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Akaflieg Karlsruhe AK-X



 
 
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  #11  
Old December 10th 17, 03:26 PM posted to rec.aviation.soaring
BobW
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Default Akaflieg Karlsruhe AK-X

On 12/9/2017 6:38 PM, Michael Opitz wrote:
I hope these students design and build a contest viable swept wing
sailplane.

Lets hope that, unlike the Horten gliders and their earlier SB-13 Arcus,
it doesn't have a nasty high-speed pitch oscillation, that seems to be
an unwanted feature of swept wing tailless aircraft.

I've seen flight reports about a Horten S.IV when it was being flown in
US comps that mentioned that a 'pecking' oscillation limited its
cruising speed and flight reports about the SB-13 show that it shared
this behaviour.

The DH.106 Swallow, an early British swept-wing jet, also showed the
same high speed oscillation. That killed Geoffrey de Havilland Jr. when
the pitch oscillation broke his neck during a high speed run in the 2nd
prototype and almost killed Eric 'Winkle' Brown in the 3rd - he said
that the oscillation was very violent and thought he only survived
because he was smaller than de Havilland and so didn't get his head
slammed into the canopy. When he slowed down below a critical speed the
oscillation stopped as suddenly as it had started


-- Martin | martin at Gregorie | gregorie | dot org


Martin,

That was my father who re-built and flew the Ho-IV in 1952 USA contests. He
limited himself to no more than 80 mph IAS in order to keep away from the
pitch "pecking" characteristics which made him uncomfortable. From the
late 1930's until the mid 1940's, he was one of the world's top flying wing
test pilots, so he knew exactly what he was doing when he flew the Ho-IV.

When I showed him the SB-13 designs and photos, the "pecking" was the
first thing he mused about before they even flew it. Once they flew it,
and it was established that it had the same issues, he just said that he'd
thought that they would have solved that issue by that time.

That is not to say that other designs did not have those issues, or had
not solved them earlier. My father and Heini Dittmar were the two
Lippisch primary test pilots who were with the Me 163 for basically its
entire existence. That team knew it wanted to go fast, and that slow
speed handling issues would only be amplified at higher speeds, so they
concentrated very hard on good handling characteristics on that bird. Their
results showed exceptional handling as reported by Capt Eric Brown among
many others. Dr. Lippisch and his team overcame those aerodynamic issues,
while the Hortens and the DH.106 Swallow apparently never did.

Dad was from the Lippisch camp, but through a unique set of circumstances,
he had also gained the trust of the competition, which was the Horten camp.
Thus, the Hortens let him fly a number of their creations as well. His
basic opinion was that the Hortens designed beautiful looking aircraft, but
the handling was always marginal at the very best, even in the slower speed
regimes. He never thought that the Hortens would succeed in high speed
flight as long as they didn't make vast improvements on their designs.

The Ho-IV which he flew in 1952 came from England. It had belonged to
Geoffrey de Havilland Jr. I don't know if it was the one that Robert
Kronfeld had brought to England, or if de Havilland had brought it there
from Germany after the war. Then, de Havilland sold it to another British
test pilot named Hollis Button who brought it to the USA, and promptly
lost control on his first take-off, thus crashing it. Now, Button was left
with a broken glider that nobody knew how to fix. He hunted Dad down after
he had heard that my father had the skills to fix it. Dad agreed to fix it
as long as he could fly it for the entire next (1952) year's contest
season. So, Dad repaired the Ho-IV over the 1951- 1952 winter and flew it
in several contests in 1952. Thereafter, the Ho-IV went to Mississippi
State University where Dr. Gus Raspet profiled the wings and made
performance measurements. After that, it was parked in a disassembled
state in various places, winding up in the desert SW USA. It was reported
that someone scavenged/stole the metal outer wing panels for use on some
experimental aircraft. Eventually, the Planes Of Fame Museum in Chino, CA
got it, and now have it hung on display in one of their hangars.
Unfortunately, it is very poorly restored with Styrofoam outer wing panels
in the wrong shape, as well as a rather grotesque looking replacement lower
fuselage/pod:

https://www.google.com/search?
q=planes+of+fame+Horten+IV&rlz=1C1CHWA_enUS602US60 3&tb
m=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwijoqS1lv7 XAhVjh
OAKHfxjArEQsAQIKA&biw=1280&bih=918#imgrc=_

