Just look at the picture below. What do you think? What year
does belong to this airplane? Possible answers are (hold you hand
before the chapter below the numbers):
Would you be surprised that the origin of this idea was made in
1954, but this version was nearly finished in 1982.
I always call the Horten HXb the forerunner of the modern
hanggliders. Hanggliders like the SWIFT, Utopia and Archaeopteryx
are pretty modern (anno 2004). Who would have thought that (to my
knowledge) the first foot-launched glider with pilot entirely in a
faired cockpit flew in ...1954! It was a complete surprise to
me.
Reimar Horten made this design to create a low-budget glider with
the same performance as the well-know Grunau-Baby. All you need are
some bucks to buy the material (65 to 100 in those days (1954) US
dollars), build it in a 4 x 2 m place, get it on the top of a hill
with a windspeed of 15 km/h and ... run. The building would be
about 2000 hours for a beginner. Ok, that seems a lot for those who
know the modern kitplanes. But ... at those days the building of a
Grunau Baby took more than double that time (5000 hours)!
Reimar Horten is very known within the world of the flying
wings. His work together with his brother didn't go unnoticed
during WW2. They made the flying wing jet at the end of the war,
which is being called "the forerunner of the B2" by many people.
Lesser known are their glider-designs. But ... they were not less
in beautifulness of design and performance. If you visit
www.nurflugel.com and go see the Horten pages, you sure will see
some remarkable gliders. And totally at the end of the list, you
find this beauty. The Horten HX.
You can see the view this configuration will give. Frontal view
will be SUPERB. Sideview will be enough. Downwards view is
excellent too as Mr. Scheidbauer mentioned about his flight in the
earlier Horten-gliders with prone pilots. "I was able to see the
winch!", he said.
The Horten HX designation has been used twice. So, don't be
surprised if you see some jet using the same designation. Euh ...
if you can give a explanation why this happened, I am a listening
ear.
Three versions were designed of this HX-glider. The HXa was build
and flown, the HXb was build but never finished (more about that
later) and the HXc never left the drawingboard. OK, Bill Moyes once
made a look-alike. But he didn't follow the design of Reimar
Horten. Euh ... that glider had little history. Probably didn't do
what the builder wanted. Should have used the Horten-system! You
can read more about it in the Horten HXc page.
The Horten HXb which was built by Heinz Scheidbauer , is not
constructed according to the original plans. He did not make the
major mistake like the person who built the Horten HXc. That person
did change the typical wingshape of the design. Heinz Scheidbauer
was one of the testpilots of the Horten brothers during WW2 and was
a close friend. He must have know that the genius part of the
Horten flying wings is the bell-shaped lift distribution. Euh ...
if you don't understand that part, don't worry. I don't understand
it too. A bit too deep into airplane-design. I hope to find a way
to study it myself and explain its consequences here later.
Let's return to the story. Heinz Scheidbauer had not the
opportunity to get the needed materials as mentioned in the plans.
Was not possible at that time in Argentina. He used what he could
fiid to replace it. But ... the empty weight of the glider got
higher than the empty weight mentioned in the plans. A lot higher.
Did Reimar Horten make a mistake in his calculations of the weight?
I guess not. Reimar Horten did a lot of similar constructions
before. I was not his first wooden glider. Even the laminated
leading edge system, which is a major part in the strength of the
wing, was used before. I MUST be possible to make the construction
at a maximum empty weight of 38 kg. Just respect the plans or
create a new set of plans with the modern materials. But keep in
mind ... 38 kg at the max.
What are the consequences of a wrong weight, you might ask. OK.
Lets try to explain easily: When you know that the wingsurface (S)
is 17,5 m2 and the total take-off weight (W) is 112 kg, you can
calculate that the wing loading (W/S) is 6,4 kg/m2 . That is not
high. Lets say it is rather low.
Just compare it with the other HX variants.
