The best choice for training are the black Masterairscrew props. You can bump a grass runway throwing mini-clumps of grass, the engine will quit and the prop will usually be ok. Touch any thing with wood prop which are more expensive and the prop will instantly snap in 2 making them even more expensive! The APC are the most efficient, are stronger than wood, but not as resilient as the MAS. They are a good match for 2nd type planes and sport planes. 3 or more blade props aren't efficient at the high rpms that the glow engines spin at. The only good reason to use a 3 blade is if you really need the extra 1/2" of ground clearance. [8D]