Yeah, I bought one a while back too (OS 50 SX) and put it on a Rapier Ripmax flying wing. It is a hand launch design, and it literally pulled out of my hand on the maiden (someone else was flying it). And, after about 6 flights, we put it against a police RADAR gun. 121.5 mph with the original prop. The guy with the RADAR gun said that with a prop change, it would easily top 140 mph. I'm not sure about that, but it sure was fast with that combination.
Later on, I put that engine on a Four Star 40 in place of the OS 46 that was on it, and it really screamed! I was surprized about the noticeable difference between the two engines. I mean, not like adding, say a 55 AX but it did do much better. That too is (I still have it) a good powerhouse. I am looking for a home for it now.. have been building a Something Extra kit. I ought to get going on that and get it finished and put that engine on there and quit procrastinating!!
CGr.