loosening chest strap/leaning forward

[jf951 1]

what flight characteristics are associated with loosening the chest strap and leaning forward (similar to what swoopers do)on both high performance and non high performance landings?

Jump more, Bitch less.

[rhys 0]

Loosening the chest strap opens the risers up and makes the wing flatter, so it is flying more efficiently.

Leaning forward helps reduce the parasite drag lifting the knees also helps, some go to the extent of lying flat on installed belly bands to reduce the drag to the maximum.

"When the power of love overcomes the love of power, then the world will see peace." - 'Jimi' Hendrix

[anticube 0]

Brian germain also says that it might be easier to transfer your weight to your feet when your body tilts forward when flaring..

http://www.dropzone.com/cgi-bin/safety/detail_page.cgi?ID=671

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6) Loosen your chest strap and lean forward in the harness. This will allow you to get your weight over your "landing gear", rather than back on your heels. The parachute will increase its pitch angle as you progress through the landing, but your body doesn't have to tilt in accordance. Freeing your body from the pitch of the system will allow you to feel more comfortable finishing the flare, as you will not feel the urge to let up on the toggles as you put your feet down to get to a more balanced pitch angle.

You can't really lean forward with chest strap tight though and it won't affect that much with bigger canopies anyway.

You may want to consider that your cutaway handles can be harder to find if you've loosened your chest strap.

[jakee 1,254]

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You can't really lean forward with chest strap tight though and it won't affect that much with bigger canopies anyway.

Less important maybe, but still has an effect. I started loosening my chest strap and pulling down the slider on a square 190 at less than 1.0 and even then the difference in feel was noticeable.

Do you want to have an ideagasm?

[davelepka 4]

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You can't really lean forward with chest strap tight though and it won't affect that much with bigger canopies anyway.

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Less important maybe, but still has an effect. I started loosening my chest strap and pulling down the slider on a square 190 at less than 1.0 and even then the difference in feel was noticeable.

You're talking about two different things. The top comment is in reference to leaning forward in the harness during landing.

Leaning forward in the harness is primarily for swooping. For the purpose of this discussion, 'swooping' includes any landing with a plane out across the ground of more than 20 feet or so, even if it's the result of a straight in approach.

The idea is that you're moving at a high rate of speed, and going to attempt to transfer from flying to running/walking. The natural position of a person running is to be leaning forward, so if you replicate that in your harness, the transition will be that much smoother.

The previously mentioned benefit of drag reduction comes much further down the line on much smaller canopies. There are 10 different things you need to do right before leaning forward in your harness is going to get you any further. That's no reason not to practice it, but in reality it's just one drop in a bucket full of things you have to do really nail a swoop.

This doesn't apply to larger canopies because the touchdown speed will be low enough that your posture at that time isn't a big deal.

The other issue, of loosening your chest strap under canopy applies to all canopies, but like anything having to do with canopies, the smaller ones will respond more to this than the larger. Unlike leaning forward in your harness, larger canopies will benefit from this, regardless of the pilot's level of performance.

[jakee 1,254]

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You're talking about two different things. The top comment is in reference to leaning forward in the harness during landing.

Maybe so, it was a little ambiguous and I read it like he was talking about both at the same time.

Do you want to have an ideagasm?

[genghis 0]

In addition to the things already mentioned another beneficial effect of leaning forward in your canopy is a shift of your center of mass/center of gravity. With the connection point still being at your shoulders (most likely slightly behind your shoulders with the chest strap loose) leaning forward will shift your center of gravity aft and up. The aerodynamic effect of the shift in weight is a flaring or planing effect similar to pulling on the both rear risers, but without the distortion to the canopy so the drag caused is less than a proportionate planing due to riser input.

Like everyone else said, this mostly applies to the smaller faster canopies that truly fly like wings and follow the principles of aerodynamics. It doesn't really apply to the blimps.

[rhys 0]

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In addition to the things already mentioned another beneficial effect of leaning forward in your canopy is a shift of your center of mass/center of gravity.

agreed entirely. I just learned that from Jay

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With the connection point still being at your shoulders (most likely slightly behind your shoulders with the chest strap loose) leaning forward will shift your center of gravity aft and up. The aerodynamic effect of the shift in weight is a flaring or planing effect similar to pulling on the both rear risers, but without the distortion to the canopy so the drag caused is less than a proportionate planing due to riser input.

