An acoustic panel (1) includes a plate (2) made of an acoustic absorbing material (3), as well as a resistive skin (4) and a backing skin (6) arranged respectively on both sides of the plate (2), the acoustic panel (1) including acoustic elements (8) able to carry out an acoustic absorption, each of them being arranged in a housing (7) provided in the plate (2) with an opening (9) in front of the resistive skin (4). The combination of the plate (2) and the acoustic elements (8) allows to combine the sound attenuation properties of these two types of elements and to increase the frequency range of sounds that can be attenuated by the acoustic panel (1), without increasing the dimension.

Systems and methods to actively control vibrations affecting an aerial vehicle are described. Vibrations affecting a location of interest on an aerial vehicle may be measured, and phases of one or more propellers of the aerial vehicle may be determined. Based on the measured vibrations and determined phases of propellers, adjustments to the phases of the propellers may be determined to modify the vibrations affecting the location of interest. In this manner, vibrations at a location of interest on an aerial vehicle may be reduced, minimized, increased, induced, or otherwise modified as desired.

A request for transport services that identifies a rider, an origin, and a destination is received from a client device. Eligibility of the request to be serviced by a vertical take-off and landing (VTOL) aircraft is determined based on the origin and the destination. A transportation system determines a first and a second hub for a leg of the transport request serviced by the VTOL aircraft and calculates a set of candidate routes from the first hub to the second hub. A provisioned route is selected from among the set of candidate routes based on network and environmental parameters and objectives including pre-determined acceptable noise levels, weather, and the presence and planned routes of other VTOL aircrafts along each of the candidate routes.

A noise reduction system for air mobility, may include a plurality of propeller modules provided on the air mobility and each including an inverter, a motor electrically connected to the inverter, and a propeller mounted to the motor; and a control unit configured to perform PWM control of power to be provided to the inverters to reduce noise attributable to carrier frequencies generated by the plurality of inverters or reduce noise attributable to fundamental frequencies generated by the plurality of motors.

According to the present disclosure there is provided an arrangement for influencing liquid flow, the arrangement comprising: a first section selectively configurable to provide a vortex generator surface to induce vortices in the liquid flow. The arrangement further comprises a second section, wherein the first section and second section are movable relative to one another to provide the vortex generator surface.

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.

An advanced acoustic awareness platform configured to classify environmental sounds. The advanced acoustic awareness platform comprises an audio signal acquisition sensor array and one or more processors programmed to augment the audio signal, extract features for the audio signal, visualize, and classify the signal using one or more labels. In at least one embodiment, the signal is classified based on transfer learning associated with a pretrained machine learning model.

According to the present disclosure there is provided an arrangement for influencing fluid flow, the arrangement comprising: a first section selectively configurable to provide a vortex generator surface, the vortex generator surface comprising a series of laterally aligned projections, to induce vortices in the liquid flow.

An anti-torque system for a rotorcraft includes a first tail fan assembly including a plurality of first fan blades and a second tail fan assembly including a plurality of second fan blades. The first tail fan assembly has a larger diameter than the second tail fan assembly. The first fan blades have a larger rotational inertia than the second fan blades such that the second fan blades experience a larger angular acceleration than the first fan blades in response to torque, thereby providing yaw control for the rotorcraft.

A fan blade assembly having integrated microphones to measure acoustic energy levels uses speakers controlled by a control unit to output anti-acoustic energy vibrations. Specific embodiments wherein the speakers and microphones are radially displaced around the fan blade assembly are also disclosed.