A paraglider always wants to go into its defined angle of attack, and this so-called active flying that is preached everywhere, saying, yes, the glider must always stay up there, that's just not true. Rather, active flying means, clearly, that a paraglider, let's say, wants to react to changes in the angle of attack, but it overshoots. So if it has too much angle of attack, it goes forward, just like during the start, it goes forward, but it would overshoot this ideal value. So I have to prevent it from entering into this oscillation. I always say, I let it have half its way; I let it go where it wants to, but I brake it at the moment I feel, okay, now you've had your way, and now I'm coming back, or, and I'm telling you what you should do.
Podz-Glidz, the Lu -Paragliding -Podcast.
Stories from the cosmos of paragliding.
Today with Otto Feucht and I am Lucian Haas.
The paraglider is the only aircraft that has its center of gravity far below the actual lifting surface as a pendulum system. From a control and stabilization perspective, this results in some peculiarities compared to other aircraft. In classic aerodynamics textbooks, such characteristics of the paraglider system are only dealt with at the very margins, if at all. And so, contradictory ideas and explanations still circulate in the scene about why a glider actually flies a turn and how it does so most efficiently. How the lift conditions on the wing change when the pilot shifts their weight, why it is sometimes so difficult to pull a glider out of a fully developed steep spiral, or what exactly so-called active flying is actually supposed to entail.
One person who has put a lot of thought into this is the paraglider. The Swiss Otto Voigt. For decades, he was not only a sailplane instructor, but also a pioneer of the Gleitschirm-Blog. From the very beginning, he wanted to understand how it all works. More than 20 years ago, he wrote a book, now unfortunately out of print, titled "Aerodynamics and Flight Mechanics of the Paraglider." It certainly wasn't an easy read, but it remains the only comprehensive theoretical treatise on the subject to this day. In this episode 122 of Podz-Glidz, Otto Voigt tells us how he supported the work on that book with practical experiments. We talk about some of the interesting questions mentioned at the beginning regarding paraglider aerodynamics.
Some passages might seem a bit too nerdy for some, but it's worth sticking with it because you're guaranteed to have "aha" moments every now and then. In the podcast, Otto Voigt also presents his self-developed system for an aerodynamic harness brake. This allows the glide path of a paraglider to be degraded as effectively and continuously as that of a glider with its spoilers during the final approach, while maintaining full controllability. Especially in times when paragliders are becoming increasingly high-performance but offering fewer usable descent aids, implementing this idea could mean a real safety gain. If you enjoy the podcast, please support my work by becoming a patron.
How it works so simply? You can find out on my Gleitschirm-Blog Lu-Glidz, specifically on the Fördern page.
Otto, where did your great interest in everything that flies actually come from? That
it started in my youth. Model building was my great passion when I was only about ten years old. And by twelve, I had already seen my first gliders; someone took me along in a plane. And a short winch launch, two minutes in pouring rain, and then I told myself, ah, you have to do this, right? And then I started gliding at 16 and later became a flight instructor. You also give theory lessons and you naturally deal with the subject more intensively. I never studied anything, but there are plenty of technical books where you can continue your education. I then later also...
Even at Swissair, I worked there as a ground instructor and even wrote a book. And that's how you just grow into it, so more or less a full professional in soaring.
Yeah, you wrote a book about paraglider aerodynamics. Exactly. Now that you've said you didn't study at all, so you didn't study aerodynamics or anything like that. Where did your expertise come from, that you'd say, hey, I'm confident enough to put together an entire program? I mean...
First, my motivation was that at the launch and landing sites, I'd listen to these discussions about why a paraglider flies or doesn't fly, and where, how, what, and so on, and I always had to shake my head and think, no, that can't be right. And then in 2001, I had some time and thought, alright, now I'm going to write a book about it. At least just start, yeah, and I didn't know my way around computers yet either, so I bought a computer and taught myself how to write on it. I couldn't write machines, I could only fly, even on my back, but not write.
And then, I had already read books before, on soaring—so there are also good books on construction in soaring—then there's also an old book.
"Aerodynamics of Pure Subsonic Flow" by Dubs, that's an old book, and then there are also books on aerodynamics in soaring, construction; I actually knew my way around those, and also knew more about aerodynamics in general. Or for example, there are those old tropes like, yeah, lift is because the flow splits at the front and the profile... because the top has a longer path than the bottom, and because the air particles have to come back together at the rear, the upper air particles have to flow faster, and according to Bernoulli, that results in low pressure on top and high pressure on the bottom, and that's the lift and so on.
And then, when you read the technical books or something, you see that it's all nonsense, it's completely off, right? Because even from the recordings in the wind tunnels, you can see that it's not true at all, the air particles don't come together at the back. So none of that is correct, and then I looked into the whole thing more and I've studied paragliding a bit more, especially the aerodynamics, and I saw that, yeah, with the paraglider, it's a bit special, especially with flight stability or angle of attack stability. You have that in an airplane, where you start from a longitudinal axis. Along this longitudinal axis, the air vectors shift back and forth depending on the angle of attack, and then you have a neutral point in the profile where the moments always stay the same, and the whole thing works via the stability analysis with the horizontal stabilizer, which creates a counter-moment.
And the stability, actually, it's quite simple. Strangely enough, for the average pilot, it's a bit incomprehensible if you tell them, yes, the surface area of the horizontal stabilizer must be larger than the surface area of the wing. That's a sentence that describes stability, where the dominance of the stabilizer over the wing is determined. But with a paraglider, it's not about a longitudinal axis, but we have a center of gravity that is very far down. And then I thought about it, then I mapped out this whole profile—there are polar diagrams of the profiles where you can see where the aerodynamic forces are plotted at the pressure point on the profile, which have a certain direction.
And the further back you go with the aerodynamic forces, the more the aerodynamic forces also swing backward, the angle of attack. And if you plot that, you get a point where these aerodynamic forces intersect. And I saw that—ah, that's also a neutral point. And if the center of gravity is below this neutral point, then we have angle of attack stability. And that's how I described it in this book, regarding the angle of attack stability of the paraglider. And generally, there's the theory that we're like a pendulum, right? Like a pendulum, the center of gravity or the pilot hangs down, so to speak, at a pivot point.
And it swings back and forth under the paraglider. And the paraglider is attached at the top. This contradicts all aviation theory, which says a free object in space has a center of gravity. And all forces generate an acceleration or a force and a torque at this center of gravity, if the line of action of these forces does not pass through the center of gravity. And now you have to see, where is the center of gravity? Where is the center of gravity in a paraglider? Well, it's near the pilot, because the pilot, let's say, has 80 kilograms of mass. And the glider also has a mass, right? And if you look at how much mass a paraglider has, you see that the glider itself has a mass, for example, of 5 kilograms.
And now comes the crux of the whole story: there is also trapped air in the paraglider. And if you calculate how much air is there, how much air is trapped, you get 10 kilograms. So the air trapped in the glider is heavier than the glider itself. Okay. And because of that, if you look at where the common center of gravity is, it's somewhere at the pilot's head height. That's the center of gravity, right? And if you look now, aha, the whole device oscillates around this center of gravity, and if it goes backward, for example, into a higher angle of attack, then it moves. Specifically, the aerodynamic forces move forward against the leading edge, but the line of action below the new pivot point goes behind the center of gravity, and this creates a head-heavy moment, so that this change in the angle of attack works against itself again and the paraglider stays in stable flight or holds a stable angle of attack.
