Rotating Cylinder Flaps for V/S.T.O.L Aircraft: Some Aspects of an Investigation into the Rotating Cylinder Flap High Lift System for V/S.T.O.L. Aircraft Conducted jointly by the Peruvian Air Force and The National University of Engineering of Peru

A SPANWISE rotating cylinder placed at a suitable location in an aerofoil with the cylinder's upper surface moving rearwards in the direction of the local air flow can serve to re‐energize the boundary layer on the aerofoil. For example, when placed between a flap and a wing with the cylinder protruding substantially into the air flow as shown schematically in no. 1, the moving surface of the cylinder destroys, by viscous shear action, the low‐energy boundary layer impinging on the cylinder from the wing and results in a new boundary layer on the flap's upper surface which has a higher energy level adequate to negotiate the adverse pressure gradients and flow conditions existing at the rear of a flap deflected through a large angle. The boundary layer re‐energizing function of the cylinder depends on its upward protrusion, on its peripheral speed, and on the local flap geometry. The beneficial effects of the rotating cylinder on the flow fields have been visualized in two dimensional smoke studies conducted by Alvarez Caldcrón and Arnold of Stanford University on a flap designed for deflected slipstream V/S.T.O.L. aircraft. Fig. 2 shows flow around the flap with the cylinder stationary. It exhibits complete flow separation at the flap which is also typical of a slotted flap deflected through a large angle. The large white disk is a cylinder end plate; the actual cylinder appears in the darker circular shade of small diameter. The photograph of FIG. 3 was taken with the cylinder rotating: it shows a radical flow change not only in the total elimination of flow separation on the flap but in the induction of strong upwash fields and low pressure regions toward the leading edge of wing itself which obviously greatly increases lift and decreases wing pitching moments.