The Townend ring was the invention of Dr. Hubert Townend of the British National Physical Laboratory in 1929. Patents were supported by Boulton & Paul Ltd in 1929. 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 217 kn (400 km/h; 250 mph).
- 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. 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.
- Patent Specification 320131: Improvements in or relating to aircraft , 8 July 1933 (amended specification from original dated 10 July 1928)
- 1930 Canadian patent CA 304755 by Hubert Townend with drawings
- "A History of Aircraft Piston Engines" by Herschel Smith, (Sunflower University Press Manhattan, Kansas, 1981, ISBN 0-89745-079-5), 255pp.
- Becker, J.; The high-speed frontier: Case histories of four NACA programs, 1920- SP-445, NASA (1980), Chapter 5: High-speed Cowlings, Air Inlets and Outlets, and Internal-Flow Systems: The ramjet investigation
- Hansen, James R. "Engineering Science and the Development of the NACA Low-Drag Engine Cowling". From Engineering Science to Big Science: The NACA and NASA Collier Trophy Research Project Winners. Archived from the original on 2004-10-31. Retrieved 2007-04-28.[not in citation given]
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- The Spotters Glossary
- North, J D (8 February 1934), "Engine Cowling: With Special Reference to the Air-cooled Engine", The Aircraft Engineer (Supplement to Flight), XXIV No. 6 (1311): 133–137
- North, J D (22 February 1934), "Engine Cowling", The Aircraft Engineer (Supplement to Flight), IX No. 2 (97): 174a–174f
- "Engine Cowling", Flight, XXVI No. 7 (1312): 157–158, 15 February 1934