HXa 10 kg/m2 HXc 8,8 kg/m2
When we look at earlier Horten gliders
HI 10 kg/m2 HII 9,4 kg/m2 HIIIa 8,3 kg/m2
HIV 17,5 kg/m2 HVI 23 kg/m2
Now lets compare that with the stallspeeds
HXa 42 km/h HXb 35 km/h HXc 39 km/h
HI 45 km/h HII 40 km/h HIIIa 37 km/h
HIV 55 km/h HVI 64 km/h
Saw the relation? Yep, as the wing loading gets higher the
stallspeed gets higher too. And since you cannot run at 60 km/h, it
would be nicer to have a footlaunched glider that will lift off
before you drop down death-tired. So, you really need a low wing
loading and some head wind (about 15 km/h) to be able to make the
needed air-speed (= run speed + head wind speed) to get the
airplane at flying speed.
One thing really hit me while searching the data for this
comparison. The Horten Parabol has a wing loading of 5,15 kg/m2 and
a stallspeed of 30 km/h! Hey, it would be ideal too. But ... when
you see the wings you will understand it is a lot more work to
built it. It only has curved lines! Still ... it might be a
interesting kit for less windy days. But it is not a footlauched
glider. Needs to be transformed if you want a foot-launchable
glider.
I got a few mails from Fernando Sairez. It tells a bit more about
the history of the Horten HXb.
"In fact there were two Pierniferos built here in Argentina by the
team integrated by Roberto Tacchi, Rogelio Bartolini and Rodolfo
Figueroa:
HXa (Piernifero I also "L'alita" ) : flown in the 50's, tested by
Ing. Bartolini, it was lost as result of exposure to the
elements.
HXb (Piernifero II): unended, because of problems with the
construction materials. Was safely kept in Cordoba by Mr Tacchi,
and he lent it to the museum to make Horten work be known by
people. In fact, there was no need of restoration, it was simply
re-assembled and hung from the roof of the museum.
Both airplanes were built by Rodolfo Figueroa, in his wood-working
shop.
I was NOT involved in any of these things (wish I had!!), I just
photographed and made some measurements on the HXb.
Well, can give a partial answer to the questions, and in all of
these we can go in further detail with photos, drawings, etc:
1) how did they make it strong enough so that the trailing edge
will not move sideways of the front spar. Is there any structure
between the ribs behind the front spar?
- The lateral movement is restricted by a small beam at the end of
each rib (trailing edge), and these small beam is glued by both
ends to stiff plywood covering plates, at the center section and at
the
elevon section.
2) details of the skid. How is it controlled?
- The skid visible on the HXa (L'alita, 7m span) was installed
because of the necessity of tow by car or airplane. If the HXa had
been able to take off just by his running pilot, it perhaps would
not be needed. The HXb ( 10 m span) was built thinking of taking
off on the pilot's legs, so, there's no skid."
MAIL2: "Apparently they had to use a plywood of bad quality and
greater thickness than the 1.0 mm one that was selected by Reimar.
That plywood was used to cover the aircraft and to form the nose
ribs. As a result, the leading edge developed some cracks; some can
be located easily because they were patched. Also, the empty weight
rose to about twice the 40 Kg projected. Surely, the 1 mm plywood
was an impossible to get import at the time of its
construction.
On the other side, the woodworking task is flawless, with all the
small plates joining the rigging strips rounded, and all the many
aligeration holes carefully executed. Really, the work is very
professional; if they used bad materials, they where forced by
circumstances.
The HXb was abandoned when the group was dissolved. The members of
the group live in Cordoba, except the woodworker Figueroa, who
sadly died some time ago."
If you like to see the Horten HXB, you need to go to Argentina. It
is still exposed in
"Museo Nacional de Aeronáutica"
Av. Eva Perón 2200
(ex Pierrestegui) Morón
Near Buenos Aires, Argentina
4697-9769/6964
mna@uolsinectis.com.ar
Be sure to check the opening hours. Here can be seen the Horten
HXb and the Horten HXVc Urubu (blue). (picture and permission to
use by Al Bowers)