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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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(Continued from page 2)

For all the hype, the aircraft was far from invisible. The RCS figures remain classified, but the airplane was more visible to radar from the sides than head-on. Planning the missions was difficult—because the jet could be seen by radar, the track had to be carefully adjusted to minimize the craft’s exposure.

The Model A of Stealth

Once Have Blue showed that attaining stealth was possible, the Air Force sought to replace it, and research began in earnest. Northrop, Boeing, and General Dynamics
launched programs plumbing shapes and technologies that promised greater stealth and better aerodynamics.

By the time the F-117A entered service, Northrop was flying the AP-1 Tacit Blue demonstrator, a stealth aircraft with curved surfaces, no inlet grills, and low-probability-of-intercept radar. The Air Force started studies of a stealthy supersonic fighter.

Al Piccirillo became the program director for the Air Force’s Advanced Tactical Fighter project in 1984. “The B-2 was there and the ATF was in development,” he says. “The feeling was that we had moved beyond the F-117, and the big effort was to fix what was wrong.”

The new jet had quite a lot wrong. The onboard computers did not have enough processing power. A rudder weakness limited speed. And maintenance was “a nightmare,” says Piccirillo.

In January 1984, the jets needed 113 hours of maintenance for every hour they flew. And at any given time, only 11 percent were judged mission-capable. The kludged-together quality of the avionics was one problem, but it was the stealth technology that was the worst.

The tailpipes were lined with ceramic bricks, made from the same quartz-like material used on the space shuttle. Each tile had to be cemented in place individually, and the seams between them filled with a putty-like material. Even a small gap could act like a tiny inlet, channeling the already blazing exhaust gas and heating it enough that it would burn through to the metal underneath.

The biggest problem resided in the fundamentals of stealth. When a radar pulse lights up an airplane, electrical currents form all over its skin—and when they hit an obstacle or jump a gap, they cause tiny sparks or scintillations, which the radar can detect. The F-117 controlled these with a coating of absorbent material, but if the coating had even the smallest gap or crack, it could betray the aircraft.

The aircraft had doors—the cockpit canopy, the landing gear and weapon bay doors, engine access doors, and so on—but they were heavy because they had to seal perfectly. The designers tried to make sure that components that needed maintenance could be reached through the doors; some of the airplane systems could be accessed through the weapons bays.

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