We work out why a soft wing flies at all and what the pilot really controls. Angle of attack, forces and balance, drag, the speed polar, glide ratio, wing geometry, loading, the turn, the stall and collapses — with formulas and worked numbers. This is the foundation: all further training rests on it, and so does the whole official exam section «ზოგადი აეროდინამიკა». Here too: pendular stability and damping, the phases of a surge, active piloting step by step, the polar and speed to fly, the speed system, air density, the dangerous configurations, and how a tandem differs from a solo wing.
A paraglider is an unpowered aircraft. It has no engine: it lives on the energy of the air and on the height of the launch. Everything that happens in flight is the work of a soft wing in the oncoming flow.
Cut the wing across the span, like a loaf of bread. The cut face is the profile: the shape of the wing in section. The line from the leading edge to the trailing edge is called the chord. On class A and B paragliders the profile is asymmetric biconvex, also called “unequal”: the upper surface is more curved than the lower one.
Now put the profile into the flow. The air over the upper surface moves faster than the air under the lower one. Bernoulli’s law works here: where the flow is faster, the static pressure is lower. Above the wing there is suction, below it there is overpressure. It is exactly this pressure difference between the large (upper) and the small (lower) surface of the profile that causes lift. The suction on top does the main work. The wing does not so much rest on the air below as get sucked upwards, like a lid pulled outwards by a vacuum.
Drag the diagram sideways to see all of it.
There is no engine: a paraglider lives on the launch height and on the energy of the air. In a glide it spends height; in a thermal the air gives it back.
In practiceEverything that happens in flight is the work of a soft wing in the oncoming flow. Height is your reserve: spend it with care.
Cut the wing across the span, like a loaf of bread: the cut face is the profile. The line from the leading edge to the trailing edge is the chord.
In practiceWhen the lessons say “profile” and “chord”, picture exactly this slice: the angle of attack and all the forces are counted on it.
On class A and B wings both surfaces bulge outwards, but the upper one is more curved than the lower one. Such a profile is called asymmetric biconvex.
In practiceIt is this asymmetry that makes the flow on top move faster than below, even at a small angle of attack.
The air over the upper surface speeds up more than the air under the lower one: the particles on top pass the profile faster.
In practiceBy Bernoulli’s law, where the flow is faster, the static pressure is lower. This is what prepares the lift.
Suction on top, overpressure below. The pressure difference between the upper and lower surfaces is the cause of lift; the suction on top does the main work.
In practiceThe wing does not so much rest on the air below as get sucked upwards, like a lid pulled by a vacuum.
The school version: the two streams must meet at the trailing edge at the same moment. This is wrong: NASA calls this theory incorrect outright. The upper stream arrives much earlier.
In practiceThe flow is sped up by the turning of the air by a wing set at an angle to it. The conclusion stays the same: lift comes from the pressure difference. Choose that answer at the exam.
From the section text: unpowered flight, profile and chord, the asymmetric biconvex profile, Bernoulli’s law and the pressure difference, the equal-time myth. Streamlines and pressure arrows are an illustration, not a calculation.
The link between speed and pressure shows in the tube experiment. Send gas through a cylindrical tube at a constant flow rate and widen its diameter. The flow speed falls and the pressure rises. Narrow the tube and the opposite happens. The upper surface of the wing works like such a narrowing: the flow speeds up and the pressure falls.
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Gas flows through a tube at a constant flow rate. Where the tube widens, the speed falls and the pressure rises; where it narrows, the opposite happens.
In practiceThe same amount of air passes through every cross-section, so in the narrow part the air has to run faster, and it presses on the walls less.
Over the curved upper surface the flow is squeezed, as in a narrowing of the tube: it speeds up, and the pressure above the wing falls.
In practiceThis is the same suction on top that makes the main part of the lift.
From the section text: the tube experiment and the top of the wing as a narrowing. The particles move so that the same amount of air passes through every cross-section.
Where does a soft wing get its profile? There are no rigid parts inside: no spars, no hard skin. The wing is sewn from airtight fabric, the upper and lower surfaces are joined by ribs (internal walls), and along the leading edge run the cell openings. In flight the oncoming air enters through them and inflates the cells from inside. This overpressure holds the shape: the wing works like an air mattress, except that the headwind is the pump. The practical conclusion: as long as the wing is moving fast enough, it is “rigid”. If the angle of attack drops, the pressure stops holding the shape, and the wing collapses.
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There are no rigid parts inside: the top and bottom are joined by ribs, and along the leading edge run the cell openings. The oncoming flow enters through them and inflates the cells from inside.
In practiceBefore launch the wing lies like a rag; only the air that has entered the openings gives it its shape.
The overpressure inside holds the shape: the wing works like an air mattress, except that the headwind is the pump.
In practiceAs long as the wing is moving fast enough, it is “rigid” and holds its profile.
If the angle of attack drops, the flow stops entering the openings and pressing from inside: the pressure no longer holds the shape, and the wing collapses.
