Akaflieg Karlsruhe AK-X

Anyone know how the Has anyone seen the Akaflieg Karlsruhe AK-X is coming along? Looked like a very interesting project.

On Fri, 08 Dec 2017 19:52:04 -0800, Jonathan St. Cloud wrote:

Akaflieg Karlsruhe AK-X

Looks like they've got a 25% scale model built and awaiting test flying.
If you read German, this looks interesting and has lots of photos:
https://akaflieg-karlsruhe.de/project/ak-x/

Be aware that your browser may object, though, because its an https site
and the certificate expired a few days ago.


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

On Saturday, December 9, 2017 at 9:07:18 AM UTC-7, Kiwi User wrote:
On Fri, 08 Dec 2017 19:52:04 -0800, Jonathan St. Cloud wrote:

Akaflieg Karlsruhe AK-X

Looks like they've got a 25% scale model built and awaiting test flying.
If you read German, this looks interesting and has lots of photos:
https://akaflieg-karlsruhe.de/project/ak-x/

Be aware that your browser may object, though, because its an https site
and the certificate expired a few days ago.


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

Exciting work!

I hope these students design and build a contest viable swept wing sailplane.

Mike

On Sat, 09 Dec 2017 09:20:40 -0800, Mike C wrote:

On Saturday, December 9, 2017 at 9:07:18 AM UTC-7, Kiwi User wrote:
On Fri, 08 Dec 2017 19:52:04 -0800, Jonathan St. Cloud wrote:

Akaflieg Karlsruhe AK-X

Looks like they've got a 25% scale model built and awaiting test
flying.
If you read German, this looks interesting and has lots of photos:
https://akaflieg-karlsruhe.de/project/ak-x/

Be aware that your browser may object, though, because its an https
site and the certificate expired a few days ago.


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

Exciting work!

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

On Saturday, December 9, 2017 at 12:44:46 PM UTC-7, Kiwi User wrote:
On Sat, 09 Dec 2017 09:20:40 -0800, Mike C wrote:

On Saturday, December 9, 2017 at 9:07:18 AM UTC-7, Kiwi User wrote:
On Fri, 08 Dec 2017 19:52:04 -0800, Jonathan St. Cloud wrote:

Akaflieg Karlsruhe AK-X

Looks like they've got a 25% scale model built and awaiting test
flying.
If you read German, this looks interesting and has lots of photos:
https://akaflieg-karlsruhe.de/project/ak-x/

Be aware that your browser may object, though, because its an https
site and the certificate expired a few days ago.


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

Exciting work!

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,

SB13 was a Akaflieg Braunschweig project.

Mike

On the SB13, the pitch oscillation was discovered to couple to the bending mode of the wing. The spar was therefore build with hogh modulus fibres (a first in aviation) in order to push the bending frequency out.

The pitch oscillation could be mostly suppressed by moving the cg aft.

Which then resulted in a very nasty stall behaviour due to span-wise flow on the swept wing. Boundary fences did help on that.

All in all, tricky optimisations. Plus a complicated lay-up plan for the swept-back spar in order to get the torsional load into the wing skin.

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

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.

---
This email has been checked for viruses by AVG.
http://www.avg.com

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

Oops... I meant AK-X and not SB-13 at the end of my last post.
Meanwhile, TW seems to confirm my suspicions. The Me 163 had a
much lower aspect ratio, and a much stiffer wing than the Horten
designs. This probably eliminated the pitch oscillation issues from
the start..

RO