Do Vortex Generators actually work? - YES!

I've been toying around with the idea of Vortex Generators for a long time. I finally got around to testing them in both "lab" and "track" conditions.  I've found some interesting findings, but the verdict is that they are worth it.

There are a lot of VG designs out there.  Delta wing, bent aluminum, dimple designs..  But I was reading up a low-velocity low-drag VG design patented in the 80's.  Well expired patent, of course.  From what I read, that particular design seemed ideal for low drag, low velocity applications such as it would be for cars.  Ever since I read that, I wondered how I could fab up a set without spending too much money or time.  I couldn't think of a solution.

I didn't have to.  Few months back, I found a company called Airtab® who makes that design and sells them for a good price.  Installation is a breeze too.  Good price point, good value; sounds like something this blog can use, eh?

Its always a risk sending your product out so some web blogger to test your product.  Especially for a smallish blog like this one; it might seem that there isn't much to gain, but a lot to lose.  And a non-professional enthusiast may make mistakes with installation, testing, etc and many things can go wrong.  Bad news travels fast right?  So I very much appreciated when Mr. Jack Latimer from Airtab, LLC sent me a bunch of his Vortex Generators for me to try out.

First Test

The test rig

Lets cut to the chase.  I first did a "lab test" using a differential manometer.  This manometer works by measuring the air pressure differences at its two nodes.  I mounted one 3.5 inches away where the spoiler edge meets the trunklid, and another node at the rooftop.  Now, I have no idea if the rooftop is an accurate representation of ambient pressures or whatever pressure that acts with the spoiler pressure to generate negative lift, so I won't be able to calculate accurate lift figures.  But it would conclusively tell me the differences between the two tests.  So, in short, it is perfect for comparisons.

My first test was a failure.  I mounted them 2.5 inches apart (thats 6.5 inches apart from center-to-center), about 13 inches from the rear edge of the roof--at the maximum manufacture recommended parameters.  The test results weren't that great.  I found out position of the VGs are pretty critical.  Aerodynamics gets pretty complicated in this area; separation points differ depending on the shape of the surfaces and that dictates where the VGs should be mounted.  Although the first test showed that the VGs were not working,  I've seen this particular design work from different tests on the internet (link), so I wasn't convinced.  I had to do another test with adjusted mounting positions.

Unfortunately I had to return the manometer before I could do another test.  School was starting soon too, I was running out of time.  I decided to do the second testing on the track.

Second Test
At the last track event, I ran two consecutive sessions on the same aero settings, one with and one without four Airtab® VGs installed much closer to the rear edge of the roof, about 2.5" apart between the VGs.  The VGs are supposed to be installed 0.75" apart, but I just wanted to do a quick and dirty test.  I placed them in the center 2 feet of the roof, and ignored the edges since my spoiler probably generates the most pressure in that area.

Picture of the rear aerodynamic layout in the second test

Because I don't drive at pro-level, it was really hard to analyze the data from my amateur-level DAQ setup.  Fortunately, temperatures, fuel levels, tire wear were all at a similar level because I didn't waste much time between sessions.  Unfortunately, and probably because of my inconsistent driving, maximum velocity of both sessions and best laptimes are equal.  What to do? After staring at my charts for a long time, I decided to look at a sector laptimes for turns 2 and 3.  These turns are constant radius, and I am fairly consistent here, and I take the same line every time I go through it.  Perfect.


   Sector times, Averaged

• Session with no VGs: 13.22
• Session with Airtab® VGs: 13.15
• Samples were from six runs each with and without the Airtabs®, with one or two outliers removed from when I was doing warm-up and cool-down laps or when I made a big driving mistake.

The 0.07 second difference in this section means there was an appreciable amount of lateral force generated.  Calculations based on this data show that the increase in lateral force, or grip, was 1%.  I got the answer of the question I've been asking for months; They work!

Conclusions - They work!
If anyone is curious, my best time with VGs installed was 1:02.1, and without was 1:02.8, with driving lines, and tire pressure adjustment variables included.  Inconclusive, but I do have one conclusion from this: My best use of the VGs was not necessarily to make an huge difference in available traction through radically increased downforce levels.  Yes, the Airtab® Vortex Generators made the car faster, but it also allowed me to adjust the car's balance to inspire more confidence to drive more consistently.  More consistency = more improvement!

This may not sound like much but it really adds up; remember, this is just one part of the course, and I only used 4 of them at less-than-optimal spacing.  And if you do, say, 20 laps, you've gotten almost 2 seconds in turns 2, and 3 alone, and even more ahead when you count time saved everywhere else.

If you think about how little you have to spend to get these parts, its hard to convince yourself that you should not get these. Remember, the Airtabs® are to be installed 4 inches apart from center-to-center.

Closing Notes

Installation is very simple.  Plot out your mounting points, mark them (I use painter's tape), remove backing and stick them on.  They can be painted also.

Note the modified airflow to the rear foil
on this hillclimb truck with Airtab VGs
installed

Remember the original intent of the Airtab® vortex generators.  They are supposed to reduce drag.  I'm sure they are doing exactly that on my car for a certain extent, but a car with a spoiler is not the best platform to test that on.   These VGs are used on commercial trucks, consumers seeking to improve fuel economies on their cars, and other race cars to improve drag profiles of their cars.  Furthermore, they can be mounted on the undertray for cars with less-than-ideal underbellies to help airflow stay attached; the effect of that would be to decrease the pressures under the undertray as well as help accelerate airflow at the diffuser.

Links:
For more information on Airtab® vortex generators, please click the logo below or here: www.airtab.com
To buy Airtb® vortex generators, please go here: www.buyairtab.com

Articles and related posts:
US Patent Number 5,058,837 - Low Drag Vortex Generators
White paper on VG effects on a Lancer Evolution
Autospeed article on VG effect on fuel economy
Paper on VG effects on drag reduction on a Honda

Photo Credits:
Airtab® logo is a registered trademark of Aeroserve Technologies, LTD.
The hillclimb truck is a picture of Mike Ryan MotorSports truck at the 2005 Pikes Peak Hillclimb