The Cowling of Air‐Cooled Engines: A Summary of Wind Tunnel Tests of the Effect on Performance of Various Types

IT is well known that the drag of an air‐cooled engine can be much reduced by the addition of a suitable form of cowling. The present tests were undertaken to investigate the cowling of an air‐cooled radial engine and in particular to develop a suitable “helmet” cowling for this type of engine. Certain other forms of cowling have also been tested. From the results obtained estimates have been made of the probable improvement in performance resulting from the various types of cowling. Most of the work has been carried out in the No. 17‐ft. tunnel at the Royal Aircraft Establishment; the tests were begun in January, 1929, and have occupied the tunnel at intervals throughout the year.