Vortex generators - where's the solid data for hatchback/van benefits?
 

Info given to me by Ron Davidson at Airtabs. (Posted with permission)

• 3rd party tests showing utility of tractor/trailer "gap" VG application at MIRA (British Motor Industry Research Association) test track, by IRTE/BTAC (Institute of Road Transportation Engineers / Brewing Transport Advisory Committee), 1994.
  http://www.box.net/public/sbj6b0xsrk
  
  
• Airtabs background info on the MIRA/IRTE/BTAC report.
  http://www.box.net/public/e192gezve1

AND most relevant to my situation:

• Images showing wind tunnel results (base pressure reduction, ie. improvements to low pressure zone at the back of the car ) on a Civic hatchback model with VG's installed only on the sides. Click to zoom.

http://images6.theimagehosting.com/a...vic-one.th.gif

http://images6.theimagehosting.com/a...vic-two.th.gif

http://images6.theimagehosting.com/a...c-three.th.gif

The Australian AutoSpeed web site recently ran a 4-part series on VG's. Some of the articles are open access, some require payment:

http://www.autospeed.com/cms/search/...vortex&x=0&y=0

The writers have done quite a few excellent articles on DIY aero mods before, and they're normally pretty rational and scientific in their approach (ie. decent methodology, healthy skepticism). I've paid the $5 to access a few of their articles in the past, and haven't been disappointed.

They claimed they "tested" VGs on the rear of an Insight and a 1st generation Prius in the last instalment of the 4-part series, so I bought access to one of the articles to read the results.

Save your money: there were no "results" because they didn't properly test them!

They did show a beneficial improvement in airflow down the rear window of the Prius via photographs of tuft tests, but they didn't quantify the results re fuel consumption changes.

http://us1.webpublications.com.au/st...0/3061_5lo.jpg

http://us1.webpublications.com.au/st...0/3061_3lo.jpg

For the Insight, they didn't even attempt to do controlled back-to-back testing - they just drove their regular commute over several weeks and then compared the results there to (apparently) a single commute with the VGs attached. That methodology sucks!

And it doubly sucks because this is the application I'm most interested in: ie do VG's have the ability to reduce wake / base pressure beyond the trailing edge of a hatchback-style vehicle?

http://us1.webpublications.com.au/st...0/3061_8lo.jpg

Still, they somehow feel confident enough to conclude that:

Quote:
(emphasis added.)

I've had a box of airtabs for quite some time, but I refuse to just stick them on the car and pretend they work.

I've prepared to do a test: attached the airtabs on flexible/removable plastic sheets that I can remove in a jiffy at the road side.

I just need to make another couple of sheets to complete the sides, and double-check with the distributor that the placement is OK.

click/zoom...


http://images6.theimagehosting.com/s...-orange.th.jpg

Above: I increased the spacing between the tabs by 50% to compensate for the 45 degree angle on the rear window.

I may not be able to place an uninterrupted line of them down the side of the car due to contours that they won't stick to. But I'll add a few more at least.

http://images6.theimagehosting.com/3-4.5c5.th.jpg

Unfortunately, I've been too busy to actually DO the test yet.

VG freeway stats
 

At last a site for milage OCD!

I drove from Vancouver to San Antonio and back in a 1995 VW Eurovan camper at the local posted speed limit. Gas auto otherwise unmodified typical 16 mpg. I would remove/install these VG's at fill ups and check mileage per tank. Considering the cost (2 yogurt containers & a meter of white electrical tape) the approx. 7% mileage increase (~$50 saved - $85 if I'd had them on the whole trip) was acceptable. Definitely a TLAR installation. Would be nice to do wind tunnel/tuft/rainy day video testing to optimize location.
A similar installation on a VERY heavy U-Haul trailer showed a 2% improvement.

Damn, I was hoping to see the bit of info I've been after..... How far from the leading edge to place :p That variable will be one of the most important ones...

Hi bryan - welcome to EM!

OK, I have to say I don't know that one. What's TLAR??

I agree. And good to hear from someone who gets the importance of data + testing.

That said... back to your anecdotal info... I'd be interested to hear more details about your experience with the things on your van & the trailer - E.G. how many on vs. off comparisons you made; whether the weather, road conditions & terrain were similar from tank to tank.

There's no shortage of customers claiming great things about airtabs in the company testimonials. But you have to take that with such a huge grain of salt, it's not really worth very much.

Again, not saying they don't work.

