Prediction techniques for jet induced lift effects during hover are available, relatively easy to use, and produce adequate results for preliminary design work. Although deficiencies of the current method were found, it is still currently the best way to estimate jet induced lift effects short of using computational fluid dynamics. Its use is summarized. The new summarized method, represents the first step toward the use of surface pressure data in an empirical method, as opposed to just balance data in the current method, for calculating jet induced effects. Although the new method is currently limited to flat plate configurations having two circular jets of equal thrust, it has the potential of more accurately predicting jet induced effects including a means for estimating the pitching moment in hover. As this method was developed from a very limited amount of data, broader applications of the method require the inclusion of new data on additional configurations. However, within this small data base, the new method does a better job in predicting jet induced effects in hover than the current method. Wardwell, Douglas A. and Kuhn, Richard E. Ames Research Center RTOP 505-68-71...

Propulsion device-induced effects on V/STOL aircraft aerodynamics in hover and transition flight.

The effects of jet density on the induced flow around an axially symmetric jet without pressure gradients are considered. The induced flow velocities decrease as the jet exit density decreases, and a scaling law proposed earlier is approximately correct for the type of jet considered.