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Ugojump
Jun 25, 2012, 1:05 PM
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Wall Strikes and how to prevent them:
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Most alpine BASE jumpers biggest fear is a wall strike:
While no one can exempt themselves of this risk, there are a number of things you can do to reduce the chance of getting near a wall, or hitting it.
Off-heading openings are a common occurrence and quick, decisive action is necessary to bring yourself back on-heading, but lets have a look at what causes off-heading openings:
1. Packing:
While your pack job can have an adverse effect on the opening it is by far the least likely cause unless youīre a sloppy packer not paying attention to symmetry. A symmetrical pack job that lifts the parachute with equal distribution of weight out of the container facilitates an on-heading opening. Make sure to check that your bridle and center cell are indeed centered and flaking of the material folds etc are equal on both sides. All other factors such as wind and body position being perfect, your symmetrical pack job will likely open on-heading.
2. Body Position:
The body position before and during the deployment, as well as your forward speed can have great effect on-heading performance. The rotation of your body once the risers load can range from nearly 0° (extreme head high) to 180° (extreme head low). While a head high, arched deployment rotates from riser load to sitting in at about 90°. In addition, depending on your forward speed at deployment, the canopy can be extracted from straight up at 0 forward speed to somewhere at 45° behind you, if you were tracking fast. If your line-stretch results in one riser loading before the other the canopy starts to inflate and fly on one side before the other. Your bodyīs attitude and speed can have a negative effect on the rotation and the subsequent inflation of your canopy.
3. Wind conditions:
Windy conditions can have great effect on the deployment and heading performance.
First the placement of your pilot chute and its position relative to your container upon bridle stretch can pull the canopy to one side during deployment. Vented pilot chutes have better performance to stay behind your back though strong wind from one side can pull the deploying parachute to line stretch. Once the pins are popped and the mess you called a symmetrical pack-job lifts out of the container. It is then exposed to the relative wind comprising of your deployment speed (and direction) as well as the wind present. Side winds can turn the pack-job as it gets to line stretch, while front wind usually has little effect on turning the canopy before inflation. If possible (distance to the wall is big) turn into the wind, else call off the jump if side winds exceed what you are comfortable with.
4. The effects combined:
Line twists are the result of the canopy turning during the opening process, loading the canopy single sided and a combination thereof:
If you find yourself in line twists and are lucky enough that they are in front of your face (as opposed to behind your head) donīt delay or start kicking like a skydiving b!"§$%ch. Reach above the twist if necessary climbing up your own lines. This maybe hard, but youīll be amazed at your super human power when your life depends on it. Make the canopy turn if youīre headed toward the wall: Preferably by pulling on lines or riser links of the rear riser as you will turn and slow things down at the same time. Front riser or lines of the nose will also turn the canopy but accelerate and increase the turn radius. Once on-heading to clear air you can take your time and unwind. (no pun intended)
Cliffs of a height more than 300 meters warrant assuming a tracking position to increase the distance from the wall before deployment. While a 300 meter cliff only allows for subterminal tracking it is still a good idea to use the 4 or so seconds to squeeze 10 or 20 meters out of the total distance away from the wall. A higher cliff warrants tracking as long as you can to gain the maximum distance, though your forward speed will be much higher at deployment. This in effect will put you're deploying canopy behind you as you fall away on a forward angle from the decelerating parachute. As your risers load they will still be well behind your head at a +-45° angle. If your body position is not completely square to load the risers simultaneously, you may just find yourself in line twists that still spool up as you wonder why this happened.
Fact is: the side of the canopy on which the riser loads first starts to fly first i.e. right riser loaded right side canopy inflates and flies forward hence causing an off-heading to the left. Since the riser on the right pulled on your right shoulder, you in turn will spin to the right and find yourself with line twists behind your head not knowing in which direction you are flying. Nevertheless, if the canopy opens hard and your body is flung with energy you may actually turn to the left and spool up into line twists left. There are other factors such as the recoil action of your dacron lines ect. but lets not add unnecessary variables.
With all the antlers of rigid camera gear and extended arms to hold them in place a line twist can make it virtually impossible to move your head to see whats going on. It would take time you donīt have to determine the direction in which the canopy is flying. The scary part here is that you need to make the canopy turn if it is aiming at the wall. You can do this by reaching up as high as possible and grab a riser or lines to pull the canopy into an asymmetric state that will make it turn. However, if you were flying awy from the cliff you may actually be turning it into the the cliff if you donīt know whats going on. So,-quickly determine if you are in danger and make the canopy turn if necessary.
To reduce your chance of line twists behind your head be sure to assume a head high, arched position before deployment.
