Special: Horten HXb

The forerunner of the modern hangglider?


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):

  • 1919
  • 1954
  • 1982
  • 1999
  • 2001

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)!

HXb 3view

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.

A 3D of something like the HXb (it looks in great lines like the Horten HXb, but I currently lack a lot of info to make exact images). Here you see the pilot "standing".

A cross section with pilot standing. You see the pilot is bending forwards.

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.

Here you see the pilot in flying position. His feets are resting on a plate. Here you can see his arms go through the center rib to reach the stick.

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

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)