	9	198
Orders	A380-800F	7	10	0	0	10	-17	-10	0	0
Deliveries	A380-800	0	0	0	0	0	0	1	7	8

Specifications

Size comparison between four of the largest aircraft. Airbus A380 (red), Boeing 747-8I (blue), Antonov An-225 (green) and Hughes H-4 (yellow).

Economy class fuselage-comparison between Airbus A380 and the front-section of Boeing 747, the next-largest passenger aircraft

Measurement	A380-800	A380-800F
Cockpit crew	Two
Seating capacity	525 (3-class) 644 (2-class) 853 (1-class)	12 couriers
Length	73 m (239 ft 6 in)
Span	79.8 m (261 ft 10 in)
Height	24.1 m (79 ft 1 in)
Wheelbase	30.4 m (99 ft 8 in)
Outside fuselage width	7.14 m (23 ft 6 in)
Cabin width, main deck	6.58 m (21 ft 7 in)
Cabin width, upper deck	5.92 m (19 ft 5 in)
Wing area	845 m² (9,100 sq ft)
Operating empty weight	276,800 kg (610,200 lb)	252,200 kg (556,000 lb)
Maximum take-off weight	560,000 kg (1,235,000 lb)	590,000 kg (1,300,000 lb)
Maximum payload	90,800 kg (200,000 lb)	152,400 kg (336,000 lb)
Cruising speed	Mach 0.85 (647 mph, 1,041 km/h, 562 knots)
Maximum cruising speed	Mach 0.89 (677 mph, 1,090 km/h, 588 knots)
Maximum speed	Mach 0.96 (731 mph, 1,176 km/h, 635 knots)
Take off run at MTOW	2,750 m (9,020 ft)	2,900 m (9,510 ft)
Range at design load	15,200 km (8,200 nmi)	10,400 km (5,600 nmi)
Service ceiling	13,115 m (43,000 ft)
Maximum fuel capacity	310,000 L (81,890 US gal)	310,000 L (81,890 US gal), 356,000 L (94,000 US gal) option
Engines (4 x)	GP7270 (A380-861) Trent 970/B (A380-841) Trent 972/B (A380-842)	GP7277 (A380-863F) Trent 977/B (A380-843F)
Thrust (4 x)	311 kN (70,000 lbf)

Tutankhamun Tomb : The richest treasures

2008-10-15T20:51:00.001+05:30

King Tutankhamun's Tomb

Howard Carter (May 9, 1874 - March 2, 1939) was an English archaeologist and Egyptologist. He is most famous as the discoverer of KV62, the tomb of Tutankhamun in the Valley of the Kings, Luxor, Egypt. Howard Carter was born in 1874 in Kensington, London, the youngest son of eight children. His father, Samuel Carter, was an artist. His mother was Martha Joyce (Sands) Carter. Carter grew up in Swaffham, in northern Norfolk, and had no formal education. His father trained him in the fundamentals of drawing and painting. Carter began work in 1891, at the age of 17, copying inscriptions and paintings in Egypt. He worked on the excavation of Beni Hasan, the gravesite of the princes of Middle Egypt, c. 2000 BC. Later he came under the tutelage of William Flinders Petrie.He is also famous for finding the remains of Queen Hatshepsut tomb in Deir el Babri. In 1899, at the age of 25, Carter was offered a position working for the Egyptian Antiquities Service, from which he resigned as a result of a dispute between Egyptian site guards and a group of drunken French tourists in 1905.

Carter and Carnarvon

After several hard years, Carter was introduced, in 1907, to Lord Carnarvon, an eager amateur who was prepared to supply the funds necessary for Carter's work to continue. Soon, Carter was supervising all of Lord Carnarvon's excavations. Lord Carnarvon financed Carter's search for the tomb of a previously unknown Pharaoh, Tutankhamun, whose existence Carter had discovered. After a few months of fruitless searching, Carnarvon was becoming dissatisfied with the lack of return from his investment and, in 1922, he gave Carter one more season of funding to find the tomb.

On November 22, 1922 Carter found Tutankhamen's tomb (subsequently designated KV62), by far the best preserved and most intact pharaonic tomb ever found in the Valley of the Kings. He wired Lord Carnarvon to come at once.

On February 16, 1923, Carter opened the burial chamber and first saw the sarcophagus of Tutankhamun.

While unwrapping the linens of the mummy, presumably looking for treasure, the skull of the ancient king fell away from the body. The impact from its fall out of the tomb made a dent in the skull. Ancient Egyptians believed a king could only be immortal if the body rested undisturbed, so some believe the name of the king must still be spoken today as a remembrance.

After cataloguing the extensive finds, Carter retired from archaeology and became a collector. He visited the United States in 1924, and gave a series of illustrated lectures in New York City which were attended by very large and enthusiastic audiences.

He died in England in 1939 at the age of 64. The archaeologist's death at this advanced age is the most common piece of evidence put forward by skeptics to refute the idea of a curse (the "Curse of the Pharaohs") plaguing the party that violated Tutankhamun's tomb. Howard Carter is buried in Putney Vale Cemetery in West London.

Excavating the Tomb

Outside the tomb before it was opened.

It took only three days before the top of a staircase was unearthed. On November 4th, 1922 Carter's workmen discovered a step cut into the rock. Then they found fifteen more leading to an ancient doorway that appeared to be still sealed.

The rumor of an ancient curse didn't stop this archaeologist from opening the tomb of King Tut. Death Shall Come on Swift Wings To Him Who Disturbs the Peace of the King was allegedly engraved on the exterior of King Tutankhamen's Tomb.

On the doorway was the name Tutankhamen. Almost three weeks later the staircase was entirely excavated and the full side of the plaster block was visible.

By November 26, the first plaster block was removed, the chip filling the corridor was emptied, and the second plaster was ready to be taken apart.

At about 4 P.M. that day, Carter broke through the second plaster block and made one of the discoveries of the century, the tomb of King Tutankhamun.

The Curse of the Mummy

When Carter arrived home that night his servant met him at the door. In his hand he clutched a few yellow feathers. His eyes large with fear, he reported that the canary had been killed by a cobra. Carter, a practical man, told the servant to make sure the snake was out of the house.

The man grabbed Carter by the sleeve. "The pharaoh's serpent ate the bird because it led us to the hidden tomb! You must not disturb the tomb!"

Scoffing at such superstitious nonsense, Carter sent the man home.

Carter immediately sent a telegram to Carnarvon and waited anxiously for his arrival. Carnarvon made it to Egypt by November 26th and watched as Carter made a hole in the door. Carter leaned in, holding a candle, to take a look. Behind him Lord Carnarvon asked, "Can you see anything?"

Carter answered, "Yes, wonderful things."

The tomb was intact and contained an amazing collection of treasures including a stone sarcophagus. The sarcophagus contained three gold coffins nested within each other (right). Inside the final one was the mummy of the boy-king, Pharaoh Tutankhamen. The day the tomb was opened was one of joy and celebration for all those involved. Nobody seemed to be concerned about a curse.

A few months later tragedy struck.

Lord Carnarvon, 57, was taken ill and rushed to Cairo. He died a few days later. The exact cause of death was not known, but it seemed to be from an infection started by an insect bite. Legend has it that when he died there was a short power failure and all the lights throughout Cairo went out. On his estate back in England his favorite dog howled and dropped dead.

Even more strange, when the mummy of Tutankhamun was unwrapped in 1925, it was found to have a wound on the left cheek in the same exact position as the insect bite on Carnarvon that lead to his death.

By 1929 eleven people connected with the discovery of the Tomb had died early and of unnatural causes. This included two of Carnarvon's relatives, Carter's personal secretary, Richard Bethell, and Bethell's father, Lord Westbury. Westbury killed himself by jumping from a building. He left a note that read, "I really cannot stand any more horrors and hardly see what good I am going to do here, so I am making my exit."

The press followed the deaths carefully attributing each new one to the "Mummy's Curse."

By 1935 they had credited 21 victims to King Tut. Was there really a curse? Or was it all just the ravings of a sensational press? Perhaps, the power of a curse is in the mind of the person who believes in it. Howard Carter, the man who actually opened the tomb, never believed in the curse and lived to a reasonably old age of 66 before dying of entirely natural causes.

Inside The Tomb

Though small and unimpressive, Tutankhamun's Tomb is probably the most famous, due to its late discovery. Howard Carter's description upon opening the tomb in 1922 was, "At first I could see nothing, the hot air escaping from the chamber causing the candle flames to flicker, but presently, as my eyes grew accustomed to the light, details of the room within emerged slowly from the mist, strange animals, statues and gold - everywhere the glint of gold.

