Why don't you JUST use the prop that is right for the plane. You are making something easy real hard. Just use the engine size and the right prop that the model calls for!!!! If you want something bigger, then go to the model shop and buy a larger plane, then you can maybe use the bigger engine along with the larger prop.

Isn't that simple enought !!!! DO THIS and go to the flying field and enjoy our self!!!!
Winbboz