New bug, .38 CD why?

[Frank Lee]

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

[aerohead]

Originally Posted by COcyclist

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

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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.

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.

[donee]

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.

[aerohead]

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!

[Rob10_99]

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.

[COcyclist]

Originally Posted by aerohead

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!

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??

[Dave's Civic Duty]

Originally Posted by COcyclist

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

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

[Frank Lee]

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

[aerohead]

Originally Posted by Rob10_99

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.

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.

[Dave's Civic Duty]

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.

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