Help me design my partial Kammback

[AeroModder]

$30 for a 4x8? Geez, I got mine for $11 per sheet.

[miket]

For $30 i can get a sheet of 10mm coroplast.

[Weather Spotter]

before I was done making the Kammbak out of coroplast the sun decided to go to bed. So I took pictures before I was 100% done. I fixed a few thing and took some more pics (lighting is not great).

First off is the lower bracket connection spot:


the brackets, I painted and clear coated them before install so that I did not have to take them back off. They are made from steel I had from my wheel skirts. Since they would be up on the glass I figured some scratch protection would be a good idea.



On the car:






Note the snow flake on the bottom:










From the inside:


After I attached the seam and after dark. I used hot glue on the whole length and a backer piece on the back half.



Tomorrow I will have to do a road test to make sure it stays on http://www.clicksmilies.com/s1106/gr...smiley-003.gif

[Weather Spotter]

Testing questions:
I have seen three types of testing done.
steady state
coast down
tuft

I am not real fond of spending several hours doing steady state testing, I might but I do not see a good no wind day in the forecast.

Coast down might work, how accurate is the test?

Tuft testing would require a camera, I can use my point and shoot set to video mode but mounting would be an issue.

what would you recommend?

[COcyclist]

If you did some tuft testing, you could experiment with the angle of the Kammback over several runs to see how steep you can go before losing attached flow. (I have a hunch you can go a little steeper) Do you have a buddy or significant other who would be willing to drive your car while you drive a chase car with a video camera? This is the quickest, simplest way to test your mod that I know of. You don't have to drive very fast or very far to get some good data.

I use coast-down as a quick way to determine if it helps or hurts. It takes a little more time and is highly dependent on ideal (no wind) weather conditions. Looking good!

[Weather Spotter]

Testing update:

Kammback testing
start at 55mph (+ 5 winks) by cruse, hit reset on scan gauge and clutch at same spot
winds, calm to 5 MPH, E,SE coasting direction was due south
was warmed up for 30 miles first
all are feet past a mile 5280 ft +XXX ft. larger numbers are better
Start is 40 feet before an embedded survey maker end is measured off the 2ed one (exactly one mile apart)
testing done B, A, B2, A2.

Graph: (the standard deviation is added to the top of the average coast down length)


data:


It looks like my 26" (22" past original cap/ spoiler) has gained me 1.92% longer coasting distance. How does this convert to MPG?

[Weather Spotter]

More pics:

I painted the under side black to reduce any issue of glare (had none but it also looks better)


A look at the curve:


Back without anything on it:


Side view:


Side view 2:


back view:


Almost a top view:


As you can see I ran out of my silver paint. Another can is on order ans should be in next week.

I am still trying to figure out how to convert my 2% aerodynamic gain into a MPG savings, Ideas?

[COcyclist]

Aerohead has said that a 2% aero improvement should yield 1% mpg increase.

[COcyclist]

Spotter, Thank you for posting your careful test data. I hope you do not find a 1% mpg increase discouraging. It is a step in the right direction. Darin (MetroMpg) has said there is no magic bullet; it's more of a magic buckshot approach, a percent or two here and a percent or two there and it all adds up.

I envy your simple and reversible construction method. I made a similar one of coroplast for testing but I don't have easy attachment holes. Do you have scraps left to make flat coroplast wheel covers? Perhaps in the future you can extend your Kammback for a longer, removable tail. I have welded up a bracket that fits in my receiver hitch for this purpose but that is as far as I have gotten so far.

[cfg83]

Weather Spotter -

Originally Posted by Weather Spotter

...

the brackets, I painted and clear coated them before install so that I did not have to take them back off. They are made from steel I had from my wheel skirts. Since they would be up on the glass I figured some scratch protection would be a good idea.

...

On the car:


...

I just wanted to say that re-purposing the existing shock mount holes is INGENIOUS! I love it when people figure out cool exploits like this.

CarloSW2