ORIGINAL: jimmyjames213
ok ill give it a go.
people at my field were like why are you running a 10x7 on that .47. you should use a 10x6
in the back of my mind im like "i have this old magnum that doesnt have much umph on a 10x6 why would i want a 10x6 on my nice and powerful gms .47?"
.....but they put a 10x6 apc on it.
There are many different engine configurations which produce differing amounts of power.
e.g. a 10x7 prop may be a bit too much for an O.S. .46LA but just right for an O.S. .46AX.
In the case of the GMS .47 it is just shy of the Tower Hobbies .46 in terms of power, but the latter is a real stump puller and I think just a hair more powerful than the AX .46, so a 10x7 is fine. On a lighter plane you may also get away with the 11x7, but the engine will need to unload in the air for effective RPM's.
ORIGINAL: jimmyjames213
would a topflight 11x4 be fine for that old magnum? (im worried i might be under proping it) its a magnum .40 GPA, a bushed engine. (on a spad stick)
I've never used that particular engine, but I assume that it is similiar to an OS LA .40.
An 11x4 may give you adecuate thrust for a .40 plane but it will fly somewhat slowly.
You may want to try a 10x6 instead.