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Old 11-17-2008, 02:24 PM   #51 (permalink)
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I think the force of drag is (1/2)(Cd)(frontal cross-sectional Area)(fluid Density)(Velocity^2), so Cd is separate from the area in the equation.

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Old 11-17-2008, 02:48 PM   #52 (permalink)
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except when you compare overall drag to complete frontal area of the vehicle, you get a true indication of exactly how aero it is.

You could potentially make something shaped like this
|
|
|
Have a Cd of .40....

Or you could have a shape like this
\
.|
..\
With a .46, but the second shape is still more aerodynamic, when you compare the Cd to the overall frontal area

That's what I meant when I said that.
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Old 11-17-2008, 09:59 PM   #53 (permalink)
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Quote:
Originally Posted by Christ View Post
except when you compare overall drag to complete frontal area of the vehicle, you get a true indication of exactly how aero it is.
But Cd is not the overall drag, it's purely a function of shape. A toy model of your van will still have the same Cd. To get total drag, you multiply the Cd by the cross-section area.
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Old 11-17-2008, 10:20 PM   #54 (permalink)
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simply put its about the amount of air a car needs to push aside and how smoothly is can do so.

a brick is less aerodynamic than an ev1 but it still has less overall drag as its smaller.
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Old 11-17-2008, 11:12 PM   #55 (permalink)
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Quote:
Originally Posted by jamesqf View Post
But Cd is not the overall drag, it's purely a function of shape. A toy model of your van will still have the same Cd. To get total drag, you multiply the Cd by the cross-section area.
SO, while I mistyped exactly what I was trying to say, you clearly understood it enough to argue with it.. essentially making less sense.

I'm well aware that Cd is not overall drag, and I'm also aware that CdA is the overall drag figure.

What you've stated here that is not entirely true is that a toy model of a vehicle will have the came Cd as the full-sized vehicle. It will not, even when built to scale, as a direct result of manufacturing inefficiencies.

But I digress, we're taking this off topic.
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Old 11-18-2008, 01:16 AM   #56 (permalink)
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Originally Posted by metroschultz View Post
Hey Phil,
I'm thinking take my Metro/Swift engine /trans and put in a stripped out Probe rolling chassis.

I would play the devil getting the weight out (and for the suspension I would not be able to remove weight), but what about the possabilities for aero on something like that?
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NOOOOOOOO!!!!!!!! Would be very unwise. The Probe weighs over 1000 pounds more. And for the suspension, Metro parts probably weigh half as much.

Makes much more sense to leave the Metro engine in the Metro chassis and do aero mods, such as basjoos and others have done.
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Old 11-18-2008, 01:18 AM   #57 (permalink)
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Imagine this car with all the wings, mirrors, etc shaved off, and front and rear wheel skirts.

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Old 11-18-2008, 01:34 AM   #58 (permalink)
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Metroschultz - think of putting 1,000 lbs of bricks in your metro... or 7 average guys. That's what it would feel like still trying to drive that thing. Noone said you had to sacrifice power or speed to get gas mileage. It helps though.

What you'll probably end up doing, is getting further into the pedal trying to accelerate safely (without impeding traffic), and end up getting worse mileage.

Unless you can take about 800 lbs off that car, don't bother.
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Old 11-18-2008, 10:06 AM   #59 (permalink)
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Quote:
Originally Posted by Christ View Post
The Silhouette is not that bad.. except, again, the hatchback rear config... It could also benefit from a Kammback or boattail with some pretty extreme benefits...

When GM says the Cd is .30, they're not giving you the proper figure... what's the actual frontal area of your nearly 7 foot tall van? When you figure that in, you're not getting that great of a deal.

Swapping a Metro/Swift 3 cylinder into that van could be relatively easy though.
yes i know the difference between cd and cda

so the van is a whopping 5'6" tall, 5'7" wide at its widest (not including mirrors,still counting airspace under car) actual frontal area is pretty close to 30sq ft.

depending on your needs, it is a good shape. do you want to bring 6 friends in your metro, depends on your friends i guess.
i can fit full sheets of plywood inside the van, compaired to a pickup, or stacking them on the roof of a car. aero is going to be much better.
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Old 11-18-2008, 01:37 PM   #60 (permalink)
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Nissan 350z is the closest I see regularly


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