In practiceThat is why the wing is especially vulnerable at a low angle of attack (for example, after a sharp surge): watch it and keep pressure in the canopy.
From the section text: ribs, cell openings, the oncoming flow inflating the cells, the “air mattress” and the collapse at a low angle of attack. The collapse is drawn in a simplified way.
Now let us put lift into numbers. The formula is short: Y = Cy · (ρ · V² ÷ 2) · S. Let us go through it letter by letter.
The part ρ · V² ÷ 2 is called dynamic pressure. It is the “force of the wind in your face”. Note the square: double the speed and the dynamic pressure grows fourfold. Two practical conclusions follow. First: at low speed the wing holds weakly, and any mistake costs more. Second: the brakes, big ears and all other controls work many times harsher at high speed than at low speed.
A worked example, step by step. All-up weight 100 kilograms, wing area 25 m², speed 36 km/h (that is 10 metres per second). Step one: the weight in newtons is 100 × 9.81 ≈ 981 N. Step two: the dynamic pressure is 1.225 × 10² ÷ 2 = 61 Pa. Step three: the coefficient needed is 981 ÷ (61 × 25) ≈ 0.64. This is a normal working value for a paraglider profile. Work out the same wing at 48 km/h, and the coefficient needed is almost half as much: about 0.36. The wing gets it by lowering its nose: the angle of attack gets smaller.
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Y = Cy · (ρ · V² ÷ 2) · S. S is the wing area, ρ is the air density (1.225 kg/m³ at the ground), V is the speed of the wing relative to the air, Cy is the lift coefficient: it holds the profile shape and the angle of attack.
In practiceCy is measured in a wind tunnel and in flight. The pilot controls it through the angle of attack.
The part ρ · V² ÷ 2 is called dynamic pressure: the “force of the wind in your face”. The speed is squared: double the speed and the dynamic pressure grows fourfold.
In practiceA small gain in speed gives a noticeable gain in dynamic pressure, and in the forces on the wing.
At low speed the wing holds weakly, and any mistake costs more. At high speed the brakes, big ears and other controls work many times harsher.
In practiceSlow flight needs care; fast flight needs smooth, small hand movements.
100 kg is ≈ 981 N. At 36 km/h (10 m/s) the dynamic pressure is 1.225 × 10² ÷ 2 ≈ 61 Pa. The coefficient needed: 981 ÷ (61 × 25) ≈ 0.64.
In practice0.64 is a normal working value for a paraglider profile.
At 48 km/h the dynamic pressure is ≈ 109 Pa, and the coefficient needed is almost half as much: about 0.36.
In practiceThe wing gets it by lowering its nose: the angle of attack gets smaller.
From the section text: the formula Y = Cy · (ρ · V² ÷ 2) · S, dynamic pressure and the worked example. Force arrows are not to scale.
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Suction on top and overpressure below: the pressure difference pushes the wing up.
In practiceThis is the language that works at the exam.
The wing throws air down (this is the downwash behind the wing), and the air pushes the wing up with the same force.
In practiceThat is why the air behind the wing moves down: it is the trace of the lift at work.
There is a bound vortex around the profile. Add it to the oncoming flow and the flow on top becomes faster, below slower. Zhukovsky’s theorem gives the lift through the strength of the vortex.
In practiceThere is no point arguing which language is the “real” one: it is one equation written from three sides.
From “A detail for pros”: three descriptions of lift: pressures, Newton, circulation. The pictures are qualitative.
The angle of attack is the angle between the chord of the profile and the oncoming flow. It is not the angle to the horizon and not the angle to the slope. It is measured from the flow, and in a glide the flow comes from ahead and below.
The angle of attack is the only thing the pilot controls directly. Speed, sink and glide ratio follow from it as its results. There are three tools:
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The angle of attack is the angle between the chord of the profile and the oncoming flow. In a glide the flow comes from ahead and below.
In practiceIt is the only thing the pilot controls directly: speed, sink and glide ratio follow from it.
The angle of attack is measured not from the horizon and not from the slope, but from the flow.
In practiceYou can see the wing’s tilt to the horizon by eye, but that is a different angle: pitch. The flow is what counts.
The brakes pull the trailing edge down: the angle of attack grows, the speed falls, the drag grows.
In practiceThe deeper the brakes, the closer the wing is to a stall: the working margin is narrow.
The trimmers let the rear risers out or pull them in and set the base angle of attack.
In practiceThis is the “default” setting: from it you then work with the brakes and the speed bar.
The speed bar pulls the front risers in and the leading edge goes down: the angle of attack gets smaller, the speed grows.
In practiceAt a small angle of attack the wing is faster, but it holds its shape less firmly: use the speed bar in calm air.
From the section text: what the angle of attack is and the pilot’s three tools. The angles in the picture are drawn larger so you can see them.
Learn this by heart: as the angle of attack increases, the horizontal speed of the glider falls. The aerodynamic drag of the wing grows, the wing seems to rear up and moves forward more slowly. You cannot increase the angle of attack without limit. Past a critical value the flow separates from the upper surface and lift drops sharply: this is a stall.
