dave ... I was told in RCU by a guy with the same set up as me to go for the 15x4 prop, he is doing rolling circles with the Chipmunk! My engine is still new, about 1 gallon only, hope to see more revs soon. Its not 'good vertical' its brilliant. I mean I can climb straight up for quite a while and then do a hammer head, it looks so kewl. I lift off with about 40% throttle! I like long scale like roll outs ... about 50' - 70' and then with a 15 degree climb