DON'T FORGET THE HORTEN SECTIONS MENTIONED IN RIGHT CORNER. ->
Who ever knows the name Horten from the aviation history does it mostly by two airplanes. The Horten HIX and the HIV. Go search on the internet and you will see i am right. So ...my site needed a page about this glider too.
I was at first doubting to make a page about it, because all is to be found on multitude of other sites. But i got lucky and got in contact with Sascha Heuser, who build a flyable replica of the Horten HIVa glider.
(go see http://holzleicht-flugzeugbau.de/Heuser_Dateien/H-IV/Prj_H-IV.html)
I am allowed to use pictures of that project in my site to show more about the special features of this glider.
Later i got word that my saying about the replica was not right. I add the letter i got through email at the bottom of this page.
Why this time legs at steeper angle?
Lets tart with the pilot position. In the book "Only The Wing" by Russell E. Lee (ISBN 1935623036) (sure is a book to have!!!) you will find that Reimar Horten did several tests to determine that angles he would use for his proned pilot position. He used it in his HIIIf design.
But there ...the pilot was nearly completely inside the very large airfoil. It had one disadvantage. Ground clearance of the wingtips. By giving the pilot a steeper angle for his legs, a pod had to be made to hold the legs and ...that could also be the basis of a lower placed skid. Also there would be no need for a very large pod on the upperside of the wing. This area is most important for the avoidance of air separation. If air separation happens in the mid section, the lift distribution will alter and the complete Horten theory of the bell shaped lift distribution would be lost. So you need to keep the upperside of the wing as clear as possible.
So ...Reimar Horten had two benefits by making a pod at the underside of the wing. Less possibility for air separation and more ground clearance.
Higher aspect ratio
If you know a bit about airplane design, you will see that for a given weight and speed, the performance (for gliders, this is mainly the glide ratio at that area of aviation history) rises with the aspect ratio. The HIIIf had a aspect ratio of 11,1. The HIV has 21.8! This makes that the wings are narrower.
Lets see at the result of this higher aspect ratio. Glide ratio of HIIIf is 28:1. Glide ratio of HIV is 37:1!
Horten tried to get the aspect ratio higher with the HVI, but ...those wings are narrow big time. And i fear it makes the construction more fragile.
(data of aspect ratio and glide ratio come from www.nurflugel.com)
I received a letter from Sascha Heuser about these last phrases.
"I have seen your new Horten IV page. It provides good information about the glider. Just the performance data are not correct. Your data were calculated in wartime by Reimar Horten himself. Karl Nickel later pointed out, that these were issued, assuming, that there is no difference in calculating the performance to an unswept wing with elliptical lift distribution. With better understanding and theory today, the gliding ratio of the Horten IV is calculated to approximately 1:32.The gliding ratio of the Horten III should be lower than 1:28 accordingly.The real gliding ratio of the Horten IV was well measured in wartime by Hans Zacher and Heinz Scheidhauer, using the Darmstadt D30 as reference. They too came to the value of 1:32. After the war, the Missisippi State University found an even lower value of 1:29. But this was caused by a corrupted shape of the fuselage, a higher mass/wing loading and an extreme forward location of the C.G.
It is planned to measure the real performance in flight with the replica too. Anyway, the main aim of the Horten IV reconstruction in all its original design was, to free this famous glider (and its sort of design) from all prejudice but also from its legends.
Combination of pilot and spar in the same area
When designing a very compact airplane the designer gets a problem when the position of the spar and the position of the pilot should be on the same place.
In the HIIIf Reimar Horten placed the pilot over the tubular spar. With the HIV he did the same, but from the pictures i saw i see he used a different type of spar. Here he no longer used the box construction filled with triangles, but he placed a bended single layer tubular bar.
To prevent it from torsion he made a triangular connection to the rear of the pilots position. You can clearly see those tubes start from the spar connection point between mid section and wing towards the very rear of the glider. The pilot lays on top of the tubular spar and between the two triangles that go to the rear.
Reimar Horten did not use a conventional stick in the HIV. You could call it a "ramhorn" stick. It was held by both hands and it slided along a tube. The sliding movement was for pitch control of course. The rotation for roll control.
