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

[trebuchet03]

^^ 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

[SVOboy]

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

[MetroMPG]

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

[DifferentPointofView]

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

[MetroMPG]

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

[Lazarus]

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.

[MetroMPG]

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

[bryan]

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.

[DifferentPointofView]

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

again with the sedans. we need some hatchback info!

[Lazarus]

Originally Posted by MetroMPG

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

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

Bryan

global climate change, evolution and reiki you should be able to prove this one pretty quickly... ie in about 2 tanks of gas

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