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Akaflieg Karlsruhe AK-X



 
 
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  #41  
Old December 14th 17, 06:40 AM posted to rec.aviation.soaring
Tango Whisky
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Default Akaflieg Karlsruhe AK-X

Yep, as I said in a post above, the oscillation was damped with an aft, but then the stall characteristics turned to nasty. Most of this nastiness was cause by spanwise flow during stall which caused the whole wing to stall very rapidly. We then installed the boundary layer fences (iirc two per wing), and things improved.
  #42  
Old December 14th 17, 11:31 AM posted to rec.aviation.soaring
Tango Whisky
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Default Akaflieg Karlsruhe AK-X

Le jeudi 14 décembre 2017 06:40:58 UTC+1, Tango Whisky a écritÂ*:
Yep, as I said in a post above, the oscillation was damped with an aft, but then the stall characteristics turned to nasty. Most of this nastiness was cause by spanwise flow during stall which caused the whole wing to stall very rapidly. We then installed the boundary layer fences (iirc two per wing), and things improved.


That should read aft cg.

There actually was another nasty effect (which probably will happen with the AK-X, too):
During the ground run of the aerotow, the SB13 would lift of before the tug (as usual with sailplanes). It would then eventually fly through the vortex which the tug leaves on the runway after rotation and pitch into the ground. This happened on the (inofficial) first flight, and the relation between vortex and pitch down was discovered on the video - there has been a thin layer of snow on the runway which made the vortex visible.
Same would happen if during tow the SB13 reached a somewhat low position and came to contact the downwash of the tug's wing and its vortex - the glider would pitch down and could only be stabilized in a typical low tow position.

So the counter measure was to aerotow with a long rope (80-100 m), brief the tug pilot to do a gentle rotation/lift-off, and stay in low tow position troughout the tow.
  #43  
Old December 19th 17, 11:23 PM posted to rec.aviation.soaring
Michael Opitz
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Default Akaflieg Karlsruhe AK-X

At 05:10 13 December 2017, Michael Opitz wrote:
At 00:34 13 December 2017, Andreas Maurer wrote:


And, second question:
Do you know if the Horton guys ever considered winglets instead

of the drag ailerons?


Andreas,

I just got my copy of the book. The only Horten design which I
found using winglets (although they were ~2-3 meters inboard of
the tips) was on a 4 engine transport, the Ae. 38. The rudders only
moved in the outboard direction, and were controlled by
aerodynamic servo tabs. It only flew once due to being forced
(by nationalistic pride) to use engines that had only 40% of the
power that the aircraft was designed for. It had 30 cubic meters of
storage space. The Ae. 38 was conceived of in 1950 in Argentina.
It eventually flew there in 1960 and was then scrapped.

JJ,

Sorry I didn't answer about your crosswind question earlier. I'm
afraid that I don't know the answer to it though. Unless I find
something about it in the book, anything I would say at this point
would only be speculation except that I don't remember Dad
addressing crosswind landings in the Ho IV. The Me 163 had a
rudder like the Genesis and a much higher approach speed, so it
handled crosswinds like most other aircraft, except when it had
been flown so fast that the transonic flutter had caused the
rudder to disintegrate so badly that only the front spar/hinge
was left. Dad found that result on approach as he tried to slip it
with no result after one particularly high speed flight...

RO



 




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