The world's first operational aircraft designed to exploit low-observable stealth technology is the F-117A Nighthawk.
In early 1977, the Defense Advanced Research Projects Agency (DARPA) gave Lockheed a contract to build and test two subscale models (about 60 percent of the size of an operational airplane) of a stealthy aircraft. The contract was known as Have Blue and was highly classified. Lockheed's plane looked like a squat pyramid with wings and two tails angled inward. When designers placed it on a tall pole outdoors and pointed a radar at it, it was virtually invisible. But they still wondered if it would fly. One Lockheed document stated that the "airframe exhibits just about every mode of unstable behavior possible for an aircraft—the only thing it doesn't do is tip back on its tail when it is parked."
Have Blue was not inherently stable in flight and would tumble out of control. But fortunately, computers also rendered this fact irrelevant, because aircraft designers for several years had been designing planes, like the F-16 fighter, that were kept stable by computers that constantly adjusted their flight controls in the same way that a person riding a bike is constantly making minute corrections to remain balanced. This same solution was applied to the Have Blue airplane. Lockheed engineers soon developed the Have Blue into a larger bomber aircraft given the designation F-117. Despite being designated a "fighter," the plane was always intended only to drop bombs, not fight other aircraft.
For the first time, every phpect of the F-117 was designed around stealth. For the plane's designers, reducing the radar signature was similar to the way that airplane designers of the 1920s had reduced drag: they identified the biggest causes of the problem and then eliminated them one by one. The cockpit, which is essentially a cavity that reflects radar in much the same way that an animal's eyes reflect light from a flashlight at night, was sharply angled and coated with a reflective material that deflected the radar energy in different directions. The airplane had no radar and its sensors and antennas could be retracted into the fuselage. The bombs, a major source of radar reflection on most airplanes, were stored internally in a bomb bay so that they reflected no radar energy. The inlets for the jet engines were covered with fine screens to prevent radar energy from reaching the face of the engine turbines. The exhaust was channeled through long narrow ducts lined with heat-absorbing material so that it was cooler by the time it exited the plane and therefore did not show up as well on heat detectors.
Five F-117 development aircraft were built and tested between 1981 and 1982. The first F-117 squadron was declared operational in 1983. Lockheed built a total of 59 F-117s for the Air Force. The F-117 was a highly secret aircraft during most of the 1980s. It was finally unveiled in 1989 and became famous in 1991 when it was used in heavily defended skies over Iraq during the Persian Gulf War. In 1999, an F-117 was shot down by a Russian-built missile over Yugoslavia, demonstrating that stealth was not invincible.
Although the F-117 is the most famous stealth aircraft, it was not the only one. Other stealth aircraft were designed and built during the 1980s. A weird and ugly-looking plane designated the Tacit Blue was built by Northrop and flown several times during the 1980s. It looked like an upside down bathtub with wings. Its purpose was to evaluate the possibility of flying behind enemy lines, but the plane proved difficult to fly and its mission soon proved unnecessary. The sole prototype was kept secret for years until it was finally placed in a museum. In the late 1980s, the U.S. Navy sought to develop an attack bomber designated the A-12 Avenger II (not to be confused with the A-12 OXCART), but it was never completed before it was canceled. Several drone aircraft, such as Lockheed's failed DarkStar, and Teledyne Ryan's semi-stealthy GlobalHawk, were also developed. During the 1990s the Army began development of the Sikorsky/Boeing RAH-66 Commanche helicopter, which incorporated technologies to reduce its radar and heat signature. The most successful stealth aircraft next to the F-117 is the B-2 Spirit bomber, first started in the late 1970s and not finished until the 1990s.www.centennialofflight.gov