Manufacture of composite laminate aircraft landing gear strut protector

Abstract: A method of forming a composite laminate and an aircraft landing gear strut fairing/debris protector are provided. The composite laminate comprises first and second fibre reinforced plastics skin elements (21, 23) with a foamed core (27) between them. The method includes the steps of providing a tool having a tool surface (15, 20) to form each said skin element, forming a lay-up (21, 23) on each said tool surface of fibrous reinforcing material and plastics matrix material and allowing the matrix material at least partly to harden, positioning the tools (8, 13) such that the two skins (21, 23) are supported in their final relationship to each other and introducing a foaming resin (27) between the skins to form a foam core.

Description: This invention relates to the manufacture of composite laminates, in particular to an aircraft landing gear strut fairing/debris protector. Aircraft main landing gear oleo struts can be a source of aircraft noise which can be particularly troublesome when aircraft are taking off and approaching the airfield for landing, when the gear is locked in the down position. The aircraft main landing gear oleo struts can also be subject to debris attack, particularly during take off and landing. Debris can be in the form of stones, broken concrete and the like and may in some cases be raised from the ground by the nose landing gear, then to be struck by the main landing gear. CA-A-1 059 487 discloses a method of making a lightweight aeroplane by foaming a plastic around a tubular framework and applying a smooth hard coating over the foamed plastic. It is an object of the invention to provide a fairing or debris protector for aircraft landing gear to be attached to the main oleo strut thereof which will reduce wind noise and avoid impact damage of debris to the gear at the same time as being light in weight and adapted to fit the shape of the gear, for secure, reliable and accurate fitting. According to one aspect of the present invention there is provided a method of forming a composite laminate aircraft landing gear strut fairing/debris protector comprising first and second fibre reinforced plastics skin elements with a foamed core interposed therebetween, the method including the steps of providing a tool having a tool surface to form each skin element, forming a lay-up on each said tool surface of fibrous reinforcing material and plastics matrix material and allowing the matrix material at least partly to harden, positioning the tools such that the two skins are supported in their final relationship to one another and introducing a foaming resin between the skins to form a connecting foam core therebetween. According to a second aspect of the invention there is provided a composite laminate aircraft landing gear strut fairing/- debris protector as manufactured according to the method of the first aspect of the invention. Fibreglass has been found surprisingly effective for use as the fibrous reinforcing material for this application. The invention will now be described by way of example with reference to the accompanying drawings of which:- Figure 1 is a front isometric view of a fairing or debris protector according to the invention installed on a main oleo strut of an aircraft landing gear, Figure 2 is a side view of the fairing or debris protector of Figure 1 taken in the direction II of Figure 1, Figure 3 is a view of the fairing or debris protector of Figure 2 taken in the direction III thereof, with the fairing or protector being truncated at the centre line, Figure 4 is a view of the fairing or debris protector of Figure 2 taken in the direction IV of Figure 2, Figure 5 is a section along the line V-V of Figure 2, Figure 6 is an end view of a splash taken from the landing gear of Figure 3, Figure 7 is an end view of an inner tool taken from the splash of Figure 6, Figure 8 is an end view of an outer tool taken from the inner tool of Figure 7, and Figure 9 is an end view of the tools of Figure 7 and Figure 8 used in combination, also showing an alternative version of the tool of Figure 8 for forming an aerodynamic fairing. Referring to Figures 1 and 3, a fairing/debris protector 1 according to the invention for attachment to a main oleo strut 2 of an aircraft landing gear is manufactured as follows. A mould impression or "splash" 3, see Figure 6, is first taken from the strut 2. This is achieved by marking desired boundaries for the fairing/debris protector on the strut 2 by attaching foam material (not shown) with adhesive tape to the strut, having first degreased the strut, and applying release agent to the strut over the area from which the mould impression is to be taken. Two coats of polyester or epoxy resin (polyester preferred) gelcoat are next painted onto the surface. Referring to Figure 6, a layup of fibreglass mat 6 approximately 10mm thick is then applied to the surface and impregnated with polyester resin 7. The resin is then allowed to cure for between four and eighteen hours at a minimum temperature of approximately 21°C. As an alternative to wet lay-up prepreg material may be used. However, the application of heat and some consolidation pressure may be necessary with this method in order to obtain the desired surface finish and structural integrity of the splash. By the use of gelcoat a smooth surface finish for the splash is achieved from which a tool of substantially identical shape and surface finish to the strut can be achieved. Next, in order to manufacture a said tool 8 from the splash 3, release agent is applied to the surface 31 of the splash which was formed from the surface of the strut 2, followed by two coats of gelcoat 9. This step is followed by the application to the surface 31 of a fibreglass lay-up 10, see Figure 7, of approximately 12mm thickness impregnated with polyester