Pictures from the Mississippi State flight performance testing, where Dad
had checked out Professor Dezso George-Falvy in order to continue the
program. These photos show how the restored glider really should look:

http://www.nurflugel.com/Nurflugel/H...s/ho_iv/Falvy_
Pics/falvy_pics.html

My own personal guess on the "hunting/pecking" problem is that it probably
resides with aero-elastic issues and the swept back high aspect ratio wing.
Given the newest carbon-kevlar+? materials, maybe the bending and torsional
stiffness of a newer construction wing can help overcome some of these
issues.... We will see if and when the SB-13 gets into the flight testing
phase...

RO


Thanks for taking time to write this up, Mike. It happens to be stuff I've
been interested in and wondered about for many years!

Bob W.

---
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  #12  
Old December 10th 17, 06:08 PM posted to rec.aviation.soaring
Kiwi User
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Default Akaflieg Karlsruhe AK-X

On Sun, 10 Dec 2017 01:38:23 +0000, Michael Opitz wrote:

That was my father who re-built and flew the Ho-IV in 1952 USA contests.
He limited himself to no more than 80 mph IAS in order to keep away
from the pitch "pecking" characteristics which made him uncomfortable.
From the late 1930's until the mid 1940's,
he was one of the world's top flying wing test pilots, so he knew
exactly what he was doing when he flew the Ho-IV.

Most interesting stuff. Thanks for posting it. On a closer look, I see
exactly what you mean about that horrid lump of block foam that passes
for a subfin, but there's not enough detail to see how bad the tip is -
except that they haven't bothered to make and fit ailerons.

I've found out a little more about that Ho S.IV. It seems to have been
taken to Farnborough by the Royal Aircraft Establishment (RAE)'s Enemy
Aircraft Flight. These were the British equivalent of Rechlin and NACA.
At first I thought it had been collected by Philip Wills or Eric "Winkle"
Brown, but this wasn't the case.

Eric Brown flew it several times while it was at Farnborough as part of a
tailless research project. He liked it and especially to 'praying mantis'
pilot position. I can see that that odd yoke is tilted for roll control,
but what about elevator - do the handles link to that by rotating the
tube they're mounted on? Similarly, I can see the tow release at the
front of the canopy but have no idea where the airbrake and trim controls
might be.

Geoffrey de Havilland must have got the glider from the RAE after they'd
finished testing it. I never knew he was a glider pilot, so can only
assume that he heard of it due to his involvement with the DH.108 Swallow.

I thought Philip Wills had brought a number of gliders back from Germany
but misremembered that. He he visited the Wasserkuppe as a side trip with
the Air Transport Auxiliary and found a lot of gliders there in good
condition. He'd been after a Reiher but, when he found a bunch of Weihes
there he got two of them back to Farnborough - at the time the US forces,
whose zone included the Wasserkuppe, were planning to burn the lot
because some troops had killed or maimed themselves trying to do
untutored bungee launches off the hill so he thought he'd best save at
least some from the bonfire. However, by the time his two arrived at
Farnborough two months later the rest were still untouched in their
hangars, so I wonder if the threatened destruction ever happened.

Anyway, Philip Wills ended up owning one of the Weihes and flying it for
two years before he sold it to Dick Georgeson in NZ, who used it for his
early explorations of mountain wave on the Southern Alps. He flew it for
what I believe was the first significant XC in wave (1953) when he flew
it from Christchurch to Dunedin, getting Gold height in the process and
missing Gold distance by just 3km due to being released a bit too far
south.

Bruce, if you're reading this: does that Weihe still exist and if it
does, is it still airworthy and who owns it?


