The Continuing Legacy of FBW Research in Aircraft Development

Fly-by-wire technology developed by NASA and the Air Force served as the basis for flight control systems in several generations of military and civilian aircraft. Many of these aircraft featured highly unconven­tional airframe configurations that would have been unflyable without computer-controlled fly-by-wire systems. An interesting example was the then highly classified Lockheed Have Blue experimental stealth technology flight demonstrator. This very unusual aircraft first flew in 1977 and was used to validate the concept of using a highly faceted air­frame to provide a very low radar signature. Unstable about multiple axes, Have Blue was totally dependent on its computer-controlled fly­by-wire flight control system that was based on that used in the F-16. Its success led to the rapid development and early deployment of the stealthy Lockheed F-117 attack aircraft that first flew in 1981 and was operational in 1983.[1286] More advanced digital fly-by-wire flight control systems enabled an entirely new family of unstable, aerodynamically refined "stealth” combat aircraft to be designed and deployed. These
include the Northrop B-2 Spirit flying wing bomber and Lockheed’s F-22 Raptor and F-35 Lightning II fighters with their highly integrated digi­tal propulsion and flight control systems.

Knowledge of the benefits and confidence in the use of digital fly-by­wire technology are today widespread across the international aerospace industry. Nearly all new military aircraft—including fighters, bombers, and cargo aircraft, as well as commercial airliners, both U. S. and for­eign—have reaped immense benefits from the legacy of NASA’s pioneer­ing digital fly-by-wire flight and propulsion control efforts. On the airlift side, the Air Force’s Boeing C-17 was designed with a quad-redundant digital fly-by-wire flight control system.[1287] In Europe, Airbus Industrie was an early convert to digital fly-by-wire and the increasing use of elec­tronic subsystems. All of its airliners, starting with the A320 in 1987, were designed with fully digital fly-by-wire flight control architectures along with side stick controllers.[1288] Reliance on complex and heavy hydraulic systems is being reduced as companies increase the emphasis on elec­trically powered flight controls. With this approach, both electrical and self-contained electrohydraulic actuators are controlled by the digital flight control system’s computers. The benefits are lower weight, reduced maintenance cost, the ability to provide redundant electrical power cir­cuits, and improved integration between the flight control s ystem and the aircraft’s avionics and electrical subsystems. Electric flight control technology reportedly resulted in a weight reduction of 3,300 pounds in the A380 compared with a conventional hydromechanical flight control system.[1289] Boeing introduced fly-by-wire with its 777, which was certified for commercial airline service in 1995. It has been in routine airline ser­vice with its reliable digital fly-by-wire flight control system ever since. In addition to a digital fly-by-wire flight control system, the next Boeing airliner, the 787, incorporates some electrically powered and operated flight control elements (the spoilers and horizontal stabilizers). These are designed to remain functional in the event of either total hydraulic systems failure or flight control computer failure, allowing the pilots to maintain control in pitch, roll, and yaw and safely land the aircraft.

Today, the tremendous benefits made possible by the use of digital fly-by-wire in vehicle control systems have migrated into a variety of applications beyond the traditional definition of aerospace systems. As a significant example, digital fly-by-wire ship control systems are now operational in the latest U. S. Navy warships, such as the Seawolf and Virginia class submarines. NASA experts, along with those from the FAA and military and civil aviation agencies, supported the Navy in develop­ing its fly-by-wire ship control system certification program.[1290] Thus, the vision of early advocates of digital fly-by-wire technology within NASA has been fully validated. Safe and efficient, digital fly-by-wire technol­ogy is today universally accepted with its benefits available to the mil­itary services, airline travelers, and the general public on a daily basis.