From: carl@SOL1.GPS.CALTECH.EDU (Carl J Lydick)
Newsgroups: sci.energy
Subject: Re: Popular Science Fly Wheel Article
Date: 21 Dec 1992 09:09:14 GMT
Organization: HST Wide Field/Planetary Camera
Distribution: world
Reply-To: carl@SOL1.GPS.CALTECH.EDU
NNTP-Posting-Host: sol1.gps.caltech.edu

In article <1h3t1nINNddb@sportster.ksu.ksu.edu>, camelsho@sportster.ksu.ksu.edu (   James A Seymour) writes:
>I'm not sure if this is the article which started the
>whole fly wheel discussion.  However, its probably
>the one most widely read.
>

>The American Flywheel Systems (AFS) battery contains a pair of 
>counter-rotating "rim wheels," suspended by magnetic bearings in a
>vacuum housing.  The rim of each wheel is made from a high-tensile-
>strength fiber, such as Kevlar.  Spoke tubes containg magnets connect
>the rims to lightweight hubs.  An electric charge sets the wheels in
>motion, and they can perform work as they continue spinning--like a 
>potter's wheel.
>
>The idea of using a flywheel to store energy is not new, but designing
>a device that works efficciently and safely has jproved difficult.  To
>power a car, a flywheel battery must be capable of rotating at 150,000-
>200,000 rpm.  If the flywheel is a metal disc, it could break into 
>shrapnel at that speed.  And if it is a spoked wheel, the rim pulls
>away from the hub at high rpms.
 
So far, so good.  Though their emphasis on "shrapnel" makes it appear we're
soon going to run into problems.

>AFS claims to have solved some of these provlems.  For example, the
>new battery's spoke-tube assembly allows the flywheel rim to expand
>without separating from the hub.  And when the rim is spun so fast 
>that it fails, the Kevlar fibers simply turn into "cotten candy,"
>says Edward W. Furia, chairman and chief executive officer of AFS.

Yup.  There we go:  "If it's fluffy, it's safe."  It won't be very effective
shrapnel, at ranges of dozens of yards (just how fast do you think the
atmosphere will stop hypersonic cotton candy?).  BUT THAT "COTTON CANDY" STILL
HAS ALL THE KINETIC ENERGY THAT YOU'D STORED IN THE FLYWHEEL.  You still need
to enclose it in some sort of containment that's capable of absorbing all the
stored energy.  If the containment can't absorb the energy, then, at the risk
of repeating myself,

	BBBBBB    OOOOOO   OOOOOO  M       M !!!
	B     B  O      O O      O MM     MM !!!
		B     B  O      O O      O M M   M M !!!
	BBBBBB   O      O O      O M  M M  M !!!
	B     B  O      O O      O M   M   M !!!
	B     B  O      O O      O M       M 
	BBBBBB    OOOOOO   OOOOOO  M       M  !


>Furia says his new battery could make GM's proposed Impact electric
>car go as far as 600 miles on an overnight charge.

Up until now, I've been giving the hypesters the benefit of the doubt, and
assuming that they were only talking about storing about 1/9 of the energy of a
tank of gasoline in the flywheel.  Apparently they're talking about a full tank
equivalent.  Maybe I should've made the BOOM! bigger.

>The Impact now
>runs on 32 lead-acid batteries and has a range of about 80 miles.
>Replacing the lead-acid batteries with 20 flywheel batteries, each
>weighting 30 pounds, would also improve the car's acceleration, 


OK, by using several flywheels, they've dealt with two problems:
	1)  Have half spinning one direction, the other half spinning the
	    other.  Then if you've bolted them down well enough, the car as a
	    whole won't have any problems due to gyroscopic effects (other than
	    metal fatigue where the housings of the flywheels are attached); and
	2)  They've reduced the energy stored in each flywheel.  I'd be happier
	    if they were using about 500 flywheels, but 20's a start.  They're
	    now only talking about something like 2 sticks of dynamite
	    equivalent in the event of a flywheel failure.
>according to Furia.  He says flywheel batteries have a high power
>density--they can give up energy quickly.

Er, yeah.  That's the problem.

>"It's very important to overcome the perception of electric cars as
>glorified golf carts of greenmobiles," says Furia.  "Electric cars
>should be capable of dazzling performance."
>
>The flywheel battery would last about ten times longer than a lead-
>acid basttery--which must be replaced after 25,000 miles.  And since
>it uses no chemicals, it wouldn't create corrowsion or disposal
>problems.

>For now, the flywheel battery exists only as a computer simulation.

Yup.  The jackass who was complaining that this discussion was talking about
theoretical considerations instead of tested technology apparently thinks that
we should just take advertisers' claims as gospel, rather than treating them as
theoretical considerations, and not tested technology.

>It will take a bout two years to build a protype for a car, Furia
>estimates.

The rest of the article implies that they're using, pretty much, off-the-shelf
technology.  Why the two-year delay?  I know Kevlar's fancy stuff, but TWO YEARS
to manufacture a flywheel for testing?  Looks to me like these guys are just
blowing smoke, hoping for a miracle to solve the obvious problems for them
sometime in the next two years (or maybe they figure that they can hide the
obvious problems for that long, then head south with the unspent research
funds).
--------------------------------------------------------------------------------
Carl J Lydick | INTERnet: CARL@SOL1.GPS.CALTECH.EDU | NSI/HEPnet: SOL1::CARL

Disclaimer:  Hey, I understand VAXen and VMS.  That's what I get paid for.  My
understanding of astronomy is purely at the amateur level (or below).  So
unless what I'm saying is directly related to VAX/VMS, don't hold me or my
organization responsible for it.  If it IS related to VAX/VMS, you can try to
hold me responsible for it, but my organization had nothing to do with it.