How wide is the working range? It is narrow. The notional zero is full speed bar. Above it comes the trim setting, then best glide, then minimum sink, and somewhere past fifteen degrees the flow separates. The exact critical angle is a property of the particular profile, and it is not written in the wing’s data sheet. What matters is this: your whole working margin fits into about fifteen degrees. Instruments do not show this angle. The pilot judges it indirectly.
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As the angle of attack increases, the horizontal speed of the glider falls: the drag grows, the wing seems to rear up and moves forward more slowly.
In practiceLearn this by heart: deeper brakes mean slower flight, and the critical angle gets closer.
You cannot increase the angle of attack without limit. Past the critical value the flow separates from the upper surface and lift drops sharply: that is a stall.
In practiceA stall is not “slow”, it is “the wing has stopped flying”. Go near it only smoothly and with a margin.
The notional zero is full speed bar, then comes the trim setting, best glide, minimum sink, and somewhere past fifteen degrees the stall. Your whole working margin is about 15°.
In practiceInstruments do not show the angle of attack, and the critical angle is not in the data sheet. The pilot judges it indirectly: that is the next diagram.
From the section text: “learn this by heart”, the stall past the critical angle and the working range. The places of the modes on the scale show their order, not degrees: the exact critical angle is a property of the profile and is not written in the wing’s data sheet.
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The pressure in the brakes grows: the angle of attack grows.
In practiceKeep a light, constant contact in your hands: this way you are the first to feel where the angle of attack is going.
The lines whistle louder: the angle of attack fell, the speed grew. It went quiet: the speed is gone.
In practiceSilence in flight is not calm, it is a signal: the wing is slowing down.
Pressed into the harness: the wing is going back. Weightless: the wing is running ahead.
In practiceYour body feels it before your eyes do: weightlessness is a reason to hold the wing back at once.
Wing behind you: the angle of attack is big. Wing ahead of you: the angle of attack is small.
In practiceA look up at the canopy is a quick check, but in turbulence your body and hands are faster.
From the list in the section: four indirect signs of the angle of attack. Instruments do not show it.
The main thing a beginner must understand: the angle of attack changes even when your hands do not move. The air itself changes it. The wing flies into rising air: the flow comes from below, and the angle of attack grows at once. The wing comes out into sinking air: the angle of attack falls.
A worked example, step by step. You are flying at 10 metres per second. The wing enters rising air of 2 metres per second. Step one: find the ratio of the vertical addition to the speed: 2 ÷ 10 = 0.2. Step two: take the arctangent: that is about 11 degrees. That is how much the angle of attack gained in a fraction of a second while you did nothing. With a working margin of about fifteen degrees, this is a huge amount. That is why air with thermals loads the wing so much, and why a wind shear at the edge of a thermal can stall it without any help from your hands.
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The wing has flown into rising air: the air comes from below, the oncoming flow turns upward, and the angle of attack grows at once. Your hands did not move.
In practiceEntering a thermal feels like a jerk backward and more pressure in the brakes: the wing slows down and goes behind you. That is the bigger angle of attack.
The wing has come out into sinking air: the air comes flatter, from above, and the angle of attack falls.
In practiceThe wing goes ahead, the brakes go soft, the harness feels lighter. A small angle of attack is closer to a collapse: keep light contact with the brakes.
Speed 10 m/s, rising air 2 m/s. Step one: 2 ÷ 10 = 0.2. Step two: the arctangent of 0.2 is about 11 degrees.
In practiceThat is how much the angle of attack gains in a fraction of a second while you do nothing. Stronger air or a slower wing: the gain is even bigger.
The whole working range is about 15°. On trim, a gain of 11° takes the wing to the edge of a stall; with the brakes pulled, it takes it past that edge.
In practiceThat is why air with thermals loads the wing so much, and a wind shear at the edge of a thermal can stall it with no help from your hands. In turbulence do not hold the brakes deep: keep a margin.
From the section text: the air itself changes the angle of attack, the worked example with 2 and 10 m/s, a working margin of about 15°. In diagrams 1–2 the angles are drawn larger so you can see them, the triangle in diagram 3 is to scale.
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Pitch is the tilt of the wing to the horizon, you can see it by eye. The angle of attack is measured from the oncoming flow, and in turbulent air the flow comes from anywhere. The wing can sit level with the horizon and be past the critical angle, if strong rising air hits it from below.
In practice“By eye it all looked fine” means nothing. Watch the pressure in the brakes: the pressure grows, the angle of attack grows.
The flow came from below, the angle of attack jumped up, the speed fell, the wing slows down and drops behind. Instinct says pull, “to hold it”: that adds a few more degrees to an angle of attack that is already too big, and gives a stall in perfect weather.
In practiceLet the brakes go fully, with a short move up: the wing speeds up and comes back. When it catches up with you, it can surge forward: meet it with smooth braking.
