Kammback drawback: extra-filthy rear end!
 

https://ecomodder.com/forum/attachme...1&d=1583509150


I have never had the back of a be-Kammbacked car get as dirty as this Mirage does. This is accumulation from normal winter highway driving - not driving on any dirt or gravel roads.


Then again, I have never put side skirts on a car before this one either. Maybe they changed flow/pressure enough at the rear to make this mess.




https://ecomodder.com/forum/attachme...1&d=1583509402


I usually delete the rear wiper/motor assembly on my cars. I can't do it on the Mirage or I won't be able to see out the rear within a short amount of time on a wet winter highway.

I wonder if adding a small extension straight back on the bumper would help? I can see a vertical line of dirt formed on the left side of your bumper. Wonder if that would change flow just enough to let the dirt be flung to the ground instead of back at your car?

I noticed that vertical line too, but I think it's just where the rain & snow has washed the dirt off - not protected from above by the Kammback.


(I haven't washed the car yet since I got it. :D )

That said... I'm thinking of testing a quick 'n' dirty box cavity. I wonder if that will keep it cleaner.

Part of it is there is an awning now preventing rain and snowfall from washing the back while it's parked.

Oh I just saw where you already said that.

Also: the Metro & Firefly had similar setups, and they didn't get nearly that filthy! I could run them without a rear wiper/washer.

One solution:
https://ecomodder.com/forum/member-v...go-2019-28.jpg

^^2x

I was going to point to the Bertone BATs. (BAT 5 or BAT7)

https://upload.wikimedia.org/wikiped...px-BATcars.jpg

Yep. Here's the same thing on a Saab 95. First pic shows the extended lip at the trailing edge of the roof, second pic shows the slot for directing a wash of air over the back window to keep it clean(ish). This is what happens when you let airplane folks design a car.

https://cdn.bringatrailer.com/wp-con...daDSC04314.jpg
https://cdn.bringatrailer.com/wp-con...daDSC04288.jpg

back-soiling
 

I wonder if placing a 'floor' in the K extension,would sequester the water-borne debris away from the glass.The high-inertia water might not be able to make the corner,and you'd
have a pond of dead air inside the extension,at high static pressure,like a box-cavity.:rolleyes:

I like it! Thanks, Phil. That's an easy test fix to slap together.

test
 

Darin,thanks for the mods and testing!:)

Unless it's a fully functional difusser with fences.

I must be dead, because I'm in slot heaven now. :D

Seriously, I've been looking for such examples for years ever since I did my slotted roof wing on my S-10 pickup truck.

A French aerodynamicists did a quick CFD study on it, and indeed a small amount of air was jetting though there.

One could slot the top plane as well as the side planes and still have the Kammback rear hood work, in my opinion.

Ferrari F12 AeroBridge
https://ecomodder.com/forum/showthre...e-25067-2.html
http://i.imgur.com/564oWm0.jpg
https://ecomodder.com/forum/attachme...p;d=1362081338

More images:
Volkswagen-GTI-W12-650-Concept (2007)
http://netcarhow.blogspot.com/2013/0...0-concept.html

This has always (since 2007) been one of my favorite cars. It makes me wonder about grafting a Rabbit roof onto an air-cooled Beetle.

He metro been posting about my niro having the same problem. It's factory rear wing is shaped like your kammaback. I was going to take it off to see the diff in the dirt on the rear. How was it before you put the kamaback on?

Please do. I have an upcoming road trip in the Golf and I am considering trying some mods before I go. Would your box cavity match up with the bottom of the back hatch?

slots
 

I went back and looked.Hucho is absolutely adamant about non-aspirated structures on road vehicles.Slots,slats,and spoilers can perform on an aircraft in 2-D flow,but never on an automobile in 3-D flow.Any boat tail or box-cavity must be airtight in order to function.Texas Tech's cab-wings were non-aspirated.
A permutation that is permissible is,to use a slot to pressurize an air-tight,fabric boat-tail envelope as I,and Bruce Ruefer (SP?) did.

I think a lot of study on slotted flaps (aircraft) and slotted wings (F1/Indy) race cars has been done after the mid-1980's.

However, I agree that the real world is 3D and very messy.

To clarify, the gentleman who so graciously did my CFD made no claims about the roof wing slot.

When I pushed him it was a concession of sorts, and visible in the graphic.

Just debatable about it's affect and meaning.

I wanted it to mean the slot introduced a high velocity thereby lower pressure area under the wing (more so than it would have with sealed leading edge), and that this promoted the air flowing over the top of the cab to collapse on top of it, which lead to the air mass encountering the truck bed cover slightly sooner, and making my rear Gurney flap all the more effective in producing down-force.

My slot was very small, not sure it had any affect larger than life as I would fantasize about on cold rainy days. :D

In this situation all we are trying to do is keep a rear window a bit cleaner.

To be honest, even with it slotted to the hilt, it's always going to be dirty - in my opinion.

https://d2d0b2rxqzh1q5.cloudfront.ne...cc66dcc08a.jpg
https://d2d0b2rxqzh1q5.cloudfront.ne...cc66dcc08a.jpg

You should tuft test that rear glass . . . .after you wash it really good!

The airflow would have to look pretty interesting back there considering the amount of accumulation it's getting

My first thought was some show that I watched as a kid where students mocked a guy that rode his bike to school and his pants had a racing stripe on the back.

I thought there was a term for that.

What is the solution?

Xist's patented skidmark retarder! :D
https://ecomodder.com/forum/attachme...1&d=1583960677
[patent pending]

You probably want to make it wider and use Aerohead's terminology. :)

You know, once you have a roof and a floor, you have half of a box cavity! :D

Isn't a box cavity 80% of a boat tail? :P

Thanks for the idea, now if I can get that CFEO approval on HER golf...... also tuft the body below the window, too.

I would bet I have a big swirl spinning such that the exhaust is following the body at slow velocity.