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8 May 2013 Fatality Skydive Deland

 

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pchapman  (D 1014)

May 14, 2013, 7:11 AM
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Re: [GoneCodFishing] 8 May 2013 Fatality Skydive Deland [In reply to] Can't Post

Fixed your (now edited out) link & clickified:
http://www.unitedparachutetechnologies.com/...hook/skyhook-all.jpg


The Skyhook does work fast, no doubt about that.

Notice how the jumper chopping the spinning "mal" rotated 180 degrees in the 1.0 seconds from the chop Wink

(Not enough to normally cause problems!)


(This post was edited by pchapman on May 14, 2013, 7:12 AM)


GoneCodFishing

May 14, 2013, 7:15 AM
Post #102 of 161 (3369 views)
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Re: [pchapman] 8 May 2013 Fatality Skydive Deland [In reply to] Can't Post

Sorry for that, been trying to get the inline image feature to work Wink

Oh, and yes, the spin after the cutaway is what i was trying to point out.


(This post was edited by GoneCodFishing on May 14, 2013, 7:32 AM)


f94sbu  (D 16017)

May 14, 2013, 7:52 AM
Post #103 of 161 (3342 views)
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Re: [pchapman] 8 May 2013 Fatality Skydive Deland [In reply to] Can't Post

pchapman wrote:
f94sbu wrote:
Lets do the math to see if your logic holds together:
[..] This means that you were subjected to 128 - 192 G just prior to the cutaway.

Come on... even many students find out that they can have a canopy "open with" just one full line twist... but they keep rotating underneath until they have a few more twists.

(Whether or not the jumper you were replying to actually had exactly 12 twists...)

RSL's might get to be more accepted if some of their proponents didn't scare others away by going so weird with the math and physics. CrazySmile

My bad, lets say that 6 of the twists were introduced during deployment and the other 6 after deployment. Thats still 64-96G of initial rotation. And it is another 3 seconds where the jumper did not do anything after the reserve was deployed (other than just watching the line twists get more and more severe.) I have a hard time understanding your point actually. People make all sorts of claims regarding RSL's and line twists, but if we dont use physics to tell things apart, we will never get closer to a common ground. All we will have is two groups of people telling that the other group is wrong on the basis of a few personal experiences. Which is kind of funny because in this thread we have had almost identical testimonies from spinning malfunctions where the outcome has been either no line twists at all or multiple line twists. Either someone is lying or the reality is not as simple as some might try to make it. I prefer the later and using physics to explain why both groups have made valid observations and why some of the conclusions are incorrect.
If you don't like physics arguments, please share with us how you would like to be convinced? Crystal balls and magic wands? Angelic


f94sbu  (D 16017)

May 14, 2013, 7:59 AM
Post #104 of 161 (3334 views)
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Re: [crotalus01] 8 May 2013 Fatality Skydive Deland [In reply to] Can't Post

crotalus01 wrote:
The RSL may or may not have factored into the linetwists - I dont know. I had one hand on each handle and was less than 1 second between the cutaway and reserve fire. I didnt look at my reserve cable to see if it was kinked after the fact. As stated I was well aware I was low and I just wanted a landable canopy over my head ASAP. However, the fact that the RSL -could- have caused the linetwists was definitely a factor in my decision to disconnect it. Another reason is that I do a lot of altitude hop and pops and CRW. Now that I am starting to do more RW I am considering reconnecting it (and since I retired the Sabre I think it very unlikely I will end up with that many broken lines again).
Edit - I was not advocating anyone to disconnect their RSL.

Fair enough. As I said, I respect your decisions to jump without an RSL and the CRW one seems like a perfectly valid one (I do not jump CRW so I have not done the maths myself). In your initial post, you made it fairly clear that your decision to jump without an RSL was based on your reserve ride with multiple linetwists and it just wasnt clear this was something you would advocate to others or keep to your self.


crotalus01  (B 28932)

May 15, 2013, 5:34 AM
Post #105 of 161 (3090 views)
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Re: [f94sbu] 8 May 2013 Fatality Skydive Deland [In reply to] Can't Post

It is strictly a personal decision and I was not and am not advocating anything, simply sharing my experience. Just for further clarification there was no spinning under my reserve - it was open and flying straight with twists from right above my neck all the way up. I believe it was 12 that I counted as I kicked them out but to be honest I was pretty fucking stressed at the time so it may have been more or less....but it was a lot, enough for my buddy to remark he had never seen that many on a reserve before.
Edit - I meant I was not twisting up under the reserve, it opened with the twists so obviously something caused the bag to spin as it came out.


