RE: Gas engine for a dynaflite super decathlon
I have not but the difference between a g38 and a 31cc ryobi is night and day. My plane was about 16 lbs and the g38 balanced it out good. I used a 20" apc prop also. I would think a ryobi would be too small and you would need a long runway for take off and not be able to do aerobatics very well. It was not overpowered with a G38 and would do scale areobatics, ie no hovering. Hope this helps.
chris