So it's a completely intoxicating feeling to have your head between the wings, like a bird seeing its wings to the right and left and then feeling that in your shoulders and thinking it with your body. That's exciting.
Podz-Glidz, the Lu-Glidz podcast.
Stories from the cosmos of paragliding.
Today with Markus
Raffel and
Lucian Haas at the microphone.
Podz-Glidz tells stories from the cosmos of paragliding. And in this episode, we're going right back to the very beginning. You could almost call it the Big Bang of this cosmos. The German Otto Lilienthal was the first human to successfully and regularly undertake gliding flights with a flight apparatus he designed. Before that, he had systematically investigated the relationships of how curved surfaces provide lift. In that sense, you can also see Otto Lilienthal as the forefather. And also as the forefather of kites—and paragliding. Now, unfortunately, I can't do a podcast with Otto. Lilienthal crashed with fatal consequences back in 1896. But there is one person who can speak in Lilienthal's name today like perhaps no one else.
Markus Raffel. At the German Aerospace Center in Göttingen, he normally researches helicopter aerodynamics. However, over the past two and a half years, he has also pursued a completely different project. He examined faithful reconstructions of Lilienthal's flying machines in a wind tunnel. And then he did everything in his power to actually get into the air with the device—which was even patented as a "normal sailing craft" at one point—and its further developed version, a biplane. In the podcast, Markus Raffel tells how it all came about for him to follow in Lilienthal's footsteps. He reports on the unique flying sensation that Lilienthal's gliders provide to pilots, the special characteristics of their controls, but also where their aerodynamic limits lie—the ones that ultimately proved fatal for Lilienthal.
In Raffel's narrative, it becomes clear what an impressive personality Lilienthal was and what decisive role he played in the history of aviation. Who knows, maybe without his visionary preliminary work, there would be no kites and paragliders today. Before we get started, just a quick note for my own sake. If you enjoy the Podz-Glidz podcast and want to hear even more stories from the cosmos of paragliding in the future, you can also support my work. How to do that very easily is on the homepage of my blog Lu-Glidz, under the "Support" section. Markus, what on earth is a Normalsegelapparat? A
A normal sailing apparatus is the world's first serial aircraft. It was patented in Germany and the USA by Otto Lilienthal in 1893.
And how do you come up with the idea to rebuild a glider like that?
The idea didn't come from me. Museums do that, of course. In Germany, perhaps more than elsewhere, Otto Lilienthal is an important historical figure. Although he was known worldwide. And museums build these normal glider models for exhibitions. But they also replicate the many other types of aircraft that Otto Lilienthal developed and built.
But you've done a bit more with such a normal glider now. You didn't just put it in an exhibition; you said you wanted to aerodynamically test the whole thing as well.
Yes, actually my employer, the German Aerospace Center, started that in 2016. To commemorate the 125th anniversary of human flight. On the occasion of an aviation exhibition. And the project started without me. In the sense that a museum, the Otto Lilienthal Museum in Anklam, built such a normal glider for the DLR. And then the DLR put this glider into a large wind tunnel to aerodynamically test it there. That is, by the way, the largest wind tunnel in Europe.
It's located in the Netherlands.
So you went there with this standard sail apparatus, set it up, and measured it in the wind tunnel. But you weren't involved in that yourself, were you? Or were you?
No, I wasn't involved in that yet. Those were colleagues from my institute in Göttingen. In Germany, we'd say Göttingen is like the cradle of wind tunnels. And they were particularly interested in this topic. That's also thanks to my boss, Andreas Dillmann, who had a special historical interest in it. And while these wind tunnel measurements are, of course, our daily bread in other ways, this was something very special. That was actually the first time a proper measurement was made—the kind you'd do with any aircraft today to prove airworthiness.
And according to the measurements, did it turn out that, yeah, this craft is airworthy or not at all?
Yes, that's how it was. They measured the apparatus the same way they do with airplanes. Essentially, they measured the NIC—the moment, the lift, the drag, and also the roll moment—on a 6-component scale. And from that, combined with the data on the technology and the weight distribution of the glider, they could determine whether it was at least stable and whether it was safely capable of flight in the most important aerodynamic parameters. So, it all worked out very nicely. They were able to show it. There were only a few limitations at the time. One was, for example, that the fabric was uncoated. They had put a lot of effort into examining the fabric that makes up the glider's covering.
They had a piece specially brought over from Moscow from a museum, from an original Lilienthal glider, and they analyzed it and had that fabric reproduced on historical looms. But it was still uncoated. They later found out that Lilienthal had coated it with collodion. Collodion, what is that? That's something you might still find today as a spray bandage. It's like cotton wool. In principle, it's a material that, if you apply it to your hand, for example, it's like a second skin. So it can close a small wound without having to stick a bandage on it. It's very well suited for coating a fabric like that because it becomes airtight but simultaneously remains flexible.
So that it doesn't flake off, for example, when you fold the glider up.