For the moment - an eternity it must have seemed to the others standing by - I was dumb with amazement, and when Lord Carnarvon, unable to stand the suspense any longer, inquired anxiously, 'Can you see anything?' it was all I could do to get out the words, "Yes, wonderful things."'

The royal seal on the door was found intact. The first three chambers were unadorned, with evidence of early entrance through one of the outside walls. The next chamber contained most of the funerary objects.

Found in Antechamber

The sarcophagus was four guilded wooden shrines, one inside the other, within which lay the stone sarcophagus, three mummiform coffins, the inner one being solid gold, and then the mummy. Haste can be seen in the reliefs and the sarcophagus, due to the fact that Tutankhamun died at only 19 years of age following a brief reign. Though extremely impressive to the modern world, the treasures of Tutankhamun must have paled when compared to the tombs of the great Pharaohs that ruled for many years during Egypt's golden age.

The tomb is much smaller than, any of the other kings tombs, with plain walls, until you reach the burial chamber. It took almost a decade of meticulous and painstaking work to empty the tomb of Tutankhamen. Around 3500 individual items were recovered.

Tutankhamen is the only pharaoh, in the valley of the kings, still to have his mummy in its original burial location.

Discovered resting on a sled dressed in silver in, the antechamber of the tomb of Tutankhamun, this wooden shrine is covered in gold leaf applied to a layer of stucco. Its form, with the roof sloping down from front to rear and the projecting cornice at the top of the walls, recalls the ancient chapels of Upper Egypt.

A double door opens on one of the short sides and is closed with two ebony latches running through gold rings. A cord would once have passed through another two and been fastened with a clay seal. Inside the shrine there is a gilded wooden support for a statue, which was probably in solid gold and removed by grave robbers. The base still carries the marks of the feet while the name of Tutankhamun is inscribed on the dorsal pillar. On the floor lay the remains of a pectoral of which fragments have been found scattered elsewhere in the tomb.

The roof of the shrine is decorated with a winged solar disc at the front and twelve images of the vulture goddess Nekhbet with outspread wings protecting the cartouches of the sovereign and his wife. Two winged serpents with long, sinuous bodies are depicted on the sides of the roof and hold in front of them the shen hieroglyph, symbolizing eternity. The lintel of the door also features a winged solar disc while the cornice above is incised with a continuous series of vertical lines.

The external walls and the doors are subdivided into panels framed by hieroglyphic inscriptions with scenes showing Tutankhamun and his wife in various aspects of married life, a theme that recalls the scenes of the Amarna Period. However, it is not only the contents of the various scenes that recall the art of Akhenaten, but also their style characterized by the fineness, grace, and sophistication of the modeling.

The couple, adorned with jewels and dressed in finely pleated, adherent clothing, appear in various poses that reveal their reciprocal affection and a sense of absolute peace and serenity. The left wall is divided into four panels. In the bottom left Ankhesenamun is crouching before the seated Tutankhamun and is receiving a liquid poured by her husband into her hands from a small ampoule.

In the other scenes Tutankhamun, always sitting on his throne, is portrayed receiving various from his wife. On the right-hand wall, divided into two registers, Tutankhamun is seen hunting in a swamp, again in the company of the queen. The rear wall and the doors, both inside and out, are decorated with scenes in which Ankhesenamun is making offerings in the presence of her husband.

The entire decorative scheme of the shrine has strong symbolic connotations associated with the religious and political spheres. The intimate ties between the pharaoh and his bride represent the serene relationship between god and man. For this reason it is almost always the queen who is the active figure, embodying the concept of humanity paying homage to the celestial being personified by Tutankhamun. The hunting scene is to be interpreted as a symbolic episode referring to the pharaoh's role in the maintenance of the cosmic order and his constant fight against chaos (symbolized by the birds in the swamp).

Thanks to the images of the king identified as a god, the sovereign¹s shrine thus becomes a reproduction of a shrine dedicated to the cult of a divinity.

These two statues were discovered in the antechamber of the royal tomb, facing each other on either side of the sealed entrance to the burial chamber. At the time of their discovery traces of the linen bandages in which they had been wrapped were found, along with two bundles of olive and persea branches placed as offerings, one on the floor, the other still propped against the wall.

The statues, of refined craftsmanship and striking in both their life-size dimensions and the black finish of the skin, are testimony to the skill of the artist who has succeeded in investing their features with a sense of the almost supernatural power they wielded as guardians of the burial chamber. Rather than being designed to frighten eventual intruders, the black skin tone was a reference to the earth and thus, given that these are ka images of the sovereign, emphasizes indestructibility of the creative nature of the king, evoking the aspects of rebirth and cyclical resurrection of Osiris.

The two statues differ only in the type of head covering they are wearing (one a khat head-cloth, the other a nemes) and the inscriptions on their skirts. The king is portrayed in a striding pose, a mace gripped in his right hand and a long staff with a papyrus stem in his left hand. A gilded bronze asp adorns his forehead while the eyes are inlaid and outlined with gilded bronze, as are the eyebrows. A gilded usekh necklace and a pectoral are worn on the chest. The pleated skirt is fastened on the hips with a belt inscribed at the rear and on the buckle with the coronation name of the king Nebkbeperura.

The protruding frontal section of the skirt of the statue with the khat head-cloth carries the vertical inscription "The perfect god, rich in glory, a sovereign to be proud of, the regal ka of Horakhty, the Osiris, and Lord of the Two Lands, Nebkbeperura, made just." The inscription on the statue wearing the nemes records the birth name of the pharaoh, "Tutankhamun, living forever as Ra each day". Both statues are wearing anklets and bracelets of gilded bronze. Although made some years after the end of the Amarna Period, these sculptures clearly show the influence of the art of Akhenaten with their prominent bellies, slim legs and pierced ears.

Thirty-four wooden statues were found in the tomb of Tutankhamun, seven portraying the pharaoh and the other twenty-seven depicting various divinities from the Egyptian pantheon. The majority of the statues had been placed in the treasure chamber inside black wooden cabinets mounted on sleds and set along the south wall. Two of these pieces, placed together in the same cabinet, are identical and depict the pharaoh stepping on the back of a panther.

The image of the sovereign is sculpted with great realism in a very hard wood, stuccoed and covered with a thin layer of gold leaf. Tutankhamun is gripping a long staff in one hand and the flail symbolizing his power in the other. He is wearing the crown of Upper Egypt, adorned with the royal asp on the forehead. The body of the snake is painted black.

The modeling of the head and body reflects the influence of Amarna-era art in the emphasis and exaggeration of certain physical details such as the long, forward-tilted neck, the protruding breasts, the swollen belly, and the low waist. It is therefore legitimate to suggest that the statue may have been made for Akhenaten, a hypothesis supported by the fact that when it was discovered it was wrapped in linen cloths that carried inscriptions datable to the third year of this pharaoh's reign.

With its serene, youthful expression, the face features eyes inlaid with obsidian, bronze, and glass. The sovereign is bare chested but is wearing a large collar that covers his breast and shoulders and terminates with a droplet motif. The pharaoh's clothing consists of a long, tightly-fitting loincloth, knotted at the front and lined with thin incisions imitating the folds in the cloth, and sandals on his feet.

The statue stands on a black-painted, rectangular pedestal fixed to the arching back of a panther, also black. The animal is portrayed with great realism, pacing slowly and furtively. Its body has a sinuous, elegant profile and the head, with gilded ears and muzzle, is slightly dipped. A second black-painted pedestal constitutes the base for the entire sculptural group.

The composition is not intended to evoke a hunting scene, since the sovereign is not bearing arms, but rather it has a symbolic value. The panther might constitute an allegorical image of the sky, which in the Predynastic era was depicted as a feline that swallowed the sun in the evening before regenerating it in rejuvenated form the following morning. With the extensive gilding of his body the sovereign could represent the sun god. According to another interpretation supported by a pictorial scene in the tomb of Sety I, the sovereign whose gilding identifies him as the sun god, is located in the under world. The panther is in fact painted black like all the inhabitants of the under world.

The Treasure Chamber in the tomb of Tutankhamun contained twenty-two black-painted wooden caskets, each of which contained one or more wooden statues portraying the pharaoh or a number of deities from the Egyptian pantheon. All of the figures contained in the black tabernacles are fixed to a rectangular base and at the moment of their discovery were wrapped in a linen cloth datable to the third year of the reign of Akhenaten.

