New bug, .38 CD why?
 

Title pretty much says it all,

For being round and what looks fairly aero, it isn't. Could it be the back wake creating most of the drag?

http://us1.webpublications.com.au/st...08675_17lo.jpg

That doesn't seem like it would have much drag, does it?

cant post images... need 2 more posts

The link states that the rear bumper is where the flow is disrupted, and that causes the lift and severe drag as well.

Think it is the rounded rear part that is detrimental to it's cd.

Why? The Bug is a fashion statement, not an aero one. That pretty much says it all.

I thought that the new Bug had a Cd of 0.45? The curve in the rear is way too steep. I doubt it has attached flow as far down the back as the picture shows...
http://us1.webpublications.com.au/st...08675_17lo.jpg

I love drawings with arrows that purport to show airflow. :heart:

.38
 

The New Beetle is short.It has a very low fineness ratio.While it has good penetration,once it gets to the frontal area cross-section,the curves rapidly approach those that cannot support attached flow,creating a significantly large wake,'poison of mpg'.
For performance,VW/Porsche/Audi squashes this shape down to create the Audi TT.

In this case, the sooner the airflow detaches the better.

EDIT: The following in red isn't exactly true, see post #10 for details.

I saw a chart somewhere (can't find it right now, grrrr). Pretty much it showed that as the rear angle gets steeper (starting from 0°=flat) lift decreases until 12°-14°, then it increases again until 26°-28° when airflow detaches and lift goes down again.

So, if you can find the spot where the tangent is 12° and make a small "step", then the airflow will detach there, reducing lift at the best point. Many new cars already have this small "step" around the top of the rear window.

If you extend this "step" into a Kammback, you keep the angle right while reducing wake area, and keeping Aerohead happy at the same time:)

for good aero you basically want a teardrop shape with a long tail. less ideal but still good you could have a shorter shape with sharp rear edges that allow for a clean sepparation of the airflow.

the beetle has none of this, the air separate very early and will become turbulent,
also the wheel wells will cause the air to sepparate and not reattach to the body.

i'd assume the air starts to sepparate much sooner, i think at the top of the rear window, and also the wheel fairings will greate much more turbulence than the image shows

Well the link shows video of the tuft testing, and it does look connected up to the end of the trunk.

OK, I looked for the chart and found it. I was a little off, I got angles right, but mixed up lift (Cz) and drag (Cx). At my age, it's good I remember anything;)
Here are two charts, they are from Piechna's book. The data is compiled by the author from a few sources.

http://ecomodder.com/forum/attachmen...2&d=1269616879

The first chart shows how drag first decreases, then increases, and finally airflow detaches, with the rear angle getting steeper.

http://ecomodder.com/forum/attachmen...3&d=1269616879

The second chart is lift. When the roofline of the vehicle is flat lift is actually negative (=downforce). It grows linearly as the rear angle steepens, zeroing around 6°-7°, then abruptly falls to almost zero after 30°.

I wonder if the wing that some people put on would help any?

I would love to have one w/ a TDI. Many folks on the TDIClub claim to be getting 52MPG's w/ a 5-speed. That would work for me. It would be interesting to see how much better am Ecomodded New Bug would do.
:turtle:
Isn't it the lightest of all the TDI offerings?:thumbup:

Dave

Does anyone want me to tuft test my sisters 08 New Beetle?

If flow is attached down to the bumper Ernie's wing would do nothing.

Lightest TDI?
 

Lightest VW TDI in the U.S.? Perhaps, although I bet a 2 door Golf is pretty close.

does it do or does it doesn't?
 

Frank, I realize you are the master of brevity but are you saying you think Ernie's wing helps reduce drag or are you suggesting it has no value?

What possible aid could the wing provide if the flow is attached down to the bumper without it?

Here is the link for the AutoSpeed article where I believe the above drawing was lifted:

Browser Warning

And Julian Edgar's explanation for the terrible drag and lift coefficients for the New Beetle:

"So the problem must be at the back? And it is. But it's a different problem to that which we've seen before. Here the flow remains attached right down to the line of the guard/boot opening. And this results in a very small wake for the (it's larger than you'd think) size of the car. But it also means that the airflow wraps in one long curve from the base of the windscreen right around over the top of the car to nearly the rear bumper. Aeroplane wing, did you say? And not only will this shape have major lift (without an undercar ground-effects tunnel, anyway; and I looked under and didn't see that), but much of the force will be upwards and rearwards - creating that monster drag".

And farther down in the article, the VW factory wing designed fix, a spoiler to combat lift at high speeds.

