Horten HXc Moyes

DON'T FORGET THE HORTEN SECTIONS MENTIONED IN RIGHT CORNER. ->

Who doesn't know the very few pictures of Horten HXc, which was build in the workshops of Bill Moyes (who financied the project), designed by Manfred Böhm who made it together with the help of Rolf Markmann?

We see Bill Moyes as pilot in a wet suit. A towline is clearly visible.

The info, i found on internet, about this glider  was confusing. Most was negative. So i wanted to get the story straight and i contacted Bill Moyes, the very known hangglider pioneer.

Our talk on 27 august 2012

Koen (pronounce my name as "soon" but with a K): Bill, your glider is very known in the small flying wing world, but there are so many controversies of what we get of info, that people are scared of it, because most stories tell it was bad.

Bill: I wouldn't say it was bad. I was very enthousiast about the Horten wing, but it was difficult to footlaunch because of the dihedral. The harness was on your hips, so the glider was never higher than that. If you raised the nose up to get the needed AoA (=angle of attack) to take off, the wingtips touched the ground.
It was easier to have it towed. It came of the ground immediately. It had 5° of dihedral, so went straight up and straight down. It was beautifull to tow. But ...in flight it had bad adverse yaw.

Koen: i have seen a 1/4 scale HXc model recently that had also 5° dihedral and it too had a lot of adverse yaw. Decreasing that angle totally changed the situation.

Bill: Well, that is the first good info i get in 30 years.

Koen: I was really happy to hear that you said it flew well, because i heard the rumour that the glider received the nickname "emu" due to its bad flight.

Bill: Well, that name was not given here. It was a handfull due to its long span (15m), but we found out it is very easy to tow. It went straight up...like a arrow. We towed it to 500 feet. I did that 30-40 times. But i need to tell you that we towed with a boat in those days and i tried to land on the shore of the lake , but ...we got it wet a lot of times.
If you look at the picture of the glider being towed you can see a small Styrofoam surfboard mounted under the wing. I used that surfboard to skim on the surface and slide up the beach, till I learnt the wings landing characteristics. 
I spend a lot of money having the glider made and i was destroying it in the water. So, i went to look for a air tow and i found Bobby Bailey and we started making Dragonfly's and we had so much fun with it, i didn't continue the Horten glider.

Koen: Have you any idea about the glide ratio?

Bill: Manfred Böhm said it would have been 35, but it was more like 27-28.

Koen: Was the open mid section a reason for that lower glide ratio?

Bill: Anything would lead to a improvement. But it was so difficult to transport. If it would have been at a airport, it would have been easier, but i had to transport it each time on trailers or rigs and ...it was a pain. Apart from that, it flew quite well.

Koen: Another question which is not clear on the internet now: did you use the non-lineair twist of the Horten or was it a lineair twist?

Bill: I gave you the phone number of Manfred Böhm and he is the guy to answer this question. But as i recall it is was a straight twist. It had no twist until that first rib that is still visible on the pictures i send you. There was 5° twist from there to the end of the wing. So ...it roughly looked like that the first 5 meters there was no twist. The twist was in the elevon section.

Koen: Now you say it had not the non-lineair twist, i guess they hotwired the foam for the wing.

Bill: Yes, they did. They used a solid block to hotwire and used the remains as a mould by glueing it to the floor.

Koen: Clever thinking. Next question is about the prone position (=lying on belly). I made a few homemade tests about prone positions and noticed that you can do it bad and good. One test nearly hurt my back after half a hour of laying in that position, the other test was really good and i could lay in that position for hours. What is your experience with the prone pilot position in this glider?

Bill: Comfort is the last thing i ever considered. If it feels good, it is no good.

Koen: Haha, you were really a pioneer.

Bill: Manfred made a harness which was like a belt around your stomach and hips, with rings at the sides. You supported yourself by clicking the rings in the clips at the sides of the hole in the wing. You could rotate around those rings, but not slide forwards or backwards. Pitch control was purely done by the stick.

Koen: I saw this picture of the stick of the glider.

Bill: These are the pictures i was looking for at home. [Bill granted me permission to use the pictures on my site]

Koen: I see in the picture they basically use the same technique of control as in the HXb made by Sheidbauer. It is a V-shaped set of control bars. I studied those a bit in the past and it was a confirmation that those rods make a mixer that is three times less sensitive in pitch than in roll. Did you feel that difference in pitch control?