And this perspective, well, how should I put it, let me compare it with,
with, with, with the solar system, right? It used to be said that the Earth is at the center and the sun and the planets and the stars revolve around the Earth, right? That is about just as wrong as saying we're hanging up there on a paraglider and everything goes around this paraglider. That's not true. The center is the center of gravity and everything revolves around this center of gravity. So you could compare it roughly like that. So, with this theory that you're hanging up there, you run into complete contradictions in aerodynamics. For example, why a paraglider—I had to find out why a paraglider flies straight at all, in that sense—and that actually comes from this tunnel geometry.
That means the paraglider is curved and the ears are pulled down, pointing downwards, and if the paraglider starts to push now—that is, diagonally into the airflow—then the trailing end of the paragliding automatically has a higher angle of attack than the other end. And a higher angle of attack means, again with the aerodynamic forces, the paraglider can't handle that; it wants to return to the normal angle of attack and therefore always turns into the airflow, even without a vertical stabilizer. And then I thought, well, I had a glider, a glider called Parallel, as far as I can remember,
and it had very unpleasant characteristics, namely, if you were flying sideways into the lift, the glider would roll out of the lift and you could be thrown toward the lift despite using the brakes, and not always out of the lift. I thought to myself, man, you have to do this differently somehow, why is it doing that and so. And it was hung quite flat in the middle and the ears were pulled down deep. And there I saw, yes, if my theory is correct, the flat suspension leads to one-sided lift from the glider resulting in a rolling moment against this lift. So you would just have to increase the tunnel geometry a bit and then that would disappear.
Those were some pretty wild times; I just tied some lines in at the top and raised the center by 25 cm to see what would happen, just without changing the angle of attack, of course, or the setting. I watched how the glider changed if I let the center down, or let the ears down, or let them down more, or something like that. And according to my theory on how the center of gravity and aerodynamic forces work, I saw, yep, it was exactly right. That means this tendency disappeared immediately, for example. And if I let it down even further, it got into its own oscillation. That side-to-side pendulum motion, we used to have that back in the day.
And it was very unpleasant that once the glider started swinging, it got progressively stronger. And if the pilot then reacted with the brake at the wrong moment, they'd be in a pretty strange situation quite quickly.
High above the canopy, it was already like that?
Yeah, not exactly, but for the student it was very uncomfortable, right? And these more beginner gliders, they're flatter in the middle. And that results in a so-called roll damping. That means if the angle of attack becomes larger on one side due to a rolling motion, a roll moment is created against that rolling motion. You know this very extremely from airplanes, for example. So, an airplane making a rolling motion—the lift or the angle of attack, of course, on the wing rolling downwards becomes larger. The lift increases and this rolling motion is immediately damped. And you can see this roll damping very well with a paraglider too.
And the high-performance ones actually have almost the same length lines, only the ears are pulled down a bit. And I also had a high-performance one and saw, well, what exactly happens to a paraglider when you brake on one side? Yes, it actually goes into a slight slide. So you can see it, if you look up and brake on one side, you see, wow, the glider turns a bit sideways into the direction of the airflow. Because of this, the angle of attack on the side where you're braking also becomes larger. And this larger angle of attack leads, depending on the curvature of the canopy, to a rolling moment as well. So this rolling moment then rolls the whole thing in the direction of the brakes.
And when I'm in a steady turn, so turning nicely around, then of course a specific thing comes into play, namely the speed of the outer wing is always faster than the speed of the inner wing. And more speed naturally means an increase in lift from the outer wing. And now it goes like this: first, there's an increase in lift from braking the inner wing. Then the thing rolls to the left, for example, braking left, rolling left, and then it starts to turn. And at that moment of turning, the lift on the other side naturally becomes greater and creates a counter-rolling moment. That's why, when braking the paraglider, it doesn't go into a rolling motion like an airplane; if you give a kick with the aileron there, then the airplane rolls and doesn't stop, it just keeps rolling and rolling until it's on its back.
The paraglider doesn't do that. It's so incredibly self-stabilizing that it immediately enters a new state of equilibrium. The side where the brake is applied has just as much lift as the side where it isn't, because while the braked side has a higher angle of attack, the outside has more speed, and those two effects compensate for each other. And if you leave the brakes symmetrical, then of course the outside wing will have more lift without braking, and it will immediately roll out of the turn and fly straight again. And this property, which is unique to the paraglider, doesn't exist with airplanes, does it?
If you have a roll, the aircraft will turn in that roll—for example, a glider in a roll with the aileron in the middle would constantly enter a steeper turn because of the faster outer wing. So it doesn't fly straight anymore if you let go of the controls or something. And a paraglider does exactly that. And that's unique. For example, if I do nothing, the pilot faints, then the thing just flies straight ahead. You can see that clearly in that accident where the pilot flew over the Halletschgletscher, fainted, and went into the slope at the back. That was also an interview of yours; I was very impressed that he found his way back to civilization after days of survival efforts.
But only thanks to these paraglider properties, right? And that's why I wrote this book, I actually tried it out, which is wild, of course, right? I also tried acceleration, looked at what happens, accelerated the thing until it finally just tipped forward and down on its own as a whole. And I did some acceleration, I thought about it—so, with trial and error, and with theory and thoughts and checking—I got really into it and saw, yes, that's how a paraglider works, with the center of gravity at the bottom, and these aerodynamic forces; you then have to go into three-dimensional vector geometry, which is a bit high-level for the average pilot.
as you say, that's always the average pilot who might not understand that, but you have to sketch it out and see what happens with something like that when you look at the center of gravity and the aerodynamic forces, which are actually always perpendicular to the surface elements, and what that implies. And I wrote a lot about that, also about lift, of course I said, okay, now I'm trying to break that down so you can say, yes, lift isn't just that particles flow faster on top and slower on the bottom or something, but then there is a very simple and very impressive theory: if you look at a profile in the airflow and map the flow around the profile with small vectors and then remove the base flow, then suddenly you see, wow, that's a vortex going around this profile.
And this vortex, that's the lift vortex, or lift circulation, that accompanies this profile and is induced by the angle of attack. And then it's clear that lift is generated, even by a flat plate or by a symmetrical profile that's the same length on top as on the bottom, and so on. And then you suddenly understand, aha, wow, that's the lift. And it's very clear. So, for example, a curved profile that doesn't generate lift—because it's curved, you can see that this lift vortex has its center exactly in the middle of the profile. At the front of the profile, downforce is generated, and at the back of the profile, lift is generated.
That creates a vortex around the profile. There is no lift, but there is a torque. And that would be this zero-moment on a profile when it no longer produces lift. You can find that in many books; you can read up on how that works. And I find these explanations—I didn't write this book for beginners in basic training or anything like that, but for people interested in thinking a bit deeper into the subject. You now...
you said, who wanted to delve deeper into that. I find it interesting first of all how you actually thought about it, because you're also saying, okay, I basically tinkered with my own paraglider to understand certain concepts and things like that. How much of what you've written in the book would you say is based on theories you already had from other books? And how much of it is the fact that you reached it in some way through a kind of learning by doing, where you said, oh, I can apply that to the paraglider and that's what's happening. And I've experienced and tried that myself now and can say, that's exactly how it is.
It's like, the basics of profile theory,
Pressure point migration and so on, of course, I've adopted that. But everything that is paraglider-specific, like this low center of gravity and the definition of this neutral point and so on, that all grew out of my own stuff. So I've formulated all of that myself through logical thinking, and it now results in a picture that could actually hold up to scientific standards. Yeah, that was, that was really a, wow, I spent quite some time thinking about that and asking, why is it like this, right? I also ended up at completely different things, for example. For instance, there's always this story with this weight shift, right? If you move your body to the left, right?
