Why do rotary aircraft engines use castor oil?

Answer 1

In the early days of gasoline engines, early Lubricants were of high viscosity, very waxy and had very poor low temperature characteristics. Castor oil was discovered to be a good lubricant. It was first used in race car engines and then many aircraft engines; NOT just rotary engines. Rotary aircraft engines relied on oil to be splashed around the cranks chamber and removed via the exhausts. No sumps were acomodated in this design. Due to the torturous nature of the rotary engine's induction system, plus the need for the oil NOT to mix with the fuel, castor based oils were the only products used in this design type. (Rotary engines were unique to WW1 aircraft. These engines were mounted on a fixed crankshaft and had odd-number of cylinders mounted around the shaft. The propellor was bolted to the engine. When the cylinders fired, it rotated the engine & propellor around the crankshaft and spun the engine. Later, Radial engines were made that had the engine bolted to the airframe and the pistons spun the propellor---the common engine used from 1920's thru WW2.) The design of the Rotary Engine resulted in the castor oil being expelled in copious quantities through the valve system on top of the engine. The pilots would often ingest much of this, leading to a quick trip to the toilets upon landing as it caused indigestion. Since castor oil was needed for lubricating airplane engines, 100,000 acres of land in the southern United States had to be planted in castor beans. Castor Oil used by the radial engine was supplanted by Voltol, an oil derived from coal. The Germans tried to use Voltol since the Allies had am embargo to stop shipments of castor oil. Source: Article on The Rise and Fall of Castor Oilhttp://www.penriteoil.com/uk/techbulletins/V3_RiseandFallofCastor.pdf