Thread: tuft testing
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Old 09-26-2010, 11:08 PM   #7 (permalink)
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Originally Posted by Varn View Post
Hi Otto,
I did notice that the wand when held down near the front wheel gave me a lot of swirling. I couldn't observe the any lower than about the top half.

There is a short smooth belly pan from the grill at the bottom to the radiator.

A couple of weeks ago I had removed the rear mud deflectors and screwed them in front of the front wheel. I thought that they might work out perfectly but they were tilted as the front of the body curls around underneath more than the shape does further back. Also they were only half as wide as the tire.

I am in the process of fabricating a custom wheel deflector. I used 9 gauge wire and bent and welded it into shape. I am hand sewing some dacron fabric onto it. I will then shrink the fabric a bit with heat then lay on some composite cloth and wet it out with epoxy. The wire and fabric can be removed after it cures.

I have taken some photos of the frame and will try and document it. I realize that these are not the photos that you are asking about. I might suggest that pictures of air flow around my front tires may not be relevant to your car.

It truly has not been tuft tested but the shape makes some sense. I may create a rubber dam under the front.
wire only:

Here is the form that I am going to carbon.

Thanks, Varn, I look forward to seeing how this works out.

Reason I asked in the first place is concern after seeing pics in Hucho of smoke trails on an Opel Calibra and in his airflow sketches, which show undercar flow at the nose to splay outboard at about 60 degrees off centerline axis. That's right, about 60 degrees, such that apparently the bow wave splatters off the pavement and flow hits the inner side of the wheels at about a 60 degree angle. So, wheel fairings should evidently be canted inboard (pigeon-toed) to fair the wheels from the relative wind as it occurs in that region.

Hucho also says wheel drag doubles at only a 15 degree angle of incidence, yet the actual flow to the wheels is about 60 degrees, nearly as bad as hanging the wheels broadside into the breeze. This is a big deal, and so proper fairing orientation could potentially yield big benefits.

So, please keep us posted, esp. regarding actual tuft results under the nose.

Maybe tape some tufts to the bottom of the nose or on inverted golf tees, and photograph or videotape as the car drives past?
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