When entering a thermal, a wing of any class goes behind you and then catches up with the pilot. The higher the class, the bigger this swing: EN A damps it almost by itself, EN B gives a small surge, EN C and D surge clearly and sharply.
In practiceOn an A wing, the wing fixes much of your pitch mistake for you. On C and D, pitch control is your constant work: hold the wing back in a surge, let it go when the wing goes back. Choose the class by your skill, not by glide ratio numbers.
From the section text: a detail for pros (pitch and angle of attack) and a case review of entering a strong thermal. The angles are drawn larger so you can see them.
All the school’s terms are in the glossary.
Only two forces act on a flying paraglider. The first is weight: the pilot, the harness and the wing. The second is the total aerodynamic force: everything the air does to the aircraft. The total aerodynamic force is split into two parts relative to the oncoming flow:
So the total aerodynamic force is the vector sum of lift and drag. These are not three different forces but one force and its two projections.
The aircraft flies steadily and in a straight line, without acceleration, when the total aerodynamic force is equal in size to the weight and points against it. An unpowered aircraft can have this balance only while descending. Part of the weight goes into overcoming drag: you pay for forward motion with height.
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Only two forces act on a flying paraglider: weight (the pilot, the harness and the wing) and the total aerodynamic force, which is everything the air does to the aircraft.
In practiceIn steady flight they are equal in size and point against each other: the wing above you, the weight below it, on one vertical line.
The total aerodynamic force is split relative to the oncoming flow: lift is perpendicular to the flow, drag points exactly against the motion.
In practiceIn a glide the flow comes from ahead and from below, so lift tilts slightly forward. Its horizontal part is what balances the drag.
The total aerodynamic force is the vector sum of lift and drag: put one arrow at the end of the other and you get the total force.
In practiceThese are not three different forces but one force and its two projections. At the exam, do not add them up as three separate forces.
Steady flight means the total aerodynamic force is equal in size to the weight and points against it. An unpowered aircraft can have this balance only while descending.
In practiceTry to fly level: nothing opposes the drag, and the speed drops. You pay for forward motion with height.
Officially the balance is stated as lift equal to weight. Strictly, in a glide lift equals the weight multiplied by the cosine of the glide angle, and it is the total aerodynamic force that equals the weight.
In practiceAt a glide ratio of 8–10 the difference is a fraction of a per cent. At the exam, the wording “lift equals weight” counts as correct.
From the lesson: two forces, splitting the total aerodynamic force, balance in a descent, the note on the cosine of the glide angle. In diagrams 1–4 the glide angle is drawn larger for clarity.
Can lift point towards the ground? In normal flight, no. A paraglider does not fly canopy-down, and lift always points away from the ground, upwards. In a turn it tilts together with the wing, but it does not turn downwards. Descending and sinking air change nothing here: you lose height, but lift still points upwards.
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In normal flight lift always points away from the ground, upwards: a paraglider does not fly canopy-down.
In practiceLift is perpendicular to the flow and “grows” upwards out of the canopy: as long as the canopy is above you, it points at the sky.
In a turn lift tilts together with the wing, but it does not turn downwards.
In practiceIts vertical part still holds you up, and its sideways part pulls you towards the centre of the turn. The steeper the bank, the smaller the vertical part: that is why in a steep turn the wing is loaded more and the sink rate grows.
Descending and sinking air change nothing: height goes, and lift still points upwards.
In practiceThe paraglider glides inside a mass of air that is moving down: relative to the air everything is as usual, the whole mass is just going down with you. The way out is to leave it, not to “pull the wing up”.
From the lesson: can lift point towards the ground: in straight flight, in a turn and in sinking air.
The pilot as a pendulum. You hang on 6–8 metres of lines under the wing. This is a classic pendulum: the centre of gravity (you) swings below the point where the aerodynamic force acts (the wing). The pendulum gives stability: the system brings you back under the wing by itself. It also causes pitch oscillation: the wing goes forward, the pilot lags behind, then the wing slows down and goes back. Damping this oscillation is the pilot’s direct job.
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You hang on 6–8 metres of lines under the wing. The centre of gravity (you) swings below the point where the aerodynamic force acts (the wing).
In practiceEverything a paraglider does in pitch and roll is easy to understand through this pendulum: long lines and a heavy load at the bottom.
The pendulum gives stability: if you are pushed aside, the system brings you back under the wing by itself.
In practiceThat is why a paraglider forgives a lot: put your hands up and it levels out by itself. But only if the wing is intact and above your head.
The same pendulum causes the swing: the wing goes forward, the pilot lags behind, then the wing slows down and goes back.
In practiceDamping this swing is the pilot’s direct job: hold the wing back when it goes forward, let it go when it goes back. How to do it is in the next sections.
From the lesson: a pilot on 6–8 m of lines is a pendulum; stability and pitch oscillation. The swing is drawn larger for clarity.
