Rear aero project - Civic notchback coupe

[brucepick]

Current status of project - added roof extension panel. Also tapered the sides inward towards the rear. Did this by cutting away the lower edge, so the side panels can rest on rear qtr panel as they taper inward towards the trunk lid edges. I also added several aluminum bar stock stiffeners to the main lower center panel.

Have been driving with this setup for two weeks with pretty good FE numbers in fall weather.

If I'm very fortunate I'll be able to do some coastdown testing this weekend.



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Original posted message starts here:


With the rear of a notchback coupe contributing seriously to car's the aero drag, I've developed a plan to try to remedy it on my Civic.

This design is based on earlier discussions in this thread:
http://ecomodder.com/forum/showthrea...les-17796.html

The concept is to plant a long, flat spoiler with the rear edge at a point meeting the template curve. While not as effective as a proper shortened boat tail that would extend to the same point, the side panels will help sequester the air in the "chamber" above the panel, more or less "faking" the template as far as the air flow is concerned. And, you can see out the rear mirror and, with a few cuts and hinges, can still open the trunk lid.

Basically, it is a flat spoiler panel, who's rear edge meets the template curve, above the bumper's rearmost point. Panel's forward edge meets the rear glass. Two side panels extend the C-pillars rearward to a point even with the bumper's rearmost point, and support the flat spoiler panel.

The spoiler's forward edge is aimed at the rear view mirror, so the spoiler should appear as a thin edge from the mirror's viewpoint, and not block the driver's view out the back.

I also came up with a design for a bracket to attach the side panels to the edges of the rear glass. I expect to need additional attachment points but this has the benefit of being cleanly removable later if needed. Attaches to glass with silicone glue or double stick foam tape.


Photo above:
Tan = spoiler panel, aimed at rear view mirror.
White lines = template curve + vertical.
Yellow = side panel.


Photo above:
Heavy tan = spoiler panel, aimed at rear view mirror.
Thin tan = fold/hinge in spoiler, to allow trunk opening.
Yellow = side panels.
Thin red = cut/hinge in side panels to allow trunk opening.


Photo above:
Mount bracket attaching side panel to rear glass.
To be silicone-glued to glass.

[Cd]

If I understand your image correctly, you have two side panels that match the shape of the template, but the central section actually extends from center of the rear glass and acts as a raised Bonneville style flat spoiler ?
If that's the case, then why not just have it extend from the roofline ? It could be mounted on a hinged edge so it could swing upwards with the trunk. It would them match the template curve without the additional drag of a flat spoiler design.
Of course it would have to be transparent.

I probably am not understanding you image . If that's the case, nevermind.

[Cd]

It might help if I actually read the post !
So yes it looks as though you intend to create a flat spoiler versus an actual Kammback.
Just curious why ? Why not go up a few inches and have it hinge from the roofline ?
Either way, I'd like to see your results with this setup .

I'm also curious to see what kind of vortices will form as the air spills over the sides and down into the depression.

[California98Civic]

Originally Posted by brucepick

I've hatched a plan to try to remedy it on my Civic. This design is based on earlier discussions in this thread:
http://ecomodder.com/forum/showthrea...les-17796.html

We have had PM exchanges on this, but I just want to note that I'm really interested in wider response to this idea and your results. Eventually, I want to build a Kammback, and this mounting may be my prototype.

Though I don't plan to use the kind of plane you plan, I like very much your effort to resolve visibility with a panel that disappears into the line of sight from the inside rear-view mirror. Very clever. I experienced that with one of my abortive "raised trunklid" designs, and I can see it working-out really well. As long as the aero benefit is real and significant... that's the debate, eh? Build it. Test it. Good luck... I'm following too.

[tru]

do you have any info on your wheel covers? they look nice!

[botsapper]

(From - Aero mods for chumps thread)

Magical numbers of 10-12 degrees.
Here are just visual concepts. (quick tire change time is valid, could use quick release 1/4 turn camlocks or just delete)

Conceptually, there are rear vertical fences that holds the new lexan rear window/fastback at the best low drag angle. Ideally a true tapered boattail is the best but this might be the easiest to fabricate & even easier to test & adjust the back angles. You could also adjust trim edges depending on your track venue.

http://ecomodder.com/forum/attachmen...5&d=1296259422

http://ecomodder.com/forum/attachmen...6&d=1296259422

[California98Civic]

Originally Posted by botsapper

(From - Aero mods for chumps thread)

Here are just visual concepts... Conceptually, there are rear vertical fences that holds the new lexan rear window/fastback at the best low drag angle... You could also adjust trim edges depending on your track venue.

http://ecomodder.com/forum/attachmen...6&d=1296259422

I love the second photo. Very cool look. It's a model for what I would hope to install one day (quite a way off right now). I would build it entirely clear for visibility.

[ChazInMT]

Brucey Babe...I was thinking of doing something similar to my 04 Civic, my plan was to design it so it had pressure points on the top of the class and rear or the trunk lid, then I was just going to put metal bracket hooks on a cinch strap and hook the front of the trunk lid on the outsides, then pull tight, so it would only rub on the car in 2 places, and the hooks would contact the bottom of the front of the trunk (bottom of the rear glass area) that nobody would ever see. It wouldn't move cause you are jamming a "V" into a "V" shaped hole essentially. I'll post an illustration later, on the road right now.

[brucepick]

Originally Posted by ChazInMT

Brucey Babe...I was thinking of doing something similar to my 04 Civic, my plan was to design it so it had pressure points on the top of the class and rear or the trunk lid, then I was just going to put metal bracket hooks on a cinch strap and hook the front of the trunk lid on the outsides, then pull tight, so it would only rub on the car in 2 places, and the hooks would contact the bottom of the front of the trunk (bottom of the rear glass area) that nobody would ever see. It wouldn't move cause you are jamming a "V" into a "V" shaped hole essentially. I'll post an illustration later, on the road right now.

I think I get your idea. Pulling the spoiler assembly forwards against the glass and down against the trunk lid. I think you would need to take it off the car to open the trunk - but maybe you have a way around that.

[brucepick]

Originally Posted by tru

do you have any info on your wheel covers? they look nice!

Thanks, tru.

Have a look here:
http://ecomodder.com/forum/showthrea...tml#post250009

There's some info there on how I made the the discs. I used the acorn nut attachment method discussed in the beginning of that thread. You might want a different attachment based on how your wheels are designed. I definitely like some version of attaching to the lug nuts or to decorative caps that go on the lug nuts, it avoids drilling into nice alloy wheels.