I also use the OS .46 AX and a 12 x 4 prop and have been very happy with it. I few weeks ago, I removed the baffle out off the square shaped muffler and gained a noticeable amount of power. I then went to an 11 x 6 airscrew prop and now deem this the best combination of engine and prop I have ever tried on this plane. The extra power allows it to easily hover on this prop and the extra top end speed is great for knife-edge flight.