CivicTail project: ginormous aerodynamic tail on '07 Civic sedan

[MetroMPG]

Those of you following my kitchen-sink-megathread about the Civic "winter beater" have obviously seen this already. But I decided to break out the boat tail + Kammback info into a dedicated thread for wider edification and amusement.

CivicTail Frequently Asked Questions:

Q: OMG, WHY???
A: For fun and edutainment! I wanted to see what kind of fuel economy improvement I could get by streamlining the back of this sedan. (Fans & students of aerodynamics know that the biggest opportunity for drag-reduction is found at the rear of a typical road vehicle.)

Q: How much does it improve fuel economy?
A: Don't know yet. MPG testing will happen when the weather warms up a bit more. (A-B-A testing format of course.)

It has been tuft tested though, and the air seems to like it (when rear fender skirts are in place).

Q: HAHA - good luck parking that thing!
A: The car+tail is the same length as North America's best-selling vehicle (look it up). So, parking isn't any more of an issue than for the tens of millions of people driving those things around. It fits inside a normal garage.

Q: How do you see out the back?
A: There's a plexiglass window in the "Kammback" section of the tail.

Q: How is it held on?
A: The inner frame is attached to the car at 5 points: hitch mount, plus screwed through the two factory licence plate holes in the back of the trunk, plus two redundant ratchet straps across the top of the trunk lid. It's removable in about 5 minutes.

Q: How much does it weigh?
A: The tail alone weighs 16 kg / 35 lbs. I haven't weighed the "Kammback" section over the trunk lid/rear window, but it's probably another 7 or 8 lbs.

Q: HAHA - I bet all that weight cancels out any aero benefit!
A: Just you wait and see!

Q: What's it made from?
A: Wood inner frame; outer shape comes from hot-glued cardboard + coroplast over cardboard inner bulkheads; the outside is shrink-wrapped in plastic film & liberal amounts of duct tape. Tail lights are from a 1992 Suzuki Swift GT.

Q: HAHA - that's not going to last!
A: It's just a science experiment -- it'll last long enough. I'll likely be selling the Civic in 3 or 4 months.

[MetroMPG]

Construction details, part 1: Kammback transformation...

Before a tapered tail can do its drag-reducing aerodynamic magic, we want to deliver clean, attached airflow to the back of the car. That's a problem with a notchback (a.k.a. 3-box) design, because airflow typically gets messy behind the rear glass:



Of course, the flow over the Civic's rear glass & trunk isn't as bad as this exaggerated image. How do I know? I taped yarn tufts on the rear window and went for a drive.





Tuft testing result: I was slightly surprised to see separation/recirculation (red/orange area), but it's there. Even though the Civic's rear glass is laid way back and the deck is fairly high, it's obviously stil too "fast" to keep attached flow.

Solution: A MORE PRIUS-Y PROFILE, PLEASE!








HOW THE HECK DO I SEE OUT THE BACK?

It's got a rear plexiglass window. Also, I built in a high-center-mounted third brake light:





Looks neat, eh? No, the snow isn't sitting on cardboard. It's all wrapped in heat-shrunk plastic at this point.

And I gorilla taped the whole thing to the back of the car.

So, no, that means I can't open the trunk anymore. But I can still access it from the cabin, through the folding rear seatbacks. I can also get the spare & tools out that way if I need to.

(For full details of the Kammback construction start at post #173 in the kitchen-sink-megathread.)

[MetroMPG]

Hello, my name is Darin, and I'm a maker of cardboard tails.

Yes, I've done this before...



http://ecomodder.com/forum/showthrea...uft-25223.html



http://ecomodder.com/forum/showthrea...mpg-10691.html

The Civic's tail follows a similar approach: plastic-skinned, cardboard shape on an inner frame. (Actually the Firefly's tail was pretty much cardboard monocoque, with just a few cross braces.)

Wooden frame:



It's mostly triangulated 1x1 extending from 2x4 base that is attached to the trunk lid (screwed through the factory licence plate holes) and the trailer hitch.



Then I added a few vertical and horizontal cross-braces for attaching the cardboard bulkheads that define the tail's outer shape.





Lots of hot glue gun use to stick the cardboard bits together.







Tail lights are off a Swift GT parts car:





I modified (ie. hacked them apart), and they connect to the Civic's trailer lights harness.





Yes, I realize the tail would work better if it was full width and covered the factory tail lights. But I like redundancy, plus the factory lights give the car more visual mass/width at night when lit up.





Whoops! It looks a bit too "fast" at the very end, when I overlay our streamlining template (v.2). Maybe I'll fix it with a little spoiler. Because racecar!

But this is the closest-to-template project I've ever done. The previous ones were just eyeballed. Because art!

[MetroMPG]

First test...

A: Tail + Kammback on
B: Tail OFF, Kammback ON
C: Tail OFF, Kammback OFF
A: Tail + Kammback on



Second test: revised tail

A: Tail + Kammback on
B: Tail OFF, Kammback OFF
A: Tail + Kammback on



Raw numbers, weather, other mods in place during test:

[Daox]

This post reserved for me to say: COOL! and nice work Darin!

[Big Dave]

Yup. That's ginormous. Ought to work well.

Stay out of British Columbia.

[Gasoline Fumes]

Originally Posted by MetroMPG

Tail lights are from a 1992 Suzuki Swift GT.

Those are 1989-1991 tail lights!

[Xist]

All of the weight cancels the aero benefits? Forty-three pounds? 1.6% of the weight of the car?

[MetroMPG]

Originally Posted by Gasoline Fumes

Those are 1989-1991 tail lights!

Merci, monsieur! I was just going with what was on the key tag! I'm not a connaisseur of the Swift GT. Just a parts car owner.

All of the weight cancels the aero benefits? Forty-three pounds? Four percent of the weight of the car?

I'm proactively responding to the exact kinds of comments that people will make on other sites without actually looking into the details.

[aerohead]

I'm calling God tonight 'n see if we can get Ontario a few Btu's.
I hate waiting!