Why Castor Oil?

[Vic_Mouton]

My understanding is that castor oil has some other intended uses than lubricating an aircraft engine. Was there no alternative that could do the job better at that time?

I can remember that castor oil was one of the ingrediants in the fuel we used in the old baby bee model aircraft engine that powered a plane we used to swing around on a string years ago.

VBR
Vic

[mike_baram]

Castor oil, from what I've been told, didn't break down as easily from the heat and forces in the rotary engines.
I think they used regular oil in the in-lines.
(Notice how effectively I qualified my response....it's called weaseling.)

[mike_baram]

Was that really castor oil in the "baby bee" engine, or 2-stroke oil with the "Castrol" name?

As far as I know (I can weasel too), Mike is correct: castor oil was the only oil that wouldn't break down in a rotary. At least rotary pilots never had to worry about constipation...

A lot has been said that castor oil was used because it wasn't soluble with gas and thus would have less chance of washing off bearing surfaces. If this were the case, then castor oil would be used in 2 cycle engines. Castor oil was used because of it's superior (to mineral oils of the time available in Europe) lubricating properties. The cylinder walls of the rotory were very thin and subject to heavy distortion, thus placing an extra heavy burden on the lubricant. Castor oil was a better lube so promoted better piston-cylinder life.

[mike_baram]

definition: Weasel (n) - a mink in the off season.

Those pilots must have inhaled a lot of castor oil fumes. No problem with constipation eh?

I think the Baby bee ran on a combination of alcohol and castor oil. The stuf tasted vile and the little prop had a habbit of catching one's fingers on startup.

Henry

Castor oil is hard to depend on. On the one hand, if it reaches engine parts requiring lubrication, it provides the greatest protection. Problem is that it does not mix well with fuel so that frequently an engine will seize as a direct result of not receiving enough lubrication. As a result, many rotary pilots using the unreliable castor would burn up an engine while in flight, often with deadly results.

This is an interesting problem which has to this day still not been effectively corrected. While castor is still thought to have the best properties of lubricity, most motorcycle racing teams using rotary engines have gotten away from castor based oils for the same old reason - inconsistent delivery of oil to engine parts as a result of poor miscibility with fuel will fry the engine.

[Richard_Schrader]

What would be a better oil to use today for rotary engines?

Richard, Full synthetic TCW3 oil is safest for any 2-cycle engine. A multitude of good brands are ou there.