Then what happens? What happens then, right? And so. And then I thought, yeah, according to my theory, the lift on this side where I'm shifting the weight should be exactly the same as on the other side. Because there's no reason why the profile up there should take a different angle of attack. And then you see, yeah, aha, okay, I'm shifting my weight to the left side and now there's just a kink at the top of this curvature, there's a small kink. And in this area of this kink, the lift vectors are no longer pointing straight up, but a bit sideways, and they create a rolling moment. And then the wing rolls to the left.
To confirm this theory, I then used a suitcase scale—or I naturally pulled the risers down a bit—and looked to see if it was true, right? It's exactly right. It's such that the lift on the left and right remains exactly the same during weight shift. It stays the same. Only the middle, this buckled middle, creates a torque around this center of gravity at the bottom, and then the wing rolls to the left into the turn, and now you get that change in speed again in a turn, where the outside wing gets faster and the torque of these pulled-down ears prevents this rolling motion from continuing, and you fly the turn stably in a specific bank angle.
So, for example, these are the trains of thought, and then you try it and test it, and surprisingly, it works very well. But if you were to ask ten paraglider pilots at the launch site or landing field, "Yeah, if you have weight shift, do you have more lift on the left side when you have your body to the left?" everyone would say, "Yeah, yeah, of course, the weight is being shifted, right?" But according to my experiments and my theory, that's just not true.
There's a steering technique for turning where, if you want to circle somewhat tightly but very flat, some people recommend shifting your weight outward. Have you looked into this question as well—why does that work?
So, the best turn—let's say the one with the least drag—is flown when the paraglider flies at the same angle of attack. This comes from the theory of induced drag. Induced drag is at its lowest when the lift behind the wing, uh, the sink behind the wing, has the same value. That's when the paraglider flies with the same angle of attack across the entire wingspan. And if you now brake heavily on the inside, that creates an induced vortex. That means the drag increases, the induced drag, and the sink increases.
So you should actually fly turns with symmetrical brakes as much as possible. And not brake heavily on one side. That means, in my experience, or when I make a turn, then weight shift and brake as symmetrically as possible. Then it climbs best. That's my... I didn't measure it, because when you're flying in thermals, you know, it goes up and down and you can't measure anything. You can at most compare it with other paragliders. And I have to say, when I go into it with the weight shift, especially with a high-performance wing, then it climbs very well. For example, that test glider I had back then, where I took the center up, it had a strong roll moment through the brake.
It also had a strong roll moment when I shifted my weight, but especially over the brakes, it had a massive roll moment and jumped directly—I mean, it really dove into the turn. But because of this strong curvature, the effect of wanting to exit the turn became stronger as well, of course. And it had a brutally bad sink rate. So, it really had an edge when circling with other gliders, and they dropped me like crazy. And as soon as I let the center back down, that went away. Because I had to brake so hard on the inside just to fly a turn at all that the induced drag from that braked wing part became so strong that the sink rate increased very significantly, and I really had the biggest problems there.
Then I thought, okay, it's funny, if I take the height up, then it rolls back and forth over the brakes like a world champion, and of course, it goes back. And that's the theory. Now you'd have to take measurements. Now you'd have to say, okay, we go on a mountain, completely still in the autumn, no lift, no sink, and then you fly side by side with the most similar paraglider possible, fly side by side, and now one person does the turns like this and the other does the turns like that, maybe five turns, and then see who lost more height or something.
Those aren't reliable statements. And then there are these theories, like the ones I just told you, where we say, okay, induced drag causes a large part of the drag in a paraglider during slow flight, and keeping it low would be good. And that's certainly not the case if you brake on the inside and move your body outwards.
So, basically, this way of flying curves, even if it's recommended by some, is nonsense from your perspective.
Yeah, I have no argument for that. I don't see any argument for it at all. Especially with high-performance bikes, they have very low braking torque, so you often have to work with this weight transfer, otherwise they don't really lean into the corner properly. And these high-performance bikes also climb best. I have a twin-cylinder too, and it clearly climbs best, in my experience, when I work into the corner with this weight transfer and keep the brakes as symmetrical as possible. But does that mean,
now just from a practical standpoint, regarding initiating the turn, you do weight shift, then you still pull the brake to, of course, pre-set the turn or maybe the radius a bit, but after that, you let both brakes out again so that they're symmetrical, or how do you do that?
Yes, but first I have to enter the turn with the glider. I have to roll into it first, right? And this rolling in, that happens very slowly through weight shift, of course, but with the brake it goes faster. But once I have the bank angle, that bank angle is what makes the turn—I mean, an airplane can't fly a turn if it doesn't take a bank angle. A paraglider can fly a turn without a bank angle by simply keeping the glider as horizontal as possible and only braking on one side. And I maintain that this way of flying a turn, where the glider has no bank angle but is only braked on one side, creating an increase in lift on the inside of the turn and thus being pulled around, is the worst thing you could do to fly a low-drag turn.
That
meaning, in a thermal you'd climb worse with that, from your experience?
Yes, I think so. So the problem is, of course, the thermals—I see the problem again and again that if it's tight thermals, they have a tight thermal core, and the people flying so-called flat turns with little bank angle, of course, they fly a correspondingly large radius. And if I then go in properly and fly really tight turns with more bank angle, I'll certainly have a greater sink rate, polar sink, but because I'm much, much better in the center of the lift, I ultimately climb better in the end. I see that often when I'm flying in a group, at the Niedere for example, and there, these dozens of pilots fly there...
large circles back and forth, and I know there's a bubble right in the middle that I have to catch, and sometimes you're tempted to turn in a bit and then climb past on the inside. Then you have everyone below you and the others just keep flying their flat circles. So I have to say, centering a lift requires a certain turn radius, and you just have to achieve that; and if you achieve it with the canopy's bank or one-sided braking—well, I'd prefer canopy bank and as symmetrical braking as possible for the same turn radius.
Because if you fall out once, you've lost much, much more than if you're probably not aerodynamically optimal or whatever, but stay in the center as much as possible.
Would you say that this intensive focus on aerodynamics, even for this book—since you'd already been flying the paraglider before—would you say that after understanding this, you've become a better pilot?
Yes, I think so, I do. For all flight situations, I have an idea of what's actually happening. So, for example, let's take those spiral dive accidents. What happens if I brake on one side? My theory says that if I brake on the left now, then for the hand that's braking, I have for a moment that the left side tries to tilt the body to the right. That's very logical, right? But what's also there—you can try it out, fly straight in the air and just sit very relaxed and brake on one side—is that you notice the braked riser also goes upwards and tilts the body outwards.
tilts. It's like, the braking and the extra lift on the braked side cause the body to tilt to the opposite side. You actually want to go left, but because of the tilting to the opposite side, it prevents you from going left. And if that happens in a steep spiral—well, from a certain steepness, the speeds from the top of the surface are the same. If you look at the center of the turn, there's no longer that insanely faster outer wing helping you get out of the turn. This effect disappears in a steep spiral.
Then there's the added effect that tilting to the opposite side, when I enter it like that, can prevent me from, for example, getting out of this steep spiral. That means I'm in a steep spiral. I'm going left, and now in this steep spiral, I brake to the right. What happens? My body suddenly tilts to the left and prevents me from getting out of this steep spiral. And if you have a pilot who's a bit stressed and says, "Yeah, I wanted to get out." Alright, I'll give a few examples. Back in Davos, a flight instructor who was in a steep spiral
...flown through a barn roof. He survived, but was injured. And I spoke with him about it. He said, yeah, he went into a steep spiral and he was a flight instructor, a really experienced pilot. And he said that even though I braked, he couldn't get out of the steep spiral. I can only explain that by saying that with this braking, how should I put it, when you see the ground coming in a left steep spiral, you'd have to brake on the right and shift your body to the right as well. But if you panic and stuff, you don't want to go there, then you move your body to the opposite side and brake on the right.
