CFECO's X-Car Project Re-Do

[freebeard]

^bwahahaha

Whachew laughing at? Hopefully not the article on STF.





It even answers teh question—more aerodynamic frontwards or backwards.

[Frank Lee]

I'm laughing at that stupid side view illustration.

[Frank Lee]

And those fender vents- I think they are *fails*.

[CFECO]

Originally Posted by Frank Lee

^bwahahaha

In the story , they were concerned with Lift on the Racetrack, not lowering Drag for Economy. 140MPH in a Bug at sounds pretty scary. I looped a Baja at 65 MPH, but i think it was a combination of it being very windy, topping a hill, and slush on the road reducing grip.

[freebeard]

Frank Lee -- Frankly, I knew that. I just used the opportunity to post some additional pictures. As for venting the front fenders:





These are about the Yokohama tire, I can't locate that picture of the Beetle body in CFD (maybe kach22i can help) that shows the air moving up at about 45° over the lower doors. I think it's caused by air exiting the front wheel wells.

I've spent some more time with that thread. Most relevant to my interest is this:



I can remove the perspective in Photoshop.

[Frank Lee]

Thinking more about it...

If the problem was hot brakes I can see those exiting fender vents improving flow past the brakes.

At the risk of sounding like Hermie, I agree that lift on a Bug can be a bad thing since they are reaching the speeds where it becomes critical. And in any circumstance, a body that creates lift is also creating drag.

Re: "The Fix": Agree the airdam is effective, and depicted but not labelled is the lowered suspension, also effective.

I have my doubts about the fenders causing lift and especially if they do, that those vents are a cure. I wonder if manometer readings on the outside AND inside of the back of the fenders would show low pressure? I speculate such because the flow past the wheelwell opening should be causing a low pressure on the inside- in the wheelwell- and the flow having to tuck in aft of the fender should also cause a low pressure on the outside- between the wheelwell and the door. I think both of those effect the drag component more than the lift. But I don't know.

I was thinking about why the top-of-the-rear-window spoilers seem to be more popular than the "Herold's (sic) Helper" style, below-the-rear-window spoilers. I'm confident the Herrod's have lower drag but I suppose the "top style" is better at reducing lift because it is more out in undisturbed flow, for the same reasons the Dodge Daytonas have their wings so high up.

That raised hood on "The Fix" made me laugh.

[aerohead]

Originally Posted by kach22i

Thought you might get a kick out of this.

Shoptalkforums.com • View topic - beetle and aero


Shoptalkforums.com • View topic - beetle and aero

The Beetle produces 57-lbs front lift at 100 km/hr (62 mph) and 100-lbs front lift at 100 mph.
The Beetle produces no rear lift.I'm at a complete loss as to why they show rear lift.

[freebeard]

Found it! I thought I was making this up.

http://www.youtube.com/watch?v=LtXOUrTc_dA

Those massive vortexes apparently aren't caused by the air exiting the front wheelwell, but by the rear fenders. Or not. At least in this simulation.

I have my doubts about the fenders causing lift and especially if they do, that those vents are a cure.

I'm more concerned with how you attenutate those in-rolling vortexes.

That raised hood on "The Fix" made me laugh.

Maybe it's a gauge cluster? I was more amused by the 'speed lines' and colored arrows that disappear with the 'fix'.

Originally Posted by aerohead

The Beetle produces 57-lbs front lift at 100 km/hr (62 mph) and 100-lbs front lift at 100 mph.
The Beetle produces no rear lift.I'm at a complete loss as to why they show rear lift.

http://http://www.shoptalkforums.com...92902#p1092902

Hi Slow1200,

I referred to the Sports Car Graphic article data, but only as their data.

Fisher cites in his "Stability and the Beetle" chapter (pg 141) of his original "How to Hotrod VW Engines" 68lbs of rear end lift on the Beetle body at 75mph, extrapolated to 136lbs at 100mph.

The numbers are from Paul Lamar, introduced by Fisher as a noted aerodynamic expert from Manhattan Beach CA, and I do not doubt his findings. Sports Car Graphic was one publication that used Lamar's information, but I don't know if Lamar had any input in the "Why Would Anyone Buy A VW" Sports Car Graphic article in which zero lift on the Bug rear end was quoted.

I went back and reread the Fisher chapter today, and it appears to be the source of the info that VW slightly raised the front suspension of the Bug (swing axle) to increase front lift and decrease rear lift.

We get all this info from different publications, but in the end it is application on the racetrack that matters. My own experience with aerodynamic extremes is with the 1973 Super Beetle IMSA car we had back in the mid-1970's which we ran at the Talladega Super Speedway for the closed-course speed record for a stock-bodied VW. That means no aerodynamic aids.

And we ran an engine that would have been illegal in IMSA B-Sedan. This was a speed record engine.

Our car could briefly touch 130mph+ on the straights, but didn't have the power to stick in the banking more than a third of the way up. And it was a handful. We had lots of rear lift that translated into the tail losing adhesion and trying to pass the front, so we were "crabbing" sideways at times.

We had a full pan but had cut away all the interior bodywork and tried to vent out air pressure filling the car's interior with holes venting to low pressure, etc.

I've got the stance down, 3 1/2" front clearance excepting the tow hook. I'm watching the PolyMetal scraps at the local recyclers; I don't want to use Coroplast (there's 10 full 4x8 sheets of that). So, a splitter/air dam, Nylon brushes about 2" deep behind the front wheels and under the running boards.

Remember the 'cheese grater'? It's a little decorative piece of tin that fits on the chrome tailpipes. I want a little baby diffuser that wraps the exhaust up behind the back bumper.




Edit: CFECO -- Sorry about what's happened to your thread. When I was a teenager my cousins on the southern Oregon coast told me about someone who topped a rise into a 100mph headwind and wound up on their back in the underbrush.

[CFECO]

No worries about the thread, when I get a chance to get more up, perhaps it'll get back to what I'm trying to do. ANY discussion of aero on the Beetle I'm interested in, so it's basically on topic.
I've prepping the 1/6 scale new beetle to cast a mold off of, so I can pour bodies to modify. I've decided to do the mold in two pieces so it will be easier to remove from the body do to the numerous negative areas on the model. The sock is full of coins to weight the body down to the cardboard base block off while the glue sets. Kinda crude I know, but it was handy.

[Frank Lee]