WO1995011159A1

WO1995011159A1 - Aircraft flight control system

Info

Publication number: WO1995011159A1
Application number: PCT/GB1994/002285
Authority: WO
Inventors: Ajoy Kumar Kundu
Original assignee: Short Brothers Plc
Priority date: 1993-10-19
Filing date: 1994-10-19
Publication date: 1995-04-27
Also published as: GB2282996B; AU7943294A; GB2282996A; GB9321510D0; GB9421048D0

Abstract

An aircraft flight control system in which wing-mounted flight control output devices are employed in a multipurpose role. The system in one form includes wing-mounted port and starboard output assemblies (24, 25) of yaw and roll control surface components (26, 27, 28; 29, 30, 31) and port and starboard flight control actuators (32, 33) which in response to a yaw demand input cause the components (26, 27; 29, 30) of the assemblies (24, 25) to produce asymmetric yawing forces on the wings (12, 13) and yawing of the aircraft (10) and in response to a roll demand input cause the components (28, 31) to produce rolling forces on the wings (12, 13) and rolling of the aircraft (10). In addition, the actuators (32, 33) in response to an air-braking demand input cause the components (26, 27; 29, 30) to produce symmetric air-braking forces on the wings (12, 13) and aerodynamic braking of the aircraft. In another form, the control surface components of the wing-mounted output assemblies provide simply for yawing and air-braking forces to be applied to the aircraft.

Description

AIRCRAFT FLIGHT CONTROL SYSTEM

The present invention relates to aircraft flight control systems and is particularly concerned with a flight control system in which wing mounted flight control output devices of the system are employed in a multi¬ purpose role.

An aircraft of conventional configuration comprises a fuselage body from which port and starboard wings extend to provide the main supporting surfaces of the aircraft, with the fuselage body extending rearwardly of the wings and being provided at its aft end with a tail unit comprising a tail fin upstanding from the body and port and starboard tail planes extending outwardly from the tail fin on opposite sides of the fin.

The flight control system conventionally employed comprises a multiplicity of flight control output devices including ailerons pivotally mounted at -the trailing edges of the two wings for applying rolling moments about the longitudinal axis of the aircraft, a rudder pivotally mounted at the trailing edge of the tail fin for imparting yawing moments to the aircraft about its normal axis and elevators pivotal on the trailing edges of the tail planes for controlling pitching movements of the aircraft about its lateral axis. In addition, flaps are conventionally provided at the trailing edges of the wings for increasing lift when deployed. It is also common practice to provide at the trailing edges of the wings arrestor surfaces which when raised serve as air¬ brakes for deceleration of the aircraft when in contact with the ground and it is also well known to provide engine thrust reversers which are also brought into operation at this time for deceleration on the ground. While the conventional aircraft configuration has many advantages particularly for passenger payloads where the long fuselage body is well adapted to accommodate large numbers of passengers and while the provision of a tail unit with tail fin and tail planes at the rear end of the fuselage provides the aircraft in flight with good stability characteristics in pitch and yaw, use of a tail fin mounted rudders has several disadvantages.

It is an object of the present invention to provide an aircraft with a flight control system in which the use of a tail fin mounted rudder on an aircraft of conventional design can be avoided.

Further objects and advantages of the invention will become apparent from details descriptions of specific embodiments of the invention hereinafter to be described.

According to a first aspect of the present invention there is provided an aircraft having outwardly extending port and starboard wings and a flight control system for imparting forces to and moments on the aircraft in order to control the flight of the aircraft, the flight control system including a port flight control output device carried by the port wing at a predetermined location on the wing at or in the region of an outboard extremity of the wing and a starboard flight control output device carried by the starboard wing at a predetermined location on the wing at or in the region of an outboard extremity of the wing and flight control actuating means responsive to a yaw demand input to cause the port and starboard output devices to produce a yawing force on one wing which is greater than that imposed on the other wing thereby to cause a yawing moment to be applied to the aircraft about the normal axis of the aircraft and responsive to a roll demand input to cause the port and starboard output devices to produce on the aircraft a rolling force on one wing in one direction and a rolling force on the other wing in the opposite direction thereby to cause a rolling moment to be applied to the aircraft about the longitudinal axis of the aircraft.

In embodiments of the invention according to its first aspect and as hereinafter to be described, the port and starboard flight control output control devices are aerodynamic control surface devices which are displaceable under the action of the flight control actuating means to predetermined aerodynamic yawing and rolling dispositions in which they exert yawing and rolling forces on the aircraft. The predetermined locations on the wings at which the port and starboard control surface devices are mounted are at the outboard extremities and the control surface devices are mounted for angular displacement at the wing extremities.

