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Any opinions?

In skydiving, the consensus was/is that the bag got into a spin during deployment. Now skydiving canopies are small and highly loaded so any asymmetry and loading issues are accentuated.

Other than being highly asymmetric or out of control during deployment of a free-packed canopy, what would cause a big-ass base canopy to open in line twists? I think other than a pilot chute that could spiral or do weird things, it is the free-packed canopy catching air during line stretch and creating an out of sequence opening.

Other opinions or evidence, please?

on sub terminal jumps I've noticed that if one leg is higher than the other at opening, it consistently ends up with a twist or the beginning of a twist.
If the right leg is up it will twist left (anti clockwise)and if the left leg is up it will twist right(clockwise).

Any thoughts on this?

Incorrect pc ,not attached crectly

bad body asymetry on opening

reaching one hand up earlier then letting canopy open

bad packing

look at someone whilst pitching

slight wind on that opening or high winds..

you have a bad canopy that is out of trim

or maybe its just pure bad luck..

as long as ya dont get em and then smash into teh wall your gonna be good

99% of the time that I've seen twists, they develop after the canopy is inflated. The canopy opens off heading, and the jumpers body is "slingshotted" back around to the canopy heading, spinning up into twists as a result.

These twists do not develop from the canopy twisting as it moves to line stretch--rather they occur after the canopy is fully inflated. The process is very fast, though, and most of the jumpers under the twists have thought that the twists were "already there" when they hit line stretch until they were shown the video (often in slow motion).

Anything which increase the velocity differential between the jumper and canopy during an off heading opening, like a good track or shallow brakes, can increase the severity of these twists (because the "slingshotting" has more force).

I've noticed if one leg is higher than the other
at opening, it consistently ends up with a twis
or the beginning of a twist.

During a normal deployment your shoulders
affect the symmetry of the risers taking load
as the drag stands you up in the harness the
load is transferred to the hip rings/junction.

On small SKY canopies you can turn the wing
just by leaning in the harness. Hence having
your legs symmetrical affect the deployment.
Try closing your legs after you pull.

I always thought shallower brakes made line twisting less likely. Wouldn't deeper brake settings increase the velocity differential?
I've tried packing sky canopies with a round of twists or two so as to practise getting out of them for base, but it never worked - canopy came out straight anyways. Spectre 135 and PD student canopy.

Perhaps people should get more used to harness turns and carving, to get more used to the "opposite slingshot" way of handling unbalance. And that people who girl-land (meet the ground with the toggle nearest to the ground in crosswind) shouldn't consider base jumping at all.

+1
Thanks Tom

Line twists on square canopies is a problem inherent to setting brakes. Just as having brakes set is a contributing factor to tension knots in the D Line cascade. I think it's just one of those fundamental flaws that we simply have to work with.

Deeper brake settings slow the canopy down, which decreases the forward surge at opening, thereby reducing the difference in velocity (speed+direction) between the canopy and jumper during an off heading opening.

I also believe this to a certain point. Though I think this to be the leading cause only on slider off jumps. There are also ways to combat the slingshot effect on rougher openings.

The most effective I've found is to get your hands between the risers and push outward to stabilize your body and stop it spinning up.

Trying to sit up during deployment also seems to help because it reduces the distance of travel as the body is brought around to the canopy's heading.

I've always found that a nice wide body position helps to reduce the inertia of the slingshot too. Some of the worst line twists I have seen happened to people who would continually rush into assuming the classic compact box man for a 1 or 2 second delay.

Don't have experience with BASE yet, but what Tom says makes a lot of sense physically.

Imagine a 180: if your canopy opens with large forward speed(shallow breaks) then it will twist you with a lot of force since there is a higher speed, but if it opens at almost zero speed the force it will exert is less. Or something like that I think

hello mr. [-rm],

girl-land?

that's pretty insulting, to say the least.

what generation are you from?

thank you,

teresa

Definitely. A wider moment arm increases the rotational inertia (of rest), reducing the total rotation.

In other words, yes, what he said.

well, we call it that up here, I guess as a joke. Lots of student girls and downsizers were getting hurt and after we started calling it girl-landings they kind of saw the flaw and worked with it. Brought attention to it. If being a joking chauvinist keeps people from getting hurt, is it still wrong?

1984, but I have a gf. thanks for asking though.

you're welcome : )

After about 250 base jumps I experienced my first linetwist this weekend. After a 6.5s delay I had an off heading opening and just spun up at least twice. Fortunately I was at the NRGB on BD. I was headed for the tracks on the north side of the bridge but was able to muscle my way above the twist and get some lines in my hand to peel it into the water before I hit the trees.

I certainly experienced the phenomenon that Tom A mentioned. The canopy probably only opened 90 left but did so in such a way that I just instantly spun up. I think my body position was OK. I know my packjob was garbage... but so were the 3 that followed it and all opened straight.

 

It would be far easier to simply adopt a wider body position for all openings.
On a side note. You shouldn't be "reaching" to catch your risers. It's a bad habit that is pointless and will eventually lead to you smacking the shit outta your hands.

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

What do you think about this opening? To bad im filming the wrong way..

Another mechanism that I haven't seen mentioned here is getting on your toggles too quickly on short slider-up delays. I pulled a delightful pilot-error-induced 180 with linetwists in Zakynthos this summer, which started out as a perfectly on-heading opening.

I was a bit low-ish and facing a rusty iron shipwreck on opening, so I just figured I'd start a 45-degree turn to the left. Problem was, it was a 4-second slider up delay, and my canopy was still nowhere near pressurized. As a result, I stalled one side of the canopy (somehow, it was the right side that stalled), which then turned 180 and surged toward the wall while my body spun around the opposite direction. Screenshot of the ensuing hijinks attached (this was a reverse helmet cam).

The embarrassing thing about this is that it wasn't the only time I had done this to myself. After figuring out what happened on this jump, I then traced this cause back to a similar 180 w/ harness twist that I had had in Istanbul (similar situation -- 4 sec slider up from ~240m) -- at the time attributing it to 'shit happens when you take 4 second slider up delays'.

Anyway, it seemed that I wasn't the only one at that boogie not yet aware of this, so I figure it's worth posting here as an added factor to consider when doing short slider-up jumps... let your canopy open before trying to control it.

Hi. during all my - not that much - jumps, I have "jumped" on my risers as soon as the canopy started "pulling". I have had few small <20 degrees opening, mostly due to a quite strong PC throw, and seeing on the video, It happens that my prompt reaction always cleared the off heading before or just after the slider reached the risers.

In order to have more points of view, I d like to know why you consider this as a bad habbit ?


As per the body position, I always sit a little after PC throw, and anticipate the opening.

Borrowed rig. No clue, but you can see the canopy twist as it being extracted.

https://vimeo.com/55721422

I would say that a big factor on this opening is that the jumper is rotating to the left while in freefall.... the kicking probably didn't help either. Seriously though it looks like the jumper is in a slow left turn, this in addition to the kicking (hip movement) possibly caused uneven harness loading as the canopy is extracted and inflates.

To me this seems to have happened because the jumper wasn't really focused on the exit. He just turned around and pushed off while trying to flash the peace sign and also look back over his shoulder, leading with the right leg which carried momentum causing a left turn. If you look at the jumpers position before the canopy opens to when he exited it looks to me like maybe a 45 degree turn while in freefall.

geek camera, off heading .

I thought the Maylasians owned that move. Ha ha!

agreed. rotation to the left seems to be a likely contributor

HAHA. I told u. BODY POSITION! Not my pack job!

Lies! You rotated the packjob before closing the container, just admit it. Theres no possible way that was the fault of the jumper