Two-element fixed hinge airfoil for low Reynolds numbers

摘要

Use of high lift devices is common practice for aircraft to enhancerntakeoff and landing performance. They enable to use smaller wing area tornobtain cruise drag reduction, while augmenting the maximum lift forrntakeoff and landing. They can also be used to reduce the loiter speed of anrnaircraft, thus enhancing its aerodynamic efficiency, especially for propellerrndriven aircraft.rnWe tried to extend high lift devices usage also for low Reynoldsrnnumbers in the range 200K- 300K, which is typical of small sized UAV’s.rnFor this class of propeller driven UAV‘s the important factor is enhancingrnthe loiter time which is proportional to C_L~(1.5)/C_D.rnHigh lift devices are used in industry including plain, and Fowler flaps.rnIn IAI wings we also used two element airfoils. We propose to use a slottedrnflap (fixed hinge flap option) which may provide several benefits. It shouldrnbe simpler to manufacture than a Fowler flap and may provide lower dragrnat cruise by closing the gap.rnFor low Reynolds numbers there is much less data on the performancernof such devices. Low Reynolds number regime is associated with longerrnextent of laminar flow and larger laminar separation bubbles which mayrncause drag increase and premature separation leading to lift loss.rnA design cycle of an airfoil with fixed-hinge flap for this Reynolds no.rnRegime was done during this work in IAI and ADE. The designed airfoilrnmodels were tested in a 2-D WT in IIT Kanpur, India, and demonstratedrngood performancernBased on the above a low Reynolds, high-lift wing concept is proposed.rnThe inboard section is based on fixed-hinge airfoil and provides highrnmaximum lift with deflected flap. The outboard section is based either onrntwo-element airfoil or on plain flap (that supports deflections for bothrnpositive and negative directions) to provide flight control in roll.rnThe presented work partially includes the results of joint ADE-IAIrnproject "High Lift Wing Design Technology".