Power plants – Combustion products used as motive fluid – Combined with regulation of power output feature
Reexamination Certificate
1998-12-16
2001-08-07
Jordan, Charles T. (Department: 3644)
Power plants
Combustion products used as motive fluid
Combined with regulation of power output feature
C244S012300, C244S02300R, C060S235000, C060S233000
Reexamination Certificate
active
06269627
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
The subject matter of this application is related to the subject matter of commonly owned U.S. patent application, filed on even date herewith, entitled “Rapid Response Attitude Control Logic for Shaft-Driven Lift Fan STOVL Engine”.
TECHNICAL FIELD
This invention relates generally to control of gas turbine engines, and more particularly to thrust control of a gas turbine aircraft engine having a shaft-driven lift fan selectively coupled to the engine for use on a 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. 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. The lift fans may also be used to control the attitude (i.e., pitch, roll, yaw) of the aircraft. The lift fans are typically disposed within the aircraft fuselage 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), 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.
The conventional thrust response control system for a gas turbine engine consists predominantly of fuel flow scheduling. Increasing or decreasing fuel flow results in a corresponding increase or decrease in the speed of both the high and low rotor spools within the engine. Fuel flow is typically changed in response to pilot-initiated movements of the throttle or power lever. Also, changing fuel flow typically changes the angle of the inlet guide vanes on the fan and compressor as well as the area of the exhaust nozzle (i.e., jet area). By increasing low rotor speed, the fan draws in more airflow and the engine, in turn, generates more thrust.
However, in a STOVL aircraft having a lift fan mechanically coupled by a drive shaft to the engine fan spool and operating in a vertical flight mode, a significant increase in the inertia (i.e., resistance to speed change) of the lift fan and low rotor spool combination results. This is as compared to the inertia of the low rotor spool alone (i.e., without the lift fan coupled to the low rotor spool). The increased inertia causes a corresponding decrease in the thrust response time of the lift fan and low rotor spool combination when the conventional fuel flow scheduling is employed as the thrust response control system. This decreased thrust response could cause the STOVL aircraft to not be able to meet certain aircraft stability, maneuverability and thrust control requirements.
DISCLOSURE OF INVENTION
An object of the present invention is to provide for rapid response thrust control of a gas turbine engine and a shaft-driven lift fan selectively coupled to the engine for use on a STOVL aircraft.
Another object of the present invention is to provide for such rapid response thrust control of the engine and lift fan while minimizing the possibility of engine instability or stall.
A further object of the present invention is to provide for such rapid response thrust control of the engine and lift fan by controlling the movement of existing aircraft components having relatively high response rates.
Yet another object of the present invention is to provide for such rapid response thrust control of the engine and lift fan by keeping constant the engine low rotor speed.
Still another object of the present invention is to provide for such rapid response thrust control of the engine and lift fan without requiring any additional engine variable geometry, actuation or system components.
The present invention is predicated on the fact that rapid response of a coupled combination of the lift fan and engine to a desired thrust change can be achieved by both keeping constant the speed of the low-pressure spool of the engine, and by varying both the fuel flow to the engine and the angle of the lift fan inlet guide vanes.
According to the present invention, a gas turbine engine is selectively mechanically connected to a lift fan by a drive shaft during operation in certain predetermined modes. An engine control is employed having logic that provides for rapid response thrust control of the coupled lift fan and low rotor engine spool when desired changes in thrust are initiated. The logic employed consists of varying the inlet guide vanes of the lift fan to vary the amount of airflow to the lift fan, together with selective fuel flow scheduling to the engine. These variations result in a substantially constant low rotor speed, which facilitates the desired rapid thrust response.
In a preferred exemplary embodiment, both the lift fan and gas turbine engine are utilized on a STOVL aircraft that can attain both horizontal and vertical flight modes. The lift fan is selectively coupled to the engine during vertical flight modes (e.g., takeoffs and landings) of the aircraft. The resulting rapid thrust response provided by the control logic of the present invention allows for corresponding control 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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Freese Richard A.
Meyers Eric T.
Dinh Tien
Jordan Charles T.
United Technologies Corporation
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