too small of a prop andyou can over-rev the engine.

Actually... its better to move to a longer, lower pitch propellor than the base recommended for the engine, when using it on a trainer. You want to keep the "dynamic load" about the same.

Lets assume the .46 you have recommends a 10X7 as the break-in prop. In that case, when using it on a typical .40 size trainer, you'd do well switching to an 11 X 5 or 11 X 6. You may even find that (if the tips will clear the ground) that a 12.25 X 3.75 "Fun-Fly/3D prop works quite well.

I had great results with the APC 12.25X3.75 Fun-Fly prop on a heavy .46 to .60 size trainer with a TT .46 Pro. Near unlimited vertical climb, alomost impossible to stall on take-off. The same plane with a 10X6, 10X7, 11X4 or 11 X 5 (I used APC, MA and Zinger in each size) wasn't nearly much fun to fly.

Something that may suprize you... the longer lower pitch prop IMPROVED the top speed too. If the plane is cruising too far bvelow the prop's calcualted pull speed (pitch X rpm, and convert to mph) the prop will be stalled, not producing as much thrust as it could. Reducing pitch, helps the prop "bite" the air better. You loose less airspeed in maneuvers, get a better rate of climb, and are able to slow down better when you want to land.

You'll note I experimented with lots of props on just one airplane and engine... you need to match the prop to the plane and the way you want it to fly.