NACA symmetrical foils - How do I find the point of balance ?

TMcRally · Oct 27, 2020

I'm designing a T Foil rudder to go on the bottom of an existing catamaran. I would like to include an engagement/disengagement mechanism that can be used in motion. To simplify and reduce weight in the control I'd like to position the pivot slightly ahead of the point of balance.

Is there a general rule for positioning this ? Does it move with AOA ? In use they will be set at rest at 0°.

I'm likely to use 0008 to 0012 foils.

Thanks
Dave

verymadmac · Oct 27, 2020

You could try reading the appropriate chapter in Abbott "Summary of Airfoil Data"

https://ntrs.nasa.gov/citations/19930090976

GregLocock · Oct 27, 2020

"Does it move with AOA ?" Yes

Cheers

Greg Locock

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Sparweb · Oct 27, 2020

Yes there is a general rule. You can find it in the airfoil plots that VeryMadMac linked you to.
The standard reference point for the pitching moment is 0.25*chord, called the "quarter-chord".
The negative moment implies the actual "aerodynamic center" is forward of the quarter-chord point. The rest is just a balance of forces.

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NACA symmetrical foils - How do I find the point of balance ?

TMcRally

Automotive

verymadmac

Mechanical

GregLocock

Automotive

Sparweb

Aerospace

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