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.

Launch methods

Gliders are initially launched into the air by one of several methods, the most common are "aerotowing" and "winching".

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Aerotows normally use single engined light aircraft, but lately, powerful self-launching motor gliders and microlight planes have also been permitted to tow gliders. The tow aircraft takes the glider to the desired height and place and the pilot releases the rope. Aerotow ropes are typically made of polypropylene rope and are between 50 and 60 metres in length. At the tow plane end, a weak link is fitted to the rope to ensure that any sudden loads imposed by the glider getting out of station do not damage the airframe of the tow plane.

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During the aerotow, the glider pilot keeps the glider "in station" behind the tow plane. This can either be the "low tow" position, just below the slipstream of the tow plane propellor, or the "high tow" position just above the slipstream. Over the years there has been great debate about which of these two positions is the safest, and there has been no universal agreement. In Australia the convention is to fly in low tow, whereas in the USA the high tow prevails.

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One interesting aerotow variation is to perform a "dual tow" in which two gliders are attached to the one tow plane, using ropes of different lengths. This certainly looks spectacular, but requires skill and precise flying by all concerned.

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Gliders are often launched using a stationary ground-based winch, sometimes mounted on a heavy vehicle. This method is widely used in many European countries, often in addition to aerotowing. The engine is usually from a large car or a diesel truck (sometimes using LPG), though hydraulic fluid engines and electrical motors are also used in places. The winch pulls in a 1000 to 1600 m long cable made of steel wire or a synthetic fiber which is attached to the glider. The glider releases the cable at a height of about 400 to 500m after an amazingly short and steep ride. A winch launch costs between EUR 3 and EUR 10, which is much less than an aero-tow. Because many launches are needed to train new pilots, winching is a useful way of keeping the cost down. One disadvantage of winch launching is that the launch height is variable with the wind strength and cable run length, which could mean that the duration of flights is slightly shorter unless the pilot is fortunate enough to make contact with a thermal or other source of lift within a few minutes of releasing the cable.

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Gliders can also be launched from the top of a hill into a stiff breeze using a rubber band, or "bungee". For this launch method, the glider's main wheel rests in a small concrete trough. The hook that is normally used for winch-launching is used instead to attach the middle of the bungee. Each end of the bungee is then pulled by 3 or 4 people. One group runs slightly to the left, the other to the right of the glider. Once the tension in the bungee is high enough, the pilot releases the wheel brake and the glider's wheel pops out of the trough. The glider gains just enough energy to leave the ground and fly away from the hill. This method is still regularly used by a club in the UK.

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Another launch method, now rarely used, is the "autotow". This needs a long runway, a large pick-up truck and a length of cable. After gently taking up slack in the cable, the driver accelerates hard and the glider rises like a kite to as much as 400 metres if there is a good headwind and a 1.5 km runway. This launch method is still regularly used by a club in the UK for launching primary gliders. A variation on this is the "reverse pulley" method in which the car drives towards the glider that it is launching; the cable connecting the car and glider passes around a pulley at the far end of the airfield.

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