Some Aspects of Helicopter Flight Dynamics in Steady Turns

This paper presents the results of a theoretical study of the flight dynamics and han-dling qualities of hingeless rotor helicopters in turning flight. Frequency responses in pitch, roll, and heave are evaluated for various advance ratios, turn rates, and turn directions; comparisons are made with criteria of the ADS-33 handling qualities specifications. The results show that couplings between lateral and longitudinal dynamics are present in turn-ing flight. Flight speed, load factor, and direction of turn affect frequency and damping of both poles and zeros. Zeros that are stable in straight flight can become lowly damped or nonminimum-phase and cause a deterioration of handling qualities. This may also cause flight control systems designed for straight flight to perform poorly in some turning flight conditions. The bandwidth criteria of the ADS-33 specifications do not explicitly address maneuvering flight conditions. Therefore, there remains an open question of whether the degradations of handling qualities identified in this study are real (possibly through mech-anisms other than those intended in the original formulation of the specification) or are a mathematical artifact