Project: making a permanent Metro Kammback extension

[aerohead]

I think you pretty much nailed it with basjoos Civic.Obviously,Honda could of had a little more roof camber than they did,but Mike doesn't have any control over that and has integrated his tail very well into car.Going "outside" means a little skin friction penalty,way better than going "inside",which would impact form drag.Sure,you can nit pick the details but basjoos has scored an out-of-the-park home run!

[aerohead]

Originally Posted by 88CRX

how about a VW Beetle? it seems like the original VW would have a low Cd.

The original beetle has Cd0.458,great by 1936 standards,not so good today.The beetle is a "pseudo-Jaray"form.It's roofline is too"fast",separating early above the rear windscreen.

[aerohead]

Originally Posted by .Cd

The AeroCivic looks even better when you compare the entire profile of the tail :

( A perfect match in fact ! )

I see what you're saying but it's very important to use the teardrop template exactly as Darin has depicted it,otherwise,all the curvature is thrown off by a factor of two and you're right back to flow separation.

[2003protege]

Originally Posted by MetroMPG

Here it is:

YouTube - Tuft testing a "Kamm back" mockup

That is so awesome!!! I love seeing all those tufts just laying flat with the road screaming by. I'm dying to do a kammback for my sedan after watching all the tufts on my rear window pointing toward the front of the car at anything above 30mph! lol. good stuff man, really enjoyed it!

[aerohead]

Originally Posted by akcapeco

Not to mention the Mercedes Bionic Concept Car, circa 2005:

I wish Mercedes would provide an overhead view.This would really tell us something,as most of the air is going around,not over that car.

[MetroMPG]

Bad news: my attempt at using sprayable foam is a bust.

After 12 hours cure time, I spent about 30 minutes this morning shaping the side section. When I went back to have a look after lunch, my handiwork was obliterated: the foam was all deformed and lumpy - shrunken in some spots and further expanded in others. Apparently shaving off the outer "skin" allowed it to start reacting with the air again.

So I'm abandoning the foam method and will lay up some thin cardboard instead, trying to get the curvature I want. I'll glass directly over the cardboard.

[akcapeco]

Originally Posted by aerohead

I wish Mercedes would provide an overhead view.This would really tell us something,as most of the air is going around,not over that car.

This is why Mercedes chose to study the boxfish: it appears to encapsulate a space that could approximate a car... let's face it, we can't all drive Insight-guppies:

[tasdrouille]

I can't wait to see the end result!

[aerohead]

That's a terrific shot,thanks!

[aerohead]

Originally Posted by MetroMPG

Bad news: my attempt at using sprayable foam is a bust.

After 12 hours cure time, I spent about 30 minutes this morning shaping the side section. When I went back to have a look after lunch, my handiwork was obliterated: the foam was all deformed and lumpy - shrunken in some spots and further expanded in others. Apparently shaving off the outer "skin" allowed it to start reacting with the air again.

So I'm abandoning the foam method and will lay up some thin cardboard instead, trying to get the curvature I want. I'll glass directly over the cardboard.

Darin,was that the high or low expansion foam? I've only used the original stuff that would buckle a doorjamb and spew out to the Mexican border.I thought that once expanded,that the material was inert.Big "I'm sorry" if I helped you chase your tail and lose precious time.