Was that also done later at the DLR as well, where this fabric was coated? Exactly,
That was the first wind tunnel measurement I took part in. We re-measured it again in early 2018 and coated the fabric then. We found it again in a newspaper report later, about the glider that went to the USA and flew for the first time, stating that these gliders were coated. And one of my PhD students, Felix Wienke, is now investigating the influence of this coating, and as a paraglider pilot, you'll know that the air permeability of the covering is extremely important for the aerodynamics of such aircraft.
Now you said that at the beginning of 2016 there was this measurement project, and you weren't involved in that yet. How did it happen that you got involved, and how did this desire arise for you to fly one of these things as well?
Yes, that was right at the beginning of 2017. After this glider passed its tests in the wind tunnel, it was only a matter of time before someone said, "Now we want to fly it too." It showed that it can basically handle the loads, it has the pitch moment curve you'd hope for, and if a pilot who's reasonably fit sits in it, can hold themselves in this glider, and can put their legs forward, then it should fly stably. It's quite clear that people actually wanted to do Otto Lilienthal a favor and, after over 125 years, finally fly the glider again for the first time. The glider had gained a bad reputation because Otto Lilienthal crashed in it in August 1896 and then died the following day.
And since then, no one has actually flown it again—at least no one has done so in a verifiable and reproducible way—and it was actually the wish of all those involved to start doing that again.
But if you know someone crashed with this thing, how do you deal with that? How do you approach it? I mean, you said you want to fly it now, but how do you start getting back into a piece of equipment like that?
Yes, it's actually quite simple. If you're in a position of responsibility, you say it's forbidden, because you can't just let an employee fly in something where someone has already died, where you're so unsure if it'll fly. But if you're the engineer in charge, you say, I'm doing it now. And then I went out next and had myself taught hang gliding in Millau by Jürgen Davis.
Millau, that's in the south of France, right? In
Southern France, where you can at least get your L-license from the German Hang Gliding Association in a course. That was a lot of fun, and from there I took off and taught myself step by step how to fly this standard sail plane.
That means you got your hang gliding L-license, did your smaller jumps in Millau, then went back to Germany with that L-license and said, okay, now I'm going to test how this Lilienthal glider flies. What did you do then? Did you take the thing, hike up the next hill, and say, okay, now I'm going to run down here and see how it goes?
Yes, I did that, of course, because Lilienthal didn't just leave behind a lot of drawings, data, aerodynamic data, and an entire book for posterity, but also many reports on how his flight attempts went. And he was the representative or founder of the school that said you do it step by step. So, let's say from running to jumping, and from jumping to flying, whereas others back then tried to build machines with a lot of money that were supposed to fly on the very first try. So I took the glider and had support from DLR colleagues and my doctoral student, and then we went to slopes that we considered suitable.
And I went down there, but I never managed to get the glider into the air, so I had to look for something else first. It should also be mentioned, however, that it is very difficult to find a hill for such a project in Germany, because the usual hang gliders,
Training slopes are, of course, at a disadvantage from an insurance perspective. They want to see that the glider is certified, that the pilot is certified. They want to have it all insured. And that allows you...
actually no one. That means you're somewhere, you've called up and said, look, I have a Lilienthal glider here, and I'd like to take off. And then they said, no, do that somewhere else.
In most cases, they didn't respond to that. And if they did, it wasn't positive. So I asked some landowners if I could go down there sometime. And occasionally they'd say, well, in my opinion or if I don't know anything about it, it's fine.
And with these
During those first slope launches you did, where you said you couldn't take off at all, were the slopes just too flat or were you too slow? Yes,
It is actually very much more difficult to find the suitable slope. People have already failed because of that back in Lilienthal's time. He sold at least nine of these standard sail apparatuses in total. To Moscow, to Dublin, to London, to Paris, to New York. To William Randolph Hearst—that's the glider that's in the National Air and Space Museum now. And that one flew as early as 1896, so that was indeed a long time before the Wright brothers.
And these slopes, they have to be very steep first. The glide ratio is in the ballpark of 1 to 4. That means the slope has to be steep and it also has to end so quickly afterwards that you can land reliably. If it tapers off completely flat, then you have to land downhill and you don't know exactly at what point, so it's the opposite. Today, if you have a meadow that you also have to be able to run down very quickly, which is free of stones and bumps etc., there's usually a fence or a path or a stream at the bottom somewhere at the threshold. You don't have those sheep meadows anymore, which you could still find in Millau, for example, that give you such short-cropped grass with the right incline and the right
...ground conditions. That means you had a problem finding a slope. But then you solved that problem differently, or you got into the air in some other way. And how exactly?
Yeah, I think I have the internet to thank for that. My kite flying instructor in Millau, Johannes, gave me a tip. People there built a trailer, a platform where you get securely strapped in and can then be pulled up behind a car to practice while being tied down. That was the first thing I did. And what I found next was this towing with a converted motor scooter. That was the next step. You see that every now and then, you can find it easily on YouTube. You're probably all aware of how that works. A cheap way to build a winch is to take a scooter like that and have yourself pulled along with a rope.
Those were the next actions I set out to do.
