RE: what size prop should i use to fly?
On a 40 I use 10x6 and never had a problem get good RPMs and power. I have one I run with a 11x4 because the plane is supposed to fly slower a 10x6 was way to fast but the engine run up good on the 11x4 same rpm but it reduced speed due to less thrust.
On a trainer I would use a 10x6 for break in. Get an APC they are a good quality prop. Especially on an ASP. It should really like the 10x6.