ORIGINAL: fly210sv
An 11x5 master airscrew works great on the alpha 40. You really need to get an electric starter, you will be surprised how well it works. The alpha 40 is a great trainer. Just get rid of the 3 blade prop.
MAS props are great for trainers because they take ground strikes and don't chip or break like APC's do. This is important as you'll have prop strikes while learning to land.
The prop I use on .46 size trainers is the Hobbico NextStar prop. It's an 11x5 and extremely tough, and on the Alpha's I've had that's what I've run. The thing this prop has going for it is the red tips which are easy to see while it's idling - when learning to start your motor it helps remind you of the danger of the Ginsu knives spinning around there which can really bit even at idle.
Hogflyer