Forums: Skydiving: General Skydiving Discussions:
A better way out of line twist!

 

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sniper1rfa  (A 59087)

Nov 8, 2010, 10:54 AM
Post #76 of 116 (3237 views)
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Re: [mjosparky] A better way out of line twist! [In reply to] Can't Post

In reply to:
Now take you little experiment and do it a 120 mph attached to an inflated airfoil that will fly in the same direction as the twists. Maybe.

I'm glad you've learned as much about the world as it's possible to learn.

Obviously one can never develop a theoretical framework to explain the phenomenon we see in our daily lives, and the only advances in technology and methodology we see are done through real world trial and error. That's why they had to deploy the GPS constellation several times before they got it to work, and why auto makers still crash 50+ prototype cars before they get the design right. That's why FEA is considered a crackpot idea touted by useless engineers and why CAD never really caught on.


I'll keep poking away, since I'm interested in the problem, but if I come up with anything interesting I'll just keep it to myself. Sorry for wasting your time.


(This post was edited by sniper1rfa on Nov 8, 2010, 10:55 AM)


DocPop  (C License)

Nov 8, 2010, 11:02 AM
Post #77 of 116 (3230 views)
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Re: [Ronaldo] A better way out of line twist! [In reply to] Can't Post

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Try this experiment: sit in an office chair (spin type with good bearings) and lift your feet off the floor. Now try to rotate yourself kicking your legs, arms, whatever you want, youll remain facing the same direction.

This is entirely false. I just did a 360 by kicking my legs on my office chair.


ridestrong  (C 38471)

Nov 8, 2010, 11:38 AM
Post #78 of 116 (3217 views)
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Re: [Trevor] A better way out of line twist! [In reply to] Can't Post

In reply to:
Here's a video of me doing this technique a few years ago on a XAOS 21 88 loaded at 2.3:1. It works every time for me and I've never had to cutaway line twists:
http://www.youtube.com/...qbS0#watch-vid-title

{edited to fix link}

Saw this in another vid about a year ago and have used it a couple times.... works great!! Way better than trying to pull the risers apart and kicking out of it.

Great post!


mjosparky  (D 5476)

Nov 8, 2010, 12:57 PM
Post #79 of 116 (3194 views)
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Re: [sniper1rfa] A better way out of line twist! [In reply to] Can't Post

You sure over complicate things.
As for learning things, I spent over 20 years in testing and development of parachutes and parachute systems. While I am a long way from having learned it all I do have a fair understanding of the topic at hand. You keep poking but there comes a time where a real live person must go in the air and see if the engineers and your theoretical framework have it right and wrong. You can call it trial and error or anything else you want but thats the way it works in the real world.

Sparky


skydivr  (D 17590)

Nov 9, 2010, 7:39 AM
Post #80 of 116 (3142 views)
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Re: [ridestrong] A better way out of line twist! [In reply to] Can't Post

In reply to:
In reply to:
Here's a video of me doing this technique a few years ago on a XAOS 21 88 loaded at 2.3:1. It works every time for me and I've never had to cutaway line twists:
http://www.youtube.com/...qbS0#watch-vid-title

{edited to fix link}

Saw this in another vid about a year ago and have used it a couple times.... works great!! Way better than trying to pull the risers apart and kicking out of it.

Great post!

Fascinating and an interesting alternative.

Best option would to try and not get the twists in the first place. Proper packing and body position would help, but the smaller the canopy gets the more likely twists will occur. I'm too old to jump that really small stuff anyway.


Ronaldo  (D 34728)

Nov 9, 2010, 12:38 PM
Post #81 of 116 (3134 views)
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Re: [DocPop] A better way out of line twist! [In reply to] Can't Post

In reply to:
This is entirely false. I just did a 360 by kicking my legs on my office chair.
Youre certainly using the static friction off the bearings as a reaction force every time you kick. According to Newtons 3rd law of motion for each action there is an equal and opposite reaction. A body simply cannot change its momentum applying force to itself. This would violate the Law of Momentum Conservation.


