Engine Nacelles and Propellers and Airplane Performance 360111
THE extensive experimental study of engine-nacelle location and cowling made by the N.A.C.A. is reviewed. The factors contributing to the efficiency of the engine-nacelle and propeller group are discussed. Several examples are given showing how the results of the experiments are applied, and how the use of improved cowlings and better nacelle locations increases the high-speed performance of airplanes. It is shown that about 25 per cent of the improvement of present-day airplanes over those of seven or eight years ago can be attributed to the increased aerodynamic efficiency of the engine-propeller group alone.
The effect of engine size on the nacelle drag is discussed, and charts are given from which values may be used in calculating the nacelle drag in preliminary performance estimates. Whether other types of engine, in-line air-cooled and liquid-cooled, can compete with the air-cooled radial is shown to depend on the provision of cooling arrangements of low drag. The question of radiator resistance is of great importance and requires extensive study; but there is reason to believe that radiator drags can be reduced to less than half of present values, which will increase the field of use of the liquid-cooled engine.
The use of engines mounted entirely within the wing, with the propeller driven through an extension shaft, has been suggested. A few experiments are described and it is shown that considerable improvement is to be expected if the engine can be cooled by methods that do not increase the drag. Further experiments with these arrangements seem to be worthwhile and offer the greatest possibility of improvement over existing types.