Analytical comparison of two wing structures for Mach 5 cruise airplanes

Mach 5 cruise airplane studies at the NASA Langley Research Center have identified technologies requiring improvements in the current art to provide adequate cruise range. As part of the overall study, this paper presents analytical results and a comparison of two titanium wing structures each designed for equal stiffness. The first structure is similar to that of the YF-12/SR-71 series airplane, but uprated by use of a better titanium alloy. It consists of spot-welded, corrugated-core sandwich panels having beaded skins, designed to minimize thermal stress, attached to multiple spars and ribs having flat z-stiffened shear webs. The second structure consists of diffusion-bonded honeycomb-core sandwich panels, designed to withstand the thermal stresses, attached to multiple spars and ribs having sine-wave stiffened shear webs. Both structures of titanium (6-2-4-2) alloy were analyzed for the thermostructural loads imposed by flight at Mach 5. The results indicate that with an insulated, integral tank fuselage, the lower surface of the wing must be insulated to satisfy the creep requirements for a 2500-h life at Mach 5; and for equal stiffness, the honeycomb-core sandwich structure is potentially 23% lighter than the corrugation-stiffened beaded skin structure.