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.

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.

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.

This disclosure relates to improved techniques for electronic noise cancellation in aircraft and other enclosures. In certain embodiments, an electronic noise cancellation device can be installed in an aircraft. In certain embodiments, the electronic noise cancellation device can include a housing that integrates: one or more audio input devices that are configured to receive an input audio signal; one or more audio output devices configured to output a noise cancellation signal; one or more lighting components; and at least one connector that enables the electronic noise cancellation device to be coupled to an overhead service component of the aircraft. In certain embodiments, the electronic noise cancellation device is adapted to be received in a lighting socket of the overhead service component included within an aircraft enclosure. Other embodiments are disclosed.

A shroud for an air moving device includes a shroud body configured to at least partially surround one or more blades. The shroud body defines an annular cavity and an annular opening. The annular opening faces the one or more blades. The shroud also includes a Helmholtz resonator defined by the annular cavity and the annular opening. The Helmholtz resonator is configured to reflect sound generated by the one or more blades out of the shroud body.

An aircraft having a fuselage, an aircraft body, at least one aircraft engine system and a feature. The fuselage defining a longitudinal centerline. The at least one aircraft engine system defining an axial centerline. The at least one aircraft engine system having a nacelle and at least one rotatable propeller. The at least one rotatable propeller having a free end that is spaced radially outward from the nacelle with respect to the axial centerline. The feature shaped to alter a flow of air between the aircraft body and the at least one rotatable propeller. The feature having a continuous rounded contour when viewed along a vertical plane normal to the longitudinal centerline and intersecting the feature.

The rotary airfoil 100 defines a cross section and a span, wherein the cross section is a function of the point along the span (e.g., spanwise point) and defines an upper surface and a lower surface at each spanwise point. The rotary airfoil 100 also defines, at a cross section, a lift coefficient (C.sub.L) that is a function of the angle of attack at which the airfoil is rotated through the air. The system can optionally include: a rotor hub to mount the rotary airfoil, a tilt mechanism to pivot the rotary airfoil between a forward configuration and a hover configuration, and a pitching mechanism to change the angle of attack of the rotary airfoil 100.

A material for use in interacting with a flow is provided. The material comprises an interface surface adapted to move in response to a pressure associated with at least one wave in a flow exerted on the interface surface; and a subsurface feature extending from the interface surface, the subsurface feature comprising a phononic crystal or locally resonant metamaterial adapted to receive the at least one wave having the at least one frequency based upon the pressure from the flow via the interface surface and alter a phase of the at least one wave. The subsurface material comprises a lattice-structured material comprising a plurality of structural elements and a plurality of voids, and the interface surface is adapted to vibrate at a frequency, phase, and amplitude in response to the altered phase of the at least one wave. A method for interacting with a flow is also provided.

Structural subsurface materials and subsurface structures adapted for interacting with a flow are provided. In one example, a structural subsurface material or subsurface structure is provided for use in interacting with a fluid or solid flow. The structural subsurface material comprises a flow interface surface adapted to be disposed adjacent a flow and a subsurface feature comprising a structural material. The subsurface feature extends away from the flow interface surface. The subsurface feature alters an effective structural compliance of the flow interface surface relative to the flow such that the flow experiences an alteration in surface skin-friction drag and/or in kinetic energy in a turbulent flow. In other implementations, methods of controlling a flow with a structural subsurface material or a subsurface structure are provided. Further, methods of designing structural subsurface materials and subsurface structures for interacting with a flow are also provided.

A system that optimizes the shape or configuration of an aircraft to minimize ground overpressure shock strength while in supersonic flight over speed restricted terrain and to morph to an optimized configuration for drag minimization while over unrestricted terrain.