On 12 Dec, 17:31, wrote:
On Dec 11, 12:00*pm, "noel.wade" wrote:

...I'm betting the change in
wing-sweep on the outboard sections is to reduce twist loads and
improve the behavior/control-authority at the stall - but that's just
a guess from an amateur aerodynamics enthusiast. :-P

There are many possible reasons for the tip treatment. One possible
reason is aeroelastic as forward sweep can lead to unpleasant flutter
characteristics due to a positive relationship between wing bending
and AOA - though it doesn't seem to cover enough of the span to do
much. Another possibility is to influence spanwise flow at the tip and
reduce vortex losses. Thene there may be weight and balance and/or
handling reasons as you mention. *Or maybe they though it looked cool.

9B

All SH gliders since the Discus have had swept back outer wing
planforms - following Will Scheumann's deduction that it would reduce
induced drag ( on his cut down ASW 12 wings). The heart-warming thing
about that was that he worked this out logically, but non-
mathematically, from consideration of the likely relative pressures at
adjacent spanwise stations - and had the courage of his convictions to
modify his glider accordingly to prove it.

.... but for me the most important reason for having the sweep backs is
that, from some viewpoints, a wing with a step change in dihedral
gives the illusion of there being a aesthetically clumsy sweep-forward
if there is not a sweep-back at that point. Walk round a DG 1000 to
see this effect at the near-tip dihedral

http://www.dg-flugzeugbau.de/Data/dg1000-6.jpg

Once the designer has got the planform as close to ellipticaI as is
practical there are extra induced drag gains to be made from going out
of plane with progressive dihedral change. Add to that the Scheumann
effect and the aesthetic desirability of sweep back and the modern SH
wing emerges.

John Galloway