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Akaflieg Karlsruhe AK-X



 
 
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  #21  
Old December 12th 17, 12:48 AM posted to rec.aviation.soaring
Jonathan St. Cloud
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Posts: 1,463
Default Akaflieg Karlsruhe AK-X

Thank you so much Andreas. This project and Mu-31 are projects that seem like they have potential to develop new technology.


On Monday, December 11, 2017 at 12:41:31 PM UTC-8, Andreas Maurer wrote:
On Mon, 11 Dec 2017 14:03:36 +0000 (UTC), Kiwi User
wrote:


Yes, I was aware that this is a complex set of three control surfaces per
wing, but I'm a little confused about their function, but I think that,
listing from root to tip they were elevator,aileron,drag rudder. Is this
a fair description.


Close.

One needs to know that the AK-X works in a completely different way
than any other flying wing ever designed. Despite its similar
appearance, it is not even similar to the SB-13 aerodynamics-wise.

1. The AK-X is a flapped wing. At low speeds, all (!!) control
surfaces move downwards, at high speeds all move upwards. Just like an
ordinary glider. The rudders are in the winglets.

2. Pitch control is done by the inner flaps which work the same way as
a canard. Pitch up: Control deflection down, and vice versa. Perfect
solution concerning lift-distribution.

3. Compare the wing sweep of the AK-X to other flying wings: It is
much greater. This shows good promise to get rid of the pitch axis
oscillations experienced by other flying wings and the CG sensitivity
that has plagued all flying wing designs so far.
However, it needs an extremely stiff wing , which has just become
possible in the last few years after the latest progress in carbon
fibre stiffness.
(Fun fact: The wing is so stiff that the structural test did not
result in the wing spar breaking but in a torsional fracture of the
wing shell!)



Comparison to previous flying wing designs:

All previous flying wings had one huge basic fault:
In order to pitch up (or to fly slow), you had to deflect the controls
up, therefore reducing airfoil camber and thus lift coefficient -
basically exactly the opposite of what you'd like to have
aerodynamically.

The wing of the AK-X works exactly like that of any flapped glider:
Low-speed flight: All flaps deflected "down"
High-speed flight: All flaps deflected "up"


The idea behind this aredoynamic design is, frankly spoken, a touch of
genius. It's the first ever flying wing design ever that in theory
will be able to compete with a conventional design in all areas of the
flight envelope up to very high speeds.

Plus, there are a couple of other benefits:
The wing uses conventional airfoils whose aerodynamic qualities can be
predicted well today. The flapped wing creates the same lift
coefficient as the wing of a conventional design, allowing high aspect
ratio and wing loading.
Behind the cockpit there's a 40 liter water tank (directly at the
center of gravity) and no other structural parts - pretty simple to
replace this tank with an angine and some serious battery capacity.


To me, the only remaining question is the influence of the wing sweep
on spanwise flow - but as I heard the guys are pretty optimistic so
far (they've got a 1:2 model flying with very good results).




Cheers
Andreas


  #22  
Old December 12th 17, 02:52 AM posted to rec.aviation.soaring
Kiwi User
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Posts: 64
Default Akaflieg Karlsruhe AK-X

On Mon, 11 Dec 2017 21:41:25 +0100, Andreas Maurer wrote:

To me, the only remaining question is the influence of the wing sweep on
spanwise flow - but as I heard the guys are pretty optimistic so far
(they've got a 1:2 model flying with very good results).

If a description I read many years ago of what makes a Hoerner tip work
and why its beneficial is true, then the spanwise flow shouldn't be a
problem.

I know that a lot of tip shapes were described as Hoerner tips, but the
one I'm talking has:

- a minimum LE sweep of 10 degrees on the outermost wing panel

- a straight edge to the tip raked outward toward the TE at at least
30 degrees and should meet the TE at an acute angle,
i.e. not rounded off

- the upper surface curves down to meet the lower surface at an acute
angle

The idea was that the LE sweep promoted spanwise flow toward the tip,
which was encouraged to oppose the tip vortex rotation as it slid over
the convex tip profile. The pointed at the end of the TE anchors the tip
vortex while the roll-down of top surface flowing spanwise out along the
panel and down over the tip shape will tend to move the tip vortex
outward.