In a specific embodiment of the invention according to its first aspect and as hereinafter to be described, each of the port and starboard control surface devices comprises a yaw control surface component which extends at the predetermined location from the wing in a direction away from the plane of the wing and which is angularly displaceable under the action of the flight control actuating means to yaw dispositions to apply to the aircraft the demanded yawing moments and a roll control surface component which extends at the predetermined location outwardly from the wing and which is angularly displaceable under the action of the flight control actuating means to roll dispositions to apply to the aircraft demanded rolling moments. In a specific embodiment of the invention according to its first aspect and as hereinafter to be described, the yaw control surface component is an upper control surface component which extends upwardly from the predetermined location on the wing and each of the control surface devices further comprises a lower control surface component which extends downwardly from the predetermined location and which is angularly displaceable with the upper control surface component under the action of the flight control actuating means to apply to the aircraft demanded yawing moments. The upper and lower control surface components are furthermore so disposed and dimensioned as to produce yaw moments on the aircraft without imposing pitching or substantial pitching moments on the aircraft about the lateral axis of the aircraft. The roll control surface components furthermore extend outwardly from the predetermined locations on the wings in a direction parallel to or substantially parallel to the lateral axis of the aircraft and are angularly displaceable from non-rolling dispositions in which they exert no rolling forces on the aircraft to rolling dispositions in which they exert oppositely directed rolling forces. Advantageously, the roll control surface components in the non-rolling dispositions lie in the planes of the wings and have a profiles conforming to the profiles of the wings at the wing extremities.

In a further specific embodiment of the invention according to its first aspect, the roll control surface component mounted on each wing extends outwardly from the predetermined location on the wing in a direction inclined to the plane of the wing and away from one side thereof and the yaw control surface component extends away from the predetermined location in a direction parallel to the normal axis of the aircraft and away from the wing on other side thereof. The yaw and roll control surface components are furthermore so disposed and dimensioned as to produce demanded yaw moments on the aircraft without imposing pitching or substantial pitching moments on the aircraft about the lateral axis of the aircraft.

In a specific embodiment of the invention according to its first aspect and as hereinafter to be described, the control surface component or components giving rise to yawing forces on each wing are angularly displaceable to air braking dispositions to cause an effective aerodynamic braking of the aircraft in the direction of the longitudinal axis of the aircraft without imposing a yawing moment on the aircraft and the flight control actuating means is responsive to an air braking demand input to cause displacement of the control surface component or components to the air braking dispositions.

In specific embodiments of the invention according to its first aspect and as hereinafter to be described, the control surface components giving rise to yawing and rolling forces form a flight control output assembly at each wing extremity. Each assembly is angularly displaceable on the wing with respect to an assembly axis fixed in relation to the wing to bring the component or components giving rise to yaw and/or air braking forces into yaw and/or air braking dispositions and the component or components of the assembly giving rise to rolling forces or parts thereof are angularly displaceable for angular movement on the assembly about a roll component axis fixed in relation to the assembly. The assembly axis is furthermore arranged parallel or substantially parallel to the normal axis of the aircraft and each assembly is mounted on the wing for angular movement with respect to an assembly axis located in the region of the leading edge of the wing.

According to a second aspect of the present invention there is provided an aircraft having outwardly extending port and starboard wings and a flight control system for imparting forces to and moments on the aircraft in order to control the flight of the aircraft, the flight control system including a port flight control output device carried by the port wing a predetermined location on the wing at or in the region of an outboard extremity of the wing and a starboard flight control output device carried by the starboard wing at a predetermined location on the wing at or in the region of an outboard extremity of the wing and flight control actuating means responsive to a yaw demand input to cause the port and starboard output devices to produce a yawing force on one wing which is greater than that imposed on the other wing thereby to cause a yawing moment to be applied to the aircraft about the normal axis of the aircraft and responsive to an air braking demand input to cause the port and starboard output devices to produce such air-braking forces on the aircraft which provide an effective aerodynamic braking of the aircraft in the direction of the longitudinal axis of the aircraft without imposing a yawing moment on the aircraft.

In a specific embodiment of the invention according to a second aspect and as hereinafter to be described, the port and starboard flight control output control devices are aerodynamic control surface devices which are displaceable under the action of the flight control actuating means to predetermined aerodynamic yawing dispositions in which they exert yawing forces on the aircraft. Furthermore, the predetermined locations on the wings at which the port and starboard control surface devices are mounted are at the outboard extremities and the control surface devices are mounted for angular displacement at the wing extremities.

In a specific embodiment of the invention according to its second aspect, each of the port and starboard control surface devices comprises a control surface component which is mounted on the wing at the extremity thereof and the control surface component is displaceable from a low- drag disposition in which the airflow over it produces a low or minimum drag component on the aircraft to high drag dispositions in which the airflow over it produces high drag components on the aircraft. Furthermore, each control surface component extends upwardly from the wing in a plane parallel or substantially parallel to the normal axis of the aircraft, each control surface component is mounted on the wing for angular displacement with respect to an axis parallel or substantially parallel to the normal axis of the aircraft and each control surface component is mounted for angular displacement with respect to an axis in the region of its leading edge.

In an embodiment of the invention according to its second aspect, the flight control actuating means is responsive to a roll demand input to cause the port and starboard control surface components to produce a rolling force on the aircraft on one wing in one direction and a rolling force on the other wing in the opposite direction thereby to cause a rolling moment to be applied to the aircraft about the longitudinal axis of the aircraft.

In embodiments of the invention according to its first and second aspects and as hereinafter to be described, the flight control actuating means comprises yaw actuator mounted on each wing and the yaw actuators hold the control surface components giving rise to yawing forces in a minimum drag disposition in the absence of yaw and/or air-braking demand inputs.