Bill: The pitch felt fine. The stick slides forwards and backwards in that tube you can see. That made the elevons go up or down at the same time. Sideways moving moved them opposite directions.

Koen: According to my calculations the secret of that system is the 71° angle between the control rod and the longitudinal axis.

Bill: Do you see the spar on the pictures? It is straight from tip towards the center and then it makes a curve. It works and i guess it comes from Reimar Horten himself.

Koen: Do you still recall the weight of the glider?

Bill: 50 kg (110 lbs). 15m span and 50 kg weight made it a handful to take off, especially with the wingtips touching the ground. That is why i choose to have it towed. I could have made a ramp to launch it, but we all were familiar with waterskying towing and so we started using a boat to tow the glider.
If i ever fly this glider again, i will test it on the ground before flight. In those days i just flew it without testing the spar.

Koen: Again ...you were a real pioneer.  :)

Additional info

The following text was the only data i had in the past of the Moyes HXc. I got it from Al Bowers via the nurflugel mailinglist.

"I talked with Bill Moyes several times about it. His adaptation of the H Xc isn't all that accurate a representation of the H Xc. Bill chose to use a linear twist, and extended the elevons further inboard than Reimar had designed. Bill chose to male a very few ribs compared to Reimar's original drawings, which results in a lot more distortion of the airfoils.

Bill commented that it had a LOT of adverse yaw (not surprising in light of the changes). He was putting a vertical on it to fix that. But he had other projects and it was on the back burner. I have several images that Bill sent me of it.

Reinhold did the reverse engineering of the design and gave me the twist it SHOULD have had (design CL OF 0.6). Based on the panel method I used, it should have been very well behaved (no adverse yaw) all the way down to a CL of about 0.2 (60+ knots TAS)..."

Letter by Manfred Böhm

When i was 12 years old, i had a Horten III RC Model. It flew not very well, but the glide ratio was amazing. But a young boy want fly fast, aerobatic models and impress the adults (" i am the boss off speed and aerobatics" ;-) ) So i forgot about the Horten III for a long time.

Years later i saw Mike Harker flight from the mountain „Zugspitze" in a Hangglider. I told my dad: "i have to have such a machine". My dad was a chess-player and his answer was : "if you win a game of chess against me, i will buy you a hangglider." I knew, i never have a chance to beat my dad. Not without a trick. I went to get 3 beer. After the 3rd beer (in my dad), i had my hangglider ;-)))

I will never forget my first flights! Glide-ratio was 1:Iron and i remembered my Horten III RC- model. I thought "building a wing like my Horten, but with new materials to make the wing light and footlaunchable, would generate the perfect hangglider"
From age 15, every year i visited a RC-glider competition close to Stuttgart (Germany). In 1979, 333 pilots were on the start. This huge amount of pilots allows you to rest a bit, until the next round. Near the "teck" (=location where the competition was happening) is the Airfield Hahnenweide. There is a Oldtimermeeting every two years. I had 4 hours to my next start in the competition and so i visited the Oldtimer meeting. There i found a yellow Book (Die Nurflügel der Gebrüder Horten- The flying wings of the Hortenbrothers). No doubt, i had to have this book! The book was expensive, 84 Deutschmark. I checked my money (was a poor soldier at this time) and found exactly 100 Deutschmark. Next i checked my car. Switched on the ignition to check my fuel tank and i estimated if i would reach my home with 16 Deutschmarks. It was as a risk, but the decision was made. The book was mine! 

Back home i contacted the author Peter F. Selinger with the request to give me Dr. Hortens Address. He told me, i can write a letter to Dr. Horten, send it to him (the Author) and he will forward the letter to Dr. Horten. Couple weeks later, i found a letter from Argentina in my Mailbox. Sender: Dr. R. Horten, Cordoba and so on. My smile was from ear to ear! A letter from my personal Lord!:-))))). From this moment i knew the direction my life would go.

Dr. Horten was happy (his words) to have a enthusiastic RC pilot for going on with experiments where the Horten brothers interrupted because they didn't have a radio-control at the beginning of their experiments. Over 8 years, i was building about 40 HXc models in scale 1:3 .

