Ground effect acting on an aerial vehicle, such as an unmanned aerial vehicle, may be simulated by discharging a gas around propeller blades of the aerial vehicle while the propeller blades are rotating. For example, a gas, such as air, may be discharged at or near the tip of the propeller blades with enough velocity to disrupt the airflow around the blade tips, thereby altering the sound generated by rotation of the propeller blade.

An aerial system having an obstacle detection and avoidance system is described herein. The obstacle detection and avoidance system includes a pair of ultra-wide angle lens cameras orientated coaxially along an optical axis. Each ultra-wide angle lens camera includes a field-of-view lens having a vertical angle of view greater than 180 degrees. The pair of ultra-wide angle lens cameras is orientated such that a portion of each corresponding camera field-of-view overlaps to define a viewable region of interest including overlapping vertical field angle.

An apparatus and method for reducing background noise captured by a UAV acoustic sensor are disclosed. The background noise may be reduced by incorporating a known UAV acoustic signature corresponding to a determined flight parameter into an adaptive filter coupled to the acoustic sensor.

Aerial vehicles may be operated with discrete sets of propellers, which may be selected for a specific purpose or on a specific basis. The discrete sets of propellers may be operated separately or in tandem with one another, and at varying power levels. For example, a set of propellers may be selected to optimize the thrust, lift, maneuverability or efficiency of an aerial vehicle based on a position or other operational characteristic of the aerial vehicle, or an environmental condition encountered by the aerial vehicle. At least one of the propellers may be statically or dynamically imbalanced, such that the propeller emits a predetermined sound during operation. A balanced propeller may be specifically modified to cause the aerial vehicle to emit the predetermined sound by changing one or more parameters of the balanced propeller and causing the balanced propeller to be statically or dynamically imbalanced.

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.

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.

A noise cancellation system for an unmanned aerial vehicle may have an audio capture module, a metadata module and a filter. The audio capture module may be configured to receive an audio signal captured from a microphone, e.g., on a camera. The metadata module may be configured to retrieve noise information associated with noise generating components operating on the unmanned aerial vehicle (UAV). The filter may be configured to receive the audio signal and noise information from the audio capture module. The filter also may be configured to retrieve a baseline profile from a database based on the noise information. The baseline profile includes noise parameter to filter out audio frequencies from the audio signal corresponding to the noise generating component. The filter may generate a filtered audio signal for output.

Mechanical vibrations are generated on a frame of an aerial vehicle as a response to operation of the aerial vehicle, such as rotation of motors and/or propellers. Likewise, environmental conditions, such as wind, humidity, etc., may also cause vibrations on the frame of aerial vehicles. These vibrations may be destructive to the aerial vehicle, impact stability of the aerial vehicle, and/or result in audible sounds. Disclosed are systems and methods for measuring and/or predicting the vibrations on the frame of the aerial vehicle, generating anti-vibrations, and outputting those anti-vibrations such that the anti-vibrations modify vibrations on the frame of the aerial vehicle.

Noises that are to be emitted by an aerial vehicle during operations may be predicted using one or more machine learning systems, algorithms or techniques. Anti-noises having equal or similar intensities and equal but out-of-phase frequencies may be identified and generated based on the predicted noises, thereby reducing or eliminating the net effect of the noises. The machine learning systems, algorithms or techniques used to predict such noises may be trained using emitted sound pressure levels observed during prior operations of aerial vehicles, as well as environmental conditions, operational characteristics of the aerial vehicles or locations of the aerial vehicles during such prior operations. Anti-noises may be identified and generated based on an overall sound profile of the aerial vehicle, or on individual sounds emitted by the aerial vehicle by discrete sources.

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.