Quote:
Originally Posted by fbov
Aerohead, I didn't see your reply... and you've listed conclusions exactly describing the car, the results, and the opportunities I see as well. Had to look up fineness ratio...
I've already noticed what gets dirty/what stays clean (the back glass). The idea would be to extend the rear quarter panels into a truncated boat tail kind of structure?
My goal in this discussion is to understand the principles and optimum approaches, regardless what I actually do to the car, so whatever I end up with will be, to some extent, based on understanding of the issues as well as external factors (e.g. I plan to stay married).
thanks!
Frnak
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Yes,the extension of the body is the ticket.
Pressure drag dominates aerodynamic drag,and the base pressure behind the car is the culprit;which in turn is governed by the separation line and magnitude of the wake.
The premise of streamlining is to reduce or eliminate the separation,thereby reducing or eliminating the turbulent wake altogether.
Fachsenfeld and Kamm,together at the FKFS (of which Daimler-Benz now has Kamm's wind tunnel at Stuttgart) started with a complete streamline body of revolution half-body of Cd 0.12 and morphed it into a more rectangular body section where the occupants would be,and chopped the tail off to help with traffic and parking issues.
They settled upon a body chopped off where the wake had a cross-sectional area equal to 50% of the frontal area of the car (about 12.5 sq-ft for Kamm's K-form cars).
The best K-car ended up at Cd 0.23 (about twice the drag of the original half-body).
Koening-Fachsenfeld envisioned and patented an inflatable tail to get the boat-tailing back out closer to that of he original half-body.
This is what Hucho's been advocating that the automotive community reconsider, since the mid-1980s.
Hucho reports in his book,that you'll achieve your minimum drag when the car has a length-to-height ratio of 5:1.Or an effective fineness ratio of 2.5:1.
After that,you go after wheel/tire drag with a vengeance.
This is a long way of saying that your ultimate drag will come down to how much elongation you can personally stomach,bearing in mind that some of that length can be active aerodynamics.
Doing everything basjoos has done with his AeroCivic,ahead of the boat tail would buy you an iron-clad insurance policy for the aft-body mods.
