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Old 09-07-2012, 04:41 AM   #1 (permalink)
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Project, the Third - Now contains collabsible boat tails (1971 VW SuperBeetle)

And so we come to the driver. I won't say daily driver because I divide my travel needs between the bicycle (Schwinn Collegiate with a banana seat), city bus (I'm of an age where I can ride for free) and the 1971 SuperBeetle.

It was pretty much stock when I got it, It is 40 years old and has less than 100,000 miles. Since then I've made the following modifications:
Renewed front suspension with adjustable MacPherson struts (we lowered it until it looked *good* and then raised it until it clears most traffic control bump strips)
Rebuilt brakes (although I now question converting the front to disks) with the drums and rotors cryogenically processed to extend the part life.
CB Performance electronic distributor (this is a billet housing full of Ford parts, the spark curve is programmable by swapping out springs) that possibly got 45 mpg increase in the first car I had it in.
AM antenna delete
Driver side mirror delete this is temporary (honest, officer)
Tire pressure maintained at 40 psi
Nut behind the wheel lightly torqued

What works against me:
Low miles travelled. The only time I would be able to gather data is on sporadic trips out of town.
Incomplete data. No Onboard Diagnostic Port, no MAF sensor, no GPS
Screwy data. The gas gauge is way out of calibration. Because the front tires are 165-45/15 the speedometer, which reads off the left front wheel, it wildly optimist. I can bury the speedometer needle at normal freeway traffic speeds.
Eh, that's enough

What works for me:
It doesn't look shabby, at least to start (it's a 5' car, get 2' away and you can start to nitpick chips in the paint and rust in the door hinges) so anything I do will reflect favorably on my fellow ecomodders.
I'm familiar with the platform. Ferinstance, from hanging out on thesamba.com I learned you can get the correct kind of activated charcoal to repack the gas vapor recovery system by buying a $14 Cadillac part.
The Bug Bearer bike rack. It is mounted with some custom brackets added to the stock bumper brackets. It peaks at the Template line and is 34" wide. I could make a K-back out of 2 or 3 layers of the plastic the use to wrap palletized freight.

What I'd like to do:
Better instrumentation. The panel van had a head temperature gauge with sending units on the #1 and #3 spark plugs on a toggle switch. I could use the AM radio antenna mounting hole to install a pitot tube for (barometrically sensitive) air speed. maybe a MAF sensor in the bottom of the air cleaner to measure intake air. Using the Airflow Meter as a Dyno I'd like an engine vacuum gauge but I'm not sure about running a vacuum line the length of the car.
Engine modifications. A Gene Berg Jet-A-Vator. Hot VWs got xx% improvement with this. Water/methanol injection so I don't have to run Premium grade gas for the octane rating. The H2O Way Part 2 Maybe electrical tape wrapped around the intake manifold runner for heat.
Aerodynamics. Eventually a boat tail or Template-shaped single wheel trailer. But also front and side air dams. When I repaint, move the turn signals down off the top of the fenders, unless I start liking them after I chop them down to half height and put in LEDs.
Replace the stock rear bumper brackets with a custom built class-1 trailer hitch. This would incorporate heavy-duty sockets for the bike rack that could double as mounting points for a single wheel trailer and tabs to mount the rear bumper. This would give me three options in back. Otherwise, I think I could build a boat tail that weighs little more than the stock bumper. I have no problem with driving around without bumpers or spare tires.
Judicious torquing on the nut behind the wheel.

But enough jibber-jabber; let's talk boat tails.

Back when I first started seriously reading Ecomodder.com, I whipped up a Template primitive .obj object and held it up against a commercial VW model to see what's what. I was kind of dismayed that the boat tail is as long as the car's wheelbase. I also looked at messing with the Template by giving it a parabolic cross section and using three for that 1930s look.


The single aeroform is maximal, I held it as far forward as I could. The interesting part to me there was the area ahead of the rear wheels. Instead of fade-away front fenders, this might offer a solution that doesn't affect the doors.

The triple aeroform in minimal. If reducing the volume of the wake is beneficial, accepting a dirtier flow off the body might be acceptable.

For purposes of this post I prepared some side views with the template:

We begin

The Template

Ground clearance

What if we only do the rear fenders?

Move the same cross-section to the roof

Truncate the lower aeroform

I think I could live with this


Last edited by freebeard; 09-07-2012 at 04:50 AM.. Reason: grammar nazi
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Old 09-24-2012, 04:59 PM   #2 (permalink)
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I think your "multi-boat-tailed" illustration -- where you fair in the rear fenders & main greenhouse separately -- would look eye-poppingly fantastic in real life.

But for best aero, you'd need to blend the fender tails into the greenhouse tail for best effect - there's going to be messy air in the gaps in between them.

Which way are you leaning? Do you have fabrication experience to tackle this kind of thing?
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Old 09-24-2012, 05:42 PM   #3 (permalink)
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Just use the right Vee and template in one, another older thread share.
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Old 09-24-2012, 11:21 PM   #4 (permalink)
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MetroMPG -- You're right, putting 'boat-tails' in the title helped. That shape silhouetted in the last picture would have in inverted T-shape to the truncation. I have 3D model of that; I will clean it up and post it.

