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Old 01-25-2012, 01:59 PM   #1 (permalink)
tru
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Convertibles, the ultimate in aerodynamics?

I was following a convertible BMW into work today and could help but think of how perfect they would be for aeromodders. its almost a blank template with the top down, has anyone modded one?

Also, could someone show what a convertible looks like in a CFD model? (top down of course)

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Old 01-25-2012, 02:07 PM   #2 (permalink)
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You can chop the top off anything!

And CFD? Don't need it. Imagine a big bowl of spaghetti following a convertible around.
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Old 01-25-2012, 02:26 PM   #3 (permalink)
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Old 01-25-2012, 02:45 PM   #4 (permalink)
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Convertibles would be fine, as long as you removed the windshield and completely smoothed over the whole passenger compartment at the level of the top of the doors.

The windshield being there means that the A (frontal area) is just about the same as the full-roofed version of the car. All of the non-smooth shapes in the passenger compartment (seats, roll bar if any, boot for the top or the folded-up top, and of course the driver and passengers!) increase the Cd a whole lot. So on the whole, convertibles are rather horrible for aerodynamics.

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Old 01-25-2012, 02:51 PM   #5 (permalink)
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Please, pretty please, don't ruin a convertible ! The whole point is to have your hair in the air.

Aerodynamic drag would be the least of my worries while driving one.
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Old 01-25-2012, 02:55 PM   #6 (permalink)
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with the window in place, wouldnt the passenger compartment act like a pickup bed and develop a nice cushion of air? i'd like to see it, even if it does look like a spaghetti monster if someone would be willing.
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Old 01-25-2012, 03:28 PM   #7 (permalink)
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They've been taking advantage of drop-tops for over half a century.

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Old 01-25-2012, 04:10 PM   #8 (permalink)
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...ask the NASCAR guys and they'll tell you "...HELL NO..." on racing convertibles!

...The early NASCAR race venues had two catagories, hardtops and convertibles, and NASCAR -- literally -- had to "pay" drivers to race convertibles because the aero "drag" was so bad the cars weren't competitive [story relayed from Richard Petty].
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Old 01-25-2012, 04:12 PM   #9 (permalink)
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The '64 Spitfire I used to have would have been great for aeromods: remove two nuts and the entire windshield and frame assy pulled off; and the cockpit was lined with snaps for the tonneau I had.
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Old 01-25-2012, 04:12 PM   #10 (permalink)
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Quote:
Originally Posted by tru View Post
with the window in place, wouldnt the passenger compartment act like a pickup bed and develop a nice cushion of air? i'd like to see it, even if it does look like a spaghetti monster if someone would be willing.
To some extent, yes. But like a truck, you need a "tailgate" to build up that pressure bubble. Some convertible cars have a solid glass (plexi? polycarbonate?) panel behind the seats, to create that pressure bubble. It's not as efficient as a solid roof, though.

See this image for an example: http://content.mamotorworks.com/img300/FR4154.jpg

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