GB2295132A - Wing construction - Google Patents

Abstract

A wing comprises leading edge spars 14, 15 trailing edges 24, 25, beams 21A, 21B, a main spar 19, upper wing surfaces 22, 23 formed by a cloth material extending from the leading edge to the trailing edge; the surface being shaped by means of a series of ribs battens, a, b; a lower wing surface formed by cloth material extending from the leading edge to the trailing edge, a plenum chamber 40 extending from the leading edge to a position part way across the upper wing, and at least one aperture X, Y at or near the leading edge of the wing whereby air can pass into the plenum chamber to create a static over-pressure relative to air pressure external to the plenum. Each aperture is located so that air pressure within the plenum is raised at low angles of attack and lowered at high angle of attack. The upper wing surface for at least 20% of the chord length of the wing is either formed of or shielded by a material substantially stiffer than that of the remaining material forming the upper wing surface. The wing may have a rear plenum chamber 41 fed from the plenum chamber 40 or at least one aperture in the wing surface at or near the leading edge, so as to provide for static over pressure in the rear plenum chamber relative to average air pressure external to the plenum. The lower wing surface may have a variable external profile. Venting means may be provided to enable air pressure in the rear plenum to be reduced in a controlled manner other than by leakage. The wing is particularly intended for a hang glider. <IMAGE>

Description

WING This invention relates to a wing. In particular it is concerned with a wing for a flying machine comprising a sequence of ribs spaced along the length of the wing and with a covering of a flexible material. In a conventional wing the ribs generally serve to define what is an upper, convex upward, surface for the wing.

When a wing of the general type referred to is in use the lift generated by the wing depends upon the angle of attack (generally defined as the angle between the chord line of the wing and direction of air flow approaching the leading edge of the wing.

According to a first aspect of the present invention there is provided a wing having an upper wing surface formed by material extending from the leading edge to the trailing edge; the surface being shaped by means of a series of ribs or frames spaced along the length of the wing a lower wing surface formed by material extending from the leading edge to the trailing edge; a plenum chamber in the wing between the upper surface and the lower surface extending over the underside of the upper wing surface from the leading edge to a position part way across upper wing; and at least one aperture in the wing surface at or near the leading edge of the wing whereby air can pass into the plenum chamber so as to provide for a static over-pressure of air in the plenum chamber relative to the average air pressure external to the plenum.

According to a first preferred version of the first aspect of the present invention a part of the upper wing surface forms a wall of the plenum chamber and over pressure of air within the plenum chamber acts to resist deformation of the upper wing surface arising from wind forces applied to the outside of the upper wing surface.

According to a second preferred version of the first aspect of the present invention or the first preferred version thereof the, or each, aperture is located relative to the leading edge so that the passage of air into the plenum chamber by way of the or each aperture serves to maintain air pressure in the plenum chamber significantly above the static pressure as the angle of attack is reduced.

According to a third preferred version of the first aspect of the present invention or any preceding preferred versions thereof the, or each, aperture is located at the leading edge of the wing relative to the chord line of the wing so that air pressure within the plenum is raised at low angles of attack and lowered at high angle of attack.

According to a fourth preferred version of the first aspect of the present invention or any preceding preferred versions thereof the material forming the upper wing surface is a flexible material such as a woven fabric or a sheet material. Typically the material forming the upper wing surface for a distance extending for at least 20% of the chord length of the wing is either formed of or shielded by a material substantially stiffer than that of the remaining material forming the upper wing surface.

According to a fifth preferred version of the first aspect of the present invention or any preceding preferred versions thereof there is provided a rear plenum chamber between the upper surface and the lower surface and at least one aperture in the wing surface at or near the leading edge whereby air can pass into the rear plenum so as to provide for static over or under pressure in the rear plenum chamber relative to average air pressure external to the plenum.

Preferably the lower wing surface has an external profile which is variable and at least partially dependent on the static pressure within the rear plenum chamber.

Preferably the lower wing surface forms a wall of the rear plenum chamber.

Venting means are conveniently provided to enable air pressure in the rear plenum chamber to be reduced in a controlled manner other than by leakage.

According to a sixth preferred version of the first aspect of the present invention or any preceding preferred versions thereof the or each aperture can be opened or closed remotely.

According to a second aspect of the present invention there is provided a flying machine equipped with a wing according to the first aspect or any preferred version thereof. Typically the flying machine is in the form of a glider or a powered aircraft.

An exemplary embodiment of the invention will now be described with reference to the accompanying drawing of a wing of a hang glider of which: Figure 1 is a plan view from above; and Figure 2 is a section on II-II of Figure 1.

The Figures variously show a wing 11 made up of a pair of mirror image sections 12, 13. Since the form and function of the sections 12, 13 are mirror images of one another only the items relating to section 12 are described hereafter the corresponding items for section 13 being shown in parenthesis.

