Design, Fabrication And Benchtop Testing Of A Rotor Blade With Warp-Induced Spanwise Camber Variation

This paper 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. A kinematic linkage allows (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 inches in length produced an 18 degree camber variation over a 45 inch span section of a modified CH-46 blade. Finite element model predictions of the active camber section showed excellent agreement with benchtop test data for both the output camber for a given warping actuation input, as well as 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; although these distortions could be alleviated with the introduction of a shear-flexible (but stiff through the thickness) core at the cost of increase in actuation force requirement.