Reattaching wake and drag penalty

[aerohead]

Originally Posted by chuckm

I hope I'm not misunderstanding you... if I attached a short Kamm profile lip to the top of my rear windshield area, I might gain a little benefit?

It's the only thing I would have great confidence in as to real drag reduction.Profile drag is the largest component of aero drag,and it is governed by the pressure differential between the stagnation pressure at the nose,and base pressure of the wake.------------- If flow is "clean" (without significant separated flow) up to the point of the vehicle's maximum cross-sectional area,then it's the aftbody which dictates where the flow will ultimately separate,and where the flow separates dictates the base pressure,which dictates profile drag.-------------- Anything you do to lengthen the body,while simultaneously reducing wake area,is,by defination,streamlining,and the only known path to lower drag.------------------- Any benefit can be calculated as a direct function of wake area reduction.------------- This is why I developed the aerodynamic streamlining template.If you follow it,you get guaranteed drag reduction as a function of your new wake area.Size matters!

[aerohead]

I was data mining for spoiler info and crossed paths with the old article by CAR and DRIVER on the 'Crisis Fighter Pinto'.
In the article they mentioned how,in March,'74,Porsche had already changed the 911 Carrera tested in February,'74,from a 45-degree upswept rear spoiler,to a very long nearly-horizontal wing-like surface with capping plates, extending from the decklid.
They surmised that the new spoiler for this 911 Carrera RSR provided the same downforce as the Carrera but without the drag penalty of the steep up-sweep.
The RSR finished 2nd at Le Mans,won at Daytona,won the Trans Am Championship,and also won the Targa Florio that year.
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I do not have a 'true-length' photo of the car,so I can't say how far the spoiler extended,but it was VERYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYY long!
No risk to pedestrians though as this was strictly a full race car.
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I do not have a large dry lakes racer database but this 1974 RSR may be the progenitor of all the 'Bonneville'-type foils.

[focus1.6uk]

Aerohead, are these the 911 spoilers you refer to?

[aerohead]

Originally Posted by focus1.6uk

Aerohead, are these the 911 spoilers you refer to?

focus,the three images we see here are what we could have bought.The 1974 911 RSR was a track car only and its spoiler made these whale-tails look like tinker toys!
I've only seen the RSR in a book.

[TimJFowler]

Originally Posted by aerohead

focus,the three images we see here are what we could have bought.The 1974 911 RSR was a track car only and its spoiler made these whale-tails look like tinker toys!
I've only seen the RSR in a book.

Was it this one?

File:Porsche RSR am 19.05.1974.jpg - Wikipedia, the free encyclopedia

[ChazInMT]

This:



Looooooooooong enuf?

[Frank Lee]

Shooda just stuckit on the roof above the window!

[aerohead]

Originally Posted by TimJFowler

Was it this one?

File:Porsche RSR am 19.05.1974.jpg - Wikipedia, the free encyclopedia

Tim,that's the animal I saw in the book.It's hyper-'Template' so maybe not a candidate for low drag as we might need,but it may have morphed into the 'horizontal' plate we're seeing with drag racing and dry lakes events.Thanks!

[aerohead]

Originally Posted by ChazInMT

This:



Looooooooooong enuf?

Yeah,I don't think it for us.
With a 6-cyl engine cantilevered back beyond the transaxle they might have needed all that downforce.'Don't think it's a good fit for us.
Maybe inverted liquid-fuel rocket boosters are next for Porsche?

[some_other_dave]

They also added another rear window, stacked on top of the original but with a shallower angle. That supposedly helped with both downforce and drag. And the front splitter was required to give reasonable aero-based grip at the front to match that at the rear.

-soD