Donīt pull too high, and definitely not too low:
Some people may argue that a higher deployment is safer, but think again:
Not making use of the available altitude = less tracking distance from the wall and upon a severe off-heading opening, 180 or line twists, you may hit the wall quite a way up from the talus only to be rewarded with a number of bounces all the way down to come to rest at the bottom. That is, if you donīt hang up somewhere in between. I consider a reasonable deployment altitude about 150-200 meters AGL for trackers and a bit higher for wing-suit flyers though this may vary depending on the terrain.
In summary:
A symmetrical pack job, a square and head high body position in low or no wind conditions help you're heading performance. While you cannot see the wind or its strength at deployment altitude, it is a good idea to know the direction and estimate by looking at waterfalls, smoke or trees and flags if itīs within your limits. Make use of your available altitude to gain as much distance from the wall as possible before deployment. React quickly and decisively to off-heading openings by going with the direction if there was a lot of energy going into it or counter acting to bring the canopy flight back on line.
Your input is welcomed and I wish you consistently on-heading openings on your future jumps!
Dominik Loyen
http://www.321BASE.eu
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maretus
Jun 25, 2012, 1:24 PM
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Re: [Ugojump] Wall Strikes and how to prevent them:
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Ugojump wrote: Cliffs of a height more than 300 meters warrant assuming a tracking position to increase the distance from the wall before deployment. While a 300 meter cliff only allows for subterminal tracking it is still a good idea to use the 4 or so seconds to squeeze 10 or 20 meters out of the total distance away from the wall.
I could not agree more on the statement above but given that you write this, can you please elaborate why do you teach on your "advanced base course" people to jump handheld slider up on box position from YO and not try to "squeeze 10 or 20 meters out of the total distance away from the wall"?
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Ugojump
Jun 25, 2012, 2:18 PM
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Re: [maretus] Wall Strikes and how to prevent them:
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Hello Markus,
I know we are divided on this issue, but to me the body position at deployment is the most important to facilitate an on-heading performance, especially in the beginning.
Thanks for your input!
Dom
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samadhi
Jun 25, 2012, 2:55 PM
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Re: [Ugojump] Wall Strikes and how to prevent them:
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I like the straightforward way its written. Do you have more introductory writing about BASE jumping???
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TomAiello
Jun 25, 2012, 3:45 PM
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Re: [blitzkrieg] Wall Strikes and how to prevent them:
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blitzkrieg wrote: Ugojump wrote: the body position at deployment is the most important to facilitate an on-heading performance 'nuff said. 
Unfortunately, I don't think it's that simple. Especially when we are talking about slider down openings.
I've been on loads from slider down objects in high cross winds where all five jumpers experienced exactly the same off-heading opening. I find it extremely unlikely that it was their body position that caused this, especially since I've seen perfect body position and wild flailing result in exactly the same off heading in these conditions.
Likewise, I've seen perfect body position and zero wind result in off headings, sometimes obviously from PC orbiting, and sometimes from no obvious factor.
There are a lot of things that can cause an off heading. Asserting that there is one cause that applies to all jumps, jumpers and conditions is likely an exercise in extreme overconfidence.
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blitzkrieg
Jun 25, 2012, 4:56 PM
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Re: [TomAiello] Wall Strikes and how to prevent them:
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nah.
i believe fully that body position is the most important contributing factor to heading performance.
jumping in high crosswinds... well you said it right there.
i also follow the rule, out delay the x wind. if it's high, you won't and you're foolish to think it won't affect your heading.
relative wind counts from fixed objects too.
what looks like perfect body position isn't always the case. obviously, "perfect body position" is not going to help if you only have one leg strap tightened, or one riser connected.
there are no absolutes.
every off heading i have experienced (which is a very low occurrence, currently 93.37% on heading) i can attribute to bad body position, or were anticipated before exit due to strong cross winds. but of course, i can only be sure of what i do myself and what has worked for me.
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TomAiello
Jun 25, 2012, 5:03 PM
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Re: [blitzkrieg] Wall Strikes and how to prevent them:
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blitzkrieg wrote: i also follow the rule, out delay the x wind. if it's high, you won't and you're foolish to think it won't affect your heading.
My rule of thumb is: Fall faster than the wind speed. If you are falling slower than the crosswind, I expect the crosswind to govern the opening. If you can delay long enough for your fall rate to exceed the wind speed, you are back in charge.
Yet another reason why deeper delays are usually safer in BASE.
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neiljarvis
Jun 25, 2012, 6:28 PM
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Re: [TomAiello] Wall Strikes and how to prevent them:
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I think its a fallacy that if you have line twists 'that you can reach above them/climb above them and steer' the canopy. In 640 jumps I've had 4 sets of decent line twist and on every occassion I could not climb above the line twists and had to resort to kicking out.
