ORIGINAL: glover1482
Yep. I use a 14*4W prop.
Fly safe, Glover
PS In my Seagull Ultimate 90, I run an OS 120 with a 17*6 prop. (A YS 110 with 16*4W also worked well in this toy.)
Doesn't your YS have a supercharger in it?
If so it is probably more powerful than the O.S. .70 he is contemplating.
He should be able to run a 12x6 or a 13x4 prop with his engine that should give him plenty of pull. The former would give him the best all around performance.