Aeroelastic optimization of an advanced geometry helicopter rotor

Sensitivity derivatives of blade loads and aeroelastic stability of a helicopter rotor in forward flight are calculated as an integral part of a basic aeroelastic analysis using a direct analytical approach. Design variables include nonstructural mass and its placement, chordwise offset of blade center of gravity and aerodynamic center from the elastic axis, blade bending stiffnesses (flap, lag, torsion) and tip geometry (sweep, anhedral, pretwist and planform taper). By means of a sensitivity study, the importance of different design variables on oscillatory hub loads and damping of blade modes is examined. Aeroelastic and sensitivity analyses of the rotor based on a finite element method in space and time are linked with automated optimization algorithms to perform optimizatio'n studies of rotor blades. The objective function minimizes oscillatory hub loads with constraints on frequency placement, autorotational inertia and aeroelastic stability of the blade in forward flight. Optimum design solutions, calculated for a fourbladed, soft-inplane hingeless rotor achieved a reduction of 25 - 60 percent of all 4/rev loads.

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