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Old 08-23-2010, 05:47 AM   #41 (permalink)
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Sorry for raising the dead.

I guess I am still confused after reading this entire thread as to why a vortex generator would not help on an xA. The Airtabs are designed for trucks obviously and have a lot of testimonials and "independent" test results confirming that they work. The size of them when placed on a car seem to appear to my "untrained eye" that they would create more drag than necessary to be inefficient.

I beg to question, if the Airtab design was scaled down to work on a car such as my xA would it give us a noticeable result?

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Old 08-23-2010, 07:25 AM   #42 (permalink)
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Quote:
Originally Posted by toxshox View Post
Sorry for raising the dead.
There are more zombies out here

Quote:
I beg to question, if the Airtab design was scaled down to work on a car such as my xA would it give us a noticeable result?
I see no reason why they wouldn't work when scaled down.
Work as in "creating vortices" that is, wether they actively reduce your total drag is something else again.

If you look at ZZ-tape or dimple tape for gliders, these are only 0.4 to 0.8mm thick, that's 1/6 to 1/3 of an inch, and they work.

Airtabs are obviously truck-sized, though MetroMPG has shown them to be smoothing out the airflow on smaller cars - though no verifiable overall drag reduction / MPG increase was noted.
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Old 08-23-2010, 08:28 AM   #43 (permalink)
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Cool thanks for the reply. I'll read up on the ZZ tape successes and probably do that next as scaling down an Airtab design looks to be a bit more difficult.
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Old 08-28-2011, 04:02 PM   #44 (permalink)
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Vortex Generators size angle

New guy first post, long time tinker/techie.
Seems like the placement of the VGs and size have a affect. Search.. Vortex Generators: Band-Aids or Magic?
This is where driving around with wool strings come into play to find where the transition from laminar flow and turbulent flow happens (based on the speed we need to improve mpg..remeber the air characteristics changes with speed). Based on were the transition happens, we need to make a few needle thin poles (as not to disturb airflow) with sowing thread sized strings to try to find the hight of the boundary layer hight. I guess a roof monted camera can come into play here since you'll need magnification from the next car to see the results. knowing the hight of the poles we can now know the hight of the boundary layer and subtract 20% to get 80% of which the vg hight will be. The angle of attac of the vg seems like it depends on how fine the VGs will be. Think of the vortex as springs trailing behind the VGs. 45 degrees fine packed coils, 10 degrees stretched spring. Think this will depend on the speed of the car. low speed on the car the finer the vortex need be, the faster the speed the more loose the vortex need be. Then the lenth of the VGs. How big the vortex will be. How much ground you wanto cover across the sides of the car. But speed also factors here. I might be wrong. I'm going to try to test this.
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Old 08-29-2011, 01:53 AM   #45 (permalink)
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Quote:
Originally Posted by toxshox View Post
Sorry for raising the dead.

I beg to question, if the Airtab design was scaled down to work on a car such as my xA would it give us a noticeable result?
I agree that the air tabs are generally too big for a small car and will do more harm than good. Again, the purpose of vortex generators is to promote attached flow on a slope that is too steep, such as a slope greater than 12 degrees. Most cars with a standard trunk have a rear window that is too steep to maintain attached flow and therefore could benefit from properly placed and selected vortex generators.

The XA has a profile that is ideal from the windscreen back since it is a hatchback with a gradual down slope. Then it just comes to an end at the back window. This is not a good application for VG's. You already have attached flow to the back of the car and they can't improve the flow over an extreme transition such as your roof line coming to an end.
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Old 08-29-2011, 05:55 AM   #46 (permalink)
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aren't vortices essentially drag? And used for airplane control surfaces so they stay effective? And don't they reduce the top speed when installed in an airplane (because they add drag instead of removing it?)

Is there ANY documented case where vortex generators were installed on a car in a wind tunnel and they reduced overall drag?

In other words, is installing vortex generators on your car much different than putting jet fuel in your tank and expecting your car to fly?
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Old 08-29-2011, 10:46 AM   #47 (permalink)
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A question about VG placement -

Most of the VGs on cars are placed on the roof, in front of or close to the rear edge before the window. I recall seeing a wind tunnel graphic here that showed recommended VG placement past the point where the body begins to taper - not before it.

Aren't you trying to hold the air down onto the tapering area (where it wants to separate)? Seems that placing them up on the roof would stop the air from following the taper and make the wake larger. Does Mitsu use them on the Evo just to make the wing more effective?

Wouldn't placing them on the front edge of the hatch/window of a hatchback (not the roof) be where they would do the most good? Doesn't seem like they would work well on a sedan.
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Old 11-11-2011, 05:39 PM   #48 (permalink)
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dredging up the dead again.

From the first time I saw the airtabs and saw their effect on tractor/trailer rigs, I was intrigued. Then I saw people trying to use them on small cars, and also saw what others have mentioned that they do appear to smooth the airflow but do not appear to contribute significantly to MPG.

What is the consensus on using them on a full-size truck such as mine?

When I first bought my truck, I considered adding them along the roof line, down the side of the cab where it sticks up above the bed line, and possibly again near the rear corners of the bed. Now that I have a tonneau, that consideration has extended to include along the back edge of the tonneau.

That's a lot of airtabs (@ ~$2.50/ea) to buy and stick on just to "test".
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Old 11-11-2011, 05:43 PM   #49 (permalink)
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I don't think anyone has produced any quality evidence that they actually help fuel economy.

I'd focus your time & $$$ on things that we know to work.
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Old 11-11-2011, 06:12 PM   #50 (permalink)
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Coming from you, I'll take that as golden.

That's still what I was figuring, and the main reason I've not bought any.

I am concentrating efforts elsewhere, but figured hey, if they can give me something and only have to be stuck on, that wouldn't take any time at all (compared to dam & pan construction time, which are my 2 big ticket aero items after the tonneau).

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