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Old Apr 04, 2005, 09:14 AM
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Joined Oct 2004
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Airfoil question for deltas/flying wings

For a "standard" airplane with a tail, the CG usually corresponds to the thickest part of the wing and is typically 25-35% of the chord. For a flying wing or delta the CG is normally set at between 10-20% of the chord, so would it make sense to make the thickest part of the wing correspond to the CG in this case also?

Opinions?

Thanks,
Adam
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Old Apr 04, 2005, 09:55 AM
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Punta Gorda, FL
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"For a flying wing or delta the CG is normally set at between 10-20% of the chord, so would it make sense to make the thickest part of the wing correspond to the CG in this case also?"

No, not the airfoil thickness but, the CG ahead of the total plane aerodynamic center (AC) or the neutral stability point (NP).
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Old Apr 04, 2005, 11:22 AM
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Palmdale, CA
Joined Oct 2000
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Adam, it's not the thickness, but the shape overall... with the trailing edge on a delta/flying wing deflected up, either at the control surface itself or built into the geometry of the airfoil that makes a delta/flying wing work.
And as Ollie says, it's the position of the c.g. relative to the aerodynamic center of the airfoil that is important.
Wings are odder beasts than conventionals, and take more design effort to get to work.
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Old Apr 05, 2005, 08:02 PM
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Jackson, MS
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What is the definition of aerodynamic center of the airfoil? My question is related to an odd-shaped flying wing that does not easily fit the formulas.

If you had an odd-shaped flying wing, could you cut out a flat pattern and and get the CG of that pattern?
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Old Apr 05, 2005, 09:29 PM
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The aerodynamic center is the pitching moment axis point in the airfoil . For most shapes, from symmetrical to highly cambered, the axis is generally found at the 25% chord line.
The c.g. of a shape can be determined by finding the c.g. of the flat pattern.
That is not the a.c. though.
And adding construction for the real thing can change the c.g.
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Old Apr 06, 2005, 09:44 AM
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Jackson, MS
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Thanks--

If I make a model with all of the parts installed, CG in front of the NP, what is the best way to test it out, short of powering up and trying to fly it? If it seems to glide well, is that a good measure that you are ready to try to fly?

Thanks from a beginner (as if you couldn't tell)
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Old Apr 06, 2005, 11:00 AM
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With the c.g. on the pattern at where you want it on the real one, toss the pattern!
With suitable verticals, of course..
Chuck gliders are the traditional way to get the c.g. in the ballpark when complex computations aren't done.
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