Patent Application
20070215751
This invention pertains to aircraft, in general, and in particular, to an unmanned aerial vehicle (“UAV”) having a pair of engines placed forward and aft of its center of gravity to provide it with vertical takeoff and landing (“VTOL”) capability, including hovering, as well as high agility and maneuverability at both very low and very high speeds.
An unmanned aircraft (“UA”), or unmanned aerial vehicle (“UAV”), is a powered, heavier-than-air, aerial vehicle that does not carry a human operator, or pilot, and which uses aerodynamic forces to provide vehicle lift, can fly autonomously or be piloted remotely, can be expendable or reusable, and can carry a lethal or a non-lethal payload. Thus, ballistic or semi-ballistic vehicles, cruise missiles, and artillery projectiles are not considered UAVs.
In recent conflicts around the world, including the global war on terrorism, UAVs have proven to be very effective, both as a surveillance and intelligence-gathering tool, and as a weapons-delivery platform. Because they are unmanned, and cost substantially less to produce and operate than conventional manned aircraft, UAVs are capable of providing effective surveillance of an enemy, and/or of effecting a devastating attack upon him, while denying him either a high-value target or a potential captive in exchange.
An important UAV task or mission that has emerged recently in the war on terrorism is the need for an aerial vehicle that can enter an urban target environment, such as a city with tall buildings, at a relatively high speed, hover and maneuver (e.g., weave between the buildings) within that environment at a relatively low speed while surveilling a very specific target area and/or deploying a weapon payload against the target in such a way as to minimize collateral damage, and then exit the area at a relatively high speed. This necessitates an aerial vehicle that can carry a relatively heavy payload (i.e., ordinance, cameras, sensors or the like), is extremely maneuverable (i.e., can effect quick changes in altitude and very small turn-radii) at slow speeds, and has a high speed (i.e., high subsonic) flight capability.
The prior art technique for meeting this need has been either to deploy a large, fast vehicle lacking low speed maneuverability, but carrying a payload capable of destroying a large target area, or alternatively, to carry a much smaller weapon/payload package aboard a relatively smaller vehicle that, although slower than the former, is capable of achieving the requisite low-speed maneuverability. Thus, the disadvantages of the prior art techniques are, on the one hand, that larger vehicles which are capable both of carrying larger payloads and meeting the vehicle speed requirements are too large to fly between buildings in an urban environment and lack the maneuverability at slower speeds required to be effective in that environment, and on the other, that smaller vehicles having low speed agility also have limited speed and payload carrying capabilities.
Accordingly, what is needed is a UAV having VTOL capabilities, including hovering capabilities, that is capable of carrying a relatively large payload, and which is also highly maneuverable at both very low and very high speeds.
In accordance with the exemplary embodiments thereof described herein, the present invention provides a VTOL aircraft, e.g., a UAV, that has a relatively large payload-carrying capability, and yet which is highly maneuverable at both very low and very high speeds.
In one possible exemplary embodiment, the aircraft comprises a conventional airframe having an elongated fuselage with an empennage and a pair of wings. A pair of substantially identical thrust-vectoring engines is respectively mounted on opposite sides of the aircraft such that their respective thrust outlets are located at substantially equal lateral and vertical distances from, and at substantially equal longitudinal distances forward and aft of, the center of gravity (“CG”) of the aircraft. That is, the respective thrust outlets of the engines are located equidistantly below the center of gravity of the aircraft, but one is located forward, and the other aft, of the aircraft's CG.
The thrust vectoring of the engines can comprise either two-dimensional, or preferably, three-dimensional thrust vectoring, and can be effected by means of, e.g., rotatable vanes, flaps or nozzles, or combinations thereof, disposed at the thrust outlets of the engines. In an efficient subsonic embodiment, the engines can comprise turbofan engines.