So, you did a tow over a meadow. Roughly what altitudes did you reach on the line? In
In the second step of this winch tow, we actually intended for me to never go more than two meters up with my feet. But the main problem, and I can say this upfront, in making this Legendary Glider flight-ready is finding the right trim. And if the center of gravity is just before the neutral point, which depends a lot on your body posture, then you can manage to keep that flight height pretty well as planned. But if you let yourself, out of fear, decreasing muscle strength, or a wrongly adjusted glider, have the center of gravity too far back, then it always overshoots upwards. Then it's unstable and nods up during the tow.
And that's something that has occasionally taken me a bit higher than those two meters.
Do you get scared? Do you think, "Oh shit"?
Yeah, in hindsight, when you see what you've done, you get a bit scared every now and then.
But didn't much happen? Or did you ever sprain an ankle or anything like that?
Yeah, yeah, things like that. I've always said it feels like after an intense football season or something, when you look back on it retrospectively, yeah.
Do you feel a bit like a flight pioneer there and think, "This is probably how Otto felt too?"
Yes, I can absolutely confirm that. At the same time, it's ridiculously little compared to what he did. He was the one who showed humanity that flight was possible. No one had succeeded in that before. People always talk about how one person or another might have gotten into the air, but no one could actually repeat it, demonstrate it, or explain it. It's thanks to Otto Lilienthal that everyone in the world suddenly knew, "Hey, it actually is possible." And that really prompted people all over the world to start, like the Wright Brothers, but also many other notable people. And that is a massive achievement. He came up with all of that himself. I didn't do anything other than take a museum director and get him into the air using modern methods.
But the steps you go through are, I believe, very similar to what Lilienthal experienced. And in fact, you can empathize much better with what it actually meant to learn to fly in his position.
How does this normal sailing craft actually fly? You're a hang glider pilot, or rather, you've done the EL certificate and all that. Is it technically comparable, or is it a different form of control? What does it feel like?
Yes, it's certainly the next thing, so the hang glider is definitely the aircraft that comes closest to the Lilienthal glider. However, it feels completely different. In a hang glider, where you hang in a harness, you feel pulled up and you have...
Actually, the feeling is that you steer with your hands. In the Lilienthal glider, it feels completely different. You can't really move your whole body forward and backward and you don't have the feeling of steering with your hands, but rather of having to perform it with every muscle in your body. Without a harness, you hold on with your hands and rest your forearms on pads, and then you feel the power of the wing and the lift of the wing in your shoulders. And that is actually more like bird flight. So you actually have the feeling that you are a bird and the wings act directly on the muscles you have, and you steer with every muscle in your body. So it's a completely intoxicating feeling to have your head between the wings, like a bird seeing its wings to the right and left and then feeling that in your shoulders and steering with your body.
That's exciting.
That means you basically feel every air movement in your shoulders first. So it practically knocks your shoulder up.
Yeah, that's how it is. It's a bit like sitting in a chair with armrests and then lifting your weight up like that. It's actually a kind of position that you can hold surprisingly well and for quite a long time. The flights are only a few seconds long, but you don't get tired. Even if it were half a minute, you wouldn't get tired. But the way you actually feel the air movement and control is much more direct than with a hang glider through the harness.
Especially when you probably need decent shoulder muscles for that. Did you do any extra training for that? Yes,
I did. So, after I finished my hang gliding license, I always trained in parallel. What gave me the most trouble were mainly my abdominal muscles. I'm at least twelve centimeters taller than Lilienthal, twelve kilograms heavier, and twelve years older, and I wasn't that fit anymore. Lilienthal was known not only for being clever and brave, but also for being very physically fit. And you see many pictures where he holds his legs straight out in front of him, at a 90-degree angle, even when the glider was doing acrobatics. I couldn't manage that anymore. But I at least trained properly to get into the...
to get close. How demanding is the control actually? With a glider, you have the stick, you push it forward or pull it back. How do you actually control a Lilienthal glider? If you say the arms are resting on it, you probably can hardly do anything with them.
Yeah, with a kite, there are two ways to explain it. I became aware of that when I was flying in California and had a different kite instructor. You can explain to a beginner on the practice slope in different ways how they manage to hold their course. You can learn it the way I actually understood it. I had learned motorplanes before, where you focus on how you, let's say, operate the control stick—basically how you use your hands. The flight instructor in California always told me, you're basically running along a line, regardless of what your hands are doing. That means you actually think of it more as if you were controlling the glider with your body. In the end, it's exactly the same. You push with your hands to the right or left.
It's just a different way of understanding the same thing. And with the Lilientagleiter, it's like you think from the start that you're controlling it with your body. You don't think about your hands, even though the movements are actually almost the same. Because the upper body has a bit less freedom of movement, you think you're mainly controlling it with your feet. That means your toes always point where you want to go. If you want to go down, you take your toes forward. If you want to go up—so take some speed off and climb—you take them a bit further back. And otherwise, it's just right and left. If you imagine your toes as pointers, then you've already got a pretty good understanding of what you need to do.
That's simply a matter of shifting your weight to get the wing rolling.
