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rchamseddine

Hard opening nightmare - help

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JohnMitchell

Having line twists lessens the angle of the lines going thru the grommets on the slider. Could that reduced friction on the grommets been a factor in the slider coming down faster, causing a harder opening?



Doesn't the force generated by the canopy inflating cause the slider to go down?

Technically the slider always has a tendency to go up, since we are always descending (why we collapse it so is not wobbling behind our heads), but once the force of the canopy inflating is greater than the force generated by the wind against the slider the slider comes down.

Now the lines friction definitely has some role on how fast the slider comes down (have seen slider hang up on a saber 170 with Dacron lines on every other jump), but if that was the major reason for hard/soft openings, then all canopys with HMA would open pretty quick.

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JohnMitchell

Yeah, good analysis. Line friction is, at best, a minor factor, I'll now assume.

Students don't have collapsing sliders, though, and their sliders don't go back up. The real reason we collapse them is to reduce drag and that annoying flapping sound. ;):)



Don't use what I say as a truth since I am not a manufacture, and since is only based on my own observations, so I am probably missing something

I agree that's the reason why we collapse our slider, I was trying to make a point that makes sense only in my head I guess and it came out confusing, but when we don't collapse our slider, the pocket of air created in the slider tend to form an upward angle, what keeps the slider down is the spread of the lines, is more or less what I was trying to say.

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JohnSherman

It appears that the opening peak had already occurred before the video begins.
Opening shock is divided into 2 modes. Snatch and inflation. What we see on the video is inflation not the snatch. The stress in the jumpers body as he is pulled up and out of the frame suggests that he has endured a strong snatch force. This interpretation is not consistent with the movement of the goggles, described by the jumper, but that is not uncommon.

I would speculate that he had a line dump.



It would have better if his video started from the moment the PC was pitched so we could get some estimate of the time that had elapsed until he began to slow down and get stood up. (And perhaps even see what the bag looks like as it exits the container; and exactly when did lines become taut and straight) Still, looks like those cells were inflating extremely early.

For comparison, here's my wonderfully snivelly pilot 188 opening at 1/10 speed (so 10 sec of video = one sec of real time): http://www.youtube.com/watch?v=xtTbrdGW-dA. Mine takes 5-6 seconds to do what his did in less than 2.

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JohnMitchell

Having line twists lessens the angle of the lines going thru the grommets on the slider. Could that reduced friction on the grommets been a factor in the slider coming down faster, causing a harder opening?

I don't know, but I would guess that it requires less force to push the slider down twisted lines (at least initially) than properly spread lines. I've never really thought about it.

The other thing is that if one riser is higher than the other, then the slider is no longer flat up at the stops. I don't know what happens then either.

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Quote



The other thing is that if one riser is higher than the other, then the slider is no longer flat up at the stops. I don't know what happens then either.



In that case you're loading one side of the canopy more than the other, at least for a short time.

That will usually cause a harder than normal opening...and depending on the canopy & it's general condition may cause some damage if the uneven loading is extreme enough.










~ If you choke a Smurf, what color does it turn? ~

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You need to speak to the instructors and ask them about openings. Because only a few of our students complained and we only noticed hard openings on a few videos we blamed it on the packing. And because most of the students didn't have a clue how a normal opening should be a lot of them didn't complain and they assumed that the parachute opens hard most of the times. We tried all of the packing tricks we know of and it didn't help. We contacted Aerodyne and they have sent us replacement sliders on all canopies larger then 230. That solved the hard openings.

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aljazm

We tried all of the packing tricks we know of and it didn't help. We contacted Aerodyne and they have sent us replacement sliders on all canopies larger then 230. That solved the hard openings.



Ok, very good to hear. Do you know the original poster that complained of the hard openings? Maybe he does not know about the new sliders.

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aljazm

We tried all of the packing tricks we know of and it didn't help. We contacted Aerodyne and they have sent us replacement sliders on all canopies larger then 230. That solved the hard openings.



Great idea, thnx. I will get in touch with instructor to check this possibility.

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AlanS

Could a line twist prevent the slider from coming down and as a result change how the chute opens (i.e. either quicker or slower)?



Think about this question a little bit.

In what position does the slider start? What is it doing to opening speed when it's there?

In what position does the slider end up? What is it doing to opening speed now?

So... if twists trap the slider close to the canopy, what is the likely effect (if any) on opening speed?
--
"I'll tell you how all skydivers are judged, . They are judged by the laws of physics." - kkeenan

"You jump out, pull the string and either live or die. What's there to be good at?

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Yes fallrate might be interesting to know, also bodyposition on opening (the video starts too late).

As said before,any canopy can open hard and bruise someribs or worse - my vengeance always opened sloooow but on my first jump during my first nationals I ended up in the hospital like you for xrays and stuff, couple bruised ribs (OUCH). Never found out why, canopy never did that to me again either in the following hundreds of jumps.

BTW what are your hands doing on the risers/3 rings? That's good way to get them hurt. Only after the canopy has opened and the slider has come down should you reach up. Otherwise you can hurt your fingers or even get trapped by a linetwist (happened to me once.... both hands!).

So, hands out to the side until you have done your visual canopy check and are at the point where you need to grab brakes or need to kick out of linetwist, but *look* before you grab.
Grabbing the 3 rings like you do in this video serves no purpose other than you 'wanting to hold on to something', better train yourself not to do that.

Of course always be ready to grab rear risers to steer away in an emergency.

ciel bleu,
Saskia

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perfect, now at least that might explained the twisted middle left finger and its pain. I guess its just a reflex thinking it would ease the load on my lower part due to previous pain. But will try to remember the advice next time.

Body position was normal arch with no turns. However as you and others mentioned it happens even everything appear normal.

Thnx :)

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