RE: Ultra RC 92
Nicola,
Maybe I can answer some of your questions. I have the old Ultra RC Zero and have been flying it for maybe 6 years or so. Appears to be the exact same model as the CY plane that you sent a link to. I don't know who makes the Troy Built model but I have seen it fly and it flies well. What I don't like about it is they lengthened the nose to aid in balancing the model and destroyed the scale look of the short nose that the Zero has. My Zero flies great. It weighs about 30 lbs. and is powered by a ZDZ 80. I have about 3 lbs. of weight mounted beside the engine and tried to mount everything as far forward as possible. To me the 80cc engine is just right for the plane. It would fly fine with a 65cc engine but I don't think the radial you mentioned would fit in the cowl. I roughly measured my cowl from the outside and it appears to be about 9.25 inches, maybe just a little over that but probably not enough for the engine you gave measurements for. I have a fixed tailwheel so as not to add any additional weight that would have to be compensated for up front adding to the overall weight. The tailwheel barely sticks out, works fine on the ground, and is barely noticeable in the air. There does appear to be an incidence problem as someone mentioned as I do have a noticeable amount of down trim but it still flies great. The wheels are 5" and are the largest that can be used. And the retract mounting area is a very weak point on the model. The ribs and the entire retract mounting area must be beefed up substantially or the gear will probably rip out on the first landing and severely damage the wing. I beefed mine up in the beginning and have had no issues. But I also make good landings. :-) Any warbird with retracts won't tolerate rough landings but the Zero wouldn't even tolerate many good landings as it comes out of the box. Unless they have changed things, the ribs that the gear blocks mount to are just balsa with no plywood reinforcement which it needs. The Ultra Zero has a fiberglass fuse and a sheeted wing and stab covered with fabric and painted. Again, looking at the CY model...it is the same model.
Hope this helps, Mac Hodges