Development of High-Lift Mild-Stall UAV Airfoil with Post-Stall Flight Capabilities

摘要

High-lift, mild-stall wings (MS-wings) are beneficial for developmentrnof Tactical UAV. The lift curves of MS-wings show plateau of liftrncoefficients at extended range of post-stall angles of attack, followed byrngradual loss of lift at the region of actual stall of the wing. Such stallrnpattern is attractive for design of small and medium size Tactical UAVrnflying at reduced airspeeds in windy air. At stall angles of attack, nornsignificant rolling moments are expected for MS-wings, improving airrnvehicle response to asymmetric stall, preventing the drop of the wing andrndevelopment of spin modes of the flight. Furthermore, intended /rnunintended stall of air vehicles that employ MS-wings is not expected tornresult in safety problems, allowing controllable recovery from domain ofrnpost-stall angles of attack. High-lift, mild-stall MS-wings allow thernstandard speed safety margin to be revised, or eliminated, allowing betterrnexploitation of available maximum lift. This can improve UAV take-off /rnlanding performance and allows more efficient loitering at higher liftrncoefficients. MS-wings allow a fully controllable flight at stall / post-stallrnangles of attack, supporting development of the option of landing at poststallrnat minimum possible airspeed with steep glide angles. This paperrndescribes design and experimental evaluation of single-element, high-lift,rnmild-stall airfoil with divergent trailing edge closure (MS/DTE airfoil).rnExperimental results indicated that expectations for enhanced maximumrnlift and extended plateau of lift at post-stall for MS/DTE airfoil realized atrnreal flow conditions in wind tunnel test. This was further substantiated inrnflight testing of fully instrumented Wing Technology Flight Demonstratorrnspecially designed for evaluation of post-stall flight capabilities of MSwings.rnOverall, it was concluded that implementations of MS-wings inrndevelopment of Tactical UAV allows completely different approach tornformulation of design objectives of air vehicles. Elimination of speed safetyrnmargin and safety aspects at stall / post-stall flight are the foundation forrnrevision of aerodynamic design principles and for modification of flightrncontrol.