NACA Chord Balance point

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Does anybody know how to mathmatically tell where the balance point
should be on a NACA 63-015 airfoil? On a single number NACA airfoil,
like NACA 0012, the number represents the balance point in percent
from the big end. With two number airfoils, how do you figure it out?
Is it 15% from the big end, 63% from the small end, or something else
all together? Does anybody know?

Dennis H.



Dennis Hawkins
n4mwd AT amsat DOT org (humans know what to do)

"A RECESSION is when you know somebody who is out of work.
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[plasticguy]

> wrote in message
...
>
> Does anybody know how to mathmatically tell where the balance point
> should be on a NACA 63-015 airfoil? On a single number NACA airfoil,
> like NACA 0012, the number represents the balance point in percent
> from the big end. With two number airfoils, how do you figure it out?
> Is it 15% from the big end, 63% from the small end, or something else
> all together? Does anybody know?
>
> Dennis H.
>
>
>
> Dennis Hawkins
> n4mwd AT amsat DOT org (humans know what to do)


Dennis..
For starters, the NACA0012 doesn't necessarily balance at 12% of chord
from anywhere. It is a full symettric airfoil that is 12% THICK. The
numbers
have very very little to do with balance points. I suggest you read
up on what the numbers mean. I'll look for a good book
BUT "THEORY OF AIRFIL SECTIONS" is a good place to start.

Scott

Scott.

[Dikkie Dik]

wrote:
> Does anybody know how to mathmatically tell where the balance point
> should be on a NACA 63-015 airfoil? On a single number NACA airfoil,
> like NACA 0012, the number represents the balance point in percent
> from the big end. With two number airfoils, how do you figure it out?
> Is it 15% from the big end, 63% from the small end, or something else
> all together? Does anybody know?
>
> Dennis H.
>
>
>
> Dennis Hawkins
> n4mwd AT amsat DOT org (humans know what to do)
>
> "A RECESSION is when you know somebody who is out of work.
> A DEPRESSION is when YOU are out of work.
> A RECOVERY is when all the H-1B's are out of work."
>
> To find out what an H-1B is and how Congress is using
> them to put Americans out of work, visit the following
> web site and click on the "Exporting America" CNN news
> video: http://zazona.com/ShameH1B/MediaClips.htm
>
>

The center of gravity of the airfoil section can be calculated, but
there is very little point in that. In the ideal case, 3 points should
be the same: The center of gravity, the aerodynamic centre, and the
structural centre (don't know what it is called exactly in english, but
it is the point where you can apply a force without causing a torque as
well). At least, that is what I have learned. For symmetrical airfoils
this is definitely true, but for curved airfoils this would mean that
there is still an aerodynamic torque in the blade.

The aerodynamic centre can be calculated from the airfoil lift and
moment curves and is usually located near 25% of the chord. It is also
important in stability: If the centre of gravity is before this point ,
the configuration is stable (like an arrow that will point its point in
the direction it flies) and if the centre of gravity is after this
point, it is unstable (hint: a piece of paper from your printer has its
centre of gravity at 50%. Watch how it flies...)

This means that blade manufacturers will normally put a balance weight
in the nose of the blade or make the rear hollow (or both)

Best regards,
Dikkie Dik

[Bob]

um...MAC...Mean aerodynamic chord?