Chord Extension Morphing for Active Rotor Track and Balance

This study examines the effectiveness of an on-blade extendable tab mechanism for rotor track-and-balance. The tab is essentially a chord-extension morphing mechanism, implemented as an extendable trailing-edge-plate over a spanwise section of each blade. A simulation model of the UH-60 Black Hawk rotor with seeded imbalance is developed, with the extendable tabs minimizing the 1/rev (1P) vibratory loads using a weighted least-squares optimization method. The extendable tab has the ability to reduce the 1P in-plane forces over the entire airspeed range with very large reductions observed in hover. The tabs are unable to reduce 1P vertical forces in hover, but are very effective in reducing these vibratory loads in cruise. The extendable tab is moderately effective in reducing 1P in-plane moments over the range of airspeeds. Best reductions in 1P loads are achieved by employing an active tab mechanism (adjusted at different airspeeds) over a passive mechanism (with constant setting over the airpseed range), with the active tab yielding additional gains in 1P in-plane forces and moments in hover and in 1P vertical forces in cruise. In hover, an examination of the load reduction mechanism indicates that a seeded radial shear and root torsional moment imbalance is cancelled by the generation of net blade root chordwise shear and root flap bending moments, respectively, on orthogonal blades. In cruise, similar mechanisms were observed, but the generation of net radial shears and root torsional moments on parallel blades were also contributors to total reduction in 1P hub in-plane and pitching moment vibrations.