Resolve the balance along the axes and you get numbers. Call the glide angle θ: the angle between the flight path and the horizon. Then lift equals weight × cos θ, and drag equals weight × sin θ. From this comes a neat result: tan θ = 1 ÷ glide ratio.
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Call the glide angle θ: the angle between the flight path and the horizon.
In practiceOn a good wing it is small, about 6°. In the diagram the angle is drawn larger so that you can see it.
The weight equals the total aerodynamic force. Resolve it along two axes: along the flow and across it. Lift = weight × cos θ, drag = weight × sin θ.
In practiceThe force triangle has a right angle: the total force is the hypotenuse, lift and drag are the two short sides, and the angle between the total force and lift is θ.
The ratio of drag to lift is tan θ. The flight path triangle has the same shape: height ÷ distance. From this comes a neat result: tan θ = 1 ÷ glide ratio.
In practiceGlide ratio is how many metres forward you fly for each metre of height. Know the glide ratio and you know the angle, and the other way round.
From the lesson: glide angle θ, lift = weight × cos θ, drag = weight × sin θ, tan θ = 1 ÷ glide ratio. The angle θ is drawn larger for clarity.
A worked example, step by step. Glide ratio 9. Step one: tan θ = 1 ÷ 9 = 0.111. Step two: θ ≈ 6.3 degrees: that is how flat your path is. Step three: cos 6.3° = 0.994, so lift is 99.4 % of the weight. Step four: sin 6.3° = 0.110, so drag is about 11 % of the weight. At an all-up weight of 100 kilograms that is about 108 newtons, that is, “eleven kilograms” of constant braking. Your height pays for it.
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Glide ratio 9. Step one: tan θ = 1 ÷ 9 = 0.111. Step two: θ ≈ 6.3 degrees: that is how flat your path is.
In practiceFor every metre of height, 9 metres forward. From the side this looks almost like level flight.
Step three: cos 6.3° = 0.994, so lift is 99.4 % of the weight.
In practiceThat is why at the exam they say “lift equals weight”: the difference is a fraction of a per cent.
Step four: sin 6.3° = 0.110, so drag is about 11 % of the weight. At an all-up weight of 100 kg that is about 108 newtons, “eleven kilograms” of constant braking.
In practiceHeight pays for it: 9 metres forward, one metre down, and so on for the whole flight, until there is rising air.
The higher the class, the higher the glide ratio and the flatter the path: EN A about 8, B 9, C 10, D about 10.5. The glide angle and the “braking” get smaller from class to class.
In practiceFrom 1000 m in calm air the difference between A and D is about two and a half kilometres. But you pay for it with a more demanding wing: the higher the class, the more actively you must pilot.
From the lesson: a step-by-step worked example for glide ratio 9. Classes: the school’s approximate figures (as on the class polar in the cross-country course). In diagrams 1 and 4 height is stretched relative to distance so that the angle is visible.
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The total aerodynamic force acts at the centre of pressure, on the wing. The weight acts at the centre of gravity, roughly at the level of the pilot’s stomach. There are six to eight metres between them.
In practiceIn calm flight both forces lie on one vertical line, and nothing rotates the system.
Any mismatch between the lines of action of the two forces creates a moment, and the system starts to rotate. The whole mechanics of a paraglider is a story about the lever arm between two points.
In practiceA gust, braking, the pilot leaning: all of these shift the lines of the forces. A long arm of six to eight metres makes even a small shift noticeable.
A wing without a pilot is poorly stable. What makes it stable is a load hung far below.
In practiceThat is why you feel the paraglider with your body: you are the very load that brings the system back. Working with your body and the brakes is working with this lever arm.
From the lesson: a detail for pros: centre of pressure and centre of gravity, the lever arm between them, the moment. Deflections are drawn larger for clarity.
A paraglider is stable not because it is clever, but because that is how its geometry works. Let us take it layer by layer.
Layer one: the pendulum. The aerodynamic force acts in the canopy. The weight acts in the pilot, six to eight metres lower. Move the pilot to the side, and gravity at once pulls the pilot back under the wing. This is a restoring moment, and the longer the lines, the stronger it is. That is why a paraglider forgives rough mistakes: the system itself tries to return to “pilot straight under the wing”.
Drag the diagram sideways to see all of it.
The aerodynamic force acts in the canopy. The weight acts in the pilot, six to eight metres lower. Two forces set far apart in height: that is the pendulum.
In practicePicture a weight on a long rope: however you push it, it comes back under the point it hangs from. Under the canopy, that weight is you.
Move the pilot to the side, and the weight ends up off to the side of the canopy: an arm appears. The arm times the weight is the restoring moment: it pulls the pilot back under the wing.
In practiceThat is why a paraglider forgives rough mistakes: a sharp weight shift, a clumsy movement in the harness. The system returns by itself to “pilot straight under the wing”, without your help.
For the same swing, the longer the lines, the bigger the arm. So the restoring moment is stronger too.
