Drag reduction experiments on a wing at incidence angles appropriate to combined tilt-rotor & tilt-wing configurations in hover

The rotor slip stream on a hovering tilt rotor airplane impinges on the wing at large negative incidence angles resulting in heavy drag penalty referred to as download. Thus, wind tunnel tests were carried out in order to reduce this download by tilting the wing in conjunction with deflected flaps equipped with Active Flow Control (AFC) devices. Sweeping jet actuators located near the flap hinge were used in these tests and their aggregate momentum output was varied between 0%<Cμ<3%. The lowest download was obtained when the wing was tilted by 30^o-40^o relative to the airplane's longitudinal axis with the tilt of rotors complimenting the wing-tilt to a total of the 90^o required for hover. The current tests suggested that a combined tilt-wing tilt-rotor configuration is more effective in hover than a pure tilt rotor. When these ideas were applied to a complete powered model with a simple flapped wing tilted at 30^o to the longitudinal axis, the measured download was reduced by 60% relative to an identical tilt rotor model without AFC.