VW Beetle TDI Kammback

[euromodder]

Originally Posted by dieselbeetle

I couldn't agree more, this would improve flow greatly. However, I ran into big problems because of the convex shape of the beetle's rear window. I'm mathematically perplexed.

If you look at the pic from behind, you'll see the top corners are near to or even outside the car's outline - that's where you could improve things a bit further.

If you loosen the connection between the vertical and horizontal panels at their corners, you can angle in the side panels.

If the curve gives a problem, make a straight score a bit above the curvature of the panel, and angle it in along that straight line.
The curve would still fit the rear window, and you get to angle in the sides.

The top panel will then automagically drop down towards the rear.
Don't make the top slope down too much - say 10-12 degrees - see if it's symmetrical left and right, fix temporarily, mark where the sides touch the top, and cut the top panels to shape.

[euromodder]

Originally Posted by dieselbeetle

I agree with you, there are a lot of variables at play here. However, I wholeheartedly achieved 55.4 miles per gallon with my kammback. No ifs, ands, or buts about it.

It's what you registered of course.
The only question is what the experimental error on that measurement is

The smaller the values you register (fuel quantity and miles driven) the higher the error will be.
The fuel pump cut-off will introduce the biggest - unknown - variable.

I did run into a problem concerning the theory of testing:

So I guess what I mean is...with a scanguage, how do you know the moment is right to take a readout?

The instant readings don't get used.
The recording is started (i.e. SG trip is reset) at a fixed point along the route.
The reading taken is the recorded average, again read out at a fixed point along the route (say an exit sign).


Even then, as with any road-side testing, there'll always be errors due to conditions beyond the control of the tester or his equipment.

[big shafe]

Any more recorded mileage done with this setup?

[SwamiSalami]

nope, sold it.

I really only did the kammback for a school project.

feel free to read the paper on my blog:

blog

[bnmorgan]

Originally Posted by SwamiSalami

That's a good point. What I'd really like, though, is to have someone design a kammback and 3d print it!

I will help you get a 3d model ready for print if you can find someone to print it.

[Cd]

Originally Posted by SwamiSalami

I couldn't agree more, this would improve flow greatly. However, I ran into big problems because of the convex shape of the beetle's rear window. I'm mathematically perplexed.

Originally Posted by Piwoslaw

Spot the differences between the picture above and the one below:



Answer: The sides are angled inward at the same angle that the top is sloped down. The teardrop we are after is a three-dimensional shape, not just 2D.

When you work on the permanent version, try to get rid of the corners, like MetroMPG did:

Bingo !
I'm glad you mentioned this .
Very important to not only round off the edges, but taper the tail in the plan view and not just the side - just as you mentioned here .

[SwamiSalami]

i LOVE that firefly and it's respective mods.

[big shafe]

Originally Posted by SwamiSalami

nope, sold it.

I really only did the kammback for a school project.

feel free to read the paper on my blog:

blog

I don't see anything related to the Beetle testing.

Why didn't you do any extended testing for a more thorough proveout?

[SwamiSalami]

welllllll

it was a humanities course...

"ancient engineers" was the course. the project was to make something. (emphasis on the period.)

i ran into some time constraints. really i would've liked to have done more in terms of testing, but i just didn't have the time (at the time). I was taking 5 classes and now i'm a stay-at-home-dad! living in korea and owning 1 vehicle that's an suv makes things harder now, too.

for me, the project WAS about improvement, of course. the paper in itself was more about the history of such efficiencies and engineering feats. but, ultimately, it was about obtaining a big number, which i did! that beetle got pretty good mileage to begin with and i tracked it pretty avidly on another website, which is how i knew where to begin.

i'm aware that my test wasn't as scientific as perhaps it should've been, which i guess i kind of regret, but hey, we live and we learn. and also to the scientific bit, i'm very well educated as to how scientific concepts work. I think at the time i did the experiment i was more excited than anything and very green in my understanding of aerodynamics and "ecomodding", if you will.

[SwamiSalami]

Originally Posted by bnmorgan

I will help you get a 3d model ready for print if you can find someone to print it.

thanks, man. unfortunately, though...I don't own the beetle anymore. honestly, i can't say i'm all that sad about it. that car was very expensive to maintain and the interior was just completely falling apart. a great example of this was I went to visit my parents across country and my dad got in the car, pulled the door handle and it came off in his hand!

whoever the knucklehead was that owned the car before me really screwed up the interior (of course i probably didn't help matters much)