beetle kammback
 

I sent a PM to swami salami (AKA dieselbeetle ) to see if I can get his pics for a reference.
I intend to make a finished product, possibly a mold that can be used to make several of them.
As they say, the devil is in the details. I can clip on the edge of the window glass as others have done, but the tricky area is the roof gutter and how to transition over that. If I don't transition outside the glass to the hard corner of the C-pillar, I feel I will be giving away too much gain.
That hard corner is certainly a "bad thing" that could use some kammback sweetness.

Famous last words... Excuse me if you do not find that comment humorous- but those were the exact words said in 2003 at Easy Racers; followed by "we will pop them out like fiberglass/kevlar garbage cans!!!". Large 400 degree oven was necessary for that 9 foot long streamliner shell, mold was wood and is still around somewhere. Many hours of sanding and/or firing. They built 2, and dropped the expensive time consuming idea.

That green unpainted fairing outlasted the mechanics of the trike and is now in a pile of useless junk; so I think I will prop it up vertically and put speakers where the wheels were.

My $3000.00 chair. Phooey! But at least it will get tremendous mileage ;)

At the very least I am happy to provide you with some humor this fine morning :D

IIRC the last time I commented about Beetle kammbacks, I told the guy he simply should have gotten a Golf.

Yeah I remember that comment, followed by somebody else saying 'another helpful post from Frank' :D
Edit:
I misremembered that.
http://ecomodder.com/forum/showthrea...tml#post274571

Ha ha, you found it. That was a while back.

"EGADS"- there, fixed it.

Watching with interest...

Thanks Freebeard. Food for thought. I was pondering lifting the hatch and re-seating it, moving the latch, etc. Big job. A Kamm is easier for sure. Raising the hatch does not obscure rear vision as much, increases cargo capacity.
Today I had time to look at things, pondered rear wheel skirts, etc.

I looked over the hatch. It is far from ideal in that it starts out narrow at the top and widens.
If I lift it up and fair that in, it will have some really *crisp* corners. Still, it will provide for an interesting A-B test. I have not found any evidence that others have tried it.

http://ecomodder.com/forum/showthrea...tml#post384969

Did you look at this post? When he added a rooftop camper to his New Beetle, his mileage dropped from 48 to 38mpg; so he moved it to behind the backlight and the milege went up to 49.3mpg. And that was an unoptimized canvas bag of stuff.

I think it has to do with the top surface catching and reattaching the vortexes that like to form.

Yes I looked at that and posted. Very very nice. I have a run to make across the mountains and will A-B a lifted hatch for starters. It is a good 160 mile run. I have my scanguage in hand, but no chance to calibrate yet. I'll have to fill and run with hatch up and hatch down.

What angle will you try? And how will you prop it open? You could seal the gap with that clear plastic they use to wrap pallets-loads for shipping. I think you could stretch it and layer it and make a custom U-shaped or O-shaped part. Then clip it to the inner lip of the opening. ..or maybe coroplast.

You could just run it open, like a wing over a pickup bed, even though it's sub-optimal; but the carbon monoxide and the base pressure pulling on everything in the interior are reasons not to.

I bought marine plastic off of e-bay for a reasonable price, they just require you to purchase at least 140 square feet.

I have some extra Coro to use. I'll pull it down against some plywood on the sides so it does not squeak or hurt the hatch, then seal it up with Coro and tape. I'll take a guesstimate at Template C.
One negative about the beetle is the roof rounds off too fast, even before the hatch. I will have a piece of Coro up there to blend the roof to the raised hatch.

The gap at the top is never more than about 1", is it?

You could split the gap with a piece 16" or so front to back and run zip ties around the hinges; then wrap the ends over and screw them to the plywood wedges.

my weather window for that little test passed, and I am glad for it. The more I looked at it, the less sense it made to even try. I will build a proper kammback.
I went to Fiberglass Supply in Burlington to attend a free seminar. These are great folks and I got some materials and ideas for the kammback, rear wheel skirts and wheel covers.
I got a half sheet of 1/8" divinycell for the structure. They tossed in a nice sized scrap for testing out how it will bend with heat in complex curves.

