Invisible Aircraft

Authors: Relly Victoria Petrescu and Florian Ion T. Petrescu

 

Invisible Aircraft

Stealth aircraft are aircraft that use stealth technology to avoid detection by employing a combination of features to interfere with radar as well as reduce visibility in the infrared, visual, audio, and radio frequency (RF) spectrum. Development of stealth technology likely began in Germany during World War II. Well-known modern examples of stealth aircraft include the United States' F-117 Nighthawk (1981–2008), the B-2 Spirit, the F-22 Raptor and the F-35 Lightning II.

While no aircraft is totally invisible to radar, stealth aircraft prevent conventional radar from detecting or tracking the aircraft effectively, reducing the odds of a successful attack. Stealth is the combination of passive low observable (LO) features and active emitters such as Low Probability of Intercept Radars, radios and laser designators. These are usually combined with active defenses such as chaff, flares, and ECM. It is accomplished by using a complex design philosophy to reduce the ability of an opponent's sensors to detect, track, or attack the stealth aircraft. This philosophy also takes into account the heat, sound, and other emissions of the aircraft as these can also be used to locate it.

Full-size stealth combat aircraft demonstrators have been flown by the United States (in 1977), Russia (in 2010) and China (in 2011), while the US Military has already adopted three stealth designs, and is preparing to adopt another.

Most recent fighter designs will at least claim to have some sort of stealth, low observable, reduced RCS or radar jamming capability, but as of yet there has been no actual air to air combat experience against stealth aircraft.

During World War I, an attempt to reduce the visibility of military aircraft resulted in the German heavy bomber, the Linke-Hofmann R.I; this had a wooden structure covered with transparent material. The first true "stealth" aircraft may have been the Horten Ho 229 flying wing fighter-bomber, developed in Germany during the last years of World War II. In addition to the aircraft's shape, which may not have been a deliberate attempt to affect radar deflection, the majority of the Ho 229's wooden skin was bonded together using carbon-impregnated plywood resins designed with the purported intention of absorbing radar waves. Testing performed in early 2009 by the Northrop-Grumman Corporation established that this compound, along with the aircraft's shape, would have rendered the Ho 229 virtually invisible to Britain's Chain Home early warning radar, provided the aircraft was traveling at high speed (approximately 550 mph (890 km/h)) at extremely low altitude (50–100 feet).

In the closing weeks of WWII the US military initiated "Operation Paperclip", an effort by the US Army to capture as much advanced German weapons research as possible, and also to deny that research to advancing Soviet troops. A Horton glider and the Ho 229 number V3 were secured and sent to Northrop Aviation for evaluation in the United States, who much later used a flying wing design for the B-2 stealth bomber. During WWII Northrop had been commissioned to develop a large wing-only long-range bomber (XB-35) based on photographs of the Horton's record-setting glider from the 1930s, but their initial designs suffered controllability issues that were not resolved until after the war. Northrop's small one-man prototype (N9M-B) and a Horton wing-only glider are located in the Chino Air Museum in Southern California.

Modern stealth aircraft first became possible when Denys Overholser, a mathematician working for Lockheed Aircraft during the 1970s, adopted a mathematical model developed by Petr Ufimtsev, a Russian scientist, to develop a computer program called Echo 1. Echo made it possible to predict the radar signature an aircraft made with flat panels, called facets.

In 1975, engineers at Lockheed Skunk Works found that an aircraft made with faceted surfaces could have a very low radar signature because the surfaces would radiate almost all of the radar energy away from the receiver. Lockheed built a model called "the Hopeless Diamond", so-called because it resembled a squat diamond, and looked too hopeless to ever fly. Because advanced computers were available to control the flight of even a Hopeless Diamond, for the first time designers realized that it might be possible to make an aircraft that was virtually invisible to radar.

Reduced radar cross section is only one of five factors the designers addressed to create a truly stealthy design such as the F-22. The F-22 has also been designed to disguise its infrared emissions to make it harder to detect by infrared homing ("heat seeking") surface-to-air or air-to-air missiles. Designers also addressed making the aircraft less visible to the naked eye, controlling radio transmissions, and noise abatement.

The first combat use of purpose-designed stealth aircraft was in December 1989 during Operation Just Cause in Panama. On December 20, 1989, two USAF F-117s bombed a Panamanian Defense Force barracks in Rio Hato, Panama. In 1991, F-117s were tasked with attacking the most heavily fortified targets in Iraq in the opening phase of Operation Desert Storm and were the only jets allowed to operate inside Baghdad's city limits.

Early stealth aircraft were designed with a focus on minimal radar cross section (RCS) rather than aerodynamic performance. Highly-stealth aircraft like the F-117 Nighthawk are aerodynamically unstable in all three axes and require constant flight corrections from a fly-by-wire (FBW) flight system to maintain controlled flight. Most modern non-stealth fighter aircraft are unstable on one or two axes only. However, in the pursuit of increased maneuverability, most 4th and 5th-generation fighter aircraft have been designed with some degree of inherent instability that must be controlled by fly-by-wire computers. As for the B2 Spirit, based on the development of the all-wing aircraft by Jack Northrop since 1940, design allowed creating stable aircraft with sufficient yaw control, even without vertical surfaces such as rudders.

