Response and hub loads sensitivity analysis of a helicopter rotor

A sensitivity study of blade response and oscillatory hub loads in forward flight for a hingeless rotor with respect to structural design variables is examined. Structural design variables include nonstructural mass distribution (spanwise and chord wise), chordwise offset of center of gravity, and blade bending stiffnesses (flap, lag, and torsion). The blade is discretized into a number of beam elements, and response equations are transformed into the normal mode space. The nonlinear, periodic, steady response of the blade is calculated using a finite element in time approach. Then, the vehicle trim and blade steady response are calculated iteratively as one coupled solution using a modified Newton method. The formulation for the derivatives of blade response and hub loads is implemented, using a direct analytical approach (chain rule differentiation), and forms an integral part of the basic response analysis. For calculation of the sensitivity derivatives, a 96% reduction of CPU time is achieved by using the direct analytical approach, compared with the finite-difference approach.