5th generation civic hatchback - improving aerodynamics

[MetroMPG]

I just noticed the cat in the photo showing off your front wheel discs. (And I'm testing the "reply" function of this thread for reported bugginess...)

[AndrewJ]

Sweet, I secretly wanted the Kammback to win anyway, so I could keep putting off those front wheel skirts for another 4 months...

So I grabbed the Chilton manual, looked up spoiler removal, and nothing. Nada. Zip. It would seem that those shop-manual chumps actually want me to get up outta my chair and go look at the car. Drat.

Several minutes later I rassled the spoiler off of my car, leaving a nice metal sub-structure thingie that will be a perfect Kammback mounting piece. But can you spot the problem? If you answered "The third brake light is just laying on top of your roof, you idiot." then you are correct!



Oh, and in the trillions of edits to this post so far due to some buggyness, one mentions that I am wearing a shirt that says "Canada - America's hat"
So Darins post has now regained it's context.

[SVOboy]

Seems like it worked alright, na? Go kammback go!

[MetroMPG]

America's hat. That's funny!

[AndrewJ]

So upon further inspection, I have an ungodly-huge wiper-motor-box on the inside of the hatch glass. As you may be able to tell, I have no wiper. Ergo, no wiper motor to occupy said huge box. Perfect place for a 3rd brake light, don't you think?




So, a quick run to the auto parts store was in order. Moments later I was in posession of a 4" long LED trailer light. It's just a "marker light" but all the 3rd brake light does is turn on and off. Believe it or not, a trailer marker light has that amazing level of functionality.
I also got some LED replacement lamps for my other two brake lights, because they were shiny and pretty looking.

[AndrewJ]

A little disassembly here, a bit of Dremeling there, a little soldering and presto! A crappy looking black plastic thing with a wirey red plastic thing stuck to it. Amazing, No?



More seriously though, I must give mad props to Gorilla glue. It's some magical stuff, like a cross between wood glue and expanding foam. I thought it was all a bunch of ape-related hype until I got some to glue cork grips onto bike handlebars (at Rivendell's recommendation) But the stuff really is pretty awesome (for glue).

Back to the matter at hand, when I got it all slapped back together, here's what it looked like. I was a little worried that the LED trailer light wouldn't be bright enough in comparison to the rest of the brake lights, but I looked at it all lit up last night and it's fine. The only indication (in the dark) that it's not an OEM brake light is that it's relatively small at only 4" across.

[aerohead]

I did all the modifications you've considered to my CRX,with the addition of a boat-tail.I drove the car from Texas to the West Coast and back in 1990,with a detour to Bonneville,where I made a number of passes,each successive run with something else removed from the car,until the last run represented the stock car in factory form.All the fore-body modifications netted me a 0.5 mph bonus to top-speed.The boat-tail,by itself gave me 8.0 mph.The car set a land speed record for the Utah Salt Flats Racing Association,and I was seeing mpg in the mid-sixties for the trip.As much as I love the "aero" look,I think you should follow basjoos lead,and go after the back of the CIVIC.I believe there is no significant separated flow on your car,up to the hatch,after which ,your dragging an enormous wake of turbulent air wherever you go.I really like what your doing,don't get me wrong,however,I truly feel like you'll miss the boat(no pun intended),unless you go after that wake.What basjoos has done in the front of his car is an insurance policy to guarantee the full effectiveness of his boattail,which is doing the lion's share of drag reduction as was proven to me at Bonneville.Please don't lose a golden opportunity to see some really remarkable mpg improvement.I think you'll find the wing a disappointment.Wish you the best with the project,Phil.

[AndrewJ]

So today I rounded up an ecomodders best friends: Cardboard, duct tape, and a utility knife, and went out into the driveway to make a Kammback.

Despite my best efforts, I have become *that* guy in my neighborhood. In the midst of duct-taping a bunch of cardboard to my car (again) and then taking lots of pictures of it, some of my neighbors peeked out of their house and started watching me.

Here's the whole gory mess




I plugged it in photoshop and measured it out. It's currently sloping down at 13.5 degrees, the rear roofline is only about 5.5 degrees.
Also, it angles in from the sides at exactly 13 degrees.

Here it is in comparison to the old spoiler.




And just as a matter of an update, heres a few shots of the car in it's current configuration (sans Kammback)

[MetroMPG]

A critical point to remember: try to round the "shoulders" - the side/top transition - on the kammback as much as possible. Sharp edges promote vortex formation; generous radii less so. You don't to be dragging a honking pair of vortices behind the car.

My kardboard kammback's transition was too sharp.

[MetroMPG]

And having said that, it looks like you're trying to achieve just that, based on the amount of creasing I can see in the cardboard template in the pic where it's on the floor.