Earlier stealth aircraft (such as the F-117 and B-2) lack afterburners, because the hot exhaust would increase their infrared footprint, and breaking the sound barrier would produce an obvious sonic boom, as well as surface heating of the aircraft skin which also increased the infrared footprint. As a result their performance in air combat maneuvering required in a dogfight would never match that of a dedicated fighter aircraft. This was unimportant in the case of these two aircraft since both were designed to be bombers. More recent design techniques allow for stealthy designs such as the F-22 without compromising aerodynamic performance. Newer stealth aircraft, like the F-22 and F-35, have performance characteristics that meet or exceed those of current front-line jet fighters due to advances in other technologies such as flight control systems, engines, airframe construction and materials.

The high level of computerization and large amount of electronic equipment found inside stealth aircraft are often claimed to make them vulnerable to passive detection. This is highly unlikely and certainly systems such as Tamara and Kolchuga, which are often described as counter-stealth radars, are not designed to detect stray electromagnetic fields of this type. Such systems are designed to detect intentional, higher power emissions such as radar and communication signals. Stealth aircraft are deliberately operated to avoid or reduce such emissions.

Current Radar Warning Receivers look for the regular pings of energy from mechanically swept radars while fifth generation jet fighters use Low Probability of Intercept Radars with no regular repeat pattern.

Stealth aircraft are still vulnerable to detection during, and immediately after using their weaponry. Since stealth payload (reduced RCS bombs and cruise missiles) are not yet generally available, and ordnance mount points create a significant radar return, stealth aircraft carry all armament internally. As soon as weapons bay doors are opened, the plane's RCS will be multiplied and even older generation radar systems will be able to locate the stealth aircraft. While the aircraft will reacquire its stealth as soon as the bay doors are closed, a fast response defensive weapons system has a short opportunity to engage the aircraft.

This vulnerability is addressed by operating in a manner that reduces the risk and consequences of temporary acquisition. The B-2's operational altitude imposes a flight time for defensive weapons that makes it virtually impossible to engage the aircraft during its weapons deployment. All stealthy aircraft carry weapons in internal weapons bays. New stealth aircraft designs such as the F-22 and F-35 can open their bays, release munitions and return to stealthy flight in less than a second.

Some weapons require that the weapon's guidance system acquire the target while the weapon is still attached to the aircraft. This forces relatively extended operations with the bay doors open.

Also, such aircraft as the F-22 Raptor and F-35 Lighting II Joint Strike Fighter can also carry additional weapons and fuel on hardpoints below their wings. When operating in this mode the planes will not be nearly as stealthy, as the hardpoints and the weapons mounted on those hardpoints will show up on radar systems. This option therefore represents a trade off between stealth or range and payload. External stores allow those aircraft to attack more targets further away, but will not allow for stealth during that mission as compared to a shorter range mission flying on just internal fuel and using only the more limited space of the internal weapon bays for armaments.

Fully stealth aircraft carry all fuel and armament internally, which limits the payload. By way of comparison, the F-117 carries only two laser or GPS guided bombs, while a non-stealth attack aircraft can carry several times more. This requires the deployment of additional aircraft to engage targets that would normally require a single non-stealth attack aircraft. This apparent disadvantage however is offset by the reduction in fewer supporting aircraft that are required to provide air cover, air-defense suppression and electronic counter measures, making stealth aircraft "force multipliers".

The B-2 has a skin made with highly specialized materials such as Polygraphite.

Stealth aircraft are typically more expensive to develop and manufacture. An example is the B-2 Spirit that is many times more expensive to manufacture and support than conventional bomber aircraft. The B-2 program cost the U.S. Air Force almost $45 billion.

Theoretically there are a number of methods to detect stealth aircraft at long range.

Passive (multistatic) radar, bistatic radar and especially multistatic radar systems are believed to detect some stealth aircraft better than conventional monostatic radars, since first-generation stealth technology (such as the F117) reflects energy away from the transmitter's line of sight, effectively increasing the radar cross section (RCS) in other directions, which the passive radars monitor. Such a system typically uses either low frequency broadcast TV and FM radio signals (at which frequencies controlling the aircraft's signature is more difficult). Later stealth approaches do not rely on controlling the specular reflections of radar energy and so the geometrical benefits are unlikely to be significant.

Researchers at the University of Illinois at Urbana-Champaign with support of DARPA, have shown that it is possible to build a synthetic aperture radar image of an aircraft target using passive multistatic radar, possibly detailed enough to enable automatic target recognition (ATR).

In December 2007, SAAB researchers also revealed details for a system called Associative Aperture Synthesis Radar (AASR) that would employ a large array of inexpensive and redundant transmitters and a few intelligent receivers to exploit forward scatter to detect low observable targets. The system was originally designed to detect stealthy cruise missiles and should be just as effective against aircraft. The large array of inexpensive transmitters also provides a degree of protection against anti-radar (or anti-radiation) missiles or attacks.

Some analysts claim Infra-red search and track systems (IRSTs) can be deployed against stealth aircraft, because any aircraft surface heats up due to air friction and with a two channel IRST is a CO2 (4.3 µm absorption maxima) detection possible, through difference comparing between the low and high channel. These analysts also point to the resurgence in such systems in several Russian designs in the 1980s, such as those fitted to the MiG-29 and Su-27. The latest version of the MiG-29, the MiG-35, is equipped with a new Optical Locator System that includes even more advanced IRST capabilities.

In air combat, the optronic suite allows:

Detection of non-afterburning targets at 45-kilometre (28 mi) range and more;

    Identification of those targets at 8-to-10-kilometre (5.0 to 6.2 mi) range; and

    Estimates of aerial target range at up to 15 kilometres (9.3 mi).

