An obturator ring was a type of piston ring used in the early of some World War I fighter aircraft for improved sealing in the presence of cylinder distortion.
Purpose
The cylinders of
rotary engine (engines with the
crankshaft fixed to the
airframe and rotating cylinders) suffered from uneven cylinder cooling as the side facing the direction of rotation received more cooling air which lead to thermal distortion. To keep weight down the cylinders on rotary engines had very thin-walls (1.5 mm)
[The Rotary Aero Engine, Andrew Nahum 1987, , p.40] and some had no cylinder liners. On engine types without cylinder liners, obturator rings, made of
bronze in the early Gnome engines,
[Aviation Engine Examiner, Major Victor W. Page, The Norman W. Henley Publishing Co., 2 West 45th Street, New York 1931, p.146] were fitted as these were soft enough to not damage cylinder walls and could flex to the shape of the cylinder.
In operation wear on the rings was considerable. Engines needed to be overhauled about every 20 hours.[I Kept No Diary, Air Commodore F.R. Banks 1978, , p.63] Clerget rotary aircraft engines also used obturator rings which were prone to overheating and seizure.
Le Rhône and Bentley BR1/BR2 rotary engines used cylinder liners and were sealed using conventional piston rings rather than obturator rings.
See also
External links
An 'L' section obturator ring is shown in Patent US 1378109A - "Obturator ring".
