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Fri Nov 06, 2015 3:09 am

Hi,

I was wondering what aerodynamic mods folks have tried on streetable Supers? Some mods will improve stability, some will reduce drag.

Reducing aerodynamic drag is more what I'm interested in - the major part of this for the SB being 'form drag'. I understand the SB drag coefficient is 0.47 approx, and that drag is related to frontal area X drag coefficient so lowering helps. But there is also streamlining opportunities and areas of the car that could be smoothed. Air dams like the Kamei front spoiler help to reduce lift and turbulence behind the car. Smooth wheel caps, skinny wheels, shaving components etc. I've read quite a bit on aerodynamic drag but am by no means a practitioner, yet. What else have folks tried in the aerodynamic field and did it work?

Perhaps there are a few nuggets of aerodynamic ideas out there that would help increase mpg, reduce noise, increase top speed etc?

Again the focus would be on street driven vehicles. Any contributions?

Fri Nov 06, 2015 3:53 am

'Street' - you may not like, or want, to hear it, but aero is just about irrelevant below around 110MPH. So you may wish to investigate other ways of increasing performance such as gearing.

What is it you want to achieve?

Fri Nov 06, 2015 5:10 am

Anything that I have read on the subject starts with lowering. Of course you could look at what the Bonneville type racers do, but that tends to be pretty extreme. Also, there is a device called Herrod Helper - check this out

http://ecomodder.com/forum/showthread.php/old-scho...-7444.html

I disagree that there is no benefit below 110 MPH. If that was true, then why the hell cant I pull my travel trailer much above 60 with a headwind?

Fri Nov 06, 2015 7:52 am

andk5591 wrote: Anything that I have read on the subject starts with lowering. Of course you could look at what the Bonneville type racers do, but that tends to be pretty extreme. Also, there is a device called Herrod Helper - check this out

http://ecomodder.com/forum/showthread.php/old-scho...-7444.html

I disagree that there is no benefit below 110 MPH. If that was true, then why the hell cant I pull my travel trailer much above 60 with a headwind?

The Herrod Helper isn't a good idea for a street car, I know from experience that engine temps will go up. I had to lift mine an inch and shift it back about an inch and a half to allow cooling air into the engine compartment; probably too far out of the slipstream for any aerodynamic benefits.

To be fair, mine was a repop...

Fri Nov 06, 2015 9:28 am

My Herrod Helper has been on the car since the late 70's and does not run hot at any speed, with a 2087cc motor. It is a '69 w/ a later vented deck lid. When my father put it on, main reason was for CB antenna mount, he found the other benefits to be true.

Fri Nov 06, 2015 10:05 am

Roll the windows up.

Fri Nov 06, 2015 10:07 am

VWCOOL wrote: 'Street' - you may not like, or want, to hear it, but aero is just about irrelevant below around 110MPH. So you may wish to investigate other ways of increasing performance such as gearing.

What is it you want to achieve?

Well what I would like to achieve is to bring down the 0.47ish number as much as possible without making the car look like a freakshow, to help increase mpg, reduce noise, increase top speed etc. Drag acts at all velocities - the cars top speed is reached when its power cannot overcome the opposing forces, and it has often been stated that aerodynamic forces make up 80-90% of the opposing forces at top speed. So, you can see why reducing aerodynamic drag coefficient is of interest.

Fri Nov 06, 2015 10:19 am

NUMBER 1 modification is the Kamei front spoiler. If you've never tried it you won't believe the difference it makes to how a Super feels at speed.

Original VW/Kamei test report with data here, makes a pretty convincing case:
http://www.gerrelt.nl/category-documents/kameifrontspoiler.html

Subtle lowering of the front of the car helps stability too.

Adding mass to the front will help because as standard a Beetle's lateral centre of pressure (think centre of area of lateral silhouette) is forward of the centre of mass - making the car twitchy in crosswinds. So the further forward the centre of mass is (given it's hard to change the car's silhouette) the less this effect is felt. Ideally centre of mass would be forward or centre of pressure.

Some people also like rear spoilers on the roof above the rear windows. These break up laminar airflow flow over the body, where the silhouette of the car looks like an aeroplane wing creating low pressure at the rear. They look good in theory but I don't know how effective they are in practice unless made substantially bigger than most available products seem to be.

