Flywheel Moment of Inertia?

[cantfindausername]

Just wondering if someone here can explain the MOI figures sometimes stated with Flywheels.

I'm not sure what is a good figure to be expecting from the lightweight flywheels that are on the market today.

Anyone have any links to articles? or just know off the top of your head?

Many thanks,
Ant

[Guy Croft]

No idea of actual figures because I've never had to measure it but here's the arithmetic:


Kinetic energy = sum of kinetic energy of individual mass elements that comprise the flywheel
= 1/2 x I x w^

where:

I = moment of inertia (ability of object to resist changes in its rotational velocity)
w = rotational velocity (rpm)
I = k x M x R^ (M=mass; R=radius); k = inertial constant (depends on shape)


(in the above equations ^ means 'squared', eg: R x R)

Inertial constants for different shapes:
Wheel loaded at rim (bike tire); k = 1
solid disk of uniform thickness; k = 1/2


GC

[cantfindausername]

Thanks Guy. Didn't think it would take long to get an answer on here!

Will see if I can get myhead round this now...

[pastaroni34]

First of all, I am impressed that some company is even quoting MOI, they always say weight which means very little..

Anyhow.. I've done just what Guy mentioned and drawn up a few Fiat flywheels in CAD software. Unfortunately this is not very accurate due to different materials, densities.. etc.. but it will get you a good ballpark and will be good to compare other flywheels derived from the same CAD software (I feel anyhow). I have compiled some of this info in a PDF here: http://www.millersmule.com/File%20Libra ... arison.pdf

and MOI on here is given in lb*in^2

Hope this helps,
-Jason

[cantfindausername]

Excellent thanks!

So is a higher or lower MOI a better thing to aim for?

Ant

[Guy Croft]

lower in every case, trust no-one that tells you a heavy fw and high MoI is ever better on a comp engine.

Anyone who disagrees e mail me or I'll wipe it.

GC