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Old 07-22-2008, 04:13 PM   #11
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you could go to wal-mart and get the 3M heavy duty outdoor double sided tape for $3.60 (or there abouts) which is a 5 foot roll.
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Old 07-22-2008, 06:10 PM   #12
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you could go to wal-mart and get the 3M heavy duty outdoor double sided tape for $3.60 (or there abouts) which is a 5 foot roll.
While you're in walmart for the tape, pick up the T-section tent pegs out of the camping section, cut the first 4 inches off a couple of packs of those and accidentally forget to order the air tabs.
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Old 07-22-2008, 09:18 PM   #13
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The air tabs borrow heavily from the profile of the NACA duct:
http://en.wikipedia.org/wiki/NACA_duct

Here are some detailed profiles:
http://www.recumbents.com/wisil/nacaduct/naca-duct.htm

Now get yourself some sheets of pvc foam (or equivalent), double faced tape and an Xacto knife (or equivalent) and experiment. Note that the edges of the duct are sharp to precipitate flow separation and create the vortex.

An aero engineer's perspective on air tabs and vortex generators:

1. Vortex generators on aircraft are not 'shark fins'. Those are marketing gimics. VG are generally rectangular. 'Shark fins' act like delta wings which are designed to produce lift. You don't want lift. You want vortices. Hence, you want a very low aspect ratio wing (a rectangle slightly longer than it is high) angled at about 20 degrees to the prevailing wind.

2. [Big] Aircraft generally don't use VG to reduce drag. They use them to maintain controllability by preventing separation in front of control surfaces. You see VG in front of ailerons. You don't see them in front of flaps.

3. Of course, for every rule there is an exception. Some Boeing 737s have shark fin VG to try to reduce the body drag caused by the very short tail cone. But on an aircraft 12 feet in diameter, there may be six VGs. Not every four inches. And this was established on very big, very expensive wind tunnels.

4. Yes gliders are using very small vortex generator strips (mini-air tabs?) to reduce drag. But this may only work on gliders because of the obsessive care to the finish. Aircraft (and cars) that have to work for a living get dirty. And they drive through air that has been driven through by the hundred cars in front of them. The calm air that provides laminar flow probably doesn't exist during most commutes.

5. Vortex generators that stick above the surface add drag. They must be used judiciously. They are only valuable if they reduce more drag than they create. The car that is fuzzy with little shark fin VG has probably only succeeded in increasing its apparent volume. Yeah, yeah, yeah. Sharks have toothlike denticles that improve their movement through the water. If your car is moving through the water, you might want to contact your insurance company. Sharks have had 1/2 billion years to get it right. I don't have that much time.

So, VG produce drag and sometimes provide a net drag reduction. They need to be applied to a specific area to solve a specific problem. And a few being good does not equal more being better.

And yes, I do have some places on my cars where I would like to try them.
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Old 07-23-2008, 08:49 AM   #14
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Why are people comparing them to aircraft and not the Mitsubishi Lancer?

If they're stuck on with adhesive, I recommend you do this: get a heat gun. Hold the tape so that the sticky side shines (reflects light). Heat the adhesive for a few seconds until it looks tacky (the shiny part will start to sweat). Press down on your car and hold for about 15 seconds.

That's how we install things like satellite radio antennas and they never come off, even in a car wash.
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Old 07-23-2008, 10:17 AM   #15
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Just adding that the Vortekz come with double sided 3m adhesive pads and are guaranteed for 3 years...if they fall off they will send you a pack of 5 replacements...also helped in my decision making
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Old 07-23-2008, 10:22 AM   #16
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Quote:
Originally Posted by lowbridescape View Post
1. Vortex generators on aircraft are not 'shark fins'. Those are marketing gimics. VG are generally rectangular. 'Shark fins' act like delta wings which are designed to produce lift. You don't want lift. You want vortices. Hence, you want a very low aspect ratio wing (a rectangle slightly longer than it is high) angled at about 20 degrees to the prevailing wind.
So, ummm delta wings make low speed lift at high angles of attack how? Oh yes, by making a humungous vortex.
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Old 07-23-2008, 10:57 AM   #17
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Just adding that the Vortekz come with double sided 3m adhesive pads and are guaranteed for 3 years...if they fall off they will send you a pack of 5 replacements...also helped in my decision making
And those little 3M pads hold so well that you can grab any fin between 2 fingers and literally shake the entire car.

My friend that has Vortekz VGs on his A6 Avant has already gone though a car wash with them...he didn't loose any.
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Old 07-23-2008, 04:11 PM   #18
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Why are people comparing them to aircraft and not the Mitsubishi Lancer?
Another thing, from what I recall (correct me if im wrong) doesn't the Evo have the "shark fins" straight into the wind and not angled? (like the "Vortekz" people say, 15 degrees into the wind)...
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Old 07-23-2008, 08:30 PM   #19
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Why are people comparing them to aircraft and not the Mitsubishi Lancer?
'cuz the Lancer is a statistical sample of one, while aircraft have been using VGs for decades. Mitsubishi (formerly a very successful aircraft company) found a VG installation that worked for the Lancer's roofline. But VGs are application specific. If you own a Lancer, putting the same VG installation on should give you the same results. If you don't have a Lancer, your results may vary. How do you learn more? Look at other applications.

Quote:
So, ummm delta wings make low speed lift at high angles of attack how? Oh yes, by making a humungous vortex.
Delta wings make vortices to produce lift at high alphas. That doesn't mean that they are the most efficient vortex generator shape. Their application also relates to controllability (a big issue in airplanes), structural efficiency, supersonic drag, etc. Very low aspect ratio wings (rectangles with AR approaching one (= square)) have been proposed depending almost entirely on vortex generation for lift. They've even been test flown. None has ever achieved production or commercial success because they don't make good airplanes. But they do make good vortex generators.

Another thing I noticed about the commercial VG is that they are smooth and rounded. If vortices are what you want, they should be sharp and angular. You want the flow to separate cleanly at an edge. (Note description of NACA inlet referenced in previous post).

Don't forget the marketing aspects of these things too. Make little triangular VGs, you can call them "Shark Fins". Make more efficient rectangular VGs, and you can call them "Perch Fins" or "Bluegill Fins". You can see the problem there.
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Old 07-24-2008, 07:39 AM   #20
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Another thing, from what I recall (correct me if im wrong) doesn't the Evo have the "shark fins" straight into the wind and not angled? (like the "Vortekz" people say, 15 degrees into the wind)...
Take a close look...They're progressively angled as specified by Mitsu.:

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