A technique of controlling tonal noises produced by an unmanned aerial vehicle (UAV) includes generating thrust with a plurality of rotor units mounted to the UAV to propel the UAV into flight. Each of the rotor units includes a bladed rotor. A rotation rate or a phase delay of at least one of the rotor units is adjusted relative to another of the rotor units. The adjustment causes a spread in the tonal noises generated by the rotor units.

A system and method for reducing a psychoacoustic penalty of acoustic noise emitted by an aircraft, including a plurality of propulsion assemblies coupled to the aircraft, wherein each of the plurality of propulsion assemblies includes a motor, and a plurality of blades defined by a propeller, wherein the plurality of blades can define an asymmetric blade spacing; a control subsystem coupled to the aircraft and communicatively coupled to the motor of each of the plurality of propulsion assemblies, wherein the control subsystem is operable to rotate each of the plurality of propulsion assemblies at a different frequency to modulate the acoustic power distribution of the emitted acoustic signature.

An unmanned air vehicle includes a generator that generates a flying force and also generates an air flow, a structural component, a microphone that outputs a first signal, a speaker, and a processor. The processor generates a second signal according to the first signal. The structural component surrounds a noise source of the generator, and includes a through-hole extending in a direction of the air flow. The through-hole is in a direction opposite to the direction of the air flow. An end, in the opposite direction, of the structural component corresponds to an end, in the opposite direction, of the noise source of the generator. An end, in the direction of the air flow, of the structural component extends, in the direction of the air flow, beyond an end, in the direction of the air flow, of the noise source of the generator.

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.

An acoustic sensor system for an aircraft, and method for operating the same, includes a transmitter, at least one microphone, and a control circuit. The transmitter is configured to emit acoustic signals external to the aircraft. The at least one microphone is positioned on an exterior of the aircraft and configured to sense the acoustic signals as sensed data. The control circuit is configured to receive the sensed data and control the transmitter through a drive circuit, and is configured to detect an environmental condition and control the transmitter to emit the acoustic signals at a reduced intensity based on the detected environmental condition.

Vertical take-off and landing (VTOL) aircraft can provide opportunities to incorporate aerial transportation into transportation networks for cities and metropolitan areas. However, VTOL aircraft may be noisy. To accommodate this, the aircraft may utilize onboard sensors, offboard sensing, network, and predictive temporal data for noise signature mitigation. By building a composite understanding of real data offboard the aircraft, the aircraft can make adjustments to the way it is flying and verify this against a predicted noise signature (via computational methods) to reduce environmental impact. This might be realized via a change in translative speed, propeller speed, or choices in propulsor usage (e.g., a quiet propulsor vs. a high thrust, noisier propulsor). These noise mitigation actions may also be decided at the network level rather than the vehicle level to balance concerns across a city and relieve computing constraints on the aircraft.

An anti-torque system for a rotorcraft includes a first tail fan assembly including a plurality of first fan blades and a second tail fan assembly including a plurality of second fan blades. The first tail fan assembly has a larger diameter than the second tail fan assembly. The first fan blades have a larger rotational inertia than the second fan blades such that the second fan blades experience a larger angular acceleration than the first fan blades in response to torque, thereby providing yaw control for the rotorcraft.

A semi-active noise control system includes a layer configured to be part of an interior panel of an aircraft The layer includes conductive tracks, a driver arrangement, tuned mass dampers, and sensors. Each tuned mass damper has an eigenfrequency that depends on a control signal applied to the tuned mass damper and is connected to the driver arrangement via a conductive track and configured to receive control signals from the driver arrangement. Each sensor is connected to the driver arrangement via a conductive track and is configured to sense vibrations and/or acoustic sounds and send measurement signals to the driver arrangement. The driver arrangement is configured to analyze the measurement signals and to generate and send control signals to the tuned mass dampers such that the eigenfrequency of the tuned mass dampers is matched with the frequency of the vibrations and/or acoustic sounds sensed by the sensors.

In some embodiments, a method, apparatus and computer program for reducing noise from an audio signal captured by a drone (e.g., canceling the noise signature of a drone from the audio signal) using a model of noise emitted by the drone's propulsion system set, where the propulsion system set includes one or more propulsion systems, each of the propulsion systems including an electric motor, and wherein the noise reduction is performed in response to voltage data indicative of instantaneous voltage supplied to each electric motor of the propulsion system set. In some other embodiments, a method, apparatus and computer program for generating a noise model by determining the noise signature of at least one drone based upon a database of noise signals corresponding to at least one propulsion system and canceling the noise signature of the drone in an audio signal based upon the noise model.