That I don't really agree with, the reason being I was just taught otherwise a couple of days ago. We load the parachute from our hips.

The rings are not the pivit point our lagstraps are, the MLW extends through the rings, risers and lines.

The C of G is moved forward while performing this manoever, placing more force on the front of the canopy and rolling it forward keeping it in level flight longer before it pitches back, as it would if all the input is made from the rear of the canopy.

Less parasite drag is also an advantage.

At least thats how I took it...

"When the power of love overcomes the love of power, then the world will see peace." - 'Jimi' Hendrix

[BMFin 0]

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In addition to the things already mentioned another beneficial effect of leaning forward in your canopy is a shift of your center of mass/center of gravity.

Could you explain this more ?

I always thought it wont affect the canopy at all, since when we look at the canopy from the side the canopy is attached to us from one point only (three rings) and it wont matter if we try to lean forward or backwards since in relation to the canopy our mass always mediates from the same three ring anyway.

Same applies to hip turns in vice versa. The only reason doing hip turns is possible is because when we look at the canopy from the front the canopy is attachet to us from TWO points. Therefore leaning on other side will reduce the load on one side which will cause turning. If we were attached to the canopy from ONE point also from this perspective, then we wouldnt be able to make hip turns.

Am I missing something here ?

[davelepka 4]

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In addition to the things already mentioned another beneficial effect of leaning forward in your canopy is a shift of your center of mass/center of gravity. With the connection point still being at your shoulders (most likely slightly behind your shoulders with the chest strap loose) leaning forward will shift your center of gravity aft and up. The aerodynamic effect of the shift in weight is a flaring or planing effect similar to pulling on the both rear risers, but without the distortion to the canopy so the drag caused is less than a proportionate planing due to riser input.

That's sounds like bullshit to me, but I'm not exactly sure why. Can you explain it differently?

Here's where I'm at - we're hanging from a single point, the three ring, and that point is flexible between the risers and harness. Additionally, the front and rear risers are fixed to each other at that point. Due to this, any force applied below that fixed point is going to effect both risers equally. So the idea that the orientation of your body is going to effect the shape of the canopy just doesn't add up.

Forgetting about that, let's think about the idea of moving the center of gravity. Even though there are left and right three rings, we'll look at it as a single point of attachment because were discussing effects to the pitch of the canopy, and any load placed on the left will be equal on the right, so we'll call it a 'single' point.

Regardless of where the weight is carried, that single point will flex, and create more or a less a straight line up to the canopy. Imagine if your lines were actually attached to the ceiling of the hanger instead of a canopy. If you were to hang in your harness from the ceiling, do you think you could find a body position that would cause the lines between the three ring and the ceiling to do anything but hang straight down?

My impression of the situation is that the only way to effect the angle of the lines on a real canopy is by balancing the airspeed and drag of the jumper and canopy.

If you can raise the airspeed of the canopy, it will move ahead of the jumper. If you reduce the airspeed of the canopy, it will move behind the jumper. Even then these effects are temporary, as graivty continues to pull stright down on the jumper, and the jumper/canopy system will react to that the want to return to 'full flight' sooner than later.

I'm going to maintain that leaning forward in the harness is primarily a function of getting your weight up ahead of your feet so when you put them down to start running, you're already in a natural posture for running. Once that was established, I think a lot of guys started doing it because that what everyone esle did, and that was now the swooping 'body position'. Kind of like the capri pants everyone wears.

Later on down the line, some of the competition guys took it to a whole new level, almost falling out their harnesses by laying down close to horizontal, at which point is became a drag reduction technique for distance runs.

[frost 1]

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we're hanging from a single point, the three ring,

But that changes when you use rear risers and/or toggles - you add another point to help shift the weight. I am not sure how much or how beneficial but i know i can feel the difference.

[davelepka 4]

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But that changes when you use rear risers and/or toggles - you add another point to help shift the weight. I am not sure how much or how beneficial but i know i can feel the difference.

I think what you might be feeling is the difference in how you apply the input, and what angle you're reaching to apply that input. The further forward you lean, the more riser input feels like pushing down behind your back then pulling down toward your shoulder. Different for you, the same for the canopy.

