Stealth aircraft use a combination of physical construction, radar-absorbing materials and electromagnetic emission controls to reduce their presence on enemy radar screens. Radar relies on the reflection of a radio wave, and stealth planes are built with jagged angles to reduce clean reflections returning to the scanner. The materials in the planes' skin also dampen radar signals, and their own electronic emissions are kept low to avoid detection.
Most planes use rounded surfaces in order to reduce aerodynamic drag. The sharp angles used in stealth aircraft make them extremely unstable, especially at high speeds. Typically, these planes use computer-controlled flight surfaces to maintain stability during flight, and a system failure can produce a catastrophic crash.
Many stealth aircraft are covered with a matte gray-black paint containing microscopic iron balls. These spheres resonate when struck with a radio wave, absorbing energy from the wave and reflecting it as heat rather than as a radio reflection. This reduces the amount of energy that returns from a radar pulse, making the plane seem considerably smaller than it actually is. This can cause a radar operator to mistake a plane for a flock of birds or some other innocuous object.
Stealth aircraft also contain features to avoid heat-seeking missiles. In many cases, the engine exhaust is spread out through vents in order to dissipate heat and avoid presenting a single strong heat source to any enemy weapons.