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.  |
1.Was the added coroplast covering the dog leg in the muffler pipe? Were the other hot bits covered or exposed? Turbulent flow at the start of the rise should be minimized. You know that, of course.
2. Outboard strakes are really wheel fairings IMO. My suggestion is to use two or three more centrally located.
3. This may be contentious (stupid), but consider making the bottom diffuser with small slots, pin holes, or screen on one side of the coroplast. Seal one open edge with RTV silicon, create a manifold out of split soft tubing on the other. Use
boundary layer control with vacuum created by flow thru the boat tail, or engine vacuum.