A method of improving a blade and also an improved blade and a advancement propeller including the improved blade. The radius of the initial leading edge circle of each airfoil of the blade is increased, and its leading edge is moved away from a pressure side half-airfoil towards a suction side half-airfoil, thereby modifying the airfoil of each cross-section of the blade and modifying the camber of each airfoil. Consequently, the absolute value of the negative stall angle of attack of the blade is increased, thus making it possible to increase the aerodynamic performance of the blade under a negative angle of attack compared with a blade that is not modified, and without significantly degrading its aerodynamic performance under a positive angle of attack.

A rotor system is provided in one example embodiment and may include a rotor duct; at least one rotor blade, wherein the at least one rotor blade comprises a tip end; and a multi-material tip extension affixed at the tip end of the at least one rotor blade, wherein the multi-material tip extension comprises an inboard portion fabricated from a first material and an outboard portion fabricated from a second material, wherein the second material is different than the first material.

A vertical landing and take-off aircraft VTOL transitions from a vertical takeoff state to a cruise state where the vertical takeoff state uses propellers to generate lift and the cruise state uses wings to generate lift. The aircraft has an M-wing configuration with propellers located on the wingtip nacelles, wing booms, and tail boom. The wing boom and/or the tail boom can include boom control effectors. Hinged control surfaces on the wings, tail boom, and tail tilt during takeoff and landing to yaw the vehicle. The boom control effectors, cruise propellers, stacked propellers, and control surfaces can have different positions during different modes of operation in order to control aircraft movement and mitigate noise generated by the aircraft.

A rotor unit is disclosed. The rotor unit includes a hub and a stacked rotor blade. The hub is configured to rotate about an axis in a first rotation direction. The stacked rotor blade is rotatable about the axis and further includes a first blade element and a second blade element. The first blade element has a first leading edge and the second blade element has a second leading edge. The blade elements are arranged in a stacked configuration. A leading edge of the stacked rotor blade is formed by at least a portion of the first leading edge of the first blade element as well as at least as portion of the second leading edge of the second blade element. In some embodiments, the rotor unit is coupled to an unmanned aerial vehicle.

A method for the control of a vertical take-off and landing (VTOL) aircraft which reduces the acoustic profile of the rotary airfoil in hover for VTOL applications. The rotary airfoil incurs an efficiency penalty in order to improve the acoustic performance during hover. The aircraft operates the rotary airfoils of the propeller during hover in the hover angle of attack range, and the aircraft operates the rotary airfoils during forward flight in the forward angle of attack range.

A gas turbine is provided, the gas turbine engine including a turbomachine having an inlet splitter defining in part an inlet to a working gas flowpath and a fan duct splitter defining in part an inlet to a fan duct flowpath. The gas turbine engine also includes a primary fan driven by the turbomachine defining a primary fan tip radius R1, a primary fan hub radius R2, and a primary fan specific thrust rating TP; and a secondary fan downstream of the primary fan and driven by the turbomachine, the secondary fan defining a secondary fan tip radius R3, a secondary fan hub radius R4, and a secondary fan specific thrust rating TS; wherein the gas turbine engine defines an Effective Bypass Area, and wherein a ratio of R1 to R3 equals

[00001]$\frac{R_1}{R_3}=\sqrt{\left(EFP\right)\frac{\left(1-{\mathrm{RqR}}_{\mathrm{Sec}.-\mathrm{Fan}}^2\right)}{\left(1-{\mathrm{RqR}}_{\mathrm{Prim}.-\mathrm{Fan}}^2\right)}\left(\frac{T_P}{T_S}\right)\left(EBA\right)}.$

This invention describes a rotating wing that provides lift to an aircraft and that is driven by autorotation. It is a naturally stable rotating wing as it does not generate torque and is very safe because it uses autorotation at all times to drive its blades. The design of the blades allows you to use the autorotation in two different ways. The first dependent on the airflow created by moving the aircraft from one place to another and which provides a cruise flight mode and the second independent of the aircraft's movement from one place to another to provide a static flight mode that includes the ability to take off and land vertically, as well as hover at a static point in the air.

This invention describes a rotating wing that provides lift to an aircraft and that is driven by autorotation. It is a naturally stable rotating wing as it does not generate torque and is very safe because it uses autorotation at all times to drive its blades. The design of the blades allows you to use the autorotation in two different ways. The first dependent on the airflow created by moving the aircraft from one place to another and which provides a cruise flight mode and the second independent of the aircraft's movement from one place to another to provide a static flight mode that includes the ability to take off and land vertically, as well as hover at a static point in the air.

Various mechanisms and methods for altering sound output from an unmanned aerial vehicle (UAV) are disclosed. The UAV can have a drive system comprising a motor or a plurality of motors, and a processor operatively coupled to the drive system to control operation of the drive system. The UAV can further have a plurality of propellers that are rotatably drivable by the drive system, the plurality of propellers having physical characteristics such that, when drivingly rotated to maintain the UAV in stable flight, a first of the plurality of propellers emits a first note, and a second of the plurality of propellers emits a second, different note, a combination of the first and second notes producing a consonant sound.

Various mechanisms and methods for altering sound output from an unmanned aerial vehicle (UAV) are disclosed. The UAV can have a drive system comprising a motor or a plurality of motors, and a processor operatively coupled to the drive system to control operation of the drive system. The UAV can further have a plurality of propellers that are rotatably drivable by the drive system, the plurality of propellers having physical characteristics such that, when drivingly rotated to maintain the UAV in stable flight, a first of the plurality of propellers emits a first note, and a second of the plurality of propellers emits a second, different note, a combination of the first and second notes producing a consonant sound.