There is obviously a styling department.
De Havilland had a unique fin and rudder design for a long time but
dropped it for the Comet and Boeing recycled the cockpit shape and
fuselage cross section of the 707 for a looong time. Right 737
drivers? This was more economics than styling though. Why change
something that works fine.
The swept back wingtip for modern gliders was invented by Wil
Schuemann, an American (Sage variometers), in the early 1980s. He
sawed the tips off an 18M ASW 12 and made it a 15M glider with his
swept back tips. See also Minimoa though a long time earlier.
With forward sweep which most gliders had on the trailing edge, the
flow at the trailing edge on the top surface can separate all the way
from the tip to to the root causing extra drag.
In his article in a late 1982/early 1983 Soaring magazine he has a
nice photo of a Kestrel 17 with thermalling flap with the
flap/aileron tufted, showing that the flow on the flap was at a 90
degree to the direction of travel from the tip to the root.
Klaus Holighaus at Schempp Hirth licensed the idea and I heard Wil
got a Discus for it.
In early 1985 Klaus visited Gawler and after flying on the day that
he and Harry Schneider managed to outland at the back of the hills in
the Platypus (aero retrieve - there was no trailer) I asked Klaus
what the advantage of the swept back tip was in terms of effective
increased span and hence aspect ratio. About 30cm. It is all about
low speed performance. He did mention that the tip really ought to
have 10 degrees of dihedral too but he thought it would look too
bizarre and nobody would buy it. Obviously people have got used to it.
When Harry Schneider first showed me a three view of the Discus I
thought it was Holighaus's idea of an April Fool's joke.
Winglets do much the same thing so are probably less effective on the
sweptback tip than on a normal one. It is the tip that counts which
probably accounts for why my Ventus C A goes so well in 17.6 m
configuration with the sweptback upturned tips compared to
15M without winglets. The multiple kinks/distributed dihedral also
makes the wing 3D. It has been known for a long time that a 3D wing
can have lower induced drag than a 2D wing. Lower even than that of a
perfect elliptical lift distribution on a 2D wing. Look up R.T
Jones of the old NACA and then NASA. May also explain why floppy
winged glass gliders like the ASW20 and Pegase climb well although
you really want most of the 3D curve closer to the wingtip than the root.
There is the possibility that the kinks in the leading edge can trip
the laminar flow according to Lemke I think it was, hence the curved,
kinkless leading edge on the SZD55, Diana 2, GP14/15 etc. There is
certainly a tendency for modern gliders to have the taper on the
leading edge rather than the trailing edge as they used to.
Wil didn't have his Discus for all that long and by 1986 had sold it
and bought a 1-26 of all things. I believe he got into pistol
shooting right after that and makes pistol barrels. He seems to still
be in business http://www.schuemann.com/ Interestingly for a guy who was
into mechanical varios and compensator boxes, I was told he was an
electrical engineer.
Some more from Wil at http://www.betsybyars.com/guy/soaring_symposia
. Worth a look. Some of it is still relevant, some historical. Yes
boys and girls we did indeed spend a lot of time trying to tune and
make work, bizarre fluidic analog computers for total energy
compensation.
Mike
07:39 AM 12/14/2016, you wrote:
or cosmetics??
On 14 December 2016 at 08:30, Richard Hatch
<<mailto:rhatch...@gmail.com>rhatch...@gmail.com> wrote:
Does anyone care to guess at why some more modern designs (Ventus 3,
JS-3) have several stages of wing kink while some older designs
(ASG29, Diana 2) don't?
Aerodynamics or economics?
Rich
On Wed, Dec 14, 2016 at 6:55 AM, DMcD
<<mailto:slutsw...@gmail.com>slutsw...@gmail.com> wrote:
>>Not only save weight but the wings wouldn't shrink, warp or
develop waviness.
Using pre pregs in the fuselage would save non lifting parts weight
and save even more wing weight.
Agreed. The German certified glider industry is not innovative these
days. All the fuss about electric gliders is only possible because
most glider pilots don't look to anywhere other than 3 factories in
Germany.
Their construction methods have not changed in 50 years. It's
staggering to see a worker with a jam jar fully of poxy bog and a pop
stick about to join a wing. The last place I saw a working manual
typewriter in use was Schleichers, about 6 years ago.
Of course, a little investment in ATL machines and proper moulds would
help. I can't understand why yacht mast makers and boat builders can
mill a mould from solid alu for a single boat while glider
manufacturers stay with low-temp resin moulds which are reused for a
decade or more.
Maybe we're not paying enough? Though I believe the problem is almost
entirely certification.
D
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