For ground targets, the suite allows:

    A tank-effective detection range up to 15 kilometres (9.3 mi), and aircraft carrier detection at 60 to 80 kilometres (37 to 50 mi);

    Identification of the tank type on the 8-to-10-kilometre (5.0 to 6.2 mi) range, and of an aircraft carrier at 40 to 60 kilometres (25 to 37 mi); and

    Estimates of ground target range of up to 20 kilometres (12 mi).

The Dutch company Thales Nederland, formerly known as Holland Signaal, have developed a naval phased-array radar called SMART-L, which also is operated at L-Band and is claimed to offer counter stealth benefits. However, as with most claims of counter-stealth capability, these are unproven and untested. True resonant effects might be expected with HF sky wave radar systems, which have wavelengths of tens of metres. However, in this case, the accuracy of the radar systems is such that the detection is of limited value for engagement. Any radar which can successfully match the resonant frequency of a type of stealth aircraft should be able to detect its direction. In practice this is difficult because the resonant frequency changes depending on how the stealth aircraft is oriented with respect to the radar system.

Over-the-horizon radar is a design concept that increases radar's effective range over conventional radar. It is claimed that the Australian JORN Jindalee Operational Radar Network can overcome certain stealth characteristics. It is claimed that the HF frequency used and the method of bouncing radar from ionosphere overcomes the stealth characteristics of the F-117A. In other words, stealth aircraft are optimized for defeating much higher-frequency radar from front-on rather than low-frequency radars from above.

Stealth aircraft have been used in several conflicts: the United States invasion of Panama, the Gulf War, the Kosovo Conflict, the War in Afghanistan the War in Iraq and the 2011 military intervention in Libya. To date, the United States of America is the only country to have used stealth aircraft in combat.

The first use of stealth aircraft was in the United States invasion of Panama, where F-117 Nighthawk stealth attack aircraft were used to drop bombs on enemy airfields and positions while evading enemy radars.

The successful first deployment of stealth aircraft to a combat zone marks a milestone in military aviation.

In 1990 the F-117 Nighthawk was used again in the Gulf War, where F-117s flew approximately 1,300 sorties and scored direct hits on 1,600 high-value targets in Iraq while accumulating over 6,905 flight hours. Only 2.5% of the American aircraft in Iraq were F-117s, yet they struck more than 40% of the strategic targets, dropping over 2,000 tons of precision-guided munitions and striking their targets with over an 80% success rate.

In the 1999 NATO bombing of Yugoslavia two stealth aircraft were used by the United States, the veteran F-117 Nighthawk, and the newly introduced B-2 Spirit strategic stealth bomber.

The F-117 performed its usual role of striking precision high-value targets and performed well, although one F-117 was shot down by a Serbian Isayev S-125 'Neva-M' missile. The new B-2 Spirit was highly successful, destroying 33% of selected Serbian bombing targets in the first eight weeks of U.S. involvement in the War. During this war, B-2s flew non-stop to Kosovo from their home base in Missouri and back.

In the 2003 invasion of Iraq, F-117 Nighthawks and B-2 Spirits were again used, and this was the last time the F-117 would see combat.

F-117s dropped satellite-guided strike munitions on selected targets, with high success. B-2s conducted 49 sorties in the invasion, releasing more than 1.5 million pounds of munitions.

The most recent use of stealth aircraft was in the 2011 military intervention in Libya, where B-2 Spirits dropped 40 bombs on a Libyan airfield with concentrated air defenses in support of the UN no-fly zone.

In the future, it is likely that stealth aircraft will continue to play a valuable role in air combat. In future conflicts the United States is likely to use the F-22 Raptor, B-2 Spirit, and the F-35 Lightning II to perform a variety of operations.

In Russia, the Sukhoi PAK FA stealth multi-role fighter is scheduled to be introduced from 2015, to perform a wide variety of missions. In India, the Sukhoi/HAL FGFA, the Indian version of the PAK FA is scheduled to be introduced from 2017 in higher numbers, also to perform a wide variety of missions.

In the People's Republic of China, the Chengdu J-20 stealth multi-role fighter is planned to be introduced around 2018. A prototype was flown in early 2011.

The only time that a stealth aircraft has been shot down was on 27 March 1999, during Operation Allied Force. An American F-117 Nighthawk's bomb bay had malfunctioned causing it to remain open for an unusually long time, allowing a Serbian Air Defense crew who were operating their radars on unusually long wavelengths to launch a Isayev S-125 'Neva-M' missile at it which brought it down. The pilot ejected and was rescued and the aircraft itself remained relatively intact due to striking the ground at a slow speed in an inverted position.

A B-2 crashed on 23 February 2008 shortly after takeoff from Andersen Air Force Base in Guam. The findings of the investigation stated that the B-2 crashed after "heavy, lashing rains" caused water to enter skin-flush air-data sensors, which feed angle of attack and yaw data to the computerized flight-control system.

The water distorted preflight readings in three of the plane's 24 sensors, causing the flight-control system to send an erroneous correction to the B-2 on takeoff. The B-2 quickly stalled, became unrecoverable, and crashed.

The sensors in question measure numerous environmental factors, including air pressure and density, for data to calculate airspeed, altitude and attitude. Because of the faulty readings, the flight computers determined inaccurate airspeed readings and incorrectly indicated a downward angle for the aircraft, which contributed to an early rotation and an un-commanded 30-degree pitch up and left yaw, resulting in the stall.

The Sukhoi PAK FA, (Perspektivny aviatsionny kompleks frontovoy aviatsii, literally "Prospective Airborne Complex of Frontline Aviation") is a twin-engine jet fighter being developed by Sukhoi OKB for the Russian Air Force.

