Airspeed, groundspeed and wind

Your wing flies in the air, not over the ground. See how headwind, tailwind and crosswind change your groundspeed, why you launch and land into wind, and why the ground rushing past on a downwind leg must never make you brake.

In this lesson you will

On your first glides down the training hill you fly into a gentle breeze, and the grass slides past slowly. On your first high flight you turn onto the downwind leg of the landing pattern, and suddenly the fields race by underneath you. Nothing about the wing has changed. Only the ground is moving differently.

That difference catches students every season. React to the ground instead of the air, and you can slow a perfectly good wing towards the stall. This lesson separates the two speeds and shows how wind decides where you go and how fast you meet the ground.

The wing only knows the air

Think of the air as a wide, slow river and your wing as a boat on it. Your airspeed is your speed through the air. Your groundspeed is your speed over the ground. The wind is the river’s current: it carries the air, and you with it.

Your hands set the airspeed. With the brakes fully up, a school wing flies at its trim speed, about 37 km/h23 mph on a typical wing¹; check your wing’s manual for its own figure. The wing does not know which way it points over the ground. A steady wind moves the whole block of air, so it changes neither your airspeed nor how fast you sink through the air².

What the wind does change is your groundspeed and your track, the path you actually follow over the ground. Groundspeed is airspeed minus the headwind, or plus the tailwind³.

You have no airspeed instrument on a school wing, so you judge airspeed by feel and sound. As you slow down the wind noise fades and the brake pressure rises⁴.

Headwind, tailwind and crosswind

Take a wing at trim, 37 km/h23 mph, in a 15 km/h9 mph wind¹³:

Into the headwind, you cover the ground at 22 km/h14 mph.
In calm air, at 37 km/h23 mph.
With the tailwind, at 52 km/h32 mph.

Figure: One wing at trim speed, three winds. Watch the dots, one per second: the wing flying into wind creeps, the one flying downwind races, yet all three lose exactly the same height. Try the second variant, where the wind beats the airspeed.

One wing at trim speed, three winds. Watch the dots, one per second: the wing flying into wind creeps, the one flying downwind races, yet all three lose exactly the same height. Try the second variant, where the wind beats the airspeed.

Each second in the air costs the same height whichever way you fly. Into wind each second buys less ground, so your glide over the ground is steeper; downwind it is flatter². The polar lesson shows why you speed up into wind to reach the landing field (LZ).

Crosswind and crabbing

A crosswind blows across your path and carries you sideways with the air. If you point straight at a landmark, you drift off downwind of it. To hold a straight track, point partly into the wind. This is called crabbing (crab): the wing faces one way while you travel another⁵.

To check your track, pick two fixed points on the ground ahead of you, one behind the other, and crab enough to keep them in line⁶. If the near point slides sideways against the far one, you are drifting.

Figure: Holding a track across the wind. Change the wind and watch the crab angle: the more crosswind, the more crab. Make the crosswind stronger than the airspeed and no heading can hold the track.

Holding a track across the wind. Change the wind and watch the crab angle: the more crosswind, the more crab. Make the crosswind stronger than the airspeed and no heading can hold the track.

Two signs that the wind is building, for example along a ridge: you need a bigger and bigger crab angle to hold your line, and your groundspeed along it keeps falling⁷. Into wind, the same building wind shows as slower and slower progress³.

When the wind beats your airspeed

When the headwind equals your airspeed, you hover over one spot. When it is stronger, you go backwards over the ground³. Near a hill that can carry you over the top into the lee side; pilots call it being blown back.

You have little speed in reserve: on school wings full speed bar adds only about 8–11 km/h5–7 mph to trim speed⁸. The wind is also often stronger higher up, because friction with the ground slows it near the surface⁹. That is one reason student wind limits sit far below your airspeed; see student weather limits.

Watch the ground below you. Normally it comes towards you and passes under your feet. If it stops coming towards you, or starts to move away ahead of you, the wind has caught up with your airspeed. Point straight into wind away from the hill as soon as you notice, never turn towards the hill behind you, and land early in front¹⁰. Blown back and cloud suck goes further.

Why we launch and land into wind

The wing needs its flying airspeed before it can carry you. On launch, a headwind supplies part of that airspeed for free, so you need less running speed over the ground¹¹. In nil wind you must run all the way up to flying speed. That is why the forward launch is the technique for nil to light wind, and the reverse launch is used as the wind strengthens¹².

On landing, the same sum works for you. Into wind you touch down at your airspeed minus the wind; downwind, at your airspeed plus the wind. One magazine writer compares a downwind touchdown at about 45 km/h28 mph with about 5 km/h3 mph into wind¹³. Downwind landings are on the list of landing-accident causes¹⁴.

SafePro has early exercises flown close to the landing field and into wind, so you cannot drift out of reach of it, and strictly avoids downwind flying close to the ground¹⁵.

A crosswind on launch makes the wing come up unevenly and pull you off line. On a hillside it also adds turbulence: one school notes that every spur and gully can make rotor when the wind blows across the slope¹⁶. That is why student crosswind limits are strict.

Standards differ How much crosswind students may launch in

Common ground: Everyone launches students as close to straight into wind as possible. SafePro, the international reference, tells students to take off roughly into wind and warns against cross, down, strong or gusty winds; its only crosswind number is at most 45° for a Stage 5 Senior Pilot¹⁷.

USHPA (USA): Recommended limits: P1 foot launches with the wind within 15° of straight up the slope¹⁸; P2 within 25°¹⁹.
BHPA (UK): No numeric student limits are published for paragliding; your school sets them in its training records²⁰.
APPI (international): Crosswind comes in step by step: an inflation with a 30° crosswind at Adventure level, then a launch with at most 45° of crosswind at APPI Pilot level²¹.