This is the basic shape I came up with. I am trying out the look of several different trailing edges.
Call this one the normal rake
http://i810.photobucket.com/albums/z...ps055b1a9e.jpg
Shallow rake
http://i810.photobucket.com/albums/z...ps892cb398.jpg
sharky

http://i810.photobucket.com/albums/z...ps5c4bad7b.jpg

I can't lift the template up or move the kammback forward without undergoing serious body rework.
The roof is immediately too steep. Not ideal. I get that and have figured a single piece design that will mount to the hatch and hit the roof a couple of inches aft of that antenna.

Looking at sharky, what I have in mind is a nice curve here to go with the rest of the body styling. I don't have the paint skills to draw it. Use your imagination and tell me what you think of that. I was thinking a nice curve from plan view as well, resembling a receding hairline of midlife crisis :P
http://i810.photobucket.com/albums/z...ps5c4bad7b.jpg

Sawtooth or shuttlecock, if you prefer.

http://i810.photobucket.com/albums/z...pse92e6045.jpg

Sell IT. As they say in auto sales: there is a rear end for for every seat. HA!

that's not happening. It is more comfortable for my rear end than anything else I have driven. I did a 590 mile run the other day and I was not broken afterward.
My camry would have left me in shambles. only the full size diesel truck is as comfortable for me, and I like the economy of this one.

The Sell it comment was in reference to ecos comment of making a speaker chair out of his homemade project. Best Tom

Tom, you can see where I was a little lost there :D

Bringing this back to the tail of the thread for suggestions/comments.

Looking at sharky, what I have in mind is a nice curve here to go with the rest of the body styling. I don't have the paint skills to draw it. Use your imagination and tell me what you think of that. I was thinking a nice curve from plan view as well, resembling a receding hairline of midlife crisis :P

My beetle is black. I grabbed this profile off the web.
The finish will be gloss carbon fiber style 284
http://i810.photobucket.com/albums/z...ps200c9c76.jpg

Does that picture represent the 1/8" divinycell?

Beware usiing The Template in plan and elevation. You don't get the whole story.
http://ecomodder.com/forum/member-fr...17-1-47-18.png

Even this is non-canonical, the bottom of The Template should be at ground level. it's height is half it's width. But it shows that relatively flat New Beetle roof needs to transition to the crown of The Template. Matching the height and width only makes it worse. The forward edge should be curved instead of straight across the car. To overcome this you might consider the squircle:
http://i.imgur.com/6EYZT.png

As for the trailing edge, here's Colani:
http://ecomodder.com/forum/member-fr...ni-desktop.jpg

That looks great but it is not going to happen. From an earlier post in the thread:
So it will be nearly straight across just forward of the window line, and that little slice of template represents my planned profile shape. It was just a handy curve tool for me to use, since I don't have the graphics "chops" to draw up things like that on my computer.

That trailing edge is similar to what I had in mind.

Kammback
 

I don't have the New Beetle with me,but I've got the New,New Beetle here.
The 2011 Beetle has a Length/Height ratio of 2.878 and Cd 0.37?
*1999 Prius-I ------------------------------2.876 and Cd 0.29
*1991 GM HX3 -----------------------------2.856 and Cd 0.258
*2000 Honda Insight-I --------------------- 2.854 and Cd 0.25
*1980 VW 2000 --------------------------- 2.781 and Cd 0.25
*1987 Renault Vesta II ---------------------2.772 and Cd 0.186
*2008 M-B Boxfish ------------------------- 2.560 and Cd 0.19
--------------------------------------------------------------------------
All these cars have 'shorter' fineness ratios than the Beetle,but better rooflines and sides.
Extending what you have along the AST contour as far as you dare will pay the highest dividend.If you went a little further,you could correct the rear fenders as well.
Going as far as the rear bumper,with a pure vertical chop (like Carl Breer did with his 1934 DeSoto Airflow (the world's 1st actual 'Kammback)) would yield the lowest drag with zero added length.
And it can all be open at the back,with 'steps' inside,like Ford did with the Merkur XR4Ti bi-wing spoiler.The flying-buttresses will create a perfect hybrid box-cavity/boat tail,forcing where turbulence can or cannot be.

Thanks Phil.
I can take is as far as my crude overlay, which is right above the top of the fender, without harming my rear view.
It would follow the plan taper and body line of the hatch surround.
You are suggesting building a lower step beyond that, so I can still see through?

