Patent Application
20070029403
The present invention relates to air vehicles and, more particularly, to air vehicles having an active flow control system for controlling vehicle attitude during transonic flight.
Attitude of air vehicles, including aircraft and missiles, is typically controlled using systems having aerodynamic control surfaces, such as flaps, spoilers, ailerons, rudders, elevators, and fins. These traditional flight control systems have numerous disadvantages. For example, these systems generally require substantial infrastructure, including hinge structures, hydraulic or pneumatic actuators, and complex under-surface fluid delivery systems to drive the actuators. This infrastructure increases vehicle complexity, thereby increasing manufacturing cost, and increases weight, thereby reducing vehicle performance.
Another disadvantage of traditional flight control systems is the relatively large surface discontinuities and level mismatches between the aerodynamic control surfaces and the adjacent air vehicle surface. That is, the control surfaces necessitate gaps between them. Further, the vehicle surface and the control surfaces are often not flush with each other. These gaps and surface level mismatches reduce vehicle performance by degrading the aerodynamic characteristics of the vehicle.
Other disadvantages of traditional flight control systems include the relatively high maintenance cost associated with repairing the complex infrastructure and the relatively slow response time to actuate the aerodynamic control surfaces for changing vehicle attitude. In addition, traditional air vehicle control systems produce relatively high amounts of unwanted aeroacoustic noise during transonic flight.
The present invention relates to an air vehicle comprising a fuselage, a first wing, and a second wing, wherein each wing extends laterally from the fuselage and has a leading edge, a trailing edge, a first surface extending between the edges, and a second surface extending between the edges opposite the first surface. The air vehicle further includes an upstream orifice and a downstream orifice positioned adjacent each other on at least one of the first surfaces, wherein each upstream orifice is positioned closer to the leading edge of the respective wing than the corresponding downstream orifice and each second surface is substantially free of orifices. In addition, the air vehicle includes an actuator positioned within each wing having orifices positioned thereon between the leading edge and the trailing edge and between the first surface and the second surface. Each actuator is operatively connected to the upstream and downstream orifices positioned on the respective wing for selectively creating a negative pressure differential at the corresponding upstream orifice so air adjacent the upstream orifice is drawn toward the upstream orifice and a positive pressure differential at the corresponding downstream orifice so air adjacent the downstream orifice is pushed away from the downstream orifice. The upstream orifice is configured so air moves into the upstream orifice at an angle of about 90° with respect to the first surface and the downstream orifice is configured so air moves out of the downstream orifice at an angle of about 90° with respect to the first surface.
In another aspect, the present invention includes a system for controlling the attitude of a flight vehicle having a first surface and a second surface opposite the first surface. The system includes an upstream orifice and a downstream orifice positioned in the first surface. The second surface is substantially free of orifices. The system further includes an actuator positioned between the two surfaces and operatively connected to the orifices for creating a negative pressure differential at the upstream orifice so fluid moves toward the upstream orifice and a positive pressure differential at the downstream orifice so fluid moves away from the downstream orifice. The upstream orifice is configured so air moves into the upstream orifice at an angle of about 90° with respect to the first surface and the downstream orifice is configured so air moves out of the downstream orifice at an angle of about 90° with respect to the first surface.
In yet another aspect, the present invention includes a method for controlling the attitude of an air vehicle including an airfoil having first and second surfaces, upstream and downstream orifices positioned in the first surface, and an actuator positioned in the airfoil and operatively connected to the orifices. The method includes operating the air vehicle so a transonic condition exists adjacent the airfoil. The method further includes selectively drawing air into the upstream orifice from a supersonic flow region adjacent the first surface at an angle of about 90° with the first surface and selectively directing air out of the downstream orifice and into the supersonic flow region at an angle of about 90° with the first surface. The method also includes preventing air from being drawn into or directed out of the airfoil through the second surface.
In still another aspect, the present invention includes a method for controlling the attitude of a vehicle having a first surface, a second surface opposite the first surface, and upstream and downstream orifices positioned adjacent each other in the first surface. The method comprises operating the vehicle so transonic conditions exist about the vehicle. The method further comprises selectively drawing air into the upstream orifice from a supersonic flow region adjacent the first surface at an angle of about 90° with the first surface and selectively pushing air out of the downstream orifice and into the supersonic flow region at an angle of about 90° with the first surface.
Other aspects of the present invention will be in part apparent and in part pointed out hereinafter.
Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.
The present invention relates to air vehicles and, more particularly, to air vehicles having an active flow control system for controlling vehicle attitude during transonic flight. Although the devices, systems, and methods for using them consistent with the present invention are primarily discussed with reference to air vehicles, they may be applied to other products (e.g., watercraft and land vehicles) without departing from the scope of the present invention.
