Question about kamm extensions. - Fuel Economy, Hypermiling, EcoModding News and Forum

Christ · 08-24-2009, 12:35 AM

So you can't see through plexi when it's at the right angle for a Kamm... same with lexan.

I wonder:

What if you made the kamm with 3" steps in it? Obviously, it would lessen the effect, but would it be that bad? I mean, you'd keep most of your rear visibility, still have an optimal overall angle (with more turbulence at the boundary layer, if the flow could even stay attached).

Does it work?

The view would look something like looking through the rear view of a car with window louvers on it.

2000mc · 08-24-2009, 01:29 AM

what about a rear view camera... i dont know how cheap you can get them now, but i remeber seeing them over a year ago in walmart for $100, and i dont know if theyre worthless for seeing at any kind of distance, but if you still have your side mirrors they could serve that purpose

Frank Lee · 08-24-2009, 01:31 AM

I think Chrysler "reattached" the flow after the window so they got the best of both worlds- good visibility and aero.

Christ · 08-24-2009, 02:18 AM

Quote:

Originally Posted by Frank Lee

I think Chrysler "reattached" the flow after the window so they got the best of both worlds- good visibility and aero.

That's kinda neet-o.

I just wonder how bad the kamm extension would really be with 2" or 3" steps in it. I don't plan on doing it, it was just a thought.

Frank Lee · 08-24-2009, 02:23 AM

The way I'm envisioning it, the steps couldn't have 90 deg edges (like stair steps) or they would most likely trip up the flow. Even if they were bevelled i.e. like the Chrysler idea only several little ones in succession... I don't know, FWIW my gut says no nice attached flow but of course I could be wrong on that; but what I'm right on is the view out the back window would be funky (visibility through bevels no good).

aerohead · 08-24-2009, 07:10 PM

I had a stepped rear plex windshield in the original bedcover.Certainly,there was a locked vortex in the void,but the thing was still good for a 13% mpg improvement,so it couldn't have hurt it too much.

Christ · 08-24-2009, 08:48 PM

Quote:

Originally Posted by aerohead

I had a stepped rear plex windshield in the original bedcover.Certainly,there was a locked vortex in the void,but the thing was still good for a 13% mpg improvement,so it couldn't have hurt it too much.

You wouldn't have a visual of the rear view anywhere stashed away, would you? Would you liken it to looking through a rear window that had louvers on it?

cfg83 · 08-24-2009, 09:12 PM

Frank -

Quote:

Originally Posted by Frank Lee

...

I think Chrysler "reattached" the flow after the window so they got the best of both worlds- good visibility and aero.

I think I see a defect in the design from a practical POV :

It *appears* that the trunk slopes into the window, so rain would accumulate there. It would need to down slope from the window in the final design. They'd probably just convert it into a hatchback at that point.

This could be a visual trick (I've been seeing a few lately).

CarloSW2

Christ · 08-24-2009, 09:36 PM

I think the light is tricking you, but you could be right on that, Carlos.

I'm almost sure that it's either flat or even tilted back slightly, to evacuate water from that area, but without more perspective to the shot, I can't say for sure. I do see how the shadows are playing light tricks with making it seem the way you see it, though.

An overhead picture with the light coming from the opposite direction can make a flat space seem downhill, when it's in an odd perspective, though.

Bicycle Bob · 08-25-2009, 10:27 AM

I think this thread is about a sloped extension to a Kamm back, which is defined by being near vertical. Let's not confuse the newcomers.
I wish I knew the reason for the waning popularity of louvered backlights on GT cars. They probably didn't help the wings work, but probably were not tested for drag, either. Then too, there's fashion, cost, and weight.