I understand your point about introducing the second point of attachment, and that is indeed what you would need to effect real change with fore/aft movement of your body. However, I don't think you can apply enough input to the risers or toggles to take up enough of the 'load' to effectively make it a useful second attachment point. In other words, you would have to be able to use those 'attachment points' to lever your body into an un-natural (against the balance of gravity), and you would stall out if you applied that much input.

Not so much 'proof', but a good example is the various freestyle moves out there. Many of them involve leaning back, or sitting square in the harness, and the canopies seem to handle it just fine. It's not an apples to apples comparison because the pilot is doing other things that may effect the canopy flight, but it's an example of different postures in the harness not creating adverse effects on the flight. It would stand to reason that if leaning forward would create one reaction, that leaning back might create an opposite reaction, but we don't see that.

[genghis 0]

First let me say that my initial post was intended strictly from a physics standpoint of theoretical benefits of it. I didn't mean to imply that it was the REASON for doing it.
"Here's where I'm at - we're hanging from a single point, the three ring, and that point is flexible between the risers and harness. Additionally, the front and rear risers are fixed to each other at that point."
To give you an analogous situation: The wing of an aircraft is similarly fixed to the fusalage of the plane. While the angle of the wing will not change relative to the aircraft, the shift of a passenger inside of the aircraft will significantly affect the flight characteristics.
"Regardless of where the weight is carried, that single point will flex, and create more or a less a straight line up to the canopy. Imagine if your lines were actually attached to the ceiling of the hanger instead of a canopy."
(In theory) a better analogy would be if your lines were attached to a plank balanced and seperately suspended to the ceiling. The angle of that plank will shift depending upon how your weight is in proportion to it. A significant shift in your weight distribution (such as a balanced front riser input) is going to cause the plank to shift forward (similar to how the aircraft noses forward slightly when a 4 way exits. The pilots are used to balancing out for it which is why the seasoned pilots can do it much better than the rookies) and an even shift of weight aft will make it lean back (part of why a pilot generally discourages an ENTIRE plane load to be standing right in the doorway on a big way)

Again, my apologies for not giving the disclaimer before that this is just hypothesis of the effect based on aerodynamics and physics. Whether it actually has a significant effect on the flight of a parachute instead of an actual wing may be entirely bullshit, I just meant it as a hypothesis. The REASON I lean forward in my swoops is still just because it feels right, my mentors and coaches taught me to lean forward (either by actually saying it or from watching them) and it has become a part of my comfortable landing sequence.

[davelepka 4]

Overall I would continue to disagree.

Comparisons between canopies and fixed wing aircraft are limited at best. On an aircraft, control inputs are made directly to the control surfaces which are hard mounted to the airframe. This is the only method of control you have with an aircraft in that if you make a control input, the elevator or aileron will move and steer the aircraft and that's it.

The control system of a canopy relies on the weight of the jumper under the wing moving around to effect significant change in direction. The toggles and risers, to some extent, are really just there to alter the position of the jumper under the wing. If you pull both brakes to slow the wing, the jumper will move ahead of the wing and line tension will cause the nose to pitch up.

The very existance of the 'secondary' input, the one made by the jumper swinging out ahead of the canopy is where the comparisons between canopies and fixed wing aircraft has to end. Aircraft are unique in their ability to maintain significant changes in attitude, while canopies are limited to the amount of time the pilot spends off center under the canopy.

Beyond that, between the single point attachment to the canopy itself, and equal line tension from front to rear, I still can't see anyway that you could effect a pitch change by leaning fore or aft in a harness.

Maybe you can explain without the comparisons to aircraft?

[rhys 0]

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we're hanging from a single point, the three ring,

But that changes when you use rear risers and/or toggles - you add another point to help shift the weight. I am not sure how much or how beneficial but i know i can feel the difference.

The rings are the point in which the parachute attaches to the harness, so the harness is hanging off the rings. The pressure on our bodies is not at the rings but at the harness about the legstraps. It travels from the legstaps, up the main lift web, through the rings, risers, links, lines, attachment points, ribs and crossbraces to the top skin. Did you guys miss my other post?

Using the steering lines and rear risers is defnately another point of contact/pressure and depending on how much input we put on them will chance the centre of gravity also, I agree totally with you there.

"When the power of love overcomes the love of power, then the world will see peace." - 'Jimi' Hendrix

[davelepka 4]

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Did you guys miss my other post?

Not at all, but you're making a mistake thinking that it has anything to do with the subject at hand.

