Stealth aircraft

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Image:Usaf.b2.spirit.750pix.jpg Image:Side View B2.jpg A stealth aircraft is an aircraft which has been designed to absorb and deflect radar (via stealth technology); these are not completely "invisible" to radar, they are simply harder to detect than conventional technology. In general the goal is to allow a stealth aircraft to execute its attack while still outside the ability of the opposing system's detection. Stealth aircraft were most notably used during the Gulf War (1991); although stealth technology has since become less effective, the United States continues to develop stealth aircraft.

1 How stealth aircraft avoid detection
2 How stealth aircraft could potentially be detected
3 Use of stealth aircraft
4 List of stealth aircraft

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How stealth aircraft avoid detection

The main method of achieving stealth employed by modern aircraft is a coating in advanced radar-absorbing material (resulting in high maintenance costs). Some aircraft, like the F-117, avoid detection with a body shape that deflects radar signals in a direction roughly perpendicular from the radar signals origin, rather than reflecting the signal back to enemy radar sensors. To a lesser extent, today's stealth aircraft are also harder to detect and track via other methods:

The normally hot exhaust is cooled by ambient air before leaving the aircraft and partially shielded from below; as a result the infrared signature of stealth aircraft is minimized.

Stealth aircraft are typically painted in dark colors and frequently fly at night to make visual identification more difficult.

Stealth aircraft such as the F-117 and B-2 bomber are not supersonic, they have no afterburners, and the exhaust nozzles are tuned for low noise rather than peak performance, making them difficult to detect via sound waves.

Whilst the first stealth aircraft may be said to include the Horten Ho 229, the first-generation of modern stealth aircraft include the F-117 Nighthawk. Modern first-generation planes tend to be composed mostly of flat radar-deflecting surfaces that were also covered with radar absorbing materials, so as to attenuate the radar signal and deflect radar waves in a direction other than that of the radar transmitter. Modern second-generation aircraft include the B-2 Spirit and F-22 Raptor. The design of these aircraft benefited from sophisticated computer modeling of radar response that allowed them to incorporate curved surfaces, which are more aerodynamic than the flat surfaces on modern first-generation stealth aircraft.

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How stealth aircraft could potentially be detected

A number of methodologies to detect stealth aircraft at long range have been developed. Both Australia and Russia have announced that they have developed processing techniques that allow them to detect the turbulence of aircraft at reasonably long ranges (possibly negating the stealth technology).

Passive (multistatic) radars are known to detect stealth aircraft better than receivers connected to the transmitters (active or monostatic radars), since stealth technology 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. In addition, it has been suggested that use of low frequency broadcast TV and FM radio signals as the illuminating source produces a much higher RCS than high frequency monostatic radars as the long wavelengths cause whole structural portions of the targets to resonate. Target detection, even at very low Signal to Noise Ratios (down to –100 dB) is theoretically possible. Target tracking, in three-dimensional position and velocity should be more accurate with a multistatic system than with a monostatic system, using either triangulation or hyperbolic (or both) target location strategies. Wide usage of such broadcast signals (esp. in inhabited regions) means a continuous and reliable coverage and source of energy, that cannot easily be neutralized by an attacker. Researchers at the University of Illinois 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).

The United Kingdom has announced a system that uses the signals broadcast from the huge number of cellular telephone towers to generate a synthetic picture, although it is not clear if this method is actually practical. A general feature of these systems is that they use a large number of low-accuracy radar systems (or signal sources) combined with heavy computer processing to generate tracking information. For this reason they tend to be useful only in the early warning role, and have limited applicability to guidance radars for missile systems, and are rarely portable. The problem of successfully countering stealth aircraft on the battlefield remains essentially unsolved.

Stealth aircraft can also be passively detected from their electromagnetic emissions (terrain-following radar, radio communications, missile guidance communications etc.). Stealth aircraft typically attempt to minimize these emissions (using low probability of intercept radars, satellite communications etc.).

