Unconventional Weapon | Military Aviation | Air & Space Magazine
Staff Sergeant Robin Walker (left) reports no foreign objects in the inlets to Staff Sergeant Greg Slavik piror to takeoff from Nellis Air Force Base in Nevada. (Tech. Sgt. Kevin J. Gruenwald/USAF)

Unconventional Weapon

What we learned about stealth technology from the combat career of the F-117

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Last March, six Lockheed Martin F-117A Nighthawk fighters took off from Holloman Air Force Base and made their last landing at Tonopah Test Range in the remote northwest corner of Nevada’s Nellis Air Force Base. Their wings removed, the aircraft will be stored in secure hangars there rather than in the customary open-space aircraft graveyard in Arizona. The retirement of the jet, scheduled for April 2008, is not a surprise.

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Despite its success in the first Gulf War, in which the F-117A fleet was credited with disabling Iraq’s air defense system during the opening stages of the conflict, it has been many years since the Pentagon invested significant money in the F-117. Neither has its reputation for invincibility survived; that died in 1999 when a wily Serbian crew shot one down with a vintage Russian missile. And although there is no direct replacement for the F-117A, there are now both fighters and missiles that can do part or all of its job.

The seeds of the stealth fighter’s obsolescence were sown at its cold war conception, when it was rushed into production in 1978 as a way to defeat Soviet air defenses in the event that NATO was called upon to defend Central Europe.

Because it was designed and built quickly, the airplane had limitations that could not easily be eliminated. But it was a historic achievement nonetheless, a first-of-a-kind that will pass on its design philosophy and operational lessons to future generations.

The F-117 might have had a longer period of gestation had Soviet-made missiles in Egypt and Syria not mauled the skilled Israeli air force during the 1973 Yom Kippur war. An assessment by the Pentagon’s Defense Science Board the following summer made depressing reading: The more sophisticated defenses in Eastern Europe would likely prevent NATO air forces from hitting their ground targets.

The assessment helped fuel interest in the idea of a low-observable or “stealthy” airplane, leading to the award of the first study contracts in January 1975. And, as the summer of that year passed, it was increasingly clear that researchers at Lockheed Martin and Northrop Grumman were on the edge of an astounding breakthrough, achieving reductions of radar cross-section (RCS, the measure of an object’s size on radar) that had been considered impossible.

The key to the breakthrough was a compromise. Engineers had known that it was theoretically possible to use shaping and materials to make an object seem smaller on radar. The snag was that calculating the RCS of a complex shape like an airplane, from all angles, over a range of radar wavelengths, while taking into account the effects of radar-absorbent material, was vastly complicated. The computers of the early 1970s simply weren’t up to it.

It was Denys Overholser, an electrical engineer at Lockheed’s Skunk Works, who realized that the problem could be worked from both ends. While more powerful computers and new software would help solve the RCS equations, the airplane could also be redesigned to make the equations simpler. That is why the Lockheed design that took shape in the summer of 1975, breaking the tradition of every airplane before it, had no curved surfaces at all.

The discovery of a 1964 paper published by Russian mathematician Pyotr Ufimtsev, which showed that a radar return is proportional to the arrangement of edges of an object, not the size, inspired a new shape of airplane (see “The Invisible Men,” Apr./May 1997). The entire shape was made of flat plates and covered in linoleum-like, radar-absorbent material.

Nobody had any illusions that the resulting airplane would set records for range, speed, or maneuverability, but the compromise was vital to Lockheed’s winning the contract for the Experimental Survivable Testbed, or XST, in April 1976. It would also prove critical in the design of the F-117—and, in the long term, seal its fate.

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