Cross-Ducted Propulsion Systems for Medium-Speed V/STOL Applications

Multiengine vertical takeoff and landing (V/STOL) aircraft have a unique requirement to at least maintain aircraft trim after losing one engine during vertical landing. The most popular scheme by which this is accomplished involves using cross-shafted fans with variable inlet guide vanes. A significantly different approach is described herein whereby cross-ducted fan bleed air is used to obtain roll control and engine out roll trim. The installation of this cross-ducted system in a twin-engine V/STOL aircraft is described in detail along with different options for obtaining pitch control, pitch trim and yaw control. The optimum engine cycle for each configuration is defined based on mission performance results and vertical landing capabilities. The cross-ducted systems were found to offer significant advantages compared to the cross-shafted systems in terms of aircraft performance as well as design simplicity, versatility, reliability, vulnerability, survivability, and safety.