The Supacat Winch

The Supacat twin-drum diesel winch is the mainstay of launch operations at Portmoak and when things are running well it can launch up to about 16 gliders per hour. On a half-way decent day the Supacat can launch a 2-seater to around 1200 feet and a single-seater to around 1500 feet which is normally enough to make a good start to a soaring flight. Despite the weight of the Supacat and tractor combination it is not unknown for the winch to pull itself down the field, even with its legs down, when launching the heaviest of the 2-seaters.

Supacat and tractor

Supacat and tractor

Supacat with Ian Meacham in charge

Supacat showing the powerful engine

Supacat drums and pulley systems

View during a Supacat launch

The Supacat winch is powered by an 8 cylinder air-cooled diesel engine with a power output of some 250 bhp at 2500 rpm and with a particularly flat torque curve over a wide speed range. Air cooling gives the advantage of quick warm-up even on a cold exposed gliding site. This is fluid coupled to the transmission shaft and thence to an enormously strong reduction gearbox arranged to give around a 55 knot cable winching speed at full engine revs. Because the glider path on the launch is longer than the direct route to the winch full revs are normally needed only during the first few seconds of the launch. In fact in particularly strong winds it is possible for the glider to gain height with the winch stationary or even with cable being paid out again rather as a child plays with a kite.
The cable is wound in through a system of dual pulleys which is free to rotate laterally to suit whatever angle the glider launches at. (In crosswind conditions it is common for the glider pilot to try to angle upwind of the winch so that during the cable recovery it does not drop outside the runway area). During winching the pulley system oscillates slowly across the take-up drums so that the cable is wound on in a relatively orderly manner. The drums themselves are around 3 feet across and 9 inches wide and can carry around a mile of heavy duty cable.
It is not unknown for the cable to break during a launch, possibly due to wear or wind gust, and the whole system is carefully designed with substantial guards to protect the winch driver and the winch equipment from the flailing end.
The winch is fitted with an amber warning beacon which flashes any time the winch is running. Before touching or approaching any part of the winch cables it is important to check that this beacon is off. It has been known for the winch driver to select the wrong cable during a launch or for the active cable to 'pick up' the free cable. Severe damage or injury is likely to be caused by any accidental contact with a fast-moving cable.
The end of the cable carries a small drogue parachute which stabilises the cable during recovery after its release from the glider. Right at the cable end is a coupling to which is connected a strop fitted with a 'weak link' and which in turn is connected to the glider winch hook. The strength of the weak link is specified for each type of glider and it is designed to give way if the winch pull ever approaches the safety limit for the glider being launched. The strops themselves are colour coded for ease of recognition and it is the responsibility of both the person hooking on the glider but ultimately the glider pilot himself to ensure that the correct strop is in use.

Winch launching is controlled from the winch launchpoint caravan using an optical signalling system. Do you know how to use it?

page last updated on 2nd May 2003 ©2002-2003 and the

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