I'd love to hear from people with a)jump numbers stated, b) number of jumps with line twists and c) if they could 'climb/reach above' and steer the canopy.
For the record I'm not a fat boy and am pretty reasonable at chin ups :-)
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TomAiello
Jun 25, 2012, 6:53 PM
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Re: [neiljarvis] Wall Strikes and how to prevent them:
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I've been able to turn above line twists.
I also had a student two weeks ago who was able to turn above twists on his 13th jump.
Both of these cases were on slider down jumps.
I think that it is possible to develop twists such that you can turn above them.
I wonder if there is a difference in likely twist mechanism between slider down and slider up openings?
Neil, were your twists slider up or slider down?
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neiljarvis
Jun 25, 2012, 11:53 PM
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Re: [TomAiello] Wall Strikes and how to prevent them:
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All slider up. Dacron lines. Physically impossible to pull lines down. In part because the twists started above the height that I could reach.
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REDAKTOR
Jun 26, 2012, 3:03 AM
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Re: [TomAiello] Wall Strikes and how to prevent them:
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TomAiello wrote: and sometimes from no obvious factor.
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Lucifer
Jun 26, 2012, 4:44 AM
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Re: [TomAiello] Wall Strikes and how to prevent them:
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TomAiello wrote: I think that it is possible to develop twists such that you can turn above them. I wonder if there is a difference in likely twist mechanism between slider down and slider up openings?
Yes there is.
Linetwists will occur on the location that requires the minimal amount of energy to constrict all the lines together. Obviously, this point is located where the lines are (on average) the closest to eachothers.
Whithout slider, that point is located at the harness-elevators junction. The only thing that can move the twists further up is your head being sqeezed between the risers.
Slider down, the twisting point is somehow spread on the risers, with a tendancy to be towards the harness-risers junction point (since the slider is generally just a little wider than the shoulder straps)
Slider up, the twisting point is spread further up, between the risers and the current position of the slider. So if the linetwists are starting when the slider is still close to the canopy, you have two spindles of lines almost parallel to eachother, between the harness and the canopy. The lines will start to twist in between, then the slider is going to push it down towards the risers, and it will stop at some point depending on the line friction and the slider size.
From my experience, it very unusual to have the canopy turn more than 180-270°
Multiple linetwists generally occur when you add to that phenomenon the rotation of the human body due to the inertia of the legs bouncing sideways on opening. Correct position and muscular tension can reduce the body momentum a lot - this is probably why experienced jumpers still have 180's but less multiple linetwists.
Obviously, it's good to have a slider starting immediately to slide down rather than staying up on the canopy for soft openings.
I've had a handful of linetwists slider up on canopies that tend to open hard - the only few cases where i wasn't able to climb over it was with a wingsuit (after dezipping) - which tend to give me softer and slower openings when i'm not pulling at full speed.
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Fledgling
Jun 26, 2012, 5:58 AM
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Re: [Ugojump] Wall Strikes and how to prevent them:
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Ugojump wrote: Your input is welcomed
You forgot to mention: "Don't jump advanced objects if you haven't yet built the skills necessary to deal with all possible outcomes".
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Fledgling
Jun 26, 2012, 6:05 AM
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Re: [Ugojump] Wall Strikes and how to prevent them:
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Ugojump wrote: Hello Markus, I know we are divided on this issue, but to me the body position at deployment is the most important to facilitate an on-heading performance, especially in the beginning. Thanks for your input! Dom
If your "students" can not deploy symmetrically from a tracking position why are you even taking them to the Valley?
As their teacher would it not be better to recommend other sites for them to jump until such a time as they are ready for the Valley?
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GreenMachine
Jun 26, 2012, 8:22 AM
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Re: [Ugojump] Wall Strikes and how to prevent them:
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Best thread in a long time!!
Hopefully the kids jacked up
on Mountain Dew like Spider
Monkeys read every word.
RE: Steering
360+ BASE Jumps, most Slider-OFF,
only 1 Slider-up 180 w/ Twists from
a tall A, off heading due to shortish
delay and cross wind, did not even
think to steer, only untwist, flew in
between a set of wires, and only
alive today due to karma & luck.
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TomAiello
Jun 26, 2012, 9:01 AM
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Re: [Lucifer] Wall Strikes and how to prevent them:
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Lucifer wrote: Multiple linetwists generally occur when you add to that phenomenon the rotation of the human body due to the inertia of the legs bouncing sideways on opening. Correct position and muscular tension can reduce the body momentum a lot - this is probably why experienced jumpers still have 180's but less multiple linetwists.
This is very true.