(This post was edited by crotalus01 on May 15, 2013, 5:42 AM)


format  (B 15348)

May 15, 2013, 9:26 AM
Post #106 of 161 (2999 views)
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Re: [f94sbu] 8 May 2013 Fatality Skydive Deland [In reply to] Can't Post

Please somebody move this whole RSL raving on another thread and leave this incident on facts


chuckakers  (D 10855)

May 15, 2013, 7:05 PM
Post #107 of 161 (2783 views)
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Re: [pchapman] 8 May 2013 Fatality Skydive Deland [In reply to] Can't Post

pchapman wrote:
Notice how the jumper chopping the spinning "mal" rotated 180 degrees in the 1.0 seconds from the chop....

Yes, and notice how the jumper's rig turns with him - as does the reserve as it deploys!!

Did we all forget that if the jumper doesn't turn fast, the rig and deploying components will just turn with him?


jumpinjackflsh  (B 27757)

May 15, 2013, 9:55 PM
Post #108 of 161 (2723 views)
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Re: [format] 8 May 2013 Fatality Skydive Deland [In reply to] Can't Post

I understand your issue.

Though the facts as known have been given.

The resulting rsl discussion was born out of the facts.

Sometimes it may not seem in-line with the topic but in this case it is.

We all know that a cutaway that low, is usually non-recoverable. When someone is equipped with an RSL or skyhook, the question remains, what happened.

In that line of thought, these discussions take the turns that they take.

I don't have an RSL or an AAD but I can say, this discussion has me wanting to install an RSL, period. I'll take line twists on my reserve any day vs not having a reserve.

Though I'll close by saying, cutting away at 300' I'm not sure an RSL or Skyhook would've prevented this.

I think it's also valid saying if you have an RSL, use it. For obvious reasons you'd disconnect "on the ground" or on approach if you see you'll have to cut away (building, tree, high winds, etc...). It's also obvious you wouldn't use an RSL in CRW where cutting away is a whole other set of rules.

Either way, at the end of the day, the discussion is valid. Anytime someone goes in, without getting a reserve over their head, discussing why can lead us down a few roads.


Terrible thing. BSBD


Jack


The111  (D 29246)

May 16, 2013, 12:53 PM
Post #109 of 161 (2477 views)
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Re: [jumpinjackflsh] 8 May 2013 Fatality Skydive Deland [In reply to] Can't Post

jumpinjackflsh wrote:
The resulting rsl discussion was born out of the facts.

It seems to me it was built around the speculation that the jumper attempted to detach his RSL in the air. That is not a known fact in this incident.


likearock  (D 24640)

May 16, 2013, 3:40 PM
Post #110 of 161 (2408 views)
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Re: [The111] 8 May 2013 Fatality Skydive Deland [In reply to] Can't Post

The111 wrote:
jumpinjackflsh wrote:
The resulting rsl discussion was born out of the facts.

It seems to me it was built around the speculation that the jumper attempted to detach his RSL in the air. That is not a known fact in this incident.

That was only part of the discussion I believe. Most of it had to do with the general question of whether or not the RSL should have been detached (regardless of when that detachment was done).


livendive  (D 21415)

May 16, 2013, 3:53 PM
Post #111 of 161 (2399 views)
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Re: [jacketsdb23] 8 May 2013 Fatality Skydive Deland [In reply to] Can't Post

I've had line twists on a reserve that could have resulted in two fatalities, but it was a rather unique situation and thus doesn't contradict the statistics.

In my case, I had three lines break at the cascades during opening, after which the rather long bits still connected to the risers sprung back in the opposite direction they had stretch, i.e. toward my student and I. The canopy began behaving quite poorly in rather short order, so I chopped it not realizing where those lines were. As the canopy went away, the lines were pulled taut across my throat and retarded the canopy departure just long enough to get the RSL-deployed freebag spinning. The number of linetwists we had was rather shocking...from the risers to the top, with the stabilizers close enough to high five each other if the slider wasn't in their way. Plus, in typical tandem fashion, what little flying the reserve was doing was of the stall-surge variety. This was somewhere in the neighborhood of 4500'. From there to 2000', I was unable to get us out of a single one of the twists. It was kick-spin-kick-stall-kick-spin-kick-surge-rinse-repeat. Completely exhausted and having tried every trick I'd ever heard of and some I hadn't, I looked down at around 2,000' to see if staff were likely to be calling a lifeflight or a coroner and found we were centered over a busy 4-lane freeway. I decided that keeping busy was preferable to just watching the asphalt and semi's get bigger, so went back to what I'd been doing. Suddenly, just a couple hundred feet later, I made progress on one twist...invigorated, I got us the rest of the way out in rather short order (after which my student's first words since leaving the plane were "thank you for saving my life!") and managed a stand-up landing. The funny way people were looking at me on the ground was a clue as to what had happened, but once I saw a mirror I understood. It's a pretty unlikely situation, but in my case, an extra second between chop and reserve would have likely made for a much less terrifying ride.

