GB2157248A

GB2157248A - A beam structure

Info

Publication number: GB2157248A
Application number: GB08409702A
Authority: GB
Inventors: David George Cook
Original assignee: METAL FAX Ltd
Current assignee: METAL FAX Ltd
Priority date: 1984-04-13
Filing date: 1984-04-13
Publication date: 1985-10-23

Abstract

An I-beam structure has top and bottom rails 10 and 12 joined by a web 14. The web is loaded in shear when the beam is supporting a load. The web is very thin, as it has been found that, provided the web is held accurately in one plane, the necessary resistance to shear can be achieved with a thin, and therefore light, web. To ensure that the web is held in this way, supports 18 are provided for maintaining the web in the right position. A strong, light-weight web as described finds particular application as the main structural beam in an aircraft wing. It is especially useful in the wing of a microlight aircraft. <IMAGE>

Description

SPECIFICATION A beam structure This invention relates to a beam structure. The structure is particularly, but not exclusively, suitable for use in aircraft wings.

In aircraft construction, it is always important to keep the whole structure as light as possible while maintaining the necessary strength. In microlight aircraft this is particularly important as the rules for the class stipulate that the aircraft weight must be below 150kg. Because of this weight limitation, and because of the weight of the essential components of the aircraft, the builders of microlight aircraft have been unable to mount sufficient power to enable their aircraft to carry any worthwhile payload. Such aircraft have been used exclusively for leisure flying.

According to the present invention, there is provided an I-beam structure having top and bottom rails and a web joining the rails, the web being thin such that it is capable of resisting shear forces in its own plane but is unable to resist any substantial forces outside its own plane, and means for maintaining the web in its own plane.

The structure may be used to form the main longitudinal support structure in an aircraft wing. The structure is very light and is able to resist the load arising on an aircraft wing. As a result it is possible, within the microlight rules, to increase the flying performance such that a passenger or a payload can be carried. This substantially extends the usefulness of a microlight aircraft.

The means for maintaining the web in its own plane may be a plurality of formers which are held rigidly in place in the structure and which have a flat surface bonded to the web. In an aircraft wing, these formers can also be used to define the contours of the wing leading edge.

The top and bottom rails should be capable of resisting tensile and compressive forces along their length. Preferably the rails include surfaces at right angles to the plane of the web and a surface parallel to the plane of the web. In a preferred construction, the rails and the web are made of different materials and the web is secured to the surfaces parallel to the web plane.

In a microlight aircraft, aluminium sections have been found to be suitable for the top and bottom rails, and top-hat sections are especially preferred.

The web can be of thin plywood; 1.2mm 3-ply birch plywood has proved satisfactory. The formers for keeping the web in its own plane can be of expanded polystyrene, or other suitable foam.

The web can be attached to the rails by direct bonding. The web may also have lightening apertures through it, but these apertures will not extend to the edge of the web. At the areas of highest load, the web may be doubled.

The invention extends to an aircraft (particularly a microlight aircraft) wing having a beam structure as set forth above forming the main structural unit of the wing.

In microlight aircraft, it is desirable for the wings to be detachable so that the aircraft can be transported by road. At the top and bottom of the end of the wing which is to be attached to the aircraft, a pair of lugs can be attached to mate with a corresponding pair of lugs on the aircraft body. Vertically extending pins then pass through holes in the mating lugs to hold the wing to the aircraft body.

Thrust pads may be needed at the leading and trailing edges of the wing/body joint to take up thrust loadings.

A tension stay may be provided from a point midway along the length of the wing to the aircraft body. However the wing structure may be strong enough to allow such a stay to be dispensed with.

The invention also extends to an aircraft having wings as set forth above. The wing system may include a central wing section, constructed as set forth above, and permanently attached to the aircraft body.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a beam structure in accordance with the invention; Figures 2a, 2b and +c show cross-sections through one of the rails at different points along the length of the rail; Figure 3 is a cross-section through an alternative form of rail; Figure 4 is a plan view and Figure 5 is an elevation of a joint between a centre wing section which is permanently part of the aircraft body and a wing; and Figure 6 is a section through a wing in accordance with the invention.

Figure 1 shows a part of a beam structure made up of a top rail 10 and a bottom rail 12 and a shear web 14 joining the two rails. The rails 10 and 12 are both top-hat sections, and the web 14 is secured to vertical faces of these sections.

For aircraft applications, the rails 10 and 12 can be of aluminium alloy He-30. Top-hat sections in this alloy are widely available as they are used for stringers on the insides of truck bodies. The web 14 can be of 1.2mm, 3-ply birch ply which can be secured to the rails by adhesive. Pop rivets may be used in addition, to hold the joint together while the adhesive sets.

The shear web 14 may have holes 16 cut out of it, if it becomes necessary to make the structure any lighter than it already is. Only one such hole is shown in Figure 1, but there may be a number of these holes along the length of the beam.

A former 18 is fitted at the front of the structure.

The figure shows only one of these formers, but in practice there will be large number of them, spaced at intervals of about 30cm along the length of the beam and at both the front and the back of the beam. The former shown has a rounded nose which will form the contour of the leading edge of the wing and a straight rear edge which is bonded to the shear web 14. As a result of this bonding, the former (together with another former bonded to the opposite side of the web) keeps the shear web in a single vertical plane, so that the web is only stressed in shear. A suitable adhesive is used to bond the former to the web.

