Vortex Generators / Hmmm Airtabs

[n0rt0npr0]

Originally Posted by JanGeo

n0rt0npr0 - how big a box did you get of them AirTabs - want to send some my way??

I only purchased what I needed which was 11 of them. And damnit, I can't say whether they've made any difference or not because I've been trying to source a 93 GM 6 cylinder computer for $20 since I got them. Ain't found one just yet. My computer keeps on resetting its fuel table optimum - verified by a Tech1 scanner. Yeah. My tank to tank FE has been eerily close for quite some time now.

[JanGeo]

Thinking about some plastic strapping material they wrap boxes with - pulled tight over the roof without any glue so it comes off easy - mount the leading edges of the airtabs to it with tape and strap it to the gutters or around the rear hatch opening or even fasten it to the rear wheel wells with hooks and put some VGs on the side too!

[smartzuuk]

If someone wants to define their test expectations and send me some VG or whatever, how about trying it on a smart?

[Ted Hart]

I had a '77 Gremlin (remember them?) with a small scoop-type wing mounted up-side down over the rear hatch window. This served to keep the dust and raindrops blasted off the rear glass. It worked extremely well! Isn't this the same sort of thing the vortex generators (supposedly) do?
Better MPG? The thought never occurred to me...such a tiny gain! MPG gains come from HP reduction...while maintaining a given velocity! People don't seem to appreciate this simple truth...it takes power to move a mass at some velocity. Burning gas makes the power. Less gas (more MPG) to move at the same speed is what a higher FE is about! Stirring the air a bit takes no power...and doesn't make any, either! Small wiggles on a MPG read-out are likely caused by the "noise" of the real world.

[MetroMPG]

I remember those glass-clearing deflectors on the back of one of my parents' station wagons when I was a kid.

I would say those would make aerodynamics worse, not better. They increased projected frontal area, and as they blast air down the rear window, they would increase pressure drag aft of the deflector and increase the size of the trailing wake.



VG's could also increase projected area, but the theory (as I understand it) of placing them at the trailing edge of a vehicle is the tight vortices they create are supposed to extend the effective aerodynamic length of the vehicle: since the vortices would be drawn inwards in the low pressure area, they supposedly create a "virtual" boat tail, and minimize trailing wake.

[MetroMPG]

I've been in touch with my Airtabs contact again.

I'll pass my test outline by him before I do the runs to make sure I don't find out after that I did something wrong (ie. placement/orientation).

He has already suggested testing in 2 separate configurations for a hatchback:

- tabs along the trailing edge of the roof only;
- tabs on the roof edge plus along the trailing edge of the sides

[FormulaTwo]

I mounted mine along the trailing edge of the roof, without any on the sides. I still have a few extras that I have not installed. let me know how your A-B-A testing works out. I may install those later on.

[JanGeo]

I'm not sure of the size of these but they are supposed to be a certain distance apart or else the vortices don't form properly. Putting them too close together will make the adjacent vortexes interfere with each other.

The problem with the rear high wing is that it produces drag where as a vortex generator does not (not much anyway).

[MetroMPG]

For standard Airtab size (I'm not even sure if there's more than one size), spacing = 4 inches on center (minimum).

[JanGeo]

Ok the are 4" on centers and 3.25" wide so 3/8" between each so they are pretty close to each other. I would have thought they would be further apart to allow the vortex to be bigger.