In embodiments of the invention according to its first and second aspects and as hereinafter to be described, each control surface component or each of the components giving rise to yawing forces in a drag reduction disposition presents a low drag profile to airflow across it during flight of the aircraft and so extends from the wing and is so shaped and oriented in relation to the wing as to produce a reduction in the drag imposed by the wing. Furthermore, the actuators hold the control surfaces in a drag reduction disposition in the absence of yaw and/or air-braking demand inputs.

In specific embodiments of the invention according to its first and second aspects and as hereinafter to be described, the actuators in response to yaw and air- braking demand inputs cause the control surface components giving rise to yawing forces to move outwardly with respect to the wings.

In specific embodiments of the invention according to its first and second aspects and as hereinafter to be described, the aircraft includes a fuselage body from which the port and starboard wings extend and wherein the fuselage body extends rearwardly of the wings and has at the rear thereof a tail unit comprising a tail fin extending therefrom in a plane parallel to the plane containing the longitudinal axis and normal axis of the aircraft. The tail unit furthermore includes port and starboard tail planes extending outwardly from the tail fin on opposite sides thereof and wherein the tail planes include elevator output devices of the flight control system for applying pitching moments to the aircraft about its lateral axis.

As yawing moment is applied to the aircraft by the wing- mounted control surface components the tail fin is advantageously a non-displaceable stabilising fin, that is to say, a stabilising tail fin without a rudder.

Embodiments of the invention according to its different aspects will now be described by way of example with reference to the accompanying drawings in which:-

Fig l is a schematic perspective view of an aircraft embodying a flight control system according to the first aspect of the invention and including wing-mounted port and starboard flight control output assemblies of yaw and roll control surface components shown in neutral dispositions in which they impart neither yawing nor rolling forces on the aircraft.

Fig 2 is a schematic perspective view of the aircraft shown in Fig 1 illustrating the roll control surface components of the wing-mounted flight control output assemblies in dispositions in which they impose a rolling moment on the aircraft.

Fig 3 is a schematic perspective view of the aircraft shown in Fig 1 illustrating the starboard wing-mounted flight control output assembly in a disposition in which the yaw control surface components of the assembly exert a yawing force on the aircraft.

Fig 4 is a schematic perspective view of the aircraft shown in Fig 1 in which the port and starboard wing- mounted flight control output assemblies are displaced to bring the yaw control surface components of the assemblies to yawing and air braking dispositions on the aircraft and in which the roll control surface components of the assemblies are displaced to roll dispositions.

Fig 5 is a scrap view of a port wing of an aircraft of the configuration shown in Fig 1, showing a wing-mounted flight control output assembly which can be employed as an alternative to those provided on the aircraft illustrated in Figs 1 to 4.

Fig 6 is a schematic perspective view of the aircraft shown in Fig 1 in which the port and starboard wing- mounted flight control output assemblies take the form shown in Fig 5 with the components of the assemblies displaced to bring the yaw control surface components of the assemblies to yawing and air braking dispositions on the aircraft and the roll control surface components of the assembles to roll dispositions.

Fig 7 is a schematic perspective view of an aircraft embodying a flight control system according to the second aspect of the invention and showing port and starboard wing-mounted flight control output assemblies with control surface components providing simply for yawing and air braking forces on the aircraft.

Referring first to Fig 1 of the drawings, an aircraft 10 of conventional configuration comprises a fuselage body 11 from which port and starboard wings 12 and 13 extend to provide the main supporting surface of the aircraft, with the fuselage body 11 extending rearwardly of the wings 12 and 13 and being provided at its aft end with a tail unit 14 comprising a tail fin 15 upstanding from the body 11 and port and starboard tail planes 16 and 17 extending outwardly from the tail fin 15 on opposite sides of the fin. Fuselage mounted port and starboard propulsion units 18 and 19 are carried by the fuselage body in a region thereof intermediate the wings 12 and 13 and the tail unit 14.

The flight control system of the aircraft 10 for producing yawing moments about the normal axis Z, rolling moments about the longitudinal axis X and pitching moments about the lateral axis Y comprises conventional elevators 22 and 23 pivotal at the trailing edges of the tail planes 16 and 17 for applying pitching moments about the lateral axis of the aircraft. In addition, flaps 20 and 21 are conventionally provided at the trailing edges of the wings 12 and 13 for increasing lift when deployed.

The flight control system in accordance with the first aspect of the invention further comprises at the outboard extremities of the port and starboard wings 12 and 13, flight control output assemblies 24 and 25 which apply yawing and rolling moments on the aircraft and which also serve to apply air-braking forces to the aircraft.

The port flight control output assembly 24 comprises an upper yaw control surface component 26, a lower yaw control surface component 27 and a roll control surface component 28. Similarly, the starboard flight control output assembly 25 comprises upper and lower yaw control surface components 29 and 30 and a roll control surface component 31. In Fig 1, the two assemblies 24 and 25 occupy neutral dispositions in which the yaw control surface components 24, 25 and 29, 30 lie in vertical planes parallel to the longitudinal axis X in which they impose no yawing forces on the aircraft about the normal axis Z.