Ronaldo  (D 34728)

Nov 9, 2010, 1:07 PM
Post #82 of 116 (3127 views)
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Re: [Beatnik] A better way out of line twist! [In reply to] Can't Post

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Next time you are under canopy try kicking yourself into a line twist. By your theories it can't be done and if you can report back and explain it.

If still are determined to say it does nothing, then I must have done something super special when I kicked myself into a line twist for a photo. Sly
Actually It would be much easier to get into twists than getting out of them for the reasons I mentioned on my previous post. If the canopy is open without line twists the risers are spread and tensioned. This means you have a reasonably stiff structure from which you are suspended. When you kick your body (torso) pushes the canopy (risers/harness) and it reacts on the opposite direction. The first kick is the key for succeeding in this attempt because it is when you have the strongest platform to start with (longer leverage). Once the first turn is made the risers are joined together losing the leverage effect and inertia helps you getting into more turns.
BTW, Im not saying that kicking does nothing, it does but due to the geometry of the system (jumper/ twisted lines) the effects are dramatically reduced. It definitely wouldnt do anything in the space (but in this case twists would be our last concernLaugh)


pchapman  (D 1014)

Nov 9, 2010, 1:44 PM
Post #83 of 116 (3122 views)
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Re: [Ronaldo] A better way out of line twist! [In reply to] Can't Post

In reply to:
In reply to:
This is entirely false. I just did a 360 by kicking my legs on my office chair.
Youre certainly using the static friction off the bearings as a reaction force every time you kick. According to Newtons 3rd law of motion.

But to extend that thought:
With line twists, one isn't hanging from a single ideal zero friction point. There is a small amount of untwisting torque at the start of the line twists at the bottom. And in a sense there may be a little aerodynamic friction, keeping someone in a stable sitting back to the wind position, or at least changing the drag up and down at different angles to the wind.

So if someone is doing the traditional kicking out of line twists under some student canopy, aren't they doing something like with the office chair?

A sharp movement twists half the body in the desired direction, then a slow movement that doesn't overcome the friction allows the other half of the body to catch up without undoing what was done before.

Or also, the quick movement is done at a wide radius, and the slower movement is done at a smaller radius so there's less torque being applied, making it easier to 'push off' the friction.

In this whole line of thought, what I haven't thought through yet is just what the friction profile is like for the office chair vs. person under line twists. For the self twisting to work, I think one needs some sort of resisting friction or force that doesn't linearly increase with the force applied -- so a small constant friction force at a low applied force works well. While it can come from aerodynamic drag in some positions, I'm not sure how it might exist in the line twists themselves.


Beatnik  (D 1051)

Nov 9, 2010, 2:13 PM
Post #84 of 116 (3116 views)
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Re: [Ronaldo] A better way out of line twist! [In reply to] Can't Post

In reply to:
Actually It would be much easier to get into twists than getting out of them for the reasons I mentioned on my previous post. If the canopy is open without line twists the risers are spread and tensioned. This means you have a reasonably stiff structure from which you are suspended. When you kick your body (torso) pushes the canopy (risers/harness) and it reacts on the opposite direction. The first kick is the key for succeeding in this attempt because it is when you have the strongest platform to start with (longer leverage). Once the first turn is made the risers are joined together losing the leverage effect and inertia helps you getting into more turns.
BTW, Im not saying that kicking does nothing, it does but due to the geometry of the system (jumper/ twisted lines) the effects are dramatically reduced. It definitely wouldnt do anything in the space (but in this case twists would be our last concern)

I can stop the turn and then keep on going, it isn't much more difficult. I understand your theory behind this but it is really easy to do whether you keep going or stop between the twists. If you stop completely then there is no inertia to keep you going. I have done it both ways and it really isn't that bad. I understand your previous post quite well, I have done more than my share of physics. In space it wouldn't do anything like you say but here there are many forces acting on you more than just the few that most people are associating with this problem.


slappy1  (A License)

Aug 9, 2011, 10:57 AM
Post #85 of 116 (2986 views)
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Re: [pilotdave] A better way out of line twist! [In reply to] Can't Post

in response to that step-through - can you explain what COULD have gone wrong there? I'm trying to figure out if normally that would be a cut-away situation (regardless of the line twists), given one had enough altitude. looks like it would generally be pretty stable to me, assuming brake lines were where they needed to be.


