STUDY OF VERY-HIGH-ALTITUDE AIRCRAFT WITH JOINED WINGS.

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. THE PROPOSED STUDY INVESTIGATES THE APPLICATION OF JOINED WINGS TO VERY HIGH ALTITUDE SUBSONIC AIRCRAFT DESIGNED TO FLY ABOVE 100,000 FEET ALTITUDE. SUCH AIRCRAFT MUST OPERATE NEAR THE DRAG DIVERGENCE MACH NUMBER, WHILE GENERATING HIGH LIFT COEFFICIENTS. FOR SUCH FLIGHT CONDITIONS THIN SUPERCRITICALAIRFOILS 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. THE PROPOSED STUDY WILL DELINEATE SUITABLE JOINED-WING CONFIGURATIONS, AND WILL SELECT ONE CONFIGURATION FOR DETAILED STRUCTURAL AND AERODYNAMIC INVESTIGATIONS.