RE: Engine for a 53" span bipe?
Magnum .91's weigh about the same as most .60/.75's, and they're on sale right now for $129. I like them so much I have 2 of the newer XLS, and an older ASP(a little heavier). But the XLS .91 with a 16x6 would do nicely. I have it on a 9.5 lb fun fly that will rocket out of a hover.