Aeromodability of a VW Bug?

[kach22i]

Originally Posted by UFO

That sounds like a "vortex generator", which may induce more drag than it reduces. My understanding of the roof spoiler is to provide a sharper cutoff to the airflow to reduce some of the drag caused by air partially detaching along the steeper back slope. By detaching the air completely you still have the full drag of the entire frontal area.

Okay, sounds like we need an "A" and "B" here at the top of the window. The "A" will be a vortex generator, the "B" will be the "cutoff" type. I have both examples shown, but did not call out the differences.

Originally Posted by UFO

Otherwise known as a Kamm back, and if long enough makes a huge difference.

Yes, this term can be applied if at the idea angle or slope. Is there another name if we just extend out at zero angle? And will that zero angle extension be a plus or minus drag wise?

Originally Posted by UFO

Ernie Rogers did a flat spoiler at the window base on his New Beetle and demonstrated a Cd reduced from 0.39 to 0.30, similar if not slightly better than the VW Golf.

On the old air cooled 911's, the tea tray and whale tail type spoilers add little down force, and don't help out the drag very much either. What they do best is to allow the cooling fan to draw in air from the top better by altering the pressure zone above the intake vent.

I'm going to look up that Ernie Rogers project. I suspect the New Bug's air flow breaks off later, maybe at the bottom of the window, in lieu of the top on older air cooled Beetles.

EDIT-1: If this is to be trusted, the New Bug air breaks off much later.
http://www.gerrelt.nl/section-aerody...planation.html

[UFO]

Originally Posted by kach22i

...

Yes, this term can be applied if at the idea angle or slope. Is there another name if we just extend out at zero angle? And will that zero angle extension be a plus or minus drag wise?
...

Since the Kamm follows the ideal shape, any deviation will increase drag. There is not much benefit to extending the roofline without dropping, as the entire concept of the extension is to return the displaced air back to it's original position with the minimum disruption. If straight back, you will be just moving the drag backwards without reducing it, at least that's my limited understanding.

[aerohead]

Originally Posted by kach22i

Okay, sounds like we need an "A" and "B" here at the top of the window. The "A" will be a vortex generator, the "B" will be the "cutoff" type. I have both examples shown, but did not call out the differences.


Yes, this term can be applied if at the idea angle or slope. Is there another name if we just extend out at zero angle? And will that zero angle extension be a plus or minus drag wise?


On the old air cooled 911's, the tea tray and whale tail type spoilers add little down force, and don't help out the drag very much either. What they do best is to allow the cooling fan to draw in air from the top better by altering the pressure zone above the intake vent.

I'm going to look up that Ernie Rogers project. I suspect the New Bug's air flow breaks off later, maybe at the bottom of the window, in lieu of the top on older air cooled Beetles.

EDIT-1: If this is to be trusted, the New Bug air breaks off much later.
Beetle Aerodynamics / Roofspoiler

I'm very suspect of that image.If the arrows were drawn to agree with tuft orientation they would not reveal vorticity,only surface effects.
The New Beetle,as the original are both pseudo-Jaray cars.Their rooflines are too 'fast' to support attached flow and other such rooflines,when investigated in the wind tunnel,revealed attached-vortices which tended to 'hold' the tufts down the centerline of the roof slope,but would give a deceptive interpretation of the flow.
The vortices themselves produce remarkably high drag.Spoilers might break these into smaller eddies,but the energy is permanently lost to viscous attrition downstream.

[JMPVW73]

Originally Posted by Frank Lee

WOW, even I (who went through Kirk's program) had never seen the 50/50 mag article before!!! It was seeing the 50/50 at a car show that got me into auto engineering in the first place.

FYI the flat windshield isn't the problem area.

A blast from the past! If I have a duplicate of that issue I will send it to you.

The wind shield creates a high pressure area that causes rain to pool at the bottom and it catches a ridiculous amount of bugs. It is an area that can be improved but the wake is a much bigger issue.

Originally Posted by kach22i

AWESOME!