The wing 12 houses a yaw and roll actuator 32 which serves to angularly displace the assembly 24 from the neutral disposition shown in Fig 1 to required yawing dispositions and to angularly displace the roll control surface component 28 with respect to the assembly to required rolling dispositions. Similarly, the wing 13 houses a yaw and roll actuator 33 for producing angular displacements of the assembly 25 and angular displacements of the roll control surface component 31.

Referring now to Fig 2, in response to a roll demand input to the actuators 32 and 33 the roll control surface components 28 and 32 are angularly displaced by the actuators 32 and 33 to the positions shown by rotation about pivotal axes fixed in relation to the assemblies 24 and 25. In the absence of a yaw demand input to the actuators 32 and 33, the assemblies maintain their neutral yaw dispositions in which the yaw control surface components 24, 25 and 29, 30 impose no yawing forces on the aircraft. As will be seen, the roll control surface component 28 is shown in a disposition in which its trailing edge is down while the roll control surface component 32 is shown with its trailing edge raised. As a consequence, the aircraft shown in Fig 2 would be subject to a rolling moment in which the port wing 12 is caused to rise and the starboard wing caused to lower.

Referring now to Fig 3, in response to a yaw demand input to the actuator 33, the flight control output assembly 25 is angularly displaced by the actuator 33 to the position shown by angular movement with respect to an assembly axis fixed in relation to the wing 12 and parallel to the normal axis Z of the aircraft. The assembly 24 remains as shown in its neutral disposition in which its yaw control surface components 26 and 27 impose no yawing forces on the aircraft. In addition, the roll control surface components 28 and 31 remain in their neutral dispositions in which they impose no rolling moment upon the aircraft. As a consequence, the starboard wing 13 of the aircraft shown in Fig 3 becomes subject to increased drag which produces a yawing moment about the normal axis Z, and which causes a turning movement of the aircraft to the right.

It will of course be appreciated that a yawing demand input would normally be accompanied by roll demand input where the roll demand input raises the trailing edge of the roll control surface component 28 and lowers the trailing edge of the roll component 31 to produce in addition to the yawing of the aircraft to the right in Fig 3 a raising of the port wing 12 and a lowering of the starboard wing 13.

Referring now to Fig 4, the flight control output assemblies 24 and 25 and the roll components 28 and 31 have all been angularly displaced under the control of the actuators 32 and 33 in response to a combination of yaw, roll and air-braking demand inputs to the actuators 32 and 33, to bring the aircraft 10 into a coordinated right turn accompanied by deceleration.

In particular, the actuators 32 and 33 in Fig 4 in response to yaw and air-braking inputs have caused the two assemblies 24 and 25 to pivot outwardly to different angular yaw dispositions, that is to say, the assembly 25 has been moved to an angular disposition with respect to the wing 13 which is greater than to which the assembly 24 has been moved with respect to the wing 12. As a consequence, the aircraft 10 shown in Fig 4 is subject to the drag imposed by the components 26 and 27 of the assembly 24 and the drag imposed by the components 29 and 30 of the assembly 25 to produce a predetermined air braking of the aircraft 10, while the increment in drag imposed by the assembly 25 as a result of its greater angular disposition subjects the aircraft 10 in Fig 4 to a yawing moment about the normal axis Z causing the aircraft to yaw to the right. In addition, the actuators 32 and 33 in Fig 4 in response to a roll demand input have caused the two roll components 28 and 31 to be angularly displaced as shown, with the trailing edge of the roll component 28 lowered and the trailing edge of the roll component 32 raised, thereby producing in addition to the yawing and deceleration of the aircraft rolling of the aircraft with the raising of the port wing 12 and a lowering of the starboard wing 13.

Each of the two assemblies 24 and 25 in the embodiment of the invention described with reference to Figs 1 to 4 is angularly displaceable about an axis in the region of the leading edge of the wing and is moveable outwardly from the neutral disposition. Furthermore, each of the roll components 28 and 31 is angularly displaceable from its neutral disposition about a pivotal axis at the leading edge of the assembly.

The two assemblies 24 and 25 in the embodiment of the invention described with reference to Figs 1 to 4 include yaw control surface components 26, 27 and 29,30 which produce yawing and/or air-braking forces only and impose no rolling forces on the aircraft which is produced by the roll control surface components 28 and 31. The required yawing, rolling and air-braking forces can however be obtained by employing flight control output assemblies having other configurations of control surface components, one of which will by way of example now be described with reference to Fig 5.

Referring now to Fig 5, which is a scrap view of the port wing 12 of an aircraft shown in Figs 1 to 4 except that the port and starboard flight control output assemblies 24 and 25 are replaced by a port assembly 34 mounted at the end of the wing 12 and a corresponding assembly mounted at the end of the starboard wing. As will be seen, the assembly 34 comprises an inclined upper roll control surface component 35 which extends outwardly from the end of the wing 12 in a direction inclined to the plane of the wing and away from the upper side thereof and a lower yaw control surface component 36 which extends downwardly from the end of the wing 12 in a direction parallel to the normal axis of the aircraft and away from the lower side of the wing.

