GB2201384A

GB2201384A - Aerodynamic control device

Info

Publication number: GB2201384A
Application number: GB08802629A
Authority: GB
Inventors: John F Riley; Ian Jenkins; Keith Martin Rogers; Arthur N Rhodes
Original assignee: British Aerospace PLC
Current assignee: BAE Systems PLC
Priority date: 1987-02-07
Filing date: 1988-02-05
Publication date: 1988-09-01
Also published as: GB8702782D0; GB8802629D0

Abstract

The present invention provides an aerodynamic control device having a slat (1) located along the leading edge of a wing, the said slat being moveable to any desired position between a first (fully retracted) position and a second (fully extended) position. In use, a gap will be formed between the trailing edge of the slat (1) and the upper skin (3) of the wing as a result of the flexing of the wing and/or the flat under aerodynamic forces; according to the invention, the gap is closed by a seal. The seal can take the form of a pre-stressed trailing portion (5) of the slat which presses against the upper skin (3) to seal the gap and/or the seal can be produced by the upper skin being detached from the rib structure of the wing and being free to move under the influence of the lift-generated during flight towards the slat (1) to close and seal the gap. The front portion of the upper skin (3) may be free to move from a position (3A) at low load to a position (3B) at high load. The slat is carried by a curved track (12) (Fig. 4) supported by rollers (16) on the wing structure, and moved by a jack (18). <IMAGE>

Description

AERODYNAMIC CONTROL DEVICES The present invention relates to aerodynamic control devices and in particular to leading edge control devices for wings known as "slats".

It is known to alter the aerodynamic characteristics of a wing by varying its geometry for instance by providing slats along the leading edge of the wing which may be extended outwards and downwards. This has the effect of increasing the amount of lift generated by the wing, i.e. the chord of the wing is increased and the camber of the leading edge is changed, both of which lead to a corresponding increase in lift on the wing surface. A problem with slats is that when they are extended gaps occur between them and the leading edge of the wing and these gaps are a source of turbulence and drag and cause a loss of lift; such gaps can be deliberately included by the wing designer or they can arise as a result of aerodynamic forces causing the wing or the slat to flex. The advantage of extending the slats is partly lost because of the gaps.

It is an object of the present invention to improve the lift efficiency along the leading edge of a wing; this is achieved according to the invention by eliminating any gaps between a slat and the leading edge of the wing thereby increasing the lift generated when the slat is extended from the leading edge of the wing.

British Published Patent Application No 2 138 756A descibes a slat extension system that can move a slat to any one of three positions: a fully retracted position, a fully extended position and an intermediate position. In the retracted and intermediate positions, the trailing edge of the slat lies against the main wing surface while in the fully extended position a gap is opened up between the slat and the wing. At a position part way between the retraced and the intermediate position, there would be a gap between the slat and the underlying wing surface and so, even if the extension mechanism were capable of moving the slat to such a part-way position, gaps would occur between the slats and the wing in these part-way positons which have the disadvantages described above.Thus, the slat is only usable in two exact positions (the retracted position and the intermediate position) if gaps are to be avoided, which limits the use of the slats.

The present invention provides a system in which the position of a slat is infinitely variable between two limits and in none of the positions is there a gap between the slat and the wing surface.

According to one aspect of this invention there is provided an aerodynamic control device comprising a slat located along the leading edge of a wing, the said slat being moveable to any desired position between a first (fully retracted) position and a second (fully extended) position, and sealing means for sealing any gap that arises between the trailing part of the slat and the adjacent wing surface, e.g. as a result of aerodynamic forces acting on the wing and/or on the slat, when the slat is extended from the said first position.

The said sealing means can be a resilient member located along a rear part of the slat and arranged to overlap with and press against the adjacent wing surface and to move with the slat to cover any gap and/or the sealing means may be a flexible skin region on the wing which is free to lift upwardly and outwardly under the action of aerodynamic lift forces to make close contact with the underside of the slat and so seal any gap.

