We'll work our way through the introduction of this subject slowly, step by step and we'll come at it from a number of different angles because the technique is hard to wrap your head around. The entire process is counter-intuitive.

Let's start here, in your imagination.

You and some other pilots have just had a great morning slope soaring off the top of a high mountain ridge but as the morning has progressed, the wind speed has been gradually building to a point where some of the gusts are now exceeding 35 knots and all of you have decided to pack it in for the day.

You disassemble your glider. As you start to stow it in your vehicle, an unrecognised car arrives and parks. The driver gets out and unloads an exotic-looking slope soarer from the back of his car. Some of the other pilots look at you with questions in their eyes. It's unusual to see a stranger up here on this ridge-top. And with the wind the way it is, why is he unpacking his model?

He prepares his model for flight. It's obvious he's serious about flying in this wind. One of the other pilots walks up to you and suggests the newly-arrived pilot must be a fruit cake. All of the pilots are watching him with interest.

Once he's ready, the new pilot launches his glider into the gale. The little aircraft is blown straight up over the top of the ridge and starts dropping into the airspace behind it; entering the region of rotor, the traditional no-fly zone for slope soarers. It's a no-fly zone because the turbulence there can be devastatingly extreme, but instead of instantly crashing into the rocks, the pilot seems to be holding control of the glider and the glider is surviving the ordeal.

The other pilots are all looking at each other with raised eyebrows. 'What's going on?' they seem to be asking each other silently. 'Why hasn't the stranger's glider crashed?'

The new pilot starts to circle his glider, alternately climbing up through the area of rotor then dropping back down through it again.

The most intriguing thing to all this is not that the man chose to launch into a gale, not that his glider was instantly whipped across the ridge-top and down into the turbulence behind the ridge, not that the glider has survived the ordeal, it's this: with every sweep of the circle, the glider has been picking up speed. It flies extremely fast, and then it flies unnaturally fast. And now it's flying so fast that it's actually hard to see.

As the wind strength continues to increase, the pilot's smile gets wider.

Next, let's establish this. Generally speaking, the speed of the airflow over the surface of the planet is slower than the speed of the airflow at altitude. The wind blowing over the surface-features of the planet, whether they be rocks or water, experiences friction as it rubs against the surface and the friction slows it down. Air moving up above the surface experiences less friction and hence flows more freely. This disparity in airspeed is measurable even from a height of fifty feet.

Meet Henry. Henry is an albatross. Henry is going to spend a couple of minutes teaching us about albatross-oriented objectives.

An albatross knows a thing or two about flying. One of the things it knows is something that apparently no other bird species has yet understood. We're going to take a close look at this thing because it constitutes the basic foundation-stone of our subject.

For our example, Henry intends on flying due west and the wind is coming from due south. Henry will tack to the west, much like a sailboat. He'll fly north-west then south-west, then north-west then south-west, inextricable manoeuvring westwards but never in a straight line. Though he's tacking like a sailboat, notice the difference. A sailboat would only tack if it intended heading directly towards the eye of the wind. In our example the wind is from the south. The sailboat would tack south-west and then south-east, always moving southwards. But that's not what Henry is doing. He's tacking westwards, across the face of the wind.

Not only is he tacking horizontally, he's also tacking vertically. The tack leg to the north-west is spent descending, the tack leg to the south-west is spent ascending, often to a height of about fifty feet, into an airstream with a different speed. The north-west leg has a 45 degree down-wind component. The south-west leg has a 45 degree up-wind component. Henry climbs on the up-wind leg and dives during the down-wind leg. He climbs up into an area of higher wind speed and dives down into an area where the wind is moving more slowly or not moving at all.

At the top of his climb, he has allowed his speed to bleed off until he's approaching his stall speed, then he swings north-west, putting the wind behind him, and using that advantage, zooms down into the slower moving air, converting his height to speed. Once he's skimming the ocean surface at maximum cruise speed, he swings south-west and, climbing up-wind, converts the speed back into height again. What's he doing? He's harnessing the kinetic difference between two air masses moving at different airspeeds.

Using this technique, albatrosses can fly for a thousand miles without having to flap their wings once, which is probably just as well because they're too long to flap.

Scientists, noticing what the albatross was doing, called the technique 'dynamic soaring.'

The pilots of full-size gliders had a look at the technique and decided they couldn't duplicate it.

The pilots of model gliders had a look at the technique and decided they could. All they needed to find were two air masses moving at different speeds adjacent to each other. They didn't have to look far because slope-soar pilots already knew where those conditions existed: in their no-fly zone, the area behind a slope-soaring hill.