 The closely spaced ribs, combined with similarly-spaced foam interstitials, resulted in a cellular structure that yields great strength and stiffness with low weight.The HP-16 wing spars were made in inboard and outboard sections, each 12 feet (3.66 m) long, and each machined to an I-beam cross-section from billets of solid 7075-T6 aluminum and then spliced together to yield a 7.5m wing panel spar.The machining of these aluminum I beams would have been cost-prohibitive under normal circumstances, but was accomplished as something of a personal challenge by Schreder's friend John Mazur at his shop in Long Island, New York.