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Old 06-29-2012, 01:28 PM   #21 (permalink)
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What did you use fpor the Kammback and where did you get it? I was looking at lowes for some plexiglass and they have lexan (I think). Anyway, a sheet large enough to do the kammback is about $50. That just seems like a lot of cash. Anyway, let me know what you did! Thanks.

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Old 07-02-2012, 11:55 PM   #22 (permalink)
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The kamm is actually just corrugated plastic. I didn't bother making it clear since at the distance it goes down the back window, there is still decent visibility out of the back window.
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Old 07-03-2012, 09:47 PM   #23 (permalink)
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what are the smooth wheel covers made of (green) in your first post?
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Old 07-03-2012, 11:24 PM   #24 (permalink)
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Also just corrugated plastic, and some zip ties
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Old 07-05-2012, 08:39 AM   #25 (permalink)
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A few more tanks, one at 41.7 - More city driving than normal.
43.4 - Slightly better than "before" average.
44.0 - Same deal, bit higher than previous average.
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Old 07-05-2012, 03:24 PM   #26 (permalink)
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Oh and dohcsvt, I got the corrugated plastic at home depot. A 4 x 8 sheet of it was $19, I got two and have done the majority of a belly pan, wheel covers and wheel skirts with it as well.
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Old 07-05-2012, 05:34 PM   #27 (permalink)
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Considering you somehow coerced a friend into stop watch duty, it shouldn't be too hard to tuft test your kammback. This will tell you if the angle is right- and perhaps allow you more improvement.

I would also encourage you to tuft test the rear of the car without any aero aids. If you can figure out where the air starts to get turbulent behind the C Pillar, you can find where to end the NASCAR spoiler. If the air is clean and attached, no spoiler needed. You just want to trap a vortex behind your turbulent window to act as a virtual kammback.

Should this work, you can use a piece of stiff, clear acrylic instead of coroplast. This will allow you full vision while taking advantage of the aero benefits and Coventry data on base plates.

I do not know how big or in what shape you should build a spoiler. You might, however, be able to rig up a test apparatus to find out. Instead of tuft testing only on the surface, you could try another technique the professionals use- 3D tuft testing.

Looking through some old Car Styling issues, I found these photos. Issue 2009.1, page 16.

From a square framework, they strung cables vertically behind the vehicle. From the cables are attached tufts about 5cm apart from each other in a careful array. You can see that the ones going straight back are "good" flow and those that are fluttering exhibit turbulence. By attaching a frame like this to the top of your trunk you may be able to see where to build a spoiler, or even kammback.



I don't know if this will work in real world situations or if it's purely a closed-environment test. Maybe aerohead can weigh in on this; it might be a fun thing to try.

PS- I'm also interested in seeing the raw data. 3-4% isn't much, and if the data varies a bit those kind of changes may not be conclusive.
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Last edited by Sven7; 07-05-2012 at 05:46 PM..
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Old 07-05-2012, 07:29 PM   #28 (permalink)
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frame

Quote:
Originally Posted by Sven7 View Post
Considering you somehow coerced a friend into stop watch duty, it shouldn't be too hard to tuft test your kammback. This will tell you if the angle is right- and perhaps allow you more improvement.

I would also encourage you to tuft test the rear of the car without any aero aids. If you can figure out where the air starts to get turbulent behind the C Pillar, you can find where to end the NASCAR spoiler. If the air is clean and attached, no spoiler needed. You just want to trap a vortex behind your turbulent window to act as a virtual kammback.

Should this work, you can use a piece of stiff, clear acrylic instead of coroplast. This will allow you full vision while taking advantage of the aero benefits and Coventry data on base plates.

I do not know how big or in what shape you should build a spoiler. You might, however, be able to rig up a test apparatus to find out. Instead of tuft testing only on the surface, you could try another technique the professionals use- 3D tuft testing.

Looking through some old Car Styling issues, I found these photos. Issue 2009.1, page 16.

From a square framework, they strung cables vertically behind the vehicle. From the cables are attached tufts about 5cm apart from each other in a careful array. You can see that the ones going straight back are "good" flow and those that are fluttering exhibit turbulence. By attaching a frame like this to the top of your trunk you may be able to see where to build a spoiler, or even kammback.



I don't know if this will work in real world situations or if it's purely a closed-environment test. Maybe aerohead can weigh in on this; it might be a fun thing to try.

PS- I'm also interested in seeing the raw data. 3-4% isn't much, and if the data varies a bit those kind of changes may not be conclusive.
If the frame could be examined at a number of locations from the backlight header rearwards,in the absence of smoke,you could visualize what the flow was doing.
As to a 'kicker' type spoiler,without a force balance it would be tough to know if you had gone too far with the angle or sizing.
The K-form roofline is a known quantity,so it's easier to predict the outcome of that kind of mod,whereas spoilers would be more of a challenge.
Re-attachment would be part of the problem,but just getting 'enough' would be the tough part.
Longitudinal vortices would be the boogaboo.This is where the frame might allow their visualization and tailoring of the spoiler.Tough assignment!
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Old 07-05-2012, 07:46 PM   #29 (permalink)
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Thanks, Phil. Clearly Mazda has done something screwy to keep attachment over that steep rear window, so I don't recommend that. I was thinking of a sort of base plate as in the Coventry thing, combined with the NASCAR approach.

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