But I would like to see some more convincing data for my application. Either that or I need more warm months in the year to gather the info myself.

randomization
 

Considering that during this 15,000 km test the combined vehicle weight was 2500 to 5500 kg, speed limits vary from 45 to 130 km/h, altitudes from sea level to 10,000 ft and a prevailing westerly wind I just alternated on/off at each tank ~500 km. This then gave me, say, 500 km on and 500 km off at the Colorado Plateau, same at 80 mph Texas freeway speeds. Once I had convincing data I just left them on for the last 3000 km or so, since by then I was driving in heavy snow & mountain passes which gets a bit too variable.
TLAR: That Looks About Right :D . These are about the size & angle of attack of aircraft VG's (400 km/h) at half spacing, installed at about the location AirTabs recommends. I didn't do the reynold's number conversion to see if the size was appropriate. I will bet double density would help.

Since then I also have tried premium gasoline which gives an 18% improvement (!) for a 10% cost increase. This is city driving and probably type-specific.

Per tank mileage variability was 9 to 25 l/100 km so the Signal to Noise Ratio here is pretty crappy. The fuel flow meter in the Saskatchewan Metro Videos would have speeded this up considerably.

I'd say if you don't have a sizeable 20-45 degree slope towards the center of the vehicle in the area after you place the air tabs, you'd be just as well off writing a check out to me as buying air tabs. But don't worry, I won't rip you off, you'll be getting the most premium magic beans sourced at great expense from exotic locations around the world.

I have some pictures, somewhere, of my buddy's rowing oars... He got them recently and have vortex generators on them (on leading edge)... I believe his immidiate comment on the first stroke was something like "These new oars are F'ing sweet" or something like that :p

The Mitsu Evo has similar fins on it.

http://www.scoobyblog.com/wp-content...006/10/011.jpg

http://www.onemotoring.com.sg/publis...0005.Image.gif

^^ Mitsu has a paper published too

http://www.mitsubishi-motors.com/cor...004/16E_03.pdf

worth a reduction of 6 points (.006) in cD :)

Indeed, those fins are where all this dicussion in the ecomodding community got started, right darin?

Yes. For my purposes, it keeps coming back to this question:

Are VG's are effective at reducing drag at the trailing edge of an abrupt cutoff (like the back of a van or hatchback) as they apparently are at delaying separation over a given radius - like airplane wings, rowing oars, or the roof/rear window transition on the Mitsu?

bryan says "yes".

The diagrams in the original post seem to suggest "yes".

Autospeed says "not likely".

And I remain respectfully skeptical. :P

When you find out tell me, cause I wanna put some on the back of my Jeep!!!

OK. Hope you're not in a hurry though - I've been mulling this over for more than a year now.

Some more anecdotal info. I made some VG's out of aluminum and tin snips using the info from the Mitsu Evo paper. I did A-B testing and had a 1.5% increase in FE at 55 mph. This was during the summer when the temps were the highest. The VG's were placed along the roof line just like the Evo pic.

On a sedan, yeah? Wasn't that on your Mazda?

Where's the solid data ? Waiting in your garage!
 

If you already have a mileage baseline (and I can't believe you'd be here if you don't!) just do it. This is the least visible and cheapest modification you can make to your car. I altered the contrast on this photo so you can see how complicated it is!

The $200 test - www.airtab.com
The $110 test - www.fuelsavers.com.au
The $2 test - right here!
Chop the bottom 1" off a relatively flat-bottomed yogurt container, then cut it into 12 or so pie slices - there are your little wings. You're after a 15 degree angle of attack to the local airflow - I'm guessing leading edge of the base perpendicular - check your dirt pattern for streamlines. Or do the tuft test. They also have to be thicker than the local boundary layer. I suspect on most trucks there is a separation bubble on the roof at the windshield, and the hood at the grill. Here 1/4" high VG's would be sufficient.

There is a natural clockwise vortex off the left corner (& vice versa) - I tried to reinforce that. It may, however,be worthwhile 'fighting' it.

I used white plastic & single side white tape - with a little more effort you could spray paint them to match. Wax the installation site, use double sided tape. A bit of citrus cleaner will take off the sticky stuff when you (re)move them.

Unlike global climate change, evolution and reiki you should be able to prove this one pretty quickly... ie in about 2 tanks of gas. The VW seems to say "yes", but don't ask me how it works. It only gets insured & driven for trips over 500 km so I can't give you anymore data for a few months. But I've been looking at my electric scooter...

Anyone who knows anything about aerodynamics feel free to jump right in.

again with the sedans. we need some hatchback info! ;)

I've done them on the Daewoo also. It was a little a little less then the Mazda.

Bryan
These improvement are too small to be seen over a tank of gas. You need instrumentation to be able to veryify results. Even with instrumentation the static between runs makes it a toss up on whether it working or not when done on the open road. YMMV:turtle:

I'm not sure I can prove anything in two tanks of gas. There are all sorts of confounding variables, the largest of which is driving style. Just a few big stops from high speed can really throw out your fuel economy.

