Blackbird
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Swing-Wing Question

Thu Apr 12, 2007 2:47 am

From what I've been told, swing-wings not only provide the ideal aspect ratio for the right speed, but also provide aerodynamic control over the plane's center of pressure without the need to shift fuel from front to aft-- since a moderately swept wing suffers a far less shift in the C/L than a wing with no sweep, and a highly swept wing suffers a miniscule shift in the C/L compared to a moderately swept wing.

Still, wouldn't swinging the wing aft like that shift the wing's C/L aft by a lot even just by moving the wing aft? How do they deal with that problem?

I have made speculations but have never actualy found the correct answer.


Andrea Kent
 
Blackbird
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RE: Swing-Wing Question

Thu Apr 12, 2007 7:34 am

Nobody has any answer?

Andrea Kent
 
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Jetlagged
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RE: Swing-Wing Question

Thu Apr 12, 2007 9:13 am

Swing wings were primarily developed to allow efficient low and high speed flight in the same airframe. It seems the extra weight and complexity just isn't worth it as no new swing wing designs have appeared for a long while. C/L shift can be dealt with by much more efficient means.

Quoting Blackbird (Thread starter):
since a moderately swept wing suffers a far less shift in the C/L than a wing with no sweep, and a highly swept wing suffers a miniscule shift in the C/L compared to a moderately swept wing.

Sweepback affects C/L shift due to shock wave formation, but once fully supersonic the centre of lift will still move to approx 50% chord regardless of planform.

Quoting Blackbird (Thread starter):
Still, wouldn't swinging the wing aft like that shift the wing's C/L aft by a lot even just by moving the wing aft? How do they deal with that problem?

As the wing sweepback increases the aircraft C.G. moves aft, which will compensate for the rearward shft of the C/L to some extent. As far as dealing with the remaining problem, that's what the pitch trim system is for!
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Blackbird
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RE: Swing-Wing Question

Thu Apr 12, 2007 1:06 pm

I looked over some swing-wing designs...

It seems also as the sweep occurs, more leading edge comes out of the glove and more trailing edge retracts in. Since the inboard wing is huge in area, that might be able to explain why the design doesn't experience a massive pitch down when the wings are swept back a lot as well partially.

It also seems as if the plane is largely optimized to have a slight tailplane leading-edge down trim-setting when the wings are swept fully aft, with the tail leading edge up when the wings are in the low-speed condition.

How much of a role do these factors play as well?

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