In the late 1970s, active developments of cross-flow fans for aero-propulsion and lift augmentation were initiated at several organizations, including the Lockheed-Georgia Company, and the Vought Systems Division of LTV Aerospace Corporation, together with the University of Texas at Arlington. Shown in Fig. 41 is an example of how cross-flow fan installation in an airfoil can be implemented. This concept was developed by Vought Systems under a Navy contract [12], using the cross-flow fan design of Harloff and Wilson [13] embedded in the trailing edge of a thick airfoil, with the inlet on the pressure side and exhaust on the suction side. The variable-geometry design allows for the entire fan housing to rotate as the aircraft transitions from the cruise configuration, where the fan provides forward thrust, to a vectored thrust STOL condition, and vice-versa. In particular, the primary and secondary vortex cavities are rotated so that the fan inflow and outflow directions are roughly 90° apart, which is the natural flow direction in the cross-flow fan as pointed out in Section 2.