I used this tip design for many years on competition free flight F1A
gliders. It worked for me. It was notable that, while models with
conventionally rounded tips needed a lot of tip washout to prevent tip
stalling, my design worked best with unwarped [flat] tip panels.
Directional stability was good too. Minimal fin area is beneficial to F1A
performance and thermal centering, the optimum being just big enough to
kill dutch rolling tendencies. On my design the fin had to be reduced to
a surprisingly small size before the first signs of dutch roll appeared.
Benefits of solid balsa fins: you keep chopping bits off until the dutch
roll appears and then stick the last bit back on.


--
Martin | martin at
Gregorie | gregorie
| dot org
  #23  
Old December 12th 17, 04:30 AM posted to rec.aviation.soaring
Michael Opitz
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Posts: 318
Default Akaflieg Karlsruhe AK-X

At 20:41 11 December 2017, Andreas Maurer wrote:

Comparison to previous flying wing designs:

All previous flying wings had one huge basic fault:
In order to pitch up (or to fly slow), you had to deflect the controls
up, therefore reducing airfoil camber and thus lift coefficient -
basically exactly the opposite of what you'd like to have
aerodynamically.

The wing of the AK-X works exactly like that of any flapped glider:
Low-speed flight: All flaps deflected "down"
High-speed flight: All flaps deflected "up"


The idea behind this aredoynamic design is, frankly spoken, a

touch of
genius. It's the first ever flying wing design ever that in theory
will be able to compete with a conventional design in all areas of

the
flight envelope up to very high speeds.

Plus, there are a couple of other benefits:
The wing uses conventional airfoils whose aerodynamic qualities

can be
predicted well today. The flapped wing creates the same lift
coefficient as the wing of a conventional design, allowing high

aspect
ratio and wing loading.
Behind the cockpit there's a 40 liter water tank (directly at the
center of gravity) and no other structural parts - pretty simple to
replace this tank with an angine and some serious battery capacity.


To me, the only remaining question is the influence of the wing

sweep
on spanwise flow - but as I heard the guys are pretty optimistic so
far (they've got a 1:2 model flying with very good results).

Cheers
Andreas



Andreas,

Thank you very much for the insights. If my father were still alive
today, he would be wanting to follow the progress very closely. The
aerodynamic genius of using the wing sweep to emulate canard
characteristics as opposed to using the sweep for high speed flight
is extremely intriguing. Being able to use current modern airfoils
while reducing drag considerably, should result in very noticeable
performance increases. Also, the advent of newer construction
materials and methods which enable the builders to achieve the
stiffness that is required to overcome other previous wing's
aeroelastic issues cannot be overstated.

Please post any progress updates here whenever you may hear of
them in the future....

RO

  #24  
Old December 12th 17, 05:50 AM posted to rec.aviation.soaring
Michael Opitz
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Posts: 318
Default Akaflieg Karlsruhe AK-X

At 14:03 11 December 2017, Kiwi User wrote:

BTW, have you see this article about the Ho S.IVb:

https://scalesoaring.co.uk/VINTAGE/D...n/Horten%20IV/
Horten_IVb.html

Lots of photos, good plan showing the three control surfaces per wing

and
a useful write-up about construction, flying characteristics and where
the airframes went.

A bigger plan is downloadable from he

https://scalesoaring.co.uk/VINTAGE/D...n/Horten%20IV/
Horten_IV_model.html



As far as I know, the replica has not flown.

Thanks for the scalesoaring links, I had not seen them before.

RO

  #25  
Old December 13th 17, 01:24 AM posted to rec.aviation.soaring
Andreas Maurer
external usenet poster
 
Posts: 345
Default Akaflieg Karlsruhe AK-X

On Mon, 11 Dec 2017 15:48:44 -0800 (PST), "Jonathan St. Cloud"
wrote:

This project and Mu-31 are projects that seem like they have potential to develop new technology.


Absolutely.

Since you mentioned the Mu-31: Also an extremly interesting project,
much more consequent wing-root design than the JS-3, and since it's
otherwise identical to the ASW-27 it should be easy to compare the
benefits of the new design.