Referring now to the figures, and more particularly to
Although the orifices 26, 28 represent discontinuities in the surface 22 of the air vehicle 10, these discontinuities have less affect on vehicle aerodynamics than the effects of the discontinuities (e.g., gaps), level mismatches, and structure (e.g., hinges) associated with traditional aerodynamic control surfaces. In one embodiment, the orifices 26, 28 are used on an air vehicle (not shown) in combination with one or more conventional control surfaces. Although the first surfaces 22 are shown as upper surfaces and the second surfaces 24 are shown as lower surfaces of the wings 14, 16, the first surfaces may be the lower surfaces and the second surfaces may be the upper surfaces without departing from the scope of the present invention.
As shown in
A timing relationship between the drawing of air into the upstream orifice 26 and the pushing of air away from the downstream orifice 28 may be characterized by a phase differential. The drawing and pushing of air may occur in phase (i.e., 0° phase difference), completely out of phase (i.e., 180° phase difference), or anywhere between. In one embodiment, the actuator 30 is selectively operated to vary the phase differential between in phase and completely out of phase. A waveform of a velocity of air moving into the upstream orifice 26 and a waveform of a velocity of air moving out of the downstream orifice 28 with respect to time may have various shapes. In one embodiment the waveforms each have a sinusoidal shape, increasing from zero velocity to a maximum velocity and then gradually decreasing back to zero velocity. In another embodiment, the waveforms are square, quickly stepping from zero velocity to a maximum velocity, continuing at the maximum velocity, and then quickly stepping back to zero velocity.
The orifices 26, 28 are positioned within the supersonic flow region II and upstream of the shock wave SW when the air vehicle 10 is traveling at transonic conditions. The positions of the orifices 26, 28 can be described with respect to the chord of the wing 14. A chord position can be described by the percentage of the total chord the orifices 26, 28 lie from the leading edge 18. Although the orifices 26, 28 may be located at other chord positions without departing from the scope of the present invention, in one embodiment the upstream orifice is located at a chord position of between about 50% and about 70% and the downstream orifice is located at a chord position of between about 65% and about 90% and the downstream orifice should typically be positioned downstream of the upstream orifice. For example, for the NACA-64A010 airfoil, 53% and 68% are effective chord positions for the first and second orifices 26, 28, respectively, for implementing the present invention. As another example, in
Although the orifices 26, 28 may be configured so air is drawn toward the upstream orifice and pushed away from the downstream orifice at other angles without departing from the scope of the present invention, in one embodiment the upstream orifice is configured so the air is drawn toward the upstream orifice at an angle θ of between about 80° and about 100° with respect to the surface 22 in the region adjacent the orifice and the downstream orifice is configured so air is pushed away from the downstream orifice at an angle ψ of between about 80° and about 100° with respect to the surface in the region adjacent the orifice. As shown in
Although the actuator 30 may be other types without departing from the scope of the present invention, in one embodiment, the actuator is a piezoelectric actuator. Other actuator types usable in the present invention include pneumatic, electromagnetic, and other electromechanical actuators, such as those including a cam or piston (not shown). A benefit of using these actuators is quick response time compared to traditional flight control systems. The actuator 30 shown in
The membrane 62 is made of a flexible material that allows the membrane to flex between a concave position 68 and a convex position 70. As will be appreciated by those skilled in the art, when the actuator 30 is a piezoelectric actuator, the membrane 62 moves between the concave and convex positions 68, 70 in response to electrical currents applied to the membrane. The membrane 62 can be intermittently moved between its concave and convex positions 68, 70 to intermittently create a negative pressure at the upstream orifice 26 and a positive pressure at the downstream orifice 28. When the membrane 62 moves toward the concave position 68, pressure within the first chamber 64 decreases to a pressure lower than an ambient pressure of air outside of the wing 14 adjacent the orifices 26, 28. Thus, air exterior to the wing 14 and adjacent the upstream orifice 26 is drawn toward and through the one-way valve 52 associated with the upstream orifice. When the membrane 62 moves toward the convex position 70, pressure within the chamber 64 increases to a pressure higher than an ambient pressure of air outside of the wing 14 adjacent the orifices 26, 28. Thus, air within the first chamber 64 is pushed through and away from the one-way valve 54 associated with the downstream orifice 28. As described above, the upstream orifice 26 can be configured so air is drawn to it normal (i.e., at 90°) to the adjacent first surface 22 and the downstream orifice 28 can be configured so the air is pushed away from it normal to the first surface.
