Transient Aeroelastic Response of a Rotor During Rotor Speed Transition in Forward Flight

Abstract

Compound helicopters often have to reduce their rotor tip speeds to achieve higher forward speeds. The rotors, therefore, have to undergo a transient process of rotor speed changes. To investigate the transient loads and the related transformation from the rotating frame to the nonrotating frame, a rotor model is used to predict the transient aeroelastic responses. The rotor model is validated by using test data of a teetering model rotor during engagement and disengagement operations. The investigations indicate that a small transient lagwise root bending moment can result in a large transient contribution to rotor torque. This transient component is triggered by the force related with the sudden change of the angular acceleration of the rotor speed. Increasing the blade damping in the lagwise direction can significantly decrease the transient components of the lagwise root bending moment and the corresponding rotor torque. Making the angular acceleration continuous will not trigger the transient components, suggesting that this is a better way for the reduction of the transient rotor loads during speed changes.