From: shadow@pro-haven.cts.com (Blaine Hufnagle)
Newsgroups: rec.autos.tech
Subject: Re: Flywheel batteries as EV power source
Date: 21 Dec 92 00:35:54 GMT
Organization: ProLine [pro-haven] - Pariahs' Haven BBS, 409/846-3177, 9600-300
NNTP-Posting-Host: cs.utexas.edu

In <51674@seismo.CSS.GOV> stead@skadi.CSS.GOV (Richard Stead) writes:

% In article <gfATnhq00iUzI1mV0H@andrew.cmu.edu>, cd1i+@andrew.cmu.edu (Christopher Bradley Devlin) writes:
% > 
% > What is all this talkk of particles blowing through the housing?  What
% > particles?  The original premise was that these flywheels disintegrate
% 
% particles of the destroyed rotor
% 
% > into a light cotton like fiber.  Heat, yeah, but how much kinetic energy
% > does a flying piece of cotton have?
% 
% The same as it did when it was part of the rotor - one hell of a lot.
% Plenty to blow through any of the simplistic housing proposed in this
% discussion.  Remember, kinetic energy is 0.5 M V^2.  The M may not be a
% lot, but the V is beyond anything in your experience (these discussions
% of speeding trucks and bullets are just nonsense in comparison).  And it's
% the V that's squared there.  The impact of the fiber with the housing
% is well beyond any elastic limits - it generates a shock wave in the housing,
% and melts or even vaporizes the housing at the point of impact.

How are you thinking that the rotor is going to fail?  Explosively?  I
seriously doubt it.  More likely, is the kevlar fibers will simply peel off,
like the skin of an orange.  That tearing action will absorb a lot of energy
in itself, and the partially peeled fibers will act as a brake.  And if I'm
reading the article correctly, these flywheels aren't that large.  I'd guess
about six inches in diameter.  (They couldn't get much bigger because of the
amount of energy needed to get that much mass spinning at the stated 200,000
RPM.)  A wheel of kevlar one inch thick with a radius of three inches doesn't
weigh that much, so the energy won't be _that_ high.  (i.e. high enough to
vaporize a housing)

% Ceramic.  Big deal.  A meteor melts the rocks it impacts and it is not
% moving as fast as the flywheel rotor - and ceramic is nothing more than
% glassy rock.   It will melt.
 
But keep in mind that that meteor usually weighs a hell of a lot more than
the flywheel.  And, many high-temperature ceramics have melting points of
several thousand degrees celsius.

% Look what up?  The melting temperatures for ceramics?  Lots of references,
% but you don't understand the physics here.  The particles have so much
% energy that they will melt any solid in existance.

Also think about the structure of Kevlar.  Long thin fibers.  In this case,
a couple of thousandths of an inch in diameter by three or four inches.  NOT
little spheres or cubes or whatever abstract shape things like sand grains
come in.  

In addition, most composite structures, like Kevlar, don't fail explosively. 
They fail progressively.  Now granted, at the above mentioned speeds, a
progressive failure can happen so quickly as to _appear_ to be explosive, but
it is still progressive.  The progressive failure mode will absorb much of
that rotational energy.


-blaine



          a.k.a. The Midnight Shadow    |  1979 Chevy Urban Assault Vehicle
Texas Aggie Bus Driver and proud of it! |  1982 Thomas Transit Liner bus
Another Bodybuilder from HELL!!         |  1982 Yamaha Vision   DoD #7192
        "Mine is not to wonder why, Mine is but to look and cry....."
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