RESULTS OF NASA/FAA GROUND- AND FLIGHT-SIMULATION EXPERIMENTS CONCERNING HELICOPTER IFR AIRWORTHINESS CRITERIA

A sequence of ground- and flight-simulation experiments was conducted at the Ames Research Center as part of a joint NASA/FAA program to investigate helicopter instrument-flight-rules (IFR) airworthiness criteria. This paper describes the first six of these experiments and summarizes major results. Five of the experiments were conducted on large-amplitude motion base simulators at Ames Research Center; the NASA-Army V/STOLAND UH-1H variable-stability helicopter was used in the flight experiment. Taken together, the results of the experiments indicate, among other things, that 1) some level of artificial stability and control augmentation is generally required for adequate flying qualities during precision instrument flight; 2) neutral longitudinal or lateral control position gradients do not result in inadequate flying qualities, given good directional characteristics, but an unstable longitudinal gradient can prove to be inadequate for instrument operations in turbulence; 3) pitch and roll attitude augmentation in the stability and control augmentation system (SCAS) plus directional augmentation including at least yaw damping is required to achieve satisfactory precision instrument flying qualities irrespective of the type of rotor or level of display assistance; 4) flight directors provide some compensation for poor flying qualities in dual-pilot situations but are of minimal assistance in this regard for single-pilot operations; and 5) the SCAS level required for ratings of satisfactory is the same (pitch and roll attitude augmentation) for the range of approach types considered (nonprecision versus precision, constant speed versus deceleration to a low speed).