  #26  
Old December 13th 17, 01:27 AM posted to rec.aviation.soaring
Andreas Maurer
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Posts: 345
Default Akaflieg Karlsruhe AK-X

On Tue, 12 Dec 2017 01:52:24 +0000 (UTC), Kiwi User
wrote:

Hi Martin,

I'm rather worried about spanwise flow originating at the wing root
(similar to the SB-13) - but let's wait and see. The guys (and gals)
know their stuff.

The idea was that the LE sweep promoted spanwise flow toward the tip,
which was encouraged to oppose the tip vortex rotation as it slid over
the convex tip profile. The pointed at the end of the TE anchors the tip
vortex while the roll-down of top surface flowing spanwise out along the
panel and down over the tip shape will tend to move the tip vortex
outward.

I used this tip design for many years on competition free flight F1A
gliders. It worked for me. It was notable that, while models with
conventionally rounded tips needed a lot of tip washout to prevent tip
stalling, my design worked best with unwarped [flat] tip panels.
Directional stability was good too. Minimal fin area is beneficial to F1A
performance and thermal centering, the optimum being just big enough to
kill dutch rolling tendencies. On my design the fin had to be reduced to
a surprisingly small size before the first signs of dutch roll appeared.
Benefits of solid balsa fins: you keep chopping bits off until the dutch
roll appears and then stick the last bit back on.


  #27  
Old December 13th 17, 01:34 AM posted to rec.aviation.soaring
Andreas Maurer
external usenet poster
 
Posts: 345
Default Akaflieg Karlsruhe AK-X

On Tue, 12 Dec 2017 03:30:19 +0000, Michael Opitz
wrote:


Thank you very much for the insights. If my father were still alive
today, he would be wanting to follow the progress very closely. The
aerodynamic genius of using the wing sweep to emulate canard
characteristics as opposed to using the sweep for high speed flight
is extremely intriguing. Being able to use current modern airfoils
while reducing drag considerably, should result in very noticeable
performance increases. Also, the advent of newer construction
materials and methods which enable the builders to achieve the
stiffness that is required to overcome other previous wing's
aeroelastic issues cannot be overstated.

Please post any progress updates here whenever you may hear of
them in the future....


I promise.
I happen to be at the Akaflieg Karlsruhe workshop two times per year
so with a little luck I can provide you with some updates if the
Akaflieg guys allow that.


But since we are talking:
Has your father ever talked about (or even flown) the Horten VI (the
24m glider)? I was always amazed that such a thing could be built in
the pre-carbon fibre aera.

There are a couple of reports about the IV, but I couldn't find any
halfways detailed source about the VI.

And, second question:
Do you know if the Horton guys aver considered winglets instead of the
drag ailerons?

Cheers
Andreas
  #28  
Old December 13th 17, 06:10 AM posted to rec.aviation.soaring
Michael Opitz
external usenet poster
 
Posts: 318
Default Akaflieg Karlsruhe AK-X

At 00:34 13 December 2017, Andreas Maurer wrote:
On Tue, 12 Dec 2017 03:30:19 +0000, Michael Opitz
wrote:


Thank you very much for the insights. If my father were still

alive
today, he would be wanting to follow the progress very closely.

The
aerodynamic genius of using the wing sweep to emulate canard
characteristics as opposed to using the sweep for high speed

flight
is extremely intriguing. Being able to use current modern airfoils
while reducing drag considerably, should result in very noticeable
performance increases. Also, the advent of newer construction
materials and methods which enable the builders to achieve the
stiffness that is required to overcome other previous wing's
aeroelastic issues cannot be overstated.

Please post any progress updates here whenever you may hear

of
them in the future....


I promise.
I happen to be at the Akaflieg Karlsruhe workshop two times per

year
so with a little luck I can provide you with some updates if the
Akaflieg guys allow that.


But since we are talking:
Has your father ever talked about (or even flown) the Horten VI

(the
24m glider)? I was always amazed that such a thing could be built

in
the pre-carbon fibre aera.




