While “stealth” is normally used as short for “radar stealth”, it actually means proper suppression of all following signatures: visual, radar, infrared, electromagnetic and sound.
Stealth vs sensors
Visual stealth depends on several factors: airframe size and contrast, presence/absence of smoke and visibility conditions.
Airframe stealth is achieved by small size and masking colors – usually light gray. Early F-16s and Gripens were delivered with a black radome, which was quickly repainted grey when it was realized how much impact it has on visual signature. Visual signature also changes depending on aspect – it is smallest from the front and largest from top/bottom.
Smoke can have a very large impact on detection range – F-104 smoked so heavily that it was detectable at twice as long range as required to see aircraft itself. However, modern fighter aircraft use engines designed to minimize smoke, so it may not be a factor, older aircraft such as F-14 and F-15 excepted.
Visual stealth is especially important for ground attack aircraft, since visually-aimed AAA has always been the greatest threat (caused 38% of casualties in the Gulf War), followed by IR SAMs (31%) and only then by radar-guided SAMs (16%) and radar-aimed AAA (15%).
Radar stealth depends on multiple variables: aspect to radar, radar’s frequency, materials aircraft is made of. For all fighter aircraft, radar signature is lowest head-on, and higher from all other angles; and due to the shape, they are only truly stealthy few degrees from horizontal. Frequency-wise, any RAM coatings are only effective against X-band radars; radar-transparent materials are effective against all frequencies, but it is impossible to make entire fighter aircraft from them – Rafale’s fin is made from radar-transparent material, but nothing else.
Aircraft with datalink may be able to pick up reflections from radars by other fighters and thus detect stealth aircraft; at very least Gripen and Typhoon have that capability. This reduces impact of shaping, as all stealth fighters (and stealth aircraft in general) are optimized for the minimum nose-on RCS. F-16s have also frequently picked up F-117s on radar; signal would come and go, but pilot would know there is something around worth looking at, and where to look at.
Actual effectiveness of radar stealth is questionable at best. F-117s during Gulf War have flown in presence of jammer support, and only at night. Two night-flying squadrons of A-10s have flown as many sorties as F-117s and suffered same number of losses: none. In Gulf War and Kosovo War, A-10s suffered 4 losses in 12.400 sorties, compared to 2 losses in 2.600 sorties suffered by F-117s. Basically, A-10 was as 2,4 times as survivable as F-117 (survivability can only be compared by using loss rate, that is number of losses relative to number of sorties). In Kosovo war, F-16 suffered 1 loss in 4.500 sorties, for loss rate of 0,02%, and F-117 suffered 2 losses in 1.300 sorties, for loss rate of 0,15% – that is, F-16 was 7,5 times as survivable as F-117. It should be noted that Close Air Support flown by the A-10 was a far more dangerous mission than missions flown by F-16 and the F-117, with A-10 often using its gun.
IRST works by detecting IR emissions. This is a problem, since all aircraft heat up when flying. Greatest source of heat is aircraft’s engine and its emissions, but there are also skin friction and electronics, particularly radar. Airframe heating is not the only source of the IR signature. There is also air compression in front of the airframe, as well as shock waves created when aircraft is supersonic.
Impact of airframe heating can be reduced somewhat by use of materials, but it will always be a major source of IR emissions. Shock waves and air compression effects are however made worse by the radar-stealth measures, since latter involve heavy aerodynamic compromises.
Only way to hide from the IRST is by using clouds. However, most clouds extend to no more than 6-14 kilometers (6 on poles, 14 on equator; this would give ~10 kilometers in Central and Western Europe and United States), where fighter aircraft typically operate at altitudes of 9-18 kilometers. Cumulonimbus clouds are dense and can extend very high up, but they are also hazardous to aircraft due to very strong turbulences (upwards and downwards drafts can exceed 1 km per minute) as well as frequent thunderstorms, large hailstones and tornadoes. These effects can damage stealth aircraft’s coating -hailstones can be as large as grapefruit or ananas, and F-35 is actually banned from flying within 40 km from thunderstorms as its fuel could ignite due to the lightning. Icing may also form on aircraft’s skin, compromising its radar stealth.
Problems with hiding at high altitude can be clearly seen in following photo of F-15s intercepting MiG-29s:
Modern RWRs can detect even so-called “LPI” radars; as a result, only defence against them is to turn off the radar. Even worse, aircraft such as Rafale and F-22 can use opponent’s radar emissions for completely passive target acquisition. Missile warners are also usually radar-based (Dassault Rafale and F-22, possibly other “stealth” fighters too, are an exception), which means that their emissions can also be detected by the RWR; and missile warners are constantly active.
Aircraft are comparably loud, especially when supersonic. This can be exploited by using a network of ground-based acoustic sensors to detect and locate aircraft by using its acoustic signature. In this area, aircraft built for radar stealth are at disadvantage due to their unaerodynamic configuration. This disadvantage is however mitigated to the extent by the fact that stealth aircraft carry missiles internally; but while this reduces noise due to the air flow turbulences around the aircraft, it means that aircraft in question needs stronger engines – which are bout hotter and louder.
Stealth is a scam, with idea of stealth and its effectiveness being spread by a mindless repetition ad nauseum: say a lie once, and some will believe it. Say it often, and many will believe it after some time. F-35 for example has lower RCS than the F-16, but is larger, hotter and louder than it; F-16 only needs IRST to become stealthier than the F-35 in real terms.