Rapid response attitude control logic for shaft-driven lift...

Aeronautics and astronautics – Aircraft – heavier-than-air – Airplane and fluid sustained

Reexamination Certificate

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C244S02300R, C060S235000, C060S233000

Reexamination Certificate

active

06270037

ABSTRACT:

TECHNICAL FIELD
This invention relates generally to control of gas turbine engines, and more particularly to attitude control of a STOVL aircraft having a gas turbine engine and a shaft-driven lift fan selectively coupled to the engine during vertical flight modes of the STOVL aircraft.
BACKGROUND ART
Short take-off and vertical landing (“STOVL”) military aircraft, also known as vertical and/or short takeoff and landing (“V/STOL”, “VTOL”, or “STOL”) aircraft (hereinafter all of which are referred to as a “STOVL” aircraft for convenience), are used when a single aircraft is needed to attain both horizontal and vertical flight modes. A well-known example is the AV-8B “Harrier” type of STOVL aircraft. The vertical flight modes comprise aircraft takeoffs and landings from, e.g., aircraft carriers or other limited-length runways. Such aircraft generally include one or more conventional gas turbine engines that power the aircraft in both the horizontal and vertical flight modes.
To achieve the vertical thrust necessary for vertical flight modes, each engine on the STOVL aircraft may be coupled in some manner to one or more auxiliary lift fans. Depending upon their placement and orientation within the STOVL aircraft, the lift fans may also be used in conjunction with the associated engines to control the attitude of the aircraft (i.e., to control the aircraft pitch, roll, and/or yaw) during vertical flight. The lift fans are typically disposed within the aircraft fuselage and separate from the engine. The primary airflow axis of the lift fan is oriented vertically within the aircraft (i.e., the fan exhaust is pointed downward to generate vertical lift for thrust and control), while the primary airflow axis of the engine is oriented in the conventional horizontal direction. However, the engine exhaust is typically adjustable in a well-known manner from a horizontal position for normal horizontal flight to a vertical position for vertical flight modes. This way, the direction of the thrust produced by the engine may also be varied between horizontal and vertical.
The lift fan may be selectively aerodynamically coupled to the fan exhaust or turbine exhaust of the engine, or the lift fan may be selectively mechanically coupled to the fan or low rotor spool of the engine by a rotating drive shaft. In the latter case, a clutch and gearbox mechanism is usually employed to selectively engage and disengage the lift fan with the gas turbine engine. Examples of these types of well-known propulsion systems for STOVL aircraft are given in U.S. Pat. Nos. 5,464,175, 5,312,069, 5,275,356, 5,209,428, which are all hereby incorporated herein by reference.
Generally, proper and stable attitude control of a STOVL aircraft during vertical flight modes is inherently difficult to achieve. The amount of force required to attain the desired aircraft attitude control, together with the reaction time of this force, is critical to proper aircraft control in vertical flight. Current, known attitude controls for STOVL aircraft burden the aircraft with extra weight. They also cause the engine to run at temperatures exceeding nominal operation.
For example, the attitude control system for the Harrier STOVL aircraft consists of additional and separate control system hardware. In the Harrier aircraft, that hardware weighs approximately 200 pounds and has no other function than to provide control power during vertical flight modes. The Harrier's attitude control system also has an undesired inherent coupling between overall system thrust and the use of control power for aircraft attitude. Further, these attitude control requirements significantly increase engine turbine temperatures in the Harrier aircraft to the extent that a water injection system is needed to meet turbine durability requirements. Clearly, the additional attitude control system for the Harrier aircraft poses undesired burdens on the aircraft, such as weight, cost and the risk e.g., of component failure.
DISCLOSURE OF INVENTION
An object of the present invention is to provide for rapid response attitude control of a STOVL aircraft having a gas turbine engine and a shaft-driven lift fan selectively coupled to the engine during vertical flight modes of the STOVL aircraft.
Another object of the present invention is to provide for such rapid response attitude control of the STOVL aircraft while minimizing the possibility of aircraft instability.
A further object of the present invention is to provide for such rapid response attitude control of the STOVL aircraft by controlling the movement of existing aircraft components having relatively high response rates.
A still further object of the present invention is to provide for such rapid response attitude control of the STOVL aircraft to thereby overcome the shortcomings of the prior art by eliminating the need for a separate attitude control system, thereby also eliminating the attendant problems (e.g., weight and risk) with such a separate attitude control system.
Yet another object of the present invention is to provide for such rapid response attitude control of the STOVL aircraft by keeping constant the engine low rotor speed.
Still another object of the present invention is to provide for such rapid response attitude control of the STOVL aircraft without requiring any additional engine variable geometry, actuation or system components.
The present invention is predicated on the fact that rapid response of a STOVL aircraft to a pilot-initiated change in the attitude of the aircraft can be achieved by varying both the angle of the lift fan inlet guide vanes and the area of the engine nozzle, thereby keeping constant the speed of the low-pressure rotor spool of the engine.
According to the present invention, a STOVL aircraft has a gas turbine engine that is selectively mechanically connected to a lift fan by a drive shaft during aircraft operation in vertical modes of flight. An engine control is employed having logic that provides for rapid response attitude control of the aircraft when the pilot initiates desired changes in attitude. The logic employed consists of varying both the inlet guide vanes of the lift fan and the area of the engine exhaust nozzle. These variations result in a constant low rotor speed, which facilitates the desired rapid attitude response of the STOVL aircraft. In a preferred exemplary embodiment, both the lift fan and gas turbine engine are disposed within the STOVL aircraft along its longitudinal axis (i.e., front to back) such that the control logic implements attitude control of the aircraft along the pitch axis of the aircraft.
The above and other objects and advantages of the present invention will become more readily apparent when the following description of a best mode embodiment of the present invention is read in conjunction with the accompanying drawings.


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patent: 5752379 (1998-05-01), Schafer et al.
patent: 5857321 (1999-01-01), Rajamani et al.

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