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Old 03-09-2008, 10:23 AM   #1
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Air tab mounting

I bought 40 air tabs to put on my car. I know that they did not do much for a Prius and hurt an Insight's mileage. I would not expect much. I am trying to decide on the best locations. I am thinking back of roof and back of trunk. Then some in front of the front wheel wells. Then maybe some under the front bumper and some under the rear bumper.

I have fooled around with vortex generators on an airplane wing and they always involved a drag penalty for me. The fellow that claimed such a huge improvement on his Dodge truck put them near the leading edges. That might correlate with tripping the boundary layer on a round object but it is not what is generally recommended.

Any thoughts on this. These cost about as much as three tanks of gas so I don't expect payback just some interesting times.
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Old 03-10-2008, 09:58 AM   #2
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40 air tabs?! That's gonna look pretty cool. At least to aero geeks
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Old 03-10-2008, 10:20 AM   #3
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All I would say is don't put them too far back, leave some surface for the flow to attach to behind them. Also would be dubious about putting any on top of the trunk, the lip of that is probably intended to separate flow cleanly.
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Old 03-10-2008, 11:07 AM   #4
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Are you talking about putting them on a Saturn? I would do the flour trick to see where the air is separating at a desired speed and go from there. It is very easy to decide on a SUV...across the roofline about 6" before the edge and down each side in the rear.

I would concentrate on your roofline and rear pillar areas first...I would ignore the front wheelwells for now...maybe put some near the rear wheelwells if you have enuff.
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Old 03-11-2008, 04:16 AM   #5
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What I did is attach the airtabs with metal foil tape, which holds them well enough for testing and comes off easily. On a car that's not a simple bluff rear end shape this would be even more appropriate. It's quite possible to accidentally put them in some configuration that hurts instead of helping. So test them out first before you permanently attach them.

Probably the rear roof and sides are your best bet, I think.

Had good results on my Honda Fit.

http://s89686473.onlinehome.us/airtabs-test.html
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Old 03-11-2008, 05:47 AM   #6
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Thanks for sharing the article.
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Old 03-11-2008, 06:53 AM   #7
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What color airtabs did you get? . . . and let us know if you are selling any that are left over that you don't need or want.
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Old 03-12-2008, 05:17 PM   #8
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Here are some pictures. Water was beading up on the sides of the roof so I mounted them forward on the sides. After two days I think they are hurting me. I have not done any coast down tests. They are just mounted with black electrical tape. I will try some on the sides soon.


I have 20 black and 20 white. I also have a little dolphin motor home. That is the logical place for these. The roof on the Saturn is pretty good already.



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Old 03-12-2008, 05:48 PM   #9
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To my eye, it looks like you might be using too many, when you've got fairly good flow already, you only want to make suggestions to it, not knock it down on the floor and kick it around until it will confess to anything and do whatever you want.

Seeing the shape of the roof it's on also, it's possible that the point where separation would have been occuring was a lot further back than typical on a sedan. A useful thing to know is that around legal highway speeds on a typical size vehicle, airflow will deflect between 8 and 12 degrees off an edge, and will attach to about 1/2 an inch or so of surface. So you can cut yourself a 172 degree angle, with 1/2 inch arms, and go testing curves with it... if the curve touches anything other than the points of the arms, the inside of them, that's about where it's probably separating... The scale of the vortices generated by turbulators should be approximately the same as the length of the turbulation device, so to allow a full vortex to form and touch back on the surface behind it, the turbulators should be about one to two lengths ahead of the separation point. Too many lengths forward and you're making unnecessary surface suction drag.

This is just simplistically explained rule of thumb stuff though for narrow ranges of situations though, so don't go designing passenger jets with it
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Old 03-12-2008, 07:15 PM   #10
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I bet if you threw flour on the roof and then a quick 55mph test you would find separation about 8" from the rear glass...just a guess of course. The arrangement (not so much the closeness but the curved shape) you have now might actually be sending vortex(s) tumbling into each other. I don't think that 9 are way too many but maybe 7 would be plenty on such a small aero surface.

I would work on the Green Saturn in your garage...might be easier to see FE results since it has more room to improve.
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OME 2.25" Lift w/ Toyo Open Country HTs 235/75/16s
ASFIR Alum Eng/Tranny/Transfercase/Fuel Skids
2002 Air Box Mod...Air Tabs (5) on Roof...(3)each behind rear windows
Partial Grill Block with Custom Air Scoop and 3" Open Catback Exhaust
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