The Air Force JB-47E Fly-By-Wire Project

The USAF Flight Dynamics Laboratory at Wright Patterson Air Force Base (AFB), OH, sponsored a number of technology efforts and flight – test programs intended to increase the survivability of aircraft flight control system components such as fly-by-wire hydraulic actuators. Beginning in 1966, a Boeing B-47E bomber was progressively modi­fied (being redesignated JB-47E) to incorporate analog computer-con­trolled fly-by-wire actuators for both pitch and roll control, with pilot inputs being provided via a side stick controller. The program spanned three phases. For Phase I testing, the JB-47E only included fly-by-wire in its pitch axis. This axis was chosen because the flight control sys­tem in the standard B-47E was known to have a slow response in pitch because of the long control cables to the elevator stretching under load. Control signals to the pitch axis FBW actuator were generated by a transducer attached to the pilot’s control column. The pilot had a simple switch in the cockpit that allowed him to switch between the standard hydromechanical flight control system (which was retained as a backup) and the computer-controlled FBW system. Modified thus, the JB-47E flew for the first time, in December 1967. Test pilots reported that the modified B-47 had better handling qualities then were attainable with the standard B-47E elevator control system, especially in high-speed, low-level flight.[1134]

Phase II of the JB-47E program added fly-by-wire roll control and a side stick controller that used potentiometers to measure pilot input. By the end of the flight-test program, over 40 pilots had flown the FBW JB-47E. The Air Force chief test pilot during Phase II, Col. Frank Geisler, reported: "In ease of control there is no comparison between the standard system and the fly-by-wire. The fly-by-wire is superior in every aspect concerning ease of control. . . . It is positive, it is rapid—it responds well— and best of all the feel is good.”[1135] Before the JB-47E Phase III flight-test program ended in early 1969, a highly reliable four-channel redundant
electrohydraulic actuator had been installed in the pitch axis and success­fully evaluated.[1136] By this time, the Air Force had already initiated Project 680J, the Survivable Flight Control System (SFCS), which resulted in the prototype McDonnell-Douglas YF-4E Phantom aircraft being mod­ified into a testbed to evaluate the potential benefits of fly-by-wire in a high-performance, fighter-type aircraft.[1137] The SFCS YF-4E was intended to validate the concept that dispersed, redundant fly-by-wire flight con­trol elements would be less vulnerable to battle damage, as well as to improve the performance of the flight control system and increase over­all mission effectiveness.