Kammback doesn't work on my sedan

[Weather Spotter]

Nice how to!

Do you have pics of some of those steps?

I would like to add it to the wiki, any objections?

[wyatt]

Don't be too discouraged with the results, I am guessing it is an improvement, even though it didn't seem like it. The only way that you are going to screw up your aerodynamics by adding a sweet kammback like that, is if you had such good tail end aerodynamics, that adding a 10-15 degree extension somehow disrupted the separation point... you could test where air is separating from your rear window with another tuft test on your rear window. If it separates above the lowest point of your Kammback, the Kammback is probably helping, if it separates below, it's probably hurting. By looking at your car's tail end, I don't think you have attached flow on your rear glass... it looks too similar to the rear end on my car! The angle looks good, it is a similar angle to what I used on my SedanKamm, and mine was a big gain! Mine was 4' long, and good for a 6% increase in Fuel Economy.
From your video, you have attached flow, which is what you want. This means you do not have to go more shallow on your angle, and could in fact probably go steeper! (I would keep it where it is) In all likelihood, the wiggle you are seeing on the sides is from having mirrors sticking off the side of your car.

[Weather Spotter]

Good point about the mirrors causing the movement!

I think that the testing is the culprit (might not be, just my thought).

For fun add 2' to the Kammback using cardboard and run the test a second time.

[wyatt]

I assume you mean 2 feet (2') not 2 inches (2"). And yes, that would be a neat experiment!

[3dplane]

Weather Spotter!- Thanks! Yes of course you can add it to the wiki!
I made some pictures of the finished pieces and edited it into the post!
It still shows what I'm talking about.
Feel free to modify it if you want to take the jokes out or spelling etc.

Wyatt! - Man you did not play around with the size there! Awesome and it works great too! Very nice smooth transition from roof to Kamm as well!

I will do another tuft test on the car without the Kammback like you suggested! It makes sense to do that!

Thanks to all for the technical tips and good thinking!

Barna

[aerohead]

3d,if I had to guess what happened,I'd say the the Protege originally had the typical notch-back downwash which would have allowed the sepatated flow from the roof to re-attach at the back of the trunklid.
The Kamm-back is causing an 'overshoot' condition,directing the air out into 'space' where it cannot re-attach,and consequently increasing the wake size and lowering the base-pressure.Both bad.
I like what you did with the plex.I would either extend it further back,or extend the back of the trunklid back and up at a 30-degree angle ( no steeper! ) with a spoiler to give the air a place for re-attachment.
Some cardboard and duct tape should make a showing on your coastdown.

[ChazInMT]

I been thinking about this some more, I wonder if ending the Kamm before the rear end of the car isn't such a good plan, here's why.

If you create lower pressure over the area above the trunk, the higher pressure air along the sides is going to want to fill that void more so than normal, so it will be pulled upwards, and by the time it reaches the downwash from the roof, it will be pushed downwards. This may be creating larger vortices trailing off the rear areas above the tail lamps which would be a real drag.



Like Aerohed says, by making it longer and making the sides taper in less as well as keeping the sides in place further back, I think this would make the Kamm effective. Also, it seems anything you do to radius the surface will help the shape create a lower Cd too.

[Weather Spotter]

your how to looks a lot better with the pictures! thanks for updatting it.

I updated the wiki page with your info:

3dplane's Kammback how to - EcoModder

[3dplane]

After digesting this for a few days I have to say yes,that's exactly
what happened what pretty much everybody is describing here: Too short...hm I've heard that somewhere before.

If I made a "Priusback" like Wyatt, it would absolutely be an improvement to the
original Protege. At the expense of not being able to open the trunk or having to deal with some kind of hinge system to allow it to be opened.


ChazInMT! May I ask what editor did you use for that swirly arrow on the picture? Great way to explain things!


Weather Spotter! Thanks for adding the procedure to the wiki!

Barna

[Weather Spotter]

glad to help, you can add stuff to the wiki just like I can, but I can do it if you want.