Tested: hatch spoiler vs. vortex generators vs. stock hatch, 1996 Ford Aspire
 

I finally got around to testing and recording the effects of VGs. The test used three setups (hatch spoiler, VGs, stock hatch) in an A-A-B-B-C-C format, using the same stretches of road. The tests were done with the least amount of time possible between trials.

With spoiler:

http://www.youtube.com/watch?v=pOZ37oopc18

http://www.youtube.com/watch?v=l1INZzGQIjY


With vortex generators:

http://www.youtube.com/watch?v=pB-BAYUJ2JU

http://www.youtube.com/watch?v=1-khQEH2Gcc


Stock hatch:

http://www.youtube.com/watch?v=JDA561vytLw

http://www.youtube.com/watch?v=Kka91kS6GmI




EDIT: Here's some photos of the mods:

Spoiler:

http://i3.photobucket.com/albums/y93...e/IMG_0231.jpg

http://i3.photobucket.com/albums/y93...e/IMG_0230.jpg

http://i3.photobucket.com/albums/y93...e/IMG_0233.jpg

Vortex generators:

http://i3.photobucket.com/albums/y93...e/IMG_0087.jpg

http://i3.photobucket.com/albums/y93...e/IMG_0086.jpg

The trip strips were in place for all three runs. After each run, the tested component was removed and all else left alone. The tufts proved the strips inneffective in preventing the air from wrapping around the pillar and producing vorticies.


Testing began at 10:30 AM with 20-25 minutes between runs.


Here's an older tuft test video showing the stock hatch:

http://www.youtube.com/watch?v=wm2RPqIE8HQ


Here's a video showing attached airflow from the vortex generators:

http://www.youtube.com/watch?v=gx084gKTLZ8

Aeromodder - I'd suggest posting in a new thread.

Edit: moved.

I think you would have to make a longer run to come to a definitive conclusion, but it looks to me as though the spoiler just edges out the stock configuration and the vortex generators come in third.

The problem with VGs is that their size and placement is critical. They are not an easy fix, if at all.

Good video though, thanks for posting.

Pendragon -

I agree. The devil is in the details.

CarloSW2

Could you add a description of each setup to this thread? (Pictures please!)

Yes, please. Added as part of post 1 would be a good spot.

I'd appreciate a results summary so I don't have to watch all those videos. Thanks for doing this test!

Updated with additional pictures and videos. As for results, I can't really tell a difference between any of the setups.

Interesting, would you consider testing a setup with the VG's slightly further forward and a spoiler(bigger than stock) at the bottom of the hatch?

http://ecomodder.com/forum/attachmen...1&d=1300983772

The idea is to keep the flow attached to the bottom and there recapture the kinetic energy of the vertical component of the airflow.

Thanks for updating with pics.

Extend that spoiler into a proper Kammback, and you'll be able to detect an improvement. :)

I'm planning on that! I was out the other day measuring and taking pictures to compare markings to the streamlining template, and got a good shape for the side supports. When the weather dries up I'll start working on it. First, I'll need to do a quick and sloppy partial mockup to see how much visibility I'll lose from the rear, and find out if I'll need to pick up some polycarbonate sheets.

On a sidenote, I can't help but smile when I see ads for new cars that get an "impressive" 35 MPG highway, beating out other models. I was getting 40 MPG combined before I did anything to this 15 year old car.

I hesitate to ask the question here...but here it goes.....

A good while back I bought 26 airtabs from Ebay for maybe 1/2 price...now I'm wondering where to put them? (please...no comments from the peanut gallery) ;)

Here's the car...or an example of it...

http://www.nonags.org/members/nijqk/ZX3aero1.jpg

http://www.nonags.org/members/nijqk/ZX3aero2.jpg

http://www.nonags.org/members/nijqk/ZX3aero3.jpg

The 2 most likely areas might be on the windshield right before it curves over onto the top...or has this been designed to keep the flow from detaching?

And maybe on the back from the tail lights down to the bumper on the sides? Maybe some in front of the front/rear wheel openings?

And while I'm asking...any other obvious ways to decrease aero drag with this shape?

And how well does the lip on top of the roof function?


Don't make me have to sell these to somebody else!!!

no good news for you
 

suspect,the turbulators were intended for a notchback type car with a backlight angle so steep as to produce immediate flow separation at the header and no chance for re-attachment on the boot/trunklid rear.
The Focus,being a wagonback type car simply has no place for air to re-attach to,as a Focus,Civic,Sentra,Accent,Lancer,etc. notchback coupe/sedan.
There is no other place you could place them which would not actually INCREASE the drag.If you have a family member or friend with a naughty notchback you might donate the tabs to the cause.
The upshot for you,is that your car has the beginnings of a really good Breer/Fachsenfeld/Kamm roofline.If you were to just extend what you have using the Aerodynamic Streamlining Template as a guide you can enjoy some real savings at the pump.

I took one Airtab out to the car and I'd pretty much agree. The rear along the sides is pretty much sloped inward from the rear wheels...probably no separation from windshield to top...

probable moves...in order of difficulty

* air dam extension...lawn edging...easiest...probably a gain

* add a sheet of something at the back to help the air out from under the car

* grill block...carefully done

* mirror reduction...would want to be able to return to OEM...2 small mirrors?

