I will probably use (2) O.S. 25's, the same engines that Check Six Plans used for their prototype. Read their own first flight test. In their own critique they said the .25's were overpowering the plane but I can live with that. If not .25's, .15's would be the absolute minimum. And I will use O.S. for their reliability and also it's the best 2 stroke engine on the market. You pay a little more but you don't have to mess with the engine(s) once they're broken in.