Some more good info and ideas on aerodynamics here: http://www.gerrelt.nl/section-aerodynamics.html

Fri Nov 06, 2015 3:25 pm

Volks Wagen wrote: VWCOOL wrote: 'Street' - you may not like, or want, to hear it, but aero is just about irrelevant below around 110MPH. So you may wish to investigate other ways of increasing performance such as gearing.

What is it you want to achieve?

Well what I would like to achieve is to bring down the 0.47ish number as much as possible without making the car look like a freakshow, to help increase mpg, reduce noise, increase top speed etc. Drag acts at all velocities - the cars top speed is reached when its power cannot overcome the opposing forces, and it has often been stated that aerodynamic forces make up 80-90% of the opposing forces at top speed. So, you can see why reducing aerodynamic drag coefficient is of interest.

It is very difficult to achieve better aero with a Bug. Flush-mounting the windscreen (the rubber is quite lumpy where it meets the top of the turret) and side glass, removing the mirrors and bumpers, shaving the gutters, adding lay-back headlights (pre-68) are all tactics that have been tried over the years

The round-screen L-Bug (1303) has an allegedly more slippery profile however I have never found any substantiated evidence of this. (I'd love to see some!) However, it makes sense - the car shares the same frontal area but is longer, and has a less abrupt windscreen.

But... theory is one thing and reality another...

My flat-screen Beetle is faster and quicker through both the 1/4-mile and standing 1000m than my round-screen 1303 with the same drivetrain swapped-in. The flat-screen Bug is a little lighter - which has more of an effect on the car's acceleration and performance.

To be honest I was surprised at this result - I expected a measureable 'win' for the round-screen car even with the weight disadvantage - especially over the standing 1000m.

My obvious conclusion to this back-to-back testing is that a Bug's aero is an insignificant/minor component of overall drag/loss below 'about' 110MPH (170km/h).

However, I can assure you the round-screen Bug feels more stable at higher speeds (above 110MPH) but wheel alignment and steering geo may be a factor here, too - my cars are set-up differently by design (of course - beam vs struts) and my alignment specs (two different purpose cars - that sometime get thrown down the same tracks ;) )

Both cars have - and do - wear a Kamei type spoiler from time to time. I have not back-to-back tested terminal speeds etc with and without it fitted, but through the seat-of-my-pants, I cannot tell any difference. That was another surprise... and a disappointment.

Another trick I am yet to try is a 'delaminator' across the roof around two-thirds of the way along the roof skin. This mildly upsets the airflow across the roof to reduce rear lift (Bugs suffer from rear lift). The bloke who told me this works in aircraft so it's on the list of things to do...

Of course aero drag rises significantly as speeds rise (square of the speed and all that..) so it will play an increasingly bigger factor at higher speeds... but not at street speeds.

But if you are building a Porsche-eating Autobahn stormer, that is a different story!!

HTH

Fri Nov 06, 2015 5:06 pm

The Kamei spoiler mainly reduces lift at the front, and gives a small reduction (4%) in drag. So that might not be noticeable by seat of pants tests.

I think you might be drawing a hasty conclusion of 100+mph being where aero matters, by comparing two bugs, given both have very similar aerodynamics.

I see what you are doing with the delaminator, by forcing the separation of the airstream earlier you detach it reducing the wing affect and reducing lift, but I assume it will also create lots of drag. It seems that the main area of drag is behind the car where air separation occurs, turbulence and low pressure is formed which 'pulls back on the car'.

It is great to have your real world feedback.

Fri Nov 06, 2015 6:36 pm

Yes "110MPH" is a somewhat arbitrary number - however it is around my terminal speed over 1000m where a 'more aero' (round-screen) car was slower than a 'less aero' (flat-screen, shorter nose) one, with identical power, gearing and grip (but different weights)

As I said, that outcome surprised me!

That leads me to believe that using the minor tactics that are possible on/over the shape of a Bug will have negligible affect on real world performance below those speeds - I am sure those tactics would have less total effect on reducing aero drag than a windscreen change from flat to round (Super Beetle)

BUT the faster you go, the more all those 'little things' add up!

I have only run the round-screen to speeds beyond that.. it is stable, but I cannot extrapolate what the flat-screen car would feel like at 120+ MPH.. maybe it would be much slower as the flat windscreen had a proportionately bigger effect on drag...

