The F-117 Nighthawk
In 1954 a paper by Russian mathematician Pyotr Ufimtsev explained how radar returns from an object is related to its angle from a surface. From this information and due to increasingly more advanced radar-guided missiles during the Vietnam war, the United States Government contracted Lockheed to build prototypes using these principles. Computers were still not as advanced as they are now and may have contributed to the fact that it was too complicated to develop a smoother curved airframe and so that is why it retains a very sharp and boxy look as compared to stealth aircraft of today. It also used lots of parts from other aircraft such as control systems, landing gear, and avionics to keep costs low and maintain secrecy. It also incorporated cold air routing around the engine and towards the exhaust to further lower the heat signature produced. It also used radar absorbing materials and special materials in the glass cockpit that would tra...