Project: making a permanent Metro Kammback extension

[Glans]

This cardboard project is 2 years old but it's on hte site as a permanent mod. Did that ever happen?

[drossdarkblood]

I'm Just curious but doesnt this also in theory boost the cars speed as well or am I wrong that aerodynamics and reduction of drag can also help with performance? Cause my aspire probably could use that design theory. And I'm wondering do any of you offer a sellable fabrication I could possibly pay you to help design for me? well atleast i mean maybe a mountable fiberglass or carbon-fiber version?

[3304hl]

Hi
Came to this via Jalop and have read through all 24 pages.
Here's a few random thoughts on "aero" from the deep recesses of my mind thanks to the 1973 OPEC "oil crisis"

First, A "teardrop" isn't actually the ideal shape for a car unless of course you're planning to drop it off a cliff. To start, gravity distorts a drop of water in ways it doesn't a car's airflow. Next, a teardrop has clear air all around it; a car doesn't. This is why all serious Aero testing is done in an open chamber tunnel with a rolling road. Interestingly, real "road testing" produces far more accurate results than a lot of very expensive tunnel time and it's way cheaper!

Regardless of how slick the bottom of your car is, it isn't as good as the top bit. Any air forced under the car is compressed by the road surface, making it a "heavier" fluid; ie: more drag. This is why Nascars use that wacking great front spoiler. You can pick up lots of MPG here.

The ideal departure angle for the rear deck should not exceed 7 degrees to maintain ideal Laminar flow regardless of all the teardrop talk. If you look at the "smoke" pic of the Insight you can see the smoke at the rear of the deck is seperating somewhat( it's thicker). This indicates that it's generating lift and drag. If you can find a pic of a second gen CRX from Europe, they have a slick little rubber duck tail that flattens out the air flow. You might try something like this on you car and see what comes of it.

Re: the discussion of flat back or open, my work on my old Hornet hatcback in '73 says open. Air coming off the bodywork creates vortex drag that acts on the rear of the car. The extension of the bodywork moves the vortex further from this panel. There's a lot of work to be done here as it's not nearly as simple as it sounds. Different sizes of cars with different aspect ratios produce different results here. I used an array of aluminum rods from an old TV antena( remember those?) mounted to a plywood panel with the fabric tufts to test this out. You may be surprised at the results! Controlling the air rushing under the rear quarters of the car really helps a lot. Rear "diffusers" aren't just about downforce.

gotta go.
hope this gives you a few new ideas to play with!
And your friends think YOU'RE strange; (insert evil laugh)

[RobertSmalls]

Hi, 3304hl. Much of what you mentioned is known to the Aerodynamics forum. Yes, actual raindrops grow larger as they fall, turning from round to oblong until they grow to an unsustainable size, turn to a parachute shape, and break apart. But an ideal streamlined body looks a lot like half of a cartoon teardrop.

Here's a thread where I learned a lot about diffuser design: http://ecomodder.com/forum/showthrea...ion-13230.html

If you're planning on sticking around, you should introduce yourself and your cars: Introductions - Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com

[MetroMPG]

Originally Posted by Glans

This cardboard project is 2 years old but it's on hte site as a permanent mod. Did that ever happen?

This kammback is still on the car.

The core of the addition is cardboard, but it was sandwiched in fiberglass - the construction details are in the thread if you want to go back and read up on it.

The finish hasn't been as durable. The paint is flaking off in places now.

Originally Posted by drossdarkblood

I'm Just curious but doesnt this also in theory boost the cars speed as well

It would help higher speed acceleration and top speed, yes.

[3-Wheeler]

Originally Posted by MetroMPG

...The finish hasn't been as durable. The paint is flaking off in places now.....

Hi Metro,

That's strange that the paint is flaking off.

What type of paint did you use? Automotive I hope.

I would think if the cardboard were sealed from the elements properly that a good grade automotive paint would stick.

Of course, if the cardboard surface is not stiff enough and flexes, then that would allow the paint to eventually peel off as well.

Jim.

[MetroMPG]

Hi Jim -

I only used gloss black spray paint over primer, not proper 2-part auto paint. Regardless, it flaked because the cardboard wasn't perfectly sealed/encapsulated.

Water has wicked in, with the result that some areas have suffered from a few freeze thaw cycles, leading to expansion & cracking of the finish.

[hotrodfeguy]

That 2.0 version looks really nice. You have me thinking of doing one for my first gen Metro.

[TOOQIKK]

awesome job! just read the whole thread!
motivated to do some ecomods to my 94 nissan sentra!

[AntiochOG]

Nicely done. I read through this whole thread, and your whole boat tail thread today. I'm now thinking of doing a kamm back on the hardtop of my Miata.