Each model was a little bit different to the model before to make a perfect end result. Normally HXc had known Horten airfoil on the root and changes to NACA 0010 on the tip. Washout starts at half span [Koen: which is different from the normal Horten system. Horten had washout over the entire wingspan, but ...not-linear.] and ends with 7 degrees on the tip. Once i made a wing with the Horten airfoil over the complete wingspan. Washout was just 3 degrees, but beginning on the root. The glide-ratio was absolutely unbelievable! But the model had a lot of adverse yaw. I thought winglets would solve the problem.

Still dreaming about building this wing manned some day. Really. Not a joke. Glide ratio, compared to the other models, it seemed like 1:100. On a flat field i could throw the wing by hand, where it made 3 BIG circles and could still catch the model by hand. I had a great time. But that is a other story. In summer 1987, my HXc model flew perfect and now it was time to build "the Big One".

At this time Rolf Markmann (member in our hangglider club) told me, he knows Bill Moyes and he already told him about this wing. Bill was willing to sponsor the project and so Rolf and me spend 6 months in the Moyes workshop in Sydney. Was a great time! We towed the wing behind Bills boat and it flew well. Bill spoke about yaw after landing. This was because off my „ Shithead“ [Eh ... I guess Manfred wants to say chaotic head] I forgot to tell Bill, that the elevons were working symmetrical (as much up as down while steering roll). So it was necessary to pull the stick a bit when changing direction. When i steered and kept the right elevon in line with the trailing edge (in left circles) it worked perfect (and opposite in right circles). I thought it was good as basic wing to start further developments from.

Back in Germany, i started to build a 12 m wingspan glider. I called it "Schmankerl"(it is a Bavarian name for something that makes you happy). This wing satisfied my expectations more than expected. One day we had a problem with the towing clutch and the wing was completely destroyed. Was a bad day for the "Schmankerl" but a very lucky one for Thomas Amberger (my very close friend and testpilot on this day)! Tom only had a few scratches. Next day we started to build the Schmankerl 2. After the maiden flight of the Schmankerl 2, the devil seemed to have come to the game ;-) ! It began with a broken ligament in my right knee during a spotlanding competition. The spot was a glider bag, i landed on this and slipped away. I won the competition but had a broken ligament (which wasn’t seen by the doctor). A friend (medicine student) found out, that the ligament was gone. But was to late for a operation. The only solution was a workout with a lot of protein and some syringes with anabolics to let the muscles overtake the job of the ligament. Worked well, but couple weeks later, i had a very bad motorcycle accident. Result: 5 weeks in bed with no moving. The protein and anabolics did their job. Result after 5 weeks: i gained 25 Kg. Same year, my ex-girlfriend had a ultralight accident and she balanced several months between life and death.

I quit my job for her and i was happy she fully recovered . Result for me: job was gone, girlfriend too (after recovering) and i had very little money left! The only "way out" for me was a insolvence and so i did. Over two months it is over and i can act as a normal person again :-). It was a bad time and i almost lost the happiness of flying machines! But now i am back. The Aliot [Koen: his new project] will be airborne soon. It is a compromise between the Hortenwing, all my experience and a very good flying RC model, which i modified and tested. More soon,

Best Regards,
Manfred

Pictures by Rolf Markmann

I am super proud to have received permission to show these not known pictures of this project. Thanks, Rolf. Copyright by Rolf Markmann.

What we see here is the foam which was hotwired. The negative part is being used as a template for the internal parts. Clever thinking! That makes it easy to get everything at the right angle. It would have been a very tough job to line everything up without this aid.

Picture below is Rolf Markmann working on the elevon.

If i understand the next pictures right, the fabric was a kind of sock being pulled over each wing half. In the middle they were put under tension using a cord. You can see that connection clearly in a later picture.

In the following pictures you can see the hangglider being carried by its pilot. The glider is at hip height. While standing upright, you can see over the nose. But ...i think to see that view was a bit of a problem when you started laying down on your belly. To me it is not very clear from the picture how the pilot attached himself to the glider. I can only see shoulder straps to be able to carry the wing while standing up. But ...how was the pilot being carried in the air? Where where the attachment points of that harness or seat?

Bill Moyes told me that if you tried to take off from a dune, the wing tips would touch the ground. But ...if i look at the following pictures, i don't see that problem.

More info about what we see on these pictures might follow.

More pictures of the progress in the workshop

[Permission to use pictures from Bill Moyes]