Method of fabricating a box beam

Claim 1

A method of fabricating a multicell, two spar box beam comprising the steps of: forming a plurality of ribs each comprising a rectangular, perforated panel having rounded corners and a flange integrally joined to and extending around the edge of said panel and projecting at a right angle from each side thereof; locking said ribs and a plurality of soluble mandrels together in alternate relation so that one of said ribs is abuttingly disposed between end surfaces of adjacent mandrels, said mandrels having surfaces which conform to the outer surfaces of the flanges to said ribs and eaCh being formed with at least one recessed end that conformably fits within one of said flanges, whereby said interlocked ribs and mandrels form a mandrel assembly having plane upper, lower, and side surfaces; placing adhesive on the outer surfaces of the flanges of said ribs, wrapping a plurality of layers of resin-impregnated fiberglass tape on the upper, lower and side surfaces of said mandrel assembly, and applying pressure to said tape while subjecting it to predetermined temperature to form a stiffened tubular laminate supported by said soluble mandrels and bonded to said ribs; bonding with adhesive upper and lower honeycomb core strips to the upper and lower surfaces of said tubular laminate respectively, the length of said core strips being substantially equal to the length of said tubular laminate and their width being greater than the width of the latter so that each of said core strips includes laterally extending flanges which project from the sides of said laminate, each of said core strips also including a pair of walls which project perpendicularly from one side thereof and which extend longitudinally of said tubular laminate and conform with the curved edges thereof; bonding with adhesive a plurality of laminated inserts and side honeycomb core strips to the side surfaces of said tubular laminate, said laminated inserts being arranged so that they respectively overlie the portions of the flanges of said ribs which are disposed between the end surfaces of opposed pairs of the walls of said upper and lower core strips, and the edges of said side core strips also being bonded to said laminated inserts and to the walls of said upper and lower core strips; bonding with adhesive a facing sheet to the outer side of each of said upper and lower core strips, and a channel spar to said laminated inserts, to said side core strips, and to the laterally extending flanges of said upper and lower core strips on each side of said tubular laminate; and dissolving said soluble mandrels to remove the same from said tubular laminate.