RESPONSE OF HELICOPTER BLADES TO A SHARP COLLECTIVE INCREASE

This article presents a theoretical investigation of the response of h elicopter blades to a sharp collective increase in hover. The modeling deals with both main aspects of the problem: 1) the spanwise distribu tion of the unsteady loads, and 2) the corresponding structural dynami c response of the elastic blades and the rotor-fuselage system as a wh ole. The aerodynamic loads distribution is calculated by the definitio n and the determination of the spanwise distribution of the aerodynami c equivalent mass, which is responsible for the time-dependent develop ment of the velocity induced by the trailing vortices. The structural modeling is based on the finite element approach, and the equations of motion are derived using Lagrange's equations. Due to the sharp chang es in time, all terms containing time derivatives are retained in the equations which results in highly nonlinear expressions. A study to id entify and quantify the role and the sensitivity of a variety of param eters has been carried out.