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Hello,

I'm not a base jumper, soon-to-be skydiver and an admirer of the sport. I accidentally came across with BASE fatality list that I'm sure all you are aware of and there was this weird statistic

177 deaths with pin rig
28 with unknown rig
23 with skydiving rig
1 with velcro rig (?)

http://www.blincmagazine.com/forum/wiki/Fatality_Statistics

I'm sure there is an explanation to that? I just wanted to ask you guys what it is because I felt pretty puzzled. If velcro rig would be that much safer I'm sure everyone would be using one...

Here are three reasons to explain this pattern:

1. Most modern BASE gear has two pins

2. Wingsuiters do not use velcro rigs

3. Acrobats rarely use velcro rigs

Hence there are less rolls of the dice
with jumpers using velcro and the jumps
that are made with a velcro rig are usually
of the simpler / safer / less technical kind.

i may be wrong but the majority of people use dual pin rigs, especially wingsuiters, and since a large portion of fatalities are wingsuiters it tends to skew the statistics. Its important to look at the cause of the fatality and whether or not the gear could have impacted the result.

It is true that there have been deaths from misrouted bridles, and accidents from pin/bridle hangups, that could not have occurred on velcro rigs.

Velcro rigs were designed to be as foolproof as possible. When BASE jumpers started moving away from them, we knew that we were being exposed to more risks from certain types of issues. And we have, in fact, seen deaths from problems that never would have happened with velcro.

Although we have not seen any deaths from the shortcomings of velcro (increased maintenance requirements, for example), it's possible that has more to do with the current predominance of pin rigs, and that if everyone were jumping velcro all the time we'd have seen some accidents there too.

That said, to get a true picture of the real statistics, you'd have to determine the total number of jumps made on each kind of system, which would be virtually impossible.

I jump a Velcro rig. I don't WS. There isn't really anything tall enough to track away from, other than a few tall sticks here and there, but tracking from a thousand feet with a well maintained (Velcro) rig is just as safe as tracking with a well maintained pin rig. For go and throws, PCA, or S/L, a Velcro rig is all you need.

I really like being able to open up my rig and check my brake settings.

I really like not having my pins pop while climbing an A.

I really like not having the possibility of a pin lock.

I like not having questions about top pin first or bottom pin first and which way the bridle comes in or goes out. Yes, the shrivel flap must go on the right way but that is the only variable. And the less you can take out the more fool proof it becomes. And stuff like that is right up my alley.

To each his own. It's not the rig, it's the user.

There was the Russian fatality from a horse shoe on a Velcro rig with shitty Velcro, but that wasn't a BASE jump.

I added a Velcro rig to my arsenal and I can't get enough of it. It has become my go-to rig for almost every jump the peace of mind that comes with the simplicity is great. I'm predominantly a low site and urban jumper

I believe that the Russian fatality that you're referring to was a skydive with a velcro rig. IIRC it was from an airplane with an unmodified door. The jumper sheared the velcro while squeezing out the door, giving himself a horseshoe. As the horseshoe cleared, the PC and bridle came under the slider before inflating, holding the slider at the top of the lines and leading to an incredibly shitty and unrecoverable snivel all the way to the dirt.
The same thing could've happened on a pin rig in this situation and this scenario is much less likely on a base jump.

Indeed, if you look again you'll see I wrote "but that wasn't a BASE jump"

Just playing devils advocate.

Doesn't velcro rig require more pull force to open the container than a pin rig, which would make (IMO) it less appropriate for go n throws? Mostly I'm talking about hesitations

I believe it was Tom who told me bridles are 9' to create extra snatch force to open the container on a Velcro rig, and it just stayed the same length for pin rigs when they came into fashion.

I watched a girl here at the bridge the other day on an fjc get a free fall assist and tow the pc for almost 2 seconds on Velcro, for what it's worth.

I thought longer bridles were made to get the PC out of the burble. Don't really understand how making the bridle longer creates more force?

That's true.

Also the "weight" at the lower end of the bridle has an extra 2 feet to fall, thus more inertia, thus more force. "Snatch" force.

More snatch force on a go'n'throw. Since your acceleration is a lot grater than of that your PC(which is next to 0 with a proper throw), the longer the bridle, the more speed you gain before bridle stretch and more dynamic force is applied to container closing element.

The burble grows logarithmically. It mostly develops at 7+ seconds. At slider down airspeeds the burble is small enough that a very short bridle would clear it just fine.

How big difference do 2 feet make?

Depends on speed at pull time. If you have a go-and-throw with a 7 feet bridle (2.1 meters) your body (if you weigh 80 kg) will have 1646 joules of energy pulling on the bridle. If your bridle is 9 feet (2.7 meters) your energy will be 2116 joules.

Those two feet increases your bodys energy by 33%.

Dislaimer: This are very simplified calculations and factors like air friction and such will have an impact on the numbers, especially with longer delays.

 

Yep, I've seen it. But with go and throw effect is much different because you fall together with the anchor point (PC) and also it's not fixed so after reaching bridle stretch it continues to go down with you.

So actually the video answers the question "in a completely different situation it has such and such effect"

But thanks for sharing anyway :)

EDIT: When I asked I meant in numbers. You can get the idea from the video, but I am more interested in answer like - "if you make 0,5 s delay it will add XX kilos to snatch force

Does that roughlty translates to kilograms/newtons of pull/snatch force? I mean the difference in force would be 33%?