Section 12 (13) incorporates a leading edge spar 14 (15). Inner end 16 (17) of spar 14 (15) is demountably secured to leading end 18 of main spar 19 to facilitate the erection and dismantling of the glider. Spar 14 (15) is connected to one end of beam 21A (21B) whose other end is connected to main spar 19. The leading edge spar 14 (15) is of circular cross section and serves to anchor front ends of each of a sequence A, (B) of aluminium alloy battens, typically battens al, a2, a3, (b1, b2, b3). These are secured into pockets in material forming the upper surface 22 (23).

The battens al, a2, a3, (b1, b2, b3) are preformed into actuate shape to provide a predetermined curvature to upper surface 22 (23). The trailing end of the sequences A, (B) provide a locus defining trailing edge 24, (25) of the section 12, (13).

Tips 32, (33) of sections 12, (13) are formed by an aluminium rib 34, (35) which is aligned at its rear end by a rib 36 (37) extending at an angle from spar 14 (15).

Reference is now made particularly to Figure 2. To avoid an excess of reference numerals reference is now only made to components in section 12 but it should be understood that components of corresponding form and function are mirrored in section 13.

The material forming the major part of the upper surfaces 22, 23 is in two regions.

The front region 22' extends from junction seam 26 to a seam 28 extending about 20% of the chord length from leading edge spar 14 to trailing edge 24. This is fabricated from a stiff fabric composed of Mylar (RTM) coated sail cloth of man made fibre. The rear region 22" extends from junction seam 26 to trailing edge 24.

Section 12 has a lower surface 38 formed by sail cloth material similar to that making up the rear regions 22" of the upper surface 22. The lower surface 38 extends from junction seam 26 to just beyond seam 38' which is located about 80% of the way to the trailing edge 24.

The upper surface 22 and lower surface 38 serve to enclose a front plenum 40 and a rear plenum 41 which are separated by an air tight diaphragm M.

Front plenum 40 The fabricating process for the section 12 provides for the front plenum 40 to be relatively air tight except for apertures X1, X2, X3 and X4 on or close to leading edges 14. These apertures X1-X4 can be opened or closed by means of flaps operable by a pilot of the glider from a flying position beneath the main spar 19.

In practice it has been found that the apertures can normally be left open. In the present example the wing span of the glider is 10 metres. The front plenum 40 of section 12 and the corresponding front plenum for section 13 extends over the greater part of the wing span. The width front to rear of front plenum 40 is 550 mms. Each aperture X is a circular hole of about 30 mms.

The 'angle of attack' P lies between relative air flow W and chord line C of section 12 and its appropriate selection is a significant factor in flying. Relative air flow W on approaching the leading edge of the wing necessarily divides into two parts: flow W1 flowing over most, if not all, of upper wing surface 22; flow W2 flowing over the lower surface 38.

The distribution of air pressure above and below the wing 11 depends on the angle of attack P. As far as section 12 is concerned with chord line C and air flow W near horizontal (the angle P being small but positive) most of the wing lift is provided by air flow W1 over the upper surface 22. As the angle P increases air flow W1 starts to flow less freely over the upper surface 22 and with P at an angle of about 20" the air flow W1 can no longer effectively follow the contour of upper surface 22 and stalling occurs. In a relatively slow flying aircraft such as a hang glider (especially a powered one) the onset of stalling can be serious and requires positive flying control action by the pilot.

When the hang glider is put into a dive (that is to when chord line C is initially directed below the relative air direction W) the aircraft will increase speed. It has been found that with conventional fabric wing surfaces the fabric between battens corresponding to those in sequences A, B tends to be pushed inwardly forming a series of parallel chordal recesses along the wing length. This appears to have an number of undesirable effects including a tendency to generate excess drag. In the present invention this has been ameliorated by allowing the passage of air through apertures X into the plenum 40 so that static pressure within the plenum rises so further stiffening the upper surface 22, and in particular the leading edge 22', so resisting the tendency of the leading edge material to sag into a series of recesses between the battens.

The apertures X are located in a position so that with chord line C of the wing nearly aligned with relative air direction W (or at least where the angle is slightly positive) the apertures X are pointing slightly upwards which in practical terms may anyway be necessary to enable a clear air flow into the plenum 40 through the apertures X without flow being impeded by the spar 14. In this case air flow through apertures X into the plenum 40 occurs readily and pressure within the plenum 40 maintained more or less at a level related to air speed.

With the wing 12 in a rising attitude the angle of attack P increases. Since in this case air speed is likely to be falling static pressure within plenum 40 is not likely to be of major significance since in these circumstances recessing of the leading surface of the wing would not normally occur.

When the wing 12 is directed downwardly into a dive the alignment between chord line C and relative air direction W is such as to bring the apertures into a fully open position relative to air flow. As a consequence an increase in air in plenum 40 pressure occurs serving to load the wing surface 22' and so enable the wing surface 22' to resist deformation by external air pressure.

