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Originally Posted by Wildncrazy,Jun 29 2006, 07:15 AM
I know that if the angle of the diffuser is between 8-12 degrees then it is possible to get downforce without the drag that you get from a wing
This is something of a myth floating around the track world -- "underbody aero does not create drag". This is not true. Any lift or downforce is going to create drag. The question is how much, and whether one lift mechinism is more efficient than another one.
I had a before and after run at Gingerman Raceway. There was no noticeable difference in the low speed turns (turns 2 and 3), but highspeed turns there was definitely more grip available. The brakes also could go a whole session without fade. It helped a lot down the front and back straights in cooling off the brakes. I really need a vented hood now though because of the loss of airflow from the bottom.
I have a Top Secret GT wing going on, and hopefully I can get the Axle rear diffuser from another board member to complete my underbody aero. I might pick up another rear diffuser down the road if I don't get the Axle. The GT wing should be enough for right now.
I also added J's carbon twin canards and the front feels more planted on the highway. More testing on those next weekend.
Originally Posted by mikegarrison,Jun 30 2006, 03:49 AM
This is something of a myth floating around the track world -- "underbody aero does not create drag". This is not true. Any lift or downforce is going to create drag. The question is how much, and whether one lift mechinism is more efficient than another one.
Underbody diffusers create less drag and more downforce than the same car w/o the diffusers. Properly designed of course. The only way to not create any kind of drag would be to drive in a vacuum or to not have any surface area on the car.
Underbody diffusers create less drag and more downforce than the same car w/o the diffusers. Properly designed of course. The only way to not create any kind of drag would be to drive in a vacuum or to not have any surface area on the car.
There are three drag mechanisms that are important here:
1) induced drag -- drag due to lift
2) form drag -- drag due to the "hole" the car leaves in the air behind it
3) skin friction drag -- drag due to friction on the wetted surface of the body
(Another one, wave drag, only applies at much faster speeds.)
The myth I am talking about is the idea that the lift (downforce) of the diffuser comes for free while the lift of the wing induces drag. This is not true. All lift comes with drag, but sometimes it can be more efficiently created than other times.
And when I say all lift comes with drag, that includes the unwanted positive lift of the stock body. In fact, if you could carefully reduce that lift down to zero (no lift, no downforce) you might well lower the total drag of the car at the same time as you are aerodynamically improving the grip.
If the diffuser reduces form drag or skin friction drag, those reductions could reduce total drag even if it creates extra induced drag.
06-29-2006, 04:04 PM
