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Does anyone know the down-force difference between some of these ducktails and the stock C2/4 tail?
The tails don't add downforce as much as they reduce lift. The bi wing or wing tails used on the newer cars create downforce. The duck tail is actually less effective than the stock pop up tail and far less than the carrera RSA tail. Although the RSA tail is about 6 pounds heavier than the pop up tail.
Here is a commonly used and somewhat accurate chart
showing some basic comparisons.
The tails don't add downforce as much as they reduce lift. The bi wing or wing tails used on the newer cars create downforce. The duck tail is actually less effective than the stock pop up tail and far less than the carrera RSA tail. Although the RSA tail is about 6 pounds heavier than the pop up tail.
Here is a commonly used and somewhat accurate chart
When 'researching' my future car-to-buy back in cough'85cough, I happened on an OLD article from '73 in one of the library's US car magazine stacks. (Library: where one went before the internet.)
It was on Porsche's then-new duck tail option.
The magazine ran an instrument to measure rear spring deflection (lifting) at speed.
The deflection vs. speed chart showed similar as above for the 911 w/o tail.
The duct tail, otoh, followed the "w/o tail" curve till 50-60 mph, then plateaued to essentially a constant value from there on as speed grew.
Not that I'm doubting the chart above... It's all just... odd.
(Has someone, somewhere been feeding someone else whooey for charts?)
I remember that story (and may still have a copy filed away) because as a (much) younger engineer I found the chart compelling evidence of an elegant aero solution.
Now... who knows?
And I didn't pick up my first 911 till 14 years later. An '85. Time flies.
Huh -- still had a copy of that duck tail vs. lift article I mentioned above.
From Car and Driver, Feb., 1974:
(Sidebar to the larger article comparing a plain 911, 911S Targa, and 911S Carrera (w/ ducktail). Prices... $12,225, $15,670, & $15,045.)
And how about the cost of that factory duck tail -- $285!
12-12-2017, 02:34 AM
