[BabyDiesel]

Originally Posted by freebeard

This is just a working hypothesis, but a longitudinal fence like NASCAR uses to kill lift when the car goes sideways, grown and rolled or canted in an outward direction opposite the tendency of the vortex to roll inward. As such:


http://blog.caranddriver.com/lemons-detroit-day-1-speedycop-civic-metsho-tempo-dmc-12-leading-classes/

Not trying to be a jerk, but that appears that it would promote vortices spinning the opposite way Maybe not if they were straight up...

Originally Posted by aerohead

Vorticity is caused by pressure differentials at flow intersections.
The lowest pressures are on the roof.
If the rear slope is too steep,the flow will want to separate do to too fast a pressure rise.
At separation,everything downstream takes on the low pressure of the separation line.
Higher pressure in the side flow 'see's' the low pressure on the roof and wants to flow there.
Where the two streams comingle,they wrap up into swirling flow as the high pressure side air races into the low pressure top air.
Generous edge rounding helps mitigate vorticity if contours are gentle but can't prevent them if the roof is too steep.
Only lofting the roofline up to the streamline path can kill the vorticity.
Like Kamm and Koenig-Fachsenfeld did.

Aerohead, I believe we have talked about this in my ZX2 Aerodynamic thread. We discussed rounding the boat tail gently from the body shape as it went farther from the car. I'll see if I can find it.

Here: http://ecomodder.com/forum/showthrea...tml#post488018

*From a practical standpoint,I think you're looking at using whatever plan taper Ford put in the Escort and blend from there.
*As to the upper radii,you could do as Jaray did in 1922.Take your more rectangular cross-section,and gently morph it into a more organic half-body cross-section as the body proceeds rearward.HVAC sheetmetal shops do this all the time in commercial/industrial ductwork when the dust must enter a chase or wall for part of the run.You can't do it with plumbing due to the pressure balooning the flat walls,but with air,it's a snap!
*The tumblehome can progressively increase as Honda does with their FIT,and the edge radii can also grow incrementally as she goes further rearwards.I worked this into the flying buttresses on the CRX to pretty good effect.

No idea it could have a huge effect on Cd. This seems to be the way to go in Kammback/boat tail design. I wonder if that is one reason Darin's boat tail did not perform as well as we hoped?

Originally Posted by 2000mc

The spoiler also raises and extends my deck lid, which ends with a much smaller radius than the rounded naked trunk lid. So whether or not I made a recirculating bubble on top of the trunk, the greater effect could be from how the spoiler effects the bubble behind the car. The effect behind the car might be positive enough that if I produced a negative effect on top of the trunk, the net result is still positive... I figure it could be very potentially misleading without tufting the whole back of the car and filming from a chase vehicle, which we can do the next time you're in Kansas

I am thinking about going out to Idaho next year to meet with Pgfpro, that is IF I can get a turbo, injectors, tuning software, etc. I'd stop by to do some tuft testing for sure!

Your spoiler resembles a Civic Hybrid spoiler, in a way. It is one of the things they use to lower Cd, so I can believe it improved Cd by ~0.1 on your Saturn and you caught it at the pump.