Project: making a permanent Metro Kammback extension

[akcapeco]

Woot, woot!

[MetroMPG]

Originally Posted by .Cd

So is the Kamm back going to have a hollow cavity or a plexiglass rear window

I remember the UC Davis Taurus mod - I'm going with a the hollow cavity too. But mostly because it's easier to make.

Yes, for testing, both sides of the kammback were finished.

Are you thinking of pushing the envelope further and making an attachable boat-tail in the future?

Definitely. Who knows when I'll get to it, but it's on the list for sure. Thinking of a clear vinyl skin over a collapseable/removeable frame. Also wondering about rigid fiberglass panels that snap into place on a light skeleton frame.

how did you mount that camera!!!!!

Black duct tape! (Which is why it doesn't show up well in the pic, above.) The white struts are pieces of quarter round trim molding, the long pole is a broom stick

Duct tape is your friend.

Have you ever tuff tested your rear wheel skirts or your front grill block ?

I haven't. No real reason to tuft test the grille block. I'm sure the skirts are mostly fine - likely some detached flow at the lower trailing edge where it curves in, and on the bumper cover behind the attachment point (mud flaps). Maybe I'll stick the camera on it just for fun. I've been thinking of adding a fairing behind them on the bumper cover.

[MetroMPG]

Here's the un-edited tuft testing video for the hard-core aero fans:

YouTube - Raw video from: "Tuft testing a Kamm back mockup"

[gascort]

very nicely done!!!!!

[Cd]

Originally Posted by MetroMPG

I've been thinking of adding a fairing behind them on the bumper cover.

That would explain why you still have the 'mudflaps' !

If you ever get around to running more tuft tests, I was wondering if I could request a favor : Both you and I have a rounded tail end to our cars.*
It would be interesting to see whether a 'trip stip' or a straight edge would have any effect on decreasing the vortexes.
I'd guess that they are rounded for a reason, but as we know, a sharp edge is usually better than a rounded end.
I meant to test this on my last failed attempt at tuft testing.

( * the tail light area )

[MetroMPG]

Originally Posted by 88CRX

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

The Beetle Cd is pretty terrible actually: 0.48 according to the Wiki gods Automobile drag coefficients - Wikipedia, the free encyclopedia

The new one is still below average.

[Cd]

I was wondering what fences would do to your Kamm back since the air is moving upwards and over, causing that vortex. ( The red arrows appear to be the direction that the airflow is currentrly moving. )

Do you think that fences ( the green things in the image) would channel the air into a straighter flow, or just cause more turbulence ?



I also wonder how that the flat template affects the vortex on that side. If the area was hollow there then it would cause a vacuum and possibly lessen the vortex .... perhaps ? Experts - what's your opinion ?

I would think that an easy way to see what the air is doing when it gets sucked into the Kamm back would be to create a vertical piece that hugs the back glass and the inside of the Kamm back. If it extended out a good foot or two past the Kamm back, you would be able to see the pattern that the tufts make and see if the wind is doing what you want.

I don't know if that makes any sense at all.

[akcapeco]

It seems only fitting
to briefly detour and salute
the late, great Bucky Fuller (Wikipedia Link)
and his Dymaxion Car of 1933:




In historical context:



Hail Bucky Fuller, here holding a folded Dymaxion Map with its
minimal land mass distortion :





We now return you to your regularly scheduled broadcast.

[akcapeco]

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

[MetroMPG]

Originally Posted by .Cd

Do you think that fences ( the green things in the image) would channel the air into a straighter flow, or just cause more turbulence?

Any raised edge that's not parallel to the flow will trip the air. Angled raised edges will spawn vortices.

The angle of the flow shown by the outer 2 columns of tufts on the upper surface is actually fairly close to parallel to the taper of the side of the Kammback. The angle of the photo and the tape line make it look worse than it really is, I think.