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Old 11-03-2008, 06:48 AM   #1 (permalink)
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slopeing dams: butt-o-meter tells me somethings wrong

i've been experimenting over the course of this tank with different wheel dam arangements

when i did my aluminum undertray the sheet of aluminum wasn't wide enough to cover the areas in front of the wheels . i've recently closed off these areas and added small dams in front of the wheels... they don't seem to yield a spectacular result but they don't really seem to harm either.

so for a while i've been playing with the idea of adding a more sloping fairing in front of the wheels.

the panels attach to the back of the bumper with a single L bracket and the dams are made from a plastic L beam which spans the gap between the edge of the bumper and the undertray. the coroplast panel simply lays on top of this and is wedged between the bumper and the dam, says in place rather well.

so what id did was take it off make two triangular sides and added another strip of coroplast to the back with the same height as the dam so i could screw that to the horizontal part of the dam

for lack of a good picture here's a sketch
before:

now:


the dam was a little less wide than the sheet so i may have added a little frontal area but the idea was that the dam might be to small in the first place and cause air to be deflected into the inner wheelwell, which looking at dams on bmw's audis, and some fords to name a few, isn't a good idea, as theres dams warp more or less around the inner wheelwell.

anyway, this morning driving the new configuration didn't feel very confident... the car drove acceptable, but it seemed as though it needed more power to maintain a certain speed, which to the butt o meter felt like there was more drag.

i can easily convert back to the previous version but i'm a little confused as to what i should aim for. perhaps a fairing that splits the air left/right would be better...

any ideas on what else i could try... perhaps the inner edge is the problem and i'd have to addopt a more smooth transition... after all you don't see dolphins with square edges

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Old 11-03-2008, 10:47 AM   #2 (permalink)
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The thing about sloping ones is that it simply redirects the air towards the bottom of the tire, not towards outside of it (away from it).

I just put a simple flat splash guard, but much bigger than yours in the first pic, for sake of easyness.

But I would think that a Convex shape would be the best by far since it would direct air towards the sides (away from the tire). It just becomes a little more complicated to do so
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Old 11-03-2008, 12:01 PM   #3 (permalink)
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When airflow hits the fairing, it is also directed to the sides as there is nothing preventing it from escaping that way. Since we can probably assume the pressure on both sides of the fairings is lower than on the fairing itself, there will be diagonal flow on both sides. Your fairings having sharp edges, there will be formation of vortices, which could be the problem.
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Old 11-03-2008, 12:28 PM   #4 (permalink)
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that might be it! the inner vortex could actially be drawn inside the wheelwell!!!...

thanx for that insight!!!

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