altitude, and so pilots plan for this eventuality before launching. During the aerotow, the glider pilot keeps the glider behind the tow-plane in either the "low tow" position, just below the wake from the tow-plane, or the "high tow" position just above the wake. In Australia the convention is to fly in low tow, whereas in the United States and Europe the high tow prevails. One rare aerotow variation is attaching two gliders to one tow-plane, using a short rope for the high-towed glider and a long rope for the low tow. The current record is nine gliders in the same aerotow. Winch launching Gliders are often launched using a stationary ground-based winch mounted on a heavy vehicle. This method is widely used at many European clubs, often in addition to an aerotow service. The engine is usually powered by LPG, petrol or diesel, though hydraulic fluid engines and electrical motors are also used. The winch pulls in a 1,000 to 2,500-metre (3,000 to 7,500 ft) cable, made of high-tensile steel wire or a synthetic fiber, attached to the glider. The cable is released at a height of about 35% of the cable length after a short, steep ride. A strong headwind will result in higher launches. Winch launches are much cheaper than aerotows and permit a higher launch frequency. A winch may also be used at sites where an aerotow could not operate, because of the shape of the field or because of noise restrictions. The height gained from a winch is usually less than that from an aerotow, so pilots need to find a source of lift soon after releasing from the cable, or else the flight will be short. A break in the cable or the weak link during a winch launch is a possibility for which pilots are trained. Auto-tow Another method of launching, the "autotow", is rarer nowadays. The direct autotow requires a hard surface and a powerful vehicle that is attached to the glider by a long steel cable. After gently taking up slack in the cable, the driver accelerates hard and as a result the glider rises rapidly to about 400 metres (1,300 ft), especially if there is a good headwind and a runway of or more. This method has also been used on desert dry lakes. A variation on the direct autotow is known as the "reverse pulley" method. In this method,