Airplanes

The Sailplane

      At first sight this might seem an odd place to start writing about aviation but the modern sleek white fibreglass sailplane soaring effortlessly, without any mechanical assistance through the sky, is the nearest we have got yet to mans earliest dream of flying like the birds. When did it begin? Who knows! Possibly one of the first cave men looked up at the Pterodactyl and thought "Ug, me want do that." and set about trying. Certainly the desire has persisted. Religion has angels in human form with wings, Greek legend has men fashioning wings and flying, not too successfully we are told, Leonardo da Vinci designed what looked as if it might have been the first practical sailplane, but it was never built, maybe for the lack of materials.
      For the next 200 years or so, much midnight oil was burnt, fanciful designs built, tested and crashed until at some point stable flight was achieved, if only for a couple of minutes. Numbered among the achievers were the Wright Brothers, who eventually came to the conclusion that the only way they were going to fly any distance at all was to use an engine and propeller. They looked around for something suitable and finding nothing available set about building their own.
      So the airplane was born and rapidly developed into a capable, if somewhat unreliable flying machine for which no practical use was found other than sport or recreation. Because there was no real understanding yet of what kept an airplane flying other than the power of the engine, our sailplane had to take a back seat whilst, thanks to World War 1, the powered airplane was found to be extremely useful for military purposes and rapidly came into its own.
      But the dream was not lost. At the end of the war the Treaty of Versailles on the building and usage of airplanes placed severe restrictions on Germany. So the resourceful Germans went back to designing and building sailplanes, which flew somewhat better than before, thanks to the knowledge gained in wing design for powered aircraft. Flight times and distances gradually increased but still, sustained flight eluded them. This was all about to change!
      At a plateau in Germany, called The Wasserkuppe, students from the Darmstadt Technical University were building and flying sailplanes from there as early as 1911 but ceased during the war. They recommenced in 1920 when interest in gliding grew and annual gliding competitions were started leading to records being set and broken for height, distance and duration. Most new designs were tested here and investigation into sustained flight began with hill soaring and the Wasserkuppe was ideally suited for this purpose, being 3100ft high and facing the prevailing winds, with a flat top for take-off and landing. As designs improved, so did flight times and it was not long before soaring flight was discovered, using the rising warm air currents to climb higher in the sky by circling in the up draft as the soaring birds do, Eagles, Buzzards, Seagulls and the like. But soaring flight was hard work for existing sailplanes made, as they were, of wood or metal with fabric covered wings, which were not very efficient, so the aim now was to build a better wing.
      Without getting too technical, some explanation of how a sailplane flies is now necessary. Because a sailplane has no motive power, when airborne it is always descending in still air. In order to remain in flight it has to fly in air that is rising at the same speed as, or faster, than the sailplane is descending. The rate of descent is determined by the particular sailplane's lift/drag ratio or L/D which is a measure of its efficiency or, if you like, its stayupability. Put simply, an L/D of 12 : 1 means that in still air a sailplane at a height of 5280ft ( 1 mile ) will travel a distance of 12 miles before reaching the ground. So improvement was the name of the game and sailplane builders in Germany, England and the USA slowly and carefully did just that until at the start of World War 2 , which effectively put a stop to gliding, the L/D of most new sailplanes was in the region of 26 : 1.
      After four years of war during which time the powered airplane again took precedence aviation in general made tremendous advances and when, at the end of the war, gliding was resumed, the sailplane designers were not slow in taking advantage of all the knowledge available. The greatest improvements were in the materials used to build sailplanes and with the coming of plastics and fibreglass the modern streamline sailplane was born.
      Today, with an L/D in excess of 55 : 1 the sailplane is an impressive machine capable of flying distances of 1000 km or more at average speeds of perhaps 140 kph the dream has become a reality and with the option of a lightweight retractable engine for take-off and sustaining flight in areas of poor or nonexistent lift man can truly fly like a bird.
If you have ever seen a sailplane flying gracefully through the sky, you probably wondered what it would feel like to do that. Soaring in a sailplane is a wonderful sensation, almost impossible to put into words and is something everyone should try at least once. But beware ---- should you come to love it, it will take over your life to the exclusion of all other sports.

 

 

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