Low-speed wind-tunnel tests were conducted to investigate the parallel blade-vortex interaction. Flowvisualization tests of vortex generation performed before the pressure tests showed that a well-defined starting vortex was generated by an impulsively pitched wing. Time history of the pressure distribution on a pressuretapped wing model was acquired as the starting vortex passed over the wing. These pressure tests revealed that a substantial pressure change near the leading edge was induced by the encountering vortex. The effects of vortex proximity, reduced frequency, and maximum pitch angle of the vortex generator on the pressure change were also investigated. Nomenclature c = chord length of instrument wing c vg = chord length of vortex generator wing Q = section lift coefficient of instrumented wing C p = pressure coefficient of instrumented wing, (P-P*)/q k = reduced frequency, ctc vg / VP -local static pressure P ini = initial local static pressurê max = maximum local static pressurê min = minimum local static pressure Pa, = freestream static pressure q = freestream dynamic pressure Re = Reynolds number T = time elapsed after vortex generation V w = freestream velocity x = longitudinal distance from instrumented wing leading edge to pressure tap x v = longitudinal distance from instrumented wing leading edge to vortex center y v = vortex generator height above wing a. = pitch angle of vortex generator «max = maximum pitch angle of vortex generator a = pitch rate of vortex generator fi m = freestream viscosity F = vortex strength Po, = freestream density

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A Practical Tiltrotor UAV (PTUAV) has been developed and flight tests are under way. The PTUAV was motivated to pursue low cost and high performance while the full-scale tiltrotor UAV development experience was reflected. The PTUAV was targeted to develop a UAV system which has capabilities of VTOL and faster-than-helicopter forward speed with practical mission load adjusting the lower cost and weight. Vehicle sizing was performed using simple analytical method and scaling full scale vehicle parameters. The rotor and drive system of PTUAV were designed reflecting the full-scale concept but simple and unique concept was adopted. An ironbird for the rotor-drive-engine was fabricated and tested on the ground to reduce risks in integration and to facilitate measurements and modifications. The air vehicle was designed and fabricated reflecting the ironbird test. The flight control system covering the test from ground to conversion flight was constructed and tested. A tethered test was conducted for the verification of flight control logic in heli-mode flight prior to flight test. Currently flight tests are under way after integration issues were resolved from ground tests with the platform.

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