Blues,
Dave


mpreil  (D 17822)

May 16, 2013, 8:46 PM
Post #112 of 161 (2295 views)
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Re: [jacketsdb23] 8 May 2013 Fatality Skydive Deland [In reply to] Can't Post

jacketsdb23 wrote:
If you choose not to jump an RSL thats fine, I don't use one either. But its not because I'm afraid of going in on line twists with the reserve.....

RSL's work and have saved lives.

Not a criticism - but I'm really curious about your calculus of risk. Why don't you have an RSL? Don't tell me it's too windy at Byron and you may need to cutaway after landing, you can always disconnect the RSL while flying - I did it all the time when the winds were up.

You have a great attitude about safety and you understand the equipment as well as anyone I know - so why not have one? I'm curious what you see as the downside. If you ever have to chop after loosening your chest strap and find the reserve handle isn't where you expected, you might really find it useful.

Again, let me emphasize that I'm not trying to start an argument. I am really interested in hearing your thought process. If you don't want to answer here just say so, I'll stop by and talk to you over a beer some evening while I'm driving home from "the other place".


JohnMitchell  (D 6462)

May 16, 2013, 10:39 PM
Post #113 of 161 (2253 views)
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Re: [livendive] 8 May 2013 Fatality Skydive Deland [In reply to] Can't Post

HOLY FUCK!Shocked


airtwardo  (D License)

May 17, 2013, 8:23 PM
Post #114 of 161 (1904 views)
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Re: [JohnMitchell] 8 May 2013 Fatality Skydive Deland [In reply to] Can't Post

JohnMitchell wrote:
HOLY FUCK!Shocked


...and THEN some! Shocked


Kudos Dave for 'keeping your head' in a bad situation! Cool


likearock  (D 24640)

May 18, 2013, 5:58 AM
Post #115 of 161 (1805 views)
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Re: [livendive] 8 May 2013 Fatality Skydive Deland [In reply to] Can't Post

livendive wrote:
It's a pretty unlikely situation, but in my case, an extra second between chop and reserve would have likely made for a much less terrifying ride.

Great job, Dave, but to put it in perspective for this general discussion, you do fly a pretty high performance canopy, do you not? The tendency and speed of "spinning up" after cutting away a cross brace is different from that of other canopies.


(This post was edited by likearock on May 18, 2013, 6:04 AM)


dzjnky  (D 28727)

May 18, 2013, 7:19 AM
Post #116 of 161 (1774 views)
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Re: [likearock] 8 May 2013 Fatality Skydive Deland [In reply to] Can't Post

likearock wrote:
Great job, Dave, but to put it in perspective for this general discussion, you do fly a pretty high performance canopy, do you not? The tendency and speed of "spinning up" after cutting away a cross brace is different from that of other canopies.

Ditto on the great job, Dave!
@likearock - this was a tandem jump for Dave - I doubt it was on a "high performance canopy" - I am not aware of many cross-braced tandem canopies Wink


likearock  (D 24640)

May 18, 2013, 4:29 PM
Post #117 of 161 (1644 views)
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Re: [dzjnky] 8 May 2013 Fatality Skydive Deland [In reply to] Can't Post

dzjnky wrote:
likearock wrote:
Great job, Dave, but to put it in perspective for this general discussion, you do fly a pretty high performance canopy, do you not? The tendency and speed of "spinning up" after cutting away a cross brace is different from that of other canopies.

Ditto on the great job, Dave!
@likearock - this was a tandem jump for Dave - I doubt it was on a "high performance canopy" - I am not aware of many cross-braced tandem canopies Wink

Missed that - my bad! Smile


sebcat  (D 22826)

May 19, 2013, 12:17 PM
Post #118 of 161 (1436 views)
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Re: [f94sbu] 8 May 2013 Fatality Skydive Deland [In reply to] Can't Post

f94sbu wrote:
pchapman wrote:
f94sbu wrote:
Lets do the math to see if your logic holds together:
[..] This means that you were subjected to 128 - 192 G just prior to the cutaway.