Exactly. And actually, because this glider doesn't have such a thrilling glide ratio, you can really only fly down the slightly steeper slopes. You certainly won't want to fly high, so you don't die if something goes wrong. And that's why you can't really fly curves, because the slope is always behind you, so the glide flight is limited to that. And that was essentially the case with Lilienthal too, that you just fly straight down the slope. The special challenge is actually the takeoff. If a wing sags a bit again, you have to do something very strange. Let's say the left wing sags downwards. Then you have to throw your feet quickly to the right, completely against intuition, as if you wanted to fall onto your left shoulder.
And that brings the glider back into level flight. If you follow your intuition and throw your feet quickly to the left—towards where you're about to fall—then you'll just go into a real nose dive.
That means the control is actually quite demanding. So, someone who doesn't have any kite experience or something like that, at least not a bit like you do now, could end up face-planting pretty quickly.
Yeah, I'd say that. I think that's the reason why no one has flown with this thing for the last 120, 130 years. The beginning is hard. And that intermediate step on the platform, on the car trailer, was also important. You can practice there without taking any risk of falling off. And at the beginning, it's really counter-intuitive. That's why every intuition. And at the winch, when you do that, it's also quite a hurdle. Having the trust. While you're walking, if the left wing is hanging, you might maybe go a bit under the left side with your feet to push it up. But as soon as you've taken off, you have to do exactly the opposite. The wing sinks on the left and you push your legs to the right to load the right wing.
Actually, it's very logical, but at first, it's always against your intuition. And you have to train yourself to do that. Once you can do that, the rest isn't so hard anymore.
Well, you've actually flown the thing by now. Not just being towed by a rope or tied down on the back of a trailer, so to speak. However, you went to the USA for these flights. Why?
Yes, there were several reasons for that. I had a three-month research stay at the California Institute of Technology. That was in early 2018. And in that sense, I actually had an inevitable break from this Lilienthal activity.
At the same time, however, it's legally difficult in Germany whether I would have been allowed to fly the glider at all. Because there's an exemption rule where, if it's not a hang glider, not a sailplane, etc., then you could fly it up to a height of 30 meters. But first, of course, you'd have to prove that it's not a hang glider. And that's all very complicated. In the US, it's the other way around. If the aircraft is certified and weighs under 154 pounds, and is not certified, then anyone can fly it anywhere. That's, of course, a nice way of putting it. Essentially, it doesn't mean much different. But it is much easier to have a legal basis for flights with such experimental devices.
And since Lufthansa was kind enough to take it as checked baggage—this glider, which I had carefully disassembled and put back together beforehand,
I seized the opportunity and flew to California with the glider.
You say carefully disassembled and so on. Well, it's a sailcloth, and then it's partly willow rods, and partly some kind of pine slats, I think you used. How small can you actually pack something like that into?
That was 2 by 3 meters with a height of maybe 80 cm. It was still too big. When I was standing there in Frankfurt with the glider on the luggage trolley, it started to become clear that they actually couldn't keep their promise because it couldn't be X-rayed at all. You also have to run carry-on and checked luggage through an X-ray machine beforehand. And then we had 1.5 hours of negotiations, and in the end, someone was kind enough to move the glider over to cargo, X-ray it there, and then back into the passenger area so it could get onto the A380. Otto Lienthal designed the glider so that you can assemble it like a hang glider. It's truly fascinating to see that you can assemble everything with slats and poles just like a hang glider in 10 to 15 minutes until it's flight-ready, and then it ends up with such compact dimensions.
I sawed off the cockpit a bit at the front and prepared some wood to glue it back together so I could get another half meter of length out of it. But the main task was done by Otto Lienthal, who had made this patented glider foldable. He had to transport it to his location partly by train and by horse-drawn carriage. So he knew what it was all about.
So you flew over to the US with it. Where in the US did you actually fly it in the end?
Yeah, I was lucky that a friend lent me his pickup truck and I rented a trailer from U-Haul and made a kind of platform that I could tie it to. And then I traveled around. So every weekend and also on some evenings, I drove to various hang gliding sites in the USA. In Trespiños up south of San Francisco, near Monterey, Marina Beach, but especially Dockweiler Beach near Los Angeles, where I met Andy Beam, where thermals were very supportive. I was at different places there and mostly was able to use their practice slopes for a lot of money. The advantage is that it's an absolutely constant, powerful, gust-free wind coming from the Pacific, normally.
And that's something you very rarely find here. If you have gliders here at the right tilt, you rarely get that gust-free, constant wind; instead, you very often get thermal lift or gusts from mountains or hills up ahead. Ultimately, that's what killed Lilienthal, too.
had. That wasn't the case there. Those were all sandy areas, basically dune sections, so if you land a bit crooked, you don't have to cry out in pain right away.
In the end, flying over the dune was actually an advantage. In Trespiños, it was grass, just like we would have had here. That hurt every now and then. But over the dune, it was still safe because if you fall, it's really cushioned nicely in the soft sand.
How are you received by the aviation community when you show up with some weird, historical, line-rigged glider? Yeah, what my
The main thing was actually Otto Lilienthal's image in the world. In Germany, people still know roughly who he was. But in the US, for example, they always tell the story of the Wright Brothers. I was at a museum once, and a tour guide said, "There was another one who tried flying, his name was Otto Lilienthal. But he crashed and died, so he was wrong. But the brothers were right." And it's like, the Wright Brothers were fascinated by Otto Lilienthal. He was their great role model. They took his data. They obviously had to improve it later. But the whole way of approaching the matter was actually from Otto Lilienthal. They also sang his praises. And that's sort of been overlooked a bit in this nationalist wave.
