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Structural Optimization of Composite Helicopter Rotor Blades



Structural optimization of a helicopter rotor blade with uniform aerodynamic surface and twist at the functional region is performed for weight minimization subject to various constraints relevant to helicopter rotor blades. The genetic algorithm based optimization is performed only for the functional region of the blade. Design variables are taken as the number of unidirectional S-glass layers in the spar cap, position of the spar web with respect to the leading edge, nose mass diameter and position of the single span wise ply-drop-off. Constraints of the structural optimization are defined as maximum strain in the critical sections of the blade in the functional region, relative distances between the feathering axis, the mass center, shear center and the neutral axis and natural frequency limits. Optimization is performed in a stepwise fashion for the hover condition while sectional analysis of the blade is performed by the VABS, loads and natural frequencies of the blade are calculated by the multibody simulation tool Dymore. The initial sectional blade loads calculated by Dymore are kept constant and they are not updated in any design iteration during the optimization process. For the optimized blade properties, blade tuning is done by lumped mass attachment to the blade and the sectional blade loads are calculated by Dymore and optimization is performed again by keeping the sectional loads as constant in any design iteration of optimization process. Load calculation, blade tuning and optimization cycle is repeated until the sectional loads calculated by Dymore do not change within a prescribed tolerance to complete full blade optimization. With this approach, the time consuming sectional load calculation process by Dymore is eliminated.

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