Flying Quality Factors Currently Limiting Helicopter Nap-of-the Earth Maneuverability as Identified by Flight Investigation

A flight investigation utilizing two modern lightweight helicopters was conducted to study the effects of flying qualities on nap-of-the-earth maneuver capability. Variation in flying qualities was provided by the markedly different stability and control characteristics which resulted from the basically different rotor systems of the two test vehicles. Several tasks were used to provide a realistic basis on which to determine the parameters most pertinent to maneuver capability. The results indicate that the initial angular response characteristics about the roll axis and the sensitivity of the height control are of primary importance. For example, the tightness of the initial roll response, as determined by the magnitude of roll-control sensitivity in combination with angular-velocity damping, had a significant influence on the pilot''s ability to attain quickly, precisely, and consequently safely, those bank angles necessary to perform the tasks smoothly. Wind velocity and direction, stick-fixed maneuver stability gradients, angular-velocity and control-system coupling, vibration, and power-governing-system characteristics were other factors that significantly influenced the pilot''s ability to maneuver the helicopters.