cutaway cable length

[The111 1]

I recently made this post to the G&R forum.

In short, I assumed the wing cables on my GTI were too long since they appeared too long to fit into the keepers at the end of the series of loops. Hell, even my BMI agreed they were too long, he suggested I just leave them hanging or insert them into the wing (which I did for a few jumps), but he said if I really wanted to I could trim them so they fit in the keepers. So I did. Trimmed 2-3 inches off each one. Then I got this reply from cpoxon that made a lot of sense. He said they probably weren't too long, that they can actually be retracted into the handles a little bit and this gives you a greater snatch force when you need to cutaway. I had no idea about this, and I tried it out, and lo and behold, he was right. Even more perfect, the amount of length the would be lost by the retraction is about exactly what I cut off (2-3 inches). So it would have been a perfect fit to use the uncut cables had I retracted them into the handles. But now that they are a bit shorter if I retract them they barely make it through the last loop and don't go into the keeper at all.

So... is this "snatch force" benefit gained from having the cables retracted a bit a significant thing? Enough that it's a safety issue to jump with the cables fully extended (not retracted at all). Practice cutaway on the ground requires virtually no force. Haven't tried in the air, I guess there could be more forces involved in that situation but I still couldn't see it being unreasonably hard.

Thoughts?

I should get to meet Jari this weekend at Sebastian so I'll ask him... I wish my BMI or suit salesperson (or manual) had mentioned something about this... However I really don't think this is a big deal and I'm probably over-reacting as usual.

www.WingsuitPhotos.com

[alain 0]

interesting things here:
http://www.dropzone.com/cgi-bin/forum/gforum.cgi?post=408778;search_string=safety%20day%20cutaway%20lbs;#408778

[The111 1]

I don't see anything there that is relevant to wingsuits...

www.WingsuitPhotos.com

[FrogNog 1]

The idea of the "snatch force" thing you ask about is (I think) to try and pass through static friction into sliding friction (which in almost all cases is lower) as easily as possible, by using momentum (of your hand/arm in this case) to assist the first bit of pull.

Is this necessary? The cutaway system on wings / legs, from what I have seen, does not use a pulley system like the 3-ring-circus to ensure the cutaway cable receives less stress than is generated by the item needing to be cut away.

So the question is whether a wing could be somehow "stuck" or under a lot of tension that would cause the start of a cable pull to be hard. Heck if I know whether this will be a problem.

Some parts of our rigs are overkill until the one time they're not. I'd look into how much it would cost to have those cables replaced. A hundred bucks is a minor humbling for a mistake, in the grand scheme of things.

-=-=-=-=-
Pull.

[The111 1]

Yup, that was the essence of my question. Just curious if the static friction generated by the inflated wing on the loops could somehow be enough to warrant the need for that extra bit of "slack" giving you a greater snatch force. I'm inclined to say it's not needed, but I'm hoping someone who has cut away their wings in the air before (knowing whether or not they had the retracted cable "slack) can verify this...

www.WingsuitPhotos.com

[LouDiamond 1]

Quote

However I really don't think this is a big deal and I'm probably over-reacting as usual.

Don't sweat the "snatch force". That sounds like a sophmoric inuendo eh What I would be concerned with is that in your trimming the cables have you created a cable this is capable of unthreading itself when pressure is applied on the loop and cable system. If you can roll your shoulders or if by moving your rig up and down on your back the cable starts to work free of the last loop you may want to look at buying a new set. Bar that the only concern would be that you seal the newly cut end off with some heat so you don't have a sharp end ripping your suit.It will also make it easier to thread the loops if it is sealed over and doesn't snag. From now on, don't cut,trim ,add or remove anything from your suit with out consultation first

"It's just skydiving..additional drama is not required"
Some people dream about flying, I live my dream
SKYMONKEY PUBLISHING

[jmfreefly 0]

No matter how fast you pull it out, the force you are overcoming is always the same. Some may say that 'jerking' the loop out might give you better leverage, and therefore allow you to apply more force to overcome the friction. I personally don't really buy it..

I generally don't cutaway fully pressurized wings I am usually cutting away wings that are partially deflated (as the canopy is opening,etc.). So in general, the forces are lower during deployment are lower than that of full flight.

My experience is that the greatest force to overcome is actually the velcro, and that isn't a problem at all.

I don't think that the little 1-2 inches of play in the loop makes one iota of difference. I usually am peeling the velcro, as opposed to tugging along the axis of the cable. Once the velcro is free, I am stripping the cable out to the side. At that point, the extra 'snatch' length really won't matter, imho.

heheh.. he said 'snatch'..

EDITED to add: Show it to Jari, but I bet you he will tell you it doesn't matter.


j

[jmfreefly 0]

Quote

What I would be concerned with is that in your trimming the cables have you created a cable this is capable of unthreading itself when pressure is applied on the loop and cable system. If you can roll your shoulders or if by moving your rig up and down on your back the cable starts to work free of the last loop you may want to look at buying a new set.

Well, I have seen people (even certain instructors) fly with shorter than full-length cables (using cables from different suits). The only downside is that your flight may not be 100% as fast (maybe 99.5%) if the cables comes out of one loop. If it comes out assymetrically (one wing but not the other), this might give a bit of pause, but I think that is pretty unlikely unless you cut them significantly different.

I think it shouldn't really be a concern, but it isn't 100% perfect.

Quote

Bar that the only concern would be that you seal the newly cut end off with some heat so you don't have a sharp end ripping your suit.It will also make it easier to thread the loops if it is sealed over and doesn't snag. From now on, don't cut,trim ,add or remove anything from your suit with out consultation first

Agreed, whipping the ends is importnat. His prior post in G&R was actually asking about that.

j

[ernokaikkonen 0]

The cables on my GTI seemed too long when I got the suit, this is what Kim Pothuisje at Birdman had to say(emphasis mine):

Quote

As for the cables, they are all basically standard sizes for general arm
lengths, whether for a GTi, a Skyflier, or a Skyflier.3. Apparently, you
have an arm length usually associated with a Skyflier, so that is what size
they sent you. They aren't measured and cut for each suit--we leave that up
to you. We would rather it be a little too long and in need of trimming
than for it to be too short.

So I guess a lot of people will be trimming their cables or jumping with excessively long cables.

[SkymonkeyONE 4]

A bit too long is better than a bit too short. when you are assembling your suit your cables should reach to the end of the keepers and maybe a tad too long (like one inch). after it's in, simply "snatching" your suit from top to bottom of the cable will distribute the rest of the cable evenly down the length of the channel. When you move around in your suit in flight and the wings are inflated, the outward tension on the attachment system will take up the slack. If your cables are too short, then they will start pulling out from the top. It's happened to me before, generally on the back of the suit. Making sure your cables are fully in after every flight (I never de-rig my suit) will prevent this from happening.

Chuck

[ernokaikkonen 0]

When I measured the cables I put the suit and the rig on without inserting the cables in the small pockets they have. Then I put the suit and the rig on, stretched the wings, the suit and the rig this way and that, and checked how much excess cable was showing. Then I marked the excess and cut it off and rounded the ends of the cables.

Four people have jumped the suit with two different rigs with no problems, so this method should work pretty well for others, too.