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Old 07-02-2012, 11:00 AM   #1 (permalink)
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1986 Jetta Carbonfiber whaletail

I am going to make a rear aerodynamic device to replace the coroplast partial Kamm tail. It was ugly. I have been driving the car without the cover since the last fill. It made the car quieter and cooler in the summer.

If any of you remember the Merkur from the 80's it is going to resemble it.
I made a drawing to show something on how it might look.

The lower wing is going be trunk mounted and will be positioned to fit under the top wing when the trunk opens and will extend a bit behind the rear of the trunk lid.

The lower wing was molded off of the trunk lid as a wet layup. The drill was to cover the trunk lid with duct tape as a mold release, spray glue the first layer down paint on the epoxy and cover it with a peel ply, a second layer was added to the first after removing the peel ply from the still green first layup. It is made from carbon fiber about 40oz.

Here is the layup after 15 hours.

The peel ply was removed. I may put on a layer of filler before I remove it from the trunk lid.

I plan on making arms to lift it the required 8" or so.

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Old 07-02-2012, 01:45 PM   #2 (permalink)
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I assume you mean the Merkur XR4Ti which wears what is essentially a Ford Sierra Cosworth spoiler.



Not sure it'll give you much gain, if any, but it'll be interesting to see.
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Old 07-02-2012, 02:46 PM   #3 (permalink)
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Yep Sven the Mercury Merkur xrti. A friend had one back then and I got to drive maybe 200 miles. What a nice car. Fast even at high speed with only a 4 cyl 2 valve turbo 140ci engine. It must have had good aero.

I am going to move the flaps up from the original Mercury design and keep them flat. Imagine putting the tips of the foils so that they are in line with the tear drop template.

Here was my prototype of the Merkur design. I was able to run down the road noticably quieter with up to 57mpg, still running the power steering and alternator just like a normal car. Since removing the coroplast the car is more noisy once again. I put the fin on last fall and it was just falling apart.

The trunk is an essential part of the vw package we usually travel with the car packed fully. I couldn't see spending the effort to make a complete boat tail and end up with reduced utility.

The front end is going to be wedged. Stock it is vertical with almost no radii on any surfaces. I am probably going to make it out of foam with the holes for the headlights made with generous radii which will double as air intakes.
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Old 07-12-2012, 04:31 PM   #4 (permalink)
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I made the top foil today.

Used duct tape to cover the bodywork I glued pink and blue board on with two part poly foam (It is similar to foam in a can but stiffer and easily sandable.). Did a bit of sanding and shaping. It has about an average 5 deg slope. We covered it with a 25 oz layer of triaxial carbon and covered that with a peel ply.

I am going to mount the lower foil on struts on the trunk lid. Obviously I won't use bricks. When the trunk lid is open the lower foil will come above the upper foil. Keeping the trunk fully usable.

Here is a pic before the carbon was layed up.


If anyone wants to guess how high the rear strut should be I would appreciate it.
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Last edited by Varn; 07-12-2012 at 04:39 PM..
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Old 07-12-2012, 09:31 PM   #5 (permalink)
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Quote:
Originally Posted by Varn View Post
I couldn't see spending the effort to make a complete boat tail and end up with reduced utility.
Hey... it's not done yet. FWIW( For What It's Worth), I'm planning on having my final incarnation having a hatch like Basjoos' Aerocivic, an air assist rear suspension to help with extra weight( a la Mike Dabrowski's http://99mpg.com/Projectcars/TheBestHybridmix/) because I always use my cars like trucks, and hopefully a rear window. All this with room to sleep on long trips( like, say Bonneville, UT).

Looking forward to where this takes you.
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Old 07-12-2012, 10:55 PM   #6 (permalink)
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Ah no not dissing your boat tail Jethro. I just need to keep it simpler for now. If later I want it longer I can extend it back.

Lots of newer cars have a big advantage in aero over these old vehicles. Square front, square roofline. Too bad that they didn't make the trunk about 6-8 inches taller.

I found a rabbit with smoke on this web site.


I combined the image it with the profile that I took of my car earlier today.

Came up with this:


I figure it the smoke wants to follow a certain line then my whaletail should be just about 2 bricks high just about where I have it positioned.
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Old 07-13-2012, 09:16 AM   #7 (permalink)
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We pulled off the peel ply.

The trunk can open, yeah! Usually the trunk is full when on the road.

We are going to use some flox and smooth out the cover. It is actually pretty smooth. Then will cover it with a layer of fine weave fiberglass.
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Old 07-13-2012, 11:19 AM   #8 (permalink)
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Carbon covered with flox. Will be sanded with 36 grit to improve shape.

Not so worried about smoothness, which isn't very important, more interested in refining overall shape.
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Old 07-13-2012, 02:57 PM   #9 (permalink)
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Sweet!
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Old 07-13-2012, 06:04 PM   #10 (permalink)
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No worries Varn. I knew you weren't. Sometimes I can't help myself.

I really like the shape of the Kamm back.

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