Flight Investigation using Variable-Stability Airplanes of Minimum Stability Requirements for High-Speed, High-Altitude Vehicles

The pilot opinion of the flying qualities of vehicles covering a wide range of longitudinal dynamic characteristics has been determined by the use of a variable-stability airplane. Particular emphasis has been placed on determining the minimum level of stability and control characteristics that the pilot can cope with. There was considerable pilot learning associated with operation in the regions of poor stability characteristics. In the statically stable region the maximum acceptable value of time to damp to half amplitude of the longitudinal mode for normal operation was about 1 second. For emergency conditions the damping could be reduced to zero over most of the frequency range. The extreme lim it of controllability corresponded to a time to double amplitude of the oscillation of about 1 - 1/2 seconds. In the statically unstable region somewhat shorter times to double amplitude were acceptable to the pilots. The boundary for emergency operation corresponded roughly to time to double amplitude of about 2/3 second and the limit of controllability of about l/3 second.