THIS INVENTION relates to a method of filling voids formed when two members are brought together in a abutting rela¬ tionship and also may assist in the bonding of the two members.

In one form the invention resides in a method of filling a void defined between members brought together in abutting relationship, comprising the steps of impregnating a mass of compressible open-cell material with a synthetic resin and positioning the mass of resin-impregnated compressible open-cell material so that the latter occupies the void when the two members are brought into said abutting rela¬ tionship, said mass of resin-impregnated open-cell material being of a volume greater than the volume of the void whereby the mass of resin-impregnated open-cell material is compressed into the void when the members are brought together in abutting relationship.

Preferably the resin-impregnated compressible open-cell material is positioned on one of the members prior to the members being brought together.

The open-cell material is preferably foam and in parti¬ cular urethane foam.

The resin is preferably vinyl ester resin.

The invention has been devised particularly, although not solely, for use in the construction of airfoils, and in particular wings of aircraft, described in the Applicant's co-pending Australian Patent Application No. 39548/85 entitled "Airfoil Construction". In Application No. 39548/85 there is disclosed a wing construction comprising an upper wing section of composite material reinforced with fibre, a lower wing section also of composite material reinforced with fibre, a leading edge spar inte-

gral with the upper and lower wing sections, an interme¬ diate spar and a trailing edge spar. The intermediate spar and trailing edge spar are constructed from channel members mounted in back-to-back relation. When the inter- mediate and the trailing edge spars are bonded to the wing sections in the manner described in the aforesaid patent application, a void exists between each spar and the abutting wing section.

The present invention provides a method of filling this void and assisting in bonding the intermediate and trailing edge spars to the wing sections.

The invention will be better understood by reference to the following description of one specific embodiment thereof. The embodiment will be described in relation to an aircraft wing construction in accordance with the invention disclosed in the Applicant's aforesaid Austra¬ lian patent application. The description will be made with reference to the accompanying drawings in which:-

Fig. 1 is a cross-sectional elevational view of the wing construction;

Fig. 2 is a view in cross-section, on an enlarged scale, of the intermediate part of the wing con¬ struction; and

Fig. 3 is a view in cross-section, on an enlarged scale, of the trailing end of the wing construction.

Referring to the drawings, there is shown a wing 10 com¬ prising a leading edge 11, a trailing edge 13, an upper surface 15 and a lower surface 17. The wing includes an upper wing section 19 and a lower wing section 21 joined together at a mating plane 22. Formed integral with the upper and lower wing sections 19 and 21 respectively is a leading edge spar 23 the construction of which is descri-

bed in the aforesaid Australian patent application. A trailing edge spar 25 is provided adjacent the trailing edge of the wing and intermediate spar 27 is provided between the leading edge spar 23 and the trailing edge spar 25 also described in the aforesaid patent applica¬ tion.

The upper and lower wing sections 19 and 21 respectively are each composite construction, comprising a core lamina¬ ted with a high strength resin-impregnated fabric.

The intermediate spar 27 is of composite construction and comprises a pair of channel shaped members 51 mounted in back-to-back relation with a core 53 bonded therebetween. The side walls of the respective channels 51 define tangs 55 which in the completed structure are bonded to the wing sections 19 and 21 with a high strength bonding material.

In the completed structure, the core 53 is spaced from the upper and lower wing sections (as best seen in Fig. 2) and thus respective void 71 are defined between the inter¬ mediate spar 27 and the upper and lower wing sections.

The trailing edge spar 25 is formed from a pair of channel members 61 and 63 mounted in back-to-back relation and spaces 64 are defined therebetween. The channel members 61 and 63 are bonded together at 65 and in the completed structure are bonded to the upper and lower wing sections at locations designated 67 with a high strength bonding material.

In the completed structure, voids 73 are defined between the trailing edge spar and the upper and lower wing sec¬ tions.

The intermediate and trailing edge spar voids are filled and the bonding of the wing sections further improved by means of a method according to the present invention. To this end, a mass of resin-impregnated urethane foam 75 or other suitable resiliently compressible open-cell material is so positioned between the intermediate spar 27 and each of the upper and lower wing sections 19 and 21 prior to the upper and lower wing sections being brought together at the mating plane, that the foam occupies the voids 71 when the wing sections are ultimately brought together.

Similarly, a mass of resin-impregnated urethane foam 77 or other suitable resiliently compressible open-cell material is inserted in each of the two spaces 64 defined between the channels 61 and 63 so that when the upper and lower wing sections are brought together, the two masses of foam 77 occupy the voids 73.

The resin impregnating the foam masses 75 and 77 may be of any suitable form of synthetic resin such as vinyl ester resin.

The foam masses 75 and 77 are each of a volume greater than that of the respective of void which it is to occupy, so that when the upper and lower wing sections are brought together at the mating plane 22, the foam is compressed into the void. The extent of compression varies within the foam itself and this varies the distribution of the resin within the foam. For example, in the foam mass 75 occupying the voids 71 the extent of compression is greater in the portions of the foam mass between the wing sections and the tangs 55 of the intermediate spar than in the portion of the foam mass adjacent the core 53. Simi¬ larly, portions of the foam mass 77 adjacent locations 65 and 67 are subjected to a greater degree of compression than the central portions of the foam mass. Higher con-

centrations of resin are present at regions of higher com¬ pression and this serves to strengthen bonding between the wing sections and the intermediate and trailing edge spars.

From the foregoing it is evidence that the void filling method according to the invention not only fills the voids 71 and 73 but assists in bonding the spars 25 and 27 to the wing sections 19 and 21 after the resin has cured.

It should be appreciated that the scope of the invention is not limited to the scope of the embodiment described. Furthermore, it should be appreciated that the invention is not limited in application to construction of airfoils.