My son has a RCV 91CD in his YT International (ESM) Spitfire, take off weight is 14lb using a 14x8 Master Airscrew, slightly extended take off due to higher pitch but flying, I have a Laser 120 in my 13.5lb BF109 turning a 15x8 Master and I struggle to keep up with him. My experience with these engines 100% reliability, I dont think I have had to touch the needle valve after the running in period on any of them, well impressed.