Aeromodability of a VW Bug?

[kach22i]

Originally Posted by some_other_dave

The "duck tail" spoiler reduced lift in the rear, to the point where the factory required people to use front spoilers if they added the duck-tail. It also decreased the drag of the car, most likely by making the air flow over the car more closely approximate the "template".

Reached just a little to far, first part is correct, everything in red is wrong.

The duck tail increased drag and cut a few mph off the top end speed as well. There is more downforce with the Duck Tail, and better cooling. The later wings/tails provided similar modest down force but much less drag.

A chin spoiler is a good idea with or without a tail. If you add a tail of any kind, a chin spoiler is a must.

[kach22i]

Originally Posted by rmay635703

Frank the passengers could sit backwards

I need to draw this, or do some sort of overlay.

EDIT-1:
Automobile pictures by kach22i - Photobucket


I could fold up the legs of the people on the rear. Remember the transaxle shown is in the middle, not where the legs are. Still, the feet have to stop short of the axle, going over the top is not an option, right?

EDIT-2: Trimmed it up, not template perfect, but closer to my earlier freehand sketches.


The human figures could sit more upright like in the original VW Beetle, but again, I was shooting for those earlier sketches which were very compact.

I'm showing a 7'-11" wheelbase, not sure if that is a perfect match for the Beetle. If stretched to 8'-5" or more, there could be more leg room, maybe even split it front and back if adding a whole 12 inches.

EDIT-3 Yepper's, a close match, which is what I remembered.
Volkswagen Beetle - Wikipedia, the free encyclopedia

Wheelbase 2,400 mm (94.5 in)

I'm showing 95", but need more length.

EDIT-4: Not a VW, but shows how far forward (and low) you might be able to go, if willing to risk your life.


EDIT-5: I forgot to think in 3D, the rear passenger will have to be a single center placement if the teardrop shape is to be followed in plan. Therefore his feet (as 6-foot male as shown) may end up raised in the air, like a lounge chair.

EDIT-6: Some body issues at the rear I did not quite expect, which is why I like working in clay verses going back and forth between different views.

Automobile pictures by kach22i - Photobucket

[CFECO]

In order to move the passengers forward, one could split the torsion tubes apart, use the lower one only, with a-arms for the upper suspension members. For proper camber control the upper arm pivots would need to be "active", (rotate on an eccentric shaft during vertical wheel travel). For best aero, your "wheel level" body sides should be generally straight from front to back in your plan view, at least from the aerodynamics expert I was using for my X-Car.

[kach22i]

Originally Posted by CFECO

In order to move the passengers forward, one could split the torsion tubes apart, use the lower one only, with a-arms for the upper suspension members. For proper camber control the upper arm pivots would need to be "active", (rotate on an eccentric shaft during vertical wheel travel).

Sounds like too much work for a guy like me, for someone with a different skill set, this is great information.

Originally Posted by CFECO

For best aero, your "wheel level" body sides should be generally straight from front to back in your plan view, at least from the aerodynamics expert I was using for my X-Car.

I agree, but a modest Coke-Bottle is not going to kill it either, is it?

This latest plan view varies from my earlier freehand felt tip pen overlay sketches, at least in the lower "wheel level" (love that term). Of course, those sketches were truncated because of paper size, and the front view did not quite match the rear view, as often is the case with quick concept sketches.

This concept needs more work, but I've already fantasized about purchasing a large plastic model of a VW Beetle and building an aero shell (or two) over it. I had a smaller model as a kid (10-11 years old), tossed the upper shell body to design my own but never did. I later went a little crazy and glued the VW wheels to a F-104 Starfighter (minus main wing and tail wing) and called it the "fastest car ever".

[Gerrelt]

Originally Posted by kach22i

Beetle Aerodynamics / Roofspoiler link

Creating a roof spoiler link

I've been lurking on this site every now and then, and I am honored that a link to my site is posted here!

I just wanted to inform you that I did some wool tuft testing with and without my spoiler.

I've got some pictures and video's on my site. I wanted to post the link and some pictures here, but I can't because I don't have 5 posts yet.

If somebody is interested in the link, e-mail or pm me.
Or go to my site and go to Aerodynamics -> Aero Wool Tuft Testing.


Greetings,
Gerrelt.

[kach22i]

Originally Posted by Gerrelt

.
Or go to my site and go to Aerodynamics -> Aero Wool Tuft Testing.

From page 3:
Without spoiler - Page 3

Look at the top tufts, they follow the shape of the rear window rubber. They are pressed against it, forcing it to follow the shape.

This is not at all what I expected. The wind tunnel smoke images I posted off of your site show the air leaving the surface at the top of the window trim. Air at the middle of the window without the roof spoiler is still attached to at least the middle of the rear window.

100 kph is equal to 62 mph, a more common highway speed in the USA is 72 mph (at least for me). Would the extra 10 mph dramatically alter the tuft results?

EDIT: at the beginning of "vw beetle wool tuft test 2" video, the tufts in the middle of the window seem to wiggle a bit, but are still flat against the glass.

Gerrelt, what level of turbulence if any is this considered?

[Gerrelt]

Hi Kach,

I don't know why the smoke in the windtunnel picture is leaving the car at the rear window. I think it's because the smoke is a little heavier then air and that's why it is "thrown" out of trajectory. It could also be that the smoke is getting to thin to see at that point.

My results are consistent with the results of autospeed, so I think it is valid.

I don't think 10 mph would make such a big difference. To tell the truth I was driving a little faster then 100 km/h in the "without spoiler" pictures/video. But it was something like 110 km/h. So, like 9 mph more.

I wonder at what speed the Volkswagen windtunnel picture is taken..

I read a chapter of a book explaining the basic principles of aerodynamics. It's also online available. I recommend that book very highly. As soon as I can post links, I will post a link.
It also covers the angle of the rear of a vehicle, and that it should be cut off like a Kamm rear, or have a certain angle (like the Prius probably).
The beetle rear is somewhere in between.. which is not good.

Greetings,

Gerrelt.

[aerohead]

Originally Posted by kach22i

From page 3:
Without spoiler - Page 3



This is not at all what I expected. The wind tunnel smoke images I posted off of your site show the air leaving the surface at the top of the window trim. Air at the middle of the window without the roof spoiler is still attached to at least the middle of the rear window.

100 kph is equal to 62 mph, a more common highway speed in the USA is 72 mph (at least for me). Would the extra 10 mph dramatically alter the tuft results?

EDIT: at the beginning of "vw beetle wool tuft test 2" video, the tufts in the middle of the window seem to wiggle a bit, but are still flat against the glass.

Gerrelt, what level of turbulence if any is this considered?

I believe that the smoke is the more accurate indicator of the flow.
The air should detach right at the window trim and then crash against the rear of the car so as to allow the engine to harvest it for cooling.
Once the tangent angle on the roofline exceeds 22-degrees(as measured against the horizon)the flow cannot remain attached.
Attached-vortices can hold the tufts against the body but it;s a 'false-signal' when reading only the tufts.
Smoke is the preferred visualization tool.

[Sven7]

[CFECO]

Rc ?