Aerohead has suggested that the "birdbath spoiler" and the double wing on the Mercury Merkur also reduce lift and drag. But I'm no expert. I only know what I read on the internet and it can be rife with unsubstantiated opinions.

video
 

It's possible that the tufts are saying something different.
Both old and new Beetle are pseudo-fast back cars.The original air-cooled Beetle took advantage of the separated flow,spanwise vortex crashing against the body where the cooling air inlet slits are located to feed the cooling fan.
It's possible that the New Beetle also suffers the same separated flow and attendant vortex which may be slamming the tufts,not attached flow.
The loose rule is,don't exceed 22-degrees unless there is a step somewhere behind to re-attach to,like Ernie's wing,or the Herrod Helper,or Porsche's Whale-Tail Carrera wing,also Daytona Charger trunklid.

I was reading on some old VW electric(youtube I think) about the herard helper, and he said his batteries had quite a bit more charge at the end of the daily trip than they usually have. So it seems that the wing helps a lot with the drag, correct?

Driving a mkiv new beetle (tdi) and my golf back to back for a few years, I'd guess they are the same weight, however the beetle has much much more engine load + wind noise at highway speed.

There is a lot to be desired in the New Beetle layout . . . Much of which could be repaired without affecting looks (noticeably), not saying the Golf is perfect, just closer.

Mags say a new new Beetle is on the way...

Edgar
 

I would respectfully disagree with Mr. Edgar's appraisal of the New Beetle's aft-body flow.If what he says is correct,then the last 90 years of aerodynamic investigation goes right out the window.
Separation,and where it occurs causes the lift he is interested in.When the separation occurs directly behind the car it suffers rearward longitudinal lift( form drag) which cannot be remedied without the reduction of separation.
The separation cannot be remedied without the curvature of the roofline and side body being relaxed to that more like the template.( the whole basis of Kamm's research,fuselage design,submarines,etc.).
Both the Herrod Helper and Ernie's wing provide a structure for partial re-attachment of the stalled flow which moves the deformation of the outer flow field closer to that of the ideal pathway,as described in the template.
The 'attached'/'captured'/'locked'- vortex created above the horizontal shelf allows the adjacent flow to make it further back before separation and when it does separate,it's at a higher static pressure than upstream,which reduces the base pressure of the wake,consequently reducing the form drag.
As Frank has mentioned,if the flow was actually attached,all the way down as Mr.Edgar has stated,there'd be no need of Ernie's wing,nor would it ( could it ) be of any benefit.
In the jargon of AeroVironment,I believe Mr.Edgar is attempting to occillate at a level higher than his assigned frequency.If he wants to better serve the readers of AutoSpeed,he might invest a bit more energy into researching his topics.

Hi All,

I have had the experience of sitting in the rear seat of a New Beetle, as it accellerated. Above 45 mph, a turburlence-like noise was heard from ear level just on the other side of the C pillar. I think the flow seration begins there.

This is very much unlike the flow pattern shown on the first page of this thread. The actual turbulence begins about 2/3's the height of the car at the C Pillar and around the back.

The first thing to try is to put Turbulators vertically on the C Pillars, and then horizontally across the rear window area.

How far forward to move them is going to need to be experimentally determined.

Ernie's wing
 

I located my photo of Ernie's New Beetle.It's in orthogonal projection,so nothings really in true-length,but the angle of the car allowed a cursory noodling.
It appears that the centerline of the backlight hits 22-degrees about 1/2 a door handle length down the glass and I would suspect that the flow is very feeble,if not separating there.
Down at the bottom of the glass,the angle is on the order of 34-degrees with the horizon.
A protractor reveals that Ernies wing relaxes that angle to about 19-degrees,well within Mair's 22-degree limit.
If you place a French-curve over the car,with and without Ernie's wing,it looks like the wing 'doubles' the apparent length of the car's aft-body at centerline ,where the imaginary line would intersect the ground.
With respect to the streamlining template,at centerline,it would be the same as taking the Beetle with 30% of an aft-body,and extending it out
to about 80 %.
Of course the sides aren't done,but you can see how the wing could definitely help push Ernie into 50+ mpg territory.Sweet!

Ah there we go, didn't find any build pics on that wing or much else about it last time I searched for it.
http://ecomodder.com/forum/showthrea...le-8412-2.html

linky for you.

Does anyone think the vortex generators would be more beneficial if they were say, 2x as tall into the connected air up at the top of the rear window? As well as some type of wing together?
I'll probably fab up something like Ernies wing, looks pretty comical on a bug.

Here is a link to more photos of Ernie Rogers' New Beetle wing.

MAX-MPG TECHNOLOGY

I wonder how necessary those tall end caps are? Would something with a flat top and sides, with respect to the angles of the teardrop template, work for a hatchback too?... sort of like an extended trunk/cargo box??

Thanks! That's what i was thinking as well!:D

IMHO Ernie's side strakes are way over the top. A styling statement added to a styling statement?

VGs
 

From what I understand,the vg will allow a 6-degree cheat on angle of attack for a non-suctioned wing.If it's the same on a car,this might allow you to cheat the wing a bit.

Ernie's Wing, well you always have a place for the tools while workin' on her.

No need to build that picnic table for the outside at home events.:p

Does it work for getting rid of the drag? I just checked out the pic, how much did he say it boosted his mileage?

I doo like the looks of the more factory looking versions of the wing/spoiler!

Dave:thumbup:

The original Beetle was not only sucking air in to feed the cooling fans, it was pushing that air out at a higher temperature. So maybe aerodynamics of pure shape don't exactly apply - same principle as a blown wing?

CO,I think that just a simple shelf would 'show' at the gas pump.I've been looking at some high-end super cars and successful racers,and they either followed the template line or pushed their rear spoilers out to meet it.
Some examples are: 1965 Ford Mk IV,Ferrari F 40,Lotus Esprit Turbo,Ford GT,Bugatti B 110,and Saleen Mustang S-351.
The end-caps ( capping-plates ) could be as small as you see on many dragsters,as these are wind tunnel tested and track proven.
Ernie may have chosen the larger caps to help the Bug's side-body flow to intersect the top flow at closer the same velocity to prevent longitudinal votices from forming where the two flows meet.Don't know.I'll read his build thread when I can.

I hope they don't ruin it like Ford is starting to do w/ the Mustang.:confused

end caps
 

Kick me if I'm repeating myself,but we kicked some of Ernie's tech around,and this is my take on it.
The New Beetle is still a pseudo-Jaray car and it no doubt suffers from attached-vortices on both sides of the car.So with respect to the endplates,I believe they are addressing this issue as span-wise flow control fences would on an aircraft wing.
I think also,that the end-plates actually 'tailor' the wake as long C-pillar bulkheads might on say the Daytona Charger and some of Mercedes-Benz AMG super cars.I think it's better with them.
With respect to the template,yes,absolutely,it will work for any car.Blending the C-pillars back is good although you do introduce a blind-spot on the passenger side ( like 1st-gen Insight) and must become more accustomed to relying on your mirrors in traffic.
Any combination of wings and caps can be fashioned to 'force' the air to follow closer the the template path.On my CRX I had a combo upper wing,extended C-pillars,and tail extension,kind of a hybrid bi-wing affair.
The only hitch is the ability to open the hatch with the unit attached,so it can't have 'thickness near the top or there'll be interference every time you try to open it.

New new Beetle:

http://gas2.org/files/2010/04/ragster.jpg

Neil, I think that is the beetle "ragtop" concept. It's rumored that the actual new beetle will use some cues from this concept, but that's not the actual design, afaik.

...MOTSOS

...More Of The Same Old Stuff.

...looks like merely a re-scupting of the current bug design.

Sorry, not "ragtop" but "ragster"

Report: VW New Beetle successor timeframe and details come into focus — Autoblog

I wouldn't discount it that badly.

Besides, that's the "Beetle" way, right? The timelessness is partly why we love the old Beetles!

One of my very first impressions of the NB from back when they came out was that rear seat headroom was woefully inadequate and that they should have been able to alter the roofline (ed zachary like new Prius did) to greatly improve it without hurting the design integrity, but the stylists won that battle and they built a car with a seriously compromised back seat. NNB proportions give me the impression they are addressing that concern.

In fact it was the lousy rear headroom that pretty much knocked NB off my potential new car list. (Yes, once upon a time I would have bought a new car or a fairly new used one)

Ford did a similar thing with the Taurus back in '98(?); when they did that totally oval redesign they TOOK AWAY back seat headroom in the name of exterior design. And I thought, how freekin stupid can these committees be- this is their bread-and-butter full-sized sedan and they're TAKING AWAY headroom for the sake of a rather dubious design direction?!? :mad: :rolleyes: I KNEW they would come to regret it, and they did. I'll give them credit for doing a great job on the freshening it got when they made the lighting more angular and raised the roof.

I was in my kid's dentist office today, and the Motor Week (or was it Motor Trend, or Road & Track?) showed a upcoming Beetle that had a flattened/lowered roofline. It is a hardtop, and they did mention that it is similar to the ragtop concept...