balancing. (long, sorry!)

[treed2 at wsu.edu (T. Reed)]

Okay, I see we've entered the 'vague semi-science' realm, but I will try
my best to understand what's being said and explain things in non-engineer
speak.

On Sat, 1 Nov 2003, David Utley wrote:

> Comments within...

[ temporary departure from topic at hand:

  I'm sure I'm not the only one who can't stand it when people reply
  without quoting (ie. "> ")

  I dunno what mail software you use, but it would make your replies a lot
  easier to read if you replied in the conventional fashion (maybe this is
  part of the reason that not many people responded to your earlier msg?)
  rather than just interspersing your comments in the message you're
  replying to. ]

> So as I understand it, David's argument is that the lumpier idle resulting
> from a lightened flywheel results in modulation of the air flow plate (ie.
> same effect as modulation of the throttle) and a decrease in fuel economy.
>
> Sort of...  Not so much a lumpier idle, as much as accelerating much more
> than necessary....  You know like young drivers are often doing, because
> they do not know how to coast well...  Constantly accelerating, then
> braking, then accelerating, etc...  Lots of wasted energy that is vented
> through the brakes as heat...

YES, especially when you have a heavy flywheel. See, you need a lot more
fuel to spin a heavy flywheel up to a particular speed than you do to spin
up a light flywheel. When you step on the brakes, that energy is dumped to
heat. With a lightened flywheel you will get better gas mileage in this
scenario (ie. city driving) because you're dumping less energy. That
energy has to come from somewhere; fuel.. so the lightened flywheel is
using less fuel since its dumping less heat.

This is about potential energy- think of a heavy flywheel as a large
bucket. You scoop water out of a bathtub with this large bucket (ie. spin
up the flywheel). Then, lift it over your head and dump it out on the
bathroom floor. If you'd used a smaller bucket, you'd have wasted less
energy lifting the water.

The same amount of fuel can be used to accelerate a heavy flywheel slowly
or a light flywheel quickly. Which would you rather do? Personally, I like
to accelerate faster on the same amount of gas.

If you want to pace me in my lightened-flywheel car side by side with your
normal-flywheel car, you will have to burn more fuel to accelerate at the
same rate as me. And when you stop, your brakes will be hotter because you
will have more kinetic energy (because you burned more fuel).

At a constant speed, the acceleration is zero, so the flywheel weight
does not matter. The bucket is already over your head so all you have to
do is keep it there; you're not expending any energy in lifting it. (Just
fighting gravity.. or friction in the engine example)


You can spin the flywheel up as fast as you want (within the power limits
of your engine and the shear strength of the flywheel bolts). To spin it
up from 1000 rpm to 3000 rpm in 2 seconds is possible for both an 8 lb
and a 12 lb flywheel. But it will take more power for the 12 lb flywheel.
This power has got to go somewhere, and it winds up as potential energy
in the flywheel. The 12 lb flywheel has more stored power.

Storing power is kind of like buying a keg of beer. If you buy a keg and
only finish half before passing out.. you wasted the rest of the beer
(pretend that it goes bad much more quickly than in reality). If you
bought a pony keg instead then you'd have more money to spend on Scirocco
parts.

Let's say the keg was too small.. ie. your flywheel was not heavy enough.
What happens? You don't get drunk! The engine stalls. This is why
you have to give cars with lightened flywheels a little more gas to get
going.. you have to store more potential energy in the smaller flywheel
by revving it slightly higher to make up for its small mass.

Now just wait for the "next VTEC" - variable mass flywheels! Oops, I guess
I should have gotten a patent on that first..!

> It is standard scientific practice to abstract the real world to the ideal
> (in this case frictionless) case in order to better understand the forces
> at hand, THEN make adjustments to model the real case.
>
> Agreed.  I guess I was a bit thrown by the indirect insults to see where he
> was...

I think part of the problem you're having here is that you're tackling the
lightened flywheel as a 'whole car' issue, rather than considering the
specific changes resulting from a change in weight of the flywheel. That
is the only part of the system that is changing, so it is best to focus on
the changes that are created by the change in weight and propogate them
outwards.

The change from a physics point of view is the energy storage potential of
the flywheel. I've already run :the results of this change: in to the
ground.. so I won't discuss them again (unless you want me to).

> Engineering is not meteorology.. when applied correctly, it's about as
> close to 'truth' as you can get. Scientists sometimes get to ignore the
> real world, but it is the playpen in which all engineers are locked. They
> don't get to design and build things for an "ideal" world!
>
> Yes, agreed...  I think the only problem we really have here "is a failure
> to communicate".  No, beyond that...  It is a perception problem...  In some
> ways I think I have received this much flack because I am relatively a new
> comer, and here I am standing up to  the one who (probably) is THE one who

I don't think it was so much that you were a relative new comer (you are?
that's news to me.. i figured you were just one of the quiet folk that
don't post often) than that Dan pretty much laid out a logical explanation
of his counter-arguments and you responded to his post with little
more than doubt and cynicism, and failed to really address any of his
arguments by further explaining your statement(s). The latter was probably
the most inflammatory part, contrary to what you might think. It's fine to
call someone wrong or even (what's that word for 'overly proud'?) but
you've got to state your position clearly and back it up or you just come
across as intentionally disrespectful rather than passionate.

> would call BS or not...  If I could speak to Dan as an equal, in a language
> that he is more familiar with, I think he would agree...  However, since we
> do not have that luxury, it will take longer to get my point across...  And
> that is okay, as long as I do not get thrown off the list inbetween now and
> then...  :)  I will either win my point, agree that I am wrong, or agree to
> disagee and move on...
>
> My 2 cents.. please take note that this e-mail is meant to have a
> light-hearted, informative tone. I'm not trying to instigate anything
> here.
>
> Thank you Toby, for the friendly mediating...  I needed it, as I feel that I
> have upset a few here with my comments...

It took me a while to write that response but I felt like it was necessary
to try and create some understanding for Dan's position, as well as try
to clarify (what I thought was.. evidently I was wrong) your argument.

Now I'm responding because I'm trying to give you an opportunity to
explain yourself using my weird "laymen's terms" parallels so that I can
correct your explanation :)

(yes, that was a mild jab.. hehe)

-Toby

BTW: when replying to this post, please trim the parts that don't matter
for the sake of our digest brethren.