Abstract: A method and apparatus is disclosed for producing propulsion underwater with minimal acoustical emission. In basic concept, the method comprises the expulsion and sucking of liquid into and out of a liquid port of a watercraft in a manner generating compression and expansion waves adjacent the liquid port. Such expansion and compression waves generate a positive net thrust on the watercraft in a direction opposite that of their expulsion. Also disclosed is a method and apparatus for reducing the drag caused by hull skin friction by actively increasing the momentum of the liquid stream boundary layer adjacent a watercraft via the expulsion of fluid (liquid or gas) from ports in the hull of such a watercraft.

Abstract: A method and apparatus is disclosed for producing propulsion underwater with minimal acoustical emission. In basic concept, the method comprises the expulsion and sucking of liquid into and out of a liquid port of a watercraft in a manner generating compression and expansion waves adjacent the liquid port. Such expansion and compression waves generate a positive net thrust on the watercraft in a direction opposite that of their expulsion. A reciprocating member and an actuator are also disclosed for generating the forces and energy necessary to create the expansion and compression waves.

Abstract: A method and apparatus is disclosed for producing propulsion underwater with minimal acoustical emission. In basic concept, the method comprises the expulsion and sucking of liquid into and out of a liquid port of a watercraft in a manner generating compression and expansion waves adjacent the liquid port. Such expansion and compression waves generate a positive net thrust on the watercraft in a direction opposite that of their expulsion. Also disclosed is a method and apparatus for reducing the drag caused by hull skin friction by actively increasing the momentum of the liquid stream boundary layer adjacent a watercraft via the expulsion of fluid (liquid or gas) from ports in the hull of such a watercraft.

Abstract: A method and apparatus is disclosed for producing propulsion underwater with minimal acoustical emission. In basic concept, the method comprises the expulsion and sucking of liquid into and out of a liquid port of a watercraft in a manner generating compression and expansion waves adjacent the liquid port. Such expansion and compression waves generate a positive net thrust on the watercraft in a direction opposite that of their expulsion. A reciprocating member and an actuator are also disclosed for generating the forces and energy necessary to create the expansion and compression waves.

Abstract: A linear electromagnetic zero net mass jet (ZNMJ) actuator incorporating a pair of permanent magnets. The magnets are arranged such that an air gap is formed therebetween and further such that opposite poles of the magnets are arranged on opposite sides of the air gap. This concentrates the flux field across the air gap. A coil is disposed in the air gap. The coil is attached to a diaphragm which acts as a piston. When an electric current is applied to the coil, the flux field across the air gap causes a rapidly oscillating motion of the diaphragm. The actuator provides an increased rate of displacement of the piston as compared to single magnet ZNMJ actuators, and thus provides a higher momentum output across a broad frequency and voltage spectrum than conventional ZNMJ actuators using a single magnet.

Abstract: A linear electromagnetic zero net mass jet (ZNMJ) actuator incorporating a pair of permanent magnets. The magnets are arranged such that an air gap is formed therebetween and further such that opposite poles of the magnets are arranged on opposite sides of the air gap. This concentrates the flux field across the air gap. A coil is disposed in the air gap. The coil is attached to a diaphragm which acts as a piston. When an electric current is applied to the coil, the flux field across the air gap causes a rapidly oscillating motion of the diaphragm. The actuator provides an increased rate of displacement of the piston as compared to single magnet ZNMJ actuators, and thus provides a higher momentum output across a broad frequency and voltage spectrum than conventional ZNMJ actuators using a single magnet.

Abstract: A porous surface on an aircraft structure driven with oscillating positive and negative pressures is used as an active control device for attenuating negative aerodynamic interactions. The porous surfaces can be driven with positive and negative pressures either continuously or when predetermined flight conditions are present. The porous surfaces can be used on rotor blades to reduce BVI noise in descent flight conditions. The porous surfaces can be configured on rotor blades for affecting blade variable twist in accordance with various flight conditions, and can further be incorporated for reducing rotor hub vibrations as well. Porous surfaces placed on aerodynamic surfaces below the rotor blades of a tiltrotor aircraft can attenuate or eliminate download and fountain flow conditions.