resin 11. Optionally some reinforcement 12 to the tool 8 is applied to the rear before cure and cured in position on the tool for strengthening purposes. Referring to Figures 7 and 8, manufacture of the second tool 13 proceeds as follows. A single sheet of thickness wax, sometimes called lay-up wax 14 is adhered to the tool surface 15 of tool 8. Release agent is optionally applied beforehand. In this case the wax is 12mm thick which corresponds to the total thickness of the fairing/debris protector which will be produced in the combined tool. Two coats of gelcoat 16 are next applied either directly or over a release agent to the exposed surface of the thickness wax. When the gelcoat is substantially dry a lay-up 17 for the second tool 13 is placed on the gelcoated surface and impregnated with polyester resin. Further reinforcement 18 is applied to the rear surface 19 of the lay-up and the lay-up is allowed to cure. Once curing is complete the tools 8 and 13 may be separated from the wax. In order to manufacture the fairing/debris protector, firstly release agents and then lay-ups are applied to the tool surfaces 15 of tool 8 and 20 of tool 13 as follows. For tool 8, which will form a skin of the fairing/debris protector 1 which will be in intimate contact with the main oleo strut 2 in use, a lay-up 21 of two plies of 280 gram fibreglass cloth impregnated with polyester resin is formed on the tool surface 15. To form the skin which will define an exposed surface 22 of the fairing/debris protector three plies of 280gram cloth are laid up on the tool surface 20 and impregnated with polyester resin, following application of two gelcoats to the tool surface 20. A resulting lay-up 23 is now allowed to cure. When both lay-ups 21, 23 have cured they may be brought together in a position separated at a peripheral region by approximately 8mm as shown in Figure 9. The requisite separation of the lay-ups is achieved by spacing means (not shown) extending between the tools 8 and 13. Appropriate stopoff means (not shown) are next applied to the peripheral region between the two tools 8, 13 and liquid foaming resin 27 is poured into a cavity 26 formed between the two tools 8, 13. The tools are then laid down flat and the polyester expanding foam resin 27 is allowed to foam out to fill the cavity. It will be appreciated that any irregularity in the shape of the cavity 26, for example due to the aerodynamic outer shape of the fairing as shown in Figure 9 will be accommodated by the foaming of the resin 27. Once the chemical reaction which causes the foaming is complete, after approximately one hour, foam is trimmed from the edges of the resulting fairing/debris protector 1 formed in the tools such that a groove 28 of 6mm depth is formed, see Figure 5, around the periphery of the fairing/protector 1. RTV silicone sealant is then applied into the groove to seal the periphery of the fairing/protector from any contaminants which the fairing/protector may encounter in use. The surface finish of both surfaces 22, 30 of the fairing/debris protector is extremely smooth when manufactured according to the method of the invention, thus aiding its aerodynamic properties, and the resulting fairing/debris protector possesses sufficient strength in the outer skin 23 to deflect small stones and other objects, whilst the combined structure of the fairing/- debris protector provides adequate crushability to avoid damage to the strut 2 when the fairing/protector 1 is struck by larger debris. In these circumstances the outer skin 23 will progressively collapse and absorb, in combination with the foamed core, sufficient energy from the impact to avoid damage to the strut 2. In addition, the fairing/debris protector 1 is extremely lightweight having regard to its aerodynamic and protective qualities and is therefore particularly suitable for use on aircraft. The snug fit of the inner surface 30 of the fairing/protector against the surface of the strut 2 ensures performance of the fairing/debris protector according to specification when installed and reduces the possibility of unwanted vibration of the fairing/protector 1 against the strut 2. The fairing/protector 1 may be attached to the strut in any convenient manner, for example by clips or by fasteners passing through the fairing/protector itself and it will be appreciated that where use as an aerodynamic fairing is contemplated a fairing manufactured according to the invention, as shown dotted in Figure 9 for example, may be fitted to the rear of the oleo strut to complement that at the front. The qualities of fibreglass in the skins 21, 23 have been found to be particularly suitable for the minimisation of impact damage, surprisingly, whereas the use of carbon fibre as reinforcement for the skins was found to be considerably less satisfactory.

Claims: A method of forming a composite laminate aircraft landing gear strut fairing/debris protector (1) comprising first and second fibre reinforced plastics skin elements (21, 23) with a foamed core (27) interposed therebetween, the method including the steps of providing a tool (8, 13) having a tool surface (15, 20) to form each skin element, forming a lay-up (21, 23) on each said tool surface of fibrous reinforcing material and plastics matrix material and allowing the matrix material at least partly to harden, positioning the tools (8, 13) such that the two skins (21, 23) are supported in their final relationship to one another and introducing a foaming resin (27) between the skins to form a connecting foam core therebetween. A composite laminate aircraft landing gear strut fairing/debris protector (1) as manufactured according to the method of claim 1.

Inventors: HUTCHINSON ANDREW, THORPE MICHAEL, HUTCHINSON, ANDREW, THORPE, MICHAEL
Applicants: AIRBUS UK LTD, AIRBUS UK LIMITED
Application year: 1997
Main classification: B29C44
IPC codes: B29C70, B64C25, B29C44