# Re: [EVDL] article: Mitsubishi i MiEV Sport



## EVDL List (Jul 27, 2007)

*Re: [EVDL] article: Mitsubishi i MiEV Sport*



> Victor Tikhonov <[email protected]> wrote:
> > I may be wrong though, but it is intuitively obvious that
> > there is big difference between propeller-generator
> > on the roof where otherwise there is no resistance whatsoever,
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] article: Mitsubishi i MiEV Sport*

It seems to me (but what do I know) that if the air turns a fan, that will 
slow down the air stream going through that "deep inside" area which in turn 
will increase the drag across the "front crossection".

Peri Hartman

----- Original Message ----- 
From: "Victor Tikhonov" <[email protected]>
To: "Electric Vehicle Discussion List" <[email protected]>
Sent: 18 November, 2007 12:29 AM
Subject: Re: [EVDL] article: Mitsubishi i MiEV Sport




> > Lee Hart wrote:
> >
> >> As soon as you put a fan out into the wind, and try to generate any
> >> power from that fan, the drag goes up in direct proportion.
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] article: Mitsubishi i MiEV Sport*

From: Peri Hartman
> It seems to me (but what do I know) that if the air turns a fan,
> that will slow down the air stream going through that "deep inside"
> area which in turn will increase the drag across the "front
> crossection".

I think your intuitive answer is correct.

It is easy to set up an experiment to verify this or not. Get two small fans with PM DC motors (preferably not brushless DC because the electronics will mess things up). I predict:

- the fan draws the most current when moving the most air
(completely free and open air flow on both inlet and outlet)
- restricting the airflow reduces current draw
(for instance, by blocking or restricting either inlet or outlet)

Now, hang the two fans from strings from the ceiling, so they are close but not touching, and just a little above your workbench. Place a ruler on the bench, with 0" lined up with the fan you will use as your generator (0" is dead vertical). Power the first fan; that is your source of wind. I predict the generator fan:

- will spin the fastest, and generate the most voltge with
no load on it
- will have the least drag (move the least away from 0") with
no load on it
- as you increase the load on the generator fan (with a variable
resistor or equivalent), the drag increases, i.e. the fan
swings farther from 0")



--
"Excellence does not require perfection." -- Henry James
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart-at-earthlink.net

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## EVDL List (Jul 27, 2007)

*Re: [EVDL] article: Mitsubishi i MiEV Sport*



> Kaido Kert wrote:
> >
> > Drag coefficients of such bodies are several times different.
> > Take a hollow cylinder and hold it out of the window when driving.
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] article: Mitsubishi i MiEV Sport*



> Victor Tikhonov <[email protected]> wrote:
> > Plug it from the back but test with fan installed
> > in the middle (loaded) and compare it with the same
> > setup with identical but unloaded fan. Air strikes
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] article: Mitsubishi i MiEV Sport*



> Victor Tikhonov <[email protected]> wrote:
> > Kaido Kert wrote:
> > >
> > > Drag coefficients of such bodies are several times different.
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] article: Mitsubishi i MiEV Sport*

I think I understand point of confusion. If you hang a cylinder
*with plugged end* on the string and put a fan near front of it,
and direct air flow to it is it going to turn?

Granted, it will turn FAR slower than if the end of cylinder
is open for the air to go through, but is it still
turning just because oncoming air strikes blades (and thus
can do *some* useful work)?

If cylinder is totally plugged it doesn't matter what's
mounted inside of it. If fan - air slowed down by its
blades and fan 9f loaded, makes some power.

With stalled fan inside (or any object like it), air energy
perhaps heating the blades more instead of turning them,
also due to higher turbulence air heats itself
more, and this is where [unrecoverable] energy goes instead of
running that fan. So without fan drag is not less, it just
does useless (heating) work. Energy doing *that inevitable
useless work only* could be captured to do useful work.
That will not be at the expense of traction pack energy.

Victor




> Lee Hart wrote:
> > From: Peri Hartman
> >> It seems to me (but what do I know) that if the air turns a fan,
> >> that will slow down the air stream going through that "deep inside"
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] article: Mitsubishi i MiEV Sport*



> Kaido Kert wrote:
> 
> > There will be no airflow in the plugged cylinder, and the fan wont turn.
> 
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] article: Mitsubishi i MiEV Sport*



> Victor Tikhonov <[email protected]> wrote:
> > Kaido Kert wrote:
> >
> > > There will be no airflow in the plugged cylinder, and the fan wont turn.
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] article: Mitsubishi i MiEV Sport*

I can't believe we're actually debating this. Good grief, I wasn't a 
physics or engineering major, and even >I< can figure it out. ;-)

If you're deriving energy from the airflow around a vehicle, it has to come 
from the vehicle's kinetic energy. Thus if your fan trick is applied at any 
time other than during your car's deceleration, the net result is a loss in 
efficiency. I don't see any way around that.