And then you can't get out of that steep spiral anymore. You'd have to...
take a video recording, but you usually can't do that when an accident like that happens. Then you might see, in some cases, that although there was still some braking on the other side to get out, the student didn't make it out anymore. Or even experienced pilots have gotten stuck in this steep spiral if they've worked contradictorily with brakes and body weight shifts. So that's also a realization from these theories where I've been rambling, let's put it that way.
With these theories you've developed and written down, you've probably had some discussions at launch sites and things like that. Did you also have discussions with any paraglider designers who might have tried to explain to you, "No, it actually works differently, we see it differently, that's why it's like that and that's why we build our paragliders this way"? Completely.
At the beginning, when I started paragliding, I have to tell you a story. My first paragliding flight was in 1977.
So, long before paragliding even started, I read an article about a person who was pulling themselves upwards with a parachute in the wind, right? Then I thought, I want to do that too, right? And then I went to a barracks, a paratrooper barracks in Germany—I had just finished an internship in glider construction, a six-month internship in Kirchheim-Teck, which was very interesting—I went to this barracks and said, give me one, please sell me one of those gliders, if you still have one somewhere. Then they asked me, yeah, for what? Why do you want that?
I want to pull myself over the snow with this glider. Yes, they had some with holes in the gliders, and it was a round canopy, it was called a Paracommander, with these slits on the back. And it already had a glide angle, so it was about 1 to 1, right? And you could also steer it in that direction with control blocks. And then I took the glider and made a release mechanism on one side from a car belt, I made a release mechanism, and then I tried it, this glider, it rose nicely upwards, about 45, 50 degrees over the head, and then pulled me over the snow. And we also went to the ski camp and I found to my amazement that, when the wind was blowing, you could pull yourself upwards wonderfully, that was still in Flims Laax.
And then I went over the glacier—those glacier tracks didn't exist yet—I just drove up over the glacier, unclipped the glider at the top, wrapped it around my waist, and rode back down in the deep snow. And then another day, a bit of Föhn wind came up, blowing more towards the other side onto a steep slope; then I drove up there with the glider and the slope got steeper and steeper, the glider was getting more and more vertical above me, and eventually came the moment where I was just in the air and then I was flying. On this parachute. And that was still crazy, and I said, yeah, that's actually not intended anymore, flying with the glider, right? And this mountain also had at the top,
it eventually came to an end and I said, if it keeps going like this, the wind is going to carry me over the mountain to the lee side, and that's not good either, is it? And I don't know what's over there or anything. I was then able to steer the glider back into the slope, unhooked it, and could go down again. My sailplane colleagues already had some concerns when they watched me do that. That was my first paraglider flight.
And afterwards, I had a student pilot who was into delta, so he had a hang gliding school, and he told me during the training, he said, "Hey, next year something completely new is coming, namely paragliding." And I was like, "What's paragliding, what is that?" Yeah, exactly, with the mattresses. I'd already seen the mattresses from the parachutist. And then he said, "Come on, I'll invite you for a trial day. Can you come in the autumn? We'll do a few trial days." Super, right? And I also knew from the parachuting scene that they always went on holiday to Mieuxy. And in Mieuxy, they go up by bus and then they fly down these slopes.
That was since the 70s, I think it was around then. And then I thought that would be good, because I was also a ski instructor in the winter. And the annoying thing about skiing was, in this ski resort, the slope down to the village was a south-facing slope, and there was often not enough snow. And everyone had to wait for half an hour, an hour for the lift to get down. I thought, if I had a glider to fly down there, that would be great. So I went to him and did a trial day course, just for one or two days, a few flights, very precisely. And I thought, yeah, that's great. Then I did the paraglider test, sometime in '86, I think.
Yeah, 1986. And I stayed in touch with him. And he also produced these paragliders as a manufacturer, I think they were called DAK. DAK meant he had a sort of ducktail on the exit edge as a feature. And I saw how he produced them. I think he had already been producing abroad, even in China. And we always discussed it. And those old paragliders didn't have a pulled-down nose yet. They just had a hole at the front. And then I also said, hey, a pulled-down nose, that makes a difference, it adds something. It pulls the profile forward, that brings a performance improvement.
And he did that too. And with every batch of 20 or 30 gliders—they were selling like hotcakes, as they say in Switzerland, like fresh Weckli, right?—he always made one glider where he made some kind of change. Two more cells, a bit more stretch, and stuff like that. And by just trying it out, simple trial and error, he saw how it worked. And I looked into that scene a bit too. And later, he took over a glider from Krippendorf called the Malibu. That probably doesn't mean much. It already had a little net at the bottom. That little net also prevented the entry openings from vibrating a bit and so on.
And this Malibu flew great. It had superb performance. I never flew it, though. And then I saw, yeah, if you take the ears into account and so on, then the glider doesn't know what to do anymore. Instead, it expands into the angle of attack and goes into a deep stall. And then I looked and thought about it a bit and saw, yeah, yeah. Yeah, why does it have such good performance? Quite simply, for the lift distribution—the elliptical lift distribution—you have to cant the wing slightly upwards on the outside. So that the angle of attack on the outside is a bit smaller, in order to get this elliptical lift distribution. That means the outer wings pull a bit more forward and the inner part brakes more.
And when these outer wings fold in, then the inner part only pulls backward and the outer wings no longer pull forward. And then it went into a deep stall without a speed bar. And then I told him, well, it's nice if there's performance, but that's not acceptable; you just have to angle the outer part back down again. And then, then it was great again, it was good. And I made some nice wings with that part, also in South America, that was great. And that's how I got into it a bit. Also with the designing—well, I wouldn't say designing, you just tried it. There were no
theories, there weren't any,
people just knew that if you do this or that with the glider, then this or that gets a bit worse or better. But real theories, like the ones I laid out in the book, where you can say, okay, we're actually working with three-dimensional vector geometry and with the geometry of the canopy and the profiles and so on, those didn't exist anywhere. I also hoped that maybe someday some manufacturers would take this book or some student or graduate might write a computer program based on it. But the only thing I saw afterwards was a scientific
study, a mathematical-scientific study, and he also has the principle from above, you're hanging at the top of the paraglider and the pendulum moment is at the bottom, right? And I read that and just shook my head and had to say, that's insane, I don't believe it, right? I mean, overall, that just gets lost again, doesn't it? That kind of stuff. I don't know, is there
Flight simulation programs for paragliders from the manufacturers? They're all sitting on that, how shall I put it, in the room and staying silent, right? Nobody is saying anything. There are programs for how to cut a paraglider and line lengths—in two minutes you can more or less enter the parameters for a paraglider and the cutting patterns come out, and you can have it manufactured, or something like that. But a flight simulation program in that sense, based on the scientific foundation of my theories, I don't know if such a thing exists. I've never heard of it.
So there are already a few manufacturers working with something like that, now I don't know if it's based on your theories there or anything, but it does exist—Nova, for example, I know they can also simulate a collapse and see at which points the glider fails, how far, and what happens with a front collapse and so on, so that they can actually look at it in 3D animation to see where the glider fails, and by now this digital prototype development has advanced so far that much of what they see in the digital model—when they then try it out in reality, they can see, okay, the collapse angles or the way the gliders deform and so on, actually shows up in reality.
But
It's about more than that; for me, it's not about the canopy and such, but about the flight characteristics. Or, through the geometry of the canopy, what kind of flight characteristics do you get, how much rolling moment is generated through curvature and so on—there could definitely be something more to be done there, couldn't there?
