Lifting-surface theory for V/STOL aircraft in transition and cruise. II

This is the second part of a two-part paper dealing with a large-tilt-angle lifting-surf ace theory for tilt-wing and tilt-propeller (or rotor) type V/STOL aircraft. Part I presented a new inclined actuator disk theory and a model for slipstream swirl. In Part II, the inclined actuator disk analysis is combined with a discrete-vortex Weissinger-type lifting-surf ace theory for application to wing-propeller combinations at arbitrary wing angle of attack, propeller tilt angle, and thrust coefficient. Configurations with one, two, or four slipstreams are considered, and effects of slipstream rotation are included in all but the single-slipstream cases. Agreement between theory and experiment is shown to be satisfactory for small slipstream inclination angles. However, at large tilt angles, the theory (with an undeformed, but displaced, slipstream and wake) is shown to predict lower downwash angles in the tail region than observed from a single set of test data, possibly due to slipstream deformation and wake rollup. Use of only one-half the calculated wake displacement is shown to give improved agreement. Insufficient downwash angle data are currently available for making a general evaluation of the theory at large slipstream angles.

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