20601 Old State Road Haubstadt, Indiana 47639Glennkarch@gte
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In the design and construction of the double flywheel gas
engines it was the accepted practice to keep the outer flywheel rim
speed below 60 miles per hour. This was the safety factor
considered necessary to prevent centrifugal force caused flywheel
explosions.
You may wonder just how fast the rim speed is for the various
Hercules built engines. Here is the formula for determining the
outer flywheel rim speed. Take the flywheel diameter in inches
times 3.14 and then divide by 12. This gives the rim circumference
in feet. Multiply this by the RPM and then by 60. This gives the
rim speed in feet per hour. Divide by 5280 to get the rim speed in
miles per hour.
Shown below is a chart for the model E Economy engines.
HP
Flywheel Diameter in inches
Flywheel RPM
Rim speed in MPH
1.5
18
550
29
2.5
22
450
29
5
28
425
35
7
34
375
43
9
38
325
37
12
44
300
39
HP
Flywheel Diameter in inches
Flywheel RPM
Rim speed in MPH
1.5
18
575
31
2.5
22
500
33
5
28
450
37
7
34
375
43
You can see that all the flywheel rim speeds on these engines
fall within the guidelines.
To continue the story, shown below is a similar chart for the
model T Thermoil engines which were also built by Hercules.
Again, there is plenty of safety factor. But there is a
complication. These early Thermoils were built on a modified gas
engine chassis. These Thermoils were also subject to erratic speed
control. If the engine speeds are increased 1.5 times, the
resulting rim speeds are 46, 49, 56 and 64 MPH. At twice rated
speed the numbers are 62, 66, 74 and 86. Add to that the increased
vibration from an engine that has begun to hop about, not only did
flywheels come apart, other parts of these weak framed engines also
began to break.
A line of engines sold by the Cummins Engine Company, which were
identical to the later model U Thermoils sold by Sears, were
governed to run at even higher engine speeds.
In searching through history of the Cummins Engine Company there
is a story about a Cummins representative who went out to a farm to
service a complaint on an engine. While he was there watching the
engine under discussion running in the barn it sped up and the
flywheels came apart and it is said that, ‘the pieces cut right
through the boards.’
So much for the discussion. I am sure that there is more to the
flywheel safety thing than is reported here, but it does point out
a hazard that can occur when any of these old engines begin to run
wild. Cracks in the flywheel or loose fits on the crankshaft can
complicate the matter.
