Good question. The Super Tigre G.61 came out of my demised Super Kaos (I'm now building a Killer Chaos to replace it) and it performed real well in that airplane. It was a very fast pattern ship that just ate up the sky with huge, graceful maneuvers. The G.61 had more horsepower than the UCD.46 really needed, in my opinion. I had to really be careful with throttle so as to not overspeed the airplane and possibly get the dreaded control surface flutter I've heard of. The main reason I replaced the G.61 is because I could not get it to run reliably in the UCD. Most of the time, the engine would suddenly quit while in flight. I couldn't find any rhyme or reason to it. I tried a different carburetor (Perry) and even added a Perry fuel pump. It may have been the inverted position the engine didn't like.

On the other hand, the Magnum seems perfectly happy in the UCD and while it doesn't have the raw horsepower the G.61 had, it makes up for it with much better low-end torque. I had to run a flatter pitch prop (13 x 4) on the G.61 to keep the speed down while still allowing the engine to run in its power band. It just seemed too frantic and out of character for a slow flying airplane and I had to manage the power settings much, much more than I do with the Magnum. I think these slower flying 3D airplanes respond better to an engine with good low-end torque, so the 4-stroke engines are better suited to the task.

-Kaos