What we learned about stealth technology from the combat career of the F-117.
- By Bill Sweetman
- Air & Space magazine, January 2008
Tech. Sgt. Kevin J. Gruenwald/USAF
(Page 4 of 10)
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.
Often, though, what would have been a routine repair on another aircraft required scraping off the material from an entire panel, replacing the material, and, finally, re-sealing it.
Early in the 1980s, the Air Force planned to build an improved B model, but the money for the project was diverted into fixing the A. Replacing the computers started in 1984, and the first updated airplanes were in service by 1988. By that time, an automated mission planning system was operational. A new tail lifted the speed restrictions.