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Visual Stealth
1963PENTAGON, WASHINGTON, D.C., USA
Spotting an aircraft visually is just as effective as spotting it on radar. In poor weather conditions at night, this obviously poses less of a threat than on cloudless, bright, sunny days. The color of an aircraft obviously affects its visibility and the range at which it can be spotted. White or brightly colored aircraft tend to be more easily discerned at great distances, as do unpainted, polished, all-aluminum aircraft. Flat black paint is very effective in reducing visibility under a variety of conditions. Camouflage patterns can also reduce an aircraft's visibility when the pattern reflects the environment in which the aircraft is operating.
Additionally, because of the heat generated by aircraft powerplants, vapor trails are often formed at various altitudes and under various temperature and humidity conditions. Vapor trails and engine exhaust by-products are easily seen with the naked eye at great distances. Chemical additives have now been developed that reduce or eliminate vapor trail production by converting water condensation into ice crystals. Engine exhaust by-products have been all but eliminated in most modern engines through improvements in combustion efficiency and fuel chemistries.
In the area of heat emissions, generally in the infrared part of the electromagnetic spectrum, the primary source is the engine exhaust. Considerable research in this area has produced an entirely new generation of jet engine exhaust nozzles and heat-dissipating systems and techniques. Among the many is the mixing of low-temperature ambient air with the exhaust gases almost at the instant of exit at the back of the engine. This causes a rapid decrease in exhaust gas temperature and a consequent reduction in the size of the exhaust plume. In turn, this reduces the aircraft's infrared signature, reducing its chances of being tracked with infrared sensing devices.
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