The current prototype is Sukhoi's T-50. The PAK FA, when fully developed, is intended to be the successor to the MiG-29 and Su-27 in the Russian inventory and serve as the basis of the Sukhoi/HAL FGFA being developed with India. A fifth generation jet fighter, the T-50 performed its first flight 29 January 2010. Its second flight was on 6 February and its third on 12 February 2010. As of 31 August 2010, it had made 17 flights and by mid-November, 40 in total. The second prototype was to start its flight test by the end of 2010, but this was delayed until March 2011.

Sukhoi director Mikhail Pogosyan has projected a market for 1,000 aircraft over the next four decades, which will be produced in a joint venture with India, 200 each for Russia and India and 600 for other countries. He has also said that the Indian contribution would be in the form of joint work under the current agreement rather than as a joint venture. The Indian Air Force will "acquire 50 single-seater fighters of the Russian version" before the two seat FGFA is developed. The Russian Defense Ministry will purchase the first 10 aircraft after 2012 and then 60 after 2016. The first batch of fighters will be delivered with current technology engines. Ruslan Pukhov, director of the Centre for Analysis of Strategies and Technologies, has projected that Vietnam will be the second export customer for the fighter. The PAK-FA is expected to have a service life of about 30–35 years.

In the late 1980s, the Soviet Union outlined a need for a next-generation aircraft to replace its MiG-29 and Su-27 in frontline service. Two projects were proposed to meet this need, the Sukhoi Su-47 and the Mikoyan Project 1.44. In 2002, Sukhoi was chosen to lead the design for the new combat aircraft.

The Tekhnokompleks Scientific and Production Center, Ramenskoye Instrument Building Design Bureau, the Tikhomirov Scientific Research Institute of Instrument Design, the Ural Optical and Mechanical Plant (Yekaterinburg), the Polet firm (Nizhniy Novgorod) and the Central Scientific Research Radio Engineering Institute (Moscow) were pronounced winners in the competition held in the beginning of 2003 for the development of the avionics suite for the fifth-generation airplane. NPO Saturn has been determined the lead executor for work on the engines for this airplane.

The Novosibirsk Chkalov Aviation Production Association (NAPO Chkalov) has begun construction of the fifth-generation multirole fighter. This work is being performed at Komsomol'sk-on-Amur together with Komsomolsk-on-Amur Aircraft Production Association; the enterprise's general director, Fedor Zhdanov reported during a visit to NAPO by Novosibirsk Oblast's governor Viktor Tolokonskiy on 6 March 2007. "Final assembly will take place at Komsomol'sk-on-Amur, and we will be carrying out assembly of the fore body of this airplane", Zhdanov specified.

On 8 August 2007, Russian Air Force Commander Alexander Zelin was quoted by Russian news agencies that the development stage of the PAK FA program is now complete and construction of the first aircraft for flight testing will now begin. Alexander Zelin also said that by 2009 there will be three fifth-generation aircraft ready. "All of them are currently undergoing tests and are more or less ready", he said. In the summer of 2009 the design was approved.

On 11 September 2010, it was reported that Indian and Russian negotiators had agreed on a preliminary design contract that would then be subject to Cabinet approval. The joint development deal would have each country invest $6 billion and take 8 to 10 years to develop the FGFA fighter. The agreement on the pre-design of the fighter was to be signed in December 2010. The preliminary design will cost $295 million and will be complete within 18 months.

On 28 February 2009, Mikhail Pogosyan announced that the airframe for the aircraft was almost finished and that the first prototype should be ready by August 2009. On 20 August 2009, Sukhoi General Director Mikhail Pogosyan said that the first flight would be by year end. Konstantin Makiyenko, deputy head of the Moscow-based Centre for Analysis of Strategies and Technologies said that "even with delays", the aircraft would likely make its first flight by January or February, adding that it would take 5 to 10 years for commercial production.

The maiden flight had been repeatedly postponed since early 2007 as the T-50 encountered unspecified technical problems. Air Force chief Alexander Zelin admitted as recently as August 2009 that problems with the engine and in technical research remained unsolved.

On 8 December 2009, Deputy Prime Minister Sergei Ivanov announced that the first trials with the fifth-generation aircraft would begin in 2010. The testing, however, has commenced earlier than stated, with the first successful taxiing test taking place on 24 December 2009.

The aircraft's maiden flight took place on 29 January 2010 at KnAAPO's Komsomolsk-on-Amur Dzemgi Airport; the aircraft was piloted by Sergey Bogdan (!5@359 >340=) and the flight lasted for 47 minutes.

A second airframe was first planned to join the flight testing in the fourth quarter of 2010 but was postponed. On 3 March 2011 a second prototype was reported to have made a successful 44 minutes test flight. These first two aircraft will lack radar and weapon control systems, while the third and fourth aircraft, to be added in 2011, will be fully functional test aircraft.

On 14 March 2011, the aircraft achieved supersonic flight at a test range near Komsomolsk-on-Amur in Siberia.

The T-50 is expected to be on display at the 2011 MAKS Airshow.

Navalized Sukhoi T-50 PAK FAs will be deployed on the Russian aircraft carrier Admiral Kuznetsov and future Russian aircraft carriers. There will be a competition between the Sukhoi, Mikoyan and Yakovlev design bureaus to choose the new naval aircraft.

Alexei Fedorov has said that any decision on applying fifth generation technologies to produce a smaller fighter (in the F-35 range) must wait until after the heavy fighter, based on the T-50, is completed.