--
Martin | martin at
Gregorie | gregorie
| dot org
  #13  
Old December 10th 17, 06:46 PM posted to rec.aviation.soaring
Kiwi User
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Default Akaflieg Karlsruhe AK-X

On Sun, 10 Dec 2017 17:08:41 +0000, Kiwi User wrote:

I've found out a little more about that Ho S.IV. It seems to have been
taken to Farnborough by the Royal Aircraft Establishment (RAE)'s Enemy
Aircraft Flight. These were the British equivalent of Rechlin and NACA.

Minor correction: I meant that the RAE was approximately equivalent to
Rechlin or NACA and Edwards.

The Enemy Aircraft Flight was a similar gang to Watson's Whizzers. They
knew each other and worked together and were known to exchange aircraft
on occasion because they operated in different parts of Germany and
surrounding countries. For instance, the only flyable Arado 2324s were in
Denmark and northern Germany, so all of the ones now in the USA were
collected by the EAF. Two were then given to WW in exchange for letting
Eric Brown interview Goering and I think one or two others were passed on
by Farnborough.


--
Martin | martin at
Gregorie | gregorie
| dot org
  #14  
Old December 11th 17, 01:55 AM posted to rec.aviation.soaring
Michael Opitz
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Posts: 318
Default Akaflieg Karlsruhe AK-X

At 17:08 10 December 2017, Kiwi User wrote:


Most interesting stuff. Thanks for posting it. On a closer look, I see

exactly what you mean about that horrid lump of block foam that
passes for a subfin, but there's not enough detail to see how bad the
tip is - except that they haven't bothered to make and fit ailerons.


It looks like someone may have tried to make the tips "all flying"
control surfaces, as they appear to be skewed off axis somehow.
Also, IIRC, those are elevons (not ailerons) that are missing. IIRC,
the Ho-IV used a system whereby an outboard spoiler was
separately deployed on one wing (or the other) for roll and yaw
control. (in addition to the elevons)


Eric Brown flew it several times while it was at Farnborough as part

of a tailless research project. He liked it and especially to 'praying
mantis' pilot position.

Dad found the praying mantis position ok, except for when he was
at the end of a long flying day, and his beard stubble started to
become irritated by the chin rest.

I can see that that odd yoke is tilted for roll control,

but what about elevator - do the handles link to that by rotating the
tube they're mounted on? Similarly, I can see the tow release at the
front of the canopy but have no idea where the airbrake and trim
controls might be.

To be quite honest, I was 1-1/2 years old when Dad flew the 1952
nationals. I was left at home with friends. I never got to look at
a Ho IV cockpit with Dad in my adult life, so I can't answer your
questions. I'm sure that the fellow(s) who precisely rebuilt a
Ho IV a few years ago in Germany can answer those questions
though.

http://www.nurflugel.com/Nurflugel/H...s/ho_iv/ho_iv_
Restoration/body_ho_iv_restoration.html


Anyway, Philip Wills ended up owning one of the Weihes and flying

it for two years before he sold it to Dick Georgeson in NZ, who used
it for his early explorations of mountain wave on the Southern Alps.
He flew it for what I believe was the first significant XC in wave
(1953) when he flew it from Christchurch to Dunedin, getting Gold
height in the process and missing Gold distance by just 3km due to
being released a bit too far south.

Dad made one or two 500 Km flights in the Ho IV during the 1952
nationals. That finished his Diamond badge. (#1 Germany, #10
International)...He was still a German citizen at the time, and did
not pick up his USA citizenship until a few years later, although
that did not stop the SSA/USA from also claiming his badge,
awarding him USA #6....

RO



  #15  
Old December 11th 17, 09:35 AM posted to rec.aviation.soaring
[email protected]
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Default Akaflieg Karlsruhe AK-X

The New Zealand Wheihe
  #16  
Old December 11th 17, 09:38 AM posted to rec.aviation.soaring
[email protected]
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Default Akaflieg Karlsruhe AK-X

The New Zealand Weihe was restored and I beleive flown by Billy Walker some years ago and was hanging in the Terminal building at Queenstown until a few years ago. Not sure where it is now, it looked great. Apparently not what the council wanted in the terminal.
Tom Claffey
....
  #17  
Old December 11th 17, 03:03 PM posted to rec.aviation.soaring
Kiwi User
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Posts: 64
Default Akaflieg Karlsruhe AK-X

On Mon, 11 Dec 2017 00:55:27 +0000, Michael Opitz wrote:

It looks like someone may have tried to make the tips "all flying"
control surfaces, as they appear to be skewed off axis somehow.
Also, IIRC, those are elevons (not ailerons) that are missing. IIRC,
the Ho-IV used a system whereby an outboard spoiler was separately
deployed on one wing (or the other) for roll and yaw control. (in
addition to the elevons)

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.

