Anti-Phase Noise Suppression Rotor Technologies

Rotor noise and vibration are two sources of operational challenges for all aircraft operating with open rotors such as helicopters, unmanned aerial vehicles (UAVs), urban air mobility personal air vehicles, drones, and aircraft operating with ducted fans such as passenger aircraft. One disadvantage of convention rotor design is the noise due to noise-induced shed vortices generated by rotor blades. The unique problem with rotor noise and vibration is the periodic blade passage that causes a harmonic reinforcement and causes the rotor blades to vibrate and generate noise sources. This technology from NASA Ames seeks to optimize the implementation of anti-phase trailing edge designs and asymmetric blade tip treatments for rotor noise suppression and integrated aircraft noise solutions by incorporating the anti-phase rotor design concepts into an aircraft flight control system to reduce noise footprint. There are several embodiments of the invention, which include the following: (1) an anti-phase trailing edge design whereby the trailing edge pattern of the leading rotor blade is offset by a phase shift from the trailing edge pattern of the following blade; (2) an anti-phase rotor design implementing asymmetric blade tips with inverted airfoil; and (3) other anti-phase enabled concepts such as unequal blade length, ducted rotors with non-radial unequally spaced struts, and multi-axis tilt rotor design incorporating the anti-phase rotor design. All rotorcraft experience rotor noise and vibration that present operational challenges due to the unsteady forces that result from blade vortex shedding. Rotor noise is often a nuisance, and excessive rotor vibration can be hazardous. Several methods exist to deal with the noise and vibration from rotor blades, though many designs either aim to reduce vibration and do not address noise, or vice versa. NASA Ames Research Center has developed a novel patent-pending design and method for reducing rotor blade vibration and acoustic signatures in rotor systems using anti-phase blade vortex suppression design concepts. The design objective is to maximize reduction of noise perceived by the community while maintaining the aerodynamic thrust. These designs could be applicable in any system that uses rotor blades.