Two twin statues in gilded wood depict Tutankhamun standing upright on a papyrus raft and engaged in a mythical hunt for the hippopotamus symbolizing evil. The pharaoh is represented as the incarnation of Horus, the god that according to the legend fought in the swamps against the evil Seth who was transformed into a hippopotamus and was finally defeated.

Tutankhamun, like the victorious god, has the task of fighting against evil and preserving the universal order of which he is the sole guarantor. The sovereign, seen in a striding pose taking a long, solemn step appears realistically to be concentrating on launching a long spear against his enemy. He is wearing the crown of Lower Egypt decorated at the front with a representation of the royal cobra above his youthful, refined facial features.

His eyes are inlaid. An usekh necklace is depicted around his neck, incised into the wood in imitation of the rows of beads of which it is composed. The soft modeling of the naked torso with the slightly protruding pectoral muscles, the swollen belly and the low hips are clear indications of the influence that was still exercised over the art of this era by the Amarna Period.

The arms are separate from the body and emphasize the dynamism of the hunting pharaoh: in his right hand he is gripping the long spear whilst in his left he is holding a rope in rolled bronze with which to capture the defeated animal. Tutankhamun is wearing a pleated skirt, knotted at the front from where the cloth falls to various levels and opens in a fan-like fashion.

The striding pose of the statue means that the narrow pleats of the cloth adhere tightly to the thighs, allowing the underlying musculature to appear. The pharaoh is wearing precious thong sandals that were part of the his official costume. The front foot is flat on the ground while the rear is poised on the tips of the toes in realistic imitation of the pose of one taking aim prior to throwing a spear.

The slim vessel on which the sovereign is floating is typical of the simple "Its made of papyrus used by the Ancient Egyptians. It is painted in green, with the prow and the stern taking the form of sophisticated images of papyrus flowers with gilded petals. The raft is attached to a rectangular pedestal painted in black that supports the entire sculptural composition.

This elegant and precious game table composed of interlocking pieces is the largest of the four discovered in the annex of the tomb of Tutankhamun. The piece takes-the form of a box resting on a base supported by four leonine legs, partially covered with gold leaf and fixed to a sled. The upper surface is veneered with ivory and is subdivided by means of strips of wood into thirty squares, five of which carry inscriptions. The game of senet was played on this board. There are the same number of squares in ivory on the lower surface of the box, three of which are inscribed. This side was used for the game tjau.

On one of the short sides there is an aperture in which a drawer (discovered empty elsewhere in the tomb) would have been inserted. This would once have contained the pieces used for the games which were probably taken away by thieves as they would have been made of precious materials.

The four sides of the box feature yellow hieroglyphic inscriptions with augural phrases in favor of Tutankhamun, to whom the board belonged. The pharaoh's names and complete titles are recorded. The rules of the two games played on this board are unknown, but it is probable that the two competing players had to move their pieces after throwing a stick or a form of die.

Senet was very popular in Egypt from the remotest times. Boards were frequently placed in tombs to allow the deceased to continue playing after their deaths. It had magical-religious values and in the tomb paintings and in the Book of the Dead the deceased appears seated alone, intent on playing an imaginary adversary in a scene symbolizing his successful passage to the spiritual world.

Tut Chalice Lamp

Taken to the Cairo Museum

Statue of Ptah

Casket

Numerous caskets and chairs were piled hazardly as a result of the violations of the tomb in the western corner of the antechamber. The containers were almost all rectangular in shape, with lids that were flat, featured triangular pediments, or were vaulted. With the exception of certain examples in alabaster and cane, the majority were made of wood, with precious inlays in ivory, gold leaf, turquoise, or vitreous paste.

Frequently a hieratic or hieroglyphic inscription indicated their function, followed by the name of the sovereign and the ritual verse in which the sovereign was augured "life, strength and health." This casket takes the form of a rectangular parallelepiped, supported on simple square feet and closed with a vaulted lid in imitation of the primitive shrines of Upper Egypt.

The two large button-like knobs in blue faience were used to fasten the casket by means of ties and are placed on the curved part of the lid and in the center of the upper part of the front side.

The decoration is of a sophisticated elegance, thanks above all to the prevalent two-tone color scheme, interrupted only by the checkered frame around the panels, which create an attractive contrast with the elegant turquoise faience inlays on the gilded surfaces.

On the long side panels there are a series of five royal cartouches set between asps surmounted by the solar disc; the birth name of the sovereign, Tutankhamun, alternates with his coronation name Nebhheperura. The two cartouches are also found on the front and rear short sides, placed centrally and flanked by the protective figures of the genii of the millions of years arranged symmetrically either side.

Tutankhamun's Throne

This throne was produced in the early years of the reign of Tutankhamun, prior to the religious counter reformation that marked the definitive end of the Amarna Period.

The grace of the forms combines well with the richness of the decoration and the luminosity of the colors, giving rise to a composition of exquisite craftsmanship. The scene depicts the sovereign relaxing on his throne with his feet resting on a low stool with cushions. He is wearing a short wig surmounted by a composite crown and the typical pleated robe of the era, which left the prominent stomach uncovered, another feature typical of the Amarna period.

The arms of the throne are in the form of two winged and crowned serpents holding the cartouche of Tutankhamun in front of them. The legs, which were linked at the front and rear with a heraldic motif symbolizing the union of southern and northern Egypt, terminate in leonine paws. Two lions' heads also emerge from the front section of the throne. The rear of the backrest is decorated with a frieze of asps.

source : http://www.crystalinks.com

Radio Astronomy

2008-10-15T20:41:00.003+05:30

Radio astronomy is a subfield of astronomy that studies celestial objects at radio frequencies. The field originated from the discovery that many astronomical objects emit radiation in the radio wavelengths as well as optical ones. The great advances in radio astronomy that took place after the Second World War yielded a number of important discoveries including Radio Galaxies, Pulsars, Masers and the Cosmic Microwave Background Radiation. Radio telescopes use many different methods to collect information, sometimes using techniques that are similar to those used in Optical telescopes (although radio telescopes have to be much larger due to the longer wavelengths being observed). The development of radio interferometry and aperture synthesis has allowed radio sources to be imaged with unprecedented angular resolution.

History

The idea that celestial bodies may be emitting radio waves had been suspected some time before its discovery. In the 1860's James Clerk Maxwell's equations had shown that electromagnetic radiation from stellar sources could exist with any wavelength, not just optical. Several notable scientists and experimenters such as Thomas Edison, Oliver Lodge, and Max Planck predicted that the sun should be emitting radio waves. Lodge tried to observe solar signals but was unable to detect them due to technical limitations of his apparatus.

The first identified astronomical radio source was one discovered serendipitously in the early 1930s when Karl Guthe Jansky, an engineer with Bell Telephone Laboratories, was investigating static that interfered with short wave transatlantic voice transmissions. Using a large directional antenna, Jansky noticed that his analog pen-and-paper recording system kept recording a repeating signal of unknown origin. Since the signal peaked once a day, Jansky originally suspected the source of the interference was the sun. Continued analysis showed that the source was not following the 24 hour cycle for the rising and setting of the sun but instead repeating on a cycle of 23 hours and 56 minutes, typical of an astronomical source "fixed" on the celestial sphere rotating in sync with sidereal time. By comparing his observations with optical astronomical maps, Jansky concluded that the radiation was coming from the Milky Way and was strongest in the direction of the center of the galaxy, in the constellation of Sagittarius . He announced his discovery in 1933. Jansky wanted to investigate the radio waves from the Milky Way in further detail but Bell Labs re-assigned Jansky to another project, so he did no further work in the field of astronomy.

Grote Reber helped pioneer radio astronomy when he built a large parabolic "dish" radio telescope (9m in diameter) in 1937. He was instrumental in repeating Karl Guthe Jansky's pioneering but somewhat simple work, and went on to conduct the first sky survey in the radio frequencies . On February 27, 1942, J.S. Hey, a British Army research officer, helped progress radio astronomy further, when he discovered that the sun emitted radio waves . By the early 1950s Martin Ryle and Antony Hewish at Cambridge University had used the Cambridge Interferometer to map the radio sky, producing the famous 2C and 3C surveys of radio sources.

Techniques

Radio astronomers use different types of techniques to observe objects in the radio spectrum. Instruments may simply be pointed at an energetic radio source to analyze what type of emissions it makes. To “image” a region of the sky in more detail, multiple overlapping scans can be recorded and piece together in an image ('mosaicing'). The types of instruments being used depends on the weakness of the signal and the amount of detail needed.

