Aeromods for 2001 VW Beetle

[kach22i]

Originally Posted by bdufur

Kach22i - are you recommending I consider some winglets instead of a kammback or other design?

I have no proof that fins on a car works, if they do then all those cars including concept cars from the 1950's - 1960's were not so silly after all.

I could not find a good Kammback diagram or wind tunnel snapshot showing the flow over the roof.

Won't any large flat-ish plane cause air to roll over it sideways and then start forming a vortex as it leaves the corner/edges?

[Frank Lee]

Compare Side-by-Side

If you can make a Kamm as well as VW did you can possibly expect 0 to +2.8 mpg.

[kach22i]

Nice link up there.

RE: MPG Estimates from Drivers Like You
Looks like 1 or 2 drivers gave real world input, I think we need a larger group to make a determination. Although as discussed before the Golf has a slightly lower Cd than a new Bug.

[aerohead]

Originally Posted by kach22i

Are winglets the answer to the vortex problem?

Industrial Design - Transportation pictures by kach22i - Photobucket



Aviation Partners Inc. - Seattle WA - Blended Winglet Technology and Performance Enhancement Systems for Winglets


Boeing 737 Advanced Blended Winglets

On the aircraft,the winglet helps spoil the flow over the tip just as tip feathers on soaring birds for which their inspiration is derived.By helping to kill the wingtip vortices,small planes can safely fly at a certain separation distance behind the larger craft.Otherwise,they can litteraly fall from the sky as in a micro-burst downdraft.
On cars,as long as airstreams are converging at different velocities,they're going to spin up into vortices.The vertical projection can wall the two streams off from one another,but once past the fin the disparate velocities will cause the vortice to begin there,unless the flow is already separated.
I think in the case of the pseudo-Jaray rooflines,the only real fix is to stuff the wake full of a proper K-form roof section.
Only these can allow stream mixing without vorticity.

[kach22i]

Originally Posted by aerohead

........... a proper K-form roof section.

K-Form?

[aerohead]

Originally Posted by kach22i

K-Form?

K-form is used by some to describe the roofline Kamm is given credit for but Baron Koenig von Fachsenfeld actually produced before Kamm.The K is inferred to respect both men's contributions.
No mention is made of Carl Breer who actually created the first truncated aero roofline during aero-modding of the Chrysler/De Soto Airflow test mule in 1934.

[SwamiSalami]

Originally Posted by bdufur

Considering the kammback approach - will keep the angles consistent with the areo template. Will taper towards center somewhat as well to follow natural lines on car. My neighbor has a Honda Fit so I'll take some cues from the rear detail on it - it seems abrupt corners are OK. Will also await your reply on the fins you are proposing two posts up... very interesting stuff guys -- many thanks!

PS Averaged just over 45 MPG on last tank - so hoping with reading the site and a slew of small aeromods, fine-tuning my driving, etc., hoping to get in the 55+ MPG category...

i did the kammback on my beetle and got 55.

[ChazInMT]

dieselbeetle...your pictures are missing of your Kamm....are you going to go into production with it or did you forget to pay your photobucket bill..(JK) Anyway, I don't remember ever seeing it.

[aerohead]

Originally Posted by kach22i

I've never assumed that the new Bug created vortex's at the rear corners. I would like to see some images of that. Below is some similar information which may or may not apply.

http://ecomodder.com/forum/showthrea...ook-10304.html

I just wanted to mention that the square-edged roof model airflow is not applicable to a rounded-roof contour as on the Beetle.
In Hucho's 2nd Edition,Chapter 4,Pg 154,Fig. 4.60,'Effect of rear end height z on drag,' an image from Buchheim et al. is shown for a rounded rear end contour of 30% 'Template' aft-body.
Minimum drag occurs when the 27.5-degree roofline is pushed upward to include an exit tangent angle of 13-degrees.Cd is cut 0.075.
On the New Beetle,the rear slope at the top of Ernie's wing is 37-degrees.Ernie;s wing relaxes that angle to 19-degrees.
From Buchheim's research,it would suggest that for the lowest drag,you would continue to extend the wing further back until it intersected the 13-degree line,as the Beetle is also a 30% aft-body car.

[botsapper]

Originally Posted by kach22i

I have no proof that fins on a car works, if they do then all those cars including concept cars from the 1950's - 1960's were not so silly after all.
?

http://upload.wikimedia.org/wikipedi...f1/BATcars.jpg

Just look at the beautiful Alfa Romeo - Berlinetta Aero Tecnica ~ BAT cars. The assumption that by neutralizing the expected vortices with counter-trailing tail surfaces will give them clean aero and high speed stability. They managed to achieve their engineering targets and more importantly, still making beautiful bodies. Cd of .19.