In practiceThe long suspension is the main source of a paraglider’s stability. A wing without a pilot holds itself badly: what makes the system stable is the weight hanging far below.
Based on the section text, layer one: the force of the air acts in the canopy, the weight in the pilot 6–8 m lower; the restoring moment grows with the length of the lines. Swings are enlarged for clarity.
Layer two: two pendulums. Specialists tell them apart like this. Upper pendulum: the wing swings relative to the pilot. A gust hits the canopy, and the canopy moves forward or to the side, while the pilot stays in place by inertia. Lower pendulum: the pilot comes back under the wing under their own weight. Because the canopy and the pilot are far apart, the lower pendulum is stronger. That is why, after a shake-up, the system in the end settles by itself.
Drag the diagram sideways to see all of it.
A gust hit the canopy, and the canopy moved forward or to the side. The pilot is heavier and stayed in place by inertia. The wing swung relative to you.
In practiceThis is what you see above your head after a shake-up: the canopy “runs away” forward or tips to the side. No need to panic yet: this is the first half of the swing, and the second half comes next.
Now your weight does the work. It hangs on long lines and pulls you back under the wing, to where the aerodynamic force acts.
In practiceIn the harness it feels like a soft “catch”: your body passes under the canopy by itself. You do not need to help this movement with your hands: the system does it without you.
The canopy is light, and almost all the mass of the system is you, six to eight metres lower. So the lower pendulum is stronger than the upper one, and after a shake-up the swings get smaller and smaller.
In practiceThe main practical lesson: in most shake-ups it is enough not to get in the way. Sharp hand movements stop the system from finding its balance; they do not help it.
Based on the section text, layer two: the upper pendulum is the canopy swinging relative to the pilot, the lower one is the pilot coming back under the wing by their own weight; because of the large distance the lower one is stronger. Angles and damping are shown qualitatively, not calculated.
Layer three: roll stability. In flight the canopy is bent into a curve: this is the arc. Tilt such a wing to the side, and it starts to slip sideways towards the low side. The air comes from the side and pushes on the ends of the canopy: because of the arc they stand almost vertical and work like a keel. This side force acts high above you, while the weight hangs below, and so the system is turned back out of the roll. The arc works at once, even before the pendulum comes in.
Drag the diagram sideways to see all of it.
Tilt the wing to the side, and the force from the canopy tilts with it. Part of it now points sideways, and the whole system starts to slip towards the lowered side of the wing. For the wing this means one thing: the air now comes not only from the front but also from the side.
In practiceThis happens from a gust into one wingtip, a sharp weight shift or an uneven hand on the brake. By itself it is not scary: this very side flow is what starts the return.
Because of the curve, the ends of the canopy stand almost vertical, like the keel of a boat. The side flow pushes on them, and this force acts high above you. The weight hangs below, on 6–8 m of lines. The force on top pushes the canopy one way, the weight below holds the pilot, and so the system is turned back out of the roll.
In practiceThe more the canopy is curved, the bigger the “keel” and the more willingly the wing levels itself. The price is area: the curved tips carry less, hence the difference between the flat area and the projected area in the wing’s data sheet.
The side force appears the same moment the sideslip starts. The return begins before you can do anything with your hands, even before the pendulum comes in.
In practiceThat is why you do not need to “catch” a random roll with the brakes. While you are reacting, the wing is already levelling, and a late correction will push it the other way. Keep your hands soft and let the system level itself.
Based on the section text, layer three: the arc, sideslip towards the low side, the side force on the canopy tips high above the pilot, the weight below. Roll angles and the curve of the canopy are enlarged for clarity; the roll record is qualitative, with no time scale.
Layer four: pitch stability. The wing has run forward: the angle of attack drops, the lift drops, and the wing falls back by itself. The wing has gone back: the angle of attack grows, the drag grows, the wing slows down and comes back. The system catches itself. The price for this is oscillation: every return overshoots the balance point.
Drag the diagram sideways to see all of it.
The wing moved forward over you, its nose went down. The angle of attack dropped, the lift dropped, and the wing starts to fall back, to its place over your head.
In practiceAbove your head this looks like a canopy that has “dived” forward. A big dive is already a surge: that is the next section. A small one the wing calms by itself.
The wing fell behind, its nose went up. The angle of attack grew, the drag grew, the wing slowed down and came forward again, to its place over you.
In practiceThis happens when you enter a strong thermal: the canopy “sits back”, and for a moment you swing out in front. The wing will come back by itself, but near the top edge of the range a stall is close, so do not add brake here.
The system catches itself, but does not stop at once: every return overshoots the balance, and the wing swings forward and back until the swings die out.
In practiceThe wing will always come back. The question is how many times it overshoots the balance on the way, and whether it touches the edge of the working range. The “Damping” diagram below is about this.
Based on the section text, layer four: wing ahead: angle of attack and lift drop, the wing falls back; wing behind: angle of attack and drag grow, the wing slows down; every return overshoots the balance. Angles are enlarged for clarity, not calculated.