Abstract: A jet actuator positioned within a hollow space in an aerodynamic structure for controlling the flow over an aerodynamic surface thereof includes a movable member linearly displaced by a voice coil mechanism and a flexible diaphragm defining a compression chamber open to the exterior of the aerodynamic surface through an orifice. Reciprocal displacement of the movable member changes the shape of the flexible diaphragm to alternately expel fluid (e.g., air) from and pull fluid into the compression chamber through the orifice. The movable member includes a pair of pistons joined by a cross element, one of the pistons being attached to the flexible diaphragm. In one embodiment, the flexible diaphragm comprises a bladder sealed around the orifice. The movable member is desirably made of composite material to reduce its inertia, and at least the piston attached to the flexible diaphragm may be stiffened with a composite laminate structure.

Abstract: A jet actuator positioned within a hollow space in an aerodynamic structure for controlling the flow over an aerodynamic surface thereof includes a movable member linearly displaced by a voice coil mechanism and a flexible diaphragm defining a compression chamber open to the exterior of the aerodynamic surface through an orifice. Reciprocal displacement of the movable member changes the shape of the flexible diaphragm to alternately expel fluid (e.g., air) from and pull fluid into the compression chamber through the orifice. The movable member includes a pair of pistons joined by a cross element, one of the pistons being attached to the flexible diaphragm. In one embodiment, the flexible diaphragm comprises a bladder sealed around the orifice. The movable member is desirably made of composite material to reduce its inertia, and at least the piston attached to the flexible diaphragm may be stiffened with a composite laminate structure.

Abstract: An actively controlled helicopter rotor blade includes a trailing edge flap actuated by a fast-acting actuator. A lightweight, rugged, fast-acting actuator suitable for use as the flap actuator comprises a pair of column actuators composed of a smart material such as piezoelectric, magnetostrictive, shape memory alloy or other material that exhibits a shape change when subjected to an external stimulus. Each of the column actuators is composed of multiple piezoelectric ceramic actuator elements bonded together to form the individual columns. Each of the column actuators engages the base of an actuator tube that, in turn, is urged against the column actuators by a tension member. Differential voltage applied to the columns causes a differential elongation of the column actuators, which causes the actuator tube to pivot about an axis proximal the tips of the column actuators. The movement of the actuator tube is coupled by a linkage to the rotor blade flap.

Abstract: An active control system for reducing blade-vortex-interaction (BVI) noise generated by a rotor blade. The active control system includes a pressure sensor assembly, a device for changing a lift generated by the rotor blade, and a controller for activating the device upon a detected change in air pressure by the sensor assembly. The sensor assembly is disposed in close proximity to the rotor blade, and is adapted to detect a change in air pressure on a surface of the rotor blade near a leading edge of the rotor blade. The device is adapted to be activated by the controller, to thereby change a lift of the rotor blade. The controller activates the device to change a lift of the rotor blade in order to introduce a compensating pressure onto the surface of the rotor blade. This compensating pressure attenuates the magnitude of the change of air pressure.

Abstract: An active control device for use on an aerodynamic structure is provided. The aerodynamic structure includes an outer aerodynamic skin and an interior volume, wherein the outer aerodynamic skin surrounds the interior volume. The active control device includes at least one aperture disposed on the outer aerodynamic skin and a diaphragm disposed in the interior volume of the aerodynamic structure. The at least one aperture connects the outer aerodynamic skin to the interior volume, and the diaphragm in the interior volume is movable between a first position and a second position. Movement of the diaphragm from the first position to the second position pushes air through the at least one aperture and out of the interior volume. Movement of the diaphragm from the second position to the first position draws air through the at least one aperture and into the interior volume. The diaphragm may be circular, or may be oval-shaped.

Abstract: A pressurized porous surface near the leading edge of a rotorcraft blade, is designed to be used as an active control device which alleviates the aerodynamics of blade vortex interactions (BVI) and thus the impulsive BVI noise levels and signature. The pressurized porous surface can be actuated on an azimuth-dependent deployment schedule or actuated continuously. The pressurized porous surface is supplied with either positively pressurized air, negatively pressurized air, or a combination of both, when actuated. The pressurized porous surface targets the local blade aerodynamics, rather than the vortex strength or blade/vortex separation distance.