Townend ring

A Townend ring is a narrow-chord cowling ring fitted around the cylinders of an aircraft radial engine to reduce drag and improve cooling.

It caused a reduction in the drag of radial engines and was widely used in high-speed designs of 1930–1935, before the long-chord NACA cowling came into general use.

Despite suggestions of it exploiting the Meredith effect, low airspeeds, low temperature differences and small mass flows make that unlikely,[4] particularly when combined with the lack of flow control as the air exits the cowling.

[5] Although superior to earlier cowlings, and uncowled engines in terms of drag and cooling, above 217 kn (402 km/h; 250 mph) the NACA cowling was more efficient and soon replaced it in general use.

[6][failed verification] Examples of aircraft with Townend rings include the Boeing P-26 Peashooter, the Vickers Wellesley, the Fokker D.XVI and the central engine on the Junkers Ju 52/3m.