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Discussion Starter #1
Some time ago I found a product at was sold to truckers to improve the air flow around the truck. They were small plastic stick on devices that looked kind of like a cut off funnel. 6 or 8 of them placed along the forward edge if the roof was supposed to make eliminate turbulent air flow across the roof and down the back.

BUT....I forgot what they were called, where to get them, or anything.

Can anyone tell me what they are called so I can gogle them?
 

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Discussion Starter #2
I found it. Its called "Airtab" Gonna try them. I was wrong, they apply to the trailing edge, not on the leading edge. Might do something on the front of the front wheel wells to smooth the air across the opening.
 

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They're vortex generators, and add energy to the airflow to reduce the separation of the flow from the surface. On a regular sedan shaped car, you can usefully put them at the back of the roof to reduce the separation as the air flows down the back window. They're not needed on the Insight, because it has a gentle rear window slope that in itself prevents separation. Putting them at the back is useless because you are unavoidably going to get separation at the Kamm transition anyway.

They come stock on some versions of the Mitsubishi EVO; here's a paper that talks about them...
http://www.mitsubishi-motors.com/corpor ... 16E_03.pdf
 

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Discussion Starter #5
Even limited success would be fine as they are quite cheap at $2.75 each. :lol:
 

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Discussion Starter #6
Dougie said:
They're vortex generators, and add energy to the airflow to reduce the separation of the flow from the surface.
The Airtab site states that they improve the air flow off the BACK edge of the vehicle reducing the drag at that edge caused by turbulence. If that is the case then they would be used at the very back edge of the car and perhaps the front edge of the front wheel wells to facilitate air flow off the aft edge of those two surfaces, not for reattaching air flow to the body. On trucks they are attached at the aft edge of the cab and on the aft edge of the trailer so they are not reattaching air to anything.

I also think they might be useful on the aft edge of the splash pan to facilitate air flow along the bottom of the car.

They are so cheap that I can buy 10 of them for less than $30 to experiment with. If there is any improvement, even minor, the cost of the Airtabs is inconsequential.

I will report back in a couple of months. Hopefully with pictures of airflow ribbons on the car.
 

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There are already bumps on the bottom of the bumper that do the same thing... But I encourage you to experiment!

When I was driving around with airflow tufts on my car, I decided that the biggest issue was flow separation at the sides of the windshield. So you might try putting them there...
 

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Discussion Starter #8
Thanks for the "heads up" I will try them there. It may be a bit difficult however since they would have to be on the glass to be in the right place and then I couldn't roll down the window. Maybe they could be fastened to the pillar in such a way that they lay just a few microns away from the glass. But there is also the problem of visibility past . It may be tricky. Maybe a few "Wrens Teeth" along the pillar itself........
 

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I read an online article at Autospeed website that mentioned they tried testing the Airtabs on a gen 1 Insight. Used at the back worsened observed FE. Used at the front just under the front air dam on the bottom, 4 tabs (I believe) used, didn't noticeably increase FE, tester noted that he recorded the best FE at the time with them in front but couldn't tell if it was traffic/driving style that was more of a factor than the Airtabs. The tester did note that using the tabs in the front did have a subjective improvement in higher speed stability when next to big semis and such... I'm looking at using them too in the front. Maybe in the sides as was mentioned as well. Did you ever try them out?

It would be nice to put a venturi tunnel under the Insight to improve grip at highway speeds without increasing drag too much. But then again, it might overload the short supsension travel of the rear suspension especially when loaded. The Insight has enough advances and technology to tempt one, but still leaving a bit wanting for those who want that little bit more... But you still gotta respect the engineers for what they did do with this car amongst the gorrillas... I like gorrillas too but just can't justify the gas bill, and don't like standing still with technology...
 

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A friend of mines used them on a geo metro. It just kept the rear window clear when it rained. No mpg increases.
 

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The merits of vortex generators are well understood when it comes to aircraft. Do a search for this on-line and many airplanes use these as it allows an airplane to maintain the same amount of lift at slower air speeds, thus making for safer takes-offs and landings.

When one try's an AirTab on a car, the LOCATION is very important. If an AirTab is placed on the Kammback on the rear window of the Insight, no appreciable improvement will be noticed. That is because a Kammback also makes the air leaving the back of the car less lossy. If you want the air moving over a smooth surface to break free cleanly, then apply a Kammback shape to it.

For those instances where this is not possible, 1) and the surface curves smoothly away, 2) and you don't want to alter that shape into a Kammback, 3) then apply a vortex generator there. This will energize the air and allow it adhere for a longer distance before breaking free into the moving air.

So when saying that a vortex generator works or doesn't work, it's important to understand 1) what the problem is, 2) what you want to do about it, 3) determine if you need a Kammback shape or 4) add a vortex generator to reduce the wake size.

Vortex generators certainly work on airplanes and placed carefully can also be made to work on cars.

The rounding trailing edge of the Insight bumper is a perfect place for a generator or two. Excite the air and reduce the wake size. A Kammback shape there would also accomplish the same thing, and allow the air to separate more cleanly.

Please note that Kammbacks or vortex generators are never a replacement for a true tear-drop shaped body. A Kammback shape is only used if the tear-drop shape can not be full length.

Just my $.02

Jim.
 

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Yeah I remember seeing my first vortex generators on crop dusters wing's and asked my dad about them. He said that they are used to help keep airflow attached at lower speeds, for an airplane, to help it maintain lift when manuvering and I suppose landing/taking off. Almost a decade ago I remember seeing some metal ones advertised mainly for trucks and semis. When I inquired about them he said he couldn't sell it to car owners yet as they were afraid of legal issues with how sharp they were and someone accidentally cutting themselves on them. I'm guessing that the F18 Hornet uses its forward strakes to generate vortices that enhance manuverability I believe. The dark art of aerodynamics! We'll we got a big leg up on the competition in that department. One of these days, I will try some Airtabs. After these then riblets, then I'll run her through a hail storm! Just kidding.
 

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I think an area to focus on the Insight would be the rear bumper high radius curves. I think a sharper definition to that corner would pay dividends. You only have to look at the Gen 3 Prius and the VW 1 litre car for similar ideas. Even the Range Rover sports have a sharp edge to control flow seperation on the D posts as manufacturers pay more attention to controlling vortex generation behind the car.

On that note a colleague (aerodynamic engineer at Jaguar Land Rover) of mine found some info on an Insight they ran at the wind tunnel at MIRA. He's trying to find the main report on what was tried but essentially the standard road spec car was found to have a Cd of 0.24 in the tunnel. He also suggested a radiator block - I said that most owners do actually do that already.
 

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Take a look at the back side of the 2008 Honda Civic EX. Notice how much sharper the whole trailing edge of the trunk and rear 1/4 panels are? The designers are slowly getting us to the classic Kammback shape.

I believe some of the old Corvettes have this shape along the top of the truck trailing edge and 1/4 panel sides. But the large radius on the underside of the newer Corvettes is too rounded and not good for good flow separation when the air leaves the car.

Jim.
 

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You think the addition of the rear diffusers from the C5/C6 racing programs would help negate some of the effect the larger underside radius of the newer vettes you mention?
 

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If I had to guess, I think the large radius is there for higher downforce, and may upset the balance of the car at high speeds if this shape is altered.

However, that same shape also reduces the gas mileage, so another compromise!!

Jim.
 
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