F-117A: Loss of #785

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Page born:April 01 2002

[F-117A and LTC Bob Ridenhauer-cover Nov/Dec 97 AeronauticalPioneers.()]

Aircraft Losses

Ltc Bob Ridenhauer (LADC)
Bandit #103 (????, 1982)
April 20, 1982
F-117A #80-785
Cause: Crossed controls

The first crashof aproduction F-117A occurred on April 20, 1982 during its first test flight(but before the acceptance flight, therefore the aircraft not beingcounted as accepted in the manifest) by Lockheed test pilotLtc BobRidenhauer in aircraft #80-785. This aircraft, like thosebefore it, was delivered to Groom Lake on February 27, 1982 by a C-5 Cargo plane in threecomponents-the body, and the two wings. Once safely inside of a hanger, the wings were thenreinstalled.

The F-117A and all of it's controls appeared to function normally on theground and in taxi tests that had started on April 17th. (However, itshould be noted that the pilots who usually accompanied in achase car were all in the simulator.)On April 20th, 1982 Ridenauer opened the throttles and released thebrakes.The aircraft rolled to takeoff speed and Ridenauer pulled back on the stick to lift the craft's nose off the ground. Reports say the instant the nosewheel left the runway, the F-117A went bezerk, first yawing violently to one side and thenpitching upward, out of control, while continuing to diverge in yaw. Ridenauer never had the chance to eject before the F-117A lost control, went inverted and going backwards, and augered in on the side of the lake bed just off therunway, catching fire in the process.

[The only pilot to fly all three great Skunk Works aircraft.()] Fortunately, thecockpit section held together and crash and rescue trucks arrived on the scene in seconds with Ridenauer still stuck in the cockpit. Once the fire was confirmed to be out, the crash crew took about 20 minutes to cut Ridenauer out of the cockpit. He survived, but was seriously injured and spent eight months in the hospital at a cost to Lockheed and the Air Force of about $700,000. He was forced to retire from flying. He was one ofonly a few to have test flown all three of the most famous SkunkWorks aircraft- the U-2, the SR-71, and the F-117A.

Investigators foundthat the flight control system on the aircraft had been assembled incorrectly not at Groom Lake, but at the factory in Burbank.A major design change in thesystem caught Lockheed workers off guard: the input points on the flight control computer were placed in a different sequence than they had been on the previous version. The rate gyros had been reversed. When the cables wereconnected the original way, the computer ended up reading pitch gyro as yaw and yaw gyro as pitch. Whenthe aircraft pitched upward on takeoff, the change in angle was detected by thepitch gyro and fed to the yaw channel of the computer. The computer instantly compared this with Ridenauer's movements of the rudder pedals, determined that the aircraft was making an uncommanded yaw movement and "corrected" it with a hefty swing of the all-moving rudders. This caused the aircraft to make a real yaw movement, opposite to the false one detected by the computer. The computer, of course, interpreted the signal as an uncommanded pitch movement and moved the elevons to correct it.

This was a high-techversion of the "crossed controls" to which older aircraft, with cable-operated controls, were vulnerable. Ridenauer had madeprevious taxi tests, moved the controls and checked their operation before flight. But as long as the aircraft was not airborne, the crossed gyros would not detect any movement, and thecomputer would operate the controls properly. It required real-world inputs-the movement of the whole aircraft-before the problem would surface."

This firstproduction F-117A (#80-785) was supposed to become a de-facto FSD aircraft. However, because of this crash, the nextaircraft delivered(#80-787) became the defectoFSD to generate performance and handling data and to test the many small improvements that Lockheedengineers had worked into the aircraft. Therefore the third aircraft delivered, thesecond production aircraft (#80-786) was the first truly operational non-evaluating aircraft.

The batteredairframeof #80-785 returned Lockheed Skunks Works in Burbank as a functional engineering airframe test fixture used to test the fit of new components. At one time, there was talk of placing a bubble canopyon the airframe, restoring it to flight status, and creating an elevated cockpit two seat trainer, but this program was canceled. Airframe #785 wascombined with structural test articles #778 (Forward fuselage/cockpit) and#779 (Mid fuselage/weapons bay) to form a "mutt" F-117Awhich now sits on a pole in front of the Skunk Works EngineeringBuilding in Palmdale, Calif. as a gate guardian. On the left side of thecanopy is "Ltc. Bob Ridenhauer". The right hand side bears the name of"Ben Rich".

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