Tow Release Wars
There was a strongly worded discussion on the hang glider discussion list about tow releases. I've watched this thread with some interest. I train quite a lot with tow, and at various points in the training, I have used many types of release.
When I train with scooter tow, my students use a Wallaby aerotow release with a motorcycle brake
lever release. This would be applicable for platform, except that the spinnaker snap
release used with these is not reliable at high pressure, so should not be used at
release pressures of more than 150 to 200 lb. Thus, for platform launch, I provide and use the
traditional 3-string release with a weak link installed in the third string.
This is very reliable except that, most two and three string releases have a failure mode that is quite common place, which is that if once highly loaded during a tow, the strings tend to take a set, and sometimes fail to release at low tow tensions. Other than for this failure mode, I have never seen a 3-string release fail to operate.
Let me emphasize this. It is essential that people new to the 2 or 3 string release be prepared for this failure mode as it is rather commonplace. The proper reaction is not to whip out the hook knife and start slashing wildly. It is to slap the weak link like Moe slapping Curley back and forth once or twice until the line falls away. If the line is under tension, the release won't fail, so this is not generally an emergency problem unless the pilot through fear creates one when he/she pulls the pin and the line hangs. Remaining calm is essential.
Here in Texas, the great majority of platform towing is done observer-less and using a 3-string release. While I neither advocate or practice observer-less towing, we have a rather good safety record. I have never heard of anyone hook-knifing a bridle, tow line or weak link and in fact think that the hook knife is better reserved for cutting parachute bridles when being dragged through a barbed wire fence in a strong wind.
We are using the two-string release, the three-string release, and the
spinnaker snap release, two different types of European double releases, and the LMFP aerotow release and the Link Knife. For various reasons, the Link Knife has not been overly popular around here, but it is extreme effective, probably it's major fault is that we haven't had an enormous amount of experience with it and it works so well that we have had a number of unexpected releases.
Now getting to the main issue. To take the hand off the control bar to release or not. It has not been my experience that having to remove a hand momentarily to operate a release causes a problem for a pilot with experience. Why? Because the glider in flight, being surrounded by several tons of air takes several seconds to react to any change. Thus there is ample time for a pilot to operate a release or even slap a 3-string release that is hanging. On the other hand, in an emergency, I see several failure modes relating to the use of a hook knife, one of which is failing to fully detach the tow line from the pilot, another of which is dropping the knife, even if on a lanyard, another is the knife getting caught in the case in an emergency. The hook knife, is like a parachute in that proper use depends on many factors including correct rigging, proper placement, and practice in it's use in an emergency.
Thus, I apply the reasoning that on platform tow, the hook knife should
be in the hand of the observer, and I invariably use an observer with a hook knife.
For scooter tow training, I prefer the student to have a release immediately under his/her fingers and instantly available, with student trained to immediately release if there is a problem.
For advanced scooter tow, I prefer the European double release using the over and under line.
For aerotow, using a V-bridle, I prefer the Wallaby or LMFP aerotow release with the lever or loop placed where the pilot can operate it without much movement of the
hand as things GO WRONG a little faster with aerotow. As a tug operator, I also require a lower release, and while I think the Panic Snap or equestrian release is Ok, I prefer a 2 or 3 string with a golf ball sized whiffle ball for the release handle which makes it extremely easy to pull blind. (Thanks to John Heiney for the recommendation.) If I tow from the harness alone, without the V-bridle, I use the same 3 string release.
Incidentally, the Panic Snap Release has been used since the early days in towing with some success, but most panic snap releases are cast from pot metal and not very strong. Further, they require positive tension to operate one handed. Keep that in mind if you use one. Keep pulling until the rope is LOOSE.
Now, all of these recommendations come from my experience, and there is no one recommendation that applies to everything.
IT IS MOST IMPORTANT THAT one realizes that there are a number of different tow methods with different requirements.
What is most important is that you have a method which you understand well, and that you apply consistently to your towing practices.
Keep those hook knife blades sharp.