# center of lateral resistance

Discussion in 'Sailboats' started by Guest, Jul 23, 2003.

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### tspeerSenior Member

Cla * a = 0.54

As a practical matter, the lift curve slope is closer to 0.1 due to boundary layer displacement.

And don't confuse the two-dimensional lift curve slope with the angle of attack required for a three-dimensional planform. Considerably more angle of attack is needed to reach the same level of lift.

The apparent lift curve slope of planform is closer to

a = a0 / (1 + a0 * 57.3 / (pi * AR * e))

a = 3D lift curve slope, per deg
a0 = 2D lift curve slope, per deg
AR = aspect ratio
e = Oswald efficiency factor

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### RHoughRetro Dude

Thanks Tom,

What is 57.3?

I've been using .7-.8 for value of e, is that "close enough" for a sailboat?

-Randy

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### jam007Junior Member

57.3 = 180 / pi

Anders M

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### Raggi_ThorNav.arch/Designer/Builder

I was just too quick to copy paste some formula...

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### chandlerSenior Member

So is that where all you rocket scientists get your formulas, copying and pasting? For a while there I thought you all Knew and understood these formulas? Silly me.

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### jam007Junior Member

No no Chandler donĀ“t confuse egineers with scientists.

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### Raggi_ThorNav.arch/Designer/Builder

Sorry again, Chandler
One thing is copy/paste or look up in a reference. The most embarrassing is not to check the answer, is it reasonable. When dynamic pressure is 0.5xROxV^2, it is not reasonable to have a lift coefficient much larger than 0.5...

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