Design, fabrication, and benchtop testing of a helicopter rotor blade section with warp-induced spanwise camber variation

This article focuses on the design, fabrication, testing, modeling, and validation of a spanwise variable camber section of a helicopter rotor blade. The lower surface skin was slit aft of the trailing edge spar and subjected to a spanwise warping actuation input. A kinematic linkage facilitates a corresponding chordwise motion of the skin along the span length (from zero at the no-camber end to maximum at the maximum camber end). Input warping actuation of 0.18 in length produced an 18° camber variation over a 45 in span section of a modified CH-46 blade. Finite element model predictions of the active camber section showed good agreement with benchtop test data for both the output camber for a given warping actuation input and the corresponding actuation force required. Finite element results suggest that some geometry distortions in the active camber section could be experienced due to the presence of centrifugal and aerodynamic loads, but these distortions could be alleviated with the introduction of a shear-flexible (but stiff through the thickness) core.