Space Race and the War in Vietnam: Emphasis on FBW Accelerates

During the 1960s, two major events would unfold in the United States that had very strong influence on the development and eventual
introduction into operational service of advanced computer-controlled fly-by-wire flight control systems. Early in his administration, President John F. Kennedy had initiated the NASA Apollo program with the goal of placing a man on the Moon and safely bringing him back to Earth by the end of the decade. The space program, and Apollo in particular, would lead to major strides in the application of the digital computer to manage and control sensors, systems, and advanced fly-by-wire vehicles (eventually including piloted aircraft). During the same period, America became increasingly involved in the expanding conflict in South Vietnam, an involvement that rapidly escalated as the war expanded into a con­ventional conflict with dimensions far beyond what was originally fore­seen. As combat operations intensified in Southeast Asia, large-scale

U. S. strike missions began to be flown against North Vietnam. In response, the Soviet Union equipped North Vietnamese forces with improved air defense weapons, including advanced fighters, air-to-air and surface-to-air missiles, and massive quantities of conventional antiaircraft weapons, ranging in caliber from 12.7 to 100 millimeters (mm). U. S. aircraft losses rose dramatically, and American warplane designs came under increasing scrutiny as the war escalated.[1132] Analyses of combat data revealed that many aircraft losses resulted from battle damage to hydromechanical flight control system components. Traditionally, pri­mary and secondary hydraulic system lines had been routed in paral­lel through the aircraft structure to the flight control system actuators. In the Vietnam combat, experience revealed that loss of hydraulic fluid because of battle damage often led to catastrophic fires or total loss of aircraft control. Aircraft modification programs were developed to reroute and separate primary and secondary hydraulic lines to reduce the possibility of a total loss of fluid given a hit. Other changes to exist­ing aircraft flight control systems improved survivability, such as a mod­ification to the F-4 that froze the horizontal tail in the neutral position to prevent the aircraft from going out of control when hydraulic fluid was lost.[1133] However, there was an increasing body of opinion that felt a
new approach to flight control system design was necessary and tech­nically feasible.