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