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Old 08-20-2011, 03:06 PM   #192 (permalink)
aerohead
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filling

Quote:
Originally Posted by Fat Charlie View Post
Even with detached airflow, wouldn't there still be a real benefit to filling in the wake? It wouldn't be optimal, but it looks a lot cleaner than simply leaving a large square hanging out back there to hold you back. I'd expect that "slightly detached" airflow would be a whole lot better than "completely abandoned" airflow. I'm thinking along the lines of "anything that brings you closer to the template helps" with the spoilers.

I'm actually asking a question here (not putting forth an argument)- I'm ignorant enough that I only have aerodynamic questions, not opinions.
In Hucho's 2nd Edition,on page 195 of Chapter 4,he mentions an open convertible in the wind tunnel,and if people or mannequins are placed in the seats,they will 'Fill up' the hollow space behind the windshield and should improve flow,lessen drag.
It's the only place in the book where I can find mention of something I've been calling 'stuffing the wake.'
I started thinking about it after reading about the aero mods to the Chrysler Airflow,DeSoto development vehicle.
An 'imperfect' but better roofline was grafted over the existing body ( just as Volkswagen is doing for the 2012 Beetle )and then an 'imperfect' 'stinger' boat-tail was added as well.
The car never achieved as low a Cd as it might for its length,but at Cd 0.244 in 1934 it was pretty amazing.
So I interpreted that even a non-ideal tail could still cut drag.
This undermines the findings of Fachsenfeld's boss,where Kamm would later come to work,who cut the tail off a wind tunnel model of a car and watched its Cd drop from 0.29,to 0.23.They don't show the car so it's hard to know what they actually did.
Hucho shows a range of Cds for the Golf/Rabbit.The lowest Cd is at the 'Template'.Cd increases as the roof gets steeper in slope,from 0.34,all the way down to 0.42.
Anything 'higher' than VW's production slope would be better even though not ideal.And any of these alternate rooflines would be 'stuffing the wake.'
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