A flap mounted on the upper surface of an airfoil, called a 'lift-enhancing effector', has been shown in wind tunnel tests to have a similar function to a bird's covert feathers, which rise off the wing's surface in response to separated flows. The effector, fabricated from a thin Mylar sheet, is allowed to rotate freely about its leading edge. The tests were performed in the NCSU subsonic wind tunnel at a chord Reynolds number of 4 × 10(5). The maximum lift coefficient with the effector was the same as that for the clean airfoil, but was maintained over an angle-of-attack range from 12° to almost 20°, resulting in a very gentle stall behavior. To better understand the aerodynamics and to estimate the deployment angle of the free-moving effector, fixed-angle effectors fabricated out of stiff wood were also tested. A progressive increase in the stall angle of attack with increasing effector angle was observed, with diminishing returns beyond the effector angle of 60°. Drag tests on both the free-moving and fixed effectors showed a marked improvement in drag at high angles of attack. Oil flow visualization on the airfoil with and without the fixed-angle effectors proved that the effector causes the separation point to move aft on the airfoil, as compared to the clean airfoil. This is thought to be the main mechanism by which an effector improves both lift and drag. A comparison of the fixed-effector results with those from the free-effector tests shows that the free effector's deployment angle is between 30° and 45°. When operating at and beyond the clean airfoil's stall angle, the free effector automatically deploys to progressively higher angles with increasing angles of attack. This slows down the rapid upstream movement of the separation point and avoids the severe reduction in the lift coefficient and an increase in the drag coefficient that are seen on the clean airfoil at the onset of stall. Thus, the effector postpones the stall by 4-8° and makes the stall behavior more gentle. The benefits of using the effector could include care-free operations at high angles of attack during perching and maneuvering flight, especially in gusty conditions.

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JOHNSTON, JOE MONROE. Experimental Investigation of Bio-Inspired High Lift Effectors on a 2-D Airfoil. (Under the direction of Dr. Ashok Gopalarathnam). Flaps mounted on the upper surface of an airfoil, called Lift Enhancing Effectors, have been shown to increase maximum lift and stall angle in wind tunnel tests. These effectors are fabricated from 0.35 mm thick Mylar and are allowed to rotate freely about their leading edges. The tests were done in the NCSU Subsonic Wind Tunnel at a chord Reynolds number of 4 × 10 5 . The maximum lift coefficient wasincreased by up to 30% and α stall was increased from 12°to at least 16°. Effectors were also fabricated out of stiff wood, allowing the deployment angle to be fixed with respect to the airfoil surface. This was not attempted in earlier research efforts and provided increased control in the current experimental study as the free-moving effectors tend to oscillate and their deployment angle cannot be controlled.Studying multiple fixed-deployment angles provided better understanding of the aerodynamics of the effectors and helped determine the optimal deployment angles. Fixed-deployment-angle effectors caused the zero-lift angle of attack to increase in proportion to the deployment angle. Drag tests on both the free-moving and fixed-deployment effectors showed marked improvement in drag at high alpha. The fixed-deployment-angle effectors showed drag improvement at increasingly higher alpha as deployment angle was increased. Oil flow visualization was conducted on the clean airfoil and the fixed-deploymentangle effectors. The surface flow pictured by these oil flow tests proved that the effector causes the separation point to move aft on the airfoil, as compared to the clean airfoil. This is thought to be the main mechanism by which the effectors improve both lift and drag. Finally CFD simulations were run and compared to the oil flow visualization. Results for separation point agree between oil flow and CFD, for most alphas. Lift tests indicate that increasing the deployment angle past 60°amounts to very little improvement in C l . Drag tests show that the free-moving effector naturally produces a drag curve in between the curves for the 30°and 45°fixed effectors.

The potential sources and paths by which the propeller produces structural responses resulting in vibration and noise in the cabin of a transport aircraft are discussed. New low-cost, convenient experimental and analytical techniques are described for evaluating the excitations-propeller airborne pressures on the fuselage shells, slip-stream-induced forces on the wing and tail, and oscillatory forces on the propeller. The techniques described make use of ground-determined structural signatures to relate forces with vibrations or noise, and of propeller signatures from flight tests which define the vibroacoustic contributions of individual propellers. Knowing these, the propeller-produced excitation forces can be deduced by the relations shown; design approaches to control the fatigue and vibroacoustic environment can then be enunciated logically.

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