To this date, the only systems that have been shown to successfully detect stealth aircraft are very old, and use long wave radar systems that have a low resolution. The shooting down of an F-117 over Yugoslavia was attributed to the tracking of the vortexes produced by the poor aerodynamic shape of stealth aircraft. It was also reported that the F-117 was downed due to the use of an "electro-optical" (TV) tracking system used in conjunction with the missile battery. The aircraft may be hard to detect using radar, but it is still visible to the naked eye.

An F-117 was also detected by a British ship during the first Gulf War, in this case because the wavelength of the radar was twice the length of the aircraft. This caused the entire aircraft to act as a dipole, leading to a very strong radar return.Template:Fact

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Use of stealth aircraft

To date, stealth aircraft have been used in several low- and moderate-intensity conflicts, including Operation Desert Storm, Operation Allied Force and the 2003 invasion of Iraq. In each case they were employed to strike high-value targets which were either out of range of conventional aircraft in the theater or which were too heavily defended for conventional aircraft to strike without a high risk of loss. In addition, because the stealth aircraft aren't going to be dodging SAMs and AAA over the target they can aim more carefully and thus are more likely to hit the target and not cause as much collateral damage. In many cases they were used to hit the high value targets early in the campaign (or even before it), before other aircraft had the opportunity to degrade the opposing air defence to the point where other aircraft had a good chance of reaching those critical targets

Stealth aircraft in future low- and moderate-intensity conflicts are likely to have similar roles. However, given the increasing prevalence of excellent Russian-built surface-to-air missile systems on the open market (such as the SA-10, SA-12 and SA-20 (S-300P/V/PMU) and SA-15 (9K331/332)), stealth aircraft are likely to be very important in a high-intensity conflict in order to gain and maintain air supremacy, especially to the United States who are likely to face these types of systems. It is possible to cover one's airspace with so many air defences with such long range and capability that conventional aircraft would find it very difficult "clearing the way" for deeper strikes. For example, China license-builds all of the previously mentioned SAM systems in quantity and would be able to heavily defend important strategic and tactical targets in the event of some kind of conflict. Even if anti-radiation weapons are used in an attempt to destroy the SAM radars of such systems, or stand-off weapons are launched against them, these modern surface-to-air missile batteries are capable of shooting down weapons fired against them! The surprise of a stealth attack, and the ability to penetrate the air defences and survive, may become the only reasonable way of making a safe corridor through which conventional bombers and other aircraft can enter the enemy's airspace. Once stealth attacks from the smaller stealth force have neutralised the most serious of the SAM systems, the larger conventional or simply less-stealthy force should be able to suppress the remaining systems and gain air superiority.

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List of stealth aircraft

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Manned

Horten Ho 229 - a German design of 1944, and perhaps the first basic stealth design
Northrop YB-49 - like the Ho 229, this USAF bomber's stealthy characteristics were not the result of intentional design
Antonov An-2 - Wooden propellor and canvas wings give it a minimal radar signature
SR-71 Lockheed Advanced Development Projects High-speed reconnaissance aircraft. RCS equal to or better than B-1B.
Have Blue - Lockheed (developed into F-117)
Tacit Blue - Northrop (technology demonstrator)
F-117 Nighthawk - Lockheed (in service)
B-2 Spirit - Northrop-Grumman (in service)
A-12 Avenger II - McDonnell-Douglas / General Dynamics (cancelled)
F-22 Raptor - Lockheed-Martin / Boeing (in service)
YF-23 Black Widow II - Northrop / McDonnell-Douglas (prototype built, lost competition to YF-22)
F-35 Joint Strike Fighter - Lockheed-Martin (under development)
MiG Project 1.44 "Flatpack" - Mikoyan-Gurevich (prototype built)
J-10 - Chengdu Aircraft Industry Corporation (projected twin engine design for stealth missions.)
T-50 / PAK-FA - Sukhoi (under development, Russian-Indian counterpart of the US F-22 Raptor)

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Unmanned

Bird of Prey - Boeing (technology demonstrator)
- Boeing X-45 - Boeing (technology demonstrator)
RQ-3 Dark Star - Lockheed / Skunk Works (cancelled)
- There is evidence to suggest that Darkstar has become a black project and is still operating covertly.
Future and current work into UAVs and UCAVs feature great focus into stealth technology.