* the kamm-back extension on the rear window...easy to think of...harder to do...once made a set of louvers out of wood and alum for a rear window and used RTV to glue them to the glass....held several years. Problem might be the lip there?

* top 1/2 fender skirts on back...if I find a way to do them right

Will likely do the 1st 3-4...then the going gets tougher....

Weren't they intended for trucks with a big squared off rear face ?
There's be no re-attachment their either.
Going by their website, the airtabs are supposed to create a virtual tail.

At least the boattail and extended Kamm-backs are proven mods. ;)

So far , no-one here has been able to proof Airtabs / VGs reduce the fuel consumption.

The rear looks a fair bit like my V50 wagon.
While the sides slope inward, they do so too fast.

I've wondered what VGs or AirTabs would do if they were used to make the air follow these fast curves better.

Airtabs and VGs are meant and shown to better "bend" the airflow - though at the expense of drag. So the benefit of bending the air must be made bigger than the loss caused by the drag ... if possible at all.


Why not try it while you've got them anyway ?
They can be re-used when adding new double-sided tape.


Make the top flush with the lip / spoiler ?


I wonder wether it'd be OK to just put a Kammback on the glass alone, leaving the side-mounted taillights free.
Using lexan on a light frame, it'd hardly be visible.

Sure, it'd mean a side-step for the air coming from the sides.
If the Kammback is short, that air will blow by - won't help, but won't harm either..
If it's longer, that air could re-attach, however briefly.
But you'd still get the benefit of the extended roofline.

I believe you can remove the lip from the hatch. User WeatherSpotter did that to his Matrix when he built his boattail.

The way I would construct the kamm-back would be to use regular fir 2x2s or 2x4s...make a frame and shape it to the rear hatch glass. Then the wood frame could be extended out in the shape wanted. If I use several coats of thinned polyurethane on the wood...this seals it against weather. Sand the wood lightly...clean the glass with lacquer thinner...glue it on with the old style silicone caulk (acetic acid cure). The shape could be covered with alum sheet...acrylic?

Sides could be acrylic...top alum.

The lip is sheetmetal...would need to be worked around. Would just continue the current overall roof shape on top...sides would be best aero-wise if they angled in some...trying to follow the established curve to some extent at the tail lights? Sort of a half boat tail.

Rear view would be reduced? Not sure what it would look like.

vortex generator positioning
 

Looks like you have placed the vortex generators a little too far back. See
www dot fuelsavers dot com dot au
What do you think?

Lots of people are saying they're too far back, but tuft testing proved that the position was good. They were placed approximately 100mm ahead of the separation point.

intended
 

Way back somewhere we spent a lot of time discussing VGs and I posted an article about an aerospace engineer who developed VGs for automobiles.
The demonstration vehicle was a Honda Accord notchback.Two photos were given with a single long yarn tuft demonstrating re-attachment onto the trunklid rear.
He was borrowing from
'turbulators' used on non-blown/non-suctioned wing flaps at high angle-of-attack.The turbulators offer short field landings at the expense of a constant level flight drag penalty.
On a 18-wheeler,the base pressure of the wake ( pressure drag of the rig ) is governed by the pressure at the separation point.
Since the VG does not alter the separation point it cannot significantly alter the wakes base pressure.
If 'steeper' panels,as Continuum Dynamics has tested with NASA at Ames were installed behind an 18-wheeler VGs would probably help to cheat the air,allowing re-attachment and the formation of locked-vortices,known to help lower drag.

If Airtabs is claiming that their product creates a virtual tail I would love to see them defend that claim in Superior Court.

I think I would settle for independent testing by a qualified lab...not likely to happen though.

UPDATE

I decided to revisit the vortex generators I had sitting in a box after reviewing the videos and data I collected, with a bit of change. I increased the angle of the VGs further out to the side from the recommended 15-15-10-5-0 to 15-15-10-10-5, and added a 1.5" extension to the spoiler on the end of the hatch.

Last time, I tested at 55 MPH, which I've noticed doesn't really show much of a difference. So this time, I increased the speed to 65 and used a different road. Testing was done in an AABBCC fashion, with the first being in one direction and the second being in the opposite. There was roughly a 2 hour span between all 3 tests, and all tests had a slight crosswind.

The first test was the bare hatch, which averaged about 38 MPG at 65 MPH.
Second test was with VGs and the spoiler, which returned about 42 MPG at 65.
The third test was the Kammback, which also returned roughly 42 MPG at 65, leaning closer to 43.

Surprisingly, my test showed that vortex generators actually do help fuel economy when properly applied, and was only slightly under the effectiveness of my kammback.

that is interesting, there does seem to need to be some precision involved to get the desired effect. So is the consensus that the VG's work better on a notch back to try to keep it attached rather than say a wagon, where there is no way to keep it attached you just have a huge wake

AeroModder -

Was the configuration in the second test close to what i described in post #9?

Just about, yes. I kept the VGs in the same place, since earlier tuft testing proved they worked in that position, but I increased the angle on the outer VGs and added the spoiler like you suggested. It's about 3.5" long, extending 1.5" past the stock lip:

http://i3.photobucket.com/albums/y93...e/IMG_2052.jpg