The former itself does not have to have any great strength to perform this function, and can thus be of a very light weight material such as expanded polystyrene which has been found to be suitable. Lightening1access holes 20 can be formed in the formers.

The loads to be supported by an aircraft wing decrease with distance from the wing root. The strength of the beam structure can therefore be varied over the length of the wing, thus saving unnecessary weight. Figure 1 shows the lightest form of the beam structure, as will be used at the outboard end of the wing. Figures 4 and 5 show the inboard end of the wing, and here a double shear web is provided by adding a second web 22 on the other side of the rails 10 and 12. This second web 22 terminates a short distance from the wing root, in an arcuate shape. Where two shear webs exist side by side, timber spacer pieces 24 are placed between them and bonded in place to prevent the webs bowing inwards.

The rails are also reinforced near the wing root, by placing reinforcing plates over the top of the section. This is shown in Figures 2 where Figure 2b shows two reinforcing plates on a top hat section.

This is used at the root of the wing, Figure 2b shows a single reinforcing plate as used in the middle region of the wing and Figure 2a shows an unreinforced section as used at the outboard end of the wing. These reinforcing plates can also be held in place by adhesive, possibly backed up by pop-rivets which hold the joint while the adhesive sets. The number or length of the reinforcing plates on the top and bottom rails may be different. The bottom rail is generally in tension and may require less reinforcement than the top rail which is generally in compression.

Figure 3 shows an alternative rail section. This section is a T-section and has a surface 50 at right angles to the plane of the shear web, and a surface 52 parallel to the plane of the web and to which the shear web can be properly secured.

Figures 4 and 5 show how a wing 30 is mounted on and dismantled from a centre wing section 32 which is a permanent part of the aircraft body. The centre wing section is constructed with a beam structure as described above, with the maximum reinforcing, i.e. a double shear web and two reinforcing plates on the top and bottom rails.

The top and bottom rails 10 and 12 on the wing 30 and the centre section 32 both end in yokes 34, 36. As can be seen in Figure 5, the yokes 34 are in pairs with a space between them for receiving the yokes 36. Each yoke has a pair of holes 38 in it.

The wing is offered up to the centre section until all the holes 38 register, and then two pins 40 are dropped through the holes to secure the wing 30 to the centre section 32.

In Figure 4, just the adjacent edges of the wings are indicated in chain-dotted lines. When the wing is fitted, these edges abut each other and prevent any fore and aft movement of the wing about an axis in the region of the pins 40. This connection is very quick to assemble and has been found to provide quite adequate strength.

Finally, Figure 6 is a cross-section through a wing, showing the former 18, a former 42 in the rear part of the wing, a skin 44 stretched over the wing structure, and a beam structure running the length of the wing, with the two rails 10 and 12 and the web 14.

Claims

1. An I-beam structure having top and bottom rails and a web joining the rails, the web being thin such that it is capable of resisting shear forces in its own plane but is unable to resist any substantial forces outside its own plane, and means for maintaining the web in its own plane.

2. A beam structure as claimed in Claim 1, wherein the means for maintaining the web in its own plane comprises a plurality of formers which are held rigidily in place in the structure and which have a flat surface bonded to the web.

3. A beam structure as claimed in Claim 1 or Claim 2, wherein the top and bottom rails are capable of resisting tensile and compressive forces along their length and include surfaces at right angles to the plane of the web and a surface parallel to the plane of the web.

4. A beam structure as claimed in Claim 3, wherein the rails and the web are made of different materials and the web is secured to the surfaces parallel to the web plane.

5. A beam structure as claimed in Claim 4, wherein the web is attached to the rails by direct bonding.

6. A beam structure as claimed in any preceding claim, wherein the web has lightening apertures through it, but these apertures do not extend to the edge of the web.

7. A beam structure as claimed in any preceding claim, wherein the web is doubled at the areas of highest load.

8. An aircraft wing having a beam structure as claimed in any preceding claim forming the main structural unit of the wing.

9. A microlight aircraft wing having a beam structure as claimed in any one of Claims 1 to 7 forming the main structural unit of the wing.

10. An aircraft wing as claimed in Claim 8 or Claim 9, wherein the web is held in its own plane by formers which also define the contours of the wing leading edge.

11. A microlight aircraft wing as claimed in Claim 9 or Claim 10, wherein aluminium sections are used for the top and bottom rails.

12. A microlight aircraft wing as claimed in Claim 11, wherein the aluminium sections are tophat sections.

13. A microlight aircraft wing as claimed in Claim 12, wherein a reinforcing plate is bonded to the section, to enclose the cavity in the section.

14. A microlight aircraft wing as claimed in any one of Claims 11 to 13, wherein the web is of thin plywood.

15. A microlight aircraft wing as claimed in any one of Claims 11 to 15, wherein the formers for keeping the web in its own plane are of a foamed plastics material.

16. A microlight aircraft having wings as claimed in any one of Claims 9 to 15, wherein the wings are detachably mounted on the aircraft by a pair of lugs at the top and bottom of the end of each wing where the wing is to be attached to the aircraft, a corresponding pair of lugs on the aircraft body, and vertically extending pins which pass through holes in the mating lugs to hold the wing to the aircraft body.

17. A microlight aircraft as claimed in Claim 16, wherein a tension stay is provided from a point midway along the length of the wing to the aircraft body.