Joys of Gliding
Gliding is a sport which is catching in rather fast in our country. Yet not many men know how it developed to its present stage. The first stage of gliding began with the towing or catapulting of an extremely light engineless aircraft downhill into the wind so that when it had taken off, it should be supported by an up current.
If the current of air was going up faster than the sink of the glide in still air, the glider could stay up suspended, like a ping-pong ball in a shooting gallery fountain.
Thus, on! suitable hillsides and ridges it is possible to fly up and down in the uprush of air almost indefinitely when the wind is in the right direction. The next stage was the unexpected discovery of “thermals”. On a normal Summer day the sun rises in a cloudless sky but within a few hours big white cumulus clouds rising up like castles and snow mountains, may appear from nowhere in particular: This happens more often on hill stations than in plains.
What is their genesis ? The sun does not heat up the air equally but in patches. Thus over a tiled and slated town or over an expanse of dry and beaten earth, the sun’s rays are reflected and heat up the air much faster than over a leafy expanse of woodland or over sea.
Above such spots a huge bubble of heated air forms and when it has reached a certain size, leaves the ground and floats upwards more or less intact. As it rises through the colder air it steadily expands in size owing to the diminution of pressure around it and when it has been cooled sufficiently by the cold air into which it rises, the vapour inside it condenses and becomes visible as cloud.
The art of soaring depends on discovering such a “thermal” in its early stages, and being lifted by it and remaining in it, as long as it is safe to do so. Foe as cloud joins with cloud, the acceleration and turbulence within the cloud increases. If the sailplane pilot, after being towed or catapulted a few hundreds of feet into the air, picks up a “thermal” he may be able to rise to 10,000 or 20,000 feet with considerable rapidity.