A propulsion system of an unmanned aerial vehicle (UAV) includes a first and a second propulsion devices each including a rotor mount assembly including a base and a lock structure arranged at the base. The lock structure includes a protrusion protruding from the base. An angle between an extension direction of the protrusion and a rotation plane of the rotor mount assembly has an absolute value larger than 0° and smaller than 90°. Each of the first and second propulsion devices further includes a rotor blade assembly configured to be locked to the corresponding rotor mount assembly by the corresponding lock structure. The rotor mount assembly of the first propulsion device is configured to not allow the rotor blade assembly of the second propulsion device to be assembled to the rotor mount assembly of the first propulsion device.

A propulsion system of an unmanned aerial vehicle (UAV) includes a first and a second propulsion devices each including a rotor mount assembly including a base and a lock structure arranged at the base. The lock structure includes a protrusion protruding from the base. An angle between an extension direction of the protrusion and a rotation plane of the rotor mount assembly has an absolute value larger than 0° and smaller than 90°. Each of the first and second propulsion devices further includes a rotor blade assembly configured to be locked to the corresponding rotor mount assembly by the corresponding lock structure. The rotor mount assembly of the first propulsion device is configured to not allow the rotor blade assembly of the second propulsion device to be assembled to the rotor mount assembly of the first propulsion device.

A rotor mast including an outer member defining a channel therethrough and an inner member disposed in the channel through the outer member, wherein the inner member is configured to apply a compressive force to the outer member.

A propulsion system includes a cylindrical shaft member coupled to a motor with a motor frame; said shaft member mechanically coupled to a disc members with radius, to rotate in a dynamically and statically balanced state with said shaft when said motor rotates; the apparatus further comprising a power source to supply power to said motor to rotate said shaft member with said disc members; each said disc members comprising an annular radial array of material segments extending radially to the radius; said material segments comprising of a material that responds to electromagnetic fields to change shape radially on said disc member; such that when power is supplied to rotate the motor, the motor rotates the disc members and when each such material segment rotates to an angular location of the shaft member relative to a fixed point on the motor frame, each said material segment is supplied with said electromagnetic field; and said material responds to said electromagnetic field to change its shape radially to a new radius different from, at said angular location, and such that the mass of said material segment is redistributed radially at the radius R2 in said material segment in said angular location; and such that the difference in centripetal forces acting on said change in radial location from R1 to R2 at said angular location creates a radial force on said shaft member in the direction of the said angular location.

A control system for a multi-rotor aircraft is described that results in lower operating noise. Allowing blades to flap during flight reduces aerodynamic interference as blades pass by other aircraft components, such as wings or the fuselage. Pitch links coupled to a rotational swashplate can be used to allow flapping during flight. The swashplates can allow the canting of the rotors to change a rotational or out-of-plane angle of the blades to decrease noise.

A method of controlling a multi-rotor aircraft (1) including at least five, preferably at least six, lifting rotors (2; R1-R6), each having a first rotation axis which is essentially parallel to a yaw axis (z) of the aircraft (1), and at least one forward propulsion device (3), preferably two forward propulsion devices (P1, P2), the at least one forward propulsion device having at least two rotors (P1_R1, P1_R2, P2_R1, P2_R2) that are arranged coaxially with a second rotation axis which is essentially parallel to a roll axis (x) of the aircraft. The at least one or each of the forward propulsion devices (3, P1, P2) being arranged at a respective distance (+y, −y) from said roll axis (x). The method further includes: using at least one of the rotors of the at least one forward propulsion device to control the aircraft's moment about the yaw and/or roll axes independently from each other.

A method of controlling a multi-rotor aircraft (1) including at least five, preferably at least six, lifting rotors (2; R1-R6), each having a first rotation axis which is essentially parallel to a yaw axis (z) of the aircraft (1), and at least one forward propulsion device (3), preferably two forward propulsion devices (P1, P2), the at least one forward propulsion device having at least two rotors (P1_R1, P1_R2, P2_R1, P2_R2) that are arranged coaxially with a second rotation axis which is essentially parallel to a roll axis (x) of the aircraft. The at least one or each of the forward propulsion devices (3, P1, P2) being arranged at a respective distance (+y, −y) from said roll axis (x). The method further includes: using at least one of the rotors of the at least one forward propulsion device to control the aircraft's moment about the yaw and/or roll axes independently from each other.

A negative hinge offset rotor head for a coaxial helicopter, the rotor head having two or more flapping rotor blades having outer and inner tips, the inner tips rotatably attached to a hinge attachment rotated by a driveshaft where the driveshaft is positioned between the rotor blades and the rotor blades' respective hinge attachment.

A negative hinge offset rotor head for a coaxial helicopter, the rotor head having two or more flapping rotor blades having outer and inner tips, the inner tips rotatably attached to a hinge attachment rotated by a driveshaft where the driveshaft is positioned between the rotor blades and the rotor blades' respective hinge attachment.

A flight control system for a rotary-wing aircraft includes a shape sensor and a controller. The shape sensor is configured to measure a shape of a rotor blade during movement of the rotor blade. The controller is communicably coupled to the shape sensor and is configured to (i) receive, from the shape sensor, a first signal indicative of a first blade shape; (ii) receive a blade characteristic regarding the rotor blade; and (iii) determine at least one of a moment or force associated with the rotor blade based on the first signal and the blade characteristic.