Martin Gregorie provided a pretty good link for a brief Horten
history:

https://scalesoaring.co.uk/VINTAGE/D.../Horten%20IV/H
orten_IVb.html

From that article:

"As Heinz Scheidhauer was the most experienced and long serving
Horten pilot, it is also strange that the test flying of the H IVb should
be passed to Strebel at such an early stage.

Scheidhauer had flown most of the Horten types and despite some
peculiarities, their handling had been generally benign as they were
highly stall and spin resistant. Although the H IVa had been liable to
flutter, it had proved possible to damp it by simultaneous use of the
drag rudders. None the less, he had refused to fly an HIII to explore
its handling at extreme rear centre of gravity positions. On 24 May
1944 he made the maiden flight of the ultra high aspect ratio H VI,
discovering that not only was it subject to flutter at both high and
low speeds but that the entire wing was far too flexible and fragile
for even an expert pilot.

If Zubert’s log book entry is correct, the pilot of the H IVb on 11
August was almost certainly Scheidhauer and this may also have
been its maiden flight – long before the H XIIIa.

Unfortunately just ten weeks after test flying the H VI, Scheidhauer
discovered that the H IVb suffered from truly appalling handling
characteristics and would abruptly drop a wing and attempt to spin
at speeds as high as 77km/h, yet above 110 km/h the wings would
flutter. Later, also he refused to fly the H XIIIa which Strebel tested
from the outset. It seems that Scheidhauer was losing faith in
Reimar’s ability as a designer."


Scheidhauer was a student of Dad's from the first military glider
pilot training class at the DFS in ~1937 where Dad was one of the
three original instructors. Dad also later got him a flight in a Me
163, even though he was from the Horten camp. By 1944 when
Scheidhauer first flew the Ho VI, Dad was pretty deep into getting
operational Me 163 units up and running. His glider logbook shows
one or two Ho III entries earlier, but no Ho VI. He never really
talked about the Ho VI at all. I doubt it flew much considering the
info from the above story.


There are a couple of reports about the IV, but I couldn't find any
halfways detailed source about the VI.

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

of the
drag ailerons?


I don't know if they considered winglets, and I can't remember what
the aircraft they designed after the war in Argentina looked like.
The person to ask is Peter Selinger. He was also a friend of
Scheidhauer's and received all of Scheidhauer's personal logs, etc
when he passed away. Peter also wrote a book on the Hortens, but
unfortunately, I don't have a copy of it.

"Nurflügel", by Peter F. Selinger and Dr. Reimar Horten
ISBN-103900310092
ISBN-139783900310097

I do have Peter's contact info in case you want it though. We have
been in fairly regular contact with each other since 1985.

RO

  #29  
Old December 13th 17, 12:46 PM posted to rec.aviation.soaring
Kiwi User
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Posts: 64
Default Akaflieg Karlsruhe AK-X

On Wed, 13 Dec 2017 01:27:16 +0100, Andreas Maurer wrote:

Hi Andras,


I'm rather worried about spanwise flow originating at the wing root
(similar to the SB-13) - but let's wait and see. The guys (and gals)
know their stuff.

I notice that initial drawings put the wing at the bottom of the pilot's
pod, but in the 1:2 model its just below the canopy rim. Was this for
wing clearance or aerodynamics?

I'm a little surprised, too, at the quite minimal root fairings. Is this
what you were referring to when you mentioned spanwise flow at the root?

It would be interesting to see flow visualisation round them. Though, as
you say, the guys and gals know their stuff, so maybe cleaning up the
wing roots is being left for full size detailed design. After all, the
1:4 model had nothing except a couple of sensor probes at its root, so
just adding the pod was quite a big step aerodynamically.


--
Martin | martin at
Gregorie | gregorie
| dot org
  #30  
Old December 13th 17, 04:32 PM posted to rec.aviation.soaring
Jonathan St. Cloud
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Posts: 1,463
Default Akaflieg Karlsruhe AK-X

This thread really highlights what a diverse interesting group, peoples the soaring world! I have immensely enjoyed not only the history told in this thread, but the technology these young engineers are exploring. Wish there was a way for non-German speakers to stay updated on the various Akaflieg projects. Thank you for all who shared!
Jon
 




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