But among kite flyers, kite and paraglider pilots, almost everyone in the US actually knew who Otto Lilienthal was. Because over there, he's considered the father of the hang glider even more than in Germany. So, Rogallo too, of course. But Lilienthal appears in almost all the books. And some of them arrived, landed their glider next to mine, and immediately said from the air—they knew right away that those were Lilienthal wings.
How far did you actually fly? Or rather, what kind of elevation differences did you have there on the coast?
Or rather, what kind of altitude differences did you have along the coast? I'd actually say "flying" is a big word. These were like the initial flights of what Lilienthal did. So, with the monoplane, I went about 70 meters and started from a maximum height of 25 meters. And with the biplane, which I flew again with Andy Beam this year—which flies even slower and more majestically—we flew a bit over 100 meters. For about 15 seconds. It certainly sounds very modest when you think about what hang gliders can do, but it's still long enough to see that the thing is controllable and flies stably.
How much does a thing like that actually weigh?
Yeah, Otto Lilienthal managed to build it with 20, 22 kilos. He really relied on thinner willow rods that were a bit more elastic. Because I did these towing tests, often with too large an angle of attack, and in level flight, and since I'm heavier, I also built the glider a bit more stably. A bit out of fear, too.
And I then brought it to about 30 kilograms and the biplane to 37 kilograms.
Okay, so you had a 25-meter difference in height, a decent weight. Who pulled that thing back up for you? Or did you haul it up yourself, or how did that work?
Yeah, well, I obviously had to step in every now and then, but I was also the oldest among the participants. And thank God, I always had enough helpers joining in. A whole host of them, though I can't remember all their names right now. I found many enthusiasts who took part. And that soft sand is a challenge in itself when you're climbing that dune. But then, with the glider, it always took three or four people to carry it. And very often, they were so kind and would say, "You do the way down and we'll do the way up." And then I only had to haul myself up. And
you do a 15-second glide once an hour.
Yeah, maybe every fifteen minutes, if everything goes really well. By the end, we were really good with the biplane, which we flew very successfully last summer. We'd go up for, let's say, about ten minutes, then get back into the air, and then down again. And every flight was a hit, so that was a high yield. With the normal glider, I had to practice over and over again for months. Constantly going around just to get into the air for the first time. Because, actually, the center of gravity has to be just a few centimeters in front of the neutral point in the correct body position. So it has to be very precise. And to set it correctly. I also had to cut off a bit of fabric here and there,
to get that right. Also things that Lilienthal did, but didn't describe very well. That really took a lot of time. Then you crash in between. Once you do, you have to take the glider apart from scratch and glue it back together. So, things like that held me up.
Now you just mentioned that you also built a biplane from Lilienthal. How do these two aircraft differ for you in terms of flight? And why did Lilienthal actually build that biplane back then as well?
Yes, Lilienthal was a truly impressive person. He was characterized by the fact that he dared a lot. He was born poor. What always pleases me is that he was rather mediocre in school, and in his studies—I believe he studied in Berlin—they gave him a certificate at the end saying he was the best we ever had. That means he developed late, but then he really dared an incredible amount and was a truly imposing personality; he was a business owner who gave his workers a larger share of his profits.
He sang, wrote poetry, wrote a play, but also built very many aircraft. He also built the first flapping-wing devices, powered by a carbon dioxide engine, and finally built the biplane to complete the soaring flight. He knew from the birds that if you manage to circle at one point, you can then fly completely without flapping your wings. And to achieve that, you need more lift, you have to increase the wing area. And that's where the monoplane principle quickly reached its limits, because with his limited weight control, it was no longer controllable. And with the biplane, he then found the possibility to
to increase the wing area to 25 square meters while still limiting the wingspan enough so that he could still do something with the weight shift. He built the biplane, but I had the monoplane built for 14,000 euros from the Otto Lienthal Museum in Anklam and then just coated and reinforced it. That was something that was, by all rules of the art, authentically reproduced from that museum based on photos. You
You just said you had it built. So, this is really a private initiative of yours, and you've put a lot of money into it.
You could put it that way. It started with the fact that the DLR had to distance itself from it officially, because it obviously wasn't within my area of work, nor would it have been, let's say, okay from an insurance or professional association standpoint, so I had to build the standard glider apparatus myself. The DLR had it from the museum. I then rebuilt it for myself with colleagues. And I had the biplane rebuilt from the museum. That means, in total, all the flights, all the trailers, all the gliders—I bought the materials for the gliders myself; a lot of personal time, sweat, tears, and money went into it.
What is so fascinating about this story for you, that you say, wow, I'm putting so much into this?
When you say 14,000 for the glider, and with all the flights and everything else, you've probably sunk well over 20,000 euros into this story. What is it about that which is so fascinating to you, that drives you to say, regardless, I'm doing this?
Well, I have to admit, that's maybe a bit snobbish. And I could afford it, or we could afford it. My wife had to be okay with it too.
