Aerodynamics of a bug
 

I've read the last aerodynamics post about the Ghia but what about the bug?
I'm still in the process of rebuilding my Oval with Porsche power (3.2 230bhp mid mounted) and as the car will weigh less than the 911 3.2 Carerra, it'll do more than the 150mph top speed capable from the 911.
The last time I ran my bug to 120mph, it was all over the place, the back end was very light.

VW have limited the new Beetle to 145mph, even the RSi with the spoiler which pops up above the rear window. They've also limited it in racing so there is def a problem.

I don't really want to change the body style hugely and a pop spoiler would be good but it looks like it'll have to be a huge wing to make any difference.

Anyone run their bug up to 130mph plus?

MG

How about looking at the floorpan.

I was thinking into making some venturi channels under the floorpan and getting some carbon sheets to close of the front and rear part of the car as much as I can. This way the air can not get in areas you do not want it and it will accelerate the air flow pressing the car down more on to the street.

Well this is all theory....do not know if this would really work.
Alex

Floor ducting
 

Alex,
I like the idea. As I'm going to be starting from scratch with the chassis, I may be able to incorporate something into the design.
I think the only street car which has ever made proper use of floor ducting is the Jaguar XJ220.
I may be able to fit a front spoiler under the bumper with ducting through the shell and out the back... I also need to feed the engine air so this may have a dual function.

Thanks
MG

Try to find a pic of the Ferrari Enzo. I have one from Auto Motor & Sport of the floor. Extremly amazing. Totally flat with 2 venturies in the front on each side and a variable difuser in the back.

I see if I find a scanner and I will email you the pic.

Alex

Re: Aerodynamics of a bug
 

Well, not quite that fast, but it went 117,3 mph (real, digitally clocked) with the 2 ltr and was still reasonably stable at that point.
Maybe you can also get some idea's of the car from dr. Jozef Gerold, when he last competed in the Käfer Cup series in Germany.
Doing s/th with the floor pan is still the best idea since it will not 'spoil' the looks of your Oval.

Good luck,
Walter

Not quite that fast either, but I run a spoiler on the track, and it makes a real difference. I know what that 'light' feeling feels like, and its not nice, but with the spoiler the rear never feels light. Couldn't tell you if the car is faster round corners with it, but it sure gives me more confidence...

I read somewhere that one of the problems with the bug is that air gets trapped under the fenders.
I've seen a couple of 'race' bugs with louvres in the back of the front fenders... maybe that's something ?

This is a pretty cool thread.....I've been looking for an excuse to get me one of Carbon Joe's rear wings :D :D :D

Rob.

I've had my bug to 180-190kph ONCE ... at that speed the rear end was VERY unstable. It felt like the rear was floating. This was with 195/65/15 tires, front 3/4" swaybar and no rear swaybar. The shocks were 14yrs old.

I'd like to try this again when I install my 18" wheels and brakes. Since then, I've installed a 20mm front adjustable and 24mm rear adjustable bar but I think I won't be able to hit that speed again as the resistance from the tires will be high. I've only got a 914 2.0 and with the foot to the floor, the car would not accelerate anymore.

I like the idea of looking at the floorpans, thus keeping the body looking stock. I'm not one for huge wings but a CarbonJoe roof spoiler would look nice.

So how do you go about modding the floorpan ? I'm sure a front spoiler would work too but not sure if thats an option for a split.

Sandeep

Hello:

I know it's not a Bug, BUT the Audi R8 has probably got a pile of airodynamic research as they do 200 mph and really want to stay attached to the race track. Remember the flying Mercedes at Le Mans a few years ago?

Anyway, there's some good photographs and interesting information at: www.mulsannescorner.com/audir8.htm

the first picture shows air management around the front wheel wells (note the slots on top of the bodywork above the wheels too) and another picture further down the page shows the rear diffuser.

I think the comments of some of the previous posts are correct that air under the car is as important as air over it. Clever work could build under trays but I think a diffuser would really help. And the slotted fenders talked about are shown in the "Japanese Racer" tech article. I wonder if you could make slotted fenders look good on a road car? Driving in the rain will produce some interesting spray patterns too!