Referring now to Fig 6 the port flight control output assembly 34 is shown at the end of the port wing 12 and a starboard flight control output assembly 46 at the end of the wing 13 which comprises an upper inclined roll control surface component 47 and a downwardly extending lower yaw control surface component 48. The roll components 35 and 37 of the two assemblies 34 and 46 are so mounted as to be angularly displaceable about their leading edges, while the yaw components 36 and 48 are mounted for angular displacement about pivotal axes at their leading edges of parallel to the normal axis Z of the aircraft.

In the dispositions shown in Fig 6 the roll components 35 and 47 and the yaw components 36 and 48 have all been angularly displaced under the control of the actuators 32 and 33 in response to a combination of yaw, roll and air- braking demand inputs to the actuators 32 and 33 to bring the aircraft 10 into a coordinated right turn accompanied by deceleration.

In particular, the actuators 32 and 33 in Fig 6 in response to yaw and air-braking inputs have caused the port and starboard assemblies 34 and 46 to pivot outwardly to different angular yaw dispositions, with the yaw component 48 having taken up an angular disposition with respect to the wing 13 which is greater than that to which the yaw component 36 has been moved with respect to the wing 12. As a consequence the aircraft 10 shown in Fig 6 is subject to the drag imposed by the components 36 and 48 to produce a predetermined air-braking of the aircraft 10, while the increment in drag imposed by the assembly 48 as a result of its greater angular disposition subjects the aircraft 10 in Fig 6 to a yawing moment about the normal axis Z causing the aircraft to yaw to the right. In addition the actuators 32 and 33 in Fig 6 in response to a roll demand input have caused the two roll components 35 and 47 to be angularly displaced about their leading edge pivotal axis, with the trailing edge of the roll component 35 lowered and the trailing edge of the roll component 47 raised, thereby producing in addition to the yawing and deceleration of the aircraft rolling of the aircraft with the raising of the port wing and a lowering of the starboard wing 13.

It is known, although less common, to provide in conventional aircraft configurations upstanding winglet structures which extend upwardly from the wing tips and which are so shaped and positioned in relation to the wing as to effect a reduction in the overall drag imposed by the wing and the flight control output assemblies in the embodiments herein described with reference to Figs 1 to 5 of the drawings provides for control surface components which are so shaped and disposed in relation to the wings 12 and 13 that they also serve in the neutral dispositions of the components to effect a reduction in the overall drag.

In the embodiments of the invention described with reference to Figs 1 to 6 the control surface components 24 and 25 serve to apply yawing moments to the aircraft and no rudder is therefore provided at the trailing edge of the tail fin 15. The tail fin nevertheless serves as a support for the tail planes and as a yaw stabilising fin in the same manner as the tail fin in a conventional flight control system.

The flight control system as hereinbefore described with reference to Figs 1 to 6 can be regarded as a new engineering concept on aircraft lateral control (roll) , directional control (yaw) and air braking, all of which can be applied individually or in any combination. The vertical and horizontal control surface components of Figs 1 or 4 or their equivalents in Figs 5 and 6 can be individually actuated to provide roll control rotation of the roll control surface components in opposite directions, yaw control by moving one of the flight control output assemblies 24 and 25 outboard to generate asymmetric drag and air braking by moving both assemblies outboard. The yaw control surface components furthermore act as winglets to reduce induced drag. If integrated with air-data sensors and microprocessor based controls (fly-by-wire) , they can also serve as yaw dampers, and, in an extreme design, can make a vertical tail fin redundant. The flight control systems described with reference to Figs l to 6 provide an integrated system as well as offering possible weight saving, drag reduction and better control responses. They eliminate the need for conventional ailerons, rudder and air brakes. Weight saving arises out of the use of a simple multi-purpose control surface components that replace several components of other flight control systems and their associates linkages. With respect to aircraft performance, they could reduce drag, move C.G. forward and offer pure yawing moment.

All aircraft require motion control on all the three- axes. Conventionally, yaw is achieved through lift generated by moving a rudder (or twin V—tail) , hinged on a vertical tail fin located at the aft end of fuselage. Lift to generate lateral forces is sensitive to airflow qualities. In the embodiments of the invention described with reference to Figs 1 to 6 yaw is generated by drag which is more reliable than lift generation.

Roll control in the embodiments of the invention described with reference to Figs 1 to 6 is carried out at the wing extremities in clean air unlike conventional ailerons at the wake of wing airflow. The embodiments of the invention described with reference to Figs 1 to 6 offer more effective roll control.

Modern high-speed aircraft, both in combat and commercial categories, require air braking to rapidly decelerate from higher speeds. Most of the conventionally designed air brakes affect aircraft pitching moment when deployed. In the embodiments of the invention described with reference to Figs 1 to 6 the air braking is effected using components which balance out undesirable pitching moments .

An increasing number of aircraft designs use winglets as a drag reduction measure. In the embodiments of the invention described with reference to Figs 1 to 6, the components of the wing-tip mounted flight control assemblies giving rise to yawing forces serve as winglets.

