jeffie8696 wrote:I am working on breaking in a Magnum (ASP/Sanye) 52 four stroke. So far it is making good power but it is not as refined as a similar Saito or OS. I suffered a crash due to electrical failure and had to start over with another test plane. Four strokes are a lot harder on airframes due to the vibration.
Yes, most 4-strokes do vibrate more -- that's because instead of two moderately strong combustion cycles every two revolutions, you get one much more powerful (and sustained) combustion cycle.
Experiment with props.
Sometimes a heavy prop will suppress a lot of vibration, other times you'll get less vibes from a light wooden prop.
Tuning has a big effect too. A 4-stroke that's too rich in the mid/low throttle range will tend to shake more than one which has been tuned properly.
If you really want to see a 4-stroke shake, get a Saito 100 or 180. They're *very* light engines for their displacement and they are bone-breakers. But they do put out very good power and for 3D flying (where power-to-weight is important) they are hard to beat.