Abstract
Airfoil selection procedure, wind tunnel testing and an implementation of 6-DOF model on flying wing micro aerial vehicle (FWMAV) has been proposed in this research. The selection procedure of airfoil has been developed by considering parameters related to aerodynamic efficiency and flight stability. Airfoil aerodynamic parameters have been calculated using a potential flow solver for ten candidate airfoils. Eppler-387 proved to be the most efficient reflexed airfoil and therefore was selected for fabrication and further flight testing of vehicle. Elevon control surfaces have been designed and evaluated for longitudinal and lateral control. The vehicle was fabricated using hot wire machine with EPP styrofoam of density 50 Kg/. Static aerodynamic coefficients were evaluated using wind tunnel tests conducted at cruise velocity of 20 m/s for varying angles of attack. Rate derivatives and elevon control derivatives have also been calculated. Equations of motion for FWMAV have been written in a body axis system yielding a 6-DOF model. It was found during flight tests that vehicle conducted coordinated turns with no appreciable adverse yaw. Since FWMAV was not designed with a vertical stabilizer and rudder control surface, directional stability was therefore augmented through winglets and high wing leading edge sweep. Major problems encountered during flight tests were related to left rolling tendency. The left roll tendency was found inherent to clockwise rotating propeller as ‘P’ factor, gyroscopic precession, torque effect and spiraling slipstream. To achieve successful flights, many actions were required including removal of excessive play from elevon control rods, active actuation of control surfaces, enhanced launch speed during take off, and increased throttle control during initial phase of flight. FWMAV flew many successful stable flights in which intended mission profile was accomplished, thereby validating the proposed airfoil selection procedure, modeling technique and proposed design.
Highlights
Interest in small creatures flying at low speeds has increased for the last three decades
Research and development organization conducted a workshop for Advanced Research Projects Agency (ARPA) on “Future Technology Driven Revolutions in Military Operations” in 1992 which resulted in the birth of Micro Aerial Vehicles [1]
In early stages of MAV development, extensive studies were conducted in low Reynolds number aerodynamics regime in which research focused on laminar boundary layer separation, transition to turbulent boundary layer and reattachment to form laminar separation bubble [10]
Summary
Interest in small creatures flying at low speeds has increased for the last three decades. Designed micro aerial vehicles were fixed wing in flying wing configurations having low aspect ratio wing for lifting characteristics. These were battery powered (lithium ion or nickel cadmium) and propeller driven with endurance up to 30 min [4,5,6,7,8,9]. In recent past with the advancements of experimental facilities, an extensive experimental research work was conducted on low aspect ratio wings at slow speeds by [12,13,14,15,16,17,18,19,20] They concluded that low aspect ratio wings at low Reynolds number posed many problems relating to aerodynamic efficiency. Span efficiency value in case of airfoil section was not found to be in conformance with commonly used values in aeronautics literature
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