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It’s also interesting for another reason. As you have pointed out, the moment of inertia for spinning around the axis of the flywheel is the largest, thus is the one we want. Note also that the other two principle axis nearly, but not quite, add up to the moment of the principle axis perpendicular to the plane of the flywheel. The theory as outlined in the maths texts I am familiar with say this should be exact.

Curved spokes are very little different. Imagine a rod sliced into a stack of biscuits. Which are then pushed into the curved shape. The developed length and hence the mass of the spoke is a little larger than the straight one, but the centre line is the same distance from the centre of the flywheel and the moment of inertia about its centre line is the same as for the straight rod. The net effect is the same as a straight spoke of larger cross section, so mass of the developed length but distributed over the same length as the radial spoke.

r/R Ia/I (%) 0.000 100.000 0.100 99.990 0.200 99.840 0.300 99.190 0.400 97.440 0.500 93.750 0.600 87.040 0.700 75.990 0.800 59.040 0.900 34.390 1.000 0.000

It certainly shows the significance of the rim mass, though I note that for flywheels like the MEM Corless, r/R is greater than 90%, so the inertia is much less than the whole disk. However, that formula shows how a small difference in r makes a big difference to the inertia.

It seems like the first step is to determine how to calculate the flywheel moment needed by the engine and the error band of that computation.

That was what I expected when I first saw the topic appear.

PS JasonP, can you please send me the dimensions for the thickness and cross section of the rim of the 6.75 inch flywheel you eventually made.