Arvoitus  (D 3917)

Aug 10, 2011, 3:26 AM
Post #86 of 116 (2881 views)
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Re: [JohnDeere] A better way out of line twist! [In reply to] Can't Post

I remember reading this thread a long time(2 years) ago but I completely forgot about his method. However I recently saw video of jumper using this method and happened to get a line twist on wing suit jump just few days later. So I decided to try this out and I really liked how well it worked : http://www.youtube.com/watch?v=eaYX8pKLhhk


Southern_Man  (C License)

Aug 10, 2011, 10:10 AM
Post #87 of 116 (2807 views)
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Re: [Arvoitus] A better way out of line twist! [In reply to] Can't Post

In reply to:
I remember reading this thread a long time(2 years) ago but I completely forgot about his method. However I recently saw video of jumper using this method and happened to get a line twist on wing suit jump just few days later. So I decided to try this out and I really liked how well it worked : http://www.youtube.com/watch?v=eaYX8pKLhhk

Nice video--what is the canopy and what is the wingloading on it? Looks like it is flying pretty level and not spinning/diving.


wildcard451  (D License)

Aug 10, 2011, 12:09 PM
Post #88 of 116 (2776 views)
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Re: [Arvoitus] A better way out of line twist! [In reply to] Can't Post

In reply to:
I remember reading this thread a long time(2 years) ago but I completely forgot about his method. However I recently saw video of jumper using this method and happened to get a line twist on wing suit jump just few days later. So I decided to try this out and I really liked how well it worked : http://www.youtube.com/watch?v=eaYX8pKLhhk

Does anyone have any video of someone using this on highly-loaded, spinning, diving x-braced thingies with any success?


Arvoitus  (D 3917)

Aug 10, 2011, 12:46 PM
Post #89 of 116 (2758 views)
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Re: [Southern_Man] A better way out of line twist! [In reply to] Can't Post

In reply to:
In reply to:
I remember reading this thread a long time(2 years) ago but I completely forgot about his method. However I recently saw video of jumper using this method and happened to get a line twist on wing suit jump just few days later. So I decided to try this out and I really liked how well it worked : http://www.youtube.com/watch?v=eaYX8pKLhhk

Nice video--what is the canopy and what is the wingloading on it? Looks like it is flying pretty level and not spinning/diving.

Its a 170 sqft Sabre 2 loaded roughly at 1.23:1.

In reply to:
Does anyone have any video of someone using this on highly-loaded, spinning, diving x-braced thingies with any success?

The video I saw of a jumper using the technique was done with a 88 sqft cross-braced, elliptical canopy loaded at 2.3:1. Also the canopy is spinning/diving when the jumper undoes the twists. Note : I'm not saying that you should definitely do this if you're spinning/diving on a highly loaded x-braced elliptical canopy.

http://www.youtube.com/watch?v=5FD2I8OqbS0


wildcard451  (D License)

Aug 10, 2011, 2:23 PM
Post #90 of 116 (2738 views)
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Re: [Arvoitus] A better way out of line twist! [In reply to] Can't Post

In reply to:
In reply to:
Does anyone have any video of someone using this on highly-loaded, spinning, diving x-braced thingies with any success?

The video I saw of a jumper using the technique was done with a 88 sqft cross-braced, elliptical canopy loaded at 2.3:1. Also the canopy is spinning/diving when the jumper undoes the twists. Note : I'm not saying that you should definitely do this if you're spinning/diving on a highly loaded x-braced elliptical canopy.

http://www.youtube.com/watch?v=5FD2I8OqbS0

Awesome. So it does work there too. I'll have to remember that next time I get spinning like a banshee.


trigger  (D 101390)

Aug 18, 2011, 1:16 PM
Post #91 of 116 (2572 views)
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Re: [JohnDeere] A better way out of line twist! [In reply to] Can't Post

I had the opportunity to try this technique for myself and as others have said it worked like a charm.
My question is though, does wingloading play a part or is wingloading irrelevant.
Skimming through this thread of the skydivers that have had success using this technique the lowest wingloading i've found was 1.4ish for the record i'm loading a shade under 2.2.