Damping is what calms the oscillations down. They are calmed by air resistance and by the change in angle of attack as the wing rotates. In roll, damping is good: the arc and the large area work at once. In pitch it is weak, the swinging dies out slowly, and all this time the wing wanders in angle of attack from almost zero to close to critical. Both edges are dangerous: a collapse at the bottom, a stall at the top.
Drag the diagram sideways to see all of it.
Oscillations are calmed by air resistance and by the change in angle of attack as the wing rotates. In roll this works well: the arc and the large canopy area resist the swinging at once, and a swing dies out in one or two goes.
In practiceThat is why in rough air you almost never need to step in on roll: by the time you get ready to do something, the wing has already levelled itself.
In pitch, damping is weak. The wing swings forward and back for a long time, swing after swing, and all this time the angle of attack wanders.
In practiceThat is exactly why pitch is the axis where your hands are really needed: brake gently when the wing goes forward, and let up when it goes back.
The whole working range of angle of attack is about 15° (section “Angle of attack”). Until the pitch swinging dies out, the wing wanders from almost zero angle to close to critical.
In practiceBoth edges are dangerous, and they are different: a collapse at the bottom, a stall at the top. A big swing is walking along the edge of the corridor, so you calm it straight away and do not wait for it to pass by itself.
An EN A wing is designed to calm the swinging by itself. The higher the class, the less of this “built-in” stability: EN C and D wings swing longer and harder after the same shake-up.
In practiceOn a beginner wing you can let your hands go and wait. On EN C and D you cannot wait: the pilot calms the swinging with active piloting, and this is part of the skill of flying such a wing.
Based on the section text: damping is good in roll and weak in pitch; the working range of angle of attack is ≈ 15° (section “Angle of attack”), with a collapse at the bottom and a stall at the top. Classes follow the school canon, swing sizes as in the section “Angle of attack”. Curves are qualitative, not calculated.
Drag the diagram sideways to see all of it.
The pilot sees a swing and answers with the hands, but about half a period late. The answer comes in step with the movement, not against it: each movement adds energy, and the next swing is bigger than the one before.
In practiceLike a playground swing: if you push in step, it goes higher. Hands that come late push the wing exactly in step.
Once you let go of the brakes, the pumping stops. Then the wing’s own damping does the work: the swings get smaller and die out.
In practiceThe cure goes against your instinct: hands up, and wait two or three swings. Here doing nothing is better than doing something at the wrong time. When the wing has calmed down, you can gently take it in hand again.
The main sign of pilot-induced oscillation: you are working hard with your hands, yet the amplitude grows with every swing. Normal work calms the swinging; pilot-induced oscillation builds it up.
In practiceIf you are “working” but it swings more and more, stop. Let your hands go, let the wing calm down, and start again, softer and earlier: meet the wing at the start of its movement, do not chase it.
Based on the section text, “A detail for pros”: the reaction comes half a period late and moves in phase with the motion; the amplitude grows from swing to swing; the cure is to take your hands away and let the system calm down by itself. Curves are qualitative, not calculated.
All the school’s terms are in the glossary.
A surge is the wing moving forward relative to the pilot. It is the most common and the most dangerous phase of a pitch oscillation: it is on the forward run that the angle of attack falls to zero and below, and the wing collapses.
Drag the diagram sideways to see all of it.
Normally the wing hangs straight above you. In a surge it goes forward, like a swing that has passed its lowest point and flies up on the other side. While the wing rushes forward, its nose drops and the angle of attack falls: to zero and even below.
In practiceA surge is the most common phase of a pitch oscillation: after a sharp release of the brakes, when leaving a thermal, in turbulence. The surge itself is not yet an accident. The danger is what can happen at its extreme point.
The canopy keeps its shape only with the air that comes in through the openings at the front. When the angle of attack goes below zero, the air hits the nose from above, not from below. The nose crumples and tucks under: this is a frontal collapse.
In practiceSo you do not wait for a surge, you damp it: brake the wing briefly at its furthest forward point. Exactly how is shown step by step later in this section.
From the section text: a surge is the wing moving forward relative to the pilot; on the forward run the angle of attack falls to zero and below, and the wing collapses. Angles and the angle-of-attack scale are qualitative, enlarged for clarity.
Let us go through the full cycle phase by phase, as it is described in the controlled pitch oscillation exercise.
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The pilot pulls both brakes down. The wing slows down, the angle of attack and the drag grow, and the wing lags behind: it goes back, behind your head. The pilot is still flying at the old speed and swings forward by inertia.
In practiceIn free flight the same thing happens when you enter a thermal: the rising air has lifted the wing and it has gone behind your back. This is not dangerous by itself; what is dangerous is what comes next.
The speed falls almost to the minimum, the wing hangs behind your back, the angle of attack is near the top edge, near the stall. In the exercise this phase is held for two or three seconds.
In practiceFrom here the stall is not far, so the exercise is done only during SIV over water, with an instructor on the radio. But it is from this point that the wing will then speed up into a surge.