Although most of information about the PAK FA is classified, it is believed from interviews with people in the Russian Air Force and Defense Ministry that it will be stealthy, have the ability to supercruise, be outfitted with the next generation of air-to-air, air-to-surface, and air-to-ship missiles, incorporate a fix-mounted AESA radar with a 1,500-element array and have an "artificial intellect".

According to Sukhoi, the new radar will reduce pilot load and the aircraft will have a new data link to share information between aircraft.

Composites are used extensively on the T-50 and comprise 25% of its weight and almost 70% of the outer surface. It is estimated that titanium alloy content of the fuselage is 75%. Sukhoi's concern for minimizing radar cross-section (RCS) and drag is also shown by the provision of two tandem main weapons bays in the centre fuselage, between the engine nacelles. Each is estimated to be between 4.9-5.1 m long. The main bays are augmented by bulged, triangular-section bays at the wing root.

The Moskovsky Komsomolets reported that the T-50 has been designed to be more maneuverable than the F-22 Raptor at the cost of making it less stealthy than the F-22. One of the design elements that have such an effect is the Leading Edge Vortex Controller (LEVCON).

The PAK FA SH121 radar complex includes three X-Band AESA radars located on the front and sides of the aircraft. These will be accompanied by L-Band radars on the wing leading edges. L-Band radars are proven to have increased effectiveness against very low observable (VLO) targets which are optimized only against X-Band frequencies, but their longer wavelengths reduce their resolution.

The PAK FA will feature an IRST optical/IR search and tracking system, based on the OLS-35M which is currently in service with the Su-35S.

Hindustan Aeronautics Limited will reportedly provide the navigation system and the mission computer.

The PAK FA was expected to use a pair of Saturn 117S engines on its first flights. The 117S (AL-41F1A) is a major upgrade of the AL-31F based on the AL-41F intended to power the Su-35BM, producing 142 kN (32,000 lb) of thrust in afterburner and 86.3 kN (19,400 lb) dry. In fact, PAK FA already used a completely new engine in its first flight, as stated by NPO Saturn. The engine is not based on the Saturn 117S and is rumoured to be called "127 engine". The engine generates a larger thrust and has a complex automation system, to facilitate flight modes such as maneuverability. Exact specifications of the new engine are still secret. It is expected that each engine will be able to independently vector its thrust upwards, downward or side to side. Vectoring one engine up with the other one down can produce a twisting force. Therefore the PAK FA would be the first fifth generation fighter with full 3-D thrust vectoring along all three aircraft axes: pitch, yaw and roll. These engines will incorporate infrared and RCS reduction measures.

The PAK FA has a reported maximum weapons load of 7,500 kg. It has an apparent provision for a cannon (most likely GSh-301). It could possibly carry as many as two 30 mm cannons. It has two internal bays estimated at 4.6-4.7 metres by 1-1.1 metres. Some sources suggest two auxiliary internal bays for short range AAMS and six external hardpoints.

Two Izdeliye 810 Extended beyond visual range missiles per weapons bay. Multiple Izdeliye 180 / K77M beyond visual range missiles. K74 and K30 within visual range missiles can also be carried. Two KH38M or KH58 USHK air-to-ground missiles per weapons bay. Multiple 250–500 kg precision guided bombs per weapons bay, with a maximum of 10 bombs in internal bays. Other possible loads include one 1,500 kg bomb per weapons bay or two 400 km+ range anti-AWACS weapons on external hardpoints.

The first flight video shows that PAK FA has no conventional rudders, its vertical tails are fully movable. This special tail fin design is mechanically similar to V-tails used by the Northrop YF-23 in 1990s, but is supplemented by dedicated horizontal stabilators (as on the F-22). The T-50 has wing leading-edge devices above the jet engine intakes that have been called a challenge for signature control.

The Chengdu J-20 (literally "Fighter aircraft Twenty") is a fifth generation stealth, twin-engine fighter aircraft prototype developed by Chengdu Aircraft Industry Group for the Chinese People's Liberation Army Air Force. In late 2010, the J-20 underwent high speed taxiing tests. The J-20 made its first flight on 11 January 2011. General He Weirong, Deputy Commander of the People's Liberation Army Air Force said in November 2009 that he expected the J-20 to be operational in 2017–2019.

The J-20 was one of the stealth fighter programs under the codename J-XX that was launched in the late 1990s. It was designated “Project 718”, and won the PLAAF endorsement in a 2008 competition against a Shenyang proposal that was reportedly even larger than J-20. Two prototypes (2001-01 & 2001–02) have been built as of the end of 2010.

On 22 December 2010, the J-20 was under-going high speed taxiing tests outside the Chengdu Aircraft Design Institute with no confirmed flight tests. The J-20 made its first flight, which lasted about 20 minutes, on 11 January 2011.

Director of National Intelligence James R. Clapper has testified that the United States has known about the program for a "long time" and that the test flight was not a surprise.

The J-20 made its first flight, lasting about 15 minutes, on 11 January 2011. A Chengdu J-10S served as the escort aircraft. After the successful first flight, a ceremony was held. The test pilot of the J-20, Li Gang, Chief designer Yang Wei and General Li Andong (Deputy-Director of General Armaments Department, and Director of Science and Technology Commission of General Armaments Department of the PLA since 2000) attended the ceremony.

China thus became the third nation in the world to "develop and test-fly a full-size stealth combat aircraft demonstrator", after the United States and Russia. The Guardian reported that experts, on the one hand, expressed "surprise" at the speed with which the aircraft was developed, but on the other hand "said the country's military prowess was still relatively backward and way behind that of the US" and that its military interests were limited to its region.

