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

[AeroModder]

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.

[suspectnumber961]

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...







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!!!

[aerohead]

Originally Posted by suspectnumber961

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...







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!!!

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.

[suspectnumber961]

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....

[euromodder]

Originally Posted by aerohead

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.

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.

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.

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.

[euromodder]

Originally Posted by suspectnumber961

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...

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.

* 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?

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.

[AeroModder]

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

[suspectnumber961]

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.

[BambuFlute]

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?

[AeroModder]

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.