Month in the Patent Office: A Selection of the More Important Aircraft and Engine Specifications Published Recently

A truss particularly for use as an aeroplane spar comprises built‐up booms with continuous Warren girder trussing between them, each boom comprising an inner substantially flat element and an outer corrugated element secured to the inner element at the bottoms of its corrugations so as to form a number of closed sections. The figure shows a spar built up from continuous strip steel stock, of high tensile stainless steel, in which all the parts are joined by spot welding. The booms comprise a flat strip 12 with turned‐over edges 13 and a superimposed corrugated strip 14 which overlaps the flanges 13 and of which the bottoms of the corrugations contact with the strip 12 as at 15. The web is formed of continuous channel section strips 16 bent to Warren girder form, each strip being opened out to plane section at its apices for welding to strip 12 and provided at these points with a strengthening groove. One member 16 is provided for each corrugation 11 and they are assembled in staggered relation, as shown. The method of assembly is first to secure the parts 12 and 16 in position and pass them through a continuous welding machine, spot welding the apices of the web girders to parts 12; parts 14 are then put in position and the bottoms 15 of the corrugations 11 contracted on to the surface of part 12 and the edges 14 overlapped on to the flanges 13, the bottoms of the corrugations being welded to the outer faces of members 12 and the edges 14 to the flanges 13. The number of sets of web bracings and of corrugations in the booms may be varied simultaneously along the length of the spar, as well as their shapes. Boom members of one width may be connected to those of another by overlapping and spot welding them in place.