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I'm posting this to provide food for thought. There seems to be a number of misconceptions...

If you jumped slider down and dipped your right shoulder significantly during pilot chute pitch and during the opening, which direction do you think your parachute will open?

Interesting question; I haven't voted yet. I'm actually not sure.

The way to answer this question is to figure out how dipping a shoulder contributes to an offheading. There are three factors I can see.

• The airstream behind the person becomes more assymetrical, although I think this is neglectible on slider down jumps.
  
• The packtray is not presented in a laterally horizontal way, this means your packjob will come out tilted to one side.
  
• One riser is loaded before the other one.

I'm probably overlooking other factors. My gut feeling says that the middle one is the biggest contributor, largely based on my observation that offheadings happen long before the lines are taut, so long before riser-loading comes into play.

 

How does dipping a shoulder affect the direction the PC pulls from? The original question asked about the effect that dipping a shoulder has on offheadings. Are you implying that dipping a shoulder affects the angle the bridle bulls at, which in turns affects your heading? I'm skeptical that dipping a shoulder will have much influence on PC oscillations.

 

Assuming you are correct in this (which I'm not convinced of, nor am I of the contrary), then what are you actually contributing the offheading to?


Hey, I like that one. You mean the side-walls of the container scraping past the packjob perhaps?

 

Think about it... It's the tensioning of the right lines prior to the left lines during the initial inflation, IMHO.

That's what I thought about. Right side being tensioned and likely pressurized before the left, therefore it would make the canopy turn left (I think).

But it might also "angle" the canopy more on the right side inducing a spiral to the right...

This is why you should not dip the shoulder

Might not a better way be to just run out and do 20 jumps, dipping the right shoulder intentionally, and see what you observe?

 

I would guess 460 means "all else being equal, what if?" My guess would be "generaly right".

In a John Lennon voice: Imagine being in freefall. At some point before pitch, you realize you're uncontrollably dipping a shoulder. Knowing instinctually which direction you canopy will open will lead you to anticipate which correction should be made once the opening is complete.

 I said to the right, because having one riser group lower than the other equals a banked turn to that side.

Dip right go right as far as I know.

Hello,
My experience, all other factors ignored, is a dipped shoulder
at deployment causes the canopy to open in the opposite direction.
Dip your right shoulder, canopy will open to the left.
To really prove the theory, well you can't.
Pilot chutes do stuff.
I don't pack perfectly.
Riser extraction is violent.

Ive done this jump several times. Dip your shoulder to the right, open right. Dip your shoulder to the left, open left. However, since the heading isnt guaranteed anyway, its more accurate to say that if you dip your shoulder in a given direction, your opening will be more in that direction on the same jump, pack job, and wind conditions at that exact same moment than if you didnt intentionally drop a shoulder. In other words, if the jump is going to be a 90 left and you dip a shoulder left, youll likely end up closer to a 180, If your opening was going to be a 90 right, and you dipped your shoulder left, than youd have an on heading. You couldnt make an authoritative statement on this question because of heading ambiguity.

Specifically, early on I did a low tower jump with cables, managed to muck up the exit, that I turned 90 degrees left in freefall; I dropped my right shoulder , and got an opening directly away from the tower...

i once did a high tower jump, (#3)with a serious tailwind, and a no-go tree line a short distace away at 0degrees... i pitched while intentionally dipping way right, and opened directly into the wind...

i believe the wind direction was as much a factor in the opening heading as well as the shoulder however...

Although I totally think we should use all of our best instincts while we're jumping, my personal belief on each and every jump is that my canopy is only going to open one way... the WRONG way. Early on I had this nugget passed on to me as I'm on top gearing up to make one of my first few tower jumps, going over the jump with a more experienced friend:

Him: So which way is your canopy going to open?"
Me: "That way (motioning an on-headng opening)."
Him: "Wrong."
Me: (looking puzzled)
Him: "You're going to open up with a 180 and line twists, you'll have a couple broken lines and your canopy will be on fire... You ready to deal with that?"
Me: (thinking for a minute) "Yeah, except for maybe the fire part."

I understand the context in which you made the statement, but I think it's important to point out a couple of things:

1. that there are no absolutes on heading performance. All of us have seen (or been) jumpers with good body position, square shoulders, good packjob, and light/varible winds have fucking horrendus openings. I think that by beleiving that you know anything about how those uncontrollable aspects of a BASE jump might play out, you're being complacent.


2. You should certainly always read your opening, but in most cases, by the time the opening is complete you should already be well-into problem-solving mode and beginning to make corrections, but again, YMMV depending on your situation. each jump/jumper has their own circumstances.

Not meant as an argument C.S., just adding my own languaging.

cheers,
pope

When I dip my right shoulder, I almost always open to the left. I completely agree with Pope, and I think his advice is pretty good. "No your going to have a 180 with line twists." This sounds like a Mick saying. In actuality, I tend to go more by the tension feel of the risers on my harness to make corrections. 180s, 180s with line twists, slider up line over malfunctions have all been dealt with properly just by going by feel.

Since the prevailing experience of others is "dip right - go right", there must be something peculiar about your particular configuration that makes you almost always open to the left.

It would be interesting to find out what exactly causes such consistency and thus better understand the mechanics of offheadings. Could it be caused by your particular canopy, how tight your chest&leg straps usually are, whether your hips are not level when the shoulder dips, etc.?

It's called chaos theory

Given 460's BKG, he could give you some insights.

Edited to add:

That is if you consider a BASE jump a deterministic system. If a BASE jump is a non-deterministic system then we are dealing with quantom chaos.

In the end as 460 pointed out, you'd better using your feel!

No, it is not.
Chaos theory is about system with:
1) Dense periodic orbits
2) Transitive flow
He was not talking about such system, was he?

