Winches and Stuff

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The Winches

Our main winch is a Skylaunch, which we've been running very successfully since May 1999. It's a twin-drum winch powered by a 320hp (240Kw) gas engine.

Prior to that, we ran two diesel winches, both twin-drum machines powered by 240hp (180kW) diesel engines. The one on the left has since been sold, and the other is our reserve.

The Skylaunch gives about 200' extra launch height, and is much more tolerant of releases under tension so there are fewer delays.

The Cables

We use 4.5mm 7/7 stranded cable, which is very reliable. The previous 4.0mm that we used tended to break frequently once it had worn down to about 3.6mm.

The sequence at the business end of the cable is

• A revolving joint which locks under tension (the cable unwinds if you put a real spinner there!)
• A parachute, to keep tension in the system when the aircraft releases.
• A hemp shock rope, 15-25m long.
• A D-shackle holding a Tost hook, which is a rigid plate with a central hole and a narrow slot.
• This is attached to the weak link by a Tost oval ring with a flat. The hook can be fitted to this ring by sliding it over the flat, which allows the weak link in the system to be changed at the launch point in a matter of seconds.
• Each weak link is a single Tost weak link. We don't use Tost's suggested two links (one slotted) because it's too easy to get it wrong at the launch point. For protection, the link is mounted in an aluminium U channel drilled with one hole and one slot.
• Each weak link is permanently attached to a strop, which is about four feet of cable inside a rigid piece of piping. The strop has the launch rings at the other end. The strop removes any possibility of the cable fouling the aircraft's wheel box.
• The piping is coloured to match the weak link, and there is a collection of strops of various colours at the launch point.

We do daily DI inspection of the cables. The Skylaunch is kind to the cable, and real cable breaks are very rare as a result. With the diesel winches, we suffered from perhaps one real cable break a week. Most of the antics in the air are simulations where the instructor is checking the student by pulling the release during the launch.

Cable breaks are repaired by joining the cut ends of the cable with two copper ferrules, crimped with a hydraulic crimper. The cables must overlap by about 4"/10cm, which is a compromise between the requirements of transit through the winch heads, and work-hardening of the cable near the joint. The cable must extend ¼"/6mm through the ferrule, as this will then bend over and protect the soft end of the copper ferrule.

Cable repairs take about five minutes, including retrieving the pieces, although the side-effects of a break (slack on the drum, loops, and birds-nests) can take much longer to clear.

Synthetic Rope

We are currently trialling a synthetic rope, called Dyneema, instead of the steel cable. Initial results have been very favourable.

We're using 5mm 8-strand rope, which is actually much stronger than the steel cable. It's also a tenth of the weight. As a result, the system is kinder to the aircraft, the winch, the retrieve vehicles, and the members' hands.

The change to synthetic rope is creating small changes to many areas of our launch operation. Once these have all bedded in, we are expecting an extra 200' of launch height, too.

Glider retrieve

We retrieve gliders from the landing area using LPG-powered golf buggies.

Cable retrieve

We retrieve cables in pairs, using Land Rovers. The cables are connected by wire weak links to hooks on the rear corners. They are not spread by a bar, so a straight-line retrieve is essential.

If we are using two winches simultaneously, we retrieve using two Land Rovers in tandem.

Tractors

We have a small Kubota B7100, for towing trailers and occasionally aircraft. We have a Ford Dexta with a hydraulic bucket for site work, and for towing the heavy diesel winch. We have a much larger and more powerful Ford 7600, which is used mainly for mowing the airfield, rolling and grading it, and other such heavy work.