Based on your theory, would there be something like the ideally shaped paraglider in terms of canopy curvature or something like that, or is it always a compromise between various things? If you say there's an ideally shaped one for maximum performance flying straight ahead, but as soon as I fly a turn, it would actually have to be the ideally shaped one.
Controllability and flight performance are a bit contradictory. For example, with extreme flight attitudes, the better the performance of a paraglider is, the more prone it becomes to collapsing and the harder it is to control in extreme flight attitudes. For instance, in soaring with a rigid wing, there are no problems. The high-performance gliders are so harmless that the pilots don't even notice they're in a stall. You have to pat them on the shoulder and say, "Hey, you're in a stall." And then, why, how, and so on. Then I say, "Yeah, move your ailerons." Then he moves his ailerons and says, "Yeah, nothing's happening." Exactly, because you're in a stall, right?
Or a sailplane that goes into a stall, it sinks, it has an even better glide ratio than a paraglider and simply doesn't react to the ailerons anymore. And as long as you don't push or anything, it doesn't go into a spin either, it just keeps flying, right? With two and a half meters of sink or something. And with a paraglider, it's a bit different. With the larger span of the surfaces, you have a small angle of attack range, which means in trim you fly with a smaller angle of attack with a high-performance glider than, for example, with a beginner glider. A beginner glider might have 18 degrees in trim, and a high-performance glider might fly with 12 degrees or so of angle of attack. Accordingly, it is also more sensitive to negative
changes in the angle of attack that lead to a collapse. And because of that, you're always moving in a compromise between controllability, performance, and safety. And I think paraglider manufacturers today have done such great work and are so good that they know exactly how much they can still demand from an A-glider, B-glider, C-glider, or D-glider so that the thing is still accepted by the scene. Even if the scene—well, it benefits them...
I don't think normal pilots believe much if they read my book or something like that. But at the very least, it prevents some false theories from circulating, let's just say. Like this story about old stuff, where I keep finding that there are things people used to know and then they just disappeared. For example, this story about the variometer and the fast variometer, where you use an accelerometer back and forth and so on, to somehow make it faster or something.
I had this problem back in 1973 when I started thinking a bit about these variometers in soaring. These variometers work with a thermos flask and a balancing airflow in this tube; when the pressure drops, air flows out of the flask, and you're supposed to measure this airflow. And this measurement of the airflow—so if you were climbing 2 or 3 meters or flying in—it took about 2 to 3 seconds for the needle to reach that value. And then there were also these electric variometers, which measured the airflow with a small heating coil, and this heating coil has a resistance-dependent
...so the thermoresistance, and if the airflow entered from one side, it cooled down more on that side, and on the other side, and if you took a reading in the middle, you could then detect a voltage difference in this heating coil and then put that onto an electrical measuring device, but the thing was also slow and such. And then I already started thinking back then, yeah, how could I make a sensor faster? And then the thought occurred to me: a sensor has an E-function, which means if a measured value changes suddenly, for example, rising three meters, then the deflection...
goes slowly upwards at a certain gradient and changes or adjusts to this final value in an E-function. And then I thought, well, if I know the sensor's behavior regarding external disturbances, then I can infer the external disturbances from this sensor behavior. And I did the following: I took the gradient, the steepness of the flanks—there were just these first operational amplifiers—and I differentiated this gradient and I...
slope, I differentiated that signal and added it. That means, when the sensor started to change its value, I knew it was rising three meters, and I added that to it, and in that way, I could make the sensor as fast as only I could—I could almost bring it down to zero. And that was a very simple idea, but I didn't have the time back then; I was somehow 17 years old and let the idea disappear into some drawer, and now, ultimately, with this new variometer you presented, I saw, wow, wow, no way, I thought, everyone knows that, everyone knows that or something, but no, apparently nobody knows anymore how to make a sensor faster without changing the sensor.
Are you with me there now, can you follow me a bit? I can follow you. So, for example, a gust of wind bends a tree, so from the bend of the tree, you can infer, aha, if it bends like this and that, then we have a 100 km/h wind, right? But if the wind suddenly starts blowing, the tree isn't over there, but rather it moves over quite slowly and reaches this final position. But from the speed at which it starts moving over, I can infer how much the wind is. And you can do the same with every sensor. Or yeah, that's how it is. Or for example, with the total energy compensation. That was mentioned before. The TEC. And this TEC...
Compensation is quite simple with gliders. You don't measure the static pressure used to measure the variometer. So, when you go higher, the static pressure decreases. The variometer notices that. And when you go lower, it increases. The variometer notices that too. But if you now measure, how shall I put it, the negative dynamic pressure—that is, you take a tube perpendicular to the airflow and you drill a hole in this tube, a hole on the leeward side of the tube. Then you have a vacuum at the back. And now this happens: if you...
when you enter a layer with higher air pressure with the glider, then you get into a layer with higher air pressure. But because you're getting faster, the pressure also drops at that tube. And there are mathematical considerations that show exactly how these two effects completely compensate for each other. And if you climb with the glider and, let's say, pull up 100 meters, then you enter an air layer with less static pressure, but the large negative pressure also becomes smaller because the speed is gone. And that's how you can fly with zero cost, you can achieve a total energy compensation like that.
And if I, for example, fly a paraglider with a variometer in the dust zone of my body, that's more or less the worst thing you can do. Because if you have your variometer in the dust zone, then when you descend, you don't just get the higher pressure from the air layer below, but you also get more ram pressure. That means the variometer then shows a double negative value. But if I move the pressure drop of the variometer to the level, for example, you can put a tube on the variometer where the variometer's pressure sensor or the pressure is fed into the variometer and just put the tube next to it, next to the harness by the risers, with the opening facing backwards,
then a pretty perfect total energy compensation would take place. So you can see for yourself what the total energy compensation is like when you fly. You go ahead and brake the glider and then release the brakes again. Then it drops a few meters, down, and when it catches itself at the bottom, you brake again and this rocking motion should happen without any variometer deflection. Then the total energy compensation would be perfect. If the variometer is swinging like crazy, from climbing two meters to sinking three meters, then you know you have poor total energy compensation, which prevents you from getting good information in the lift.
Where did you mount your vario? I have mine in the front too, and I didn't go to the trouble of it, but I tried it out and noticed, yeah, it would be better in the back or the front, but the effects aren't as big as with a sailplane and I just know it. I know it because I feel it when I fly into a horizontal or a vertical gust. If I fly into a horizontal gust, the speed of the paraglider increases.
Lift increases. Then it's the same as when I apply the brake, the glider goes back, it goes up, it swings up, the speed decreases. At the moment it decreases, the lift drops again and then it goes forward again, and that climb that was happening suddenly disappears. And that wasn't a climb, so no lift, but a horizontal gust. And that's how I know. And that's why I can say, okay, that's not lift. I can just feel it. When the glider goes back, when it pitches up like that, that's not lift. That's my theory. Like you also said, you can't really measure that, because you would need an independent
...measurement system, or a defined measurement system where the air movements are known and you fly a paraglider into it to see how it behaves when you fly through different types of shear. For example, you're on a 20 or 30-meter final approach and you dive with your paraglider into this zone with less headwind. So, what does the glider do? It suddenly has less airspeed. Relative to the ground, it's still flying the same, of course. But now you have less lift. As a result, the flight path goes steeper downward with less lift. The angle of attack on the glider increases, and that's why the glider now wants to go forward.
