A drone includes a motor, a noise receiver, a camera, a distance measure, and a directed sound beam generator. The noise receiver is configured to detect a noise caused by the motor. The camera is configured to capture an image of an area when the drone is in the air. The distance measure is configured to measure a distance between the drone and a particular point in the captured image. The directed sound beam generator is configured to emit a sound beam that is directed to a particular direction. The drone further includes a processor configured to analyze the detected noise to determine a frequency spectrum of the detected noise. The processor is further configured to analyze the captured image to identify a target, and cause the directed sound beam generator to emit a sound beam to actively cancel at least a portion of the noise directed to the target.

Unmanned aircraft have aligned forward and aft propulsion systems possessing different performance and/or noise characteristics. According to some embodiments, unmanned aircraft have a forward engine and a forward tractor propeller and an aft engine and an aft pusher propeller. Selected ones of forward and aft propulsion systems will thus be provided to have greater and lesser operational flight performance characteristics and greater and lesser noise signature characteristics, respectively, as compared to the other. For example, the forward propulsion system may be provided with the greater operational flight performance and higher signature characteristics as compared to the aft propulsion system, while conversely the aft propulsion system may be provided with a lesser flight performance and lower noise signature characteristics as compared to the forward propulsion system.

A takeoff location and a landing location are received for an autonomous vertical takeoff and landing (VTOL) vehicle that includes a plurality of rotors. An autonomous and noise-reduced flight trajectory for the autonomous VTOL vehicle is determined based at least in part on the takeoff location, the landing location, a jerk function, and a noise function, including by minimizing the jerk function and minimizing the noise function. A set of one or more desired forces or moments is determined for the autonomous VTOL vehicle based at least in part on autonomous and noise-reduced flight trajectory. A plurality of motor control signals is determined for the plurality of rotors based at least in part on the set of one or more desired forces or moments.

The present invention includes an a plurality of first variable speed motors mounted on a tail boom of the helicopter; one or more fixed pitch blades attached to each of the plurality of first variable speed motors; and wherein a speed of one or more of the plurality of first variable speed motors is varied to provide an anti-torque thrust.

A noise mitigation system for an aircraft comprises a cyclic pitch mechanism arranged to apply a cyclic pitch schedule to rotor blades of an unducted propulsive rotor (UPR) under control of a processor. The processor receives input data corresponding to the position and attitude of the UPR, the position of one or more ground points stored in a memory and the velocity of the aircraft. If the processor determines that a ground point will enter the plane of the UPR, a control signal is output to the cyclic pitch mechanism as necessary to adjust the phase of the cyclic pitch schedule such that the azimuthal position of the ground point on entry to the plane of the UPR lies within an azimuthal interval over which the blade pitch of the cyclic pitch schedule is below its average value, thus reducing noise in the direction of the ground point.

Systems and methods for controlling an unducted turbofan engine to limit noise. The unducted turbofan engine may include an unducted fan drivingly coupled with a low-pressure turbine and a plurality of unducted outlet guide vanes. The unducted fan may include a plurality of fan blades and a pitch angle of the fan blades may be variable. A pitch angle of the unducted outlet guide vanes may be variable. A controller is configured to control the engine to limit noise based on a noise sensitive condition.

A propeller includes a hub coaxially surrounding a longitudinal axis. A ring shroud coaxially surrounds the longitudinal axis and is spaced radially from the hub. At least one propeller blade is fixedly attached to both the hub and ring shroud and extends radially therebetween for mutual rotation therewith. At least one stub blade has a first stub end radially spaced from a second stub end. The first stub end is fixedly attached to a selected one of the hub and ring shroud. The second stub end is cantilevered from the first stub end and is radially interposed between the first stub end and the selected one of the hub and ring shroud.

The present invention includes an a plurality of first variable speed motors arranged in a first matrix pattern and mounted on a tail boom of the helicopter; one or more fixed pitch blades attached to each of the plurality of first variable speed motors; and wherein a speed of one or more of the plurality of first variable speed motors is varied to provide an anti-torque thrust.

An urban air mobility (UAM) noise reduction system and method are provided, where the UAM noise reduction system includes a UAM configured to detect and to provide rotation per minute (RPM) information of a propeller and location coordinate information, and a noise canceling device configured to predict a noise canceling sound wave amplitude on the basis of the RPM information of the propeller and the location coordinate information received through the UAM and to output a noise canceling sound wave corresponding to the predicted noise canceling sound wave amplitude to the UAM.

This disclosure is directed to varying a speed of one or more motors in an unmanned aerial vehicle (UAV) to reduce unwanted sound (i.e., noise) of the UAV. A UAV may include motors coupled with propellers to provide lift and propulsion to the UAV in various stages of flight, such as while ascending, descending, hovering, or transiting. The motors and propellers may generate noise, which may include a number of noise components such as tonal noise (e.g., a whining noise such as a whistle of a kettle at full boil) and broadband noise (e.g., a complex mixture of sounds of different frequencies, such as the sound of ocean surf). By varying the controls to the motors, such as by varying the speed or revolutions per minute (RPM) of a motor during operation by providing random or pseudo-random RPM variations, the UAV may generate a noise signature with reduced tonal noise.