Re: An-124 and wing dihedral

Date:         18 May 98 16:03:04 
From:         Ken Rose <rose@acm.org>
Organization: Netcom On-Line Services
References:   1
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Karl Swartz wrote:
> Last Thursday there were a couple of Antonov An-124s parked at Moffet
> Field.  (I've seen one there before.  Anyone know what they might be
> doing there?)  They reminded me of a question I've had about wing
> dihedral.

...

> The An-124 also has substantial wing dihedral, but its wing tips are
> *lower* than its wing roots, just the opposite of the 777.  Various US
> cargo transports with high wings (C-141, C-5, C-17) are similar, though
> not as pronounced as the An-124.
>
> I can't see what "negative" dihedral (like the An-124) would accomplish,
> or why it would even be desireable.
>
> Would someone care to enlighten me on the aerodynamics of wing dihedral?

  I seem to remember hearing, in the context of the B-52's wing, that
dihedral is measured in the plane of the wing's chord, and when the wing
is set at a substantial angle of incidence the sweep can make it appear
to have a negative dihedral when in fact the dihedral is positive.

Perhaps this is what is going on.

 - Ken Rose <rose@acm.org>