Well, that may be what thrusthp says, but in reality those numbers are wayyy optimistic. I had my Irvine .53 on a 6 lbs plane, so theoretically 12 lbs of thrust should give it spectacular vertical performance. It doesn't.

Don't get me wrong, the IRvine .53 is one strong motor and IMHO the best premium sport engine in this size category. Smooth transition, extremely low idle, swings big wood, and runs on 5% or no nitro all day long. However, 12lbs of thrust it does not make.