Premier DSE  (D 29060)

Aug 18, 2011, 2:31 PM
Post #92 of 116 (2527 views)
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Re: [trigger] A better way out of line twist! [In reply to] Can't Post

as long as the twists are above the riser, the squeezing method works well for me when I'm loaded as high as 1.7:1. Never jumped a higher W/L


MarcusS  (D 105592)

Aug 30, 2011, 2:25 PM
Post #93 of 116 (2420 views)
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Re: [DSE] A better way out of line twist! [In reply to] Can't Post

After reading this post a week or so ago, I had a diving spinner over the weekend from a 6k hop and pop on a new line set! Trying to kick them out from 6500 to just under 4000 with no luck, I thought I'd give this technique a try......worked in an instant! Very impressed.

FYI, it was on a Velocity 96 at wl of about 2.15..... video attached, and thanks for the post!!

http://www.youtube.com/watch?v=fS59IHMec9Q


ridestrong  (C 38471)

Aug 31, 2011, 12:01 PM
Post #94 of 116 (2333 views)
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Re: [MarcusS] A better way out of line twist! [In reply to] Can't Post

Here's another... a vid of me using the same technique on my old canopy... I initially tried kicking out of the twists but kept twisting up. I then used my hands to twist the risers, taking the twists out of the lines. From there I pretty much automatically spun out of the twists.

Technique is at the very begining of the vid.

http://www.youtube.com/watch?v=D-FoTdfQ8FM


champu  (D 28302)

Sep 1, 2011, 12:45 PM
Post #95 of 116 (2216 views)
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Re: [ridestrong] A better way out of line twist! [In reply to] Can't Post

Just a note / something to think about for everyone watching and posting examples of pressing together / counter-twisting risers to get out of line twists...

...remember that although it may work really well, you should still have and obey a hard deck. It's easy to think this method foolproof and say, "who cares if it takes me down to 1000 ft to get out of these twists? It works every time!" And that's all fine and dandy until you go to pop your brakes and one of your steering lines jams and now you're under a spinning main below 1000 ft.

Getting out of twists on your main before impact does not automatically equal a safe landing.


sundevil777  (D License)

Sep 1, 2011, 8:23 PM
Post #96 of 116 (2175 views)
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Re: [champu] A better way out of line twist! [In reply to] Can't Post

Good point, but it should also be said that one steering line jamming can simply be countered by the other side - no need for it to be spinning. Flaring it for the landing is not going to be the usual method, but it can still be done.


mdrejhon  (C 3268)

Sep 8, 2011, 7:28 PM
Post #97 of 116 (2081 views)
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Re: [trigger] A better way out of line twist! [In reply to] Can't Post

In reply to:
Skimming through this thread of the skydivers that have had success using this technique the lowest wingloading i've found was 1.4ish for the record i'm loading a shade under 2.2.
Mine's a 1.1, and it worked.


theonlyski  (D License)

Oct 2, 2011, 5:18 PM
Post #98 of 116 (1958 views)
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Re: [mdrejhon] A better way out of line twist! [In reply to] Can't Post

1.2 wl, Safire2 169... guess it's a good way to keep on your toes.

http://www.youtube.com/watch?v=AdTVAjEOSm4


popsjumper  (D 999999999)

Oct 3, 2011, 12:15 AM
Post #99 of 116 (1904 views)
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Re: [theonlyski] A better way out of line twist! [In reply to] Can't Post

In reply to:
1.2 wl, Safire2 169... guess it's a good way to keep on your toes.

http://www.youtube.com/watch?v=AdTVAjEOSm4

Body position, dude. Body position.
LaughLaughTongue


ksjumper  (D 12628)

Oct 3, 2011, 8:12 PM
Post #100 of 116 (1830 views)
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Re: [popsjumper] A better way out of line twist! [In reply to] Can't Post

I had some pretty good line twist this weekend on a jump and used this method and it seemed to work.


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