The first test flight coincided with a visit of United States Secretary of Defense Robert Gates to China, and was initially interpreted by Pentagon officials and media pundits[who?] as a possible signal to the visiting delegation from the U.S. However, after meeting with senior Chinese officials including Chinese President Hu Jintao, Secretary Gates remarked, "The civilian leadership seemed surprised by the test and assured me it had nothing to do with my visit." Jin Canrong, a professor at Renmin University in Beijing who specializes in China-U.S. relations, suggested that President Hu's ignorance of the test raises questions about the nature of civilian control of the Chinese military. However, as Michael Swaine, an expert on the PLA and United States – China military relations, explained, although it's possible and even likely that "senior officials in the [Chinese] leadership did not know that this flight test would occur on this precise day," this is not necessarily evidence of a military-backed effort to insult Secretary Gates' delegation or embarrass President Hu. Rather, decisions regarding the production, development and testing of such military aircraft are routinely managed by engineers and low-level officials more than by senior civilian or military leadership. Coupled with the fact that there was relatively limited coverage of the event in Chinese media initially, it is likely that the test may not have been considered a significant enough event to warrant notification to President Hu. Moreover, the Chinese military has conducted important tests (including the 2007 anti-satellite missile test) on 11 January in the past; thus, the test may have been related to this.

A second test flight of an hour and twenty minutes took place on 17 April 2011. On 5 May 2011, a 55 minute test flight included retraction of the landing gear.

The full initial test program of 10 to 20 test flights is expected to take years to complete.

Globalsecurity.org states that China probably declined to participate in joint development and production of new fifth generation fighter with Russia given the belief that Russia stood to gain more from Chinese participation. Chinese leaders may have determined that their design was superior to the Russian PAK FA. United States House Committee on Armed Services chairman Howard McKeon said on the J-20 "my understanding is that they built it on information that they received from Russia, from a Russian plane, that they were able to copy".

Balkan military officials told the Associated Press that China and Russia may have adopted some stealth technology from a Lockheed F-117 Nighthawk, which was shot down by the Serbian military in 1999 during the Kosovo war. If Chinese experts used the F-117 stealth coatings, the result would be decades behind current American state-of-the-art. However, Chinese test pilot Xu Yongling said that the J-20 was a "masterpiece" of home-grown innovation, he also said the F-117 technology was already "outdated" even at the time it was shot down, and could not be applied to a next-generation stealth jet. Janes editor James Hardy agrees that it was unlikely China would have learned much from the wreckage.

Retired USAF General Thomas G. McInerney has suggested that the J-20 design may have been based on cyber-espionage of the Lockheed Martin FB-22 project.

A federal prosecutor has suggested that China may have used technology from the Northrop Grumman B-2 Spirit for their stealth aircraft which was supplied by Noshir Gowadia.

Chief of the Air Staff of the Indian Air Force Pradeep Vasant Naik has suggested that the J-20 is entirely reverse engineered with no Chinese R&D involved, and questioned if the practice was ethical. The Deccan Chronicle has called Naik's comment an "unusual outburst of helplessness" as China surpasses Indian airpower.

Russian military commentator Ilya Kramnik conjectures that China is still 10 to 15 years behind the United States and Russia in fighter technology and may not be able to manufacture all the advanced composite materials, avionics and sensor packages needed for such aircraft, and could instead turn to foreign suppliers. However, he speculates that China may be able to produce the J-20 at a cost 50% to 80% lower than US and Russian fifth-generation jet fighters, and that potential customers may include Pakistan, the Middle East, Latin America, Southeast Asia and the richest countries in Africa. Konstantin Sivkov of the Academy for Geopolitical Issues argued that the US is correct to be alarmed at the progress of Chinese military technology.

Bill Sweetman speculates that China will have problems meeting its production requirements, as it has several other jet fighter projects in production. Aviation Week raised the question of whether the aircraft is a prototype, like the Sukhoi T-50, or a technology demonstrator similar to the Lockheed YF-22.

The J-20 is a single-seat, twin-engine aircraft which appears to be somewhat larger and heavier than the comparable Sukhoi T-50 and Lockheed Martin F-22 Raptor. Bill Sweetman estimates that it is approximately 75 feet (23 m) in length, has a wingspan of 45 feet (14 m) or more, and is expected to have a takeoff weight of 75,000 to 80,000 pounds (34,000 to 36,000 kg) with internal stores only. The prototype could be powered by twin 32,000 pounds (15,000 kg) thrust Saturn 117S engines provided by Russia, a sign of problems in the development of the aircraft, according to Pentagon spokesman Col. David Lapan. Chinese sources have claimed that production aircraft will be powered by two 13,200 kilograms (29,000 lb)/WS-10 class high thrust turbofan engines fitted with Thrust Vector Controlled (TVC) nozzles, both made in China. However Richard Aboulafia has said that the WS-10 engine has suffered catastrophic failures in flight.

The J-20 may have lower supercruise speed (yet greater range) and less agility than a Lockheed Martin F-22 Raptor or PAK FA, but might also have larger weapons bays and carry more fuel. The J-20 has a long and wide fuselage and low jet engine intakes with a forward chine, a main delta wing, forward canards, a bubble canopy, conventional round engine exhausts and canted all-moving fins. The front section of the J-20 is similarly chiseled as the F-22 Raptor and the body and tail resemble those of the Sukhoi T-50 prototype. As early photographs of the prototype surfaced, Bill Sweetman commented that the design may suggest a large, long range ground attack aircraft, not unlike a "stealth version" of the General Dynamics F-111 Aardvark. Douglas Barrie has noted that the canard-delta configuration with canted vertical fins appears to resemble the MiG 1.42. Yet, Barrie notes that key differences include greater forward fuselage shaping as the basis for low observable characteristics, along with the different engine intake configuration. It is suspected that cyberespionage may have assisted the development of the J-20, with information used by subcontractors of Lockheed Martin for the F-35 project in particular having been significantly compromised during development of the J-20.

