When ever anyone says flywheel I remember the old(really old)one cylinder gas engines with huge fly wheels. It was a hoot watching one run with only one explosion about every 3 or 4 seconds and the engine cycling through the other 3 strokes silently. However, they were able to do what they were designed for, run a generator or other farm equipment and the fly wheel took forever to stop turning after the engine died.
What was that engine used for? I have seen them running at small engine shows.