Sounds are generated by an aerial vehicle during operation. For example, the motors and propellers of an aerial vehicle generate sounds during operation. Disclosed are systems, methods, and apparatus for actively adjusting the position of one or more propeller blade treatments of a propeller blade of an aerial vehicle during operation of the aerial vehicle. For example, the propeller blade may have one or more propeller blade treatments that may be adjusted between two or more positions. Based on the position of the propeller blade treatments, the airflow over the propeller is altered, thereby altering the sound generated by the propeller when rotating. By altering the propeller blade treatments on multiple propeller blades of the aerial vehicle, the different sounds generated by the different propeller blades may effectively cancel, reduce, and/or otherwise alter the total sound generated by the aerial vehicle.

An unmanned aircraft includes: a sensor that includes at least a microphone that generates sound data; and a processor. The processor determines the quality of a target sound by use of the sound data generated by the microphone, identifies a sound source direction from the unmanned aircraft to the sound source of the target sound by use of data generated by the sensor, and controls an unmanned aircraft state that is a state of the unmanned aircraft such that a direction of a sound pickup area is aligned with the sound source direction, in accordance with the determined quality. The sound pickup area is a range in which sound pickup quality of the microphone is higher than that of another area.

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/or noise signature characteristics as compared to the aft propulsion system, while conversely the aft propulsion system may be provided with a lesser flight performance and/or noise signature characteristics as compared to the forward propulsion system.

According to one embodiment, a noise reduction device includes speakers, microphones, and a processing circuit. The speakers are arranged around a rotor and emit control sound based on control signals. The microphones are arranged around the rotor and convert the control sound and noise emitted by the rotor into microphone signals. The processing circuit generates the control signals for reducing acoustic power in positions of the microphones, based on the microphone signals, rotation speed of the rotor, and a phase of noise that reaches the microphones from the rotor.

An aerial vehicle is provided including rotor units connected to the aerial vehicle, and a control system configured to operate at least one of the rotor units. The rotor unit includes rotor blades, wherein each rotor blade includes a surface area, and wherein an asymmetric parameter is defined, at least in part, by the relationship between the surface areas of the rotor blades. The value of the asymmetric parameter is selected such that the operation of the rotor unit: (i) moves the rotor blades such that each rotor blade produces a respective vortex and (ii) the respective vortices cause the rotor unit to produce a sound output having an energy distribution defined, at least in part, by a set of frequencies, wherein the set of frequencies includes a fundamental frequency, one or more harmonic frequencies, and one or more non-harmonic frequencies having a respective strength greater than a threshold strength.

The present invention relates to a fixed wing drone for delivering objects, a takeoff and landing device for a fixed wing drone, a system made up of a drone and a takeoff and landing device, and an approach method for said system. The fixed wing drone comprises wing control surfaces, at least two drive units, at least one tail assembly, at least one structure element which protrudes to the rear and is accessible from the rear, an object holding device, a receiving unit, and a control unit. The takeoff and landing device permits a fixed wing drone to land silently on a vertical structure.

A drone is disclosed having a low acoustic signature. The drone includes a fuselage, a main inboard wing attached to the fuselage, a pylon located towards an aft end of the fuselage and having an end that is higher than the main inboard wing, and a propulsor connected to the pylon and situated above the fuselage. The drone includes a plurality of booms connected to the main inboard wing and a plurality of horizontal tails attached to the plurality of booms. The horizontal tails have an outboard tail arrangement and are tiltable.

A drone is disclosed having a low acoustic signature. The drone includes a fuselage, a main inboard wing attached to the fuselage, a pylon located towards an aft end of the fuselage and having an end that is higher than the main inboard wing, and a propulsor connected to the pylon and situated above the fuselage. The drone includes a plurality of booms connected to the main inboard wing and a plurality of horizontal tails attached to the plurality of booms. The horizontal tails have an outboard tail arrangement and are tiltable.

Rotor noise cancellation through the use of mechanical means for a personal aerial drone vehicle. Active noise cancellation is achieved by creating an antiphase amplitude wave by modulation of the propeller blades, by utilizing embedded magnets through an electromagnetic coil encircling the propeller blades. A noise level sensor signals the rotor control system to adjust the frequency of the electromagnetic field surrounding the rotor and control the speed of the rotor. An additional method comprises of incorporating a phase lock loop within the control system configured to determine the frequencies corresponding to the rotors and generate corrective audio signals to achieve active noise cancellation.

A method of reducing noise generated by a tilt-rotor aircraft includes transitioning the tilt-rotor aircraft into an airplane mode from a helicopter mode, and reducing a speed of a first pair of fans of the tilt-rotor aircraft to be less than a speed of a second pair of fans that are positioned in-line with the first pair of fans. A flight control system configured to reduce a noise level of a tilt-rotor aircraft includes a flight control computer comprising a processor, a propulsion system communicatively coupled to the flight control computer, a first pair of fans and a second pair of fans communicatively coupled with the flight control computer and the propulsion system. The processor is operable to implement a method that includes transitioning the tilt-rotor aircraft into an airplane mode from a helicopter mode, and reducing a speed of the first pair of fans to be less than a speed of the second pair of fans that are positioned in-line with the first pair of fans.