A vertical takeoff of the aircraft is effected by deflecting or redirecting the exhaust of both engines substantially downward, resulting in a substantially upward thrust of the engines, increasing the thrust of the engines until the combined thrust exceeds the weight of the aircraft and it rises to a selected altitude, and then rotating the direction of thrust of the engines forward until the aircraft accelerates to a speed at which a lifting surface of the UAV, e.g., its wings, produce lift. A vertical landing of the aircraft is effected in substantially the reverse of the foregoing procedure.
During high speed flight, and in addition to the conventional mechanisms normally used to control the aircraft's lift and attitude relative to the conventional roll, pitch and yaw axes extending through its CG, i.e., its wings, elevators, ailerons, and rudders, the pitch of the aircraft can also be effectively controlled by rotating the respective direction of thrust of the engines vertically, i.e., upward or downward and laterally in opposite directions such that the aircraft pitches down or up, respectively, in a selected direction about the pitch axis of the aircraft. Additionally, by rotating the respective directions of thrust of the engines vertically and in opposite directions relative to each other, the aircraft is made to roll in a selected direction about a roll axis of the aircraft. Finally, by rotating the direction of thrust of respective ones of the engines in the either the same or in opposite lateral directions, the aircraft can be made to translate horizontally or yaw in a selected direction about the yaw axis of the aircraft.
During low speed operation of the aircraft, in which the above conventional lift and attitude control mechanisms of the aircraft are substantially ineffective, hovering is achieved by directing the thrusts of the engines substantially upward, increasing the thrust of the engines until the thrust exceeds the weight of the UAV and it rises to a selected altitude, and then decreasing the thrust of the engines until the combined thrust of the engines is equal to the weight of the UAV and it hovers at the selected altitude. Low speed maneuvering of the aircraft is effected by increasing the thrust of the engines until the thrust exceeds the weight of the UAV, and then rotating the respective directions of thrust of the engines in the same or in opposite horizontal directions until an upward component of the thrust is substantially equal to the weight of the aircraft, and the aircraft either translates horizontally in a selected direction, and/or yaws in a selected direction about the yaw axis of the aircraft, in the manner described above.
A better understanding of the above and many other features and advantages of the VTOL UAV of the present invention may be obtained from a consideration of the exemplary embodiments thereof described in detail below, particularly if such consideration is made in conjunction with the appended drawings, wherein like reference numerals are used to identify like elements illustrated in one or more of the figures thereof.
Of importance, the aircraft 10 is provided with a pair of substantially identical thrust-vectoring engines 20, which are respectively mounted on opposite sides of the fuselage 14 of the aircraft such that their respective thrust outlets 22 are located at substantially equal lateral and vertical distances Da and Dv from the aircraft's center of gravity (“CG”) 24, and at substantially equal longitudinal distances D0 forward and aft of the CG, as illustrated in the left side elevation, bottom plan, and front end elevation views of
In an exemplary subsonic embodiment of the aircraft 10, i.e., one capable of speeds of up to about mach 0.85, the engines 20 preferably comprise thrust-vectoring turbofan engines, in which the thrust-vectoring function is achieved by rotatable nozzles, flaps or vanes 26, or combinations thereof, located at the engine thrust outlets 22. These mechanisms can effectively deflect, i.e., direct, the exhaust vector E, and hence, the equal in magnitude and oppositely directed thrust vector T, of the engines as much as 90 degrees relative to the thrust vector of a conventional “ax-isymmetric” engine nozzle, as indicated by the engine exhaust arrows E of
Thus, for example, to effect a vertical takeoff maneuver, the respective thrust vectors T of both engines 20 are directed substantially upward by the thrust deflectors 26 such that the respective longitudinal and lateral components T0 and Ta of the thrust vectors are substantially zero and their respective vertical components Tv are substantially equal to T. The thrust is then increased until the combined thrust of the engines exceeds the weight W of the UAV acting through the aircraft's CG 24, and the aircraft 10 rises vertically, without any rolling, pitching or yawing, to a selected altitude. The direction of the thrust vectors T of both engines are then rotated, or directed, forward such that the vertical components of the respective thrust vectors Tv approach zero and the respective longitudinal components T0 approach T. The UAV then begins to accelerate to a forward speed at which a surface of the vehicle, e.g., its wings 18, produces a lifting force L, which acts through the aircraft's CG in the opposite direction to its weight W, as illustrated in
