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Old 05-27-2006, 05:39 AM   #11
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VG

Quote:
Originally Posted by katman
And my Tahoe!
Yeah but what percentage of your fuel consumption is to air drag compared to other drags of your vehicle? I know my xB gets better MPG at lower speeds and drops off over 40mph. Also think about AirTabs for $2.50 each in clear, black or white which have been wind tunnel tested.
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Old 05-27-2006, 07:59 AM   #12
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Quote:
Originally Posted by JanGeo
Yeah but what percentage of your fuel consumption is to air drag compared to other drags of your vehicle? I know my xB gets better MPG at lower speeds and drops off over 40mph. Also think about AirTabs for $2.50 each in clear, black or white which have been wind tunnel tested.
I've thought about Airtabs in the past but then thought about making some and then people post other cool stuff and I start thinking about that and I procrastinate and get nothing done!
With the brush guard stuff on the Tahoe, which I don't want to take off, I know aerodynamic mods would help, but I'm having problems deciding what to use that won't change the looks too much. Clear Airtabs are a definite possibility. I've wondered about belly pans but are they effective on vehicles with large ground clearances? I never use the luggage rack so I could remove the cross bars. Then I could add a Ram Implosion Wing!
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Old 05-27-2006, 03:10 PM   #13
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Quote:
Originally Posted by katman
Then I could add a Ram Implosion Wing!
Do you know anybody that tested that thing. It looks pretty hokie. It would be the ultimate whale tail. http://www.electrifyingtimes.com/Rob...Patterson.html
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Old 06-14-2006, 04:33 AM   #14
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I've studied the vg thing and have installed some.

I'd have to guess that the ones on the roof are in an area where the boundary layer has already separated to some extent....probably reducing their effectiveness. Maybe try moving them forward about a foot?

The ones on the deck lid are at a place where the air has pretty much separated for sure from the sharp drop at the window.

I had some on the roof of a hatchback with less slope...slightly different design of vg though...similar to the Mitsubishi kind. Found that silicone caulk is best for permanent mounting.

Good to see the accurate testing....and some positive results.


Here is a similar car with similar flows:

http://www.mitsubishi-motors.com/cor...004/16E_03.pdf


vgs:

http://www.thirdshift.com/jack/firefly/firefly18.html

http://www.thirdshift.com/jack/firefly/firefly19a.html

Notice that he has his version of vg mounted the other direction? This plane cruises at around 60 mph.
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Old 06-14-2006, 07:18 AM   #15
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Quote:
Originally Posted by ZugyNA
I've studied the vg thing and have installed some.

I'd have to guess that the ones on the roof are in an area where the boundary layer has already separated to some extent....probably reducing their effectiveness. Maybe try moving them forward about a foot?

The ones on the deck lid are at a place where the air has pretty much separated for sure from the sharp drop at the window.

I had some on the roof of a hatchback with less slope...slightly different design of vg though...similar to the Mitsubishi kind. Found that silicone caulk is best for permanent mounting.

Good to see the accurate testing....and some positive results.


Here is a similar car with similar flows:

http://www.mitsubishi-motors.com/cor...004/16E_03.pdf


vgs:

http://www.thirdshift.com/jack/firefly/firefly18.html

http://www.thirdshift.com/jack/firefly/firefly19a.html

Notice that he has his version of vg mounted the other direction? This plane cruises at around 60 mph.
Your right about the direction. I don't know how I screwed that up. I'll have to swing them around and retest. Mybe this weekend. I was disappointed with the original results. Maybe this will get it around 3%.
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Old 06-14-2006, 06:51 PM   #16
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Box drivers might be better served by adding a boat-tail to break up the inevitable turbulence behind the vehicle:

Some now well-known articles:
http://www.greencarcongress.com/2005...at_tail_d.html
http://www.maxmpg.org/the_cap.html

PDF warnings:
http://www.nasa.gov/centers/dryden/p...ain_H-2283.pdf
http://www.osti.gov/fcvt/2000-01-2209.pdf

On a vehicle with a blunted rear end (as opposed to the back of a pickup cab), it seems that the air space created by some plates does more to reduce drag than their angle of taper.
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Old 06-15-2006, 09:03 PM   #17
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Quote:
Originally Posted by Silveredwings
On a vehicle with a blunted rear end (as opposed to the back of a pickup cab), it seems that the air space created by some plates does more to reduce drag than their angle of taper.
You are right, at least with my application. I turned the VG's around and ran the same test protocal as before with the same results.
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Old 06-16-2006, 02:50 AM   #18
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I got "inspired" by your 1.5% gain and made up some vgs for use above the rear window on my hatchback. I combined the Mitsubishi research and the vg design from the ultralight. Also some some oil flow testing to determine air flow direction. Will post some specifics and a pic when I get them finished.

I have some vgs on the sides of the same car (3 per side)...they are oriented the same as your roof vgs...2 vanes that point to the rear in a "V" shape.

The Mitsu research shows that mounting them around 4" from where the rear window starts was the ideal position on that car.
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Old 06-16-2006, 06:34 AM   #19
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Quote:
Originally Posted by ZugyNA
I got "inspired" by your 1.5% gain and made up some vgs for use above the rear window on my hatchback. I combined the Mitsubishi research and the vg design from the ultralight. Also some some oil flow testing to determine air flow direction. Will post some specifics and a pic when I get them finished.

I have some vgs on the sides of the same car (3 per side)...they are oriented the same as your roof vgs...2 vanes that point to the rear in a "V" shape.

The Mitsu research shows that mounting them around 4" from where the rear window starts was the ideal position on that car.
"Vortex generators (VGs) were studied to install
immediately upstream of the flow separation point
in order to control separation of airflow above the
sedan?s rear window and improve the aerodynamic
characteristics. It was found that the optimum
height of the VGs is almost equivalent to the thickness
of the boundary layer (15 to 25 mm) and the
optimum method of placement is to arrange them
in a row in the lateral direction 100 mm upstream of
the roof end at intervals of 100 mm. The VGs are not
highly sensitive to these parameters and their optimum
value ranges are wide."


Keep us posted with the results.
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Old 06-16-2006, 01:53 PM   #20
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Using the Mitsu research and ultralight info...I made 5 vgs from alum flashing material 2 1/2" long....with 2 vanes each set 3" apart. The vanes are about 5/8" high.

Did an oil flow test first by drawing a line 3-4" back from where the roof starts to slope down...marked 7 different points along this line...had an eyedropper of engine oil...put a good sized drop in all 7 places and drove about a mile and a half down the road at 60 and stopped. Found the center 3 flowed straight back...the 2 points in one from the ends angled in around 8* towards the centerline of the car. The 2 places right near where the roof dropped off to the side had a pretty disturbed flow...lot of buffeting here?

So they are mounted about 3" back from the "break line"...the two vgs on the ends are angled 8* inwards...glued on using silicone caulk. Each vg is 4 1/2" apart.

Expecting that each vane creates a vortex that rotates conterclockwise on the right side and clockwise on the left (looking to the back)...so that they don't tend to cancel each other out.

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