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lift curve slope vs span?

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rtfm

Well-Known Member
Joined
Jan 3, 2008
Messages
3,900
Location
Brisbane, Australia
Hi,
I've been hanging out in the Flying Flea forums for a while, and came across a French article (aren't they all?) which I translated into English and worked my way through. It made for interesting reading, but it uses a weird method for measuring lift coefficients, which they call "100cz" for some reason. 100cz values are very different from what we have come to expect as Cl values, and range from 0 to over 120. I have no idea where these come from.

Also, they measure "K" the lift curve slope very differently from what I'm used to. Working with NACA 23012, I was expecting a lift slope of 0.108, but in their system it is 9.68!

The article goes on to say:

The slope "K" decreases when the span “A” decreases.
Practical formula (for this NACA 23012)
K = 9.68/(1 + (1.765/A))
See Prandtl Formula


And I've not heard of the K being dependent on the span. And as for the formula quoted, I have no idea where they get the 1.765 constant from either.

Anyone care to offer any help on any of the above issues?

Regards,
Duncan
 
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