CivicTail project: ginormous aerodynamic tail on '07 Civic sedan

[MetroMPG]

Yeah, it's a bit of a mystery. Before this car, I would have said you'd be richly rewarded by slapping a tail on just about anything.

Maybe it's something about the Civic in particular.

But I'm still willing to bet the Kamm/tail design isn't as good as it could be. This project needs a wind tunnel for fine tuning... but I'm fresh out of wind tunnels. This one's done!

[California98Civic]

Originally Posted by MetroMPG

...But I'm still willing to bet the Kamm/tail design isn't as good as it could be.

That has to be true, because a more template-like overall shape should reduce the Cd quite a bit, certainly enough to benefit the vehicle more than 3% in FE. The tail design must be interacting with other features a lot? Maybe the design currently is a bit too "fast" still? ... maybe it needs to be a little slower than template even?

[mikeyjd]

Originally Posted by 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.

Thanks for retesting. It makes sense that you'd get less benefit than say a lean burn capable Insight, but I would have guessed more than what you got. I wonder if it has something to do with where you're at on the bsfc map when aero is improved. Maybe your engine isn't getting the benefit we'd expect to see, because Honda has gone to great lengths to tune the car based on the known aerodynamic characteristics of the vehicle? A bit of a head scratcher...

[Cd]

Metro, before you remove the tail, could you please do a coast down test for us ?
With talk of the BSFC being a culprit, your mileage might not improve with the 'tail, but if the 'tail had a change in aero much like previous designs, it would certainly show an improvement in the length of the coast.

( I'm not suggesting you do it this weekend, but rather at your convenience before you trash the tail.)

You, sir are a scientist. Thank you for presenting the facts as they are. Something such as this could come as a huge blow to the ego, and it would have been easy to simply avoid this re-test all together, or make up some excuse.
By presenting the facts - no matter how depressing the results - you help us all.
Thank you.

[Piwoslaw]

^^ I second this. If it turns out that the Cd improvement is larger than the FE improvement suggests, then you would know how to work around the BSFC problem (for example: remapping and/or regearing).

[BabyDiesel]

I third Cd's post.

The pressure is building. Quick, more people post so that he will crack!

[sheepdog 44]

My 2 cents is that the top could be redirecting air downwards much better than the sides or where the tail lights are. Could it be churning a vortex in the back of the car?

[Fat Charlie]

Coast down, indeed. I'm still trying to come to grips with how to maximize the benefits of my first ever aeromod. My numbers are improving as I learn how to drive my now different car differently to take advantage of it, so the mpg numbers tell a story that's more about me than the mod.

Yes, the trip numbers are the practical result, but they tell about how the mod helps one driver on one route. My search fu is weak this morning, but there was a thread some time ago about removing wiper arms from an Insight (I think) and getting somewhere like a 15% jump in FE. The OP was suspicious and determined that at his normal speeds the slightly reduced aero load let the car stay in lean burn where it otherwise wouldn't have been. I think the Civic may have the opposite problem, a drag reduction that for some reason isn't translating directly in to higher mpg.

[MetroMPG]

That Insight thread might be mine. I tested a group of mods all at once including wiper deletes:

http://ecomodder.com/forum/showthrea...-km-18930.html

And yup, load reduction on a lean burn vehicle translates to bigger dividends than on a regular car.

[MetroMPG]

Sorry guys! I already pulled off the tail & Kammback and am getting the car ready to sell.

The Mystery of the Somewhat Disappointing Only Moderately Effective Ginormous Aero Tail will have to remain just that -- a mystery.

PS: ABA numbers & charts coming today ... I didn't have time to finish that up this weekend.