http://ozreport.com/12.080#4

Rohan Holtkamp at Dynamic Flight <<email>> writes:

I knew Bernie from the Aussie comp circuit, he was a nice guy, loved the hot weather and strong thermals of the outback. Bernie did a lot of flying in areas remote from mainstream hang gliding groups so getting hold of the latest equipment may have been difficult at times. From what I read it was a shame Bernie did not throw his 'chute after the snag, or have a hook knife handy.

The ski rope used in tow bridles back in the early nineties (and in Bernie's case) was well suited to a V bridle with the release at the bridle apex. This ski rope is a hollow braid close weave nylon with less than 3 percent stretch and was favoured in 4 to 5mm diameter. Yield load with a spliced end was over 300kg, - that's six times stronger than the weaklink when used in a V bridle.

I believe Bernie chose to have his release at either or both ends of the V bridle. I read/heard that his VG rope also got snagged/tangled into the bridle, negating the harness-end release.

The keel and or harness release facilitates easy stowage of the bridle after the tow but requires the bridle rope to slide through a ring (clip in this case?) at the apex after release activation. This is a common bridle system in the US flight parks, where one end is released and the bridle slips through an alloy carabineer attached to the tow line. The ski rope is a little stiffer and about 2mm thicker than the vectran or spectra used at Wallaby and Quest. The ski rope threads are thicker and somewhat less prone to catching than the non waxed spectra, but more than waxed spectra.

During 18 years of tow competitions I have seen lots of different systems, I have witnessed many occasions where a spectra keel release bridle has hitched onto an apex ring - resulting in barrel rolls on tow! To avoid problems we only allow the apex release V bridle at Dynamic Flight.

In the majority of bridle-not-flowing-through-the-ring cases, the ring has been problem, not the rope. Testing showed that at specific ring thicknesses (not diameter) and rope speeds, a shock/pressure wave builds on the loose side of the bridle rope as it slips through microseconds after release. When the rope is almost through the ring and the free end is of the right length and mass, it can whip around and hitch itself onto the ring, snap-hook clip/carabiner! This has dire implications if there is not a weaklink on the (other) attached end of the bridle or, in static towing, the remaining tow force is lower than the weaklink breaking strength.

If Bernie used a snap hook clip it represents an additional variable in the hope-it-slides-clean through the ring equation. Since my testing I would expect any rough ring or snap hook to eventually catch any types of bridle rope, even if the offending article was a few inches ahead on the tow rope side of the weaklink!

History has shown us that the V bridle is one of the safest tow bridles when the reliable release is at the apex. Have your release at the apex to eliminate the hitch/snag variable.

In respect to the chain link, there are so many types of chain, unless we are able to examine the exact piece Bernie used, I would be unable to make a link in this case, if you will pardon the pun.

There are other factors to consider in Bernie's accident. If there were no trees to snag the tow line perhaps this accident may have been no more than an incident. If his VG rope was shorter he may have been able to release the harness end of the bridle. If he used a clip where the bridle was to slide through, then that's a dire oversight on his behalf, but not the end of options after it snagging the bridle. A hook knife could have saved the day, so could throwing the chute.

In the new edition of the HGFA Towing Guidelines you will find the Twelve Towing Commandments. Read them well, share them around. They have evolved to help reduce variables and therefore accidents. Carry a hook knife to provide more options.

http://ozreport.com/forum/viewtopic.php?t=11591&start=3