Unconventional Weapon

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

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)
Air & Space Magazine

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Air Defense Assassin

In November 1978, after the XST prototypes (renamed Have Blue) had flown, Lockheed was awarded a contract to develop the aircraft, under the code-name Senior Trend. The Pentagon’s leaders had recognized the power of stealth and initiated a secret debate about how to exploit it.

The final decision was to field, as quickly as possible and in complete secrecy, a stealth aircraft designed primarily for one mission: putting a bullet through the brain of the enemy’s air defense system in the first hours of war.

Lockheed would build five development airplanes while starting an initial batch of 20 production aircraft. The goal was to fly the first aircraft in July 1980. The need for speedy design defined the F-117. Its external shape was as close to Have Blue as the designers could get, while achieving a just-acceptable range, altitude, and landing speed.

Overholser believed that it was possible to incorporate curvature on the wings, but he could not prove it. “Very simply, the configuration of the F-117 was entirely designed by radar signature requirements,” engineer Alan Brown summed up in a 2003 paper. “No compromises were made in this respect at all.”

Neither was there time to design parts for the entire jet. The navigation system came from the B-52 bomber. The engines were from the Navy’s F/A-18 Hornet fighter. The infrared targeting system, from Texas Instruments, was assembled from parts of other systems. The F-16 contributed the computers and flight control system. The biggest cockpit display was from the Navy P-3 Orion patrol airplane.

Like the Have Blue, the F-117A was covered with radar-absorbent material—almost a ton of it. It was made in the form of flat sheets, cut to fit the skin panels, and glued in place. A putty-like material dubbed “butter” filled the gaps between the sheets. The engines were concealed from radar by Chrysler-like grills, and the hot exhaust gas from the engine was expelled through slits.

The jet had no radar. There were ideas for “low probability of intercept” radar that could work without giving away the jet’s position, but the technology could not be ready in time. (Such LPI radar uses tricks with modulation, frequency hopping, low power, and huge bandwidth to obscure its signal.) The aircraft’s use would be confined to attacks under the cloud base or in clear weather.

Even so, the jet was hard enough to build. The engineers were “inventing to schedule,” solving problems like keeping ice from forming on the inlet grills (a chemical-dispensing squeegee is hidden in the wings in front of the inlets) and on the air-data probes. They concealed the infrared sensor turrets from radar with a titanium wire mesh.

The haste paid off. The aircraft reached operational capability in October 1983, later than envisioned, but still only five years after the go-ahead on development. The angles of the wings were calculated to disrupt the radar waves as they scattered away from the aircraft and thus prevent them from returning to the source. Likewise, all the doors and opening panels featured saw-toothed forward and trailing edges to disrupt reflection of radar.


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