DaveM

Whoow... This are the topics that I like.. where i'm very interesting in....:silly:

How does the air have to move under a bug to be so optimal as possible?

I'm going to mold a aluminium spoiler (high wing)for downforce and of course for the looks.

Works holes in de fenders really???

Greetings Wiebrand

Here's what we need to do .... does anyone have a video of a bug running down the highway with small peices of yarn taped to the car ? I saw this somewhere once (new beetle I think) and judging by the way the small pieces of yarn react, you'd have an idea of high and low pressure areas ?

I'm still unclear as to how the underpan system would work.

I thought that the reason the Porsche at Lemans a while back flipped was because of air getting under the front of the car ?

Sandeep

have spent most of today under a lotus elise and it has a compleatly flat under try with a small venturi[?]at the rear,also 2 small naca ducts under engine/gearbox.ducting also from the grill in the front exits from the bonnet vents after flowing through the rad.worked an a exige[motorsport elise]a few weeks ago and that had vents in the back of front wings and sort of vanes directing air towards the sides and the rear venturi.also a big wing up in clean air.
i know a lotus is no bug but,you have to take ideas from any whare.
cheers rob

I just bought a 74 pan for my 64 bug and I am going to replace the floor pans with sheet metal just flat as I do not need the extra head room provided by the lower area of the floor pan. I am installing racing seats that sit low. What I am planning on doing is building 3 or 4 sections of flat sheet metal probably aluminum for weight to have a completely smooth underpan. Removing the floorpans will give me a smooth flat pan all the way back like a RC car. I am also installing a 13b Turbo rotary inback and plumbing it for the rad up front. sence my motor will not need the air to cool it I am going to inclose the bottom of the engin bay too. I am going to run some small channels in back to create a defuser ie down force. right before the transmission on each side I am going to install two naca ducts to feed the tranny with air. up front I am going to have a small spoiler to draw air to the radiator. Next installing two channels forcing air to the side for the brakes. I will also do the same in the back to direct air to the rear brakes. The front and rear sections will be removable for service on the suspenstion and engin. This should reduce drag under the car and give a bit of down force at the rear. I may go as far as cutting out part of the rear apron to create a real difuser.

I have looked at this subject for quite a while. One of the problems with looking at other race cars is that the aerodynamics are often dictated by the rules and not the possibilities of the engineering. Most of that you see is the car designers ideas to get the most out of what the rules allow.
For example the vents to the rear and top of the fenders is to relieve lift in the fender wells as a result of the of the GT racers going airborne. The rules made these mandantory. They do decrease lift, but also create drag.
The flat pan is also rule mandated. It is not the best undercar design, but it is required. Since I am not rule directed I have come up with some interesting ideas.
You have to approach the aero as a package not just individual parts. The following is some of my ideas, many which are hard to explain quickly without pictures.
Closing all the air catcher holes around the front end is a start. It is good to keep air out of the box section where the steering box and MC are located. To the front of the fender a plate can be placed in the fender to keep air from getting into the fender well. The rear of the well also has a plate used to direct air out of holes in the fender at about a 45 to 60 degree angle. This would be a lot of work for limited benefit unless you are going really fast. The same applies to the rear fender well.
A front spoiler is a necessity. Sorry it just is. You can use it to keep air from under the car or to channel air to your underbody aero mods. Another mod for the front is small strakes (triangular plates set at angles to the ground) on the outside of the fenders. Effective but obvious.
A rear spoiler is a necessity also to break the rear lift. It doesn't have to be very big. The angle is important. It and the underbody difusers output should create a defined flow much like using sheet metal. If drawn it would look like a pointed tail coming off the rear of the car. The spoiler can also be used to pump a wing. In order to work properly the wing must be positioned over the ground with no car parts under it and as low as possible. This would look quite weird and work very well, maybe to well as it might lift the front end. Raising the wing until the airflow from the spoiler flows below the wing would pump the wing and perhaps create the same effect.
At the least I believe you need both a spoiler to keep air from under the front and a spoiler to break the lift in the rear. The rear spoiler is going to have to be used. Most of the rear spoilers I have looked at don't work right or they have other problems like blocking the cooling vents.
I have some really good ideas on modifying the pan which work very well. I have tested them with a model and I was impressed with the downforce and the self correcting aspect. It seemed to create more downforce if one of the ends or sides lifted causing it to bring down the raised side or end. I will have to draw up some pictures to explain it. It is quite simple to make and is totally hidden under the car.
These are some, but not all of the areas I have been investigating. I hope some of it is of help.

for some really good info, check out this site:
http://autozine.kyul.net/technical_s...ooth Undertray

Thanks for the link to the article. It expains alot.

