GB2282353A - Vectored thrust flight control - Google Patents

Abstract

A method for the control of adverse yaw in an aircraft, for example, to compensate for engine failure, uses vectored thrust from the APU to provide a directional control means to augment aerodynamic control. In another aspect vectored thrust from wing mounted engines is utilised to provide a twisting force to restore a deformed loaded wing to an optimum aerodynamic profile to minimise drag. Thrust vectoring may be achieved by variable nozzles (figures 1 and 2), variable exhaust flow deflector plates (figures 3A, 3B) or vanes (figures 6 to 8), or pivotally mounted engines (figures 4A to 5A). <IMAGE>

Description

TITLE Flight control systems for aircraft.

This invention relates to a flight control system for an aircraft and is particularly concerned with an auxiliary system which may be selectively brought into operation following a complete or partial failure in the primary control system of an aircraft. This invention also relates to a flight control system, which may be a primary system, for achieving both control and more efficient operation of an aircraft.

Conventionally, control of an aircraft is effected by means of movable aerodynamic control surfaces operated by mechanical linkages, hydraulic systems, electrical means or by a combination thereof. Whilst back-up systems are often provided to give some degree of control on failure of a system these back-up arrangements themselves can become unserviceable or the control surface itself may be damaged resulting in catastrophic loss of control of the aircraft.

An object of this invention is to provided an independent auxiliary system which is capable of providing at least some degree of control over the aircraft to supplement or replace aerodynamic control.

Another object is to provide a system of control using the aircraft engines to achieve directly or indirectly control and/or trimming through thrust or aerodynamic action.

Broadly, and in accordance with one aspect of this invention, there is provided an auxiliary control system for an aircraft said system comprising a thrust generating unit mounted on the aircraft structure and means to vector thrust from said unit relative to the line of flight whereby directional control of the aircraft may be effected.

In a preferred embodiment the thrust generating unit comprises an auxiliary power unit mounted adjacent the empennage and including a vectoring nozzle or directional thrust venting means whereby the aircraft may be controlled in yaw producing a rolling moment derivative by secondary effects, and/or pitch. Additional control in the roll axis may be effected by thrust applied each side of the longitudinal axis of the aircraft.

In an alternative preferred embodiment the thrust from the aircraft engines themselves may be vectored, for example by pivoting the engines to effect control especially where engine failure has resulted in asymmetric thrust.

Preferably this invention makes use of the auxiliary power unit which is conventionally located in the empennage of an aircraft with the provision of means to vector the thrust.

Control of the thrust direction is preferably effected by means associated with the pilot's controls forming an independent system directly subject to pilot command input.

In a further embodiment and in accordance with this invention thrust modulation and vectoring may be effected by extension of a movable rear cone and/or rear shroud to minimise drag. In many aircraft the thrust angle relative to the aircraft angle is fixed at an angle of inclination to give best performance, i.e. minimum drag during the cruise. The best performance that can be achieved is fixed at an angle under one set of conditions (i.e. one speed, height, temperature, payload).

However, by varying the thrust vector in flight by vectoring or deflection, the thrust vector can be optimised in flight longitudinally and laterally as fuel is consumed, speed and atmospheric conditions change.

Modulation of the deflected/vectored thrust can be used to twist the wing in flight to minimise drag.

Control may be by electronic or mechanical systems using existing arrangements or as an additional system using existing controls or through small thumb wheels or the like. Instead of using deployable cones deflectable paddles or vanes may be included in the jet stream of an engine to effect thrust vectoring.

In a further aspect this invention provides, and primarily for aircraft with wing mounted engine pods, for the use of vectored thrust from the engines to achieve trimming by restoring any loading twist or deformation of the wing to the untwisted or undeflected design state to achieve minimum drag and to provide also emergency control.

Wing twist (wash out, wash in) is normally built into an aircraft on manufacture. In this invention the effect is to optimise the structure of the main wing in flight by modulation and vectoring of thrust by controlled increments to assist in restoring the main wing (for example) back to the original untwisted and undeformed form against aerodynamic effects. For example during a fourteen hour flight, a four engine aircraft would follow a high altitude cruise procedure for range and minimum drag. Due to the varying distribution and mass of fuel in the wing throughout the flight, and due to the thrust setting and aerodynamic effects, the wing will twist and deform. However, by increasing the thrust on an outer engine and decreasing the thrust on the inner engines the wing can be brought back into a shape with minimum drag (near to the undeflected design shape).A badly trimmed aircraft due to twisting and deflection of the wing detracts from optimised wing profiles for minimum drag and maximum lift. This invention therefore provides a means to restore the wing in flight, so that the wing profile flies at its correct design angle of attack along the whole span at minimum drag.

