Using periodic perturbations for download alleviation on tilt-rotor airplane models in hover

This paper covers the design improvements of the tilt-rotor download test fixture at the University of Arizona and the study of using active flow control and Kruger flaps for download alleviation on a tiltrotor aircraft. The investigation was done using two 3-D aircraft type; a 16.7% scale XV-15 and a 10.5% scale V-22 Osprey models. The study focused on the tilt-rotor in hover, a condition where approximately 10% of the total thrust is lost due to aerodynamicdrag on the airframe. Of this total download the wing accounts for a little more than 50%. Active flow control was used as a method to prevent or delay normal separation at the leading and trailing edges of the wings. This would decrease the download, which would effectively increase the payload capacity of the aircraft. The 3-D experiments follow successful demonstrations in two-dimensional wind tunnel testing. The intention of the 3-D setup was to validate the results of the 2-D testing and then lead to a flight demonstration of the technology on the XV-15 aircraft. Also, the 3-D setup incorporated the use of internal actuators to provide active flow control, an improvement over some initial studies. The 3-D configuration was a key step as a method to prove the concept in an unsteady, three-dimensional flow field that would be experienced in actual flight. The use of active flow control was able to demonstrate a download reduction of almost 15% on both models using an active trailing edge. When combined with an active leading edge the download reduction was approximately 30%. The subsequent flight demonstration of an active flap confirmed the validity of these results and shows promise for future study. The discussion of the experiment design and results now follows.