Thread: Discussion 3DHS 47" Osiris
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Old Nov 09, 2012, 12:09 PM
kcaldwel is offline
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Joined Jan 2007
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I made a mistake in the sweep on the 62" Osiris. The 7" CG position is actually an 11% static margin. The equivalent point on the 47" Osiris would be about 146mm back from the wing LE/fuse junction.

Stability, unless there are severe low Re effects and poor airfoils with very non-linear lift curves, is not really affected by scaling. My calculated neutral point for the 47" Osiris seems to be very close from flight testing. With the CG back to 165mm it is still reasonably pitch stable.

I am a bit surprised that these airplanes are being flown with even an 11% static margin. That would be considered very pitch stable in the sailplane world. Re effects do start to come into play on the stability of sailplanes at the low speeds they can fly at, but even so the effects are usually quite small with decent airfoils.

I suppose there are certain compromises in the CG position to get the knife edge behaviour correct for pattern airplanes.

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