So am I right in concluding that pan modifications (venturi) on a bug will have a negligible effect on downforce ? The article said that the car would have to be very low to the ground for the venturi to work ?

Sandeep

Negative! The car can be high, but the closer to the ground the greater the effect of a venturi. To get around this and have sufficient down force you will have to hang a rubber skirt down to direct the air through the venturi. On a street or race car the rubber will eventually wear. I am going to use what is called industrial wall edging. It goes around the wall where it meets the floor to give a clean look in a factory. It is stiff, cheap, and readily available at Lowes or Home Depot. It is usually vinyl and about 1/8 inch thick.
Think of a venturi )( and then draw it on the bottom of your car.
])([ The )( part goes from the forward two body mounts on each side to the rear of the wishbone. AH crap I wish I could draw this as it is simple as dirt. Anyway you would pop rivet 1/2 inch aluminum angle in to the proper curve to the pan then pop rivet the vinyl to the aluminum letting hang down to the gound. You should trim the vinyl a little, but it will wear down as you drive the car till it is perfect. Warning the waist or narrow part of the venturi must be about six inches foward of the jack mounts. The jack mounts are the CG of the car and the max down force should be before them to keep the front end on the ground.

0 0
])([
0 0

The ][ is the edge of the pan.
This is still not a clear picture, but I hope it is better than before.

Wing/Fender vents
 

One thing that I have been looking at is wing/fender vents.

These are used in racing on full bodied cars. Holes or vents are placed at the top of the front wings, just behind the centreline of the wheel and then again at the back of the wing close to the bottom to release the pressure which builds up within the wheel well.
Thinking about the air when it is travelling around the front of the car, a lot of it is deflected around the front wings and in behind the wheel creating drag and also a small amount of lift as it has to go down to the bottom of the wing to get out.

At the back, a vent at the back of the rear wings does the same job of lessening lift as the air from inside the wheel well struggles to get out.

One of the big problems I have looked into on my car is how to get air to the engine. I thought about putting naca ducts in the rear windows but the bodyshell starts to taper in from the door pillars and this may create more or a vacuum at the rear windows than pressure if I were to fit ducts there.
Another idea was one I saw on a Bug which had a mid-mounted configuration where rear vents from a T3 had been fitted just below the rear windows to feed the engine. Again this is just after the bodyshell starts to taper in.

Another idea I have seen is from Porsche racing cars. The GT1 uses a duct which runs over the top of the roof, where as I'm not too into the looks of this on my Oval roof! I can appreciate how well this must work. One other idea has come from the 962 where the fan intake is on the roof, it's basically a huge naca duct which feeds only the fan to cool the engine. Looks pretty cool and if almost out of sight although it means cutting a large hole in the roof!!!

Lots of ideas!! Anyone got anymore?

Thanks

Mike Ghia

Re: Wing/Fender vents
 

I am still going to cover my floor as much as possible with 2 venturi channels in the back. I hope to work with Carbon Joe on this so that he can sell the stuff later.
I am also planning to close off the fender as much as possible to reduce air getting trapped there. I hate to cut the fenders and use any kind of spoilers on my split.
Rolf Klaus also told me that there was actually a kit available for the front of a standard to close of the gaps and holes at the front beam. He has an original that he thinks of reproducing.
He also send me a video that I still have to convert to NTSC and then to digital for the site from one of his autobahn cruises with his split.

As for getting extra air into the engine.....Gerd Weiser has a scoop under the pan on his Oval and routes the air into the engine compartment....similar as what Sandeep did for his interior oilcooler.

When I had my bug in Germany with the T1 was not scared to drive at 180km/h. I did it all the time and that was without a fancy suspension. Konis all around and lowered quite a bit without swaybars.
The brakes were the scary part........VW disks on the front and drums at the back.

