An In-Flight Investigation to Develop Control System Design Criteria for Fighter Airplanes. Volume 1

The effects of control system dynamics on the longitudinal flying qualities of fighter airplanes were investigated in flight, using the USAF/CAL variable stability T-33 airplane. Two pilots evaluated a total of 57 different combinations of control system and short-period dynamics at two flight conditions, while performing tasks representative of the 'combat' phase of a fighter's mission. The pilot rating and comment data from this investigation indicate that the dynamic modes of the flight control system can cause serious flying qualities problems, even if the short-period mode is well behaved. The data do not correlate with the control system requirements of MIL-F-8785B. In addition, the data demonstrate that the C* criterion does not adequately account for the effects of control system dynamics. Pilot-in-the-loop analysis of the data is shown to describe effectively the pilot's difficulties in control of pitch attitude, providing insight into how the pilot flies the airplane. A design criterion, based on this analysis, is shown to be applicable to a wide range of short-period and control system dynamics. A simplified version is also presented to provide the designer with preliminary estimates of flying qualities.