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

[aerohead]

Originally Posted by euromodder

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.

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.

[Pendragon]

Originally Posted by aerohead

<snip>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.

[AeroModder]

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.

[dupree]

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

[jakobnev]

AeroModder -

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

[AeroModder]

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: