Quote:
Originally Posted by Frank Lee
I found airfoils here: Airfoil Investigation Database - Showing NACA 0021
Then fattened the NACA 0021 profile 2x (that ground plane thing):
The NACA 0018 is listed as having somewhat lower drag vs the 0021; it appears they are the same shape only reproportioned e.g. 0018 is 18% as thick as it is long while the 0021 is 21% w/l. Here is the 0018 fattened 2x:
And they look like this template:
NOW, bear in mind that these airfoil profiles are 2-D. I came across this (slightly edited by me here):
The NACA 0018 reproportioned as above:
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Frank,the template,as mentioned in the thread,is based on the 2.5:1 streamline body of revolution as depicted by Hucho,at Cd 0.04 and Cd 0.08 in ground-reflection,after Prandtl.
With wheels it goes to Cd 0.13.With wheel fairings it goes to as low as Cd 0.089,as per GM's results with Sunraycer.
My drawing is a *******ization of Hucho's image and W.A.Mair's 22-degree boat-tail for the sake of construction simplicity.It's not mathematical but I quarantee it.