The trailer design I touched on will fit into the current plan. I figure I can sacrifice rear view when towing, as that is what I am used to anyway.
I would continue with a solid add-on section to the bumper, and the trailer would tuck up to that. It would clip on with a few fasteners.

I will leave the above as a reminder to thought processes :D
Now i see your slotted version, and maybe I can keep the top of the trailer low enough to have a decent rear view through the slot :)

Here, I was treating the upper and lower body separately. The original Beetle had more distinction between the upper and lower body taper.

http://i.imgur.com/UcfCC.png

The upper section could be truncated different to the lower section, for visibilty. Here's one in the opposite direction.

http://i.imgur.com/bEz6x.png

The second image is close to what I want as far as the shape/attachment to what I have.
Snip it off right at the apex of the fender and that is what I have planned, with some of that curvaliciousness of that Colani trailing edge.
I can attach to that to reach back to the trailer on trailer days.
Thanks for the inspirations :)

lower step
 

Yes,below the backlight,like the Harrod Helper and Ernie Roger's Bug wing.It helps compartmentalize the turbulence.
What freebeard has rendered in his upper drawing of #30 permalink is the idea.
Any of that length would help if it didn't interfere with the trailer.

http://ecomodder.com/forum/member-fr...6-12-58-10.png

There are an infinite number of squircles between the circle and the square. One of them will be the closest match to the profile of the New Beetle at the A-pillar. These are not it*, at 50/50. Something about 65-75% toward a square would be closer. The rear quarter windows should be unobscured.

The lower body is held to the original overall length; the wheels are covered and the 'shoulder' is moved forward for aero reasons. The upper body is sized to the length of the rear hatch and could be extended.

*Truncated, widened and stretched to fit.

I'll park it for a week and mock up something in cardboard I can photograph. I know the shape I want and can make it better than I can draw it.
Thanks for your images and inspiration.

It will be interesting to see what ou come up with. This was my first attempt at a mock-up, working with that external drip rail.

http://ecomodder.com/forum/member-fr...1-100-0577.jpg

What I'm working with now are 16ft long redwood strips that go from the stagnation point to the rear in one sweep (on a different Beetle). I've learned some interesting things, but I don't have a camera right now. :(

The older I get the more I can appreciate the comfort factor. I much prefer driving my truck to driving the wife's Avenger, even though the car gets better mpg.

I personally like the look of the sharky version. Deep or shallow doesn't seem to have as much "style". Not sure if there's an aero difference.

Freebeard's graphics have inspired me; I think I will go with two pieces now.
A front fixed fairing that starts aft of the sunroof, and the main piece which rides on the hatch. I have several small and large pieces of 1/8" Divinycell to play with.
I'll use 1" XPS foam to make bulkheads and hand shape them, then skin with divinycell strips.
Once I sand the joints smooth, I will coat it with epoxy with black pigment. This is to make sure the finished product looks good. It is easy to get small gaps in the carbon fiber cloth, and the green divinycell would look terribad.
Then I'll hand lay up the carbon/epoxy and coat it out clear till it looks reasonable.
I'll knock out almost all of the XPS bulkheads and put some light cloth on the inside.
Since early November I have been back at work again, many hours and even Sunday shifts. Needless to say, it cuts into any modding.

Freebeard, this image represents the initial profile of my trailer as I see it, thank you. :)
I hope to get the air stuck back onto it behind the beetle as soon as I can. The big challenge is how I can taper/transition the three curves into one that gets as template C-like as I can by the ending out of the trailer.
Washing out those sharp inside corners will be fun.

I see mention of a trailer in the 'tapeee' thread. What trailer did you get?

'three curves' The top and two sides?

'sharp inside corners' I guess I'd need to see a picture. I don't know what other old posts you've found, so here's a comparison of [half-] circular, squircular and square cross-sections.

http://i.imgur.com/m9sOrUx.png

The square section has the worst cross-wind performance.

squircle
 

The 'squircle' can produce as low a drag as a proper half-circle streamline body.
Jaray proved this as early as 1922.
Here are very different cross-sections of identical Cd
http://i1271.photobucket.com/albums/...d2/Solar-1.jpg
http://i1271.photobucket.com/albums/...itled11_15.jpg
:)