- #1
Rescuetech
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Greetings; I am a firefighter so physics is pretty much Greek to me. I work primarily as a rope rescue/USAR tech. We work a lot with rope, pulley's, and anchor points. All of these systems have angles that affect the loading in our system. Now I been taught rules of thumb when constructing a rescue system, for example; I am told when using a change of direction pulley, the greater the angle the less force required to pull the load, so fine I just follow this rule and all is golden, but I always wondered why.
Anyways, I recently attended a training session where we built a Kootenay high line patient retrieval system (See image). This system is basically a long rope that extends from one anchor point, the line can span over a ravine, river, etc. The patient is placed in a litter and transferred across the line using tag lines.
One critical aspect is the slack in the mainline, too tight and the load on the anchors can cause a anchor failure. Too loose and the patient will not be retrievable once approaching the ravine edge or similar.
Now my question;
I have a rope rigging software called Vrigger that will do the force calculations. It is apparent from my simulations that the greater the angle on the line, the less force on each side of rope where the pulley is. (hope that made sense). The numbers are quite drastic, can someone explain to a firefighter why this is so, I just don't get why the angles make such a difference. I wanted to find a formula for this but did not know where to look in my old trig book.
http://img14.imageshack.us/img14/9094/ti4.gif
Anyways, I recently attended a training session where we built a Kootenay high line patient retrieval system (See image). This system is basically a long rope that extends from one anchor point, the line can span over a ravine, river, etc. The patient is placed in a litter and transferred across the line using tag lines.
One critical aspect is the slack in the mainline, too tight and the load on the anchors can cause a anchor failure. Too loose and the patient will not be retrievable once approaching the ravine edge or similar.
Now my question;
I have a rope rigging software called Vrigger that will do the force calculations. It is apparent from my simulations that the greater the angle on the line, the less force on each side of rope where the pulley is. (hope that made sense). The numbers are quite drastic, can someone explain to a firefighter why this is so, I just don't get why the angles make such a difference. I wanted to find a formula for this but did not know where to look in my old trig book.
http://img14.imageshack.us/img14/9094/ti4.gif
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