F-8 Digital Fly-By-Wire

F-8 Digital Fly-By-Wire. The F-8 Digital Fly-By-Wire (DFBW) program was a pioneering NASA flight research project that first demonstrated a digital, computer-controlled flight system without a mechanical backup. Conducted at the NASA Dryden Flight Research Center (now Armstrong Flight Research Center), the program modified a Vought F-8 Crusader fighter to serve as the testbed. Its successful flights proved the viability of digital fly-by-wire technology, which became the foundational standard for modern military and civilian aircraft, including the Space Shuttle.

Development and Background

The genesis of the program stemmed from earlier analog fly-by-wire research, notably the Lunar Landing Research Vehicle and the Apollo Guidance Computer developed for the Apollo program. Engineers at the NASA Dryden Flight Research Center, led by figures like Calvin R. Jarvis, sought to advance this technology using digital computation for greater flexibility and reliability. The United States Air Force had also explored similar concepts, but the NASA initiative aimed specifically at proving a pure digital system. The selection of the Vought F-8 Crusader was strategic, as its design allowed for the removal of its conventional mechanical flight controls to be replaced entirely by the experimental system. This project was part of a broader wave of aerospace innovation during the late Cold War, seeking technological advantages for future vehicles like the planned Space Shuttle.

System Design and Components

The core of the system was a triplex-redundant set of IBM AP-101 computers, the same general-purpose digital computers later used on the Space Shuttle. These computers received pilot input from a side-stick controller and processed it through flight control software, sending electrical signals to hydraulic actuators on the flight control surfaces. A critical design philosophy was the use of redundant, fault-tolerant computing rather than a traditional mechanical backup, a concept championed by engineers like John G. McTigue. The software, written in HAL/S (a high-level language developed for the Space Shuttle), managed the complex tasks of flight control laws and system redundancy management. Supporting components included specialized inertial sensors and avionics developed through collaborations with IBM and the Massachusetts Institute of Technology.

Flight Testing and Results

The first flight with the digital system active occurred on 25 May 1972, with NASA research pilot Gary E. Krier at the controls. The test program, based at Edwards Air Force Base, systematically expanded the flight envelope and demonstrated the system's robustness. A significant milestone was the first flight without the mechanical backup system engaged, proving total reliance on digital control. Throughout hundreds of flights, pilots evaluated handling qualities, performed aerial refueling with a Boeing KC-135 Stratotanker, and tested advanced control modes. The program successfully demonstrated fault-tolerance by simulating computer failures in flight. The data gathered provided invaluable validation for the fly-by-wire system designed for the Rockwell International Space Shuttle, directly influencing its development.

Legacy and Influence

The program's success irrevocably changed aerospace design, providing the confidence needed to implement digital fly-by-wire in production aircraft. The direct technological lineage is clear in the Space Shuttle, which flew its first mission, STS-1, in 1981. Subsequently, the technology proliferated into next-generation military aircraft like the General Dynamics F-16 Fighting Falcon and the McDonnell Douglas F/A-18 Hornet. In the commercial realm, it became central to the flight control systems of Airbus airliners, starting with the Airbus A320, and later Boeing aircraft such as the Boeing 777. The research also laid groundwork for unmanned aerial vehicles and modern flight control systems. The test aircraft itself is preserved at the Armstrong Flight Research Center in California.

Category:NASA aircraft Category:Experimental aircraft Category:Fly-by-wire Category:Vought aircraft Category:Individual aircraft