In the described case the amount of energy harvested, and the amount of lost 
efficiency, are probably both negligable. So if you want to do it for show, 
just like Steve Clunn's hood ornament did, there's surely no harm. 

But there's also no real point. Why bother? Why not expend your effort on 
something that really IMPROVES efficiency? 

David Roden
EVDL Administrator
http://www.evdl.org/


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] article: Mitsubishi i MiEV Sport*

----- Original Message ----- 
From: "Kaido Kert" <[email protected]>
To: "Electric Vehicle Discussion List" <[email protected]>
Sent: Sunday, November 18, 2007 4:08 AM
Subject: Re: [EVDL] article: Mitsubishi i MiEV Sport


> No. The intuition is wrong in this case. The air drag is not function
> of cross sectional area alone ( grille area ) but also the shape of
> the body. You are essentially comparing the air resistance of two
> different bodies:
> a) air pipe with the grille area cross section, that goes through the
> body of the car
> b) air pipe with the same cross section, but its plugged ( with loaded
> fan ) in the middle
>
> Drag coefficients of such bodies are several times different.
> Take a hollow cylinder and hold it out of the window when driving.
> Then plug it at one end and try to hold it against the wind, with the
> open end facing the wind ...
>
> -kert

I can prove that you're over-thinking this, but you get to supply the wind 
tunnel... ;^)

To compared hollow and plugged cylinders to vehicle's frontal area and 
underhood airflow is quite an oversimplification, not to mention that the 
fan is already there to do other useful work.

Lon

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## EVDL List (Jul 27, 2007)

*Re: [EVDL] article: Mitsubishi i MiEV Sport*

Ask your self this. If air is passing through a fan mounted inside
your car somewhere and this air is moving from in your car because of
the car's motion is there a force on the fan and hence fan mount
pushing toward the rear of the car? You'd have to say there was and
this could be measured relatively easily with various simple devices.
Since there is a force on the fan toward the back of the car, there is
an opposite force on the air provided by the fan. The action is: air
pushes on fan. The reaction is: fan pushes on air. In order for the
fan to continually react to the force of the air (assume zero
acceleration along the direction of the car's motion) the fan has to
push on the car body (through the fan mount). The action: fan pushes
on car. The reaction: car pushes on fan. Since the car has to push on
the fan it has to get the energy to do so from the traction pack.

Unless the slowing down of the air through the rest of the car, the
changing of the turbulence, etc (as others pointed out) reduces the
drag to match or exceed the force required to push the loaded fan the
car will experience a decrease in efficiency. In any case, the
practicality of the situation is, as David R put it, "Why not expend
your effort on something that really IMPROVES efficiency?"

>From a Physicist's point of view the only reason is to understand how
our universe works.

-- 
David D. Nelson

http://www.austinev.org/evalbum/1328

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## EVDL List (Jul 27, 2007)

*Re: [EVDL] article: Mitsubishi i MiEV Sport*



> Victor Tikhonov wrote:
> > there is big difference between propeller-generator on the roof where
> > otherwise there is no resistance whatsoever, and propeller-generator
> > behind the grille where there is [almost] the same resistance based
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] article: Mitsubishi i MiEV Sport*

To summarize, we all agree that the fan/generator is gimmicky, but there's a 
great deal of disagreement as to whether or not it's useful or lossy. My 
inclination is to believe that because it's already there working (I assume 
to cool a radiator) and may even be spinning under 12V supply just prior to 
performing as a generator, it may be marginally useful.

Many manufacturers apply aerospace principles to underhood airflow, 
directing air past the hottest parts of the engine, ducting some to the 
brakes and venting via top or side gills, out the bottom of the engine bay, 
or even down a channel to a diffuser at the rear. Now imagine a boundary 
layer of compressed and turbulent air at the vehicle's frontal area. At 
steady state vehicle velocity without active aero and steady wind speed, the 
boundary layer of high pressure at the vehicle's nose disperses into various 
ducts or around the outside of the body at consistently measurable pressures 
and velocities. Change any variable (vehicle speed, active aero 
flaps/spoilers, wind speed/direction) and the dynamic changes all across the 
frontal area. This is the normal state of affairs for any vehicle. IIRC Cd 
(drag coefficient) is not an average measurement, but one taken with steady 
wind velocity from directly in front of the vehicle. Still, we don't hear 
about vehicle aerodynamics shifting radically simply because wind direction 
shifts a few degrees, nor does a modern vehicle become unstable at anything 
less than 180 km/h.

