CivicTail project: ginormous aerodynamic tail on '07 Civic sedan

[MetroMPG]

Well, the side taper is now significantly less than before. About half as much. It's now slightly less of an angle than the curvature/angle on the side of the rear bumper itself.

The pic below makes it appear the tail is now as wide as the car, but it's not. That's just the camera. I added 12 inches / 30 cm to the overall width of the "transom".

I also added a little spoiler to raise the top surface closer to template, and hopefully promote cleaner separation.







Thanks for the advice & encouragement, everyone. I was ready to stuff the whole thing in the recycle bin yesterday.

Re-test to come!

[CigaR007]

Interesting approach. Looks promising.

[Cd]

I think I can understand why there is the tendency to create a boat-tail that is too 'steep'.
One part of our brains is saying " keep it on the template curve", while the other is saying " If I can just get it to taper in just a little bit more, my wake will be so much smaller ! "

I actually like the look of the upturned end ( the spoiler ). It's very ascetic. I guess maybe I'm just used to seeing an upward sweep at the back of a car in that area.
Good luck

Edit : Ahhh... a box cavity. I see it now.
Nice.

[Sven7]

I'm liking this. The box cavity is cool to see, since so few people seem to be experimenting with them. Keep it up!

[2000mc]

possible area to be optimized?

[BabyDiesel]

Originally Posted by MetroMPG

Thanks for the advice & encouragement, everyone. I was ready to stuff the whole thing in the recycle bin yesterday.

Re-test to come!

The only failure there would have been was if you would have given up. Instead Metro, you're using this a platform for improvement! And you have made some good ones, I see

If this test doesn't go better, just send it to North Carolina and I'll put it to good use

[MetroMPG]

Originally Posted by 2000mc

possible area to be optimized?

Good eye.

That bump is actually directly behind the tire, so I didn't worry about it. Just inboard of that, the bottom surface of the tail tucks neatly inside a coroplast undertray that goes from the rear axle to the bumper.

If this test doesn't go better, just send it to North Carolina and I'll put it to good use

Come and git 'er!

[MetroMPG]

Originally Posted by Cd

I think I can understand why there is the tendency to create a boat-tail that is too 'steep'.
One part of our brains is saying " keep it on the template curve", while the other is saying " If I can just get it to taper in just a little bit more, my wake will be so much smaller ! "

Funny thing is: the first two that I made were COMPLETELY eyeballed, and way off the template, yet had great results (10-15% at similar testing speeds). This one I consciously kept close to the template, and it made the smallest improvement.

Though the previous two were on hatchbacks, so there was more room for improvement.

[MetroMPG]

Conditions were great late today, so I got out to the test route again.

Short story: 3% improvement @ 90 km/h / 56 mph

(Doing AAA-BBB-AAA where each A or B is a 2-way averaged run. So 18 individual runs. A = Kamm+Tail; B = naked rear end)

Compare that to the 2% change I saw last time.

So the revised tail appears to work better, but overall it's still not a very big difference vs. no rear end work. Don't get me wrong, though -- I'll happily take a 3% boost! I'm just surprised it wasn't more.

I'll post the final details & graphs & standard deviations sometime this weekend.

[California98Civic]

I am always amazed at your energy for these projects... still 3% would just a little over 1 mpg on the freeway, which is something but so much less than we'd expect. Has the basic Civic body design been so optimized that it has become that difficult to improve upon?