Chaos theory deals with systems that are extremely sensitive to initial conditions, to the point that experiments seem unrepeatable even with what seems to be the same initial conditions. Quantum plays no role here. The so-called butterfly effect though is the idea taken to the wrong extreme. The is something called the KAM theorem that plays a significant role in preventing the butterfly effect from generating a hurricane on the other side of the world.

Keep in mind, it is widely believed by aerodynamicists that the parachute opening is the most complex aerodynamic process known. I try to minimize some of the chance by simply staging my opening. But that's another story. I don't believe chaotic dyanamics play what I would call a major role in the openings, but that's just an opinion.

You are a bit mistaken here.
1) Sensitivity to initial conditions is not enough to get chaotic behaviour
2) Sensitivity to initial conditions comes from dense periodic orbits and transitive flow. This is theorem from late nineties, really nice one :-)

If there was a physics forum, you know I'd be moving this discussion...

I'm inclined to agree, and I'll cite the fact that I have found I can predict off-headings in certain scenarios (say, crosswinds on a static line) with great repeatability as evidence. I suspect that shoulder-dropping on an otherwise clean jump is one such scenario.

I also think Tom's on the right track. We could sit here and BS about it for weeks, or somebody could bomb out to a forgiving 'S' and do five in a row with each shoulder low. I know what's on my agenda for my next trip south. Heck, I might give it a shot on my next trip west, though that'll be largely S/L and less forgiving objects.

Just watch any Bridge Day video and you can see the effect of dipping a shoulder. In most cases, dipping your right shoulder will cause your canopy to open to the right. But let's not forget about how important wind direction is, which may provide some influence in 460's openings to the opposite side.

I think we might be talking about different things entirely.

You first must define the initial condition. If the initial condition is the pack, then I can make it in a way that the behavior of the opening will be chaotic

For our case, let's assume the initial condition is the body position (1) and the chaotic motion the canopy deployment (2). Is 2 sensitive to 1? You decide.

How do we know, or don't, that a body in FF does not follow periodic orbits and transitive flow?

How do we know, or don't, that the opening of a canopy gives rise to strange attractors? Honestly if I had to bet my few pennies, just out of gut, I'd say that it does.

I think the first point to be analyzed is the determinism or not of a BASE deployment, that nobody has addressed quite yet.

Is a BASE deployment a deterministic or non-deterministic system?

Here is my ignorant 0.02.

From the jumper's view at the exit point, the deployment is clearly a non-deterministic system. He only knows enough variables to be unable to determine the next state. However as 460 pointed out, sometimes going by "feel" could lead to some sort of determinism.

This leads to my other point.

Knowing enough variables, a BASE deployment could be a deterministic system. Now, the problem is, how many variables do we really have to know in order to have this system of deterministic nature? Do we need to know every single wrinkle in the fabric of the canopy, the relative humidity of the air at every single point of the deployment, a front coming in that is 300 miles away, the location of dark energy?

Bottom line is this before I get too damn metaphysical: I think that a BASE deployment is very much dependent of the initial condition along its variables, whatever the initial condition might be.

The system as far as we are concerned at the exit point is non-deterministic however knowing enough relevant variables, it might be possible to model a BASE deployment with an isomorphic deterministic system. Maybe.

You should use unpredictable instead of non-deterministic here. Hamilton systems with positive Ljapunovs' koeficients are non-predictable but deterministic. To get nondeterministic systems you have to go outside continuum mechanic (e.g. QM, cause we now there are not hidden parameters due to non-validity of Bells' inequalities).
Ps.: I guess we will be banned quite soon for usage of inappropriate vocabulary :-)

Hay guys,

I'm just a wannabe and all...but consider this.

In "a year in the life off" Jeb Corliss hits the falls. In the latest movie (the one with the duane footage) he talks about letting his left shoulder drop.

Dropped left shoulder, went left.

Take care!!!!

Could you point me in the direction of some background reading on this?

/is an engineer, not a physicist

I guess my definition of non-determinism is different than yours and that would not surprise me because I encountered in at least three different types of indeterminism.

At any rate, I am seeing this with a Systems Science (SS) view because we are dealing, at least I thought so, with a system here.

In SS a non-deterministic system is one in which a state has multiple points of continuations where the p for the continuations is not known from previous states.

Predictability or non-predictability is a feature of a system state but not the system label.

In the deployment system the next state, at least from the jumper's prospective, cannot be determined and can have multiple continuations hence the indeterministic nature (one continuation is just as random as another).

Now, if the most relevant variables were known, then the next state's uncertainty could be known (the deterministic system).

I do not understand your point about Bells inequalities and how it applies to this situation.

Simply put if hidden variables were present and those were responsible for the outcome then yes, the distributions generated will have to obey to Bells inequalities.

Quantum mechanics does not suggest that this does not hold water, only that under certain conditions Bells inequalities could be violated but honestly our example does not offer any proof of this kind, unless I am missing something fundamental, case that very well may be.

One more thing, many quantum physicists are still split about the deterministic or non-deterministic nature of the universe...I got my view but it's just an insight, if that.

I've found that if I eat a burrito my offheadings tend to be more to the left. Hot Pockets tend to cause more rights....

Exits delta>0 with following properties:
For every epsilon>0 exists t>0 such, that:
1) Distance of points in time 0 is less than epsilon
2) Distance of points in time t is greater than delta

I think this is generic definition of sensibility to initial conditions.

But what I want to say is that such sensitivity is not enough for chaotic behaviour. Check wikipedia http://en.wikipedia.org/wiki/Chaos_theory, they state three conditions, sensitivity, mixing and dense periodic orbits. And sensitivity is result of mixing and dense periodic orbits.

Try James Gleick, "Chaos". Nice introduction, a bit of history.
Ps.: We drifted far away from topic, don't we?