Radio telescopes

An optical image of the galaxy M87 (HST), a radio image of same galaxy using Interferometry (Very Large Array-VLA), and an image of the center section (VLBA) using a Very Long Baseline Array (Global VLBI) consisting of antennas in the US, Germany, Italy, Finland, Sweden and Spain. The jet of particles is suspected to be powered by a black hole in the center of the galaxy.

Radio telescopes may need to be extremely large in order to receive signals with low signal-to-noise ratio. Also since angular resolution is a function of the diameter of the "objective" in proportion to the wavelength of the electromagnetic radiation being observed, radio telescopes have to be much larger in comparison to their optical counterparts. For example a 1 meter diameter optical telescope is two million times bigger than the wavelength of light observed giving it a resolution of a few arc seconds, whereas a radio telescope "dish" many times that size may, depending on the wavelength observed, only be able to resolve an object the size of the full moon (30 minutes of arc).

Radio interferometry

The difficulty in achieving high resolutions with single radio telescopes led to radio interferometry, developed by British radio astronomer Martin Ryle and Australian-born engineer, radiophysicist, and radio astronomer Joseph Lade Pawsey in 1946. Radio interferometers consist of widely separated radio telescopes observing the same object that are connected together using coaxial cable, waveguide, optical fiber, or other type of transmission line. This not only increases the total signal collected, it can also be used in a process called Aperture synthesis to vastly increase resolution. This technique works by superposing (interfering) the signal waves from the different telescopes on the principle that waves that coincide with the same phase will add to each other while two waves that have opposite phases will cancel each other out. This creates a combined telescope that is the size of the antennas furthest apart in the array. In order to produce a high quality image, a large number of different separations between different telescopes are required (the projected separation between any two telescopes as seen from the radio source is called a baseline) - as many different baselines as possible are required in order to get a good quality image. For example the Very Large Array has 27 telescopes giving 351 independent baselines at once.

Very Long Baseline Interferometry

Since the 1970s telescopes from all over the world (and even in Earth orbit) have been combined to perform Very Long Baseline Interferometry. Data received at each antenna is paired with timing information, usually from a local atomic clock, and then stored for later analysis on magnetic tape or hard disk. At that later time, the data is correlated with data from other antennas similarly recorded, to produce the resulting image. Using this method it is possible to synthesise an antenna that is effectively the size of the Earth. The large distances between the telescopes enable very high angular resolutions to be achieved, much greater in fact than in any other field of astronomy. At the highest frequencies, synthesised beams less than 1 milliarcsecond are possible.

The pre-eminent VLBI arrays operating today are the Very Long Baseline Array (with telescopes located across the North America) and the European VLBI Network (telescopes in Europe, China, South Africa and Puerto Rico). Each array usually operates separately, but occasional projects are observed together producing increased sensitivity. This is referred to as Global VLBI. There is also a VLBI network, the Long Baseline Array, operating in Australia.

Since its inception, recording data onto hard media has been the only way to bring the data recorded at each telescope together for later correlation. However, the availability today of worldwide, high-bandwidth optical fibre networks makes it possible to do VLBI in real time. This technique (referred to as e-VLBI) has been pioneered by the EVN who now perform an increasing number of scientific e-VLBI projects per year.

Astronomical sources

A radio image of the central region of the Milky Way galaxy. The arrow indicates a supernova remnant which is the location of a newly-discovered transient, bursting low-frequency radio source GCRT J1745-3009.

Radio astronomy has led to substantial increases in astronomical knowledge, particularly with the discovery of several classes of new objects, including pulsars, quasars and radio galaxies. This is because radio astronomy allows us to see things that are not detectable in optical astronomy. Such objects represent some of the most extreme and energetic physical processes in the universe.

Radio astronomy is also partly responsible for the idea that dark matter is an important component of our universe; radio measurements of the rotation of galaxies suggest that there is much more mass in galaxies than has been directly observed. The cosmic microwave background radiation was also first detected using radio telescopes. However, radio telescopes have also been used to investigate objects much closer to home, including observations of the Sun and solar activity, and radar mapping of the planets.

Dark Energy

2008-09-29T20:17:00.002+05:30

In physical cosmology, dark energy is a hypothetical exotic form of energy that permeates all of space and tends to increase the rate of expansion of the universe. Dark energy is the most popular way to explain recent observations that the universe appears to be expanding at an accelerating rate. In the standard model of cosmology, dark energy currently accounts for 74% of the total mass-energy of the universe.

Two proposed forms for dark energy are the cosmological constant, a constant energy density filling space homogeneously,and scalar fields such as quintessence or moduli, dynamic quantities whose energy density can vary in time and space. Contributions from scalar fields that are constant in space are usually also included in the cosmological constant. The cosmological constant is physically equivalent to vacuum energy. Scalar fields which do change in space can be difficult to distinguish from a cosmological constant because the change may be extremely slow.

High-precision measurements of the expansion of the universe are required to understand how the expansion rate changes over time. In general relativity, the evolution of the expansion rate is parameterized by the cosmological equation of state. Measuring the equation of state of dark energy is one of the biggest efforts in observational cosmology today.

Adding the cosmological constant to cosmology's standard FLRW metric leads to the Lambda-CDM model, which has been referred to as the "standard model" of cosmology because of its precise agreement with observations. Dark energy has been used as a crucial ingredient in a recent attempt to formulate a cyclic model for the universe.

Evidence for dark energy

[edit] Supernovae

In 1998, observations of type Ia supernovae ("one-A") by the Supernova Cosmology Project at the Lawrence Berkeley National Laboratory and the High-z Supernova Search Team suggested that the expansion of the universe is accelerating.^[4]^[5] Since then, these observations have been corroborated by several independent sources. Measurements of the cosmic microwave background, gravitational lensing, and the large scale structure of the cosmos as well as improved measurements of supernovae have been consistent with the Lambda-CDM model.

Supernovae are useful for cosmology because they are excellent standard candles across cosmological distances. They allow the expansion history of the Universe to be measured by looking at the relationship between the distance to an object and its redshift, which gives how fast it is receding from us. The relationship is roughly linear, according to Hubble's law. It is relatively easy to measure redshift, but finding the distance to an object is more difficult. Usually, astronomers use standard candles: objects for which the intrinsic brightness, the absolute magnitude, is known. This allows the object's distance to be measured from its actually observed brightness, or apparent magnitude. Type Ia supernovae are the best-known standard candles across cosmological distances because of their extreme, and extremely consistent, brightness.

Cosmic Microwave Background

Estimated distribution of dark matter and dark energy in the universe

The existence of dark energy, in whatever form, is needed to reconcile the measured geometry of space with the total amount of matter in the universe. Measurements of cosmic microwave background (CMB) anisotropies, most recently by the WMAP satellite, indicate that the universe is very close to flat. For the shape of the universe to be flat, the mass/energy density of the universe must be equal to a certain critical density. The total amount of matter in the universe (including baryons and dark matter), as measured by the CMB, accounts for only about 30% of the critical density. This implies the existence of an additional form of energy to account for the remaining 70%. The most recent WMAP observations are consistent with a universe made up of 74% dark energy, 22% dark matter, and 4% ordinary matter. (Note: There is a slight discrepancy in the 'pie chart'.)

Large-Scale Structure

The theory of large scale structure, which governs the formation of structure in the universe (stars, quasars, galaxies and galaxy clusters), also suggests that the density of matter in the universe is only 30% of the critical density.

Late-time Integrated Sachs-Wolfe Effect

Accelerated cosmic expansion causes gravitational potential wells and hills to flatten as photons pass through them, producing cold spots and hot spots on the CMB aligned with vast supervoids and superclusters. This so-called late-time Integrated Sachs-Wolfe effect (ISW) is a direct signal of dark energy in a flat universe, and has recently been detected at high significance by Ho et al. and Giannantonio et al. May 2008, Granett, Neyrinck & Szapudi found arguably the clearest evidence yet for the ISW effect, imaging the average imprint of superclusters and supervoids on the CMB.

Nature of dark energy

The exact nature of this dark energy is a matter of speculation. It is known to be very homogeneous, not very dense and is not known to interact through any of the fundamental forces other than gravity. Since it is not very dense—roughly 10⁻²⁹ grams per cubic centimeter—it is hard to imagine experiments to detect it in the laboratory. Dark energy can only have such a profound impact on the universe, making up 74% of all energy, because it uniformly fills otherwise empty space. The two leading models are quintessence and the cosmological constant. Both models include the common characteristic that dark energy must have negative pressure.

Negative Pressure

Independently from its actual nature, dark energy would need to have a strong negative pressure in order to explain the observed acceleration in the expansion rate of the universe.