I'd also like to know the theoretical basis behind vortex generators placed before abrupt ends of things, as MetroMPG says. I can understand how they'd work on something like a 20-40 degree slope, and Mitsubishi wrote a paper on it. But the back of a van? Color me skeptical.

After reading the paper it looks like delta shaped VGs would help the aereodynamic characteristics of most notch back sedans. I think I'm going to try them on my 1991 Honda Accord 4D.

I'm with Lazarus & Newton on this one - tank-to-tank testing doesn't generally produce reliable results.

And as a matter of fact - I have no "baseline" to go from. I don't commute with the car, so it doesn't see either typical or frequent use. Check my fuel log - it's all over the map.

I actually did stick the VG's on my car for a 200 km highway trip. Not surprisingly I couldn't conclude anything from the results - and I didn't really try. (Mostly I put them on to show the guy who lent them to me.)

The best way to test them is in a wind tunnel. :)

Following that, the best way to test them is with instrumentation & a series of back to back A-B-A runs on a deserted road using cruise control to remove the driver from the equation.

I had every intention of trying just that, but my play time in the past year was occupied with other stuff (ie. ForkenSwift). Maybe in '08 I'll add the "hatchback" VG test to Lazarus' sedan test.

At the very least it looks like these things will help clear the snow (something we've been having a regretable amount of lately) off the rear window.:D

True, but you'll have to "detail" the darned things on the roof after every snowfall too. I expect they'd fill in, at which point they're just hurting your Cd (and poss increasing A). And how long before you crack one or knock it off with the snow brush?

You may be right but when the car gets snow covered or worse like two weeks ago ice covered (1/2 inch) I expect Cd and A get blown out pretty badly not to mention the added weight.

VGs on hatchback
 

Here is a row of VGs on the trailing edge of my 2005 smart car.

I have no empirical numbers to offer - I do so many mods to my car that I can never isolate the results of any one at a time!

The most interesting result is a noticable improvement in straight-line tracking at highway speed on this 8ft long car!

http://i170.photobucket.com/albums/u...-07_1549-1.jpg

Cheers, all.

Bil :thumbup:

That's pretty nice looking, where'd you get them?

Welcome to the site!

Thanks for the welcome - glad to be aboard!

The VGs are from Nish Motorsports Contact our buddy Mike Nish and tell him "Bil the smart car guy" sent you!

Thanks for the link! Perhaps we'll get some more testing on these things going...

Don't forget to make an intro thread, :D

I posted this in the GS forums as well, but I installed 'Vortekz' fins on my 240 wagon about 3 weeks ago. I'll post pics as soon as my host server come up again.

Hello Bryan! cudos to your mods, love them
i got an 80's rabbit and a Benz td wagon i need to
do. how did you get started, what were your baselines
and what would your suggestions be for my cars?

your tabs look as if they lack "dimensional stability"
how do you know that they are working correctly
while they might be fluttering?

Here are my 'Vortekz' VGs:
http://gallery.newbug.org/albums/vol...3850.sized.jpg
http://gallery.newbug.org/albums/vol...3852.sized.jpg
http://gallery.newbug.org/albums/vol...3851.sized.jpg

Cool... but the little spoiler behind them kind of negates their presense. Unless you're going for the aesthetics. :)

Alright! This is the info I was looking for for the Camry. Thanks for the info, I look forward to seeing the results on hatch backs as well.

they look injection molded
 

where did you dig those up?

also what angles (if any) did you use for the arrangement?

they would be so easy to make, a 2 piece wooden mold
(Plug/mold) with ample allowance for material thickness then just insert a small sheet of solarheated plastic
of your choice in between them and push together

woud make for great christmas presents for likeminded friends :)

there u go
 

just like the "undraftable" 928 that was raced and subsequently banned back in the 80's!
had they only turned the driver seat backwards
they would have had a near perfect car aero shape
:D

just wheeeere did you buy those, are they strips or individual elements?

http://www.vortekz.com

Templates are included. Mounting angles are as follows:

/0deg/5deg/10deg/15deg/15deg^15deg\15deg\10deg\5deg\0deg\

Hello again SL8,
I went to the vortekz site but couldn't find pricing. Hmmm?

I'd consider a second set of 10, to use 5 each on the vertical rear sides. They could extend down as far as the taillight assembly.

Of if using the ones from Performance Products, the same idea could apply.

Hello Bruce!
Click on the "Retailers" icon...then "Manufactures Depot". They're $19.95 +shipping.

Vortekz doesn't recommend using the delta fins on the sides, which is kind of understandable since that would essentially make them mini canards. I think Airtabs would be more effective when mounted vertically.