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.

Polish sports plane PZL Ł.2 with a Townend ring

Development

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][3] 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. 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]

A Luftwaffe Ju 52/3m being serviced in Crete in 1943: Note the narrow-chord Townend ring on the central engine and the deeper-chord NACA cowlings on the wing engines.

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.[lower-roman 1]

Notes
  1. The wing engines of the Ju52 had longer NACA cowlings, but the central engine only had space for the shorter Townend ring.

References
  1. Patent Specification 320131: Improvements in or relating to aircraft, 8 July 1933 (amended specification from original dated 10 July 1928).
  2. 1930 Canadian patent CA 304755 by Hubert Townend with drawings.
  3. https://patents.google.com/patent/US1813645
  4. "A History of Aircraft Piston Engines" by Herschel Smith, (Sunflower University Press Manhattan, Kansas, 1981, ISBN 0-89745-079-5), 255 pp.
  5. Becker, J.; The high-speed frontier: Case histories of four NACA programs, 1920–1950, SP-445, NASA (1980), Chapter 5: High-speed Cowlings, Air Inlets and Outlets, and Internal-Flow Systems: The ramjet investigation.
  6. 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.
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