For conventional empennage, the size of the vertical tail fin including rudder area, depends on its distance from the CG, along with other parameters e.g. wing area etc. It would benefit flight control design to make use of aircraft semi-span dimension, normally longer than tail- arm dimension, and to use this as the leverage arm for the moment required to generate yaw through drag effect than to use flow-sensitive lift generation and the tail- arm dimension as the leverage arm.

The embodiments of the invention described with reference to Figs 1 to 4 and 5 and 6 greatly improve design by combining all three requirements to be met by one set of control surface components. Moreover, unlike conventional design, the control surface components are positioned away from the wing wake and/or engine efflux i.e. away from any adverse effects of airflow.

The flight control output assemblies of the embodiments of the invention described with reference to Figs l to 6 can be employed in any type of aircraft and have the following advantages:-

i) Weight reduction by eliminating or reducing the size of conventional systems and their linkages, and/or replacing them by one system. ii) Drag reduction on account of winglet effect and surface area reduction as referred to in (i) .

iii) Air braking with minimal pitching moments.

iv) Superior yaw damping (micro-processor based control) and directional control by drag generation and not by flow sensitive lift in conventional design.

v) More effective roll control in a combined system.

vi) The assemblies are positioned away from the wing wake and/or engine efflux i.e. away from any adverse airflow.

vii) Overall simplification by system integration.

Referring now to Fig 7, the aircraft 10 is of the same configuration as that shown in Figs 1 to 4 and includes a flight control system which includes conventional port and starboard ailerons 38 and 39 pivotally mounted at the trailing edges of the two wings 12 and 13 for applying to the aircraft rolling moments about the longitudinal axis of the aircraft and elevators 22 and 23 pivotal at the trailing edges of the tail planes 16 and 17 for applying pitching moments about the lateral axis Y of the aircraft. In addition, flaps 20 and 21 are conventionally provided at the trailing edges of the wings 12 and 13 for increasing lift when deployed.

The flight control system in accordance with the second aspect of the invention further comprises at the output extremities of the port and starboard wings 12 and 13, flight control output assemblies 40 and 41 which apply yawing moments on the aircraft and which also serve to apply air-braking forces to the aircraft.

The port flight control output assembly 40 comprises a yaw control surface component 42 and the corresponding starboard assembly 41 comprises a yaw control surface component 43. In the disposition in Fig 7 in full line, the control surface components 42 and 43 occupy neutral dispositions in which they lie in vertical planes parallel to the longitudinal axis X and in which they impose no yawing forces on the aircraft about the normal axis Z.

The wing 12 houses a yaw actuator unit 44 which serves to angularly displace the control surface component 42 from the neutral disposition shown in Fig 7 to required yawing dispositions. Similarly the wing 13 houses a yaw actuator 45 for producing angular displacements of the control surface component 43.

In response to a yaw demand input to the actuator 45, the component 43 is angularly displaced by the actuator 45 to the position shown in broken line by rotation with respect to an axis which is fixed in relation to the wing 13 and which is parallel to the normal axis Z of the aircraft. The control surface component 42 remains as shown in its neutral disposition in which it imposes no yawing forces on the aircraft. As a consequence, the starboard wing 13 of the aircraft shown in Fig 7 becomes subject to increased drag which produces a yawing moment about the normal axis Z and which causes a turning movement of the aircraft to the right.

A yawing demand input would, as previously described, normally be accompanied by a roll demand input to aileron actuators provided to activate the ailerons 38 and 39 to produce a rolling moment on the aircraft by a raising of the wing 12 and a lowering of the wing 13.

In response to yaw and air-braking inputs to the actuators 44 and 45 the control surface components 42 and 43 can be moved to angular dispositions with respect to the wings by different amounts, as a consequence of which the aircraft 10 is subject to the drag imposed by the component 42 together with the drag imposed by the component 43 to produce a predetermined air-braking of the aircraft 10 while the increment in drag imposed by the component at the greater angular disposition subjects the aircraft 10 to a yawing moment about the normal axis Z causing the aircraft to yaw as well as to decelerate.

The flight control system described with reference to Fig 7 offers aircraft directional control and air-braking. The wing tip mounted vertical control surface components 42 and 43 are selectively actuated to provide yaw control through increased drag and the same surfaces serve as air-brakes when actuated simultaneously^"on both wings. The control surfaces 42 and 43 also act as winglets offering induced drag reduction. When integrated with air-data sensors and microprocessor based controls (fly- by-wire) , they can also serve as yaw dampers.

An advantage of the flight control system described with reference to Fig 7 is that the it is simpler than the conventional systems and offers weight saving, drag reduction and better yaw control. It eliminates the need for separate rudder and air-brakes. Weight saving arises out of the use of a single set of flight control surface components and their associated linkages in a multi-purpose role. With respect to aircraft performance, it can be used to reduce drag, move the C . G . of the aircraft forward and provide pure yawing moment.

Air-brake devices of conventional form as hereinbefore referred to give rise to pitching moment, the magnitude of which depends on the location of the device from the aircraft CG in the asymmetrical plane and positioning of the device can be critical. The flight control system as described with reference to Fig 7 considerably eases such positioning constraints as the control surfaces 42 and 43 can readily be positioned close to the plane of the aircraft CG.