The J-20 has a pair of all-moving tailfins that are swept back in the F-35 style instead of being trapezoid like the F-22 and PAK-FA tails and ventral stabilizing fins. It also has an F-22 style nose section, but with F-35 style dropped nose, forward swept intake cowls with diverterless supersonic inlet (DSI) bumps and a one-piece canopy. It was reported in November 2006 that a T/W=10 17,000 kilograms (37,000 lb) class turbofan (WS-15/"large thrust") was being developed for the J-20. One (2001-01) prototype is fitted with AL-31F, the other (2001–02) is fitted with the improved WS-10G with a new "stealth" nozzle possibly to reduce RCS and IR emission.

The J-20 may become the first operational combat aircraft that carries sufficient fuel to supercruise throughout its missions, doubling its sortie rate.

Pentagon spokesman Geoff Morrell has said that it was premature to call the J-20 a stealth fighter or to judge if it had any other fifth generation characteristics.

The production J-20 may incorporate an advanced fly-by-wire (FBW) system fully integrated with the fire-control and the engine systems. Its fire-control radar is expected to be Active Electronically Scanned Array (AESA) (Type 1475/KLJ5?).

According to recent pictures from the internet, two small dark diamond shaped windows can be seen on both sides of the nose, which could house certain EO sensors, such as MAWS and/or IRST. Two additional windows are seen underneath the rear fuselage, plus two more on top of the forward fuselage above the canard wings, suggesting a distributed situational awareness system similar to the EODAS onboard American F-35 was installed providing a full 360° coverage.

The aircraft features a "pure" glass cockpit (two large color liquid crystal display (LCD) and several smaller ones and a wide-angle holographic head-up display (HUD)). Many of these subsystems have been tested onboard J-10Bs to speed up the development.

The J-20 has a large belly weapon bay for short/long-range air-to-air missiles (AAM) (PL-10, PL-12C/D & PL-21) and two smaller lateral weapon bays behind the air inlets for short-range AAMs (PL-10).

Carlo Kopp has suggested that the J-20's overall stealth shaping is "without doubt considerably better" than the F-35 and PAK FA, but he agrees with others, such as Shih Hiao-wei of Defense International monthly and Bill Sweetman of Aviation Week, that some parts on the J-20 will challenge its ability to remain stealthy from all directions: "The aft fuselage, tailbooms, fins/strakes and axi-symmetric nozzles are not compatible with high stealth performance, but may only be stop-gap measures to expedite flight testing of a prototype." As of January 2011 the engine nozzles were clearly non-stealthy; this may be due to the fact that the final "fifth generation" engines had not been completed yet. However, one of the prototypes uses WS-10G engines with stealthy jagged-edge nozzles and tiles, however without the reduced RCS afterburners of the F119 and F135 this would have limited impact.

Robert Gates has also questioned how stealthy the J-20 might be although he did say the development of the J-20 had the potential to "put some of our capabilities at risk, and we have to pay attention to them, we have to respond appropriately with our own programs.” Kopp and Goon have further speculated that the J-20 is designed to operate as a heavy interceptor, destroying opposing AWACS and tanker aircraft. If true, this would make it more similar to a MiG-25 with stealth capability. Sweetman agrees that this is the most likely role for such a large aircraft with low thrust to weight ratio and limited agility that is optimized for range and speed. Lewis Page has said that it is unlikely that the Chinese will soon have an American style Low Probability of Intercept Radar and so the J-20 would be limited to attacking ground targets like previous generations of American stealth aircraft such as the Lockheed F-117 Nighthawk. In that case the J-20 would carry a radar, but using it would instantly give away its location. However, the J-20 is expected to use a AESA radar, which should have Low Probability of Intercept modes. Given that the F-35 can already track and jam even the F-22's radar, this might not be sufficient.

Loren B. Thompson has said that this combination of forward sector only stealth and long range will allow the J-20 to make attacks on surface targets while the United States lacks sufficient bases for F-22s in the area to counter these attacks and American allies have no comparable aircraft. Thompson has also said that a long-range maritime strike aircraft may cause the United States more trouble than a shorter range air-superiority fighter like the F-22.

A canard delta offers greater efficiency in both subsonic and supersonic flight (which may help supercruise range), but it is unknown if the Chinese have the same software used on the Eurofighter Typhoon to control the otherwise non-stealthy canards. Teal Group analyst Richard Aboulafia has also raised doubts about the use of canards on a design that is intended to be low-observable: “There’s no better way of guaranteeing a radar reflection and compromise of stealth”. Aboulafia has also called the J-20 a kludge made of mismatched parts and questioned if the Chinese have the skills or technology to produce a true fifth generation fighter. Nevertheless, canards greatly boost the aircraft's maneuverability over that of a pure delta wing without canards. Sweetman notes that the canard delta works with the Whitcomb area rule for a large-volume mid-body section supersonic aircraft. Also, while the DSI intakes are easier to maintain than more complex stealth-compatible intakes, such as on the F-22, their fixed form limits the aircraft to around Mach 2.0. J.D. McFarlan of Lockheed Martin has said that the J-20 DSI inlets resemble those of the F-35, but it is unclear if the Chinese have perfected their own design.

