Townend ring

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Polish sports plane PZL Ł.2 with a 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.


The Townend ring was the invention of Dr. Hubert Townend of the British National Physical Laboratory[1] in 1929. Patents were supported by Boulton & Paul Ltd in 1929.[2] In the United States it was often called a "drag ring". 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.[Note 1]

Examples of aeroplanes with Townend rings were the Boeing P-26 Peashooter, Douglas O-38, Vickers Wellesley, the Westland Wallace and the Gloster Gauntlet. Early claims portrayed it as a superior design to the NACA cowling, but later comparisons proved aircraft performance using a Townend ring was inferior to that of a NACA cowling when flying at airspeeds above 250 mph.[5]


  1. ^ It has also been said that the ring exploited the Meredith effect to generate forward thrust from the expansion of the air as it passed over the engine. Such an effect is physically implausible given the low airspeed, low temperature differences and small mass flows involved.[3] Although in theory the expansion of the air as it was heated by the engine could create thrust by exiting at high speed, in practice this required a cowling designed and shaped to achieve the high speed exit of air required.[4]


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