A method for adaptive phase control of a distributed propulsion (DP) aircraft includes deriving an estimated source noise level of the aircraft's propulsors with respect to a designated low-noise area on the ground. Responsive to the estimated source noise level, a phase generator module estimates a ground noise level using the source noise level. The method includes determining an optimized set of relative azimuthal propulsor blade positions/phase angles, via the phase generator module, with such optimized phase angles being sufficient for reducing the estimated ground noise level. Phase control signals from a flight controller to the respective propulsors establishes the optimized set of relative phase angles, and thereby reduces community noise in the designated low-noise area. The DP aircraft includes an aircraft body, the flight controller, and the above-noted phase generator module.

An unmanned aircraft includes: rotor blades; a duct that shrouds the rotor blades and through which airflow generated by rotation of the rotor blades passes; and a processor that controls rotation of the rotor blades. The height to width ratio of an inner space of the duct in which the rotor blades are shrouded is at least 0.5.

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 and/or configuration of one or more propeller blades of a propulsion mechanism to generate different sounds and/or lifting forces from the propulsion mechanism.

A noise reduction system in a vertical takeoff and landing (VTOL) vehicle is provided. The noise reduction system is configured to: identify a noise level at which the VTOL vehicle can operate; dynamically determine a motor-specific fan RPM and a motor-specific fan pitch that will allow the vehicle to not exceed the noise level based on vehicle noise characteristics and an ambient noise level; determine whether the determined motor-specific fan RPM and motor-specific fan pitch will allow the vehicle to operate within its safety envelope; and cause a motor-specific fan RPM command and a motor-specific fan pitch command to be sent to the lifter motor controller to cause the vehicle lifter motors to operate at the determined motor-specific fan RPM and motor-specific fan pitch when it is determined that the determined motor-specific fan RPM and motor-specific fan pitch will allow the VTOL vehicle to operate within its safety envelope.

An unmanned aerial vehicle (UAV) may emit masking sounds during operation of the UAV to mask other sounds generated by the UAV during operation. The UAV may be used to deliver items to a residence or other location associated with a customer. The UAV may emit sounds that mask the conventional sounds generated by the propellers and/or motors to cause the UAV to emit sounds that are pleasing to bystanders or do not annoy the bystanders. The UAV may emit sounds using speakers or other sound generating devices, such as fins, reeds, whistles, or other devices which may cause sound to be emitted from the UAV. Noise canceling algorithms may be used to cancel at least some of the conventional noise generated by operation of the UAV using inverted sounds, while additional sound may be emitted by the UAV, which may not be subject to noise cancelation.

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.

An aircraft control system and method to optimize aircraft control based on noise abatement volumes. A noise abatement component computes optimal flight and engine control based on a line-of-sight distance to minimize direct operating cost (DOC) while complying with community noise regulations.

The present disclosure relates to devices, systems, and methods for controlling and/or augmenting acoustic sounds emitted from flight vehicles, such as unmanned aerial vehicles (UAVs). For example, while in flight, a UAV may emit a characteristic sound or tone (or a plurality of such tones), which may be a result of propeller and/or motor noise. To mitigate such noise from UAVs, disclosed embodiments may include acoustic resonators that may provide additional tones to complement the sounds or tones emitted from the UAV. Namely, the acoustic resonators may be shaped, adjusted, or otherwise controlled to emit additional tones that form pleasing intervals in combination with the characteristic tone(s) from the UAV.

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 shape of a propeller blade of an aerial vehicle during operation of the aerial vehicle. For example, the propeller blade may have one or more joints that adjust to alter the shape of the propeller blade. The altered shape of the propeller blade causes the propeller to generate different frequencies of sound as it rotates. By altering multiple propeller blades of the aerial vehicle, the different sounds generated by the different propeller blades may effectively cancel or reduce the total sound generated by the aerial vehicle, and/or alter the total frequency generated.

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.