It would be great to have a wind-tunnel!

I have read often that some racers (and other designers etc interested in aero) have been quoted: 'if it looks right, it is right'!

https://www.google.com.au/search?q=Aero+Look+Beetl...m-0uz2M%3A

Fri Nov 06, 2015 7:17 pm

Simple (sorry) mods include bubble headlight covers and the removal of antennas and wipers.

I can't help but think that flatter wheels benefit aerodynamics much when dealing with wheels that are already inset from fenders. Filling the fenderwells by lowering the car and widening the stance should help.

Bumpers of course you already know about- but if you must run them, perhaps tucking them closer to the body?

Running boards that are flat on the bottom should help too.

Fri Nov 06, 2015 10:22 pm

VWCOOL wrote: My obvious conclusion to this back-to-back testing is that a Bug's aero is an insignificant/minor component of overall drag/loss below 'about' 110MPH (170km/h).

However, I can assure you the round-screen Bug feels more stable at higher speeds (above 110MPH)
your second statement contradicts your first.
Aero is the biggest factor in high speed stability, so if your '03 is much more stable than your std Beetle, it's aero must be significantly better. And very significant at 110mph.

Sat Nov 07, 2015 6:08 am

Years ago Hot Rod did some wind tunnel testing with an older Camaro and for some reason I am thinking something like a 32 Ford. Been many years, so trying to remember some of the things.

I do recall that lowering was a big improvement and removing as many protrusions as possile (mirrors etc) helped. Also blocking off the grill and using headlight covers I think made a difference.

Problem though was some things that you would think helped didnt. I had mentioned the Herrod Helper and had included a link to some other ideas, but usually wings and such are more to increase downforce since they usually increase drag. But some designs clean up the air behind the car, which do help.

There is a LOT to this topic and without there being real data, most of us are just guessing.

Sat Nov 07, 2015 6:15 am

How about good ol fender skirts?

Sat Nov 07, 2015 7:41 am

fender skirts on a super? :!: - no thanks.

Sat Nov 07, 2015 8:25 am

The easiest thing to do is to reduce your speed. No, that doesn't reduce the coefficient of drag. But it does reduce the amount of aerodynamic drag.

To reduce the coefficient of drag I'd say:

1. Front spoiler.

2. Rear wheel skirts.

3. Lower the front and rear.

4. Something to break up laminar flow more or less at the bottom of the rear window. If not a Herod Helper maybe a 3/4 inch ridge of metal cut in triangular spikes.

Sat Nov 07, 2015 8:38 pm

Bruce wrote: VWCOOL wrote: My obvious conclusion to this back-to-back testing is that a Bug's aero is an insignificant/minor component of overall drag/loss below 'about' 110MPH (170km/h).

However, I can assure you the round-screen Bug feels more stable at higher speeds (above 110MPH)
your second statement contradicts your first.
Aero is the biggest factor in high speed stability, so if your '03 is much more stable than your std Beetle, it's aero must be significantly better. And very significant at 110mph.

Not contradicting myself.. don't assume stability and drag the result of the same aero factors: it is possible that something can be slippery and unstable, or stable and slow.

Based on my cars' speeds and behaviours, I regard the aero difference between the two cars as negligible at 110MPH.

ABOVE this speed I reckon the Super 'feels' more stable.

However... I have no speed data for the two cars in the same conditions above 100-110MPH so this is a 'seat of the pants' summary, not something I can back with data... but yes the Super feels more stable. However as I mentioned other factors such as alignment specs etc may be influencing this independent of the cars' aero

It IS possible - but I reckon unlikely - that the Super does in fact have more drag and will be slower through the air than a flat-screen. Aero can be a funny beast...

Sat Nov 07, 2015 11:26 pm

I can't see the Super being any better or worse than a Standard. Perhaps the most important area is the rear of the vehicle. Yes, a rounded front is better than a square front, but regardless of the frontal shadow air trends to move out of the way one way or another. But it's much better to have a sloping rear, and the Super and the Standard have the same rears and neither are sloped enough.

If you want real gains in aerodynamics, look up boat-tail cars.

Sat Nov 07, 2015 11:28 pm

drafting semi's when on interstates is best aero drag eliminator