According to General Relativity, the pressure within a substance contributes to its gravitational attraction for other things just as its mass density does. This happens because the physical quantity that causes matter to generate gravitational effects is the Stress-energy tensor, which contains both the energy (or matter) density of a substance and its pressure and viscosity.

In the Friedmann-Lemaître-Robertson-Walker metric, it can be shown that a strong constant negative pressure in all the universe causes an acceleration in universe expansion if the universe is already expanding, or a deceleration in universe contraction if the universe is already contracting. More exactly, the second derivative of the universe scale factor, , is positive if the equation of state of the universe is such that $w < - 1 / 3$ .

This accelerating expansion effect is sometimes labeled "gravitational repulsion", which is a colorful but possibly confusing expression. In fact a negative pressure does not influence the gravitational interaction between masses - which remains attractive - but rather alters the overall evolution of the universe at the cosmological scale, typically resulting in the accelerating expansion of the universe despite the attraction among the masses present in the universe.

Cosmological constant

The simplest explanation for dark energy is that it is simply the "cost of having space": that is, a volume of space has some intrinsic, fundamental energy. This is the cosmological constant, sometimes called Lambda (hence Lambda-CDM model) after the Greek letter Λ, the symbol used to mathematically represent this quantity. Since energy and mass are related by $E = m c 2$ , Einstein's theory of general relativity predicts that it will have a gravitational effect. It is sometimes called a vacuum energy because it is the energy density of empty vacuum. In fact, most theories of particle physics predict vacuum fluctuations that would give the vacuum exactly this sort of energy. This is related to the Casimir Effect, in which there is a small suction into regions where virtual particles are geometrically inhibited from forming (e.g. between plates with tiny separation). The cosmological constant is estimated by cosmologists to be on the order of 10⁻²⁹g/cm³, or about 10⁻¹²⁰ in reduced Planck units. Particle physics predicts a natural value of 1 in reduced Planck units, quite a bit off.

The cosmological constant has negative pressure equal to its energy density and so causes the expansion of the universe to accelerate. The reason why a cosmological constant has negative pressure can be seen from classical thermodynamics; Energy must be lost from inside a container to do work on the container. A change in volume dV requires work done equal to a change of energy −p dV, where p is the pressure. But the amount of energy in a box of vacuum energy actually increases when the volume increases (dV is positive), because the energy is equal to ρV, where ρ (rho) is the energy density of the cosmological constant. Therefore, p is negative and, in fact, p = −ρ.

A major outstanding problem is that most quantum field theories predict a huge cosmological constant from the energy of the quantum vacuum, more than 100 orders of magnitude too large. This would need to be cancelled almost, but not exactly, by an equally large term of the opposite sign. Some supersymmetric theories require a cosmological constant that is exactly zero, which does not help. The present scientific consensus amounts to extrapolating the empirical evidence where it is relevant to predictions, and fine-tuning theories until a more elegant solution is found. Philosophically, our most elegant solution may be to say that if things were different, we would not be here to observe anything — the anthropic principle.Technically, this amounts to checking theories against macroscopic observations. Unfortunately, as the known error-margin in the constant predicts the fate of the universe more than its present state, many such "deeper" questions remain unknown.

Another problem arises with inclusion of the cosmic constant in the standard model: i.e., the appearance of solutions with regions of discontinuities at low matter density. Discontinuity also affects the past sign of the pressure assigned to the cosmic constant, changing from the current negative pressure to attractive, as one looks back towards the early Universe. A systematic, model-independent evaluation of the supernovae data supporting inclusion of the cosmic constant in the standard model indicates these data suffer systematic error. The supernovae data are not overwhelming evidence for an accelerating Universe expansion which may be simply gliding. A numerical evaluation of WMAP and supernovae data for evidence that our local group exists in a local void with poor matter density compared to other locations, uncovered possible conflict in the analysis used to support the cosmic constant These findings should be considered shortcomings of the standard model, but only when a term for vacuum energy is included.

In spite of its problems, the cosmological constant is in many respects the most economical solution to the problem of cosmic acceleration. One number successfully explains a multitude of observations. Thus, the current standard model of cosmology, the Lambda-CDM model, includes the cosmological constant as an essential feature.

Quintessence

In quintessence models of dark energy, the observed acceleration of the scale factor is caused by the potential energy of a dynamical field, referred to as quintessence field. Quintessence differs from the cosmological constant in that it can vary in space and time. In order for it not to clump and form structure like matter, the field must be very light so that it has a large Compton wavelength.

No evidence of quintessence is yet available, but it has not been ruled out either. It generally predicts a slightly slower acceleration of the expansion of the universe than the cosmological constant. Some scientists think that the best evidence for quintessence would come from violations of Einstein's equivalence principle and variation of the fundamental constants in space or time. Scalar fields are predicted by the standard model and string theory, but an analogous problem to the cosmological constant problem (or the problem of constructing models of cosmic inflation) occurs: renormalization theory predicts that scalar fields should acquire large masses.

The cosmic coincidence problem asks why the cosmic acceleration began when it did. If cosmic acceleration began earlier in the universe, structures such as galaxies would never have had time to form and life, at least as we know it, would never have had a chance to exist. Proponents of the anthropic principle view this as support for their arguments. However, many models of quintessence have a so-called tracker behavior, which solves this problem. In these models, the quintessence field has a density which closely tracks (but is less than) the radiation density until matter-radiation equality, which triggers quintessence to start behaving as dark energy, eventually dominating the universe. This naturally sets the low energy scale of the dark energy.

Some special cases of quintessence are phantom energy, in which the energy density of quintessence actually increases with time, and k-essence (short for kinetic quintessence) which has a non-standard form of kinetic energy. They can have unusual properties: phantom energy, for example, can cause a Big Rip.

Alternative ideas

Some theorists think that dark energy and cosmic acceleration are a failure of general relativity on very large scales, larger than superclusters. It is a tremendous extrapolation to think that our law of gravity, which works so well in the solar system, should work without correction on the scale of the universe. Most attempts at modifying general relativity, however, have turned out to be either equivalent to theories of quintessence, or inconsistent with observations. It is of interest to note that if the equation for gravity were to approach r instead of r² at large, intergalactic distances, then the acceleration of the expansion of the universe becomes a mathematical artifact, negating the need for the existence of Dark Energy.

Alternative ideas for dark energy have come from string theory, brane cosmology and the holographic principle, but have not yet proved as compelling as quintessence and the cosmological constant. On string theory, an article in the journal Nature described:

String theories, popular with many particle physicists, make it possible, even desirable, to think that the observable universe is just one of 10⁵⁰⁰ universes in a grander multiverse, says [Leonard Susskind, a cosmologist at Stanford University in California]. The vacuum energy will have different values in different universes, and in many or most it might indeed be vast. But it must be small in ours because it is only in such a universe that observers such as ourselves can evolve.

Paul Steinhardt in the same article criticizes string theory's explanation of dark energy stating "...Anthropics and randomness don't explain anything... I am disappointed with what most theorists are willing to accept".

Yet another, "radically conservative" class of proposals aims to explain the observational data by a more refined use of established theories rather than through the introduction of dark energy, focusing, for example, on the gravitational effects of density inhomogeneities or on consequences of electroweak symmetry breaking in the early universe.

Implications for the fate of the universe

Cosmologists estimate that the acceleration began roughly 5 billion years ago. Before that, it is thought that the expansion was decelerating, due to the attractive influence of dark matter and baryons. The density of dark matter in an expanding universe decreases more quickly than dark energy, and eventually the dark energy dominates. Specifically, when the volume of the universe doubles, the density of dark matter is halved but the density of dark energy is nearly unchanged (it is exactly constant in the case of a cosmological constant).

If the acceleration continues indefinitely, the ultimate result will be that galaxies outside the local supercluster will move beyond the cosmic horizon: they will no longer be visible, because their line-of-sight velocity becomes greater than the speed of light. This is not a violation of special relativity, and the effect cannot be used to send a signal between them. (Actually there is no way to even define "relative speed" in a curved spacetime. Relative speed and velocity can only be meaningfully defined in flat spacetime or in sufficiently small (infinitesimal) regions of curved spacetime). Rather, it prevents any communication between them and the objects pass out of contact. The Earth, the Milky Way and the Virgo supercluster, however, would remain virtually undisturbed while the rest of the universe recedes. In this scenario, the local supercluster would ultimately suffer heat death, just as was thought for the flat, matter-dominated universe, before measurements of cosmic acceleration.