The Advanced Medium Combat Aircraft (AMCA), formerly known as the Medium Combat Aircraft (MCA), is a single-seat, twin-engine fifth-generation stealth multirole fighter being developed by India. It will complement the HAL Tejas, the Sukhoi/HAL FGFA, the Sukhoi Su-30MKI and the as yet undecided MRCA in the Indian Air Force. The main purpose of this aircraft is to replace the aging SEPECAT Jaguar & Dassault Mirage 2000. Unofficial design work on the MCA has been started. A naval version is confirmed as Indian Navy also contributed to the funding. $2 billion funding is set to be allocated over the next three years.Number of AMCA orders are expected to reach 250 units.

In August 2006, India's then defence minister Mr. Pranab Mukherjee announced in Parliament that the government is evaluating experiences gained from the Tejas programme for the MCA.

In October 2008, the Indian Air Force asked the Aeronautical Development Agency (ADA) to prepare a detailed project report on the development of a Medium Combat Aircraft (MCA) incorporating stealth features.

In February 2009, ADA director P.S Subramanyam said at a Aero-India 2009 seminar, that they are working closely with Indian Air Force to develop a Medium Combat Aircraft. He added that according to the specification provided by the Indian Air Force, it would likely be a twenty ton aircraft powered by two GTX Kaveri engines.

In April 2010, the Indian Air Force issued the Air Staff requirements (ASR) for the AMCA which placed the aircraft in the twenty five ton category.

The AMCA will be designed with a very small radar cross-section and will also feature serpentine shaped air-intakes, internal weapons and the use of composites and other materials.

It will be a twin-engined design using the GTX Kaveri engine with thrust vectoring with the possibility of giving the aircraft supercruise capabilities. A wind-tunnel testing model of the MCA airframe was seen at Aero-India 2009.

As well as advanced sensors the aircraft will be equipped with missiles like DRDO Astra and other advanced missiles, stand-off weapons and precision weapons. The aircraft will have the capability to deploy JDAM's. The aircraft will feature Extended detection range and targeting range with the ability to release weapons at supersonic speeds. The aircraft's avionics suite will include AESA radar IRST and appropriate Electronic warfare systems and all aspect missile warning suite.

DARE, Bangalore has appointed a special team to begin identifying avionics and cockpit packages for the first prototype vehicle, and will supply this in published form to the ADA by July 2010. This will include cockpit electronics, cockpit configuration, man-machine interface, mission console systems and computers/software with a focus on data fusion and modular architecture. The LRDE will, in about the same time frame, provide a separate project proposal for an all new radar, to be re-designated for the AMCA, as a derivative of the MMR currently being completed with technology from Israel's ELTA. LRDE will independently look in the market for a partner for active array technology, though it communicated to ADA in June 2009 that it had sufficient R&D available to build a reliable AESA prototype with assistance from Bharat Electronics Ltd and two private firms based in Hyderabad.

The Next-Generation Bomber program (formerly called the 2018 Bomber) is a medium bomber under development by the United States Air Force. It was originally projected to enter service around 2018 as a super stealthy, subsonic, medium range, medium payload "B-3" type system to augment and possibly to a limited degree replace the U.S. Air Force's aging bomber fleet.

On 24 June 2010 Lt. Gen. Philip M. Breedlove said that the term "next-generation bomber" was dead and that the Air Force was working on a long-range strike "family" that would draw on the capabilities of systems like the F-35 and F-22 to help a more affordable and versatile bomber complete its missions.

On 13 September 2010 Air Force Secretary Michael Donley said that long range strike would continue cautiously with proven technologies and that the plan to be submitted with the 2012 budget could call for either a missile or an aircraft. General Norton Schwartz clarified that the bomber will not itself be nuclear capable, but will be the basis of a future nuclear capable aircraft.

USAF Air Combat Command in 2004-06 studied alternatives for a new bomber type aircraft to augment the current bomber fleet which now consists of largely 1970s era airframes, with a goal of having a fully operational aircraft on the ramp by 2018. Speculation that the next generation bomber would be hypersonic and unmanned were laid to rest when Air Force Major General Mark T. Matthews, head of ACC Plans and Programs said "Our belief is that the bomber should be manned" at a 1 May 2007 Air Force Association sponsored event. He later cited that the bomber would also likely be subsonic due to the higher cost of development and maintenance of a supersonic or hypersonic bomber. The 2018 bomber is expected to serve as a stop-gap until the more advanced "2037 Bomber" enters service.

USAF officials expect the new bomber to have top end low observability characteristics with the ability to loiter for hours over the battlefield area and respond to threats as they appear. Major General David E. Clary, ACC vice-commander, summed it up by saying the new bomber will be expected to "penetrate and persist". Deployment of cruise missiles is another issue for the new bomber. The B-52 is the only aircraft currently in the Air Force inventory allowed under treaty to carry and fire the cruise missiles. Major consideration was paid to operation readiness and flexibility. In 2006, the program expected that a prototype could be flying as early as 2009. In September 2007, Air Force generals stated that even though the development schedule for the bomber is short, it could be fielded by 2018.

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Petrescu, Relly Victoria; Aversa, Raffaella; Akash, Bilal; Bucinell, Ronald; Corchado, Juan; Berto, Filippo; Mirsayar, MirMilad; Apicella, Antonio; Petrescu, Florian Ion Tiberiu; 2017a Modern Propulsions for Aerospace-A Review, Journal of Aircraft and Spacecraft Technology, 1(1).

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