Yeah, it grabs you. Once you've been in the air with that glider, you want to do it again immediately. And I was actually pushed a bit—but also by the idea of bringing up this Lienthal topic and making his place in history a bit more visible—that really drove me. I'm in the US a lot for work, and the fact that he's been pushed to the side outside of Germany, whether he crashed or not... in my view, the story is always told wrong. Everyone knows he crashed. Many still tell the story that he said, "sacrifices must be made," while dying. But because he crashed, people often assume that his aircraft designs weren't successful.
That's not the case. Those were fantastic constructions. And the story is always told a bit backwards. The fact that he died at the age of 48 isn't as important as the fact that he was the first human who could fly in a repeatable, reproducible, and explainable way—and he did it about 2,000 times.
How exactly is this replica you made, or the replicas? First this normal sailing apparatus, then the biplane. Is it really one-to-one? Except maybe for the fact that you say you adjusted the size a bit to fit your body size. But otherwise, is it pretty much exactly what Lilienthal built back then?
Yes, I would say so. The Otto Lilienthal Museum in Anklam ensured that. I don't think anyone else has ever put in so much effort to properly analyze the fabric beforehand and even have it rewoven on historical looms, as the Otto Lilienthal Museum and the DLR already did for the first glider. And of course, we continued that. As I said, material samples from the original Lilienthal glider in Moscow were analyzed. And I was just at the National Air & Space Museum in December, and we carried out a 3D measurement of the Lilienthal's normal sailing apparatus. We then compared this data with our glider to ensure that the geometry is correct.
And with a few very minor exceptions, I believe these are the best reproductions of such gliders that exist. The exceptions we allowed ourselves lie essentially in the wires. Those were two to three millimeter steel wires that Lilienthal used. And we used these two millimeter steel cables that can then be joined in some way using these Nikopress clamps to make them aviation-worthy. That was a concession to modern safety considerations. Have
Have you ever thought about just rebuilding these models with modern materials? Like, saying, I won't use a canvas sail, but I'll use a really light nylon spinnaker fabric or something. And I'll use thin aluminum slats or carbon fiber or something. Yeah, the
There was a plan. And we also had a very, very cheap offer from a passionate model builder near Göttingen, the company Weber Schock. They would have made it for us using the best materials. And that was the plan. But it just happened to coincide politically with the time when the DLR distanced itself from these activities. For insurance law reasons, I'd say to simplify it. And so it didn't happen. I didn't go back to it because then somehow the connection to Lilienthal that we have here would be severed. Because then you've actually built a glider out of modern materials and it's less plausible to claim that you're flying a Lilienthal glider. And this historical significance was always a special concern of ours.
That's why we didn't go back to it.
But if you say that the feeling of flying with this Lilienthal glider is different again and so much more wing-like, how should I put it, bird-like or what should I call it? Like, you really have wings on your shoulders and so on. So even more than what kite flyers actually say about their craft. Wouldn't that be something where you'd say it could still fascinate people today, by getting a modern version of the Lilienthal glider into the air?
Anyway, I'd think so. And now, in December, after visiting the National Air & Space Museum, we also drove to Kitty Hawk, North Carolina, where the Wright Brothers made their glider flights and then apparently their first successful powered flight in 1903. The anniversary of that first powered flight is celebrated there on a big scale on December 17th. And we were there on December 14th, 15th, and 16th to fly one of those Wright gliders—so, a glider, almost like a sailplane—together with the Lilienthal biplane. We were lucky that the owner and founder of this Kitty Hawk Kite, kite-flying school, agreed to let us do it.
And they offer flights in a historical Wright glider, and now they're considering whether they'll also offer them in the Lilienthal biplane. So, my biplane stayed there for now, so that you could fly there in both a historically relevant replica of a Lilienthal biplane and one from the Wright Brothers. And that's surely very interesting for people. At least for me. I treated myself to a flight in the Wright glider too. It was fascinating. You're actually physically connected to a piece of history for a moment and get to fly it. That's a very special experience. I don't know if the replica makes much sense, though. You could fly higher and further with it.
But you have to admit that Lilienthal designed this apparatus to fly close to the ground. And his crash was also caused by him getting caught in a gust of wind at a height of 15 meters. And if you lose your balance like that—since you're not strapped in, you're just holding on with your hands—then you're of course at an even greater risk. So I would qualify it by saying that this glider is safe as long as you don't fly it so high and in gusty winds. That's exactly how Lilienthal always tried to do it. But in his effort to complete a curved flight, he eventually dared to go very high on his final day. And that's something you should avoid at all costs.