As those of skill in the art will appreciate, in addition to the conventional mechanisms that are normally utilized at high speeds to control an aircraft's attitude relative to its respective roll, pitch and yaw axes R, P and Y, i.e., its ailerons, elevators and rudders, the attitude, and hence, the maneuverability, of the exemplary aircraft 10 can also be effectively controlled and enhanced during high speed flight by the thrust-vectoring engine 20 arrangement of the present invention. Thus, as illustrated in
Similarly, by rotating the direction of the respective thrust vectors T of the engines 20 such that the respective lateral thrust components Ta are zero and the vertical thrust components Tv are respectively directed upward or downward and in opposite directions to each other, the combined, non-zero moment of the respective vertical thrust components about the aircraft's CG 24 will cause the aircraft to roll about its roll axis R in the direction of the applied moment.
Likewise, by rotating the direction of the respective thrust vectors T of the engines such that the respective vertical thrust components Tv are zero, and the lateral thrust components Ta are directed in opposite directions to each other, the combined, non-zero moment of the respective horizontal thrust components about the aircraft's CG 24 will cause the aircraft to yaw about its yaw axis Y, in the direction of the applied moment.
As those of skill in the art will further appreciate, the conventional mechanisms normally utilized at high speeds to control the aircraft's attitude relative to its respective roll, pitch and yaw axes R, P and Y are substantially impaired or altogether non-functional at low speeds, including a still, or hovering situation. However, the thrust-vectoring engine 20 arrangement of the present invention also enables a precise control of the attitude of the exemplary aircraft 10 under such conditions. Thus, the aircraft is caused to hover by directing the respective thrust vectors T of the engines substantially upward, increasing the thrust of the engines until the combined thrust exceeds the weight W of the aircraft and it rises vertically to a selected altitude, as in the above vertical takeoff maneuver. The thrust of the engines is then decreased until the combined thrust is equal to the aircraft's weight, whereupon the aircraft hovers at the selected altitude. Low speed control of the aircraft's attitude, or maneuvering, is then effected in a manner similar to that described above in connection with its high speed maneuvering, except that substantially all of the lift L of the aircraft is provided by the thrust of the engines, rather than its wings 18.
For example, low speed horizontal translation of the aircraft 10 is effected by increasing the thrust of the engines 20 until the thrust exceeds the weight W of the vehicle, rotating the direction of the respective thrust vectors T of the engines in the same lateral directions until the combined upward components Tv of the thrust vectors are substantially equal to the weight of the aircraft, the sum of the moments of the respective horizontal components Ta and T0 of the respective thrust vectors about the aircraft's CG 24 is zero, and the aircraft translates horizontally in the same direction as the combined horizontal thrust vectors Ta and/or T0, as illustrated in
Low speed yawing of the aircraft 10 about its yaw axis Y is effected in a manner similar to that described above, except that the thrust vectors of the engines are directed in opposite lateral directions such that the combined, non-zero moment of the respective lateral thrust components Ta about the aircraft's CG 24 causes it to yaw about the yaw axis in the direction of the applied moment.
By now, those of skill in this art will appreciate that many modifications, substitutions and variations can be made in and to the materials, apparatus, configurations and methods of the VTOL UAV of the present invention without departing from its spirit and scope. In light of this, the scope of the present invention should not be limited to that of the particular embodiments illustrated and described herein, as they are only exemplary in nature, but instead, should be fully commensurate with that of the claims appended hereafter and their functional equivalents.