JMPVW73, very informative posts, a breath of fresh air.

Thanks, it took a while to convert years of acquired knowledge filed away in random corners of my brain to an internet reference source and post it here.

I have been away from the forum for a while because it consumed all of my time for 5 straight days.

[JMPVW73]

It doubles as a snow plow.
UK Resto-Cal Volkswagen Forums :: View topic - Kamei Aerofix front wing

On the KAMEI website...
KAMEI "Horizontal Stabilizer": 1953 Premiere of the original Spoiler In the last days of the war, when the Volkswagen factory manufactured wings for Junkers, Karl Meier had also gained some experience in aircraft construction. Although he was only marginally concerned with aerodynamics at the time, this knowledge was later to play an important role in the KAMEI success story. Irritated in the early fifties by the tail weight of the VW Beetle and its unstable handling, particularly at speeds around 100 km/h – which was really pushing it in those days – Meier came up with a remedy. He constructed a "horizontal stabilizer". Today this aerodynamic aid is known as a spoiler. To test the market for his "stabilizer" and at the same time bring his Interior Extras into the limelight, Meier set out for the Geneva Salon in 1953. Barred from exhibiting inside the famous gates for want of the necessary funds for entry he simply declared a few square meters of roadside in front of the Salon as his outdoor exhibition site. He was nevertheless unable to convince his contemporaries of the advantages of his strange gadget and so the original spoiler was packed away until its time was ripe. 25 years later it was hard to imagine cars without spoilers and at high speeds they were imperative. Not surprisingly, KAMEI was one of the leading manufacturers right from the start.


A later more successful version...

[JMPVW73]

I have one of these but never ran it. The some of the old timers swear it really works.

[kach22i]

Originally Posted by JMPVW73

Herrod Helper

That little wing spoiler looks to be right where it is on a Merkur XR4Ti biplane.

Does anyone have a true side view of the Herrod Helper?

john7
http://www.thesamba.com/vw/forum/vie....php?p=4793591

heres the story.
my old boss used to be the guy selling those.

see that newport beach address on the magazine ad? its his apartment

he made them in his back yard in his spare time.

it gets better. he didnt have a high tech bender or metal brake.
he bent them in between the boards in his fence.

he about fell over when i came to work with one of the herod helpers on my car. so he preceded to tell me the story with 27 color glossy pictures with circles and arrows and a paragraph on the back explaining what each one was.


Oh and the one on my oval window made it run about 10-15 degrees hotter

http://www.thesamba.com/vw/forum/vie...er=asc&start=0


Current Internet Ad.
http://www.thesamba.com/vw/classifie...php?id=1072166

[rmay635703]

Originally Posted by Frank Lee

Yeah, but it "leaves more room for boattailing" only if the passengers have been shifted forward, or if the rear passengers are headless. Pretty much can't shift them forward on a regular Bug chassis- their feet are already virtually up against the front suspension/steering stuff.

Frank the passengers could sit backwards

[some_other_dave]

Originally Posted by kach22i

On the old air cooled 911's, the tea tray and whale tail type spoilers add little down force, and don't help out the drag very much either. What they do best is to allow the cooling fan to draw in air from the top better by altering the pressure zone above the intake vent.

The "duck tail" spoiler reduced lift in the rear, to the point where the factory required people to use front spoilers if they added the duck-tail. It also decreased the drag of the car, most likely by making the air flow over the car more closely approximate the "template".

I am less certain of this, but the tea-tray and whale-tail were used for the same purposes, reducing lift and reducing drag. They were better at one or both than the duck-tail, so the race cars were equipped with them and the duck-tail was phased out.

The other two tails also provided room for the intercooler that was used on all but the first 911 Turbos, which contributed to its popularity.

-soD

[Frank Lee]

Originally Posted by rmay635703

Frank the passengers could sit backwards

Yes they could; then you'd need to stretch the whole thing because now there's no "nesting" of legs and plus they'd want to put their feet on the floor in front of the engine and trans.