The present invention will now be described by way of example and with reference to the accompanying drawings of which: Figure 1 is a sectional view of the leading part of a wing and shows a wing-mounted slat in a fully retracted position; Figure 2 is identical to Figure 1 except the slat has been moved to a fully extended position; Figure 3 is a sectional view of a second embodiment and shows the leading part of a wing and a wing-mounted slat in a fully extended position; and Figure 4 is a sectional view through a wing and shows the slat extension and retraction mechanism.

Referring to Figure 1, a slat 1 is extendibly attached to a wing including an upper skin 3 and a lower skin 4. In a fully retracted position, the slat 1 lies along the leading edge of the aircraft wing and is conformal therewith to form a desired aerodynamic shape for normal flight. A portion 5 of the rear edge of slat 1 is formed of a downwardly urged flexible material, which is preferably the same material as the slat is made of, e.g. aluminium. The elastic properites of the slat material-cause the rear edge of the slat to flex downwardly and press onto the upper wing skin 3 and form a seal.

The flexible region 5 of the slat is chosen to have a stiffness coefficient to suit the expected aerodynamic loads on the wing; for example the material used for a high performance wing, which is subjected to high loads, will be made stiffer than a wing which is to be subjected to lower loads. In general the material stiffness of rear edge 5 of the slat 1 is stiffer than the wing skin 3. The region 5 may be a portion of the skin of the slat (as shown), which may be reinforced, or it may be provided by a separate member attached to the rear edge of the slat.

During conditions of no, or very low, lift with the slat fully retracted, the skin 3 of the aircraft wing lies in the position as shown at 3A and the slat blends into the top surface of the wing to provide a smooth surface. During conditions of high lift, the wing skin 3 is moved outwardly by the prevailing aerodynamic forces into position 3B. The seal provided by the flexible rear edge 5 of the slat is thus supplemented by the wing skin moving outwards to press against the rear edge of the slat which improves sealing contact between the surface of the wing skin and the rear edge of the slat.Such flexibility of the wing skin may be achieved by not attaching a portion of the wing skin to riblets in the supporting rib structure of the wing and this enables the unattached wing skin to lift upwards and outwards, under aerodynamic lift, to enhance sealing; generally, the unattached portion will be the skin extending from spar 2 forward to the wing leading edge.

When it is desired to extend the slat fully, it is moved from the position shown in Figure 1 to that shown in Figure 2.

During deployment, the rear edge of the slat 1 slides along the upper surface of the wing from position 6 shown in Figure 1 to position 7 in Figure 2 and sealing contact is maintained between the slat and the wing skin at all times. The length by which the slat overlaps with the skin 3 of the aircraft wing is sufficient to prevent the occurence of a gap when the slat is moved into the fully deployed position shown in Figure 2. It will be appreciated that when it is desired to extend the slat to any position intemediate between that shown in Figure 1 and that shown in Figure 2, the rear edge of the slat 5 presses against the skin 3 of the wing to form a seal; in this way, any gap between the slat and the wing is eliminated.

Referring to Figure 2, the operation of the seal when the slat is in a deployed position (i.e. when it is partly or fully extended) is essentially the same as when the slat is in the retracted position. During conditions of no or very low lift, the wing skin lies in position 3A and the elastic properties of rear edge 5 of the slat are sufficient to provide a seal between the slat and aircraft skin. Under conditions of high lift, the skin 3 moves from 3A to 3B to enhance sealing between the wing and the slat. When the slat is extended, a small gap 8 occurs in the underside of the wing in a region where the lower edge of the slat 1 separates from the wing. High pressure air in this region flows into the wing and acts against the underside of wing skin 3 further improving the seal between the wing skin and the slat.

A further embodiment is illustrated in Figure 3, in which the upper skin 3 is attached to the riblets of the supporting rib structure of the wing in the conventional way. Sealing of the gap between the slat and the wing is brought about by by the prestressed trailing portion 5 of the slat as described above but the sealing is enhanced during conditions of lift by a flexible secondary skin flap 10 attached to the upper skin 3 at point 11 behind the slat 1. During conditions of lift, the free end of the flexible skin flap 10 is lifted under the action of aerodynamic forces from its rest position lox away from the upper surface of the wing to position 10B where it presses against the underside of the slat and thus helps seal the gap between the slat and wing.Apart from the inclusion of the flap 10 and the attachment of the skin 3 to the underlying riblets, the arrangement of Figure-3 is the same as that of Figures 1 and 2 and like reference numerals have been used to indicate like parts.

