| This thesis considers high-frequency modelling of the directional axis dynamics of single-rotor helicopters, with particular attention to those vehicles which achieve anti-torque and directional control using a ducted tail rotor. Although the work was initiated as part of the development of the first Boeing-Sikorsky RAH-66 Comanche prototype aircraft, the thesis presents insights into problems of general relevance to the design and analysis of high-bandwidth rotorcraft directional-axis feedback systems. A new analysis of the unsteady thrust response of a ducted tail rotor in an arbitrary flight condition is developed and correlated to the RAH-66 Comanche's FANTAILTM behavior using a variety of flight and ground test data. The general problems of airframe elastic response modelling and identification from flight data are considered and applied to Comanche flight data. A simplified analytical model which captures the salient effects of a flexible fuselage is developed and applied to the prediction of closed-loop stability robustness in the presence of these effects. Analytical insights into the three-dimensional nature of a coupled elastic drive system model are discussed. Finally, the implications of the new results for control law design are discussed. |
