I have built three of them, a great flier with an Saito 80 w/ 13 X 8 prop.......Try a 14 X 7 or 14 X 8 prop......flew my first one for 3 years then recovered it.....Be sure to have two large BLACK Stripe on the underside....hard to tell the top from the bottom. The other ones were built for other people w/ .60 2 Stroke engines.....I like the 4 Stroke best.