As far as fabrication skills go, wood>metal>fiberglass. Cost of materials is another consideration. I have a good supply of redwood benderboard, 1/4"x4"x12'. If it was vacuum-bagged it could produce something like this:

Howard Hughes airframe crew produced those during downtime while they were building the H-4 Hercules. Wouldn't one of those be a barn find?

What I'm leaning toward right now, is to replace the rear lid with this plastic cargo pod. Here it is mocked up on the '58 baja:


and it would be easy to hang K-back on the bike rack:


My focus right now is calibration and instrumentation. (I did replace the outside mirror). I found a city radar trailer (You are going xx mph) and drove into it at 3 speeds spread across 15 mph. It only reported 4 mph difference, so that didn't help. Next week, after a train trip to Seattle, I'm going to take a road trip and burn a tank of gas just to get a base-line for comparison.



botsapper -- I've got one of those, too! That's more work than I would ever tackle, the only part you could reuse would be the chassis and nose. You can totally get a Type II that low, but I'm skeptical about the rear door hinge line.
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Old 09-25-2012, 01:07 AM   #5 (permalink)
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I don't believe an air-flow meter in the bottom of the air cleaner will help. Not unless you mean just over the carb throat. There are three different air-flow meters that I know of; one uses a swinging flap (a "barn door") that gets pushed out of the way by incoming air, one uses a piece of wire that gets heated and measures how much heat is lost to the incoming air, and the third uses a similar method but has a film that is heated.

The first can, especially in older engines like the L-jet Bugs, simply run a rheostat--a variable resistor. You can hook that to a gauge easily. The other two require electronics to feed and read. Those can be connected to a data-logging system or DIY meter, similar to the MPGuino.

You may be able to find some vintage rally equipment, like a gear-reduction box for the odometer cable. That way you can calibrate your speedometer and odometer.

I wonder if there's a reasonable way to read fuel flow from the tank to the carb? That would be a bit of a lagging indicator, because the fuel measured would be going into the float bowl and not directly into the engine immediately. But it could still be a help.

Hmmmm.....

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Old 09-25-2012, 01:13 PM   #6 (permalink)
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I've got one of those, too! That's more work than I would ever tackle, the only part you could reuse would be the chassis and nose. You can totally get a Type II that low, but I'm skeptical about the rear door hinge line.[/QUOTE]

Just warped it into the aero template shape. Just waiting for someone to make it.
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Old 09-25-2012, 02:05 PM   #7 (permalink)
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Quote:
I don't believe an air-flow meter in the bottom of the air cleaner will help. Not unless you mean just over the carb throat. There are three different air-flow meters that I know of; one uses a swinging flap (a "barn door") that gets pushed out of the way by incoming air, one uses a piece of wire that gets heated and measures how much heat is lost to the incoming air, and the third uses a similar method but has a film that is heated.

The first can, especially in older engines like the L-jet Bugs, simply run a rheostat--a variable resistor. You can hook that to a gauge easily. The other two require electronics to feed and read. Those can be connected to a data-logging system or DIY meter, similar to the MPGuino.

You may be able to find some vintage rally equipment, like a gear-reduction box for the odometer cable. That way you can calibrate your speedometer and odometer.

I wonder if there's a reasonable way to read fuel flow from the tank to the carb? That would be a bit of a lagging indicator, because the fuel measured would be going into the float bowl and not directly into the engine immediately.
The moving flap sounds easiest, but I like the no-moving-parts-covering-the-intake part with the other two. I believe the MPGuino would work with a carbed, non-OBD-II engine.
The gear reduction box will have to get in line behind marks painted on the speedometer face.
I saw some discussion here of in-line flow meters that made it sound like it's hard to measure the small volume flow accurately. But late model cars do it somehow.

botsapper -- Easier in Photoshop than in actual metal. Back in the 70's I saw a VW bus with the fastback roof from a 1950 Kaiser grafted on; that would be the closest I've ever seen. This design needs more taper in plan. I will address this with another photochop.
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Old 09-25-2012, 02:05 PM   #8 (permalink)
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This is the only correct template application you posted.



You can't "fudge" it onto other parts of the car. I'd start by tuft testing the stock one first and see where you need to begin fabrication. Maybe you can start the tail at the trim line/rain gutter on the back of the car. Maybe not. Only one way to really tell.
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Old 09-25-2012, 02:25 PM   #9 (permalink)
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Quote:
This is the only correct template application you posted.
What about this one:

I have a copy of the template with a caption that suggests treating the upper and lower surfaces differently (match height for the top, match wheelbase for the underbody). I did drop the ball on matching the underbody in the subsequent illustrations.

Quote:
You can't "fudge" it onto other parts of the car.
I read that as "if your going to 'fudge' it, you should really know what your doing."

botsapper -- How about front half VW bus, back half Bowlus Papoose (clone).
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Old 09-25-2012, 02:45 PM   #10 (permalink)
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Can't wait to see the results! Keep us posted! I like your ideas.

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