Summarised from each body’s published material, which changes over time. Check the current official documents and follow your school.

The downwind-turn illusion

Turn from into wind to downwind in our 15 km/h9 mph wind, and your groundspeed jumps from 22 km/h14 mph to 52 km/h32 mph, more than twice as fast³. Your eyes shout “too fast!”. Your ears and hands say nothing has changed: the wind noise and the brake pressure are exactly as they were, because your airspeed is exactly as it was.

The danger is braking to “slow down”. The brakes cut your airspeed, not the wind’s push, so the wing goes quiet and soft while the ground keeps racing past. Pilots who brake downwind to slow down can stall²². You will meet this first on the downwind leg of the landing pattern, which you fly with height beside the field; ridge pilots meet it on every downwind beat²².

Downwind you also cover ground fast. Near a ridge, the downwind half of a circle can carry you behind the hill or into it²³. Keep turns well away from the ground and the hill; Turns and load factor explains why low turns are a trap of their own.

Myth vs fact

Myth: Turning downwind makes the wing lose airspeed.
Fact: In a steady wind your airspeed is the same whichever way you point. Only your groundspeed changes².

The wing flies in the moving air and never feels the ground. The rushing ground is a picture, not a warning.

Flying with the air, not your eyes

Using the wind instead of fighting it

Before you launch, read the wind’s strength and direction from every clue you have.
Cue Windsock, streamers, trees, and what other wings are doing.
Why Your groundspeed and track in every direction depend on it.
Launch and land into wind.
Cue The windsock streams towards you as you face into wind.
Why You leave and meet the ground at your lowest groundspeed.
In a crosswind, line up two fixed points ahead and crab to keep them in line.
Cue The near point stays in front of the far one.
Why Pointing straight at a target lets the wind drift you downwind of it.
On a downwind leg, keep your hands where they were and let the ground rush past.
Cue Steady wind noise and the same light brake pressure as before the turn.
Why Your airspeed has not changed; braking only takes away your margin above the stall.
Into wind, keep checking that you are still moving forward over the ground.
Cue Landmarks come steadily towards you and pass underneath.
Why If they stop, or start to move away ahead of you, the wind has caught up with your airspeed: move away from the hill and land early.

Common mistakes

Common mistake Braking on the downwind leg

Symptom: The ground looks fast, so you add brake; the wind noise fades and the wing feels soft and slow.
Cause: Judging airspeed by the ground. Your groundspeed rose; your airspeed did not.
Fix: Keep the hands where they were before the turn. Listen to the wind noise and feel the brake pressure²².

Common mistake Pointing at the target in a crosswind

Symptom: You fly straight at the landing field, yet you keep arriving downwind of it and have to turn back into wind low down.
Cause: The crosswind drifts you sideways while the wing points at the field.
Fix: Crab partly into the wind and keep two ground points in line⁶. Plan your approach so the final leg is into wind with height to spare.

Common mistake Turning back into wind too low

Symptom: You find yourself low and heading downwind, so you crank a steep turn to land into wind and arrive swinging and fast.
Cause: A late plan, then a low turn. Below about 20 m70 ft on a downwind heading, more on a smaller, faster wing, you may not finish the turn at all (one magazine writer’s figure)²⁴.
Fix: Plan early so you never need that turn. If it happens anyway, keep the wing level, land straight ahead, flare fully and be ready for a PLF (parachute landing fall), which many schools teach for any landing likely to be hard²⁴²⁵; see the parachute landing fall.

Instructor's note Where wind really can change your airspeed

A steady wind never changes your airspeed. Close to the ground it can, for a moment: as you sink into a weaker headwind, on final or in the turn onto it, the wing loses some airspeed until it speeds up again, and a gust that dies or swings behind you does the same²⁶. It has nothing to do with which way you point at height. The gradient lesson covers it.

Instructor's note Low and downwind: the least-bad choice

Low and still flying downwind, a low turn can hurt you more than a downwind landing: keep the wing level, flare fully and prepare for a PLF²⁴²⁵. Some experienced pilots even choose a fast downwind landing on smooth ground over an into-wind landing on dangerous ground; that is a judgement for later, not a student rule¹³.

Questions students ask

If my airspeed does not change, why does flying downwind feel so different?

Your eyes see the ground race past and expect speed; the wing feels the same. If it really feels different, suspect turbulence or the wind gradient near the ground, not the wind direction.

How do I know my airspeed without an instrument?

Hands up is your reference. As you slow down, the wind noise fades and the brakes get heavier⁴.

Can my GPS tell me if I am too slow?

No. A GPS measures your speed over the ground. Downwind it can show a high speed while your wing is close to the stall.

What should I do if I stop moving forward?

Point straight into wind away from the hill straight away, never turn towards the hill, and land early in front of it¹⁰. Better still, do not launch when the wind is near your limit.

Key points

Airspeed is your speed through the air; groundspeed is your speed over the ground. Wind changes only the second.
Groundspeed is airspeed minus the headwind, or plus the tailwind. When the headwind beats your airspeed you go backwards.
Into wind your glide over the ground is steeper; downwind it is flatter. Your sink rate stays the same.
In a crosswind, crab into the wind and keep two ground points in line.
Launch and land into wind, so you leave and meet the ground at your lowest groundspeed.
Downwind the ground races past, but your airspeed has not changed. Never brake to slow down; judge speed by wind noise and brake pressure.

Ground to Solo is a study aid. Paragliding is learned in person with a qualified instructor at a recognised school; nothing here certifies you to fly.