Why not using a conventional stick? Well, during my own tests with prone pilot positions, i noticed quickly that the freedom of movement of the hands is not like i hoped to be. It is ...different. So you need to keep that in mind while making a stick for a prone pilot.
Reimar Horten probably found out by tests on cushions how he could solve the problem here. Remember ...the elbows are located next to the pilot at the same height as the shoulders. This was needed to get the pilot inside the wing. It also gives less freedom of movement. But ...it seems to be good enough for this kind of stick.
The dragrudders were controlled by the feet. You did not see your feet. So ...in case you did slide off the pedals, you had a hard time finding the pedals back. Reimar solved that by making a small cage for your foot. Sliding your foot of the pedal is no longer easy to do.
The landing gear
"Keep it simple" is what many designers try to do. Reimar Horten did it too. Just two skids. One became the underside of the pod under the wing which housed the legs of the pilot. The other was located at the front and could be retracted.
The front skid did not blend into the body of the glider at this point. In the later version, the HIVb (which had a totally different airfoil), it was more blend in and had a wheel too. It gave the glider a higher AoA (angle of attack) during take off, which was a improvement.
The transparent parts
Just look at the picture below. Man, that is a sexy cockpit! The leading edge is transformed into a canopy. The underside of the pilots position too. But at the underside they made the view angle wider by adding some extra transparent parts to the sides.
I placed a question about the Horten IV to Mr. Scheidbauer, one of Hortens test pilots. He did answer through Peter F. Selinger (member of the Nurflugel Mailinglist): "he told me that he appreciated the downward view specifically at winch-launch. He said, riding into the sky nearly vertically and seeing the winch and airfield was impressive and he never will forget this....."
The modified HIVa at Mississippi State University
Original Horten H IV photos from Dez Gerogy-Falvy. These were from the summer of 1958, at Mississippi State University. Thanks to Albion Bowers for sharing these with me.
The pictures show that the fuselage was rebuild. Reasons were not hard to find. Scheidbauer, the German testpilot, was really a small person. To let the fuselage house a "normal" pilot it had to be larger. And at the same time they wanted to make the fuselage more streamlined by placing the front skid inside the fairing.
The flyable replica by Sascha Heuser
This is not the first wooden construction of Sascha Beuser. This kind of craftsmanship you don't get from the first time.
It deserves a special page about it. Luckily for me somebody already did a excellent job about writing about this replica. And ...he placed his article online. Go see here to know more about this beautiful replica.
Later i got a email with more data about the replica project.
From Peter F. Selinger, i got:
no, Sascha Heuser builds this H IV at the order of the Felix Kracht
Foundation, which pays totally all labour and material. The president
of this foundation is Professor Bernd Ewald. Additionally Sascha
Heuser he didn't made all in his workshop.The foundation received a
lot of support, e.g. the center section has been supplied by
Lufthansa Technik at Hamburg, or the ribs have been built by the the
members of the workshop specialized in training and instruction of
future mechanists of DLR. The plane belongs to this Felix Kracht
Foundation only , and nobody else.
From Manfred Poznanski
Sascha Haeuser did the biggest part building this Horten IV and he did agreat job, but please allow a correction. It is not his own project and isnot for himself. The project starts about 10 years ago as an idea of Prof.Dipl.-Ing. Bernd Ewald (Technical University of Darmstadt) after meetingChris Wills, the founder of the Vintage Glider Club. Ewald build some smallparts while he was searching for support. The tubular center section wasmade by apprentices of Lufthansa Technik at Hamburg, the AkademischeFliegergruppe Darmstadt build the main wing spars and all the ribs are madeby apprentices of the DLR Braunschweig. Owner is the Felix Kracht Stiftung(Hessisches Institut fuer Luftfahrt).
On August 29th the freshly painted and nearly finished Horten IV waschristened at the German Glider Museum Wasserkuppe to honor HeinzScheidhauer. If you like to see my pictures go to the following link:
Sorry for my wrong interpretation of the data about the replica. Thanks, guys, for setting it right.