Project, the Third - Now contains collabsible boat tails (1971 VW SuperBeetle)

[aerohead]

Originally Posted by freebeard

I showed my work in post #10

The original file name was 'template MRT1022.jpg'. I find a proportion of 7 to 4 or 1.75. Width at the base of the B-pillar is 56".



So if I 'eat' the vortexes at the drip-rail, I could lose attached flow down the back. But if the vortexes impact on the flat top of the boat-tail instead of the road, wouldn't that break them up? Or would the degenerate into new vortexes on the edge of the tail?

The Coanda thing is a little in-joke among myself. You can ignore it. The fenders would probably go to an aero-form, but they would be a lot more work, with the compound curves. I know the bottom half of the boat-tail is compromised.

Looking at an image of a 1966 VW 1300 Beetle from car-blueprints it looks like a workable plan-view tail would come to a point at about 33.5" behind the body ducktail.And if the rear wheels were 'inside' the body,as with EV-1 and the 1st-gen Insight she might do okay as a minimum.
The problem I see is in elevation,where the body is twice as blunt as what we see,completing a mirror image of itself below the ground.
From wind tunnel studies,any roofline faster than the "Template" is going to invite separation and vorticity formation,produced by disparate flow velocities and pressures along sides and top,as well as the slope of the back itself.
With the boat tail below the greenhouse,it does nothing to mitigate the velocities of the air along the sides and top,so it can't really prevent the separation and vortex formation.
And it may be that the vortices will simply propagate outwards above the tail.
If they strike the tail's top surface it will cause an asymmetric discontinuity in the vortices themselves as they crash into the tails top.
The only fix I can think of is to raise the 'roof' of the tail to mimic something like the 'Template.' It should kill the vortices.
You'd need a 'tunnel' to preserve rearward vision and you might want to move the mirrors outward to help with the blind spot created by the tunnel.
If you truncated the tail even with the back of the original bumper you'd have the potential for around Cd 0.25.It would look like the images on page-3 of your thread.

[freebeard]

COcyclist -- I remembered I keep a copy of Chrome around for viewing Flash content, so I saw the Sim-Drive. I remember it for the external door braces. But that's basically it.

I'm still trying to resolve the backlight without going to that two piece design. I lean more toward a Tropfenwagen/Studebaker Starlight plastic window laid over the stock glass one, or sail panels on either side of the stock backlight like an El Camino (the good years).

Originally Posted by aerohead

...a point at about 33.5" behind the body ducktail.

If by that you mean the rear apron (overall length less the bumper), then we concur. I will work up something that shows the fender situation. Even though my profile picture shows a design with a narrowed rear track, this car will never see that.

Raising the rear deck height would bring it more in line with racing practice. I'm a little concerned about compromising engine cooling air, but maybe I can make it *better*.

[freebeard]

Here we have two aero additions, the longer one is truncated to the length of the shorter. And the second picture shows the two combined.

This is a Preview, there's something funny about the way the wireframe and transparency don't agree. A little fiddling with Material Zones and I can show a rendering with the backlight.

[AndrzejM]

Don't you think that the horizontal part should taper to the back a bit more?

[elhigh]

Hi,
I've always been an aircooled fan, though I've never owned a Beetle. Time and money, I guess, though the initial buy-in on a VW is, I know, pretty low.

Anyway. Part of my enthusiasm has been expended reading "Hot VWs" magazine, and a couple of years ago they ran a series of articles on what they were calling a "mileage motor." The goal was to achieve 40mpg while keeping up with California traffic - not poking along at 45, but hurtling with everybody else at 70.

They never made it. But they got darned close.

Link to the entire series of articles, as hosted by CB Performance parts. Interestingly, to optimize the engine for economy, they wound up building one that was also impressively more powerful, WAAY more torquey than the original.

The best numbers I saw were around 38mpg. That's not bad, and for a 40 year old car it was amazing.

[freebeard]

AndrzejM -- The Template is unforgiving. In this case I added a section in the middle and changed the width/height ratio, but that is an otherwise accurate truncation of the Template form. If anything it could slide forward until stopped by the door opening, but the tops of the rear tires are the constraint. Them being 3' further back and 17" wider than the B-pillar gives the result you see.

Here is an earlier mock-up:


I think in the next iteration, I will move the back bumper back 18", curve the lower aeroform to fit and let the upper aeroform overhang the bumper by 18". Doing so would not lose much taper.

elhigh -- I've driven nothing else since my current car sold new in South Dakota in 1972. Except for all the Type IIs and Type IIIs.

Economical; but I spent money every month on HVW ...and VW Trends ...and VW Greats ...and Porsche/VW ...and Volksworld and UltraVW from Europe, and etc. I got the MIleage Motor series off the newsstand and the VW Greats article on Karcey's Ghia.

HVW should have put that Mileage Motor in a top-chopped Rat Rod, and hit 50 mpg (see my Profile Picture). I want to go half drivetrain and half aero to get to Prius-like mileage, 42-45mpg.

For a good look at VW mileage discussion try:
Gas mileage discussion + thread collection

[elhigh]

I see I have little useful to add.

Carry on!

[freebeard]

Well thanks for commenting in the thread. I'm on a fixed income and things move slowly. I can use all the encouragement I can get.

[euromodder]

Originally Posted by freebeard

If anything it could slide forward until stopped by the door opening, but the tops of the rear tires are the constraint. Them being 3' further back and 17" wider than the B-pillar gives the result you see.

Here is an earlier mock-up:

The lower design is the way to go.

[slowmover]

Originally Posted by elhigh

I see I have little useful to add.

Carry on!

The description of intention was appreciated. I spent years trying to figure out best economy for a trailer towing sedan. Got close . . . and had cubic yards of hot rod mags going back a few decades. There are plenty others around here as well who've trod this road with their dream vehicle.

I didn't know about the econo series, but have read a few VW mags along the way. I was quite impressed by EFI, electronic ignition and extra gears. The last Bug I drove was a Super Beetle back about 1977. A pig. But, because a Bug, fun!

Glad someone is trying something out.

Time or money, but never both, eh, freebeard?

.