Flight Dynamics Modeling, Trim, Stability, and Controllability of Coaxial Compound Helicopters

Coaxial compound helicopters feature high-speed characteristics that are not possessed by conventional helicopters. The aim of this paper is to develop a flight dynamics model of coaxial compound helicopters and investigate the trim, stability, and controllability. A flight dynamics model including a coaxial rotor model and a propeller model is introduced. Based on the flight dynamics model, the trim of hover and level flights of a coaxial compound helicopter is performed. Considering the influence of flapping motions, stability and control derivatives are assessed under the small disturbance hypothesis by using a numerical differentiation method. Then, stability and response of the coaxial compound helicopter are presented. The results of trim show good agreement with those of the reference, which verifies the flight dynamics model. The speed static stability derivative is stable in whole trim range, while the angle of attack static stability derivative is unstable. The yawing control with collective differential of the coaxial compound helicopter will induce serious roll effect in high-speed flights.