Alex

I am going to incorporate an air channel at the base of the wing with a slight curve to force air into the top of the deck lip. You want to try not to have it forcing air into the carbs as that can upset the carbs fuel metering.

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If you can figure out this picture you are a better man than I am.

I wonder if wider fenders would help or hurt handling at high speed. Say 150 mph (240 km/h).:confused:

Hello,

Wider fenders would certainly hurt top speed. Take a look at the Ruf CTR, this was at one time the fastest road going car. This was also due to the narrow body Ruf used. If he had used the Turbobody is would have cost him certainly 15 km/h in top speed. But, do you really want to go 240 km/h in a bug?
My racecar lifted almost 10 cm ( about 4") at 210 km/h at the main straight. This was without any spoiler though, and 2" wider fenders. So.....;)

Cheers,
Richard

on one of Porsche's cars when they changed to a smaller mirror, they were able to go 3 mph faster. So, Im sure wider fenders would have a negative effect.

I will be interested in seeing what the difference is going to be when my bug hits the road in spring 2004.

I'm sure my top speed will drop with 18" wheels and wider fenders but by how much will be interesting. I'm sure the weight of the car will increase as well but by how much is the question.

Sandeep

Well now I have a reason to buy the RUF mirrors. I'll just need more power to push against the wind. :D

Yes, yes I do. There are some pretty fast cars around my neighborhood. Supercharged viper w/900 hp. A 9 second grand national. A 9 second mustang who's my neighbor. And one really fast 930 wide body which I have only seen once at a car show, garage queen. And yes I want to go 240 km/h at least just to beat those cars. What can I say, I have high expectations.;)

Don't forget your death wish either...
Walter

I don't have a death wish, I just have a lack of rational thinking when it comes to things that are dangerous.;)

LOL!:hehehe:
I like your way of thinkning, 240k isn't fast enough in my books, when you think of it I'd rather die in a car then in a bed some where!!

Good Call genius


John

Hello,

Well, I used to a bit like that too. But, getting older seems to mean that I'm getting less sack and more brains:confused:
You really can't compare a bug with a Viper or 911, certainly not at speed.
Let me know what you were thinking when you have done 200 km/h in a bug with a little crosswind. I know what I was thinking!:silly:
It was something like: "mmmmmh, wasn't I about 4 meters to the left, a millisecond ago?"

But, nothing beats the experience!:D

Cheers,
Richard

Hey john. Go to www.weissach.com to see the mirrors I was talking about.

WOW!:D Brendan you weren't kidding... those mirrors are tiny. I wish I wasn't doing a one peice window or I would use them too...
But instead of shaving the mirrors, I might check into the sports mirrors for the 996, they have....mmmmm HEEEEAAAATTTT!!!
Very cool!:D

Thanx for the link, I'm gonna use it more often now, to check stuff out..... maybe even look at the body kits:hehehe:
I like the 996 fornt spoiler....clean and stylish!


John

So expensive.:(


There is a reason that they want you to contact them for a price.:silly:

I don't know, It could be worth doin....in the long run, and it would look better than any of the front bumpers that I have chosen...:):D



John

John. there is a photo of a beetle in the general galleries with a stock 911 front bumper. I think it's on page 4 or page 6.:D

Brendan, I liked the red GL with the '993' bumper, it looked really good, I'm looking for something that speaks a little louder, but I thank you for the info:D:D

I just got the price quotes back for the parts I was wondering about....are you ready for this?

993 Instrumentaion:$1320 USD
993 Door Sills:$299 USD
993 Steering wheel:$895 USD ( I wonder if it has an air-bag)

996 Front Spoiler RGT:$2400 USD ( sounds like this idea is out!)
996 Sports mirrors:$995 USD

OUCH!!!:reallysad



John

Try www.betterbodiesusa.com for some more extreme front bumpers and porsche body kits.;)

Check out the used and discontinued section. There are some pretty awesome deals on wings and things. www.betterbodiesusa.com

They have a nice 935 front bumper cap for sale.:p

Thanx for the site Brendan, I love it, it fits me perfectly:D

I like the used and discontinued products......$$$$ SAVER!:D





John