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This paper presents an analytical method developed by the author over a period of years, and was applied to the Breguet 941 STOL aircraft, reported in the Supplement of NASA TN D-2231. The flight data in this report were given in exceptional detail, includingthe propeller characteristics, which are never available in wind tunnel or even in flight test research. The method solved the perplexing problem of calculating transitional velocities, of climb, take-off, and landing distances with highly deflected flaps. The method is particularly interesting from the standpoint of integrating the high static thrust of 18,000 lb produced by four propellers into a 37,000 lb aircraft. It may be used with confidence when applied to an entirely new form of deflected slipstream design.

The influence of propeller slipstream on lift and drag of deflected trailing edge flaps was previously described by this author in SAE paper 960C, as applied to the Breguet 941 STOL. The method calculating transition velocities proved to be very accurate. Recently the Ames Research Center conducted tests of a four propeller model, a close replica of the Breguet, applying the same method and obtaining very accurate results. This paper gives detailed analysis of how the method can determine CL and CD under transition conditions. Designers of STOL aircraft where thrust approaches large values compared with gross weight will find the procedure useful.