Archives

Hello,

I'm relatively new and I have purchased a set of these Air Tabs for my 2006 9-3 wagon to reduce turbulence behind the vehicle. They're made more for trucks, but I bought them anyway because the principles behind how they work seem sound.

http://www.airtab.com/

I haven't put them on yet, (was only going to put them on the roof to test them and for appearance reasons), but I'm wondering if any of you have experience with them or know them to be effective (or ineffective).

Thanks,
Atul

It looks like they work similarly to a lip on the tail of the car. I expect it might help a bit. I'm not sure if it is worth the money or not though. Like you said, it is based on sound principles. The question is if the implimentations is good.

According to a quick google search, the current production Saab 9-3 has a reasonable but not stellar drag coefficient of 0.33 (the same as my 2002 Honda Accord, actually.) So you're starting off in pretty good shape.

Before you go and stick them on the car, I have a few suggestions. The first would be to try to quantify aero drag of the car as it sits now. One way to do this would be with coast-down testing, which basically involves picking a nice, flat stretch of road, getting up to a set speed, putting the car in neutral (only if safe to do so!) at a specific point on the road, and timing how long it takes to lose xx miles per hour. This should be repeated at least 5 times (preferably more) to build a distribution that will help assess whether the "after" results are conclusive. Be sure to do this after a thorough warmup (10-20mi of driving to get the drivetrain warm) and in calm clear weather, noting the temperature for future reference. Do the same after you install the airtabs.

As to whether or not they will work, it's hard to say. I've been doing some literature research on drag reduction and I'm convinced that significant improvement only comes from very careful design for each particular application. I'd love to give you better advice but I'm still at the start of the learning curve.

Good luck.

Thanks for the advice Tim. Yes, coastdown is a goo method to figure out drag improvement. (I used to do performance and fuel economy simulation when I worked as an engineer at Ford). I could almost do this after installing 2 tabs of the 6 I would put on the roofop, actually the top of the hatch on the spoiler. I had the sedan version of my car which had a Cd of .29 and the wagon is still pretty good. The other thing I want to help prevent is all the crud that builds up on my rear glass. I like my 1997 Saab 900 S better in this respect. The angle of the hatch keeps the glass completely clear at speeds above 50 mph or so.

Interesting...

I had to register to revive this thread... I'm currious if anybody has definitive results from using vortex generators. Might not be useful for insights or modern hybrids, but for older cars and SUVs...

To add some meat:

Autospeed (AU) article on using vortex generators for MPG and stability, wool-tufting to detect airflow... Seems promising but not quite conclusive.

Vortex:
http://autospeed.drive.com.au/cms/A_3061/article.html
http://autospeed.drive.com.au/A_3060/cms/article.html
http://www.autospeed.com/A_3059/cms/article.html
http://www.autospeed.com/A_3058/cms/article.html

Aero testing:
http://autospeed.drive.com.au/cms/A_108676/article.html
http://autospeed.drive.com.au/A_108675/cms/article.html
http://autospeed.drive.com.au/A_108674/cms/article.html
http://autospeed.drive.com.au/A_108656/cms/article.html

Aerodynamics:
http://autospeed.drive.com.au/cms/A_107773/article.html
http://www.recumbents.com/car_aerodynamics
http://www.edmunds.com/advice/specialreports/articles/106954/article.html
http://www.ibsinger.com/gallery.htm?code=GAER&galleryId=768

Under car airflow (Prius +5MPG):
http://autospeed.drive.com.au/cms/A_2456/article.html
http://autospeed.drive.com.au/cms/A_2455/article.html

Undertrays spoilers and bonnet vents
http://autospeed.drive.com.au/cms/A_2162/article.html
http://autospeed.drive.com.au/cms/A_2160/article.html
http://autospeed.drive.com.au/cms/A_2159/article.html

Wiper blade deflector for noise
http://autospeed.drive.com.au/cms/A_2445/article.html

Products:

Airtabs $2.50 ea.
http://www.airtab.com
Vortekz: $20 for 10 fins
http://www.manufacturersdepot.com/ProductDetail.jsp?LISTID=800000A6-1180622063
FuelSavers AU$10/kit:
http://www.fuelsavers.com.au/
Airflow systems
http://www.prfprod.com/


Tidbits:

"Another cool feature on the Ridgeline is a "vortex generator" on top of the side mirrors. It's nothing more than little plastic ridges molded on top of the mirrors. As the air flows across the mirror, the ridges help to redirect the flow away from the windows. The ridges help to hold down wind noise and keep the cabin quieter."

Mitsubishi EVO MR vortex generator ($300): R3 brand RM38 RM50
http://lacar.com/modules.php?name=News&file=article&sid=479

http://flight.engr.ucdavis.edu/~hjshiu/research/irflowviz.html
"[planes] They use these Boundary Layer Energizers, BLEs for short (the little tiny speed bumps) to preserve boundary layer integrity. In fact, you can't fly the aircraft with more than 2 missing and even 1 missing is very bad. "

Have you or anyone installed these and monitored the results? I have a Ford Aerostar and it is very tempting to try this. However the car looks good and I'm not too inclined to stick these things on it unless there is a strong enough recommendation from someone who's done it! Thanks!

Didn't try, though I was interrested.

I decided to start with basics first before going there (Scangauge and PG).

Call me a sucker - but I went out and bought them and installed them yesterday. Driving around today at local speed 35-45. I did hit higher #'s than usual( 50-55)mpg on segments but cant pin it down to them. I'll post a pic when I get some time later.

Note that these are aero mods, so I expect them to be more useful at highway speeds where aerodynamics has more impact.

You put that on the Xb? Does it already have a spoiler in the back?

My Xb does not have a spoiler - You can get a factory spoiler for $200 + shipping. So for $20 I'll give it a try. You can see a picture of my XB in about me , near my posts.