DURING the last year studies by subsidiaries of United Aircraft Corp. on cowls for radial air-cooled engines have been continued in the wind tunnel and in flight. Model tests comparing the performance of fixed cowls under various conditions are reported, and further research on flapped cowls for controlled cooling is described.
Tests were made over a wide range of flap angles to show the possibilities of this type of cooling regulation, and a new form of cowl with flaps located well behind the engine at the fuselage firewall was studied. Flight tests with such a cowl showed that the qualitative variations indicated in the wind tunnel adequately represent full-scale conditions. The results of these flight tests are described in some detail.
An attempt is made to reduce the various wind-tunnel results to a form suitable for estimation of cowl characteristics for design purposes, and the results of this work are correlated with information obtained in flight.
The paper then discusses the structural design of flapped cowls and includes data relative to the air loads on flaps and to the resulting flap-hinge moments. A powerplant installation with flapped cowl is described in detail. It incorporates a novel operating linkage to control flaps located at the firewall. No inner or wrapper cowl is included, but an exhaust-manifold shroud prevents overheating of the accessory compartment and provides a supply of hot air for the carburetor.