I have a UCD 46 with an OS91 4stroke on it that I have been flying for a year. I seems to be about right for the plane. I had a YS63 on it for several months and that worked too. The UCD 46 is a BIG 46 plane that will fly with a .46 2 stroke but not as well as with a .91 4 stroke with 10 lbs of static thrust.