Aeromodability of a VW Bug?

[aerohead]

Your beetles Cd should be more like 0.50 rather than 0.41.
The 1934 Chrysler Airflow had essentially the same drag coefficient.
With a bellypan,bumper delete,flush glass,raked nose,blended fenders and semi-decagonal panoramic windshield they aero-modded the car down to Cd 0.373.
Next,by bulking in the body void over the beaver tail,up close to the Template line,and chopped off vertical just like Fachsenfeld and Kamm recommended later,the drag dropped to Cd 0.32.
A 36" stinger boat tail was added finally for Cd 0.244.
For you to go to Cd 0.18 you'd need to stay right on the Template and extend the tail a bit further.
I've never seen a Beetle do better than 28 at real highway speeds.The Karmann Ghia( Cd 0.39 and approx 18.5 sq ft frontal area) body will produce 40 mpg on the same chassis wityh zero powertrain mods.

[gtkid2002]

Aerohead - If I had an all custom body that had a Cd of .18, using the stock VW engine, what do you think the mileage would be?

Also, I noticed on Aerocivic that the rear underside of the boat tail slanted upwards. Is something like that ideal or should I just stick as closely to the template as possible.

Right now I've got the top-looking-down view mostly sketched out, overlaid on the chassis. I can't use photoshop for crap so I'm doing it by hand. Right now I'm trying to follow the template for the most part, but I don't really like the idea of having it inflated a complete foot over where the chassis is, so it goes down in steps. Here's a picture of what I mean.



(Yes, I know not all the lines match up, but the jist of it is all I need right now)

Should I try and follow the lines I drew up, or just inflate the sides so it very strictly follows the template?

[Joenavy85]

yeah, i'm not sure if you would need the lockout on 1st gear or not, just putting it out that i have seen problems before (albeit with a significantly larger engine)

[euromodder]

Originally Posted by gtkid2002

Also, I noticed on Aerocivic that the rear underside of the boat tail slanted upwards. Is something like that ideal or should I just stick as closely to the template as possible.

Air doesn't know where it is
So the aero-template can theoretically be used on all sides.
That said, the bottom flow is more disturbed by the proximity of the ground so treat it more gently .

You can still gently lift up the rear bottom (and reduce the size of the wake further ) if you add or have a (partial) boattail.

See the tapering (but still cut off) shape a) in the drawing.
Drag will be reduced most with about 3° angle.

and


Taken from the rear-diffuser thread at
http://ecomodder.com/forum/showthrea...er-1831-2.html


Without distracting from Mike's work, the rear of the Aerocivic might be slightly overcooked
If only someone would wind-tunnel test it

Should I try and follow the lines I drew up, or just inflate the sides so it very strictly follows the template?

That looks almost area-ruled
You don't plan on going supersonic, do you ?

Try to more smoothly "boattail" the front fenders along the sides - they drop off way too sharply on the Beetle.
Something like this :

( Illuminati Motor Works )

Or this :


The doors may get in the way of the fairing though.

You could use a vertically hinged gap cover and a rounded leading edge on the covered part of the door to continue the boattail fairing on the door, much like a flap on an aircraft :
(see the covered gap on the bottom of the picture / top of the wing which is is upside down here)



Whatever solution you opt for, don't add extra frontal area by inflating the sides above the height of the front fender.


I'd fatten the rear fender ever so slightly (if necessary at all) and fully cover the rear wheel arc.

[some_other_dave]

Originally Posted by Joenavy85

... one of my dad's friends swapped a small block chevy into a Porsche 914 and the torque was enough to strip the teeth out in 1st gear...

That is a known weakness in the early 911 and 914 transmissions. First gear is cantilvered off the end of the mainshaft, and it can't handle much torque. The Bug transmission is a different design; blocking out 1st should not be necessary.

-soD

[Pendragon]

euromodder,

I don't have the technical background to make definitive statements, but it has seemed to me that the "aero-template", for reasons unclear to me, has quite simply ignored half of the equation by presuming that airflow under the car was either irrelevant or beyond the ability of the tester to influence. Its shape is half an airfoil.

Plainly, there are gains to be made by optimizing the under car airflow. Just how large the are I can not even guess, except to infer that they must be sufficiently large that VW and others have made an effort to work in that area on their project cars.

There are some circumstances where an increase in frontal area is worthwhile for aerodynamic reasons. One is "wheel pants" on fixed landing gear aircraft, although there are additional benefits to wheel pants in that application (mud, stones and other debris are not thrown into the aircraft, prop or whatever). Here are some others to illustrate the idea of making a fairing around the rear wheels.
Chief Aircraft Inc - Accessories - Airframe Accessories - Graphtech Wheel Pants

Wheel pants, ultralight wheel pants, ultralight wheel fairings, ultralight wheel skirts.

Here is a link to a homebuilt aircraft with wheel pants fabrication shown.

There have even been some fairings on the front wheels of street rods.

The point being that I agree with you that a fairing over the rear wheels would be worthwhile even at the expense of a small increase in frontal area.

Underbelly pans are complex and have to deal with the reality of suspension components, engine and exhaust temperatures (certainly don't forget the catalytic converter) and the need for access for service.

My thought, without substantiating data, is that attention to the rear underbelly of the car, as you have suggested will likely result in less drag from the low pressure area in "the hole in the air" and associated turbulence that all cars have to one extent or another. Someone or other recently made the pertinent observation that the rear bumper covers of many cars look like a giant scoop to catch air coming out the back of the car.

Here is a brief article about Richard Whitcomb, father of the "area rule", with some wind tunnel models. His observations are still benefiting the aerospace community and are employed in every jetliner you fly on today, but apply to transonic flight. I think the only earth bound vehicles to employ area ruling are the various supersonic "cars" making speed runs.

Cheers

[123]

Improving the Aerodynamics of a bug is an interesting idea. I am familiar with them I have one and also used to have a baja. What ever your car gets FE wise is better then my high performance engine with dual carbs.

The biggest issue with aeromodability of a VW Bug is the fact that you cant do anything that will effect air flow, not enough air is death to an air cooled engine.

Also I have never used a freeway flyer trans but many people don't like then because of the fact that they lower rpms. Lower rpms of engine = less rpm of cooling fan.

If you have never seen TheSamba.com its dedicated to old vws you will find lots of information and help there.

[botsapper]

I personally hate to destroy a cherry one but the Type 2 would be a better platform to create retro pillbugs, Teagues or Dymaxion-like projects. Just sayin...




Edit; Vapor concept requires expert-level metal fabrication skills & $$$. Interesting VolksWorld enthusiast and aero-awareness concept vehicle.

[Pendragon]

botsapper,

Those are some nice images, but would require some uber fabrication skills to build one like that.

[gtkid2002]

On the bit about the fenders, here's a different sketch of what I'm trying to go for. It's drawn over a basic stock VW chassis, although I don't think the seats are quite right. Should be ROUGHLY 1/10th scale. I think it's under 17Ft long, and so long as it's shorter than a Ford Excursion, I think I'll be okay.
As for the drawing, I need to find somebody who could do a fluid dynamics thing with it.


Botsapper - Nice P$hop work. Only concern with a type 2 (That's a bus I'm guessing) is that I think some of those parts are hard to find and rather expensive. A bug may have a few of those, but most should be easy enough to find.

123 - Yeah. Air cooled would require the fresh air source, which'll make things slightly difficult, but I'll work around it as best as I can for now. Isn't there some way to swap a pulley so it makes the fan spin faster with the freeway flier? Although if I do a diesel swap to the flier, it'll be liquid cooled and I won't have to stress as much..