Rear plenum 41 The rear plenum 41 extends over the entire wing width that is to say of section 12 and 13. A single aperture P at the mid point of the leading edge of the wing 11 provides for a supply of air to be fed into the rear plenum 41. Aperture P provides for air pressure within the rear plenum 41 to be varied above and below static pressure. With a relatively high air pressure maintained in rear plenum 41 the lower surface 38, all or some of which is of relatively flexible material, is driven outwardly to conform to a profile S1 where the wing has a maximum thickness. As the pressure in the rear plenum 41 drops to a minimum the lower surface 38 contracts to a profile S2 where the wing has a minimum thickness to provide for an optimum lift/drag ratio.In order to produce a suitable profile for the underside of the wing at different internal pressures for section 12 the lower surface can be fabricated with inserts, panels, strips or whatever of different characteristics such thickness, elasticity or porosity for example.

In the exemplary embodiment the apertures X14 supplying front plenum 40 are separate from aperture P for rear plenum 41. However the same apertures at or near the leading edge of the wings could be used to supply both plenums 40, 41 by separate channels. Alternatively it is conceived that the plenum 41 could be fed, to a greater or lesser extent from plenum 40.

In practice it is observed that plenum 40, and the corresponding plenum for section 13, are relatively air tight. Plenum 41 is by comparison somewhat leaky.

It will be apparent that by making use of apertures P, X placed on or close to the leading edge it becomes possible by means of an attitude change in the wing section 12, causing a change in the chord line C relative to air flow W, to increase or reduce air flow into the plenum 40. An increase serves to maintaining the shape of the relatively flexible leading edge of the wing when it is likely to be subject to deformation. Likewise if desired air flow can be used to increase or decrease pressure in plenum 41 to change the shape of the wing profile to optimise air flow for a given flying configuration.

If necessary the plenum 41 can be provided with means for positively venting air from the plenum when required so as to provide for a swifter change of lower wing profile than can be obtained using inherent leakiness to reduce over pressure. To this end one or more vents can be supplied which are caused to act by a change in air flow over the wing generating a relative low pressure area into which the vent can be opened either automatically by way of a flap valve (as occurs when the flight configuration of the wing reaches a particular attitude), or by way of a manually operated valve.

The invention provides for a number of advantages over existing wing types to be achieved relatively easily, safely and economically.

While reference has been made to a hang glider wing in the exemplary embodiment the invention is applicable to wings for other aircraft. In particular the use of a pressurisable plenum within the wing for the leading edge of the wing can be used in aircraft operating at much higher speeds to provide for a wing of increased strength but using less material.

Claims (15)

1A wing having: a leading edge; a trailing edge; an upper wing surface formed by material extending from the leading edge to the trailing edge; the surface being shaped by means of a series of ribs or frames extending along the length of the wing a lower wing surface formed by material extending from the leading edge to the trailing edge; a plenum chamber in the wing between the upper surface and the lower surface extending over the underside of the upper wing surface from the leading edge to a position part way across upper wing; and at least one aperture in the wing surface at or near the leading edge of the wing whereby air can pass into the plenum chamber so as to provide for a static over-pressure of air in the plenum chamber relative to the average air pressure external to the plenum.

2 A wing as claimed in Claim 1 wherein a part of the upper wing surface forms a wall of the plenum chamber and over pressure of air within the plenum chamber acts to resist deformation of the upper wing surface arising from wind forces applied to the outside of the upper wing surface.

3 A wing as claimed in Claim 1 or Claim 2 wherein the, or each, aperture is located relative to the leading edge so that the passage of air into the plenum chamber by way of the or each aperture serves to maintain air pressure in the plenum chamber significantly above the static pressure as the angle of attack is reduced.

4 A wing as claimed in any preceding claim wherein the, or each, aperture is located at the leading edge of the wing relative to the chord line of the wing so that air pressure within the plenum is raised at low angles of attack and lowered at high angle of attack.

5 A wing as claimed in any preceding claim where the material forming the upper wing surface is a flexible material such as a woven fabric or a sheet material.

6 A wing as claimed in Claim 5 wherein the material forming the upper wing surface for a distance extending for at least 20% of the chord length of the wing is either formed of or shielded by a material substantially stiffer than that of the remaining material forming the upper wing surface.

7 A wing as claimed in any preceding claim having a rear plenum chamber between the upper surface and the lower surface and at least one aperture in the wing surface at or near the leading edge whereby air can pass into the second plenum so as to provide for static over pressure in the rear plenum chamber relative to average air pressure external to the plenum.

8 A wing as claimed in Claim 7 characterised by a lower wing surface whose external profile is variable and at least partially dependent on the static pressure within the rear plenum chamber.

9 A wing as claimed in Claim 8 wherein the lower wing surface forms a wall of the rear plenum chamber.

10 A wing as claimed in Claim 7, Claim 8 or Claim 9 wherein venting means are provided enabling air pressure in the rear plenum chamber to be reduced in a controlled manner other than by leakage.

11 A wing as claimed in any preceding claim wherein the or each aperture can be opened or closed remotely.

12 A wing as hereinbefore described with reference to the accompanying drawings.

13 A flying machine equipped with a wing as claimed in any preceding claim.

14 A flying machine as claimed in Claim 13 in the form of a glider.

15 A flying machine as claimed in Claim 13 in the form of a powered aircraft.