Figure 4 shows the mechanism for extending the slat 1; the mechanism is shown in the fully extended position (in solid lines) and in the fully retracted position (in dashed lines).

This mechanism is well-known in the art and the present invention is not limited to the use of any particular sort of extension and retraction mechanism. The mechanism includes a curved guide track 12 attached to the slat 1 by brackets (not shown). The track 12 has a central slot or groove 14 which engages with roller bearings 16 that are attached to the internal wing structure (not shown). A jack 18, which may be either mechanically or hydraulicallycontrolled,is pivotally connected at one end to a bracket 20 that is integral with strut 2 and at the other end, the jack 18 is pivotally connected to a further bracket 22 which is fixed to the slat 1.When it is desired to extend the slat from the retracted position shown in dashed lines to the extended position shown in solid lines, the jack 18 is extended which pushes the slat outwardly and downwardly along a path dictated by the engagement of the rollers 16 in slot 14. As a result, the jack 18 pivots about bracket 20 and, in order to accommodate such movement, a part of the lower skin 4 of the wing is constructed in the form of a door 24 attached to the jack 18 and the door 24 thus opens when the jack pivots to extend the slat 1 and closes when the slat is retracted. Retraction of the slat is achieved by reversing the above steps.

Although two embodiments of a sealing arrangement have been shown in Figures 1, 2 and 3, other arrangements are possible without departing from the scope of the invention. For example a seal could be achieved by using flexible material between the slat and the wing. surface instead of using the resilience of the trailing edge 5 of the slat 1. In addition, when a seal between the slat and the wing is provided by the pre-stressed portion 5 (or similar resiliant sealing means), it is not necessary for the skin 3 to be free to move under the influence of prevailing aerodynamic forces nor is it necessary to provide a flap 10 but it is desirable to do so because the loose skin 3 or 10 improves the seal formed by pre-stressed portion 5. Furthermore, the sealing of the gap between slat 1 and wing skin 3 can be achieved solely by the action of the loose wing skin 3 or 10 and its ability to seal the gap under the influence of aerodynamic forces, i.e. it is not necessary to provide a pre-stressed portion 5 although it desirable to do so.

Claims

1. An aerodynamic control device comprising a slat located along the leading edge of a wing, the said slat being movable to any position between a first (fully retracted) position and a second (fully extended) position, and sealing means for sealing any gap arising between the trailing part of the slat and the adjacent wing surface when the slat is in any extended position.

2. A device as claimed in claim 1, wherein the sealing means comprises a resilient member located along a rear part of the slat, the member being arranged to overlap with and press against the adjacent wing surface and to move with the slat to seal any gap between the trailing part of the slat and the adjacent wing surface.

3. A device as claimed in claim 2, wherein the resilient member is formed by the trailing part of the slat which has been prestressed.

4. A device as claimed in claim 2 or claim 3, wherein the sealing means further includes a flexible region of skin on the wing, the said region being located at least partly under the slat when the slat is in any position between and including the first and second positions and wherein the skin of the said region is free to move under prevailing aerodynamic conditions to seal any gap between the trailing part of the slat and the adjacent wing surface.

5. A device as claimed in claim 4, wherein the said region is part of the skin of the wing and wherein the skin in the said region is not secured directly to the underlying wing structure.

6. A device as claimed in claim 4, wherein the said region is a flap that is attached to, and overlies, the skin of the wing.

7. A device as claimed in claim 1, wherein the sealing means comprises a flexible region of skin on the wing, the said region being located at least partly under the slat when the slat is in any position between and including the first and second positions and wherein the skin of the said region is free to move under prevailing aerodynamic conditions to seal any gap between the trailing part of the slat and the adjacent wing surface.

8. A device as claimed in claim 7, wherein the said region is part of the skin of the wing which is not secured to the underlying wing structure.

9. A device as claimed in claim 7, wherein the said region is a skin flap that is attached to, and overlies, the skin of the wing.

10. Aerodynamic control devices substantially as hereinbefore described in connection with and as shown in Figures 1 and 2 or Figures 3 and 4 of the accompanying drawings.