Aeromodability of a VW Bug?

[aerohead]

On the Bug,since it's air-cooled,you're most likely going to have to respect engine cooling first.When I did my VW bus,I purposely left the bottom of the boat-tail 'empty'.I had no facility to evaluate cooling performance and since the #3 exhaust valve, stretched-failure-mode is very real,I was reluctant to take any chances on that.
Aside from that,the diffuser angle should be as shallow as the studies encourage,and THEN,as reality intrudes on our wishes,make compromises to keep the thing alive,i.e. make it steeper in order to preserve it!
GM licked this problem with it's EPCOT car which had a variable-pitch diffuser.

[aerohead]

Originally Posted by gtkid2002

Yeah. I'm not sure if I should allow compensation for if I hit a speedbump or if I hit a pothole, as stupid as that sounds. I'm thinking of this thing for being used only for highway and some mild city use, so the suspension wouldn't be being used much.

Although it would be kinda cool to have it be fiberglass or something till the last four to six inches between the body and the road, and extend it down to about two inches or so of easily replaceable chloroplast or something for makeshift wheel pants (I really didn't know that's what they were called. Kind of a silly name, but it fits!). Or cardboard so it's recyclable, and if it does scrape off, it'll be a bit more biodegradeable than a Styrofoam cup, haha. I guess I have to keep in mind that I will use a socket wrench for a hammer now and then. Probably should design the car for higher clearances so it doesn't get the belly pan raped every time I take it up a steep driveway.

I know my skillz aren't anywhere near the caliber of some of the stuff Botsapper posted, but they should be enough to make a roll cage with a skin. That's basically all I'm doing.

Although I still have no clue how the crap I'm going to make doors. That is the only thing that concerns me. I should be keeping the original VW doors, so I could always repurpose those hinges or maybe even a good portion of the door. Make it so it uses the stock window, but chop the top part so it only goes halfway up or something.

Another thing has me wondering - Could I get away with using Plexi for the windows on this, or does it -have- to be safety glass? If I can use Plexi, I will for as much as I can, but if I must use the original windows, then chances are this thing will have funny looking windows.

I was playing with that online fluid program a bit more, and I ended up making a design that didn't seem to do too badly. It kinda looks like a messed up ice cream cone. Here's a link.

I know the aerodynamics are different, but I figure if rockets can use pointy nose cones, why can't I, at least for testing?

Another thing - That Aerodynamic template reminded me of a Deer Hoof. Just one side of it. Randomness Achieved.

I believe that you can use Plex/Lexan for everything but the windshield,it must be laminated safety glass and clearly labeled.
With respect to 'pointy',on ballistic structures drag is ruled by shockwaves and sharp,pointed leading surfaces are a must.
On cars,up to around 250 mph,drag is ruled by separation.For below these transonic speeds,a blunt semispheric nose is adequate for satisfactory flow penetration and the fore-body should be about 1/3rd the body length.To prevent separation the air needs about twice the distance for deceleration to prevent separation.The Template does this.It is separation-free.Beyond 70% the air will form a 'phantom' boat-tail locked-vortex with the outer flow skipping over it like a solid structure.
The modified Bonneville bug pictured earlier might be inclined to swap ends.It's center of pressure would lie in front of its center of gravity.Extremely unstable!
As far as your body,you can use metal lath and plaster over bulkheads/formers and stringers,shaped foam,wood,FRP,hammered metal on tree stumps,shot bags,English-wheel,shrinker,planisher,-------------------.
Many ways to go.
In 1928 Paul Jaray took a standard Chrysler 72,unbolted the body,tossed it,and replaced with metal-on-wood body of his creation with less than half the Cd of original car.58% better mpg and half the horsepower at 60 mpg.Fun!

[aerohead]

Originally Posted by gtkid2002

I wonder if I can get tires like in the video that skyl4rk posted and use them legally nowadays...

Nimblemotors - I would try and do something like that, but I don't really want to play with the original body. Considering for starters I'm just having a roll cage and a wire mesh/fiberglass skin to start with, that seems like a ton of work. I would consider doing an EV, but the kits for those are uhh.. pricey. I know doing an engine swap is as well, but I also would really be stuck at home with that because of a lack of charging stations.

Heh. But the concept of driving a backwards VW Bug does sound really amusing.

