Quote:
Originally Posted by kach22i
Autogryo, I trust you don't mind my marking up some of your images so that I can explain the whole tangent line thing as I see it.
Your first one:
Automobile pictures by kach22i - Photobucket
Your second one:
Here is my car at 30 degrees - approx.
Some other P-Cars:
An old racing Porsche modified with roof line per race rule allowances.
I stand by my earlier statement that 10-15 degrees is best, you can get away with 20 degrees on a good day, and that 30 degrees has air lifting off of it quite easily at speed. I also think the template works and is an "Idea" we should strive for but maybe not marry. |
W.A.Mair,who's work is shown in Hucho's book would argue that 'angles' must be taken within the context of 'where' they occur,with respect to the position of max. roof camber.
This is why the 'point' is a centerpiece of the 'Template.'
The aft-body can slope as steep as 22-degrees,but you cannot get to 22-degrees without separation until you are 1.1 free-air body diameters ( twice the body height )behind the point of max. roof camber.
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*Looking at the Porsche 911 RS America,the backlight is already 21-degrees ( nearly Mair's limit of a maximum 22-degrees )by 20% of 'Template' aft-body.
*As the rear contour just comes onto the 'tea-tray' rear spoiler it is at 23-degrees,already exceeding Mair's maximum for attached flow.
* At 44.4% 'Template' aft-body the trailing edge of the tea-tray gives the 'apparent' backlight/angle 13-degrees,rather than 32-degrees without the spoiler.
*If the Porsche 'template is followed to the ground,the 911's exit tangent angle is 40-degrees.
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The 911 has survived since 1963 when it bowed at the Frankfurt Auto Show as the 901.They already had to 'fix' the roofline a bit for 1964 production,which has become the iconic sillouette.
None of the other Porsches use the 911 roofline.
*With the 1996 911 GT1 they spent 33-days in the wind tunnel trying to kill the 'inherent' lift caused by the 911s steep roofline.They ended up lowering the car 5.6" and adding 16.6" to the rear,ending up with a 3.991:1 fineness ratio,excedding even Jaray's pumpkin seed of 1921.
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The early Porsche designs,dating to 1910 were all tulip or teardrop forms.
*The 1937 R-Type Auto-Union GP teardrop racer of to-be Porsche designer Erwin Komenda clinched the victory,setting Porsche in such a favorable light with Herr Hitler,that he would beat out GM and Ford for The People's Car program.
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Porsche 'Template' aero-modded race cars include the 907,917,and 956 long-tails,which all ran 100%'template' rooflines and boat-tails.
*The short-tail 917 spyder,Cd 0.57,would see Cd 0.44 when the windshield and roof were installed.
* When the long-tail was added,the drag dropped to Cd 0.33.
* This is exactly what the 'Template' is structured to do.
* The 'EcoModded' LeMans long-tail 907,of 1968,saw Cd 0.27 when the 911 had the Cd of a VW Bus.