It oscillates forward. That's not very pleasant near the ground, of course, but if you prevent it through so-called active flying—the idea that the glider must always stay above me—then you force the glider to maintain that large angle of attack. Even though it actually wants to return to a healthy angle of attack on its own. And against the ground, this means you end up coming down somehow at the stall point with more or less a high sink rate and can no longer flare. Then it really drops you. And if you have a bit of nerve and let the glider move forward a bit to regain some speed, then it's better. And this awareness also comes a bit from my theoretical considerations,
a paraglider always wants to stay in its defined angle of attack. And this so-called active flying, which is preached everywhere and says, yes, the glider must always stay up there, that's just not true. Rather, I interpret active flying as a paraglider wanting to react to changes in the angle of attack, but it overshoots. So if it has too much angle of attack, it goes forward, just like during takeoff it goes forward, but it would overshoot this ideal value. So I have to prevent it from entering that oscillation. I always say, I let it have half its way. I let it go where it wants, but I brake it the moment I feel like, okay, now you've had your way and now I'm coming back, right?
And tell you what you should do. I see a lot in the footage, where people fly into turbulence and so on, and then at some point the glider wants to go forward because it's getting a lot of angle of attack. Then they pull on the brakes and fall into a stall, and suddenly the ears pull forward and they're in a stall and they don't even know they're in a stall and panic, panic, back and forth, right? And if they could feel the glider, to let it go forward just once, right? In that moment. Then the problem wouldn't have been there at all. That
is that what they always say at the flight school, let your glider fly, and that it will actually handle it best on its own in most cases. The
The truth lies somewhere in the middle, right? You don't let the glider have its way, but only half of it. So I have to let it have its way, but only as much as half, right? Because it overshoots. If it comes from behind somewhere to the front, a high-performer or something, and you don't do anything at all, then it undershoots or it exceeds its ideal angle of attack and then goes into such small angles of attack that it undershoots the canopy and collapses, or something like that. I'm saying it's somewhere in the middle, right? That's also what, for example, in this book I wrote, deals with this topic relatively precisely: how does a glider react in which wind shear models?
There are all different kinds of shear surfaces; so a shear surface can be vertical, it can be horizontal, but it can also be at any angle in between, and the wind at the shear surface can come from bottom to top, top to bottom, back to front, and so on. The subject is incredibly complex, and only the glider's reaction can provide me with information about what the air around me is doing. That is very important to know. And now this theory comes in: if I say, okay, I'm really flying into a lift, the shear surface is vertical, I'm flying from sinking into climbing, then the glider gets more angle of attack.
And with this increased angle of attack, it has more lift. There are two effects. The first effect is that the glider wants to move forward, reducing the angle of attack. The second effect is that the flight path goes upward. The sink rate relative to the rising air decreases immediately. And this pulling forward into the lift, for me, that's the feeling where I say, "Yeah, that's lift, right?" The speed doesn't decrease, it stays the same, or the glider even bites forward. But as soon as it goes backward, the glider, then that's not lift for me, but rather a component of horizontal wind shear. But well, you would have to
you'd have to calculate that and somehow work with a system where you could verify it. And that's almost impossible, isn't it? That's pretty difficult.
Before we theorize any further about that, a question. Your book is unfortunately out of print now.
Will there be a new edition of it?
give it a reissue in some way?
Yes, I've thought about it and seen that it would have to be rewritten completely from scratch, in detail, and also with
Yeah, I've thought about it and seen that you'd have to rewrite that completely and in detail, and also with support, because writing something like that takes so much work, that you'd really have to, how shall I put it, it's just a theoretical construct, right? But that you could go deeper, go even deeper into it, or something, maybe with some aerodynamicists, that would be nice. But I've received relatively few responses, either there was nothing at all, or? No feedback, or partly positive feedback. Finally, someone who's writing some proper stuff, right? About all that stuff, and not because so much is written about it at times, it's crazy, right? But no, I have other things going on at the moment
projects going on, like reissuing this book that's been out of print for a while.
Speaking of other projects, we've been chatting for over an hour now and there's actually a development I know about from you that I mainly wanted to talk to you about because I find it so interesting. You recently re-engineered something very special, namely a brake parachute for your paraglider, or rather for the Kurzeug. Why do you think such a development is necessary at all?
This comes from my experience and the possibilities I had as a sailplane pilot that I no longer have with a paraglider—being able to adjust my drag, which is very, very valuable at certain moments and would provide a lot of benefit. So, if I can vary my drag, meaning I can vary my glide ratio on my glider, I can not only fly a straight glide out of a cloud or from a thunderstorm where there's five meters of lift; with the speed bar, I can get out of that stuff at seven or eight meters per second.
I can also fly controlled approaches with a straight final. That's something that's actually unknown in the paragliding scene. With a paraglider, you have a specific glide angle, and this glide angle—in trim—is fixed. It's only influenced by the wind. More headwind means worse lift, then it goes up again, down, back and forth, wind shear comes into play and so on. And if you're ever too low, you're too low, then you're too short, and if you're too high, you're too high and then you have to do something. Either they do another turn or another turn, or they go to the stall point and shake themselves down, or there are different...
...approaches, for example, back and forth, and those are all things that I don't consider very...
uncritically attracted to. We just had an accident two weeks ago here during a landing on the
Didamskopf. He ended up with two broken vertebrae and his feet. He wanted to be an accuracy pilot, a great accuracy pilot, wanted to land up there with his fluttering style in turbulent air, and the flow just ripped away from him and he fell from ten meters down. And that's always a shame, isn't it? And I say, even here where I live, we have small meadows with trees and houses and, I don't know, everything all around, and you can't really operate with big curves in the final approach and so on. And this business with the pumps and back and forth, I don't like that either. And then I saw in Saint-Hilaire how they fly down with impossible things on their backs back there, and I just asked.
You mean Saint-Hilaire in Kubica, where they do the canopy flying and have all sorts of different constructions hanging off the back? Exactly, and then I asked them how it works, what you're allowed to do, how much, and the back-and-forth. I've already seen it, the glide angle is absolutely terrible the way they fly. And then they just said they can do whatever they want, as long as they don't do anything to the glider. They can hang whatever they want off the harness. The sink rate just increases, and at the bottom during landing or whatever, depending on the flare, there's nothing left to flare. Instead, it just goes down at two meters against the ground and somehow they're already standing there. You can have some fun with that.
watch. And then I thought, yeah, I want to try that with a brake glider too, so I built a brake glider and attached it to the seat and flew around with it, first a larger one, and then an even larger one. And it worked like crazy, I almost don't believe it. It went down five meters in trim, it just dropped. But then I had a deployment issue, meaning I couldn't pull it in with my feet through the leg stretch, I could pull it over the main line and it got stuck once and I couldn't pull it in anymore, and then I did a small hard landing that actually cracked a vertebra in my back. Then I knew, watch out, this all has its limits.
I also had a
I made a quick release for the suspension lines so that it collapses and such. But I saw that I can't do a controlled landing approach with it. I can do a steep one, but I can't make it flatter, because in an airplane you always have the option; you fly in at an approach angle where options for up and down are possible. That means in motor flight, if I see I'm coming in too far, I reduce the power and then the plane flies steeper. In a glider, I extend the flaps a bit, then I see I'm coming in front of the landing field, that's too short, so I have to improve the glide angle again, then I retract the brakes a bit and it flies flatter again. That way I can adjust the approach in fractions of a second
constantly monitor and correct, without turns in the final approach. I wanted to do that with this glider too, and then the idea came to me: I could cut the glider at the back, in the middle where the center lines are, so that it forms a tube, and if I pull in or push out the center line with my feet, it pulls that hole at the back together and then it brakes more, or I open the hole and then it brakes less. I did that and saw, yeah, that works beautifully, and I've been flying with three different sizes made since then, and another pilot has already flown it too, and he was a competition pilot as well and said, hey, if there's a way to buy this, I'm the first customer.