Couldn't you adapt a construction like that, not necessarily in that exact form, to say, okay, we're giving it a kind of harness or at least a seat board, or simply something where we say the body is carried along, it doesn't have to rest entirely on the shoulder load? Yes,
That would certainly be possible. Of course, you'd be deviating a bit from the original concept. But we've also discussed a harness a lot. It would increase safety. It's a bit difficult to attach, though, because you still want to be able to move back and forth in the harness. For that, the attachment point has to be slightly higher than the body's center of gravity. Finding such an attachment point on a biplane might still be possible. On a monoplane, it gets difficult. However, it's also the case that Lilienthal actually built in something very great here. He built a horizontal stabilizer that flips upward if it's ever loaded in the wrong direction. And the reason for that is: when you see hang gliders on the practice slope,
then they mostly make the mistake during landing of catching it a bit hesitantly. This leads to the airflow separating unevenly, and they then always do another right or left turn in those last few meters. You've probably seen that often. Essentially, you have to do it in a way where you bring the glider all the way down to the ground and then perform your flare landing very decisively, let's say. That stabilizes the airflow over the wing and creates a two-dimensional separation. And to be able to do it correctly with the Lilienthal glider, the tail actually always touches down. That means if he had made the tail fixed like on an airplane, it would break off at that moment. It's a thin bamboo pole that is only connected to the main body, to the wing, with cords.
And so that this glider never has to transmit upward forces through that tail, the horizontal stabilizer is designed to flip upwards if it ever catches wind from below. However, the fact that it can also transmit forces from bottom to top is important for flight stability after a stall. So, if we take an airplane, for example, because it has a horizontal stabilizer, it stalls in the air, then you rely on the force on the horizontal stabilizer pushing upward to get the nose back down. That wouldn't work with a Lilienthal glider. If it stalls once, it stays stalled. And it can't get out of that flight attitude again. That is intentional. That's also part of the patent, at least it's very nicely described in the American patent.
It's a brilliant invention for making a nice flair landing, but it also limits the glider to low-altitude flights. In that case, it's good if you catch it too early at the last moment, so the nose doesn't get pushed back down. That's what would destroy an airplane if it stalled near the ground. But if you're high up in the air, it has to work. If you make the mistake of stalling high up, the craft has to automatically push the nose down and accelerate again. That's not possible with the Lilienthal glider.
That means if you're really up at a high altitude and the thing stalls too much, you'll end up on the ground because it can't recover anymore.
Then you're dead, just like Lilienthal. That's exactly what he did. His loyal assistant Beilig saw it all. He even outlived him by 40 years. There are even film recordings of interviews where he describes it. He went out on an August day at a meteorologically unfavorable location, where there are also thermal updrafts in the low mountain ranges, as we know them here. He flew up to 15 meters to practice his turns. Then, at the top, it just stalled on him. He didn't manage to throw his legs forward far enough to regain speed. Then he just tipped over sideways and broke his neck.
Not nice either. Let's go back a bit historically. You said you were at Kitty Hawk Park in December 2019. You guys were flying in parallel. Those ride gliders with the standard sail apparatus. With the biplane.
What was that like for you? Did you actually fly with him yourself?
I have to tell you something really interesting. I've met a lot of people. I'm still in touch with the guys in Mio—Jürgen and Johannes—they were incredibly grateful for that beautiful time. And after that, I also met some hang gliding instructors. Some of those were negative experiences. But I met a truly wonderful person there, Andy Beam from Winsports in Los Angeles. And at some point, after he had really supported me for months, he said he wanted to fly too. Now, he has 30 years more experience and 30 kilograms less weight. He flew so well from the very beginning. He showed such incredible dexterity in handling the craft right away that from then on, it was basically just him flying.
So I still managed to get the biplane into the air. I did what I wanted to do. But when I saw how quickly and easily it took off and how well it handled, it was always just Andy Beam flying from then on. And he also flew the biplane at Kitty Hawk. We were a bit unlucky there because we still had to tow it with a line. Because on those days, with the wind direction, we couldn't find the slope to fly it free. But in California, Andy Beam pulled off these really beautiful flights that look wonderful, where you can also see how wonderfully even the biplane, which is actually a bit more cumbersome to fly, still reacts to the commands and the weight shifts.
During that flight in Kitty Hawk, the American kite flyer was the one flying it. There's actually a film of that too, on YouTube as well. I'll link to that in the show notes.
And from the observation, you were standing there, I think you can see it in the film, you're standing next to him, watching the whole thing. What were you thinking when you saw, wow, here is real aviation history flying by? What goes on inside you?
Yeah, that was actually the crowning achievement of everything. I really, let's say, put my heart and soul into it. And it was something like a knighthood that he flew on the dunes where the Wright Brothers also practiced, and that the American colleagues supported it so intensely. They're even talking now about doing another flight demonstration in Oshkosh this summer, where the largest aviation, the largest air show in the world, takes place. That was wonderful. And I was very satisfied with handing that over to Andy Beam. Although, of course, it always felt to me like his fingers were itching, because that was also Lilienthal's credo. On his last weekend before his crash, he gave an American, a Robert Wood,
...who later became a well-known physicist, handed over the biplane and said, "Here, you try flying too." Unlike the Wright brothers, he didn't try to protect his knowledge, but rather to share it with the world and get others to fly for themselves. And that's why I saw myself in Lilienthal's footsteps again when I said, "Now Andy Beam is flying, not me anymore." I
passing the baton. If you see the two of them flying side by side—Lilienthal's glider and the Wright glider—which one was better? Well, it's
It's a bit hard to say, but I'd say it's quite clear, even in the opinion of those present, that both have their advantages. The Lilienthal glider's advantage certainly lies in the fact that it's more intuitive to control, easier to handle, and it glides. He also only flew on that rope where they pulled him forward a bit because the slope wasn't steep enough otherwise. The Wright Flyer had to be secured. It still had ropes on both wings. So you can see that even with little wind and close to the ground, the Lilienthal glider can be flown more safely. But of course, you also immediately see what a beautiful shape and what a wingspan the Wright brothers managed to give their glider.