Come on... even many students find out that they can have a canopy "open with" just one full line twist... but they keep rotating underneath until they have a few more twists.

(Whether or not the jumper you were replying to actually had exactly 12 twists...)

RSL's might get to be more accepted if some of their proponents didn't scare others away by going so weird with the math and physics. CrazySmile

My bad, lets say that 6 of the twists were introduced during deployment and the other 6 after deployment. Thats still 64-96G of initial rotation
How did you come up with those numbers?

We're talking about a human body revolving around its centre at about one, two revolutions per second after cut away, during the reserve deployment process. Just taking the figure skating analogy previously posted in this thread and applying it to this situation makes me wonder if your numbers are correct.

I don't think 12 line twists happening would be unlikely. Partly because, as previously stated, some/most of those twists would occur post-deployment.

I don't have an RSL (CRW). I believe in personal choice. I'm not opposed to RSL's and if anyone asked me I would recommend having one. But you're gonna have to show some calculations or I would second what pchapman wrote.


f94sbu  (D 16017)

May 20, 2013, 5:00 AM
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Re: [sebcat] 8 May 2013 Fatality Skydive Deland [In reply to] Can't Post

Lets say that you create 6 line twists during your reserve deployment, that means that your body must have rotated 6 times around its axis during the time the reserve deployed. I just approximated the reserve deployment speed to the max time allowed for a reserve to deploy (In reality, I would expect most reserves to open quicker).
This gave me 2 revolutions per second.
In order for your body to rotate like this after cutaway, it must have been rotating with the same speed before the cutaway. The cutaway itself does not change how quickly the jumper is rotating around his bellybutton. During a spinning malfunction, you can model your body like the bellybutton is making a wide circle and the body itself is rotating around the bellybutton. Both will have the same revolutions per second.

The G-forces applied to a body moving in a circle can be calculated using: G = w^2 * r / 9.81 where w equals the rotational speed in radians per second and r equals the distance between the center of the rotation and the body itself. 9.81 is used to convert true acceleration (m/s^2) to the nominal value that you experience standing in the surface of the earth.

I have to admit that I made a mistake when I halved the number of line twists as I only halved the G forces. As the G-forces are proportional to the square of the rotational speed, the correct numbers should have been 32 - 48G for a rotational speed of 2 revolutions per second. Still a fairly respectable G force if you ask a fighter pilot or an astronautSmile. The analogy with a figure skater does not apply here as the center of gravity of the figure skater is not moving in a circle. The figure skater may be spinning very fast, but if you made the figure skater spin around a point 2 meters away from him/her, it would result in an immediate blackout .

Keep in mind that I have tried to skew all the numbers to get as low G-forces as possible. When I had a choice, I made the line lengths shorter and the rotational speed slower, I still get incredibly high G-forces. All I am trying to prove with this is that if line twists under a reserve is tightly coupled to a spinning main, the main would have to rotate much faster than a human would be able to sustain.

Your point about the line twists increasing after the deployment is fully noted, however, I do have to ask you why that matters? A jumper that is unable to stop themselves from spinning for lets say 3 seconds, under a fully deployed reserve, do you think that they are better off trying to stop the spinning while accelerating towards the earth with no canopy out?

Personally, I think that the twists/no twists under the reserve has a lot of other factors other than just the rotational momentum left from the spinning main. Cutting away, pulling silver and arching as hard as you can is probably a much better recipe for survival compared to cutting away, trying to get stable and then pull silver.Given that people are regularly cutting away from spinning mains with an RSL connected, without getting line twists makes me think that it is perfectly possible to do so.
The number of lives lost every year which could have been saved by an RSL makes me very concerned about the logic that some people use when they try to convince others why an RSL is dangerous. There are situations where the RSL is introducing trouble, but lets keep those separate from the situations that most skydivers find themselves in.


sundevil777  (D License)

May 20, 2013, 6:39 AM
Post #120 of 161 (1160 views)
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Re: [f94sbu] 8 May 2013 Fatality Skydive Deland [In reply to] Can't Post

In reply to:
your body must have rotated 6 times around its axis during the time the reserve deployed.

Have you ever had linetwists on a main? Was it because you were rotating?

