Rotary‐Wing Dynamic Stability

Abstract

Abstract The dynamic stability of a rotary‐wing aircraft is assessed by predicting and observing the aircraft motion following a disturbance from trimmed flight. Varying time scales for the dynamic stability assessment separate the stability modes. A short time scale of 2–3 s highlights the control response. A longer time scale up to a maximum of typically 60 s describes the “classical” dynamic stability. For a conventional helicopter, the effects of the main rotor dominate the control response and dynamic stability characteristics, although other key contributions must be considered. These contributions can be quantified via stability and control derivative sets enabling estimates of engineering parameters. Comparisons can be made of these parameters against handling quality metrics to predict handling quality rating (HQR) levels. Flight testing involving longitudinal and lateral‐directional control response tests and dynamic stability tests are relatively straightforward but will always be supported by mission‐related handling tasks, where HQR values are assigned by qualified test pilots. Cross‐coupling assessments are a significant feature of control response and dynamic stability testing. The principles and practices of dynamic stability modeling and flight testing have applications to unconventional rotary‐wing configurations but only after cautious appraisal of the likely outcomes.