Four engines.
The sun heats the ground, the ground heats the air, and a bubble or column breaks away. Available almost everywhere, gone by evening, and the only one that needs no terrain at all.
Wind meets a slope and has nowhere to go but up. Works from the first hour of the day to the last, works in cloud shadow, and stops the instant the wind drops or backs off the hill.
A stable airmass pushed over a ridge oscillates downstream like water over a rock. Smooth, enormous, and the only lift in gliding that routinely reaches the flight levels.
Two airmasses meet and the loser goes up. Sea breeze fronts, valley convergences and the line where two thermal regimes collide — narrow, long, and worth flying straight down.
The hill does the work.
Ridge lift is the simplest idea in soaring and the least forgiving in practice. Air arriving at a slope must go over it, and a glider parked in that rising layer stays up as long as the wind keeps blowing. The band of usable lift extends from somewhere below the crest to a height that grows with the wind and with the size of the hill — and it is upwind of the crest, which is exactly the place a nervous pilot instinctively avoids.
The rules that keep ridge pilots alive are unglamorous and absolute: fly along the hill, never turn away from it, and always keep a way out that does not involve crossing to the lee side at low height. The lee side is where the same wind that was holding you up becomes sink, curl and rotor. And the whole system has a single point of failure — the wind. When it drops or backs a few degrees, the lift does not fade gently; it goes, and it takes your height band with it.
Push a stable airmass over a ridge.
Start with a light wind and watch the streamlines stay flat: below roughly 8 m/s at ridge height there is nothing to oscillate. Bring the wind up and the train appears — and note what happens to the wavelength, which stretches with wind speed and shortens as the layer gets more stable. That single number decides where you go looking: the first crest sits about half a wavelength downwind of the ridge, which on a strong day can be five kilometres behind a hill you have not even reached yet.
Wave: the smoothest lift and the roughest way in.
Mountain wave needs three things at once: a wind roughly perpendicular to the ridge, a wind that increases with height without changing direction much, and a stable layer for the disturbance to oscillate in. Get all three and the airmass behaves like water flowing over a stone — a standing train of crests and troughs, fixed relative to the ground, each crest a band of lift that can be glass-smooth and run for tens of kilometres.
Underneath that elegance is the rotor: a churning, turbulent roll under the first crest where the flow separates. It is the most violent air a glider pilot meets in normal operations, and it is unavoidable, because the classic way into wave is to climb through it. That is the honest trade — the smoothest lift in soaring is guarded by the roughest layer in soaring, and every wave briefing spends more time on the rotor than on the climb.
The instruments earn their place here. In laminar wave the vario is calm and the numbers are trustworthy in a way they never are in a thermal, so the climb is flown on the readout: hold the crest by watching the wind, the netto and the ground track, not by feel. And because wave climbs run out of airspace long before they run out of lift, this is the article where the airspace warning you configured properly stops being theoretical.
Convergence: a line, not a place.
Where two airmasses meet, one has to rise. A sea breeze pushing inland against the day's wind, cool valley air meeting warm plain air, the boundary between two thermal regimes over different ground — all of them make lines of lift, sometimes marked by a row of clouds and sometimes completely invisible.
The flying technique is the opposite of thermalling. The lift is long and narrow rather than round and deep, so the answer is to fly straight along it and let the height come, resisting the trained instinct to circle at the first beep. When the average over a straight run beats what you would climb turning, you have found a convergence and you should stay on it — a good line will carry a glider a hundred kilometres without a single circle.
Reading which engine is running.
The signatures are distinct once you know them. Thermal: lift in lumps, best when circling, dies in the evening. Ridge: lift that depends on your position relative to a slope and is indifferent to the sun. Wave: lift that stays in the same place over the ground while you fly through it in a straight line, with a vario that is unnaturally smooth. Convergence: lift along a line you can follow, often with a wind that changes direction as you cross it.
And the days that reward the most are the mixed ones — thermals to reach a ridge, the ridge to reach a convergence, and the convergence to reach a wave that takes you higher than the whole plan assumed. That is not luck. It is the recognition, made early enough to act on.
Wind, netto and the thermal assistant on one screen — the readouts that tell you which of the four engines you are actually flying in.
3D terrain and airspace on the biggest 80 mm display, which is exactly what a wave climb toward a flight level needs.
Inertial variometer and instant wind computation — the fastest wind estimate available, and wind is the whole story here.