I think my design is flawed... help?
 

So I think I've messed up a little bit and was wondering if I could get some feedback. I'm thinking that my angle is too steep. From the side view, it appears to follow the template, but only in the very center. As you deviate from the centerline, the slope is too great? I think I need to raise the trailing edge of the corogated plastic and square off the transition from roof to side of the car.

The first pic here is from last week or so:
http://img.photobucket.com/albums/v4...y/IMG_0710.jpg

I had an issue with the pressure from the "springiness" of the curve, so I cut it a little. The duct tape was being pulled off on the sides. The next three pictures were taken this morning. Overnight we had a good snow (all powder) and you can see the result of driving at 60mph or so...

[IMG]http://img.photobucket.com/albums/v4...25688E2C_1.jpg[/IMG]

[IMG]http://img.photobucket.com/albums/v4...43771ACB_1.jpg[/IMG]

[IMG]http://img.photobucket.com/albums/v4...57CA3D2BE0.jpg[/IMG]

You have a good start, but you need to continue your pattern to the rear of your car.

Gotta love that "powder snow" aero testing techniques!

That seems to be the challenge, giving up visibility, or learning to shape Lexan.

How about tuft testing?

It does look good, though. Can you taper in the sides on the body, not the Kamm-back?

Here's the deal as I see it. The #1 thing auto makers have done for 20 years is design cars so they don't create MPG sucking vortexes behind their cars. Your Honda was designed so the air coming off the sides and roof create a smooth linear air flow with out a lot of swirling about. Anything you add to you car will only upset this balance and decrease efficiency. Look at the sedans with insane CD's, the new Mazda 3 .255 CD, and Benz CLA .23 CD.

https://lh3.googleusercontent.com/-Z...ss_ser1_11.jpg

http://image2.chaobuoisang.net/cs/20...am-2014-11.jpg

The 2 things that I take away from these 2 designs is the long sweeping top arch of a line from the base of the front windscreen to the base of the back glass, with only a slight break to the trunk lip. The other is the straight-up front grills, pushing as much air around the sides as possible.

Back to your Civic, I think the only hope you might have is to make whatever you do on the back work is make sure whatever you do goes all the way back. The Kamm thing to the trunk extension break I think is your issue. But however you craft the back, you'll never be able to tell how that is interacting with the air coming around the sides and it is improbable that you'll get it nailed without a wind tunnel and passel of engineers.

Don't mean to be a downer, these are just the thoughts I had when I was contemplating modifying my 04 Sedan, as always YMMV and I could be 100% wrong. (well maybe 95%)

That's as far back as I could go while still being able to open the trunk...

I'm not sure I follow... do you mean cut the body of the car??

ChazInMT has good points. My 6th gen Civic has very similar lines to yours. The coupes are the best of the Civic stable in terms of aero. The lines are good enough that most improvements require a lot of experimentation. If this were mine, I would take off the kamm and play with the trailing edge stuff. On my Civic there is a little taper beginning toward the aft edge of the car. If yours is like that--it's very subtle--experiment with continuing it a few inches or a foot. ... or you could build a full boat tail. ... The side skirts probably help. I have them too. I am still planning a belly pan and diffuser and maybe another version of the rear box cavity I tried without results last summer.

I was referring to the trunk extension, although I realize that it is not very long. If you continue the top of the trunk, you may be able to have air reattach after your Kamm-back, but why did you extend the sides? The boat tails that I have seen tapered, like a boat, although you can hardly taper in that space; it almost looks like it flares out somewhat, which would leave a larger wake. As for dealing with a Kamm-back and a trunk, not a hatchback, I cannot imagine a better solution than Christofoo's:

http://ecomodder.com/forum/showthrea...tml#post390835

That took me way too long to find. I am going to go not fail some school.

I'm going to assume that the below image is similar to your car.

2003 Honda Civic Classic Pictures/Photos Gallery - The Car Connection
http://images.thecarconnection.com/m...00038998_m.jpg

A newer Honda undergoing wind tunnel testing:
Honda Factory News - Acura TSX Forum
http://www.bloomberg.com/apps/data?p...d=iQqIa4mn7bjw

Combining the two (I could not find the proper image) we get:
Aerodynamics Photos by kach22i | Photobucket
[URL=http://s184.photobucket.com/user/kach22i/media/Aerodynamics/honda-overlay_zps56b8eb8c.jpg.html]
http://i184.photobucket.com/albums/x...ps56b8eb8c.jpg

Based on viewing maybe a hundred wind tunnel images, I'm going to guess that detachment on your car occurs about 2/3rds of the way down the rear glass.

This air flow then jumps over to the top of the truck lid without too much turbulence, and goes on to provide a tiny bit of down-force.

My suggestion is to focus on the rear deck lid and rear sides, cant inward at about 10 degrees with some attachments, minding not to obscure your brake lights.

Think 3D
Honda Worldwide | March 29, 2007 "Honda Adds New Type R to Civic Lineup"
http://world.honda.com/news/2007/407.../images/30.jpg