He said it was an intuitive, great system and that it changes how you manage your options in the final approach, because you might come in with a glide ratio—let's say, slowed down, not fully braked, but slowed down—you can manage with a glide ratio of 5 or 4, and then you're roughly in your approach angle, and in the final approach you see, "Aha, I'm coming in a bit too far," then you brake a bit more and it goes down steeply, and then you see, "I'm coming in a bit too short," and so I can somehow land on a tennis court, more or less, between the trees with meter-precision, right? No problems.
The fence would obviously still be in the way or something, but I also made a video of the whole thing, and you can deploy that thing in a moment and retract it very quickly and use it again and again, and it's not heavy, it's maybe 300 grams, this brake glider, and at first I also thought the problem is, I have a two-liner and with this two-liner, putting the ears on and so, you can forget about that or it doesn't work well, and steep spirals don't work well either, and there were no anti-G gliders when I did that, and I thought, I need a brake glider, and then an idea came, then I could also control the approach characteristics like that, and since then...
Funny enough, I also feel a sense of security during the approach with this thing; it's actually priceless. Well, if you have a normal glider and a large field and you can do turns and go back and forth, then you don't have any problems, but in certain moments, a thing like this is worth its weight in gold, let's just say.
You just mentioned the Anti-G; those are small gliders that you hang from a carabiner, throw backwards with a connection line, and they reduce the G-forces during steep spirals because this glider also acts as a brake. What is different about your brake compared to an Anti-G, or couldn't you achieve the same thing with your brake as you could with just a simple Anti-G?
It's like this: the Anti-G glider is either open or it collapses; there are no middle positions with it. And I see people doing approaches with them sometimes, so they just leave it on and come down and land with this Anti-G glider and all that. The problem is, it doesn't work that much; in a straight glide, instead of braking slightly and sinking at about 1 meter, you sink against 2 meters, so it's not much more, right? So with this fan there, you are a bit steeper, but you always have the same problem when you're steeper: you either go too far or too short with this Anti-G glider, you have no steering options with the whole thing.
The second thing is, for flaring before landing, this brake shouldn't actually be open, otherwise you lose the option to flare to stop and then out, and that happens automatically for me when I take my feet out of the leg bag, then it collapses and I can do a completely normal landing and I can brake it until the very end, actually I can brake it fully until a few meters before the ground and then out with my feet, then it collapses and I can do a normal landing. The problem with the anti-G glider is its controllability, that doesn't work, and secondly, retracting it again, because I might want to use it several times.
and a third problem with this, let's say if I have an anti-G glider with three lines at the back and I stall or do some kind of extreme flight maneuver, then it goes up and almost certainly gets tangled in the suspension lines, and that doesn't happen to me, so it has various advantages. That
meaning, there's no long connection line being made from the harness, but it's basically like an additional shell that widens out at the back of the harness, so roughly, yeah.
You saw the video, right? Yes, I did, but the listeners—you have to put a link there, and there's a video of the whole thing, of this glider, which sits like an eggshell directly behind the pilot. The main line—so the canopy of the glider—is maybe 50 cm behind the butt, right? And these lines from the carabiner are a meter long, so that's very close to the back, very, very close, and because of that, it's very stable against twisting. It doesn't twist, which is also a problem with these anti-G gliders; they eventually twist to the left in the airflow, and they have a stabilizer in there so that this connection doesn't twist, otherwise you can't collapse it anymore if the lines somehow twist and so on. These problems don't exist at all with my glider; it always flies stably behind.
It doesn't twist and can be controlled; it's actually a very simple matter.
The concept of a brake glider—if you hear that, you'd normally always ask, yeah, by how much does it brake? Like, how much slower do you fly then? And now, you're allowed to do a little bit of aerodynamic clarification again.
Ah yes, exactly. When you use the glider—that's my point again with the center of gravity—as long as I generate an aerodynamic force that acts near the center of gravity, the moment on the paraglider doesn't change. That means the paraglider simply stays at the same angle of attack. So, if I throw it out and brake fully, the big one, which brakes about 4 meters...
In trim, the following happens: when I throw it out, at that moment I notice, wow, I notice I'm getting slower, but at the same time, as I get slower, the canopy above also experiences less lift, I get steeper, then the canopy moves forward and pulls so much forward that the speed remains stable. The ground speed decreases a bit, logically, because that's just one component of the speed I have relative to the air, because I'm flying down steeper. So, for example, I have 38 trim without the glider, then I have a ground speed of, say, 36, but the airspeed is still the same. And it's the same when pulling in; when I pull in, the glider flies like an intercept arc and then continues at the normal glide angle without changing the speed much. That's what's happening now...
simply because of this additional surface area that's basically built around the back, around the harness. If I imagine a classic lying harness now, I could actually still stand up in the harness, in the bag, and spread my legs a bit, then my leg bag would just inflate like that too—wouldn't that actually be exactly the same effect?
The effect would be the same in principle, but much less intense. I mean, I don't know how much of a glide angle it has with a Submarin, how much worse it gets there, but I'd say you come down a bit steeper, but never with the same effect as my glider. My glider has a much greater effect; you have to fly it once to really have your jaw drop and say, "Wow, it goes down with that thing in the back, that's incredible." I just had one with a 6-meter base circumference and it goes down, it's incredible, you can really go over any obstacle, I've already flown over houses into...
and then just barely and then completely out and I was somehow standing down in a meadow, you can forget all about that with a normal glider or a normal approach tactic, that's not possible. That would be totally something for
the X-Alps people who then pump themselves into the smallest meadows, only the thing naturally weighs, you said, 300 grams more, and probably with the whole construction around it to be able to pull it in, which would have to be modified on the harness and stuff like that, it would naturally have become a bit more complex. Could something like that actually be combined with any kind of harness?
Principally, I have to say with a liege harness, because this rescue tube goes from the seat in the back to the toes in the front, and if you have a rescue tube with a brake glider inside, you obviously have to consider the lines too—it can become a real mess down there, or can the lines and the rescue tube be integrated quite well into a liege harness?
So the rescue tube would be like a kind of tube that it's pulled into, and that tube is shaped by fabric and then sewn at the bottom like a second layer underneath your leg bag, right?
Exactly, I sewed that on at the bottom and it's about, yeah, you can fit your fist in there, let's say in terms of diameter. So aerodynamically, it hardly has any impact if the rescue tube is there, but it's also not very large, it's just long—it's about 1.30m to 1.40m long.
Have you ever spoken with harness developers? What do they think of your idea?
I've contacted several of them with the idea, sent a video and all that, and no one wanted to get involved. Either they're like, "Yeah, we see that,"
...not suitable for the width or for the width of the pilots and and and or we have no capacity because you'd really have to get into development now to make it truly production-ready and marketable, then there are still certification questions or and all that stuff, even though the anti-G glider isn't certified in that sense, right? In any case, I haven't found a manufacturer yet who wants to get into that and take on this risk.
Maybe you should put the key manufacturers or the pilots in your harness and tell them to try it out and then...
I'm at the stage right now where I let other people fly and see how they react.
From your aerodynamic understanding, since a brake glider is what this is, maybe you could optimize the landing with it because you can do a much more precise landing approach with it, or maybe fly in front of storm clouds because then you can say, okay, I don't have to fly any spirals here, I just pull out this brake glider and come out with a sink of five to eight meters, so the storm cloud might still have significantly more lift, but with other clouds at eight meters, you can probably just fly away from many of them accordingly. Are there any other things where, based on your thoughts, you could aerodynamically optimize the paraglider or the paraglider system? Do you have any other ideas there?
