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Old 05-17-2011, 01:51 PM   #11 (permalink)
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New to this. Do you totally want to block the air under the car? Don't your want the high pressure air under the car to meet the low pressure air in the rear?

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Old 05-17-2011, 03:07 PM   #12 (permalink)
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Quote:
Originally Posted by minAirForce View Post
New to this. Do you totally want to block the air under the car? Don't your want the high pressure air under the car to meet the low pressure air in the rear?
If you have a smooth belly pan covering up the under-body, you don't need
a large air dam. (Just some shorts ones for the wheels).

But normally, the underbodies of cars have all kinds of non-aerodynamic
junk hanging down in the air-flow..

So, sometimes, there is a need to keep the air flow off that junk..

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Old 05-17-2011, 04:07 PM   #13 (permalink)
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I don't see how the parts on the sides can possibly reduce drag!

You're "shielding the tires" but you're doing it with flat sheets. The Cd of a flat plate is 1.0. You're also redirecting all the sideways flowing air from the bumper straight out to the sides. Hold a flat knife under a faucet-- it's just like that.
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Old 05-17-2011, 04:25 PM   #14 (permalink)
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Okay, your right! They don't work.. Guys use air dams because they look Cool..



And, that's how they get the hot chicks!!




And, I'm never wrong about these things!!
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Old 05-17-2011, 05:46 PM   #15 (permalink)
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Neither of those air dams extends to the side of the vehicle where they act as air brakes, which is what I was talking about.
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Old 05-17-2011, 08:41 PM   #16 (permalink)
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I recently put a lawn edging type air dam on a 2003 Focus that doesn't have that stock dam back from the front edge. I found that it tends to hit when entering driveways and will be an issue in winter for sure.

The poly lawn edging is tuff stuff and is ideal for an air dam....and putting it back on that OEM dam would be ideal in that you wouldn't have the scraping issue. For stiffness you can insert a metal rod into the hollow part at the bottom....and shape it how you want.

Home Depot 20 ' ...for $7.


I have noticed a lot of women crowding around and people thinking I'm driving for NASCAR though.
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Old 06-10-2011, 03:11 PM   #17 (permalink)
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Your dam is so much rearwards under the front end that I have doubts it will improve something. The air can flow only sidewards, with difficulty... I would focus first on this :http: //imageshack.us/photo/my-images/189/focusonthis.jpg/
I have the same problem with my Astra G

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Old 06-10-2011, 06:12 PM   #18 (permalink)
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Im thinking that due to its location, it might not be a bad idea to have it angled down towards the meeting point of the tires/asphalt.
this would have the benefit of redirecting the air away from the under body, but not acting as a wind plow.

sort of like this:
---\
___|
-/
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Old 06-11-2011, 07:01 AM   #19 (permalink)
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i have a few remarks. you may not want the dam to reach to cover the whole width of your tires as you'll increase your side wake. i flat plate will have a very broad wake so even if it's smaller than the wdith of the tire behind it it will still send the air around in a clean path,


second you may not want the central dam to be so low, nascar cars have a front ends that coupled with a full airdam will send all oncomming air over the car, where you have the dam it'll send the air around the car.

this graph althoug generic and incomplete sugests that an airdam can be to low and that beyond a certain point, only downforce will decrease but drag will increase again.

(Katz, "Race Car Aerodynamics", p.208)
reasearch on the ople calibra found that raising the center of the airdam also reduced drag (A)

sketch (b) however sugests that the area in front of the tires can should be as low as possible although there's a point where the improvements are minimal so ground clearance is likely more important to keep them in one piece

i don't want to come across negative or as if i know it all, And by all means test what you have because it might just work, but it seems to me that you're puttin a lot of effor into something that might be a dissapointment. and if you have that much plastic you may as well start a modest undertray , but again, just my thoughts...
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Old 06-11-2011, 10:16 AM   #20 (permalink)
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there is something off on your first graph, majorly off
the first cylinder shows a CD of 1.2, the teardrop and the 2nd cyl shows the same, but then the last cyl shows a CD of 0.6

looking at the "wake" pattern flowing behind each object shows no discernible reason for the #1 & #2 cyl object and teardrop to have the same CD, while cyl #3 has a less than CD and a smaller wake behind cyl #3 than behind #1 & #2.

re @ OP
trial and error are going to allow you to find the best combination, but I do agree with what others have posted about it being too far from the actual to make much of a difference, if any, or even the opposite effect.

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