Aerodynamic design question. - Fuel Economy, Hypermiling, EcoModding News and Forum

binarycortex · 05-22-2009, 06:55 PM

I am hoping to get an old aircooled volkswagen again sometime in the future. I have always been fond of the beetle and would love another one. However I was looking at my son's VW Fastback Matchbox car the other day and was remarking at the shape. Since I have always wanted one of these too... I want to know what you guys think. Immediate plans would include bumper deletion (replace with T-bars) and rear wheel pants.

Image courtesy of Mo in wikimedia commons (permission cc-by-sa-2.5):

edit: I don't suppose anyone knows the Cd on one of these?

evolutionmovement · 05-23-2009, 01:52 PM

I don't think I've even seen one of those in 20 years that wasn't rotting into the weeds. I always kind of liked them, though. I doubt it's very good aerodynamically, but I would think it would beat the Beetle.

aerohead · 05-23-2009, 02:14 PM

I don't have any specific data for that car.Like the Beetle,it is a quasi-fastback roofline,too steep for attached flow,so some sort of rear modification would be required to accomplish wake modeling and reduction.Other than the fact that there is no grille opening in the front,the car just doesn't have any remarkable attributes for a project car.If you like to lay under there and adjust valve lash every 3,000 miles and you happen to really like VW then go for it.W/O emission controls,these early engines are kind of an environmental liability.A Karmann Ghia might be a better starting point.About 18.5 square feet frontal area and Cd 0.39,and a much better roofline to, start with.Just my opinion.

Frank Lee · 05-23-2009, 02:59 PM

They have nice flat bellypans too

binarycortex · 05-24-2009, 12:54 AM

Quote:

Originally Posted by aerohead

I don't have any specific data for that car.Like the Beetle,it is a quasi-fastback roofline,too steep for attached flow,so some sort of rear modification would be required to accomplish wake modeling and reduction.Other than the fact that there is no grille opening in the front,the car just doesn't have any remarkable attributes for a project car.If you like to lay under there and adjust valve lash every 3,000 miles and you happen to really like VW then go for it.W/O emission controls,these early engines are kind of an environmental liability.A Karmann Ghia might be a better starting point.About 18.5 square feet frontal area and Cd 0.39,and a much better roofline to, start with.Just my opinion.

Yes as a matter of fact I am a VW fanatic and I don't mind adjusting my valves. I would love a Ghia but I'm not sure I would fit in a Ghia cause i am 6'4" but I know I would fit in a fastback/squareback/notchback. This would not really be a project car for me, especially since I dont have the time or money to do much. Now if the fastback roof line is too steep for attached flow I could either use zig zag tape or go for a squareback and a mini kammback. But then again I could just go for the original beetle and pull an Ernie Rogers. I wonder if my new beetle would benefit from zig zag tape? Hmm...

Frank Lee · 05-24-2009, 01:28 AM

The VW Fastback would probably respond nicely to a spoiler.

binarycortex · 05-25-2009, 01:07 AM

Quote:

Originally Posted by Frank Lee

The VW Fastback would probably respond nicely to a spoiler.

Where at do you think? The very end of the fastback roof line (trunk transition to vertical) or higher up like maybe under the rear window.

Frank Lee · 05-25-2009, 02:27 AM

I don't know. I'd think that, for max effect, the lower the spoiler mount while allowing it to work, the better.

Geebee · 05-25-2009, 03:10 AM

Roof guters would have to go.
The big question is what the air intake and outlet would do to the airflow.

aerohead · 05-26-2009, 06:37 PM

Quote:

Originally Posted by binarycortex

Yes as a matter of fact I am a VW fanatic and I don't mind adjusting my valves. I would love a Ghia but I'm not sure I would fit in a Ghia cause i am 6'4" but I know I would fit in a fastback/squareback/notchback. This would not really be a project car for me, especially since I dont have the time or money to do much. Now if the fastback roof line is too steep for attached flow I could either use zig zag tape or go for a squareback and a mini kammback. But then again I could just go for the original beetle and pull an Ernie Rogers. I wonder if my new beetle would benefit from zig zag tape? Hmm...

I'm 6'1" and my hair brushes pretty close to the headliner on the Ghia.If I had to choose between fastback and squareback,I'd go with the fastback since its roofline is already "going away".A rear spoiler like Frank has mentioned would get you re-attached flow.You could also do multiple foils like Merkur did in the 1980s with the Xr4Ti.MetroMPG has a thread for a" permanent Kammback".If you do a search for that,you'll find an aerodynamic template which would provide the proper geometry for your spoiler(s).That would get you started.A fresh 13-mm 6-point open-end wrench and feeler gauge for the valves and you're good to go!