There are some very speculative ideas about the future of the universe. One suggests that phantom energy causes divergent expansion, which would imply that the effective force of dark energy continues growing until it dominates all other forces in the universe. Under this scenario, dark energy would ultimately tear apart all gravitationally bound structures, including galaxies and solar systems, and eventually overcome the electrical and nuclear forces to tear apart atoms themselves, ending the universe in a "Big Rip". On the other hand, dark energy might dissipate with time, or even become attractive. Such uncertainties leave open the possibility that gravity might yet rule the day and lead to a universe that contracts in on itself in a "Big Crunch". Some scenarios, such as the cyclic model suggest this could be the case. While these ideas are not supported by observations, they are not ruled out. Measurements of acceleration are crucial to determining the ultimate fate of the universe in big bang theory.

History

The cosmological constant was first proposed by Einstein as a mechanism to obtain a stable solution of the gravitational field equation that would lead to a static universe, effectively using dark energy to balance gravity. Not only was the mechanism an inelegant example of fine-tuning, it was soon realized that Einstein's static universe would actually be unstable because local inhomogeneities would ultimately lead to either the runaway expansion or contraction of the universe. The equilibrium is unstable: if the universe expands slightly, then the expansion releases vacuum energy, which causes yet more expansion. Likewise, a universe which contracts slightly will continue contracting. These sorts of disturbances are inevitable, due to the uneven distribution of matter throughout the universe. More importantly, observations made by Edwin Hubble showed that the universe appears to be expanding and not static at all. Einstein famously referred to his failure to predict the idea of a dynamic universe, in contrast to a static universe, as his greatest blunder. Following this realization, the cosmological constant was largely ignored as a historical curiosity.

Alan Guth proposed in the 1970s that a negative pressure field, similar in concept to dark energy, could drive cosmic inflation in the very early universe. Inflation postulates that some repulsive force, qualitatively similar to dark energy, resulted in an enormous and exponential expansion of the universe slightly after the Big Bang. Such expansion is an essential feature of most current models of the Big Bang. However, inflation must have occurred at a much higher energy density than the dark energy we observe today and is thought to have completely ended when the universe was just a fraction of a second old. It is unclear what relation, if any, exists between dark energy and inflation. Even after inflationary models became accepted, the cosmological constant was thought to be irrelevant to the current universe.

The term "dark energy" was coined by Michael Turner in 1998. By that time, the missing mass problem of big bang nucleosynthesis and large scale structure was established, and some cosmologists had started to theorize that there was an additional component to our universe. The first direct evidence for dark energy came from supernova observations of accelerated expansion, in Riess et al and later confirmed in Perlmutter et al.. This resulted in the Lambda-CDM model, which as of 2006 is consistent with a series of increasingly rigorous cosmological observations, the latest being the 2005 Supernova Legacy Survey. First results from the SNLS reveal that the average behavior (i.e., equation of state) of dark energy behaves like Einstein's cosmological constant to a precision of 10 per cent. Recent results from the Hubble Space Telescope Higher-Z Team indicate that dark energy has been present for at least 9 billion years and during the period preceding cosmic acceleration.

source : Wikipedia

Quasar

2008-09-29T20:08:00.002+05:30

A quasar (contraction of QUASi-stellAR radio source) is an extremely powerful and distant active galactic nucleus. They were first identified as being high redshift sources of electromagnetic energy, including radio waves and visible light that were point-like, similar to stars, rather than extended sources similar to galaxies. While there was initially some controversy over the nature of these objects, there is now a scientific consensus that a quasar is a compact region 10-10000 Schwarzschild radii across surrounding the central supermassive black hole of a galaxy.

Overview

Quasars show a very high redshift, which is an effect of the expansion of the universe between the quasar and the Earth. When combined with Hubble's law, the implication of the redshift is that the quasars are very distant. To be observable at that distance, the energy output of quasars dwarfs every other astronomical event. The most luminous quasars radiate at a rate that can exceed the output of average galaxies, equivalent to one trillion (10¹²) suns. This radiation is emitted across the spectrum, almost equally, from X-rays to the far-infrared with a peak in the ultraviolet-optical bands, with some quasars also being strong sources of radio and of gamma-rays. In early optical images, quasars looked like single points of light (i.e. point sources), indistinguishable from stars, except for their peculiar spectra. With infrared telescopes and the Hubble Space Telescope, the "host galaxies" surrounding the quasars have been identified in some cases.^[1] These galaxies are normally too dim to be seen against the glare of the quasar, except with these special techniques. Most quasars cannot be seen with small telescopes, but 3C 273, with an average apparent magnitude of 12.9, is an exception. At a distance of 2.44 billion light-years, it is one of the most distant objects directly observable with amateur equipment.

Some quasars display rapid changes in luminosity in the optical and even more rapid in the X-rays, which implies that they are small (Solar System sized or less) as an object cannot change faster than the time it takes light to travel from one end to the other; but relativistic beaming of jets pointed nearly directly toward us explains the most extreme cases. The highest redshift known for a quasar (as of December 2007) is 6.43, which corresponds (assuming the currently-accepted value of 71 for the Hubble Constant) to a distance of approximately 28 billion light-years. (NB there are some subtleties in distance definitions in cosmology, so that distances greater than 13.7 billion light-years, or even greater than 27.4 = 2*13.7 light-years, can occur.)

Quasars are believed to be powered by accretion of material into supermassive black holes in the nuclei of distant galaxies, making these luminous versions of the general class of objects known as active galaxies. Large central masses (10⁶ to 10⁹ Solar masses) have been measured in quasars using 'reverberation mapping'. Several dozen nearby large galaxies, with no sign of a quasar nucleus, have been shown to contain a similar central black hole in their nuclei, so it is thought that all large galaxies have one, but only a small fraction emit powerful radiation and so are seen as quasars. The matter accreting onto the black hole is unlikely to fall directly in, but will have some angular momentum around the black hole that will cause the matter to collect in an accretion disc.

Knowledge of quasars is advancing rapidly. As recently as the 1980s, there was no clear consensus as to their origin.

Properties of quasars

More than 100,000 quasars are known, most from the Sloan Digital Sky Survey. All observed quasar spectra have redshifts between 0.06 and 6.4. Applying Hubble's law to these redshifts, it can be shown that they are between 780 million and 28 billion light-years away. Because of the great distances to the furthest quasars and the finite velocity of light, we see them and their surrounding space as they existed in the very early universe.

Most quasars are known to be farther than three billion light-years away. Although quasars appear faint when viewed from Earth, the fact that they are visible from so far away means that quasars are the most luminous objects in the known universe. The quasar that appears brightest in the sky is 3C 273 in the constellation of Virgo. It has an average apparent magnitude of 12.8 (bright enough to be seen through a small telescope), but it has an absolute magnitude of −26.7. From a distance of about 33 light-years, this object would shine in the sky about as brightly as our sun. This quasar's luminosity is, therefore, about 2 trillion (2 × 10¹²) times that of our sun, or about 100 times that of the total light of average giant galaxies like our Milky Way.

The hyperluminous quasar APM 08279+5255 was, when discovered in 1998, given an absolute magnitude of −32.2, although high resolution imaging with the Hubble Space Telescope and the 10 m Keck Telescope revealed that this system is gravitationally lensed. A study of the gravitational lensing in this system suggests that it has been magnified by a factor of ~10. It is still substantially more luminous than nearby quasars such as 3C 273.

Quasars were much more common in the early universe. This discovery by Maarten Schmidt in 1967 was early strong evidence against the Steady State cosmology of Fred Hoyle, and in favor of the Big Bang cosmology. Quasars show where massive black holes are growing rapidly (via accretion). These black holes grow in step with the mass of stars in their host galaxy in a way not understood at present. One idea is that the jets, radiation and winds from quasars shut down the formation of new stars in the host galaxy, a process called 'feedback'. The jets that produce strong radio emission in some quasars at the centers of clusters of galaxies are known to have enough power to prevent the hot gas in these clusters from cooling and falling down onto the central galaxy.

Quasars are found to vary in luminosity on a variety of time scales. Some vary in brightness every few months, weeks, days, or hours. This means that quasars generate and emit their energy from a very small region, since each part of the quasar would have to be in contact with other parts on such a time scale to coordinate the luminosity variations. As such, a quasar varying on the time scale of a few weeks cannot be larger than a few light-weeks across. The emission of large amounts of power from a small region requires a power source far more efficient than the nuclear fusion which powers stars. The release of gravitational energy by matter falling towards a massive black hole is the only process known that can produce such high power continuously. (Stellar explosions - Supernovas and gamma-ray bursts - can do so, but only for a few minutes.) Black holes were considered too exotic by some astronomers in the 1960s, and they suggested that the redshifts arose from some other (unknown) process, so that the quasars were not really so distant as the Hubble law implied. This 'redshift controversy' lasted for many years. Many lines of evidence (seeing host galaxies, finding 'intervening' absorption lines, gravitational lensing) now demonstrate that the quasar redshifts are due to the Hubble expansion, and quasars are as powerful as first thought.

