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Old 09-15-2012, 09:34 AM   #1 (permalink)
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Tuft Test YouTube Civic Kamm Roof Extension

Thread title says it all.

1st video, Tuft Test Kamm Roof Extension on '97 Civic HX Coupe - YouTube



and
I think this one shows better detail:
2nd video, Tuft Test Kamm Roof Extension on '97 Civic HX Coupe - YouTube



These are HD videos, there should be plenty detail.

I'll try figure out how to make the YouTube screens show up right here in this thread.

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Last edited by brucepick; 09-15-2012 at 10:59 AM..
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Old 09-15-2012, 10:51 PM   #2 (permalink)
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Way, way-cool. When I look at the way the tufts behave at the trailing edge of the kam, I wonder if the flow is worse than stock. I ask because of this image:



This is a pic of tufts as they stuck to my car's dewy surface one morning last year, peak speed was about 45mph, maybe 50mph. The rear window seems much cleaner than I thought it would be. Not very good data, but something to think about.

Could you do a test with more of the rear of the car covered and with the kamm and no kamm. (Probably not, that's a tall order!)

Thanks, man!!
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Old 09-16-2012, 12:21 AM   #3 (permalink)
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Quote:
I'll try figure out how to make the YouTube screens show up right here in this thread.
When you do, as ChazInMT demonstrated, I get a blank frame that says "A plugin is needed to get this content. Install Plugin...", and yet the link just above that displays it in YouTube works just fine.

I think the embed forces it to Flash™, but if you go to YouTube it queries the browser and uses something that will always work. Flash™ must die.
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Old 09-16-2012, 02:21 AM   #4 (permalink)
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Quote:
Originally Posted by California98Civic View Post
When I look at the way the tufts behave at the trailing edge of the kam, I wonder if the flow is worse than stock. I ask because of this image:

Assuming that Brucepick's Kammback has the ideal 12-14° degree slope, then the stock Civic's effective rear slope is greater. Since Cal98's tuft testing showed that the slope isn't steep enough to get separation, then the air flow must be producing lift.


So the Kammback reduces lift and Cx, but at the cost of larger wake area. Which is better in this case must be A-B-A-B tested. And that would be a great chance to also test a longer Kammback
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Old 09-16-2012, 12:53 PM   #5 (permalink)
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Sorry, But I feel I must point out that the Hucho Car and Civic are very different due to the transition radius at the top of the back glass. It is a Very Significant change, I really don't think they have much in common. I am noticing people don't seem to take this radius into account when considering their aerodynamic performance ideas, it is all just Angles, when indeed the radius makes a big difference as well.

I measured the Honda angles just the same, the back glass itself is at 19°, the top of back glass to trunk lid rear edge is 16°.



Again, the huge radius really helps to pull the air down in a smooth controlled fashion, but still, because it is "Sub-Template", it is pulling the air too hard there by reducing it's optimization.

The short Kamm is really messing things up IMO, you can see the tufts close to the top in front are angled up a lot, you really don't want that. Also the tufts on the trailing edge are pointed out. This looks to me like you have set up a tornado like vortex which is killing any kind of drag reduction you were hoping to achieve here. You need to do a full Kamm on this car, with radius side edges, or do nothing, it is already a fairly optimized shape and anything you put on that's half-baked will only create drag.

You really need to do ABA coast down testing on a flat or a hill to see whether it is making a difference, the tufts while helpful in visualization of what the air might be doing, is still a shot in the dark guess as to if there is any improvement.
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Old 09-16-2012, 01:35 PM   #6 (permalink)
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A while after I joined this site, I got enamored of a possible raised trunk lid or spoiler. Through several attempts, I learned the significance of "optimization" more fully. I did not seem to have the fabrication skills to mod the vehicle in a way that would not produce new problems and seemingly make things worse. The rear of the Civic is not "good" but it is thoroughly optimized in its form. Changes are tough to make effective. I suspect, however, that a small, flat, decklid spoiler would help. I say that because I see Honda do it on the high FE versions of the Civic coupe.
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Old 09-16-2012, 03:29 PM   #7 (permalink)
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Quote:
Originally Posted by ChazInMT View Post
...
The short Kamm is really messing things up IMO, you can see the tufts close to the top in front are angled up a lot, you really don't want that. Also the tufts on the trailing edge are pointed out. This looks to me like you have set up a tornado like vortex...
Leading edge behavior:

The forward row yellow tufts are taped to the original roof; some at center front are indeed angled up. That's original Honda design territory.

The second row yellow tufts are taped to the tape that holds down the Kamm's leading edge. The Kamm panel's leading edge is lifted up approx 1/4" as the tape's bond to roof is not perfect.

At center of that (second) row of tufts you can clearly see a tuft firmly sucked down against the Kamm panel, down against the tape. This is after the forward part of that tuft is lifted, either due to some separation caused by the raised forward edge of the Kamm panel - or - due to separation forward of the panel, ultimately reattaching at that point.

Also note:
The side panels bulge out from car body 1/2" or maybe more, this is a design and execution error. I'm sure this is the reason for some of the turbulence at and near the sides. Next version, if built, will use thinner material for side panels, and trimmed smaller so they can be located closer in to car's center line.

My purpose in writing this, only to share a few details maybe not immediately apparent.

My purpose in tuft testing:
To learn whether flow is attached to this panel. If attached, l can rebuild with a 10" longer panel, and the sides can be improved as I described above.
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Last edited by brucepick; 09-16-2012 at 11:18 PM..
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Old 09-17-2012, 11:43 AM   #8 (permalink)
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Bruce: it's also ideal to have a radius at the transition of the "side" to "top" of the addition. Harder to build, but airflow likes it better. The hard "fold/corner" as you have there can be problematic (maybe just a quick 'n' dirty mockup?).
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Old 09-17-2012, 01:46 PM   #9 (permalink)
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Quote:
Originally Posted by MetroMPG View Post
Bruce: it's also ideal to have a radius at the transition of the "side" to "top" of the addition. Harder to build, but airflow likes it better. The hard "fold/corner" as you have there can be problematic (maybe just a quick 'n' dirty mockup?).
You're correct of course, a radiused corner edge would be better. If I can think of a way to do it with the modest skills I have... I don't do fiberglass or welding. Maybe sheet aluminum ... Hmmmm...

I really want to hear what Phil (Aerohead) thinks about the tuft test videos.
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Old 09-17-2012, 03:36 PM   #10 (permalink)
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A cross section of PVC pipe, maybe?

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