Non-harmonic deployment of trailing-edge flaps for rotor-performance enhancement and vibration reduction

A computational method involving a multi-objective evolutionary based optimizer is investigated which provides an optimal set of non-harmonic deployment schedules for a multi-segment, trailing-edge flap. The trailing-edge flap is added to the UH-60A's rotor, with the flap's span, deflection magnitudes, and start/end deployment azimuth positions all optimized to minimize the total power of the rotor and the three resulting hub force vibratory loads at a target flight condition of μ=0.30. Single-objective optimizations are carried out, prior to the multi-objective study, where the non-harmonic deployment schedule of a single and dual segment trailing-edge flap is optimized to minimize power required over a target flight envelope of 0.05 < μ < 0.37. The formal optimization effort is carried out through the coupling of a comprehensive analysis code, RCAS, and one of two evolutionary algorithm based optimizers, CMA-ES (single objective) and ε-MOEA (multi-objective). The single-objective investigations using the CMA-ES solver generated promising results. With regards to a single-segment flap, peak power savings over the flight envelope have reached 9.5% (at μ=0.30) with associated F_z and F_xy hub vibration reductions of 66% and 22%, respectively. The dual segment optimization yielded power savings of 8.9% at the same flight condition. Several representative points were selected from a pareto front created by the four-objective optimization effort to show how the optimized solutions can vary. One of these optimized solutions found a 6.7% power savings, 68% F_z hub vibration reductions, and a 53% F_xy hub vibration reductions. The interdisciplinary character between rotorcraft dynamics and aeromechanics of the computational method hence presents an innovative way of improving rotorcraft performance while also reducing vibratory loads.