balancing.

[mr.utility at highstream.net (David Utley)]

Comments within...

-----Original Message-----
From: Mark [mailto:mardak@cogeco.ca]
Sent: Saturday, November 01, 2003 9:49 PM
To: mr.utility@highstream.net; 'T. Reed'
Cc: 'Dan Bubb'; scirocco-l@scirocco.org
Subject: RE: balancing.

* ------I am resending this note, as there was not much response, esp.
from
> the sender...  We may, or may not get to the bottom of this
discussion,
> but
> if we do not it won't be from a lack of trying on my part...  :)

We're all trying, you're just not understanding! LOL  :)  I'm not an
engineer, so my ability to try and convert my thoughts into technical
discussion is lacking...

Basically at the heart of your argument you're saying that an engine
with a 12 pound flywheel will require less throttle (and therefore less
fuel) to maintain the same rpm as an engine with an 8 pound flywheel,
right?
* No, or not exactly...  I am saying that you will not have to change the
throttle position as frequently, with road changes, wind, etc...  As in, say
you are at 70...  A strong wind comes up, and you have to make a speed
correction to maintain the same speed...  You have more inertia with the
stock flywheel, therefore you will have to depress the throttle less to
maintain the same speed...  Not only wind of course, but also with slight
hills, overcoming semis, whathaveyou...

It takes energy to spin both flywheels up to 4000 rpm.  It takes MORE
energy to spin the 12 pound flywheel to speed than the 8 pounder.  There
IS more kinetic energy in the heavier flywheel, but it's not free - the
engine used more fuel to spin that heavier flywheel to 4000 rpm.
Yes....  However, we are talking about maintaining speed, not always
accelerating...  You will coast/maintain speed a LOT longer than you will
accelerate...
  On the
flip side, this extra potential kinetic energy (vs a lighter flywheel)
can be used to accelerate the vehicle more, but it can only output what
was input!  So if you used an extra "X" number of Kj of energy to spin
the heavier flywheel to 4000 rpm, that's all that's available as an
advantage over the lighter flywheel to "give back" to accelerating (or
maintaining speed).   This kinetic energy doesn't "regenerate" itself.

           If I understand what you are saying here yes...  Don't ask me to
repeat it, though...  :)

This is why I think fuel mileage will actually be better with a lighter
flywheel.  When you decelerate you're wasting that extra "stored"
kinetic energy of the flywheel as heat.
           Only if you brake...  I am referring to a cruise on the
highway...  That will not happen for some time...
 Plus it takes more energy to
spin it back up to speed when you resume acceleration. You lose in both
cases.  As for maintaining a constant speed, if you were to isolate ONLY
the energy needed to keep the flywheel spinning at a constant 4000 rpm
it would be VERY VERY small compared to the energy "lost" to pumping and
friction of the engine alone.  For this reason I think a mpg difference
between the two engines would be practically immeasurable at a constant
rpm.
             It will depend on driving style, I think...  If you are
cruising over 300 plus miles, you would notice the difference either way...
In town, you would prolly gain mpg, depending on driving syle...


As I said, I'm no engineer, but hopefully someone will chime in with a
few formulas/laws of physics, etc. to prove that a heavier flywheel will
not improve fuel economy.  Actually, I believe science will prove that
the reverse is true...
            (Voice of Don Pardo)"And so the battle raged on...."   :)


Mark.

David, and thanks for entertaining my theories...

>
> -----Original Message-----
> From: Mark [mailto:mardak@cogeco.ca]
> Sent: Friday, October 31, 2003 11:10 PM
> To: 'T. Reed'; mr.utility@highstream.net
> Cc: 'Dan Bubb'; scirocco-l@scirocco.org
> Subject: RE: balancing.
>
> But I don't think the "engineering talk" is going to
> convince David he's wrong
>
> If it is written in a manner where I feel all of my points have been
hit
> upon, then I will be convinced, which has not yet happened...
>
> Place two identical engines on engine stands - except one has a 12 lb
> flywheel, the other has an 8 lb flywheel.  Start both engines up and
run
> them at a constant simulated cruise speed of 4000 rpm.  Both engines
> have NO load on them.  Now picture the amount of work the engine has
to
> do just to keep it spinning at 4000 rpm - there's friction from the
> rings on the cylinder walls, friction at each bearing point, the crank
> sloshing through the oil, all kinds of frictional losses in the
> valvetrain + work to overcome valve spring pressure etc. etc. (try
> turning a cam shaft with a wrench, then try to imagine how hard it
would
> be to spin it at 2000 rpm!)  There is a substantial amount of energy
> needed JUST TO turn all these parts at 4000 rpm and convert up and
down
> motion to circular motion.
>
> In comparison, how much energy is needed to keep JUST the
> flywheel
> spinning once it's up to speed - whether it weigh 12 or 8 pounds, not
a
> hell of a lot.  We're talking fractions of a single horsepower here,
> compared to a healthy percentage of the total output of the engine
just
> to keep everything else spinning at 4000 rpm...  Don't forget we're
> talking about engines on stands here with no direct load other than
> "internal losses"...  So EVEN IF your (David's) scenario were true
> (which I believe it isn't) there is only a tiny fraction of a single
> horsepower difference between keeping the two engines spinning at 4000
> rpm with no load.  Now how in the hell is that going to make ANY
> difference when those engines are in a car that's trying to poke a big
> hole through the air at 75 mph at 4000 rpm.  The energy that's
required
> to push the car at a steady 75 mph is ASTRONOMICAL compared to what's
> needed to keep an 8 or 12 lb, twelve inch diameter disk spinning.
There
> is just NO WAY that a 4 pound difference in the flywheel is going to
> make even close to a measurable loss in fuel mileage, on a stand or in
a
> car...
>
> Yes, however, that 4 lbs, which in actuality, someone correct me if I
am
> wrong, but the diff. Between stock and lightened flywheel is more like
15
> lbs, isn't it?  (23-8.5lbs)...  Anyways, there is a calculation that I
> have
> in my ARP book at work that tells you how much an ounce weighs at 4K
rpm,
> as
> you illustration suggests...  Carroll Smith was talking about
balancing an
> engine, and he said that one reason why you balance an engine is
because
> at
> 7K rpm (his illustration), the weight is (I think) 15 Geometric
fold...
> That is, 1.2oz, times itself, 15 times, which turns into quite a
sum...
> Now, if this is going to happen for a few ounces, imagine what a few
> pounds
> will generate...  And do come back with "that is balancing, it is not
the
> same".  It is the same, we are talking about balanced weight here, no
> extra
> vibrational forces, just momentum...  In other words, 4-15 lbs,
whatever
> it
> is, spinning on the flywheel generates many thousands of pounds, which
is
> why a flywheel that shatters at 7K rpm will often kill its driver
after
> shred several different chunks of hard iron...
>
> David
>
> Again, sorry to be so short and sweet, in a rush, more later...
>
> David
>
>
> Sorry for the length, it was much more concise in my head!  :)
>
> Mark.
> 80 S
> 81 S  ABA/JH/4K - with a power robbing 8.5 lb flywheel  :)