The cylinders of
rotary aircraft engines (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) and some had no cylinder liners. On engine types without cylinder liners, obturator rings, made of
bronze in the early Gnome engines, 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.
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==