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Old 07-30-2014, 04:18 PM   #11 (permalink)
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The volt and cruze have similar stance, yet the volt has a much lower air dam. There is no way gm would put to big an air dam on its star hybrid. I agree the height of the air dam likely more a matter of practicality than anything

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Old 07-30-2014, 05:53 PM   #12 (permalink)
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go as low

Quote:
Originally Posted by Vman455 View Post
I don't buy the whole "an airdam only needs to go as low as the lowest component on the underbody," when, in every Bonneville class that allows an airdam, you'll see cars with that thing extended all the way to the ground--because the benefit comes not from "shielding" something sticking into the airflow, but from disallowing as much air to get under the car in the first place, instead sending it around the streamlined upper body (which is why even cars like the hydrogen Fusion tout a benefit from a smooth underbody and a very low airdam). So, I think if you're going to go with an airdam, make it as low as practically possible. The Volt's airdam used to be much lower, in fact, until enough owners complained of scraping that GM raised it.
*In Feysal Ahmed's masters thesis research on a RAM pickup he recommends the airdam go no lower than existing components.
*In a racing application the airdam can go to 3" of ground clearance,picking up less than 1% drag reduction,and less than 1/2% mpg.(1974 CAR and DRIVER 'Crisis Fighter Pinto').
*bondo tried a lower dam,then had to reverse himself after losing fuel economy.
*With the VW do Brasil 1600 X,the airdam creates a drag increase when it's length extends beyond 80mm .
*On VW's Volkswagen 1600 notchback wind tunnel calibration car,attachment of a front airdam created a 11.7% drag increase.
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Factoring SAE approach angle guidelines,without vigilant driving techniques,the low airdam is gonna end up on someone's driveway ramp,just like Trans Am Firebirds,Corvettes,and New Beetles.
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*Active airdams (front and rear) would be a solution for some,although best when combined with active suspension.
*With $200,000 and the A-2 tunnel you could figure it all out.
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Old 07-30-2014, 09:03 PM   #13 (permalink)
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Quote:
Originally Posted by aerohead View Post
*On VW's Volkswagen 1600 notchback wind tunnel calibration car,attachment of a front airdam created a 11.7% drag increase.
Air cooled VW's and RR cars in general, already have a near perfectly smooth underside.
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Old 07-30-2014, 09:24 PM   #14 (permalink)
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hmmm..........

first off, air dam- vertical aerodynamic fairing in the form of a skirt (for the purposes of this thread) or flap for the purpose of forcing air below protrusions as to lower aerodynamic drag.

spoiler/splitter, creates downforce, and/or splits the air in a deliberate way to control lift otherwise caused by the body of the car and aerodynamic forces.

I digress

So, I went back to the chevy dealership today, and gathered some data for consideration/discussion.

I use the cruze/volt because they are the successor to my car, the same size, and look like they are pretty close to the same in relationships to dimensions important to this project.

For the data... well, my phone deleted it, so let's go from memory. figures are pretty close.

the malibu, impala, and cruze were all around 7-7.5" for ride height (measured behind the front wheel), the volt was about 5.75". the malibu and cruze were the only two with stepped air dams, so I think this is styling/practicality, not aerodynamics. all the air dams except the volt's had stuff hanging down slightly below them, and height from the ground varied (despite the constant ride height), so this seemed to be dictated by the lowest hanging object* erring on the side of clearance slightly over efficiency.

my car sits at 9 inches ride height with 9.5 at the front bumper cover.

*the lowest hanging object argument. the volt varied here, it had an air dam that went from 3.75 to 4 inches from the ground in the center, so I got to looking at the cars, and noticed something, then I looked at the camaro and it shared this characteristic. the thing these two cars shared that the others didn't (didn't look at cadillacs, here, as they are more about performance than economy, try squeezing 45mpg from a twin turbocharged ~450HP v6) is not only did nothing hang down below the air dam, but they had a chine/splitter (what exactly it is could be debated, but that's not the point) allow me to explain. the attached picture shows a cross section of the bumpers with the deflector. the deflector is about the same distance from the front of the car, but on the volt and camaro, there is a jut out to split the air just above the lower air dam. this increases cooling (camaro) and lessens how much air hits the air dam, possibly limiting the increase in drag experienced by users on this forum, if not eliminating it. this splitter/spoiler goes the full width of the radiator opening then tapers off.



front tire spats, they all had them except the volt, and forgot to look at the camaro, but they were between 1.5 (cruze) and 2.5 (impala) inches tall. they all met with the air dam, likely to eliminate air spillage mentioned in the stickied first gen prius thread. these will likely be integrated into my air dam.
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Old 07-31-2014, 02:37 PM   #15 (permalink)
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Quote:
Originally Posted by oldtamiyaphile
Air cooled VW's and RR cars in general, already have a near perfectly smooth underside.


If only that were true. Here's a bus example. Suprisingly, only the area between the wheelwells is flat. The bellypan panels were optioned for vehicles with the sunroof, otherwise it's an open ladder frame. The front gets an access panel that isn't particularly smooth.

From the rear torsion bar housing back, the Beetle is the same. Even my Superbeetle has a crossmember about an inch deep that runs laterally at the front of the pan. That will trip the air into turbulence all across the 'smooth' part.

2007 ion2 -- I'd put spoilers at the back and splitter/diverter at the front. Those 'spoilers' from the 70s-80s were basically an air dam with the part in front of the front tires missing.

And I think the purpose of the splitter/diverter is to lower the stagnation point.
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Old 07-31-2014, 05:36 PM   #16 (permalink)
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Why would you showcase a Bus? The Bugs have much, much flatter bellys.
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Old 08-01-2014, 11:45 AM   #17 (permalink)
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Because I didn't have a picture of a Beetle in a rotisserie?

Quote:
Originally Posted by myself
From the rear torsion bar housing back, the Beetle is the same. Even my Superbeetle has a crossmember about an inch deep that runs laterally at the front of the pan. That will trip the air into turbulence all across the 'smooth' part.
The [botom half of the] engine compartment is a mess, and those pockets behind the rear wheelwells are probably like blowing across the top of an empty jug.
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Old 08-01-2014, 01:04 PM   #18 (permalink)
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Old 08-01-2014, 05:10 PM   #19 (permalink)
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2013 Malibu aero

From media.gm.com's "2013 CHEVROLET MALIBU AERODYNAMICS" graphic,they show 5 counts saved with the airdam,and 10 counts saved with the front tire deflectors,for a total Delta-Cd 0.015 for both mods.
Shame we don't have access to this data for all models.
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Old 08-01-2014, 08:53 PM   #20 (permalink)
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Frankly, it looks about the same to me. A hot mess from the torsion bar on back.

Quote:
The point of this thread is to discuss the next step for me, front deflector, tire spats, smooth wheels, and rear diffuser.
Check out this 'vette at Bonneville. Looked at one way, the outer half of the rear wheel spat is missing, which might bleed air out of the wheelwell. Another, and it looks like a massive end cap on the difusser to prevent the smooth air mixing with turbulence from the wheelwell. The pic doesn't show it but they curved outward for the width of the tire tread.


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