The U.S. Air Force New World Vistas program envisions future large transports with lift-to-drag (LID) ratio approaching 40. Large-aspect-ratio wings will likely be a characteristic of such transports as well as any other available high-lift technology. Circulation control in the form of pneumatic blowing of the boundary layer has been under study as a means for augmenting the lift of airfoils. Boundary-layer blowing may also be a viable means of control, replacing the traditional mechanical trailing-edge control surface. The large aspect ratios of likely future large transports may enhance the effect of the blowing technology, in that the flow about such wings is nearly two dimensional over a large portion of the span. The principle is based on the Coanda effect, whereby a high-energy jet of air is injected into the boundary layer on the suction surface of an airfoil. The boundary layer is thereby energized, delaying or even preventing separation of the boundary layer, with the attendant loss in lift. The principal blowing parameter is the momentum coefficient, which is a measure of the momentum flux of the jet of blown air.
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