Lagwise dynamic analysis of a variable speed rotor

An aeroelastic simulation of a variable speed rotor in forward flight is conducted to investigate its dynamic characteristics in steady and transient states. The system equations of motion are derived based on the generalized force formulation by using Hamiltonʼs principle. The periodic and transient aeroelastic responses of a four bladed stiff in-plane rotor are analyzed to investigate the loads transfer phenomenon in the lagwise direction. The transient lagwise moment increases sharply during the 2/rev resonance crossing. This high transient load in rotating frame is not transferred to the fixed frame. Flap motion has vital contribution to the periodic and transient lagwise loads. The 1/rev flapping motion in the rotating frame can excite the 4/rev rotor torque in the fixed frame due to the Coriolis force. The faster the blade crosses the resonance area, the smaller the transient lagwise loads and the higher the rotor torque. For the dissimilar rotor with 5% reduction of one blade mass at 60% to 70% rotor radius, the unbalanced 2/rev lag moment in the rotating frame is transferred to the fixed frame as the 2/rev rotor torque. Increasing blade lag critical damping from 1% to 5% can reduce the peak-peak lagwise root bending moment by 64.9%, and the rotor torque is reduced to the level without dissimilarity. The dynamics of a stiffer rotor during the 4/rev resonance crossing is also addressed.