Optimum Aeroelastic Design of Helicopter Rotors for Longitudinal Handling Qualities Improvement

This paper describes an optimization study in which the torsional stiffness of a hingeless rotor blade and its cross-sectional offsets are designed to stabilize the phugoid oscillation of the aircraft by increasing the stabilizing effect of the rotor. The real part of the phugoid eigenvalues is minimized at a specified advance ratio, subject to aeroelastic stability constraints hi forward flight, blade root peak-to-peak load constraints for flap bending and torsion, and a longitudinal cyclic response requirement. The aeroelastic analysis and the flight mechanics analysis are connected indirectly to the numerical optimization algorithm through the use of a sequence of approximate optimization problems. A new algorithm to generate a high quality set of starting vectors is presented. The results of the study show that the combined analysis/optimization program can generate designs that have stable phugoid modes and satisfy all the aeroelastic and flight mechanic constraints.