Quote:
Originally Posted by RobertSmalls
Aerohead,
I'm happy to say that the up-sweep starts around the middle of the gas tank, right behind the front seats. It's a gradual up-sweep, gradually working its way from 0° to 7°, from 6" ground clearance to 10". I think this is an unconventionally good feature, and I hope it will allow me to have an unconventionally short boat tail.
I've added coroplast paneling to cover the rear axle, making a smooth transition from gas tank to spare tire box. There's still a lot of room for improvement under there, like in front of the gas tank, and around the exhaust. All four wheel wells are also wide open.
I'd offer my interpretation of the video, but I really want to hear from experienced tuft testers. I'm not sure that the 4° run was good, nor that the 13° run was bad. Tufts were lively in all runs, but not consistently attached or reversed in any of the runs.
You mean to suggest strakes in my diffuser? Hmm. That led me to read an eng-tips forum post on diffusers. Diffusers reduce drag and lift relative to a flat underbody. 7-10° is recommended, at least in the context of race cars with low ground clearance, looking to maximize downforce.
Strakes? They're supposed to make the diffuser less sensitive to body pitch and probably crosswinds. Okay, they're easy enough to add on. I will run at least two strakes, in the form of deflectors behind my rear tires. Speaking of which, I couldn't tell from the video at what angle to install those deflectors. I guess I'll have to build a prototype and tuft-test it.  |
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.'