An analysis of longitudinal-control problems encountered in flight at transonic speeds with a jet-propelled airplane

Abstract : During flight tests of a jet-propelled airplane, a sudden pitch-up motion of the airplane occurred in a recovery from a high-speed dive, although the pilot had not moved the controls so as to produce this motion. The pitch-up occurred at a Mach number of 0.85 as the Mach number was being decreased from 0.866 and resulted in a change of lift coefficient from 0.49 to 0.89 in about 1 second. Measurements of the stability anc control characteristics of the airplane and of the wing pressure distribution during the dive and recovery are presented. An analysis based on flight and wind-tunnel data indicated the probable causes of the abrupt pitch-up were an abrupt restoration of elevator effectiveness and a nose-up change in balance caused by a shift in the angle of attack for zero lift both due to the decreasing Mach number.