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Old 10-19-2007, 02:18 PM   #1
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Ordered Airtabs today!

I ordered my set of black airtabs today http://www.airtab.com/

Im planning to install them as seen here to start:

http://www.airtab.com/Images/gallery/Paulst/2.JPG

http://www.airtab.com/Images/gallery/Paulst/3.JPG

Exerpt of his experience with these....
We've increased our fuel mileage by about 9mpg on a full load, from 11-12 MPG to 20-21 mpg. We pull fast, heavy and long most of the time. With the Airtabs as installed, wind noise is reduced and the trailer stability is phenomenal. Evidence the Airtabs are working is most noted in rainy weather, in cross winds and meeting larger semi-trailers on two lane highways. The unloaded truck will get 25 mpg but with Airtabs fitted as per our pictures, we are getting 32-34 mpg. The Airtabs on the top rear of the cab eliminate 80% of the bugs on the front of the trailer. If you watch the bugs, they tell you where the air is going. The Airtabs on the hood of the truck keeps the windshield cleaner and reduces wind noise with the windows open.

There are 67 Airtabs on the truck and 95 on the trailer. A small investment for this kind of fuel economy and stability, not to mention the extra horsepower. It seems with Airtabs we aren't bucking wind, but directing it. This outfit gets a lot of curious looks but these results prove the Airtabs usefulness. The savings on a 1000 mile trip fully loaded would be approximately 35 gallons of fuel. At $3.00 per gallon, that's $105.


Ill post back installation pics and eventually MPG data once available for anyone interested in how these do. This could be a good front wheel skirt replacement option for just about any car possibly and maybe a front windshield deflector? For me, Im hoping it does that as well as also help around the back of the cab and bed maybe... anyway - I have them coming, will see how they do.

-Jeff
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Old 10-19-2007, 02:28 PM   #2
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He Jeff, when you get them... Can you possible take some detailed pictures of them (preferably with a ruler or some sort of scale for dimensions) before they are installed?

I'd like to model them and do some CFD on their specific design (or as close as I can get) for application on a human powered vehicle... It'll probably be useful to others too. I have to do research anyway, so it seems like a good idea to start with a commercial product


Out of curiosity -- how did that gentleman find the separation points on his truck?
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Old 10-19-2007, 02:32 PM   #3
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Separation points? meaning how far apart to space them is what I think your asking. If so, Im not sure how he did it, but the airtabs themselves come with 2 spacing templates, fill them both up, then move the first template beyond the 2nd (becoming the 3rd) and so on - like leapfrog. I will be using this method as closely as possible. I expect something to hinder complete compliance, but it will be close.

I will be glad to get some close up pictures with a ruler. It will be late next week at the earliest.
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Old 10-19-2007, 02:46 PM   #4
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Quote:
Originally Posted by jeffreymccoy View Post
Separation points?
So air tabs add energy to the boundary layer much like the tabs on airplane wings or dimples on a golf ball do (in fact, exactly like they do). Separation is a fluid (in this case air) interaction where the flow that is attached to the skin of the vehicle (boundary layer) just lets go. It was discovered that if you give this layer a little bit of energy slightly BEFORE this separation occurs - you effectively move the separation point further back. In the case of a plane wing - you create more lift and thus lower the stall speed.

The easiest way to see what I'm talking about....


Notice how the red dye just lets go

Mitsubishi posted a paper on this - showing a reduction in cD by 6 points (.006) when they placed their vortex generators (basically, air tabs) 100mm in front of the separation point.

The trick is, and the focus of research, is how tall to make them. Optimal height is equal to the height of the boundary layer. But, the height of the layer increases with velocity. Make them too tall, and all you do is create turbulence -- make them too short, and they don't add much/enough energy to be effective :/

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I will be glad to get some close up pictures with a ruler. It will be late next week at the earliest.
Thanks Much appreciated I guess it would be beneficial to mention that a top, side and front is the most helpful
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Old 10-19-2007, 04:29 PM   #5
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FWIW I am running AirTabs on my hard top and I haven't noticed any quantifiable increase on FE. YMMV

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Old 10-19-2007, 04:40 PM   #6
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9mpg improvement just from airtabs sounds like a stretch to me. I've spent a lot of time on the road towing a lot of equipment, box trailers, backhoes, etc. There just wasn't that much difference. Pulling the backhoe mileage went down only 2-3mpg.

That said it doesn't mean that I don't want to try them. I'm seriously considering getting some to try on my saturn. I just don't know if there the right size for my application.
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Old 10-19-2007, 04:43 PM   #7
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Quote:
Originally Posted by Red View Post
FWIW I am running AirTabs on my hard top and I haven't noticed any quantifiable increase on FE. YMMV

Red, my guess would be that the airflow has not reattached to the roof before it hits the air tab. I've looked at the jeeps before and there quite possibly one of the most unaerodynamic vehicles out there. I imagine that they would work better on the sides of the jeep. D
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Old 10-19-2007, 05:42 PM   #8
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I'd be interested to see a documented increase in MPG related to installing this product. To me it seems like a miracle product for anything other than sustained driving at a highways speed, but I'm quite the skeptic.
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Old 10-19-2007, 05:58 PM   #9
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Quote:
Originally Posted by lovemysan View Post
Red, my guess would be that the airflow has not reattached to the roof before it hits the air tab. I've looked at the jeeps before and there quite possibly one of the most unaerodynamic vehicles out there. I imagine that they would work better on the sides of the jeep. D
And mar a perfectly vertical surface? Always worth a shot
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Old 10-19-2007, 06:45 PM   #10
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Quote:
Originally Posted by Danronian View Post
I'd be interested to see a documented increase in MPG related to installing this product. To me it seems like a miracle product for anything other than sustained driving at a highways speed, but I'm quite the skeptic.
Ask and you shall receive Okay, so it's not mpg increase - it's decrease in cD. It's also not for this specific product, it's for Mitsubishi's design (which is a basic delta wing foil).

Let me know if that link is dead
http://www.mitsubishi-motors.com/cor...004/16E_03.pdf

The juicy images

Left with - Right without

^^ Notice the Blue low pressure zone on the windscreen is larger without the VG's.
Left with - Right without

Despite the lower pressure just behind the VG's (deeper blues), Mitsubishi got a decrease in cD - notice how the larger green area behind the VG's compared to without.

Here's Mitsu's Design


Here's what you might find on a plane


I too was skeptical until reading that paper -- I had thought the velocities needed to have an effect needed to be much higher...

Oh, I also forgot to mention -- you can also find VG's under aircraft flaps - for increased stability at lower speeds
http://www.nasa.gov/centers/langley/.../Micro-VG.html

I feel it also necessary to state that this is in no way an endorsement for the Airtab product. Flow control does work, intelligently designed - anyone can make something look cool - but that doesn't mean it works. Claiming to lower mpg is ballsy in my opinion - the much safer (and likely more accurate) claim is that it can reduce cD when properly installed.
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