F-117 Nighthawk

The F117 is a stealth aircraft designed for the USAF by Lockheed. It is commonly referred to as the "Stealth Fighter." This is inaccurate. It actually fills the roles of ground attack aircraft and reconnaissance aircraft. It routinely flew reconnaissance missions over the Eastern Bloc countries during the 1980s.

Because of its odd design (which is not very aerodynamic), it uses a fly-by-wire system; were it not so, the pilot would not be able to fly it at all. The aircraft uses a number of technologies to gain stealthiness:

The materials used in the construction absorb some of the RADAR energy

The shape of the aircraft reflects most of the rest of the RADAR energy away from the source

The aircraft is painted with a color called Cannonball Black. This makes it very difficult to see it at night.

The engine housings are shielded to greatly reduce the IR signature of the aircraft, making that form of attack difficult.

The F117 does not carry any RADAR equipment itself. Instead, it uses an FLIR to target. It is capable of dropping self-guided RADAR missiles, however.

Despite all of these methods, the aircraft is still somewhat visible to RADAR; however, F117 pilots are trained to fly close to the terrain (below 400 ft.) which allows them to blend in to the background noise. They also use special techniques like "threading the needle" which involves knowing the location, type, and range of all RADAR sites in the area and taking a carefully planned route that winds in between the coverage of the sites. Even if you can't find a blind spot to fly through, you can also fly in a circle around the site to further minimize the amount of useful data returned to the RADAR array. The visibility to RADAR increases when engaged in banking or other maneuvers. The point of greatest RADAR visibility is when the bay doors are open.

Nicknamed "The Wobblin' Goblin" because they were difficult to control, and when pilots flew them at night, they occasionally got extremely disoriented and bought the farm, especially during night air refueling.

The F-117 also gained a bad reputation during the invasion of Panama when a majority of them didn't hit their targets, and instead bombed schools and private property. First flight was on December 1, 1977 as the XST - codename Have Blue - a test platform that only vaguely looks like the F-117. The first formal flight of the Lockheed fighter version was April 1982. It remained largely secret, with the exception of an erroneous Testor's model kit in 1986 and blurry photos in Aviation Week in 1989, until the Gulf War.

Lockheed Martin was fortunate to come across a paper written by the Russian physicist P. Ufimtsev, the details of which are:

P.Y. Ufimtsev, "Approximate computation of the diffraction of plane electromagnetic waves at certain metal bodies (I and II)", Sov. Phys. Tech., vol 27, pp 1708-1718, Aug 1957.

This paper detailed a technique which allowed engineers to calculate the non-uniform diffracted (scattered) electric fields from edge shaped discontinuities on conducting radar targets. This technique was combined with the well-known EM scattering approximation known as Physical Optics (PO) into a technique now called the Physical Theory of Diffraction (PTD). This brought a much greater level of accuracy and fidelity into computer-based radar cross section (RCS) modeling which had not been previously available.

It is notable that the Soviet technical community did not see much use for the paper and it was American engineers that saw its potential use.

The PTD was instrumental in the design of the shape of the F117. Using computer simulation to design an aircraft shape which minimizes the RCS is much more economically feasible than making 20 different planes just to measure the RCS.

It is worth noting that the greatest portion of the incident radar energy is NOT absorbed by the F117, but rather scattered in directions other than the direction the incident energy originated. The F117 also has a greater RCS at non nose-on aspects, so it is incorrect to suggest that the F117 has a tiny RCS over all viewing angles. The engine intakes of the F117 are covered not only to reduce the IR signature, but to eliminate the very high multiple-bounce cavity radar returns seen in engine inlets.

A bit of trivia: During development of the F117 one engineer designed skunk works coffeemugs with a picture of a cloud with the nose of the F117 sticking out. These were immediately classified as "top-secret" and had to be locked away when not in use.