Stability and Control Issues Associated with Lightly Loaded Rotors Autorotating in High Advance Ratio Flight

摘要

This paper describes the modeling and analysis of a compound autogyro configuration operating at high advance ratio. The flight dynamics are modeled using the comprehensive analysis software FLIGHTLAB. An isolated rotor model is used to establish rotor trim conditions and rotor speed sensitivities to swashplate controls. The isolated rotor trim analysis shows that the rotor can be trimmed for zero hub-moments and zero-torque over a range of angles of shaft incidence to the freestream, however the control sensitivities are very nonlinear at some conditions. A coupled rotor and airframe model is used to extract a five-state linear model by a perturbation method to predict the longitudinal and rotor-speed modes. Time integration of the non-linear model is used for simulated flight test data, and system identification is applied using CIFER to independently predict the same modes. The dynamic modes as determined by the different methods are compared. The choice of trim condition is seen to affect the rotor speed sensitivity to swashplate controls in a highly nonlinear manner, resulting in a choice of rotor trim conditions being preferred when using the swashplate inputs to create frequency sweep data for system identification.