Gliding

Gliding (or soaring) is a recreational activity and competitive sport where individuals fly un-powered aeroplanes known as gliders or sailplanes. Properly, the term gliding refers to descending flight of a heavier-than-air craft when gravity (its own weight) is its sole motive force; soaring is the correct term to use when the craft gains altitude or speed from movements of the atmosphere during the flight.

Cross-country

Gliders can stay airborne for hours if there are places where the air is rising faster than the glider is descending. This enables gliders to fly long distances at surprisingly high speeds. Although Klaus Ohlmann's world record is obviously not a typical flight, even in less favourable places in Europe, good pilots usually have flights over 500 kilometres every year at average speeds of 80 km/h or faster.

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In addition to just trying to fly farther, gliders also race each other. As the performance of gliders improved, the concept of flying as far away as possible became unpopular in the 1960s with the crews who had to retrieve the gliders. Pilots now win contests by being the fastest around a pre-defined course back to the starting point, or, if the weather is not as good as expected, the furthest round the course. Originally proof of getting to the turning points was by observing the gliders from the ground. Later the pilots took photographs of the turn-points but nowadays gliders carry secure devices that record the position every few seconds from GPS satellites. National competitions generally last one week but international championships are normally over two weeks. The winner is the pilot who has amassed the greatest number of points over all the contest days. Because it would be unsafe for many gliders to cross a start line at the same time, pilots can choose their own start time. Gliders are not visible to spectators for long periods of each day's contest and scoring is complex, so gliding has been a difficult sport to televise. This means that soaring is a sport in which most contestants are still amateurs. However, a new format contest has been introduced see Sailplane Grand Prix. Also gaining popularity in recent years is an informal online contest called the OLC where pilots upload their GPS data files and are automatically scored based on distance flown. Nearly 9,000 pilots worldwide participate.

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Soaring pioneer Paul MacCready developed a mathematical theory for optimizing cross country soaring speeds. His theory allows one to compute the optimal cruising speed between thermals, accounting for thermal strength, sailplane performance and other variables. The theory accounts for the fact that, as a pilot flies faster between thermals, the glider also sinks faster, requiring the pilot to spend more time circling to regain the altitude, reducing the overall average speed for the flight. The MacCready speed represents the optimal tradeoff between cruising and circling. Most competition pilots make use of MacCready theory to optimize their flight speeds, and have the necessary calculations programmed in their flight computers.

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