I have a Saito 125 pulling my Great Plane Skybolt turning a three blade 15 x 7 prop.

A 20 cc gasser should be fine.

I would not suggest anything less than one cubic inch.

Zor

P.S.: Edited on 14 Sep 2011 at 10:42 EDT to correct typo.
It is a 15 x 7 but was written 18 x 7 and was not noticed on reading again before posting.

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