Quasars have all the same properties as active galaxies, but are more powerful: Their Radiation is 'nonthermal' (i.e. not due to a black body), and some (~10%) are observed to also have jets and lobes like those of radio galaxies that also carry significant (but poorly known) amounts of energy in the form of high energy (i.e. rapidly moving, close to the speed of light) particles (either electrons and protons or electrons and positrons). Quasars can be detected over the entire observable electromagnetic spectrum including radio, infrared, optical, ultraviolet, X-ray and even gamma rays. Most quasars are brightest in their rest-frame near-ultraviolet (near the 1216 angstrom (121.6 nm) Lyman-alpha emission line of hydrogen), but due to the tremendous redshifts of these sources, that peak luminosity has been observed as far to the red as 9000 angstroms (900 nm or 0.9 µm), in the near infrared. A minority of quasars show strong radio emission, which originates from jets of matter moving close to the speed of light. When looked at down the jet, these appear as a blazar and often have regions that appear to move away from the center faster than the speed of light (superluminal expansion). This is an optical trick due to the properties of special relativity.

Quasar redshifts are measured from the strong spectral lines that dominate their optical and ultraviolet spectra. These lines are brighter than the continuous spectrum, so they are called 'emission' lines. They have widths of several percent of the speed of light, and these widths are due to Doppler shifts due to the high speeds of the gas emitting the lines. Fast motions strongly indicate a large mass. Emission lines of hydrogen (mainly of the Lyman series and Balmer series), Helium, Carbon, Magnesium, Iron and Oxygen are the brightest lines. The atoms emitting these lines range from neutral to highly ionized. (I.e. many of the electrons are stripped off the ion, leaving it highly charged.) This wide range of ionization shows that the gas is highly irradiated by the quasar, not merely hot, and not by stars, which cannot produce such a wide range of ionization

Iron Quasars show strong emission lines resulting from low ionization iron (FeII), such as IRAS 18508-7815.

Quasar emission generation

This view, taken with infrared light, is a false-color image of a quasar-starburst tandem with the most luminous starburst ever seen in such a combination.

Since quasars exhibit properties common to all active galaxies, the emissions from quasars can be readily compared to those of small active galaxies powered by supermassive black holes. To create a luminosity of 10⁴⁰ W (the typical brightness of a quasar), a super-massive black hole would have to consume the material equivalent of 10 stars per year. The brightest known quasars devour 1000 solar masses of material every year. The largest known is estimated to consume matter equivalent to 600 Earths per hour. Quasars 'turn on' and off depending on their surroundings, and since quasars cannot continue to feed at high rates for 10 billion years, after a quasar finishes accreting the surrounding gas and dust, it becomes an ordinary galaxy.

Quasars also provide some clues as to the end of the Big Bang's reionization. The oldest quasars (redshift >~ 6) display a Gunn-Peterson trough and have absorption regions in front of them indicating that the intergalactic medium at that time was neutral gas. More recent quasars show no absorption region but rather their spectra contain a spiky area known as the Lyman-alpha forest. This indicates that the intergalactic medium has undergone reionization into plasma, and that neutral gas exists only in small clouds.

One other interesting characteristic of quasars is that they show evidence of elements heavier than helium, indicating that galaxies underwent a massive phase of star formation, creating population III stars between the time of the Big Bang and the first observed quasars. Light from these stars may have been observed in 2005 using NASA's Spitzer Space Telescope, although this observation remains to be confirmed.

History of quasar observation

The first quasars were discovered with radio telescopes in the late 1950s. Many were recorded as radio sources with no corresponding visible object. Using small telescopes and the Lovell Telescope as an interferometer, they were shown to have a very small angular size. Hundreds of these objects were recorded by 1960 and published in the Third Cambridge Catalogue as astronomers scanned the skies for the optical counterparts. In 1960, radio source 3C 48 was finally tied to an optical object. Astronomers detected what appeared to be a faint blue star at the location of the radio source and obtained its spectrum. Containing many unknown broad emission lines, the anomalous spectrum defied interpretation — a claim by John Bolton of a large redshift was not generally accepted.

In 1962 a breakthrough was achieved. Another radio source, 3C 273, was predicted to undergo five occultations by the moon. Measurements taken by Cyril Hazard and John Bolton during one of the occultations using the Parkes Radio Telescope allowed Maarten Schmidt to optically identify the object and obtain an optical spectrum using the 200-inch Hale Telescope on Mount Palomar. This spectrum revealed the same strange emission lines. Schmidt realized that these were actually spectral lines of hydrogen redshifted at the rate of 15.8 percent. This discovery showed that 3C 273 was receding at a rate of 47,000 km/s. This discovery revolutionized quasar observation and allowed other astronomers to find redshifts from the emission lines from other radio sources. As predicted earlier by Bolton, 3C 48 was found to have a redshift of 37% the speed of light.

The term quasar was coined by Chinese-born U.S. astrophysicist Hong-Yee Chiu in 1964, in Physics Today, to describe these puzzling objects:

So far, the clumsily long name 'quasi-stellar radio sources' is used to describe these objects. Because the nature of these objects is entirely unknown, it is hard to prepare a short, appropriate nomenclature for them so that their essential properties are obvious from their name. For convenience, the abbreviated form 'quasar' will be used throughout this paper.

– Hong-Yee Chiu in Physics Today, May, 1964

Later it was found that not all (actually only 10% or so) quasars have strong radio emission (are 'radio-loud'). Hence the name 'QSO' (quasi-stellar object) is used (in addition to 'quasar') to refer to these objects, including the 'radio-loud' and the 'radio-quiet' classes.

One great topic of debate during the 1960s was whether quasars were nearby objects or distant objects as implied by their redshift. It was suggested, for example, that the redshift of quasars was not due to the expansion of space but rather to light escaping a deep gravitational well. However a star of sufficient mass to form such a well would be unstable and in excess of the Hayashi limit. Quasars also show unusual spectral emission lines which were previously only seen in hot gaseous nebulae of low density, which would be too diffuse to both generate the observed power and fit within a deep gravitational well. There were also serious concerns regarding the idea of cosmologically distant quasars. One strong argument against them was that they implied energies that were far in excess of known energy conversion processes, including nuclear fusion. At this time, there were some suggestions that quasars were made of some hitherto unknown form of stable antimatter and that this might account for their brightness. Others speculated that quasars were a white hole end of a wormhole. However, when accretion disc energy-production mechanisms were successfully modeled in the 1970s, the argument that quasars were too luminous became moot and today the cosmological distance of quasars is accepted by almost all researchers.

In 1979 the gravitational lens effect predicted by Einstein's General Theory of Relativity was confirmed observationally for the first time with images of the double quasar 0957+561.

In the 1980s, unified models were developed in which quasars were classified as a particular kind of active galaxy, and a general consensus emerged that in many cases it is simply the viewing angle that distinguishes them from other classes, such as blazars and radio galaxies. The huge luminosity of quasars results from the accretion discs of central supermassive black holes, which can convert on the order of 10% of the mass of an object into energy as compared to 0.7% for the p-p chain nuclear fusion process that dominates the energy production in sun-like stars.

This mechanism also explains why quasars were more common in the early universe, as this energy production ends when the supermassive black hole consumes all of the gas and dust near it. This means that it is possible that most galaxies, including our own Milky Way, have gone through an active stage (appearing as a quasar or some other class of active galaxy depending on black hole mass and accretion rate) and are now quiescent because they lack a supply of matter to feed into their central black holes to generate radiation.

source : Wikipedia

Plasma Television

2008-09-13T20:27:00.003+05:30

A plasma display panel (PDP) is a type of flat panel display now commonly used for large TV displays (typically above 37-inch or 940 mm). Many tiny cells located between two panels of glass hold an inert mixture of noble gases. The gas in the cells is electrically turned into a plasma which then excites phosphors to emit light. Plasma displays are commonly confused with LCDs, another lightweight flatscreen display but with very different technology.

History

Plasma displays were first used in PLATO computer terminals. This PLATO V model illustrates the display's monochromatic orange glow as seen in 1981.