The actuator 30 may be vented (not shown) to facilitate movement of the membrane 62. For example, without venting, air pressure in the second chamber 66 is greatly increased as the membrane 62 attempts to move toward the concave position 68. The electrically actuated membrane 62 must move with a force sufficient to contract the air in the second chamber 66 enough to allow the membrane 62 to reach the concave position 68. Further, air accelerating through the supersonic region II over the wing 14 creates a negative pressure on the outside of the wing adjacent the orifices 26, 28. Thus, with a non-vented actuator, the membrane 62 must work against the increasing force resulting from the increasing pressure in the second chamber 66 and the opposite force resulting from the negative pressure differential above the wing surface 22 as it moves towards its concave position 68. These two forces impede actuator operation and may render it inoperable. Venting the actuator 30 allows free movement of the membrane 62 by balancing relative pressures. As will be appreciated by those skilled in the art, the actuator 30 may be vented in a variety of ways.
The membrane 62 can be continuously moved between its concave and convex positions 68, 70 with a desired frequency to create a pulsing or periodic effect. Although the actuator 30 may operate at other frequencies without departing from the scope of the present invention, in one embodiment the actuator 30 operates at a frequency of between about 150 Hz and about 350 Hz. As will be appreciated by those skilled in the art, the amount and force of the air being drawn into and directed out of the actuator 30 depends on the configuration of the actuator, including the size of the membrane 62, and the intensity with which the membrane is displaced. The air being drawing into and directed out of the actuator 30 affects air vehicle flight by affecting the air traveling over the surface 22 of the wing 14. The force, volume, and frequency at which the actuator 30 draws and pushes air determines how the actuator affects the air traveling over the wing 14 and thus the flight of the air vehicle. The primary flight characteristics affected by the actuator 30 are lift, drag, and moments.
Having orifices 26, 28 instead of traditional control surfaces (not shown) reduces aeroacoustic noise, such as cabin noise, by lowering the size and number of gaps in the surfaces 22, 24 of the wings 14, 16 and substantially eliminating level differences on those surfaces. Further, aeroacoustic noise that may result from shock waves during flight at transonic speeds can be attenuated through selective operation of the actuator 30. For example, characteristics (e.g., the path) of the air traveling adjacent the wing 14 can be changed to reduce the aeroacoustic noise associated with the shock wave.
The flight system, including the actuator 30 and two orifices 26, 28, is referred to as a dual point air flow control system because flight conditions can be controlled using these components. The particular force, volume, and frequency necessary to create particular changes in air vehicle 10 flight depends on geometries of the airfoil and flight conditions, such as the angle of attack α and Mach number at which the air vehicle is moving. Thus, all of these can be adjusted to control air vehicle attitude and/or attenuate aeroacoustic noise during flight. The actuator 30 may be operated to move the shock wave in a predetermined manner to control vehicle attitude. Further regarding attitude control, depending on airfoil geometries and flight conditions, the force, amount, and frequency of air pulsed in and out of the orifices 26, 28 can affect lift, drag, side forces, and/or moments (i.e., yaw, pitch, and roll) experienced by the airfoil. These forces and/or moments are controlled by controlling the shape of the aerodynamic characteristics passing adjacent the airfoil. In one embodiment, the amount and force of air passing through the orifices 26, 28 remain generally constant. In this embodiment, the frequency at which the actuator 30 is operated and changes to the frequency primarily determine the affects the actuator 30 has on the aerodynamic characteristics of the airfoil at any given angle of attack α and Mach number. In embodiments where orifices 26, 28 and an actuator 30 are employed on only one wing 14 of a dual wing air vehicle 10, vehicle roll can be controlled by increasing or decreasing the amount of lift on that wing 14. In embodiments where orifices 26, 28 and an actuator 30 are employed on both wings 14, 16, the vehicle can be rolled by increasing or decreasing the lift on either of the wings 14, 16 by simultaneously increasing the lift on one of the wings 14, 16 and decreasing the lift on the other wing 16, 14, or by affecting a lift differential between the wings. In embodiments where orifices 26, 28 and an actuator 30 are employed on only one wing 14 of a dual wing air vehicle 10, vehicle yaw can be controlled by increasing or decreasing the amount of drag on that wing 14. In embodiments where orifices 26, 28 and an actuator 30 are employed on both wings 14, 16, the vehicle can be yawed by increasing or decreasing the drag on either of the wings 14, 16 by simultaneously increasing the drag on one of the wings 14, 16 and decreasing the drag on the other wing 16, 14, or by affecting a drag differential between the wings. Air may also be selectively drawn into the upstream orifice 26 and directed out of the downstream orifice 28 to control pitch. For example, the actuator 30 may be selectively operated to create a level differential between the leading edge and trailing edge of the wings thereby controlling vehicle pitch.
Application of the present invention is not limited to use on air vehicles 10 having fixed wings 14, 16. For example, orifices can be positioned on other air vehicle surfaces (e.g., aircraft or missile fuselage surfaces) and on rotor blades.
When introducing elements of the present invention or the preferred embodiment(s) thereof, the articles “a”, “an”, “the”, and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including”, and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.
As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.