So it's naturally more powerful. That means we're talking about glide ratios of 1 to 6 instead of 1 to 3.8 or something like that. So you can see the further development very clearly. The wingspan in their positive, I mean the aspect ratio of the wings—that was something Lilienthal and even the Wright Brothers weren't consciously aware of, how important an influence that has on performance. And the Wright brothers then discovered that with wind tunnel tests. That you get much better in the glide ratio if you get more wingspan and not so much wing depth. But that requires control that differs from this weight shifting. And that was their big trick with the wing warping, that they then had a roll control
...added. What do you think, what would Lilienthal fly today if he were still alive and said he wanted to fly a glider, or a non-motorized aircraft in any form? What do you think he would choose?
Yeah, it's interesting that you ask. He himself actually thought that aviation wouldn't be much of anything, at least for the time being, if it were practiced as an individual sport. That is, one could imagine him flying a sport aircraft now. However, he also wrote at the same time that he hoped that once people in general could fly—which he had already seen happening—that it would continue, and that the world would become more peaceful, because guarding borders wouldn't make much sense anymore, nor would defending them, if you could easily fly over them. I think that's both wrong and right at the same time. We know how much the airplane has done to wage wars. But it has also actually brought the world and cultures together in a certain way.
So he would certainly have flown a sports plane more likely, but he definitely told himself, he made a great effort to also build a powered aircraft. His company built and sold accessories for steam engines and steam engines. And he had this miniaturized steam engine that powered a flapping wing apparatus—so a glider whose wingtips were supposed to be accelerated again by flapping wings. But he powered this steam engine with compressed coal, so CO2, because then you don't have to take the flame with you. And that's what, I mean, he even flew it, but he hadn't finished the flapping propulsion yet. I think that would have been his dream: using a flapping wing apparatus to make glider wings that could then also be powered.
Well, you're an aerodynamicist, but in your work, you usually deal with completely different things. It's mainly helicopter aerodynamics and everything that happens with the rotors and such. From all this development or this story with the Lilienthal glider that you rebuilt, is there anything at all that you take away as an insight for your current work, where you say, wow, I've actually learned something for my modern projects from this history?
Yes, you can actually learn a lot from Lilienthal. I think especially the scientific or engineering methodology. He was someone who approached a problem for which he didn't know the solution from the start in a very systematic way. The most impressive thing is actually how, years before he started flying himself, he proved using scientific methods that curved wing surfaces were the ones to choose. People up until then had actually thought that to minimize drag, wings should be as flat as possible. And then he built a device, which the Englishman Lord Cayley had also used, which has a rotating arm equipped with a scale where you can measure both lift and drag on a wing profile simultaneously.
And he systematically investigated all of that and then developed the optimal wing shape. I think that's an approach you can learn from Lilienthal. That you also have to have the courage to approach an unknown topic analytically in such a way that you get reliable data. I think that's actually the best thing you can take away from it. This scientifically and engineering-wise clean approach, how to get reliable data in an unclear situation.
Are you going to continue with this Lilienthal research in any way, or is the project finished for you now?
Yes, I'm still thinking a little bit about whether there shouldn't be an English-language biography. I'm hoping to find people like Bernd Lukasch, the former director of the Otto Lilienthal Museum in Anklam, to help me perhaps manage that as the next project. There are very good books in German, but there's actually nothing equivalent for the English-speaking world yet.
And will you be traveling to the USA again next summer, when this Lilienthal glider gets its big debut in Oshkosh?
Anyway, yeah. I've left the glider over there now. I think it will be exhibited at least. Maybe it will even perform some flights again during the winch tow. Not by me, but under the responsibility of that hang gliding club. And I'll probably give a lecture as well. I'll definitely be watching it all.
Well, in any case, I wish you lots of fun and I hope you can stand there with full pride over everything you've pushed for. Thank you for this story about Lilienthal and the Lilienthal glider and your experiences with it. I think it's always very good to make yourself aware of the historical roots of our aviation, which are also, in a way, the roots of paragliding. Thanks for the story.
Yes, thanks a lot, Lucian.
You're very welcome.
That was Markus Raffel in conversation with Lucian Haas. If you want to learn more about Otto Lilienthal and the flight tests with the replicas of his flying machines, check out the show notes for this episode on the Lu-Glidz blog. I've put together some links there, including videos where you can admire the normal glider and Lilienthal's biplane in flight. As mentioned at the beginning, you can also support my work on Podz-Glidz and the Lu-Glidz blog as a patron. How much you want to give as a contribution is entirely up to you. If you're unsure, I recommend a non-binding guideline of 1 Euro per podcast episode and 2 Euro per reading month on Lu-Glidz. Payments are easily possible via PayPal or bank transfer.
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