The plasma video display was co-invented in 1964 at the University of Illinois at Urbana-Champaign by Donald Bitzer, H. Gene Slottow, and graduate student Robert Willson for the PLATO Computer System. The original monochrome (orange, green, yellow) video display panels were very popular in the early 1970s because they were rugged and needed neither memory nor circuitry to refresh the images. A long period of sales decline occurred in the late 1970s as semiconductor memory made CRT displays cheaper than plasma displays. Nonetheless, the plasma displays' relatively large screen size and thin body made them suitable for high-profile placement in lobbies and stock exchanges.

In 1983, IBM introduced a 19-inch (48 cm) orange-on-black monochrome display (model 3290 'information panel') which was able to show four simultaneous IBM 3270 virtual machine (VM) terminal sessions. That factory was transferred in 1987 to startup company Plasmaco, which Dr. Larry F. Weber, one of Dr. Bitzer's students, founded with Stephen Globus, as well as James Kehoe, who was the IBM plant manager.

In 1992, Fujitsu introduced the world's first 21-inch (53 cm) full-color display. It was a hybrid, based upon the plasma display created at the University of Illinois at Urbana-Champaign and NHK STRL, achieving superior brightness.

In 1996, Matsushita Electrical Industries (Panasonic) purchased Plasmaco, its color AC technology, and its American factory. In 1997, Fujitsu introduced the first 42-inch (107 cm) plasma display; it had 852x480 resolution and was progressively scanned. Also in 1997, Pioneer started selling the first plasma television to the public. Many current plasma televisions, thinner and of larger area than their predecessors, are in use. Their thin size allows them to compete with large area projection screens.

Screen sizes have increased since the introduction of plasma displays. The largest plasma video display in the world at the 2008 Consumer Electronics Show in Las Vegas, Nevada, USA, North America was a 150-inch (381 cm) unit manufactured by Matsushita Electrical Industries (Panasonic) standing 6 ft (180 cm) tall by 11 ft (330 cm) wide and expected to initially retail at US$150,000.

Until quite recently, the superior brightness, faster response time, greater color spectrum, and wider viewing angle of color plasma video displays, when compared with LCD televisions, made them one of the most popular forms of display for HDTV flat panel displays. For a long time it was widely believed that LCD technology was suited only to smaller sized televisions, and could not compete with plasma technology at larger sizes, particularly 40 inches (100 cm) and above. Since then, improvements in LCD technology have narrowed the technological gap. The lower weight, falling prices, and often lower electrical power consumption of LCDs make them competitive with plasma television sets. As of late 2006, analysts note that LCDs are overtaking plasmas, particularly in the important 40-inch (1.0 m) and above segment where plasma had previously enjoyed strong dominance. Another industry trend is the consolidation of manufacturers of plasma displays, with around fifty brands available but only five manufacturers. In the 1Q of 2008 a comparison of worldwide TV sales breaks down to 22.1 million for CRT, 21.1 million for LCD, 2.8 million for Plasma, and 124 thousand for rear-projection.

General characteristics

Plasma displays are bright (1000 lux or higher for the module), have a wide color gamut, and can be produced in fairly large sizes, up to 381 cm (150 inches) diagonally. They have a very low-luminance "dark-room" black level compared to the lighter grey of the unilluminated parts of an LCD screen. The display panel is only about 6 cm (2.5 inches) thick, while the total thickness, including electronics, is less than 10 cm (4 inches). Plasma displays use as much power per square meter as a CRT or an AMLCD television. Power consumption varies greatly with picture content, with bright scenes drawing significantly more power than darker ones. Nominal power rating is typically 400 watts for a 50-inch (127 cm) screen. Post-2006 models consume 220 to 310 watts for a 50-inch (127 cm) display when set to cinema mode. Most screens are set to 'shop' mode by default, which draws at least twice the power (around 500-700 watts) of a 'home' setting of less extreme brightness.

The lifetime of the latest generation of plasma displays is estimated at 60,000 hours of actual display time, or 27 years at 6 hours per day. This is the estimated time over which maximum picture brightness degrades to half the original value, not catastrophic failure.

Competing displays include the CRT, OLED, AMLCD, DLP, SED-tv, and field emission flat panel displays. Advantages of plasma display technology are that a large, very thin screen can be produced, and that the image is very bright and has a wide viewing angle.

Functional details

Composition of plasma display panel

The xenon and neon gas in a plasma television is contained in hundreds of thousands of tiny cells positioned between two plates of glass. Long electrodes are also sandwiched between the glass plates, in front of and behind the cells. The address electrodes sit behind the cells, along the rear glass plate. The transparent display electrodes, which are surrounded by an insulating dielectric material and covered by a magnesium oxide protective layer, are mounted in front of the cell, along the front glass plate. Control circuitry charges the electrodes that cross paths at a cell, creating a voltage difference between front and back and causing the gas to ionize and form a plasma. As the gas ions rush to the electrodes and collide, photons are emitted.

In a monochrome plasma panel, the ionizing state can be maintained by applying a low-level voltage between all the horizontal and vertical electrodes – even after the ionizing voltage is removed. To erase a cell all voltage is removed from a pair of electrodes. This type of panel has inherent memory and does not use phosphors. A small amount of nitrogen is added to the neon to increase hysteresis.

In color panels, the back of each cell is coated with a phosphor. The ultraviolet photons emitted by the plasma excite these phosphors to give off colored light. The operation of each cell is thus comparable to that of a fluorescent lamp.

Every pixel is made up of three separate subpixel cells, each with different colored phosphors. One subpixel has a red light phosphor, one subpixel has a green light phosphor and one subpixel has a blue light phosphor. These colors blend together to create the overall color of the pixel, analogous to the "triad" of a shadow-mask CRT. By varying the pulses of current flowing through the different cells thousands of times per second, the control system can increase or decrease the intensity of each subpixel color to create billions of different combinations of red, green and blue. In this way, the control system can produce most of the visible colors. Plasma displays use the same phosphors as CRTs, which accounts for the extremely accurate color reproduction.

Contrast ratio claims

Contrast ratio is the difference between the brightest and darkest parts of an image, measured in discrete steps, at any given moment. Generally, the higher the contrast ratio, the more realistic the image is. Contrast ratios for plasma displays are often advertised as high as 1,000,000:1. On the surface, this is a significant advantage of plasma over display technologies other than OLED. Although there are no industry-wide guidelines for reporting contrast ratio, most manufacturers follow either the ANSI standard or perform a full-on-full-off test. The ANSI standard uses a checkered test pattern whereby the darkest blacks and the lightest whites are simultaneously measured, yielding the most accurate "real-world" ratings. In contrast, a full-on-full-off test measures the ratio using a pure black screen and a pure white screen, which gives higher values but does not represent a typical viewing scenario. Manufacturers can further artificially improve the reported contrast ratio by increasing the contrast and brightness settings to achieve the highest test values. However, a contrast ratio generated by this method is misleading, as content would be essentially unwatchable at such settings.

Plasma is often cited as having better black levels (and contrast ratios), although both plasma and LCD have their own technological challenges. Each cell on a plasma display has to be precharged before it is due to be illuminated (otherwise the cell would not respond quickly enough) and this precharging means the cells cannot achieve a true black. Some manufacturers have worked hard to reduce the precharge and the associated background glow, to the point where black levels on modern plasmas are starting to rival CRT. With LCD technology, black pixels are generated by a light polarization method and are unable to completely block the underlying backlight.

Screen burn-in

See also: Phosphor burn-in

An example of a plasma display that has suffered severe burn-in from stationary text

With phosphor-based electronic displays (including cathode-ray and plasma displays), the prolonged display of a menu bar or other graphical elements over time can create a permanent ghost-like image of these objects. This is due to the fact that the phosphor compounds which emit the light lose their luminosity with use. As a result, when certain areas of the display are used more frequently than others, over time the lower luminosity areas become visible to the naked eye and the result is called burn-in. While a ghost image is the most noticeable effect, a more common result is that the image quality will continuously and gradually decline as luminosity variations develop over time, resulting in a "muddy" looking picture image.

Plasma displays also exhibit another image retention issue which is sometimes confused with burn-in damage. In this mode, when a group of pixels are run at high brightness (when displaying white, for example) for an extended period of time, a charge build-up in the pixel structure occurs and a ghost image can be seen. However, unlike burn-in, this charge build-up is transient and self corrects after the display has been powered off for a long enough period of time, or after running random broadcast TV type content.

Plasma manufacturers have over time managed to devise ways of reducing the past problems of image retention with solutions involving gray pillarboxes, pixel orbiters and image washing routines.