DFBW F-8: An Appreciation

The NASA DFBW F-8 had conclusively proven that a highly redun­dant digital flight control system could be successfully implemented and all aspects of its design validated.[1165] During the course of the pro­gram, the DFBW F-8 demonstrated the ability to be upgraded to take advantage of emerging state-of-the-art technologies or to meet evolv­
ing operational requirements. It proved that digital fly-by-wire flight control systems could be adapted to the new design and employment concepts that were evolving in both the military and in industry at the time. Perhaps the best testimony to the unique accomplishments of the F-8 DFBW aircraft and its NASA flight-test team is encapsulated in the following observations of former NASA Dryden director Ken Szalai:

DFBW systems are ‘old hat’ today, but in 1972, only Apollo astronauts had put their life and missions into the hands of software engineers. We considered the F-8 DFBW a very high risk in 1972. That fact was driven home to us in the control room when we asked the EAFB [Edwards Air Force Base] tower to close the airfield, as was preplanned with the USAF, for first flight. It was the first time this 30-year-old FCS [Flight Control System] engineer had heard that particular radio call. . . . The project was both a pioneering effort for the tech­nology and a key enabler for extraordinary leaps in aircraft performance, survivability, and superiority. The basic archi­tecture has been used in numerous production systems, and many of the F-8 fault detection and fault handling/recovery technology elements have become ‘standard equipment.’ . . . In the total flight program, no software error/fault ever occurred in the operational software, synchronization was never lost in hundreds of millions of sync cycles, it was never required to transfer to the analog FBW backup system, there were zero nuisance channel failures in all the years of flying, and many NASA and visiting guest pilots easily flew the aircraft, includ­ing Phil Oestricher before the first YF-16 flight.[1166]

In retrospect, the NASA DFBW F-8C is of exceptional interest in the history of aeronautics. It was the first aircraft to fly with a digital fly-by­wire flight control system, and it was also the first aircraft to fly with­out any mechanical backup flight controls. Flown by Ed Schneider, the DFBW F-8 made its last flight December 16, 1985, completing 211 flights. The aircraft is now on display at the NASA Dryden Flight Research Center. Its sustained record of success over a 13-year period provided a
high degree of high confidence in the use of digital computers in fly-by­wire flight control systems. The DFBW F-8C also paved the way for a number of other significant NASA, Air Force, and foreign research pro­grams that would further explore and expand the application of digital computers to modern flight control systems, providing greatly improved aircraft performance and enhanced flight safety.