In aircraft structures hitherto proposed air brakes have been mounted on the fuselage to achieve structural integrity and to reduce any asymmetric effects. In contrast, the air-braking action is, in the embodiments of the invention described with reference to Fig 7, achieved by simultaneous equal outboard extension of the wing tip control surface components 42 and 43 which cancels yawing moments and leaves the pure drag imposed by the projected areas of the control surface components to effect air-braking.

If integrated with Fly-by-Wire technology, the control surfaces 42 and 43 can also serve as yaw dampers. Yaw control effects should be found to be superior to that of the conventional tail fin and rudder assembly.

The flight control system described with reference to Fig 7 the drawings also greatly facilitates design by arranging for yaw demands, air-braking and drag reduction to be controlled by one set of flight control surfaces. Moreover, unlike conventional designs, the winglet structures are positioned away from the wing wake and/or engine efflux, that is to say, away from any major "spurious" airflows.

The control surface components 42 and 43 may in their simplest form be laterally actuated end-plates at the wing tips, and resemble drag reduction winglets. The actuators for them offer articulation for lateral outward deployment on one side or both sides simultaneously. The sizing, positioning and rate of deployment are optimised to generate appropriate forces which act to provide (i) yaw control, (ii) air-braking or (iii) drag reduction, depending on the deployment mode.

The flight control system according to the second aspect of the invention and as described with reference to Fig 7 can be used in any type of aircraft and has many of the advantages of the flight control system according to the first aspect of the invention and as described with reference to Figs 1 to 6.

Claims

1. An aircraft having outwardly extending port and starboard wings and a flight control system for imparting forces to and moments on the aircraft in order to control the flight of the aircraft, the flight control system including a port flight control output device carried by the port wing at a predetermined location on the wing at or in the region of an outboard extremity of the wing and a starboard flight control output device carried by the starboard wing at a predetermined location on the wing at or in the region of an outboard extremity of the wing and flight control actuating means responsive to a yaw demand input to cause the port and starboard output devices to produce a yawing force on one wing which is greater than that imposed on the other wing thereby to cause a yawing moment to be applied to the aircraft about the normal axis of the aircraft and responsive to a roll demand input to cause the port and starboard output devices to produce on the aircraft a rolling force on one wing in one direction and a rolling force on the other wing in the opposite direction thereby to cause a rolling moment to be applied to the aircraft about the longitudinal axis of the aircraft.

2. An aircraft according to claim 1, wherein the port and starboard flight control output control devices are aerodynamic control surface devices which are displaceable under the action of the flight control actuating means to predetermined aerodynamic yawing and rolling dispositions in which they exert yawing and rolling forces on the aircraft.

3. An aircraft according to claim 2, wherein the predetermined locations on the wings at which the port and starboard control surface devices are mounted are at the outboard extremities and wherein the control surface devices are mounted for angular displacement at the wing extremities.

4. An aircraft according to claim 3, wherein each of the port and starboard control surface devices comprises a yaw control surface component which extends at the predetermined location from the wing in a direction away from the plane of the wing and which is angularly displaceable under the action of the flight control actuating means to yaw dispositions to apply to the aircraft the demanded yawing moments and a roll control surface component which extends at the predetermined location outwardly from the wing and which is angularly displaceable under the action of the flight control actuating means to roll dispositions to apply to the aircraft demanded rolling moments.

5. An aircraft according to claim 4, wherein the yaw control surface component is an upper control surface component which extends upwardly from the predetermined location on the wing.

6. An aircraft according to claim 5 wherein each of the control surface devices further comprises a lower control surface component which extends downwardly from the predetermined location and which is angularly displaceable with the upper control surface component under the action of the flight control actuating means to apply to the aircraft demanded yawing moments.

7. An aircraft according to claim 6, wherein the upper and lower control surface components are so disposed and dimensioned as to produce yaw moments on the aircraft without imposing pitching or substantial pitching moments on the aircraft about the lateral axis of the aircraft.

8. An aircraft according to any of claims 4 to 7, wherein the roll control surface components extend outwardly from the predetermined locations on the wings in a direction parallel to or substantially parallel to the lateral axis of the aircraft and are angularly displaceable from non-rolling dispositions in which they exert no rolling forces on the aircraft to rolling dispositions in which they exert oppositely directed rolling forces.

9. An aircraft according to claim 8, wherein the roll control surface components in the non-rolling dispositions lie in the planes of the wings and have a profiles conforming to the profiles of the wings at the wing extremities.

10. An aircraft according to claim 4, wherein the control surface component mounted on each wing extends outwardly from the predetermined location on the wing in a direction inclined to the plane of the wing and away from one side thereof and wherein the yaw control surface component extends outwardly from the predetermined location in a second direction parallel to the normal axis of the aircraft and away from the other side of the wing.

11. An aircraft according to claim 10, wherein the yaw and roll control surface components are so disposed and dimensioned as to produce demanded yaw moments on the aircraft without imposing pitching or substantial pitching moments on the aircraft about the lateral axis of the aircraft.

