On 7/16/2012 11:11 PM, BruceGreeff wrote:

Basically - look at an older design like an ASW20 in a high load
situation the wingtip has substantial vertical displacement. It appears
the wing is flexing to high Angle of attack on the outboard panels.
Possibly this is caused by a combination of the rotational drag force
from winglets as well as the aerodynamic load induced bending.

The straight leading edge means that the centre of pressure on the wing
remains ahead of the main spar all the way to the wingtip - at high load
this tends to rotate the weakest (torsionally) part of the wing to
higher AoA than desired.

I think you are making unwarranted assumptions:

* that Schleicher did not make the ASW 20 wing torsionally stiff enough
to avoid twisting; in fact, it had plenty of glass fiber in the skins
(the part of the wing that gives it torsional stiffness - the spar is
mostly for bending loads) to do just that.
* That the ASW 20 had winglets - it did not
* That the outer part of the wing is is the weakest torsionally; even if
it is, it is also the portion with the least torsional load on it

Modern two seaters often have the wing swept forward until about
midspan, which contradicts your claim.

The basic claim that the trapezoidal wings are a way to deal with
flutter might be right (I have not seen this claim before -
references?), but to claim wings without it are inadequate to meet their
design requirements is unsupported. There are several ways to increase
flutter speeds, even with straight leading edges, and designers used
them as needed.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
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