In contrast to known vectored thrust systems this invention uses the wing pod mounted engines to modulate and twist the wing back using differential thrust settings and/or vectoring, to counter the aerodynamic and aeroelastic effects twisting the wings, and varying the angle of attack of the wing profile along its span for minimum drag.

The twisting and deflection of the wing for example could be measured and controlled using transducers (strain gauges) bonded to the wing skins at a datum (wing root) and at positions coinciding with engine thrust lines and the wing tips. An alternative method would be to use a light beam/lasers to gauge the deflection and twisting against premarked calibrated datum marks on the wing structure. The transducer signals could then be inputted to the flight computer, programmed at a given thrust setting to seek out and find the best flight velocity. Without the transducers and input to the flight computer and engine controls, it would not be otherwise possible to accomplish the efficiencies and emergency control.

Minimum parameters required per wing side could be: Thrust engine 1, twist of wing at pylon wing section = Angle of attack profile determined Thrust engine 2, twist of wing at pylon wing section = Angle of attack profile determined Thrust engine 3, twist of wing at pylon wing section = Angle of attack profile determined Thrust engine 4, twist of wing at pylon wing section = Angle of attack profile determined Twist/deflection of wing tip - Angle of attack profile.

The processing could be performed using strain gauges electronically. The whetstone bridge principle could be used to determine the net twist/deformation.

The signal from the whetstone bridge could be fed directly into the flight computer, or signalled to the pilot on an instrumentation display. For example, the centralised flight management computer could be reprogrammed to display an additional picture of the wing twist. The pilot could then differentiate and adjust the throttles and/or vectoring to give minimum twist.

The centralised aircraft flight management could be modified to automatically adjust the engine thrust and/or vectoring.

The twist could be measured direct using lasers against external calibrated marks on the wing structure at the positions above the engine thrust lines and wing tip profiles. The signal could be fed directly into the flight computer, or signalled to the pilot on an instrumentation display. For example, the centralised flight management computer could be reprogrammed to display an additional picture of the wing twist. The pilot could then differentiate and adjust the throttles to obtain minimum twist as above.

Further and preferred features of this invention are described with reference to the accompanying diagrammatic drawings showing embodiments by way of examples. In the drawings: Figure 1, shows an aircraft empennage with a vectored thrust auxiliary power unit, Figure 2, shows an alternative method of vectoring the thrust, Figures 3a and 3b show a further method of vectoring the thrust, Figures 4a and 4b show an alternative method of control by vectoring thrust from the main engines, Figures 5a and 6b show a method of vectoring thrust of the main engines, Figure 6 shows an engine thrust vectoring system, Figures 7 and 8 show in detail the thrust control means, and Figures 9 and 10 show diagrammatically the thrust vector control operation.

Referring firstly to Figure 1 of the drawings the empennage 1 of an aircraft includes an auxiliary power unit (APU) comprising a gas turbine engine with exhaust duct EX feeding nozzle NZ. The nozzle is rotatable about the aircraft's longitudinal axis X and includes a curved section whereby the position of rotation may be set to provide a lateral component of thrust to give pitch control thrust Pz or yaw control thrust Py. Alternative positions of the nozzle NZ are shown in broken lines.

Figure 2 shows an alternative construction of nozzle NZ wherein the nozzle outlet may be normally open but may be closed-off by obturating means OB such that exhaust is then through an aperture AP in rotatable core sleeve SL.

A coaxial outlet OT includes vents VT through which vectored thrust exhaust may exit the direction being controlled by the rotational position of the sleeve SL.

Figure 3 shows a further embodiment wherein deflector plates DP are positioned in the exhaust flow EX from the power unit in order to provide vectored thrust.

Figure 3A shows the undeflected thrust whilst Figure 3B shows the plates DP deflected to provide vectored thrust.

Figures 4 and 5 show an alternative arrangement wherein means are provided to vector thrust from the main wing mounted aircraft engines. As shown in Figure 4a the engines EN normally have a line of thrust directed forward but in the event of failure or loss of an engine the remaining engines can be pivoted to provide vectored thrust as shown in Figure 4b.

Figure 5 shows one means of vectoring the thrust of engine EN which is pivotally mounted in a pod on wing W at P with an operating linkage LK having guide means comprising a slotted track TR which allows pivoting. A means JK may be provided to effect movement of the engine about pivot P, through angle 6 as example from a normal position shown in Figure 5a to the position as shown in Figure 5b.

