RC Hobby Guys
Here is a Ryobi 31cc string trimmer
engine that I converted to airplane
usage.  On this one I used conversion
parts from Paragon Aero.  
Unfortunately they are no longer in
business.  I think their conversion parts
were the best in the business.  At least
Jag Ltd. is still available.
Click on any thumbnail image to see a larger picture.
Here are pictures of my Ryobi engine
mounted on a test stand in my driveway
where I do all my engine testing.
Here it is mounted on my Dynaflite PT-19.  It
flew the PT-19 for the first six flights but the
plane was underpowered.  I later replaced it
with a US41 engine.
All of my takeoffs involve a runway.
Ryobi 31cc string trimmer engine
Unfortunately not all of my landings do.