The hands go up quickly. Nothing holds the wing any more, and it speeds up by itself, like a dog let off the leash. It passes over your head and starts to overtake the pilot.
In practiceThe sharper you let the brakes go, the further the wing goes forward and the stronger the surge. In turbulence, do not raise your hands as fast as you pulled.
The wing goes far ahead, its nose is down. Here the angle of attack is the smallest in the whole cycle: near the bottom edge, about zero.
In practiceThis is the most dangerous phase of the whole oscillation: this is where a frontal collapse happens. You recognise it at once: the brakes go empty, your body feels light, the wind noise rises.
At the furthest forward point the pilot briefly pulls both brakes. The wing slows down and comes back, the oscillation dies down, the wing is overhead again.
In practiceThe key here is the moment: pull exactly when the wing is in front, and let go at once. Too early or too late, and the same movement makes the wing swing even more.
From the section text: the five phases of a controlled pitch oscillation. Wing position, speed and angle of attack are shown qualitatively and enlarged for clarity. The exercise is done only during SIV over water, with an instructor.
Now the same thing through the pilot’s eyes in real flight. There are three phases: recognise, stop, release.
Drag the diagram sideways to see all of it.
You recognise a surge with your body, not your eyes. The brakes suddenly go empty: the pressure in them is gone. Your body feels light, like on a swing at its highest point. The wind noise rises because the wing is speeding up. The canopy moves forward out of your field of view.
In practiceAll four signs come within one second. Recognise even one of them, and your hands are already ready for the next step.
One quick movement down with both brakes. The wing slows down and stops going forward. The depth of the movement depends on the strength of the surge: the wing goes forward sharply, pull deeper; only a little, pull less.
In practiceBoth hands pull the same: one brake will turn the wing, not stop it. The travel is for one time only: it is a short pulse, not a long pull.
Right after the pulse the hands go up. Not as fast as you pulled, but always all the way. The wing gains speed and flies overhead again.
In practiceHolding the brakes down longer than needed is a mistake: the wing will go back and can stall. Let the wing fly.
From the section text: the pilot’s three steps in real flight: recognise, stop, release. The signs, the hand travel and the wing position are shown qualitatively.
The key thing in a surge is timing, not force. The same hand movement at the right second damps the oscillation, and half a second later makes it bigger. Hold the brakes too long and you get a secondary stall. Do not pull enough and you get a collapse. Both results come from the same movement made at the wrong time.
Drag the diagram sideways to see all of it.
The wing has gone forward and stopped for a moment at its furthest point. At exactly this moment the pilot briefly pulls the brakes: the pulse goes against the wing’s movement, and the oscillation dies down at once.
In practiceIt is like a swing: push against it and you stop it, push with it and you make it swing more. The brakes are your push against it.
If you pull when the wing is already going back, the pulse goes with the movement. The wing goes back even further, then surges forward harder, and each swing is bigger than the one before.
In practiceHalf a second is the whole difference between “damped it” and “made it swing”. So you pull exactly at the furthest forward point, not chasing the wing.
Hold the brakes down too long and the wing stops and goes far back, past the top edge: a secondary stall. Do not pull enough and the wing keeps going forward, past the bottom edge: a collapse.
In practiceBoth mistakes are the same movement, made at the wrong time or to the wrong depth. So you damp a surge with a short pulse matched to its strength, and let go at once.
From the section text: in a surge timing matters, not force; half a second later the same movement makes the oscillation bigger; brakes held too long give a secondary stall, not pulled enough give a collapse. The curves are qualitative, not calculated; the stall and collapse zones are schematic.
Drag the diagram sideways to see all of it.
The force with which the brakes slow the wing grows as the square of the speed: it is the same dynamic pressure as in the lift formula. Speed doubled: the same hand movement brakes four times harder.
In practiceA typical mistake of an experienced pilot: damping a surge with the same hand travel they use in a thermal at low speed. On a fast wing this travel brakes several times harder and takes the wing straight into a stall. Match your hand travel to the speed, not to habit.
The rising air has ended, the angle of attack has dropped, the wing speeds up and overtakes you. A few more degrees down and the leading edge will tuck under.
In practiceOne quick movement: both brakes to about shoulder level, exactly at the furthest forward point, and then hands up at once. Pull during the forward run; once the wing has collapsed, it is too late to pull.
On leaving the same thermal, a wing of any class goes forward. The higher the class, the deeper and sharper this surge: EN A damps it almost by itself, EN B moderately, EN C and D surge deep and fast.
In practiceOn EN A the wing will largely forgive a timing mistake. On EN C and D timing and dose decide everything: you must be able to damp a surge before you move to such a wing.
From the section text: a detail for pros (brake effectiveness grows as the square of the speed: the dynamic pressure from the lift formula) and a case review of leaving a strong thermal. The speeds in the first part are an example for the calculation. Classes are qualitative, as in the sections “Angle of attack” and “Pendular stability”.
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