From: gary@ke4zv.uucp (Gary Coffman)
Subject: Re: A gripe, and Re: Flywheel batteries...
Reply-To: gary@ke4zv.UUCP (Gary Coffman)
Organization: Destructive Testing Systems
Date: Thu, 31 Dec 1992 03:16:34 GMT

In article <1992Dec28.165210.28613@samba.oit.unc.edu> Blair.Haworth@launchpad.unc.edu (Blair Haworth) writes:
>
>The progress of this (interminable) thread has done a lot to dull my
>initial optimism about the applicability of flywheel energy storage to
>automobiles. I think the real grief will come from bearing design, and
>from technologicical overreach in going directly for automotive
>application.  Why not start with a static device, like a peak-load
>storage or a backup power source, where you don't have to worry about
>accelerations and you can put it in a pit, just in case?

Such flywheels exist. The one at MIT has been cited. It has the same
order of energy storage capacity as those we've been examining for
vehicles. But it is very large by comparison and turns much more
slowly. That way the materials aren't under nearly as much stress
and failure is less likely than with a small rapidly rotating mass. 
Multi-ton flywheels, turning at a few thousand RPM aren't remotely
suitable for auto use.

Now even auto clutches sometimes fail explosively, that's why the NHRA 
mandates an approved scattershield to protect the driver and spectators.
I've seen clutch explosions literally cut a race car in two despite the
scattershield. Now that clutch is storing a tiny fraction of the amount
of energy required for a flywheel battery, and it is turning at a mere
6,000 RPM.

>I'm not totally convinced by the energy-is-conserved-and-that's-that
>crowd, although I think containment will be daunting.  I suspect though,
>that at least a partial solution exists today, in production-line
>automotive technology, in several thousand examples.  Consider the M-1
>tank: it carries its forty rounds of main-gun ammo in an armored
>compartment designed to vent upward in the event of an explosion: the
>rules say energy is conserved, they don't say which direction it has to be
>conserved in.  The total energetic content is typically about (40 x 10kg=)
>400kg of propellants and very roughly, assuming half the warload is
>HEAT-MP, (20 x 10kg x 15% explosive filling by weight=) 30kg explosive
>(numbers from _Jane's_ via memory).  Do these sound like familiar numbers? 
>Yes, we're talking about a 60-70 ton tank, here, but keep in mind that
>we're talking about what happens to be one of the most thinly-armored
>parts of the tank.  It would also be foolish to ignore the, ah, distinctly
>directional character of flywheel failure, but consider that the same tank
>is designed to defeat just that sort of attack (shaped-charge warheads). 
>Both these features worked pretty well in combat; their descendants might
>(for all we know) work on the road.  I won't bet the rent money, and of
>course, the relevant technology is heavily classified, but it is there. 

The M1A1 has never survived a main ammo locker failure to my knowledge.
Like the Hood, once the main magazine lets go there's little mere steel
can do to resist. The crew is history.

Note that the main threat to MBTs is the kinetic penetrator called a
APDS round. This round uses pure kinetic energy to destroy enemy tanks.
Mere HEAT rounds are considered ineffective against modern armor. That
armor, called Chobham after the military establishment where it was
developed, is not in any way light. Most of the mass of a 65 ton tank
is armor designed to defeat a 10 kg penetrator travelling at 5,000
m/s. Since the flywheels we are talking about would have a rim velocity
of 5,000 m/s or greater, and would mass more than 10 kg, it should become
obvious that containment would need to exceed 65 tons of armor to stop
it should it fail.

Gary
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