Quote:
Originally Posted by silverinsight2
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Quote:
Originally Posted by aerohead
Robert,I don't have my book with me,but my failing memory is emphasizing that nobody would see attached flow with more than 4-degrees up-sweep on a diffuser.
The other thing mentioned,is that the diffuser is worthless without a complete and well-executed bellypan ahead of it.
I like the strakes.This is something Dr. Morelli used on his Cd 0.23 CNR car for directional stability in crosswinds.
I don't know about the racer stuff.I 'think' that in racing,that allowing the low pressure of the wake to be communicated forward under the car could help with downforce on the track,especially if spoiler dimensions were limited by the sanctioning body,and this would be an advantage during high-speed cornering.
So my intuition tells me that going over 4-degrees is a downforce issue.
And certainly,'departure' angles for the real world ( 10-degrees ) severely limit diffuser angles unless 'active.'
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Quote:
Originally Posted by RobertSmalls
Piwoslaw posted a graph from Piechna's book:
This agrees with my tuft testing as well. For minimum drag, 4° looks great. Even up to 7° looks fine. But things do not rapidly fall apart until 15°. From 15-30°, it looks like you'd be better off just not having an underside. I will avoid these angles. |
This seems to match up with the Piechna graph posted earlier if I read it correctly. I always wondered why sports car diffusers were so much steeper than the oft quoted 4º ideal. A friend has a Lotus with a diffuser like the one in the photo above. It also has a factory belly pan and a huge (for the size of the car) rear spoiler. It would seem Lotus is willing to sacrifice low drag for downforce.