Application of Empirical and Linear Methods to VSTOL Powered-Lift Aerodynamics

This paper critically reviews available prediction methods and provides an assessment of their strengths and weaknesses. The methods are applied to selected problems which represent the major aero/propulsion interactions for short takeoff and vertical landing (STOVL) aircraft of current interest. The first two problems deal with aerodynamic performance effects during hover: a) out-of-ground effect, and b) in-ground effect. The first problem can be evaluated for some multijet cases; however, the second problem is very difficult to evaluate for multijets. The ground-environment effects due to wall jets and fountain flows directly affect hover performance. In a related problem c) hot-gas ingestion affects the engine operation. Both of these problems as well as jet noise affect the ability of people to work near the aircraft and the ability of the aircraft to operate near the ground. Additional problems are d} the power-augmented lift due to jet-flap effects (both in- and out-of-ground effects) and e) the direct jet-lift effects during short takeoff and landing (STOL) operations. The final problem is f) the aerodynamic/propulsion interactions in transition between hover and wing-borne flight. Areas where modern computational fluid dynamics (CFD) methods can provide improvements to the current computational capabilities are identified.