Use of flow injection and extraction to control blade vortex interaction and high speed impulsive noise in helicopters

A method for lessening high speed impulsive blade noise in rotors of aircraft having a plurality of rotor blades extending radially in spaced relationship from a central hub, each blade having spaced apart upper and lower surfaces, an interior volume between the surfaces and leading and trailing edge portions at the respective joined edges of the upper and lower surfaces of each blade;

• the surfaces of each blade having air intake passages proximate the leading edge and tip edge and air output passages proximate the trailing edge and tip edge, the method comprising:
• during rotation of said aircraft rotors, controllably admitting air into the interior volume of each rotor blade through said air intake passages and controllably expelling air from the interior volume through said output passages, said admitting and expelling of air into and out of each blade being controlled in accordance with one or more sensed conditions of that blade,
• wherein a sensed condition of each blade is its position during a cycle of rotation.

A method for reducing rotor blade noise in an aircraft which comprises controllably expelling pressurized air from the interior of each of a plurality of rotor blades of said aircraft, said controllable expulsion of air being through passages in the outboard tip of each rotor blade in response to determined flight conditions of the aircraft,

• wherein said condition is determined by sensors mounted on said aircraft, and
• wherein said sensors are mounted on the aircraft's fuselage.

A method for lessening high speed impulsive blade noise in rotors of aircraft having a plurality of rotor blades extending radially in spaced relationship from a central hub, each blade having spaced apart upper and lower surfaces, an interior volume between the surfaces and leading and trailing edge portions at the respective joined edges of the upper and lower surfaces of each blade;

• the surfaces of each blade having air intake passages proximate the leading edge and tip edge and air output passages proximate the trailing edge and tip edge, the method comprising:
• during rotation of the aircraft rotors, controllably opening and closing at least one of the air intake passages and air output passages to admit air into the interior volume of each rotor blade through the air intake passages and to expel air from the interior volume through the output passages, the admitting and expelling of air into and out of each blade being controlled in accordance with one or more sensed conditions of that blade.

A method for reducing rotor blade noise in an aircraft, comprising:

• controllably introducing air, from a pressurized air source, into an interior of each of a plurality of rotor blades of the aircraft;
• and
• controllably expelling pressurized air from the interior of each of the plurality of rotor blades of the aircraft through passages in an outboard tip of each rotor blade responsive to noise, produced by the aircraft, measured by sensors mounted on the aircraft.