The freebag can rotate due to the container giving it a kick while it is leaving, which is more likely if you aren't shoulder-level.


f94sbu  (D 16017)

May 20, 2013, 8:36 AM
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Re: [sundevil777] 8 May 2013 Fatality Skydive Deland [In reply to] Can't Post

sundevil777 wrote:
In reply to:
your body must have rotated 6 times around its axis during the time the reserve deployed.

Have you ever had linetwists on a main? Was it because you were rotating?

The freebag can rotate due to the container giving it a kick while it is leaving, which is more likely if you aren't shoulder-level.

Thats my whole point, thanks for missing it Cool. The standard reasoning against the use of an RSL is that a spinning main would give you line twists on the reserve. Now you are saying that there are other reasons why you might get line twists on the reserve? Those are rarely mentioned by people who had the line twists. With my physics argument, I just showed that the number of line twists that people are describing is simply not possible to create with your rotational momentum _alone_. You just pointed out a factor that could make a difference regardless the use of an RSL. And thats my whole point. Dont blame the line twists on the spinning main.

Regarding your main vs reserve comparison, keep in mind that the reserve freebag is stowless, it doesnt have a kill line, the pilot chute is more or less unused and the riser covers are open. (If you cutaway from a spinning main). I dont have any data for this, but I get a feeling that frequency of reserve line twists are lower than the frequency of mains with line twists.


Ron

May 20, 2013, 1:22 PM
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Re: [f94sbu] 8 May 2013 Fatality Skydive Deland [In reply to] Can't Post

Quote:
Thats my whole point, thanks for missing it Cool. The standard reasoning against the use of an RSL is that a spinning main would give you line twists on the reserve. Now you are saying that there are other reasons why you might get line twists on the reserve?

An unstable main deployment can give you line twists on your main... The same can also give you line twists on your reserve. And flipping after a chop is being unstable.

The wind hitting your main bag can spin it up... The same for your reserve. And flipping or spinning after a chop can put the wind on your back.

If you are sideways or flipping when you deploy your main, you risk a malfunction.... The same thing applies to your reserve.

There is no doubt that having something out is better than going in at full speed... But there is also little doubt that it is better to be stable when you deploy a canopy.


f94sbu  (D 16017)

May 20, 2013, 2:16 PM
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Re: [Ron] 8 May 2013 Fatality Skydive Deland [In reply to] Can't Post

Thank you very much for taking my quote out of contextFrown I never said that it is not possible to get a malfunction on the reserve, it was a rhetorical question. My point was that the number of reported line twists are higher than the number you would get from just rotating. Line twists on reserves are caused by a lot of other factors too (although they are minimized due to the design of the rig, the freebag etc.) However you cannot guarantee that they wont happen. When people argue that they are caused by RSLs deploying the reserve too fast after a spinning main, they have discounted a lot of other factors.


The111  (D 29246)

May 20, 2013, 4:09 PM
Post #124 of 161 (872 views)
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Re: [f94sbu] 8 May 2013 Fatality Skydive Deland [In reply to] Can't Post

f94sbu wrote:
32 - 48G for a rotational speed of 2 revolutions per second. Still a fairly respectable G force if you ask a fighter pilot or an astronautSmile.

If by "respectable," you mean will cause most people to either die, experience some semi-permanent injury (like a popped out eyeball for example), or at the very least black out... then sure. Considering the way a parachute harness attaches to the body and leaves the head completely unsupported, I suspect that any skydiver experiencing harness load at 30G+ will have his neck broken as a bare minimum. I also wouldn't be surprised if lines/canopy failed in multiple places at a ridiculous hypothetical load like 50G.

Those are insane G loadings that I suspect very few if any living skydivers (and humans period) have ever been exposed to. I'm not going to even begin to make an engineering analysis of the forces at work in a dynamic situation like this, but whatever the equation is, it's very unlikely to commonly result in such a high loading on a human body.


(This post was edited by The111 on May 20, 2013, 4:10 PM)


f94sbu  (D 16017)

May 21, 2013, 1:18 AM
Post #125 of 161 (704 views)
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Re: [The111] 8 May 2013 Fatality Skydive Deland [In reply to] Can't Post

Quote:
Those are insane G loadings that I suspect very few if any living skydivers (and humans period) have ever been exposed to. I'm not going to even begin to make an engineering analysis of the forces at work in a dynamic situation like this, but whatever the equation is, it's very unlikely to commonly result in such a high loading on a human body.

That's my point. When someone says "Witnesses estimated the rotation to be 2 revolutions per second", the above G-forces would be the result. All I am trying to prove with my logic is that no one is able to rotate that quickly without dying.


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