U.S. Patent Specifications

In the application of a thin sheet metal covering to an airplane wing frame including a spanwise spar and a plurality of ribs fixed thereto, the steps of inserting an electrode structure internally of one of said ribs in bracing relationship between and against inward collapse of the upper and lower elements thereof, applying said covering over said frame, arranging a welding electrode exteriorly of said covering, connecting said electrode structure and said electrode to opposite sides of a source of electric current, pressing said external electrode against said covering in line with said rib while resisting said pressure from the opposite side of said wing and causing a flow of electric current between said electrode structure and said electrode to effect a spot weld between said covering and said rib.