12. An aircraft according to any of claims 4 to 11, wherein the control surface component or components giving rise to yawing forces on each wing are angularly displaceable to air braking dispositions to cause an effective aerodynamic braking of the aircraft in the direction of the longitudinal axis of the aircraft without imposing a yawing moment on the aircraft and wherein the flight control actuating means is responsive to an air braking demand input to cause displacement of the control surface component or components to the air braking dispositions.

13. An aircraft according to any of claims 4 to 12, wherein the control surface components giving rise to yawing and rolling forces form a flight control output assembly at each wing extremity wherein each assembly is angularly displaceable on the wing with respect to an assembly axis fixed in relation to the wing to bring the component or components giving rise to yaw and/or air braking forces into yaw and/or air braking dispositions and wherein the component or components of the assembly giving rise to rolling forces or parts thereof are angularly displaceable for angular movement on the assembly about a roll component axis fixed in relation to the assembly.

14. An aircraft according to claim 13, wherein the assembly axis is arranged parallel or substantially parallel to the normal axis of the aircraft.

15. An aircraft according to claim 14, wherein each assembly is mounted on the wing for angular movement with respect to an assembly axis located in the region of the leading edge of the wing.

16. An aircraft having outwardly extending port and starboard wings and a flight control system for imparting forces to and moments on the aircraft in order to control the flight of the aircraft, the flight control system including a port flight control output device carried by the port wing a predetermined location on the wing at or in the region of an outboard extremity of the wing and a starboard flight control output device carried by the starboard wing at a predetermined location on the wing at or in the region of an outboard extremity of the wing and flight control actuating means responsive to a yaw demand input to cause the port and starboard output devices to produce a yawing force on one wing which is greater than that imposed on the other wing thereby to cause a yawing moment to be applied to the aircraft about the normal axis of the aircraft and responsive to an air braking demand input to cause the port and starboard output devices to produce such air-braking forces on the aircraft which provide an effective aerodynamic braking of the aircraft in the direction of the longitudinal axis of the aircraft without imposing a yawing moment on the aircraft.

17. An aircraft according to claim 16 wherein the port and starboard flight control output control devices are aerodynamic control surface devices which are displaceable under the action of the flight control actuating means to predetermined aerodynamic yawing dispositions in which they exert yawing forces on the aircraft.

18. An aircraft according to claim 17, wherein the predetermined locations on the wings at which the port and starboard control surface devices are mounted are at the outboard extremities and wherein the control surface devices are mounted for angular displacement at the wing extremities.

19. An aircraft according to claim 18, wherein each of the port and starboard control surface devices comprises a control surface component which is mounted on the wing at the extremity thereof and wherein the control surface component is displaceable from a low-drag disposition in which the airflow over it produces a low or minimum drag component on the aircraft to high drag dispositions in which the airflow over it produces high drag components on the aircraft.

20. An aircraft according to claim 19, wherein each control surface component extends upwardly from the wing in a plane parallel or substantially parallel to the normal axis of the aircraft.

21. An aircraft according to claim 20 wherein each control surface component is mounted on the wing for angular displacement with respect to an axis parallel or substantially parallel to the normal axis of the aircraft.

22. An aircraft according to claim 21, wherein each control surface component is mounted for angular displacement with respect to an axis in the region of its leading edge.

23. An aircraft according to any of claims 19 to 22, wherein the flight control actuating means is responsive to a roll demand input to cause the port and starboard control surface components to produce a rolling force on the aircraft on one wing in one direction and a rolling force on the other wing in the opposite direction thereby to cause a rolling moment to be applied to the aircraft about the longitudinal axis of the aircraft.

24. An aircraft according to any of claims 1 to 23, wherein the flight control actuating means comprises yaw actuator mounted on each wing, and wherein the yaw actuators hold the control surface components giving rise to yawing forces in a minimum drag disposition in the absence of yaw and/or air-braking demand inputs.

25. An aircraft according to any of claims 1 to 24, wherein each control surface component or each of the components giving rise to yawing forces in a drag reduction disposition presents a low drag profile to airflow across it during flight of the aircraft and so extends from the wing and is so shaped and oriented in relation to the wing as to produce a reduction in the drag imposed by the wing.

26. An aircraft according to claim 25, wherein the actuators hold the control surfaces in a drag reduction disposition in the absence of yaw and/or air-braking demand inputs.

27. An aircraft according to any of claims 1 to 26 to 43, wherein the actuators in response to yaw and air- braking demand inputs cause the control surface components giving rise to yawing forces to move outwardly with respect to the wings.

28. An aircraft according to any of claims 1 to 27 including a fuselage body from which the port and starboard wings extend and wherein the fuselage body extends rearwardly of the wings and has at the rear thereof a tail unit comprising a tail fin extending therefrom in a plane parallel to the plane containing the longitudinal axis and normal axis of the aircraft.

29. An aircraft according to claim 28, wherein the tail fin is a non-displaceable stabilising fin.

30. An aircraft according to claim 29, wherein the tail unit includes port and starboard tail planes extending outwardly from the tail fin on opposite sides thereof and wherein the tail planes include elevator output devices of the flight control system for applying pitching moments to the aircraft about its lateral axis.

31. An aircraft substantially as hereinbefore described with reference to Figs 1 to 4, Figs 5 and 6 or Fig 7 of the accompanying drawings.