Pendragon - I'm going to leave the stock suspension in place, I was just thinking about leaving the body (at least some of it that would be easily replaceable) in areas that could get damaged so I could streamline a bit further. Although that just got me thinking. It would be a pain, but make individual wheel pants for the front wheels, and still have them enclosed by the main body (with access hatch of course) so that way the wheel pants would bounce with the tires and not be damaged.

In anticipation of the debut of it's Airflow in 1934,Chrysler Corp. constructed a special DeSoto with backwards body which a famous race driver of the day drove from coast to coast to illustrate how cars were designed 'backwards.'
Reversing the body reduced the DeSoto's drag from Cd 0.612,to Cd 0.51.By 1935-1/2 Carl Breer and his team had modded the Airflow's drag down from Cd 0.51 to Cd 0.244.

[JMPVW73]

http://www.youtube.com/watch?v=9XUKO...eature=related

[rmay635703]

I remember you mentioning liking the idea of a pointy front end like a rocket, well here is one that already did that.

Subaru itself modded its VW buglike clone the air cooled subaru 360 into a bullet car.

http://ecomodder.com/forum/showthrea...0-a-14887.html
Subaru Drive Magazine: Summer 2006

Given the fact your car is aircooled a bullet car would make more sense than a more effective tadpole shape. Remember though that a bullet car by area is not as affective as a tadpole but it works with your VW motor.

Now the issues, a subaru 360 sucks air from the sides (force vented over the motor) the rocket car tunneled it from the front through the ducting over the motor, your VW would have to be modified in a similar way to get enough air.

Good Luck
Ryan

[gtkid2002]

Gotta love last minute hectic changes. Right now I'm slowly working on stripping the Baja down to the chassis. I have the body unbolted, and I'm working on ripping out the rest of the internals while trying to keep the wiring system intact. So far it's easier said than done.

Aerohead - Thanks for the heads up about the front window. I might have to do some editing on the design to allow for the rear window to be the front or something. It's quite a bit more curved than the front, and might work at least a little better. On that step, I'm frankly unsure of how to get my hands on a decent sheet of safety glass for cheap, but for now I'll manage.

I'm hoping for the final version to have an old rabbit diesel engine in it, so air cooling shouldn't be an issue for long. I might just have to do a partial undertray and have the rear exposed so the engine stays cool for now, then patch it up when I have the engine and one of those Kennedy adapter plates. I just really want something FI'ed so I can use some sort of an economy gauge. I know I could use a vacuum gauge on a carb, but I don't really know how to read one of those. That and I'm more used to an FI setup than a carb. Fighting with tuning the friggin thing every few thousand miles isn't quite my cup of tea. I know you're supposed to with injectors, but at least those can go a bit further before needing to be messed with.

[SwamiSalami]

Hey man, just wanted to say good luck with the beetle. I drive a new beetle that I'm currently aeromodding for my engineering class. I'll be putting up the pics when I'm done. Look forward to seeing your progress.

[Pendragon]

Originally Posted by dieselbeetle

Hey man, just wanted to say good luck with the beetle. I drive a new beetle that I'm currently aeromodding for my engineering class. I'll be putting up the pics when I'm done. Look forward to seeing your progress.

Here is a diesel VW Beetle which used some fairly practical aero mods to clean up the back end flow. You might want to take a look at it for your own project.

It was covered in a number of articles such as this one which raised the interesting question of what the OEMs could do if a back yard project could accomplish so much.

There is, of course, VW's BlueMotion project which utilizes some surprisingly simple vehicle modifications to help out the drive train which is the star of the effort.

[Edit]
P.S. My personal favorite is the Opel Eco-Speedster project.

[gtkid2002]

Friggin criminy. One would think it would be -easy- get get rid of some off road tires and such. Just for reference, this is the bug/baja I'm going to be stripping down and rebuilding from scratch. It's not pretty, but it has a clean title, which makes this car perfect. I have to rebuild the carb before it'll run without me dumping gas down it and run rich for thirty seconds before dying.

[tjts1]

Originally Posted by Flipper_1938

Aircooled vws don't live very long with a lean fuel map. They historically have used excess fuel to help with engine cooling.

If you really want fuel efficency, swap in a small water-cooled motor.

With an EFI system and wide band O2 sensor working in closed loop, you could use water injection to allow you to run the engine as lean as you want. It would also be interesting to see if you can replace the belt driven fan with PWM electric fan run in closed loop with a cyl head temp sensor.