Well, I'm no pro yet but I'll try to explain it the best I can. The flatter the pitch, the better pull type performance you will get. It will spool up faster & get you off the ground easier. The higher the pitch, the faster the plane will fly at high speed. For instance, the OS .46FXI flys very well with an 11X5 or 11X6. It has plenty good pulling power as well as pretty good top end speed. A smaller diameter prop with a high pitch will make for high speed, while a larger diameter prop with a lower pitch will give better low end performance while still being plenty fast enough for learning & most sport flying. This should be enough to get you started & the others with more experience will chime in & correct any mistakes in my attempt at explaining this to you.


http://www2.towerhobbies.com/cgi-bin...?&I=LXUR78&P=0

This is the engine you bought right? According to Tower's recommendation a 12X6 or a 13X6 is your prop. I think it will fly well with this prop & not get so fast at top speed that it scares you. I have a TS .56 swinging a 12X6 & it feels real good, lots of torque, & plenty fast enough if I want it to be. It's on a much lighter, faster type airframe, but it will go straight up no problem. Since this is a Trainer that you are gonna learn on buy a few props of each of those sizes, you're gonna need them anyway. It's plenty big enough to swing the 13X6, ground clearance shouldn't be a problem. The only time I broke props on my Trainer was on the ground. Not so much from bad landings although there were a few of those too, but mostly from the the wind tipping a wing over after landing while taxiing back to the pits. Tower likes to recommend Top Flite wooden props, but the general concensus around here is that a nylon prop is safer while in training. Like an APC or a Master Airscrew. It's easy to scuff a wodden prop & as a student not notice a hairline crack in it. There was a post about this a few months back which I found to be very true as I allready had a bag of Top Flite 10X8's that came with my Tower Trainer. Every time the wing tipped I was putting on a new prop. Good luck in your training & welcome to the great Hobby/Addiction.