WINGS FOR UAV BASED ON HIGH-LIFT AIRFOILS

摘要

Wing design for tactical UAV applications requires a special approach which is different from man-operated airplanes. The maximum lift is a primary factor to achieve high endurance factor values and short take-off and landing distances. The permanent design problem for UA V wings design is engineering compromise between achieving maximum lift, reducing drag penalty for high speed flight and providing flight envelope capabilities from low-lift maximum speed flight up to stall lift levels. Speed safety margins and acceptable stall characteristics have too to be taken in attention. The relatively small UAV size and low level of flight speed which correspond with low Reynolds numbers bring specific design difficulties. While classic thin single-element airfoils lift increment is limited, the high-lift potential is based on multi-element airfoils, in particular two-element. The special feature of two-element airfoils is extremely low local Reynolds numbers on second element (flap section) providing danger of flow separation, especially for deflected flap. The rear part of main element must provide enough length for flow recovery after laminar-turbulent transition, hence limiting airfoil laminar capabilities. The engineering optimum in low Reynolds numbers airfoil design is search of compromise between the above mentioned parameters. The different approaches of two-element airfoil design are presented - the airfoils with permanently opened slot and airfoils with retracted flap were designed and experimentally tested. Advantages and drawbacks of proposed two-element design concepts are analyzed. The computational methods and comparison with experimental wind tunnel results are performed for both design concepts. The present paper not only addresses airfoil design, but also the complex 3-D high-lift wings design development potential for low Reynolds number application. The attempt to analyze complex wing that combine two different two-element airfoil concepts is presented. UAV configurations employing high-lift low Reynolds wings are presented to demonstrate high-lift flight concept advantages. The presentation partially includes the results of joint ADE-IAI Project "High Lift Wing Design Technology".