Quest for a more realistic Hit-Miss Model Engine

Jake M said:
I think you're right that it's not going to scale well. The first and primary issue is that the "size" of the engine is related to it's linear dimensions, while the mass is related to the cube of any given dimension. So the mass does not scale linearly with the size. I'd wager that this is the biggest hurdle.
I'd imagine that this could be "somewhat", and "to some degree" be addressed by carefully selected materials to get the reciprocating parts as light as possible, and (maybe.... Thinking on this...) to move the concentration of mass in the flywheel as close to the circumference as possible. Not sure on that one yet, that's math I haven't done since I don't remember when... Still, it's probably going to be difficult (at best) to overcome the weight to size ratio.
Click to expand...
What about casting the flywheels out of lead?

Or lead weights installed in them.
 
The moment of inertia of a flywheel is proportional to MR^2, where M is the mass, and R the radius. This means it's usually more effective to increase the diameter of the flywheel. Due to the R^2 term, you get the most bang for the buck by concentrating the mass on the outer rim, as the hub and spokes don't contribute much.
 
RaisedByWolves said:
What about casting the flywheels out of lead?

Or lead weights installed in them.
Click to expand...

That would help with that issue for sure. The difference in density between steel and lead is real, but it isn't great enough to make up for the cube relationship between the diameter of a flywheel, and it's mass. In other words, the size reduction is going to reduce the mass of a solid lead flywheel by that cubed relationship. For a SMALL reduction in size (I'm not crunching that out), but for a small reduction in size, it probably could be done with lead weights, escalating to all lead, but it's still not going to scale from a working engine to a bench top model.
 
Jake M said:
That would help with that issue for sure. The difference in density between steel and lead is real, but it isn't great enough to make up for the cube relationship between the diameter of a flywheel, and it's mass. In other words, the size reduction is going to reduce the mass of a solid lead flywheel by that cubed relationship. For a SMALL reduction in size (I'm not crunching that out), but for a small reduction in size, it probably could be done with lead weights, escalating to all lead, but it's still not going to scale from a working engine to a bench top model.
Click to expand...
I was only pondering best case scenario for the size, not scaling.
 
Thanks Chris

I decided to take a closer look at "Red" the engine shown earlier at post 57.

I worked only on the governor assembly by changing spring tension and length.
I was rewarded with these figures.
High RPM = 540 down from 600
Low RPM =420 down from 480
The engine now fires 16 times a minute down from 21 times a minute.
The engine now coasts for 3.75 seconds between firings over a second longer than before.

I do find it interesting that both the high speed and low speed rpms dropped the same amount.

Thanks for looking
Ray
 
Ray you put me to shame. I tested several of my engines which I felt had a good hit/ miss action. The best engine was still about 40 cycles per minute and about 700 rpm.
 
Chris your engines have proven to be good reliable runners and you should be proud of them.

Ray
 
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