11 July 2009
whether they are called sailplanes or gliders, these silent and graceful aircraft can be the ultimate challenge to a pilot's skill. they come in two flavors -- those without engines, and those with an engine and retractable propellor. in either flavor, many sailplane pilots consider this to be the purest form of flying, short of becoming a bird. the pilot sits well forward of the wing, beneath a wraparound canopy that affords unparalleled visibility.
for planes without benefit of an engine or propellor, a tow plane will assist them aloft by means of a tow cable, which is then cast loose when at altitude. at that point the sailplane is free to do one of three things: (1) glide back to earth, with it's extreme aerodynamic design and long wings giving it a very generous glide ratio; (2) seek out thermals, rising columns of air which are differentially heated by the sun shining on heat absorbing/reflecting land surfaces; or (3) seek out updrafts created when the horizontal movement of air masses (wind) is deflected upwards by ridges or mountain ranges.
for planes with an engine, the tow plane is not needed. there is the additional benefit of having backup propulsion in the event of flying too far from a suitable landing area. the trade-off (and there is always a trade-off in aviation) is the added weight, which can mean a slight decrease in glide performance.
recently a new design in engine-assisted sailplanes was announced, the Antares DLR-H2. unlike most such craft, this model is a twin-engine, single-propellor sailplane powered by fuel cells rather than traditional internal combustion engins. this makes for a much quieter, environmentally cleaner plane whose only emission is water. here is a link to a video of the test flight.