A low-noise multi-propeller system includes at least two propellers, each propeller including at least two blades. The propellers rotate in a first direction and define an angular phase relative to one another. A drive system corotates the propellers at substantially equal rotational rates in the first direction. The propellers are substantially phase-locked at a predefined relative phase offset that reduces the overall sound power of the fundamental tone at a blade passage frequency.

A low-noise multi-propeller system includes at least two propellers, each propeller including at least two blades. The propellers rotate in a first direction and define an angular phase relative to one another. A drive system corotates the propellers at substantially equal rotational rates in the first direction. The propellers are substantially phase-locked at a predefined relative phase offset that reduces the overall sound power of the fundamental tone at a blade passage frequency.

An interconnect drive system for an aircraft has a driveline and clutch control system. The driveline comprises a shaft for each propulsion assembly, each shaft for transferring torque to and from the associated propulsion assembly, and a clutch operably coupling the shafts and configured for selective engagement. The clutch is capable of transferring a first amount of torque between the shafts while engaged and a second amount of torque between the shafts while disengaged. The system also has a clutch control system, comprising a computer operably connected to the clutch for controlling operation of the clutch and sensors for sensing torque applied to the driveline, output from the sensors being communicated to the computer. The computer commands operation of the clutch in response to the output from the sensors, the clutch being commanded to disengage to relieve a transient torque imbalance in the driveline.

A tail-sitter aircraft is provided and includes a fuselage having first and second axisymmetric sides, first collectively controllable prop-rotors, which are formed to define a first pair of rotor disks and which are respectively supported at the first axisymmetric side of the fuselage, and second collectively controllable prop-rotors, which are formed to define a second pair of rotor disks and which are respectively supported at the second axisymmetric side of the fuselage.

A tail-sitter aircraft is provided and includes a fuselage having first and second axisymmetric sides, first collectively controllable prop-rotors, which are formed to define a first pair of rotor disks and which are respectively supported at the first axisymmetric side of the fuselage, and second collectively controllable prop-rotors, which are formed to define a second pair of rotor disks and which are respectively supported at the second axisymmetric side of the fuselage.

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.

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.

This disclosure describes aerial vehicles and systems for altering the noise generated by the rotation of a propeller during flight of the aerial vehicle. In some implementations, propellers of the aerial vehicle are paired in a coaxially aligned configuration in which the pair of propellers both rotate in the same direction, are rotationally phase aligned, and separated a defined distance so that the noise from high pressure pulse of the induced flow from the lower propeller is at least partially canceled out by the noise of the high pressure pulse of the induced flow from the upper propeller.

This disclosure describes aerial vehicles and systems for altering the noise generated by the rotation of a propeller during flight of the aerial vehicle. In some implementations, propellers of the aerial vehicle are paired in a coaxially aligned configuration in which the pair of propellers both rotate in the same direction, are rotationally phase aligned, and separated a defined distance so that the noise from high pressure pulse of the induced flow from the lower propeller is at least partially canceled out by the noise of the high pressure pulse of the induced flow from the upper propeller.

A multi-rotor aircraft includes a fuselage, a propulsion engine coupled to the fuselage that generates thrust to propel the aircraft along a first vector during forward flight, and rotors coupled to the fuselage, each rotor comprising blades, each rotor coupled to a motor, and each motor configured to supply power to and draw power from the coupled rotor. The aircraft includes a flight control system configured to control the motors coupled to the rotors in a power managed regime in which a net electrical power, consisting of a sum of the power being supplied to or drawn from each rotor by its motor, is maintained within a range determined by a feedback control system of the flight control system. The flight control system can also be leveraged to adjust rotor control inputs to modify at least one of thrust, roll, pitch, or yaw of the multi-rotor aircraft.