Method for estimating downwash behind swept airfoils

A theoretical investigation has been made relative to the adaptation of the simple Prandtl wing theory to wings with highly swept lifting lines for purposes of computing downwash. Equations have been developed relating the characteristic geometry of this type of wing to the associated vortex pattern and the Biot-Savart Equation has been integrated in such a way as to most facilitate engineering calculations. The assumption is made that the distribution of circulation about the wing has been predetermined by one of the recently developed span-loading theories. The general method of approach as has been used by Silverstein, Katzoff and Bullivant in Reference (1) is used herein. The primary deviation from the procedure outlined by these authors is the extension of computational methods from the two dimensional plane-of-symmetry analysis to three dimensions. Though it is not always stated implicitly, some of their devices are employed unchanged and others are altered to fit different conditions. Calculations have been made (see Appendix A) for a wing for which experimental data on downwash are available. The comparison between theory and experiment is found to be relatively good. Charts and tabular forms have been presented which are expected to be of use to designers interested in tail loads on swept-winged aircraft whose landings and take-offs take place at high angles of attack