This project investigates the application of joined wings to subsonic aircraft designed to fly above 100,000 feet. Joined-wing airplanes employ two sets of wings rigidly connected together to form a triangulated self-bracing structure. Structural analyses and wind-tunnel tests have shown that, compared to cantilever wings, joined wings are lighter, stiffer, and have higher span-efficiency factors, giving lower induced drag. Aircraft flying above 100,000 feet must operate near the drag-divergence Mach number while generating high lift coefficients. For such flight conditions, thin supercritical airfoils are desirable. Cantilever wings employing such thin airfoils tend to be heavy and/or excessively flexible. For joined wings, however, reducing thickness-chord-ratio gives only small penalties in structural weight and rigidity. The net effect is that the joined wing can increase the altitude and payload capabilities of very high altitude aircraft. This project will delineate suitable joined-wing configurations, and will select one configuration for detailed structural and aerodynamic investigations.
Potential Commercial Applications: The results would apply to very-high altitude aircraft intended for atmospheric sampling or earth resources surveys and may also yield improvements in range, speed, and payload of transport aircraft.