The system according to this invention and as described may be brought into operation following conventional control loss and will involve starting the APU, in the embodiments of Figures 1 to 3, if not already operational and engaging the means to control the thrust vector. This will preferably comprise a mechanical linkage connected directly to the pilot's controls such as the rudder pedals and control column and giving normal sense control. The embodiment of Figures 4 and 5 will require the engine pivoting system to be armed and connected to the controls.

Reference is now made to Figures 6 to 8 of the drawings showing a further embodiment with means for controlling the thrust vector of an engine. As shown in Figure 6, an aircraft gas turbine engine 60 is housed within a pod attached to pylon 61 carried by wing structure 62. Paddles or vanes 63 are provided in the jet exhaust from the engine itself and these paddles are arranged to be pivotable about a vertical axis to thus cause thrust deflection in a horizontal plane. A further paddle 64 is provided centrally located and pivotable about a horizontal plane whereby thrust deflection in a vertical direction may be achieved. The paddles 63, 64 may be operated by mechanical means with hydraulic actuators with control means such as linkages, chains or push rods being housed within the pylon 61 and possibly accommodated in blisters 65.Figure 7 illustrates diagrammatically the two paddles 63 which are located one above the other on a common pivot shaft 66.

The horizontal paddle 64 is illustrated in Figure 8 and this is movable vertically about pivot 68 connected to horn 69 coupled in turn to push rod 70 which is hydraulically actuated. In Figure 7 the shaft 66 may be coupled through a chain drive and pinions 71, 72.

Figures 9 and 10 illustrate schematically the control vectors which are possible using the above described arrangement and in accordance with this invention. As shown in Figure 9, a conventional four engined transport aircraft may incorporate the thrust vectoring means in all engines or possibly just one engine on each side. By adjustment of the paddles 63 in the jet exhaust, the line of thrust T from each engine may be modified to provide a turning moment M around the vertical centre of momentum. By this means, directional control may be established through means other than aerodynamic control surfaces.

In a similar way, and as shown in Figure 10, the paddle 64 may be actuated in order to provide a vertical deflection of the thrust T in order to provide a pitching moment about a horizontal axis.

A further aspect of this invention provides for a method of operating an aircraft utilising the vectored thrust from a pod mounted engine to achieve flexure and thus twist of the wing to which the engine is attached.

The purpose of effecting control in this manner is to provide for the wing to be placed into an optimum position or aerodynamic shape in accordance with the flight conditions at any particular time. Thus any deformation of the wing due to varying load conditions and thrust may be compensated by slight adjustment of the engine thrust through paddles 64 in particular whereby the wing can be brought into a profile offering minimum drag or best angle of attack in relation to the fuselage or main thrust line. This effect is achieved by virtue of the fact that the engine thrust acting through the pylon may cause a localised twisting moment to be applied to the wing which can be specifically controlled to provide optimum characteristics.

These and other features of operation of an aircraft using vectored thrust from wing mounted engines has already been described in detail herein.

Claims (10)

1. An auxiliary control system for an aircraft, said system comprising a thrust generating unit mounted on the aircraft structure and means to vector thrust from said unit relative to the line of flight whereby directional control of the aircraft may be effected.

2. A control system in accordance with Claim 1, wherein the thrust generating unit comprises an auxiliary power unit mounted adjacent the empennage and including a vectoring nozzle or directional thrust venting means whereby the aircraft may be controlled in yaw producing a rolling moment derivative by secondary effects, and/or pitch.

3. A control system in accordance with Claim 1 or 2, wherein the thrust from the aircraft engines are vectored by pivoting the engine relative to the airframe or by vectoring the line of thrust relative to the engine.

4. A control system for an aircraft having wing mounted propulsion units, wherein the thrust from one or more propulsion units is directionally vectored for the purpose of twisting or deforming the wing to a required datum.

5. A method for the control and operation of an aircraft utilising the vectored thrust from a pod mounted engine to achieve flexure and thus twist of the wing to which the engine is attached.

6. A method for the control of adverse yaw in an aircraft, for example, to compensate for engine failure, wherein vectored thrust from the APU provides a directional control means to augment aerodynamic control.

7. A method for control of an aircraft wherein vectored thrust from wing mounted engines is utilised to provide a twisting force to restore a deformed loaded wing to an optimum aerodynamic profile to minimise drag.

8. A method for the in-flight control and adjustment of the aerodynamic profile of a wing which includes an engine mounted by a pylon thereon, in which method the thrust vector of the engine is subject to directional control to produce a bending moment acting on the wing at the pylon attachment, the thrust vector being controlled in accordance with measured parameters relating to the wing profile at any instant to produce and maintain a required profile under the flight conditions at that instant.

9. Control system for an aircraft substantially as described herein and exemplified and with reference to the drawings.

10. A method for controlling an aircraft as disclosed and described herein.