System for controlling higher harmonic vibrations in helicopter rotor blades

Abstract

Higher harmonic control (hereinafter HHC) of helicopter rotor blade vibrations is provided by an actively controlled, rotatable, slotted cylinder which is mounted at an outboard section of each blade. Continuous rotation of each cylinder about its longitudinal axis produces a periodic aerodynamic force on the blade at a frequency of twice the rotational frequency of the cylinder. The amplitude of force is controlled by the size of a slot opening in the cylinder while the rotational speed of the cylinder is synchronized to run at a multiple of the speed of a rotor blade drive shaft. The amplitude and phase of the HHC force is regulated, either manually or by active feedback control, to minimize any vibratory load transmitted to the airframe through the rotor blade drive shaft. A significant advantage offered by this concept relative to other HHC methods, such as high-frequency blade pitch motions actuated either by the swash plate or by moveable tabs at the blade trailing edge, is its low power requirement.

Dependencies are inferred from the claim text.