Flying wing airfoil
This is true - the ideal gas law should be obeyed and density changes will inevitably result. Those who argue against modeling the lift process with the Bernoulli equation point to the fact that the flow is not incompressible, and therefore the density changes in the air should be taken into account. Correlating the pressures with the Bernoulli equation gives reasonable agreement with observations.
Such pressure measurements are typically done with Pitot tubes. Those who advocate the Bernoulli approach to lift point to detailed measurement of the pressures surrounding airfoils in wind tunnels and in flight. Conservation of angular momentum in the fluid requires an opposite circulation in the air shed from the trailing edge of the wing, and such vortex motion has been observed. Many discussions of airfoil lift invoke such a vortex in the effective circulation of air around the moving airfoil. The lift on a spinning cylinder has been clearly demonstrated, and its discussion includes a vortex in the circulating air. Those who prefer to discuss lift in these terms often invoke the Kutta-Joukowski theorem for lift on a rotating cylinder.
From the conservation of momentum viewpoint, the air is given a downward component of momentum behind the airfoil, and to conserve momentum, something must be given an equal upward momentum. The fact that the air is forced downward clearly implies that there will be an upward force on the airfoil as a Newton's 3rd law reaction force. Those who advocate an approach to lift by Newton's laws appeal to the clear existance of a strong downwash behind the wing of an aircraft in flight. But perhaps it can at least indicate the lines of the discussion. This physical validity will undoubtedly not quell the debate, and this treatment will not settle it. Conservation of momentum and Newton's 3rd law are equally valid as foundation principles of nature - we do not see them violated. The Bernoulli equation is simply a statement of the principle of conservation of energy in fluids. Both are based on valid principles of physics. If the question is "Which is physically correct?" then the answer is clear - both are correct. Which is best for describing how aircraft get the needed lift to fly? Bernoulli's equation or Newton's laws and conservation of momentum? This has been an extremely active debate among those who love flying and are involved in the field. 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.Ħ-DOF modeling flight tests flying wing micro aerial vehicle selection of reflexed airfoil wind tunnel experimentation.Airfoils, Bernoulli and Newton Bernoulli or Newton's Laws for Lift? 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. The left roll tendency was found inherent to clockwise rotating propeller as 'P' factor, gyroscopic precession, torque effect and spiraling slipstream.
Major problems encountered during flight tests were related to left rolling tendency. 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. It was found during flight tests that vehicle conducted coordinated turns with no appreciable adverse yaw. Equations of motion for FWMAV have been written in a body axis system yielding a 6-DOF model. Rate derivatives and elevon control derivatives have also been calculated. Static aerodynamic coefficients were evaluated using wind tunnel tests conducted at cruise velocity of 20 m/s for varying angles of attack. The vehicle was fabricated using hot wire machine with EPP styrofoam of density 50 Kg/ m 3. Elevon control surfaces have been designed and evaluated for longitudinal and lateral control. Eppler-387 proved to be the most efficient reflexed airfoil and therefore was selected for fabrication and further flight testing of vehicle. Airfoil aerodynamic parameters have been calculated using a potential flow solver for ten candidate airfoils. The selection procedure of airfoil has been developed by considering parameters related to aerodynamic efficiency and flight stability. 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.