Obturator ring

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An obturator ring was a type of piston ring used in World War I aero engines for improved sealing in the presence of cylinder distortion.



The cylinders of rotary aircraft engines of World War I (engines with the crankshaft fixed to the airframe and rotating cylinders) were notoriously difficult to keep cool leading to thermal distortion. To keep the weight down they had very thin-wall (1.5 mm) steel cylinders. [1] Obturator rings, made of bronze in the early Gnome engines, [2] could flex to the shape of the cylinder. Wear on the rings was considerable. Engines needed to be overhauled about every 20 hours. [3] The reliability of Gnome engines license-built by The British Gnome and Le Rhone Engine Co. gave an overhaul life of about 80 hours mainly as a result using a special tool to roll the 'L' section obturator rings. [4] The problem of thermal distortion was effectively cured on the Bentley BR1 engine by using aluminium cylinders, for good thermal conductivity, with cast iron liners shrunk in. [5]

An 'L' section obturator ring is shown in Patent US 1378109A - "Obturator ring". [6]

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  1. The Rotary Aero Engine, Andrew Nahum 1987, ISBN   1 900747 12 X, p.40
  2. Aviation Engine Examiner, Major Victor W. Page, The Norman W. Henley Publishing Co., 2 West 45th Street, New York 1931, p.146
  3. The Rotary Aero Engine, Andrew Nahum 1987, ISBN   1 900747 12 X, p.40
  4. I Kept No Diary, Air Commodore F.R. Banks 1978, ISBN   0 9504543 9 7, p.63
  5. The Rotary Aero Engine, Andrew Nahum 1987, ISBN   1 900747 12 X, p.27
  6. https://patentimages.storage.googleapis.com/31/ba/4e/d0d1dff885aaff/US1378109.pdf [ bare URL PDF ]