These numbers are the amount of kg/n that the body generates downward. The pilot will react in the different direction and snatch force will be these forces working against each other. How big this force is will depend on the size and type of the pilot chute.

Looking at the physics on this one part of the deployment we see that we can increase the pilot size to achieve the same as increasing the bridle length, but as bridle length is also good for other things it's kind of a win-win situation.

Perhaps we should try measuring the differences. I have a good recording scale that I could probably rig into a bridle (with appropriate back up) and try to test the actual numbers.

Twelve pounds of force to open it now matter how full or how empty the container is. Iv'e jumped a 280, Iv'e jumped a 249, and a 260 and didn't have to change anything. I can pack the 280 wet and loose and the force required to open it is the same. Something you don't get with a pin rig...

Lol okay, sure there, bill nye.

But when jumping from sub-terminal objects, real men throw their PC to bridle stretch, so length doesn't matter, only (PC) size.

Trust me, your mom taught me all about snatch force.

I don't really agree when you say that it doesn't matter. Your pilot will go to line stretch 90 degrees to your side (where you threw the pilot), but your pins/velcro won't open before the pilot is right behind you. It will move in a circular motion where the bridle length is the radius of the circle. My numbers above wont be correct in that kind of movement, but as the bridle length gets longer the radius gets longer and the speed on the pilot increases, increasing the snatch force.

Unless of course you are so strong that you throw hard enough to get bridle stretch, pins popped and canopy to line stretch without the help of gravity.

I'm just making some theories here, and feel free to dissent, but I don't think snatch force is a big issue at really low airspeeds (go and throws) **when using the proper PC**.

Here's why:

I've personally used a 52" pc on a short bridle (47" from the top pin) just longer than my arm to free fall some really low stuff. I used the factory size, type II sleeving closing loops. No special modifications other than the short bridle and a 52 pc.

My two observations about this were A) the burble is negligible at those airspeeds and B) as the pc was already inflated at bridle stretch directly above me as I exited, the snatch force was less important than the pull force. Ultimately, I believe the proper size PC is designed to deploy your system at the properly designated airspeed, regardless of how much snatch force it can apply due to bridle lengths/pitch technique/etc.

Most people I know use 48" pc's for their "low jumps" which usually means about 230-250 feet. This is really overkill I think for most people (except maybe big boy canopies). I have used a 46" down to 200' comfortably (though granted on a 225 canopy). My point is if you are using a 48 for go and throws that aren't ridiculously low, then it really shouldn't matter if you have a ridiculous amount of snatch force. That 48 already puts out a crap ton of drag. I would think that the proper pc for the delay would open that velcro just fine, and certainly pop pins on pull force alone.

On the PCA dropped (mentioned earlier by someone) it was likely a 42 (at the bridge?) and therefore it's not supposed to open the rig up at nil airspeed. So, of course it took a couple seconds to open the rig (velcro yes, but probably even pin rigs would demonstrate this at least a little bit).

To get slightly back on topic, I will say that I think that my pin rig opens with less force than my velcro rig, even when I tightened the pin tension beyond the factory setting... so it's the one I'd use for low jumps. My personal choice because it gives me warm fuzzies.

Facepalm...do it now!

I read your first few lines then had to stop out of protection of my own Intelligence Quotient.

If the bridle is at bridle stretch horizontally when it inflates, and then simply swings up, the "snatch force" is pretty much nil. Maybe there is a language barrier, but snatch force usually occurres when a PC opens and creates a surge of drag that snatches the pins or shrivel flap from the closed container. A longer radius (arm would be the aeronautical term) will not result in a stronger drag unless you calculate the drag caused by more bridle fabric minus the weight of that fabric. Tracking? That will be $2.

Sorry, I don't agree. Maybe there are some language thing that makes me not explain it well enough for you to understand, but I stand by my original post. I will try to explain a little better.

When you throw the pilot horizontally to bridle stretch the only snatch force here will be the force you used to thrown with, and that is pretty much negligible here. At that point your pilot will vertically be at the same level as you. Now you will keep falling down and the pilot will (relatively to your body) swing up. During this swing very little of the force of the pilot will pull on your pins/velcro as the pilot will find the easiest way and that is to move sideways to the point where it is over your body. The pilot will catch air and start inflating, but it is first when the pilot is over your body it will use all it's energy to working against your body moving downward, and that is when the snatch force opens your container.

A longer bridle will make the pilot move 9 feet vertically instead of 7 feet and that will also here create a larger force.

If snatch force was nil when the pilot was over you then the container would not open.

In an effort to end this useless bickering...if you limp-wristedly toss the PC into clean air at the same nearness of your feeble, slow moving body in subterminal freefall, then a longer bridle will allow your non-athletic body to accelerate marginally, thus creating a fractionally greater "snatch force." Don't get a tension knot.

våpenhvile

I don't think figuring out how a pilot chute and bridle works is "useless bickering". I am trying to give the facts based on physics as people were asking about it. As far as I can see you are the only one bickering and telling that my comments makes your IQ lower.


If you look at my first post about this you will see that the energy generated after a limp throw in a slow moving freefall will be increased by 33% with a longer bridle. That is in no way "marginal".


Sure, not a problem