THE development of an N. A. C. A. cowling giving a low drag and satisfactory engine cooling for a particular airplane and engine installation requires the construction and flight testing of numerous experimental cowlings.
An investigation has been undertaken by the National Advisory Committee for Aeronautics to determine a rational basis for the design of the N. A. C. A. cowling.
The effect of front and of rear openings and of inner and outer lines of the cowling on the quantity of air flowing through the cowling, the pressure drop, and the drag have been determined from tests of models in a wind tunnel.
The quantity of air and the pressure drop required for satisfactory cooling of a given design of air-cooled cylinder have been determined from tests of a single-cylinder engine.
The results obtained from the tests of the models and the single-cylinder engine are being checked in a large wind-tunnel using a 550-hp. radial-engine fitted with a propeller.
The effect of air speed, air density, and cooling-air temperature on the temperature of air-cooled cylinders has also been investigated.
The multi-cylinder-engine tests have been found to check the model tests and to give the effect of the propeller on the quantity of air flowing through the cowling.
The method proposed for designing the N. A. C. A. cowling is outlined in the report.