In my experience, slider down line twists almost always develop _after_ the canopy is flying. The off heading canopy surges in one direction and the jumper is headed another. The jumper is then "slingshotted" back around under the canopy, and spins up into twists after opening. There is almost always a short time when there is a half line twist (or less), before the jumpers body spins up into more twists. Jumpers who are stiff during this period tend to be spun up harder. Jumpers who are more relaxed and responsive can often minimize the twists, or even stop them altogether.
Experienced jumpers can generally relax enough to just feel things out, but beginners would probably benefit from some instruction in terms of how best to reduce twists.
In general, my experience is that twists are more severe with a tracking body position (head low and arms and legs in tight). The head low position makes the twists more violent, and the lower rotational inertia of the jumpers body allows more twists to develop.
I think that a more head high (or standing) position, with a more relaxed (arched, rather than tracking) position at line stretch can help reduce twists. Unfortunately, it can take a fair amount of practice to track until the last moment (for best separation) and then return to a relaxed, head high arch after line stretch.
Does anyone else have any thoughts on the best body position to assume during opening to reduce the possibility of twists?
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GreenMachine
Jun 26, 2012, 9:28 AM
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Re: [TomAiello] Wall Strikes and how to prevent them:
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Here is a good tip I got once:
On deployment try to close your legs
and look at the horizon so you load
the harness evenly during inflation.
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Mikki_ZH
Jun 26, 2012, 10:56 AM
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Re: [neiljarvis] Wall Strikes and how to prevent them:
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neiljarvis wrote: I'd love to hear from people with a)jump numbers stated, b) number of jumps with line twists and c) if they could 'climb/reach above' and steer the canopy. For the record I'm not a fat boy and am pretty reasonable at chin ups :-)
Hi Neil, I once climed above a linetwist to turn my canopy into the wall, no joke :-) of couse this was not my best idea so I climed up again and turned it away again. I therfore climed above linetwists already two times!
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TomAiello
Jun 26, 2012, 11:13 AM
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Re: [Mikki_ZH] Wall Strikes and how to prevent them:
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Mikki_ZH wrote: Hi Neil, I once climed above a linetwist to turn my canopy into the wall, no joke :-) of couse this was not my best idea so I climed up again and turned it away again. I therfore climed above linetwists already two times!
Were you slider up or slider down, Mikki?
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Treejumps
Jun 26, 2012, 11:18 AM
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Re: [GreenMachine] Wall Strikes and how to prevent them:
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I would not recommend moving one's legs around at deployment. I have seen numerous line twists induced after good openings by the jumper moving their legs around. The best thing to reduce line twists is to relax (the opposite of what most people's instinctive response is) at opening.
Be like Fonzi, He's Cool!
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OuttaBounZ
Jun 26, 2012, 1:56 PM
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Re: [TomAiello] Wall Strikes and how to prevent them:
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line dump
Always check your velcro. Line dump can cause line twists too. When my buddy landed we looked at his tail pocket and the velcro was blown open. Looking at the video it looks like line dump put slack in the lines and the bridle causing the canopy to spin like a noisy whizz wheel (see picture below for description of noisy whizz wheel)
(This post was edited by OuttaBounZ on Jun 26, 2012, 2:00 PM)
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Mikki_ZH
Jun 26, 2012, 3:01 PM
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Re: [TomAiello] Wall Strikes and how to prevent them:
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TomAiello wrote: Mikki_ZH wrote: Hi Neil, I once climed above a linetwist to turn my canopy into the wall, no joke :-) of couse this was not my best idea so I climed up again and turned it away again. I therfore climed above linetwists already two times! Were you slider up or slider down, Mikki?
Slider up from Smelvegen, about 5 years ago. The PC fell over the nose at opening so I thought I was flying backwards :-)
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Fledgling
Jun 27, 2012, 10:15 AM
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Re: [GreenMachine] Wall Strikes and how to prevent them:
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GreenMachine wrote: Here is a good tip I got once: On deployment try to close your legs and look at the horizon so you load the harness evenly during inflation.
I prefer to remain as large as possible as I feel that the smaller your surface area the easier your body will be spun around ie. like those figure skater chicks. May not help prevent 180s but I feel it does a lot in preventing line twists following a 180. And I've had some pretty violent 180s :-)
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sum1sneaky
Jun 27, 2012, 6:35 PM
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Re: [Ugojump] Wall Strikes and how to prevent them:
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No one has mentioned, yet I find relevant especially for slider off jumps = properly tuned and tested deep brake settings.
If you're jumping with the same brake settings your canopy came with, you might find it's not really that "deep". I found mine flying much different following recent weight loss.
http://www.basejumper.com/...orum.cgi?post=471986
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