RE: Propeller acts as brake?
First, it assumes low or idle speed. If the engine it full bore opened, it's just going to go faster.
A rough example is the comparison between the spiral shaft in a childs top. You push down on it and it turns the top. That shaft is a screw with a very course pitch. Enough of a pitch that it will impart a truning movement when forced straight through the threads. Now compare that to a screw and nut from the hardware store. In comparison, you have a very fine pitch and no amount of pushing will cause the nut to turn.
If we compair that to the props, the finer the pitch the less the wind trying to push through it will be able to turn it. So, using the abouve example, a courser pitch will tend to windmill more than the finer pitch. It' all mechanical advantage. The fine pitch will allow the motor to transfer more enegery to move the plane, but not a fast. The course prop takes more enegery to get to the same rpm but will move the plane faster. The fine prop will not transfer the rush of air past it to rotation of the motor so it acts as an air brake. The courser pitch will feed rotation into the motor and make it dificult to get to the low rpm to act as an air brake.
Comparing a 11x 5 to an 11x6 would not result in any noticable difference in braking power. Comparing a 11x3 to an 11x9 though would be noticable.
I tend to fly the low pitch props on slow planes. I need to watch my landing speed as I can easilly go to slow to quickly and stall them. The higher pitched props will result in less braking, but also be faster, so which is better. Untill you get to the point that you can tell the difference, go with what was recomended for your setup. It will be the best compromise. After you get a few hours under your belt, you can start expermenting. If you are anything like I was first starting out, I got the chance to buy a lot of props, so expermenting with size and pitch wasn't very costly, well additionaly cost anyway. In my first couple months, a good day was one that I still had a spare prop left when I went home.
Don.