So, make it better, not worse. Right now, I'm looking at how to create drag or how to generate controllable drag, and if you're asking how I could make the performance even better, I already have a concept, but it's very futuristic. Let's say it's a concept for a rigid paraglider; it has a spar, an inflated spar and ribs, and only has a line suspension—so not ABC, but just a main suspension plane and one in the back where you brake, right? So basically a classic kite construction. Exactly, you could say, yeah, like a Mustache too, but only with a main line and so on, but it has ribs, right?
He had really solid ribs in there, those ribs, he
inflatable tube, in
spanwise direction, when you let the air out, you can slide the ribs together and it would then be so easy to pack away that it could also be taken in the car and on public transport. The advantage of this system would be that you could choose the canopy curvature, i.e., the curvature of the canopy, arbitrarily, because we need the pressure buildup at the moment so that the shape of the paraglider and the curvature remain at all, and we still have the line planes; we are at the optimum where if we did even fewer line planes, we would have to—we're already pushing rods in now so that they don't slide together in the profile depth and
it would be completely free in terms of design parameters, such as aspect ratio and canopy curvature, and also, if you were to inflate this tube here, you could create a tension in the transverse direction—so, let's say with 10 or 15 ribs, at a distance of about 1 meter, you could create a cross-tension so that there's almost no...
the corrugated sheet geometry would smooth itself out, so the construction would also be much simpler and you'd naturally have a performance jump—I'd say a glide ratio of 20 would be easily achievable. The problem now with such wings is how they behave when they collapse, because every wing eventually hits negative angles of attack and there's drag, and a suspended wing that generates drag goes down, right? And with a paraglider, it stalls forward and then, when you... that's all been tried already, and then it stalls and you can't open it anymore, it just goes back and forth, and that would be completely unacceptable.
My idea there would be to give the surface only wing properties, in the sense that if the surface goes down under drag, it is angle of attack stable, even without line tension at the bottom. That means you would have to give the thing an S-shaped profile when it's unloaded, that generates a self-righting moment, so that if the wing goes down, it immediately generates lift again and goes back up instead of flipping over. That is the prerequisite for such concepts. Wings fly a lot, after all. I've flown it too, it's insane, right? The center of gravity of the wing simply has to be ahead of the profile's neutral point.
That means you'd have to arrange the weight distribution in the wing so that it flies with angle of attack stability, even without line tension. And then this wing would probably fly stably and be manageable even in turbulence. And if it also pitches down, in that area where it pitches down, the angle of attack stability would immediately turn the wing back into the direction of the airflow and pop it back up. But that's the only way it would be possible, right? But that would be such a leap, it's just a dream, let's put it that way. It goes far beyond my capabilities.
So you're dreaming about it, but you're not thinking about how you could actually realize it, at least for yourself?
Yes, in my imagination, I've already got everything; I've already drawn it and thought about how, where, and when, and how it folds and unfolds, and where the fixed parts are and so on, and how it's built so that it retains the famous paraglider characteristics, so that you can unpack the thing and get it flying again within five minutes, and pack it up and carry it on your back somewhere again. And the whole thing shouldn't be much heavier either. That's the thing with all constructions—you can think a lot about what you could do in terms of performance and so on, but if the thing ends up being 25 kilos and takes half an hour to set up, then you're back with the hang gliders, aren't you?
And the kite flyers, they fly with S-shaped profiles too, everything to fly stably, or those Atos things, but then you need your own tube on the car to power that, and then you're back with the kite flyers again, and they have this big problem—and here we go again—my glider, right? That would be the optimum for a kite pilot. Because they have glide ratios of 20, right? And they have exactly the same problem: if an Atos is approaching, it does have a spoiler, but that spoiler does provide more descent, but you can't just retract it, because otherwise it loses lift. So these flaps it has, it's the same with airplanes, airplanes also have flaps that you can extend; they generate not only more lift but also more drag, you can descend more steeply, but you can't just retract them to correct, because if you get there and see, I'm falling short,
and then if they just retract them, the drag is lower, but so is the lift, and then the plane drops, right? And that would be a very bad thing during the approach, and especially in the final approach.
That means the motor glider controls it with additional thrust before saying, okay, I'm going to speed up again, but the glider can't do that?
Yes, the paraglider, or an Atos with a winglet, can't just do that, otherwise it might stall at the end, right? And it can't vary much either, so a brake glider—a controllable brake glider—would be an ideal landing aid for paragliding.
for precision landings and to control it accordingly to the flair. It's just like with a glider; when I fly a glider towards the start of the runway,
The approach speed is optimal, 100 kilometers per hour, and I retract the spoiler at that moment, then I have a flare distance of, let's say, 300 to 400 meters. But if I extend the spoiler before landing, before the flare, I take the thing up, and then I have a flare distance of 20 meters. So you have to imagine that you can fully control the flare distance with the drag. And a kiting pilot would need that, it would be great of course, because he comes in, then he's still a bit too high at the end, and some kind of S-curve in the final approach for a kiting pilot isn't any fun either. Then he pushes or pulls it—it's the opposite of flying—he pulls it forward and down toward the landing field, then he gets there, but with excess energy, and then he has to get rid of that too, otherwise, if he's too early
If he releases it too early, he'll climb again and then drop at the end. So he has to reduce the speed in a controlled way, like in ground effect, and release it at the very end, and the touchdown point is pretty much a lottery, let's just say. And with such variable resistance, you have something like a trump card where you can vary and master these things. You can also say, I'm coming in way too short, let go of the resistance, cancel it, and then you really glide in the ground effect until the point where you want to touch down, and then you take it out again, and so on. So variable resistance is indispensable in aviation. You couldn't operate like that at the moment with normal aircraft, only in the paraglider and kite range.
you just don't have that, and you have corresponding problems, especially the higher the performance becomes.
Alright Otto, maybe your idea will take hold or find fertile ground with some listener who says, "Hey, I really want to develop more of that, or with you," or "I'm a vehicle manufacturer, I know him, let's develop a prototype of a harness that actually integrates such a glider, a brake glider, so that everyone can then test it out a bit more precisely, including in terms of other pilots as well." Maybe that will actually turn into an idea where, above all, I could imagine, the high-performance pilots or the competition pilots—if they say, "I don't care, my harness already weighs nine kilos and whether there are another 300 grams of brake glider in there, it's already... I have two rescue parachutes and everything else in there, and I've simply built in an additional safety factor that I can use for all sorts of things"—it could be that such ideas will eventually prevail.
I hope you'll come by this area sometime, and then I'll give you my harness and you can fly it.
I'd love to try that out sometime. Otto, thanks so much for your story. Thank you too. In the meantime, for those who made it through—I think some of you might have tuned out a bit at points, wondering, "Oh, am I still following this theoretically? What does he mean by neutral point, center of gravity, and all that stuff?" But I think there were always these very valuable aerodynamic bits of information in there where you could say, "Hey, I can even understand that with my basic pilot knowledge, and maybe I'll fly my curves soon, trying to keep my brakes as neutral as possible, or at the same height, and so on." So, with the things you pulled out there, you can really get some perspective. Otto, thanks so much. Thank you very much. And all the best to you.
I was happy to do it. See you soon, hopefully.
That was episode number 122 of Podz-Glidz with Otto follows. In the show notes for this episode on the Gleitschirm-Blog du gleitst, you will find some additional links. Among others, to the mentioned videos about the special paraglider Bremsscher. If you enjoyed the episode, then subscribe to Podz-Glidz. You can do that anywhere podcasts are available. If you also leave a positive rating there, you help make Podz-Glidz even better known. Or simply tell your paragliding friends about it. Podz-Glidz and Lu-Glidz are completely free of paid advertising. I do this out of conviction and in the interest of independence. Nevertheless, professional work and, of course, costs are involved in these products. To finance these, I rely on the concept of voluntary support.
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