Dad found the praying mantis position ok, except for when he was at the
end of a long flying day, and his beard stubble started to become
irritated by the chin rest.

:-)

To be quite honest, I was 1-1/2 years old when Dad flew the 1952
nationals. I was left at home with friends. I never got to look at a
Ho IV cockpit with Dad in my adult life, so I can't answer your
questions. I'm sure that the fellow(s) who precisely rebuilt a Ho IV a
few years ago in Germany can answer those questions though.

Fair enough. I didn't realise you were so young at the time.

http://www.nurflugel.com/Nurflugel/H...s/ho_iv/ho_iv_
Restoration/body_ho_iv_restoration.html

Do you know if this replica was completed and flown? All I know about it
is in that article about the ongoing building project. About all I know
about it it that it is not the glider in NASM, which is the second IVb
prototype.

Dad made one or two 500 Km flights in the Ho IV during the 1952
nationals. That finished his Diamond badge. (#1 Germany, #10
International)...He was still a German citizen at the time, and did not
pick up his USA citizenship until a few years later, although that did
not stop the SSA/USA from also claiming his badge,
awarding him USA #6....

What a nice way to get Diamond distance!

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


Last but not least, there's a great write-up on the restoration of the
example in the Deutsches Museum, Munich:

http://www.twitt.org/HoIVrest.htm

It has decent cockpit photos and says exactly how the control yoke
worked: it slid back and forth on a central tube for pitch and rocked
from side to side for roll control.

FWIW, the example in NASM seems to be the restored S.IVb 2nd prototype,
though its described as a VI both by NASM and elsewhere. It seems as
though these are interchangeable names for the same design.

The best comprehensive list of Horten designs I've found so far is on

http://www.nurflugel.com under

http://www.nurflugel.com/Nurflugel/Horten_Nurflugels/
horten_nurflugels.html



--
Martin | martin at
Gregorie | gregorie
| dot org
  #18  
Old December 11th 17, 06:08 PM posted to rec.aviation.soaring
Andy Blackburn[_3_]
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Default Akaflieg Karlsruhe AK-X

Great stories Mike.

There is no greater gentleman in soaring (or aviation) than Rudy Opitz. I'm proud to have had the opportunity to know and fly with him during his life..

There's also Albion Bowers' work at NASA Armstrong on the Prandtl wing which has a lift distribution that appears to eliminate adverse yaw, and therefore (some of) the need for vertical stabilizers. Obviously Prandtl's ideas go way back to the early days of flight along with the above-described flying wing concepts. Not sure about the implications for crosswind landings and other practical concerns but it appears to work pretty well.

https://www.nasa.gov/centers/armstro...-106-AFRC.html

Andy Blackburn

  #19  
Old December 11th 17, 09:41 PM posted to rec.aviation.soaring
Andreas Maurer
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Default Akaflieg Karlsruhe AK-X

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

  #20  
Old December 11th 17, 11:39 PM posted to rec.aviation.soaring
[email protected]
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Default Akaflieg Karlsruhe AK-X

On Friday, December 8, 2017 at 9:52:07 PM UTC-6, Jonathan St. Cloud wrote:
Anyone know how the Has anyone seen the Akaflieg Karlsruhe AK-X is coming along? Looked like a very interesting project.


An old movie of the 1952 National Contest in Grand Prairie, Texas USA is available on YouTube ...

https://www.youtube.com/watch?v=0M84...11A& index=12

at 1:20 or so is Rudy Optiz flying his Horten IV

Bob
 




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