Just thought I'd weigh in with some high-altitude thoughts on the UCD 46. I fly at 5000 feet and am on my second engine in this plane in an attempt to get the vaunted unlimited vertical. The Magnum 61 on a 13 x 4W would not do it, though with a mousse can muffler it came close to hovering. Now I'm running an MVVS 77 with a mousse can setup on a 14 X 4W, bingo! I'm still trying to get used to how it flies on high rates, and get the CG dialled for blowing the tail around. I'm a rookie, flying since October, so that doesn't help either