A technique for obtaining a physical picture of the flow behind a wing, combination of wings, or other aircraft components is described. This technique involves photographing from far downstream the action of a large number of tufts of uniform length mounted on a screen. This procedure permits obtaining, in an approximate fashion, an important result of a piton-yaw-head survey;namely, a vector plot of the flow field in a plane normal to the air stream at a station downstream of an aerodynamic surface. A preliminary examination of the tuft-grid tech¬nique as discussed in this paper indicates that quantitative analyses concerning such factors as trailing-vortex strength and location, approx-imate downwash and sidewash angles over a large field behind lifting surfaces and other aerodynamic forms may be satisfactorily conducted with the data obtained by this technique.
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