I think Chuck fiqured it out once to be 1% per inch. A 72 in. prop will produce 12% more thrust than a 60 in prop. Dad has made a few Dominators with a 68in prop and they were awsome. When he decided to have jigs built he did not want to build three sets so he got rid of the 68 in airframe. I am not sure but you might be able to just use the chrome moly parts from a two place and raise the mast to accomidate it. You would also have to use a two place tail. That being said you'd have to check with him to see if he would sell you these parts for a single place. I can tell you this a single place Dominator with a 618 with a 68 in prop is an awsome beast. I just happen to know someone that has the only one left. You may know him from the forum. His name is Russ King. His was that last one dad built.
scottessex said:Rotax builds a fine product without a doubt.