These are my thoughts for the glow engines. I've never had electric power and have no clue about them.

GMS 32 - 9x6, 10x4 or 10x5 (tower recommends using 8x6 for break-in)

OS 40 - which one is it? LA, FP, FX, other?

Magnum 25 - 9X5, 9X6, 10X4

ASP 46 - 10x6, 10x7, 11x5, 11x6, 12x4. Magnum, similar to ASP (some say identical), recommends a prop the lets the engine turn 13000-16000 rpm on the ground. Magnum recommends using 10x6 for break-in.


For learning, the black nylon props from Master Airscrew seem to be good. They have some flexibility that lets them take abuse that would break a wood prop or a stiff plastic prop like an APC.


Prop selection sometimes seems like black magic. One person will rave about a certain engine/prop combination and the first reply will be about how bad the combination is. You pretty much have to buy a sack of props and try different ones until you find the setup YOU like, no matter what the next guy likes or doesn't like.


On all of the engines, I think you should go for the largest diameter that provides decent ground clearance. Lets assume (a dangerous thing) that the Magnum 25 will turn a 9x6 or 10x4 prop at about 14000 rpm (and the number is pretty close for both props). The 10 inch prop would provide more thrust (pulling power) than the 9 inch prop. Depending on the weiught and aerodynamics of the model, the 9 inch prop (with higher pitch) might make it go faster at full throttle than the 10 inch. Since the planes are trainers, thrust is probably more desireable than speed.