In other words, airflow ingress and egress remain *reasonably* consistent in 
spite of constant flux at the vehicle's front boundary layer, though we can 
safely assume that energy consumption to move the vehicle's mass through 
space is varying constantly even when vehicle speed is constant . 
Nevertheless, the variances aren't always discernable by the seat of our 
pants or at the pump (we don't say, "Gee, I paid an extra 10 cents for this 
tankful; the wind must have shifted east a few degrees."). I believe this is 
because the effect on boundary layer density and turbulence have less of a 
linear effect on overall Cd than we might imagine.

When examining the efficiency/inefficiency of addition of a fan, too many 
factors come into play to describe fully here, not least of which are fan 
size vs.dimensions of alternative air ingress, Reynolds number, Helmholtz 
resonance, and vehicle design as it relates to dispersal of increased 
pressure (and therefore thickness/turbulence of the boundary layer) at 
localized areas of the frontal area. In other words, the fan will spin, it 
will generate electricity, but it may have negligible effect upon energy 
used to maintain velocity *if airflow management prevents a significant 
enough increase in cumulative Cd to negate energy gained by the generator*.

As far as I'm concerned, all argument here is moot. Wind tunnel testing with 
a dynamometer is the only way to be sure.

Lon Hull,
Portland, OR 

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## EVDL List (Jul 27, 2007)

*Re: [EVDL] article: Mitsubishi i MiEV Sport*



> Lee Hart wrote:
> > Victor, try converting this problem to an electrical analogy. The air
> > coming in is your source of power -- the battery. The twisty path
> > through the grille, radiator, around the various parts and back out the
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] article: Mitsubishi i MiEV Sport*

There is never a free lunch. Any energy you can get from the airstream can 
only be gotten by adding additional back pressure to the air entering the 
front of the car, which increases drag. Since the generator is less than 
100% efficient, it will come at a net loss. The energy going into the fan 
blade is in addition to the loss of pushing the air through the path inside 
the front of the car, so drag goes up. If the fan doesn't add backpressure, 
then by definition, there is no drop across the blade and it doesn't turn 
either (no energy to recover), it's just dead weight.


----- Original Message ----- 
From: "Victor Tikhonov" <[email protected]>
To: "Electric Vehicle Discussion List" <[email protected]>
Sent: Tuesday, November 20, 2007 6:02 PM
Subject: Re: [EVDL] article: Mitsubishi i MiEV Sport




> > Lee Hart wrote:
> >> Victor, try converting this problem to an electrical analogy. The air
> >> coming in is your source of power -- the battery. The twisty path
> >> through the grille, radiator, around the various parts and back out the
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] article: Mitsubishi i MiEV Sport*

Why not instead of 'substituting' a resistor with a fan, eliminate the 
resistor. If you can reroute the air flow causing a loss to get a fan into 
the stream, just reroute it to eliminate the loss instead.

----- Original Message ----- 
From: "Victor Tikhonov" <[email protected]>
To: "Electric Vehicle Discussion List" <[email protected]>
Sent: Tuesday, November 20, 2007 6:02 PM
Subject: Re: [EVDL] article: Mitsubishi i MiEV Sport




> > Lee Hart wrote:
> >> Victor, try converting this problem to an electrical analogy. The air
> >> coming in is your source of power -- the battery. The twisty path
> >> through the grille, radiator, around the various parts and back out the
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] article: Mitsubishi i MiEV Sport*

hey Victor the e-vision you sent has a ribbon cable that is too short for my rear wheel drive bradley will there be any problem with a ribbon cable that is close to 20 ft in length ? also do have the parts to change the one you sent from a dash mount to in dash ? . no problem if not I just figured out how to put it in the dash rather than on the dash . you help is appreciated .
----- Original Message ----- 
From: Victor Tikhonov<mailto:[email protected]> 
To: Electric Vehicle Discussion List<mailto:[email protected]> 
Sent: Tuesday, November 20, 2007 6:02 PM
Subject: Re: [EVDL] article: Mitsubishi i MiEV Sport




> Lee Hart wrote:
> > Victor, try converting this problem to an electrical analogy. The air
> > coming in is your source of power -- the battery. The twisty path
> > through the grille, radiator, around the various parts and back out the
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] article: Mitsubishi i MiEV Sport*

Marty,

What Victor is saying is suppose that by adding the fan you don't
change the back pressure of the air entering the grill. Since the air
which has passed through the fan will be moving slower then it will
have less drag against other parts of the car as it passes through. If
this decrease in drag exactly compensates for the fan being in the
airstream then you have successfully captured some energy which would
have been lost any way and turned it into some other useful purpose.
This is what his two 5W "resistor wires" analogy was trying to say.

David



> Marty Hewes <[email protected]> wrote:
> > There is never a free lunch. Any energy you can get from the airstream can
> > only be gotten by adding additional back pressure to the air entering the
> > front of the car, which increases drag. Since the generator is less than
> ...


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