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Great article on downforce (Read 2944 times)
Noah
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Great article on downforce
Jun 12th, 2016 at 1:26pm
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https://nasaspeed.news/tech/aero/air-dams-splitters-spoilers-and-wings-downforce
-increases-grip-grip-decreases-lap-times-and-isnt-that-the-whole-point/
  

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Raye
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Re: Great article on downforce
Reply #1 - Sep 26th, 2016 at 12:07am
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Great article... Enjoyed reading...
Balance is key it seem and there is much science to this.
  

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STEELSHOE
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Re: Great article on downforce
Reply #2 - Jan 9th, 2017 at 8:14pm
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Article was fairly accurate for someone to read and understand that isn't technical.  Down force and drag do go up with the square of velocity, in terms of feet per second, or meters per second.  But only to a point.  Certain other criteria must be met for that to be true.  That is a correct air flow to the parts creating down force.  Pretty easy on the front of the car, but really difficult on the rear.  If you have detached or turbulent flow to the rear spoiler or wing, your aero device isn't going to work very well.  And this flow changes with the speed of the car.  Once the flow is detached, the drag goes up, and the efficiency of your spoiler or wing goes down.  So if you test for this, you must test the flow at all the speeds your car operates in.  Remember also that a wing or spoiler or air dam affects the air stream in front of and behind your device.  How do you know what the flow is on your car?  Forget the smoke and the wind tunnel.  The physics is backwards, even if that will give you some sort of feeling something is happening.  Go get a roll of small diameter yarn that is the opposite color of your car, and a get a roll of masking tape.  Cut pieces of yarn 2 to 3 inches long and tape the front edge down.  Place these all over the car.  Get a GO PRO camera, and make a mount so you can video all this.  Mount it far enough from the surface so that the camera does not interfere with the air flow.  Or get another car to follow and record all this.  If you use another car to video, make sure it is at least two car lengths away.  As you drive the car at different speeds, you want to watch the yarn.  You want the yarn to stay against the surface of the car.  You want it to be stable, as in not waving around.  If the yarn does this, the air flow is attached, and that is a good thing.  If the yarn lifts up and or waves around, it is detached, and that is a bad thing.  More attached flow means less drag.  The rear spoiler may help attach the flow to the rear window.  A wing may have a harder time attaching that flow.  I say may.  I haven't tested this on my car.  I have done extensive testing on race cars and airplanes, which led to drastic improvements to drag and aerodynamic efficiency.  I mean drastic.  As for wings and spoilers, wider ( span ) is better.  But the width ( chord ) is also very important.  The narrower the chord is, the more difficult it is to get the air to work for you.  This gets in to something called Reynolds Number. Continued
  
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STEELSHOE
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Re: Great article on downforce
Reply #3 - Jan 9th, 2017 at 8:21pm
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The smaller chord needs a different airfoil to work correctly.  In simple terms, there isn't enough time for the air to follow a small chord correctly.  So the air separates from that airfoil easier.  When the air separates, the efficiency goes down the toilet.  Attached air flow is king.  It is remarkable how a device can affect the air in front of and behind.  And just as remarkable how far in front of and behind the air is changed.  It is a very complex problem.  But for about 5 bucks, you can skip the wind tunnel and learn more about what is really going  on.  And if you change the size, shape, location, or angle, the whole test needs to be done over again.  Everything changes.  Don't assume.  End plates don't do much to a properly engineered aero device.
  
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Noah
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Re: Great article on downforce
Reply #4 - Jan 11th, 2017 at 3:08am
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Great insights Steelshoe. Thanks for your contribution. I think I'll perform these aero tests you suggest in the springtime.
  

non-purist retro-grouch with questionable taste
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STEELSHOE
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Re: Great article on downforce
Reply #5 - Jan 11th, 2017 at 10:47am
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Would love to see the pictures you get
  
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mike p
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Re: Great article on downforce
Reply #6 - Apr 21st, 2017 at 5:50am
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nice!
  
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