Flywheel weight

Bruce R. · Jan 23, 2020

Got a case of cabin fever so I’m in the middle of building my third Deppenbusch engine. I’ve scaled it up slightly and decided to go with heavier flywheels, I’m thinking this would make the engine coast longer between hits and run slower. Anyone out there have any thoughts on this ?

TonyM · Jan 24, 2020

For full scale engines heavier flywheels or even adding a second flywheel was used as a means of reducing the surges especially for generator sets so the hit and miss effect is reduced. In small scale the effects you desire may be more achievable, certainly slower running.

Bruce R. · Jan 26, 2020

The slower the better, I’m thinking that I should’ve gone with a longer stroke as well but I’m too far along with it now.

Brian Rupnow · Jan 27, 2020

Flywheel weight is one of those "Try it and see" situations. Yes, for a given impulse by the piston, the flywheel should revolve a bit longer with heavier flywheels. However, you have to take mass and inertia into consideration. If the flywheel is heavier, it has more inclination to stay "at rest". That means that with the weight increased but the piston giving the same "push" as it did with the lighter flywheels, the heavier flywheel won't revolve as fast as it did with lighter flywheels. It might rotate longer before the engine "hits" again, or since the starting rpm from the piston will be a bit less due to the heavier flywheel weight, it may not. I already tried this heavier flywheel thing with my Kerzel hit and miss engine, and it didn't work out very well.

Rustkolector · Jan 28, 2020

In my experience replacing a flywheel with a heavier flywheel of the same diameter yields only small operation improvement. However, changing to a larger diameter flywheel usually does improve running. The most effective mass of a flywheel is at the rim. Foos, Otto, Nash, etc. electric lighting engines used very large diameter, but not overly heavy flywheels.
Jeff