SOME ASPECTS OF HELICOPTER PLIGHT DYNAMICS IN STEADY TURNS

Results are presented of a theoretical study of the flight dynamics an d handling qualities of hingeless rotor helicopters in turning flight. Frequency responses in pitch, roll, and heave are evaluated for vario us advance ratios, turn rates, and turn directions; comparisons are ma de with criteria of the ADS-33 handling qualities specifications. The results show that couplings between lateral and longitudinal dynamics are present in turning flight. Flight speed, load factor, and directio n of turn affect frequency and damping of both poles and zeros. Zeros that are stable in straight Eight can become lowly damped or nonminimu m phase and cause a deterioration of handling qualities. This may also cause Eight control systems designed for straight flight to perform p oorly in some turning flight conditions. The bandwidth criteria of the ADS-33 specifications do not explicitly address maneuvering flight co nditions. Therefore, there remains an open question of whether the deg radations of handling qualities identified in this study are real (pos sibly through mechanisms other than those intended in the original for mulation of the specification) or a mathematical artifact.