"Any staked pulley should be checked regularly during the flying session to verify its security"
Recently rumours from Europe reached the BMFA Silent Flight Technical Committee to the effect that "a person had been killed during the towing of a model glider". Remarkably, very little information was available from official stories but SFTC members used various contacts throughout the Continent and have managed to piece together what appears to have happened. The accident happened at a rocket SE8 competition but the person concerned was not flying in this event; he was relatively inexperienced and was using the site to practice glider flying.
A pulley launch system was being used whereby the towline was anchored to the ground by stakes, the towline being passed round a hand held pulley and back to the glider. On the signal to start the two towers ran away from the fixed stake to pull in the line and launch the model. Much the same system is used competitively all over the world to launch model gliders. On the day in question, after "about 30 launches", the stake anchoring the pulley to the ground was pulled out by the force of the towline and struck one of the towers, a sixteen year old, in the back of the head and killing him.
UNDERSTANDING THE CAUSE OF THE ACCIDENT HOWEVER IS OF EQUAL IF NOT MORE IMPORTANCE TO SPORT GLIDER FLYERS using the "pulley tow" technique than for competition flyers.
It appears that the holding stake had been fixed at the start of the day's flying and had probably not been checked for security subsequently. Repeated towing had caused it to loosen until it reached the point when it was pulled from the ground by the towline at high tension. The only direction it could then take was towards the towers which it did with tragic and fatal consequences. In competition flying, holding stakes are required to be a MINIMUM of 450mm long and 15mm diameter of which 350mm must be driven into the ground.
Stakes are often moved or lines re-attached during competition and are therefore regularly checked by default; this is not usually in the case of sport or practice flying. The lesson is very clear any staked pulley must be regularly checked to verify its security -failing to do this could be your last mistake ever!
The SFTC would advise anybody new to pulley towing to seek advice from an experienced (probably a competition) flyer. Similar risks are also presented by bungee and winch launch systems so seek advice if you are unsure and check these stakes regularly as well. more clamping action to spread the load.