Old Sep 19, 2010 | 04:39 PM
  #19 (permalink)  
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onehundred80
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From: Ontario
Default Re: Found out how much downforce the wing puts out

Originally Posted by synikol
I have an observation regarding the rear spoiler / down force issue. Before I say this, let me qualify it by saying I am not a mathematician, but I do enjoy fig newtons.

Yesterday I found myself at the car wash without having brought my detail kit with me. I live very near the George Bush (boo!) Tollway in Dallas, so my plan was to clean the car, leave it wet, and "air dry" it by driving 90 mph for an extended period of time. We've all done it, so please don't send me a link for microfiber towels!

Anyway, it worked like a champ EXCEPT for the rear glass on the hatch. The water droplets left from the car wash literally did not move an inch and virtually dried in place.

I've looked for some type of wind tunnel test videos on our car to no avail. But because of what I saw, and the fact that the rear wing is directly below and on top of the rear glass, I don't believe that the entire surface of the wing sees an appreciable amount of down force-generating air. I do think that the outside edge might... or maybe the outer half (if you drew a line across it in the center), but not all of it. I would guess the only way to really test this would be to tape multiple one inch long pieces of ribbon all over the rear wing and watch how they move while driving. This will also probably make the car look like a runaway gay pride float, so I probably won't be attempting it.

I could be wrong.
The water beads are in the boundary layer, this is a quite thin layer that exists over surfaces that have moving air or water over them in a lamina flow. Increased flow results in the layer getting thinner and turbulence occurring. You just wasn't going fast enough.

The water beads are really evident on the hood, you can see beads just idly wandering rearward at a speed that is a small fraction of the forward velocity of the car.
I had a wasp clinging onto the wind shield yesterday and he had no trouble to stay there at 55 mph. He may have pooped himself though.


This is also an area with less air pressure and air under the car will push the car away from the road.
That's why the wing is there, to disrupt the flow and minimize the low air pressure.
 
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