Rotor Vibration Reduction Using an Embedded Spanwise Absorber
Abstract:This paper examines the effectiveness of an embedded spanwise Coriolis absorber in a rotor blade in reducing the in-plane vibratory hub loads. Simulations based on a light, four-bladed, hingeless rotor helicopter similar to the BO-105 showed that in high-speed flight (140 kt), over 85% reductions in both 4/rev longitudinal and lateral hub shears could nominally be achieved using an absorber mass 3% of the blade mass situated at 60% span, oscillating at 3/rev with an amplitude of about 0.03 ft. If the baseline in-plane vibration levels of the helicopter are increased to 0.1–0.12 g, the reduction achieved with the same absorber mass are in the range of 60%–70% while the absorber motion increases to 0.15 ft. The phase of the 3/rev absorber motion is critically important to realizing hub vibration reduction, and the absorber tuning frequency is set to a value close to, but not exactly at 3/rev, to achieve correct phasing. The absorber reduced the 4/rev in-plane hub forces by reducing the magnitude of the 3/rev blade root drag shear while simultaneously reversing the phase of the 3/rev blade root radial shear. The reductions in vibratory hub forces observed at 140-kt high-speed flight condition were largely preserved as the flight speed was reduced to 100 kt cruise condition, without any need for retuning of the absorber.
Document Type: Research Article
Publication date: 2012-04-01
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