Flying without an engine is applied physics.

A paraglider wing is two skins of ripstop fabric joined by ribs into dozens of cells. Openings at the leading edge let air in, and that ram-air pressure inflates the cells into an aerofoil: a curved shape, thicker at the front, that turns the oncoming air slightly downward. By Newton's third law, pushing air down pushes the wing up. The same effect also shows up as lower pressure over the top surface than under the bottom (Bernoulli's principle). They are two descriptions of one flow.

The lift equation

Every wing, from a paraglider to a jet, obeys L = ½ × ρ × v² × S × C_L: air density ρ, airspeed v, wing area S, and a lift coefficient C_L set mostly by the angle of attack (the angle between the wing and the oncoming air). The pilot changes C_L with the brakes and the speed bar.

Speed squared: small changes, big effects

Because v is squared, 20% more airspeed means 1.2² = 1.44× the lift at the same angle of attack, and 20% less means only 0.64×. Drag follows the same law. This is why gusts feel so strong, and why a wing that loses airspeed close to the ground loses its lift quickly.

Drag: the cost of making lift

Drag is the force pulling backwards along the flight path. Part is parasitic (lines, pilot, harness, fabric), part is induced (the unavoidable cost of making lift with a finite wing, including the swirling wingtip vortices). In steady glide the pilot's weight is balanced by lift (up) and drag (back), and the glider descends at exactly the angle where they balance. For the reference wing, drag = weight ÷ glide ratio = 981 ÷ 8.5 ≈ 115 N.

The glide ratio (L/D) is how many metres you travel forward for each metre of height lost in still air. It equals lift ÷ drag. Beginner wings are typically quoted somewhere around 8 to 9; high-performance competition wings go well above 10. The sink rate is how fast you descend: airspeed ÷ glide ratio.

The polar curve and the speed bar

Every wing has a "polar": a graph of sink rate against airspeed. Minimum sink comes at a slow speed (best for staying up in weak lift); best glide comes at a slightly faster speed (best for going far in still air). Into a headwind or through sinking air, pilots speed up with the speed bar to get through the bad air faster. They give up a little glide through the air to gain glide over the ground.

If your wing sinks at 1.2 m/s and you're inside air rising at 3 m/s, your vario reads +1.8 m/s. All soaring comes down to this subtraction. The two main lift sources are thermals (heat) and ridge lift (wind on a slope).

Thermals: buoyancy you can ride

Sunlight heats the ground unevenly: dry fields, rock and villages warm faster than forest or water. Air touching a warm patch gets warmer and less dense than the air around it, so it rises (Archimedes again, as with a hot-air balloon). Bubbles or columns break away and climb, often marked by circling birds or, higher up, by a cumulus cloud.

Rising air expands and cools at the dry adiabatic lapse rate: about 9.8 °C per 1,000 m. Its dew point falls more slowly, roughly 2 °C per 1,000 m. When temperature meets dew point, water vapour condenses and a cloud forms. That gives pilots a rule of thumb:

Ridge (dynamic) lift

When wind blows onto a slope, the air has to go up. The upward component near the face is roughly wind speed × sin(slope angle).

Simplified: real lift is strongest just in front of and slightly above the ridge line, and fades with height. Kamshet's evening sea-breeze soaring on the Western Ghats ridges is a classic example (Nirvana Adventures describes "lift bands" as the breeze creeps up the Ghats).

Wing loading is all-up weight divided by wing area. Every certified wing size comes with a weight range in its manual, and flying inside it matters. From the lift equation, if weight goes up, speed must rise as √(weight) to keep the same angle of attack.

Thin air at mountain sites

Air density falls with altitude. In the standard atmosphere it is about 1.225 kg/m³ at sea level and about 0.97 kg/m³ at 2,400 m. To make the same lift, true airspeed rises by √(1.225/0.97) ≈ 1.13.

Hot days make it worse: warm air is less dense, so "density altitude" can be higher than the real altitude. You need a longer, stronger run to launch, and you land faster.

Too much angle of attack: the stall

Lift coefficient rises with angle of attack, but only up to a critical angle. Beyond it the airflow can no longer follow the curved top surface, separates, and lift collapses. On a paraglider this usually comes from too much brake for too long. The wing slows, falls back behind the pilot, and recovery needs exactly the right, trained response. A stall happens at a critical angle, not at a fixed speed you can read.

Too little angle of attack: collapses

A paraglider holds its shape only by internal air pressure. If turbulence suddenly reduces the angle of attack (for example a strong gust from above, or flying fast into sinking air), part of the leading edge can fold under: an asymmetric or frontal collapse. Modern wings are tested to reopen by themselves. Under EN 926-2, beginner wings are class A (most passive); B, C and D demand progressively more skill.

Turning costs height: load factor

In a banked turn the lift must hold you up and pull you round the circle, so the wing has to make more lift than your weight. Load factor n = 1 ÷ cos(bank).

Stall speed scales with √n, and sink at the same lift coefficient scales with n^1.5. A spiral dive, used deliberately to lose height fast, can reach several g and heavy sink rates. That's why it's taught under supervision and why pilots must know how to exit it.

The safety layers

SIV (Simulation d'Incident en Vol) courses teach collapses, stalls and recoveries over water with an instructor on the radio and a rescue boat below. Pilots also carry an emergency (reserve) parachute; APPI's rules require a certified reserve on high flights from APPI 2 onward. Himachal Pradesh's 2025 amendment to its Aero Sports Rules requires tandem pilots to complete a safety (SIV) course; already-registered tandem pilots were given until 31 August 2026 (news reports; see sources.md).

Wind gradient near the ground

Friction slows the lowest layers of air, so wind is usually weaker near the ground than at take-off height. On final approach you descend into slower-moving air and your headwind component drops. Keep a little extra speed near the ground and don't hang on deep brake until the flare.

Venturi, rotor and gusts

Wind squeezed through a gap or over a pass speeds up (continuity: same flow through a smaller area). Obstacles (trees, buildings, ridges) leave turbulent rotor downwind. A forecast "average" wind of 12 km/h with gusts to 30 km/h is a very different day from a steady 12.

Storms: cumulonimbus

A cumulus that keeps growing vertically can become a thunderstorm. Its updraft can be strong enough to carry a paraglider into the cloud ("cloud suck"), and its downdraft hits the ground as a gust front that spreads outward. When towers start building, pilots land early.

India's flying seasons are monsoon-shaped