Of course the load can be traced from the top of the system to the bottom, but we're not talking about where the load is ultimately carried, we're talking about shifting the load fore and aft, and it's effects on the canopy.

When talking about shifting the load fore and aft, and looking at how it effects pitch changes to the canopy, the three ring becomes the 'hinge point'. Given the tension allpied to the harness via your weight, the harness from the three rings down can be viewed as a solid piece in that it's parts don't move independently from each other. The same can be said of the canopy above the three ring, so you have two solid forms joined by a hinge.

(Keep in mind that this is limited to fore and aft weight shifts. Of course the harness is dynamic along the left/right axis, as in harness turns, and the canopy is dynamic all over the place above the three ring via the risers and toggles)

The other significant factor about the three rings in this case is that it's where the front and rear risers are joined together. Any input made below this point will effect both the front and rear equally, and input made above can be exclusive to the front or rear.

This is why the three ring is the key point to this discussion, not the bottom of the legstraps. If you want to talk about harness turns, or opening shock, then the bottom of the legstraps becomes the focal point, but not here.

[rhys 0]

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Not at all, but you're making a mistake thinking that it has anything to do with the subject at hand.

Of course the load can be traced from the top of the system to the bottom, but we're not talking about where the load is ultimately carried, we're talking about shifting the load fore and aft, and it's effects on the canopy.

When talking about shifting the load fore and aft, and looking at how it effects pitch changes to the canopy, the three ring becomes the 'hinge point'. Given the tension allpied to the harness via your weight, the harness from the three rings down can be viewed as a solid piece in that it's parts don't move independently from each other. The same can be said of the canopy above the three ring, so you have two solid forms joined by a hinge.

Whatever you say, but that is contrary to what I was taught by the current world champion only a matter of days ago. That is why I bought it up.

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The other significant factor about the three rings in this case is that it's where the front and rear risers are joined together. Any input made below this point will effect both the front and rear equally, and input made above can be exclusive to the front or rear.

This is why the three rings is the key point to this discussion, not the bottom of the leg straps. If you want to talk about harness turns, or opening shock, then the bottom of the leg straps becomes the focal point, but not here.

This is where I believe you are wrong, we are talking about moving the C of G. and our weight is suspended by the leg straps, leaning forward moves our C of G and leaning against and even lying on the chest strap will pull tension on the MLW and therefore down on the rings.

The hinge point is somewhere between the attachments of our weight to the harness both hips and chest strap and the toggles rear.

When the canopy pitches forward or back the weight stays in a straight line from topspin to harness. The rings are part of that straight line. The hip rings and the MLW about the chest strap are the pivot points.

"When the power of love overcomes the love of power, then the world will see peace." - 'Jimi' Hendrix

[davelepka 4]

I had to resort to illustrations to make my point. I'm not that good at drawing, and not good enough with computers to do digitally, so bear with me and my primitive cave drawings.

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This is where I believe you are wrong, we are talking about moving the C of G. and our weight is suspended by the leg straps, leaning forward moves our C of G and leaning against and even lying on the chest strap will pull tension on the MLW and therefore down on the rings.

You can indeed pull down on the rings with various movements in the harness, but any input to one ring is going to effect both the front and rear risers equally on that side. By applying different amounts of force to the left or right, you can induce a harness turn, but becuase the front and rear risers are connected above the ring, you cannot apply force exclusive to one or the other.

The reason I focus on the three ring as the hinge point is because everything above it connected to the canopy and held fast by line tension, and everything below it in the harness is held fast by gravity.

If you reference figure A on my drawing, you'll see a canopy, hings point, and a load. The dotted line is the C of G, and you'll see that this figure represents a jumper sitting upright in the harness. The weight falls directly on the C of G.

Now look at figure B. In this figure, the load is offset due to the bend introduced to the arm. However, because there is no 'hard' connection between the canopy and load, the weight simply finds it's way back to the C of G by way of the pivoting around the hinge point.

No matter how hard you try to shift the load, it will always pivot about the hinge point, and return to the C of G.

A hang glider is a good example of how you could make weight shifting work in order to effect the pitch. The reason it works on a hang glider is that the pilot does have a 'hard' attachment to the wing via the control bar which is connected to the framework of the wing. The pilot can push on this control bar, and shift his weight back to pitch up the nose of the glider, and he can hold his weight back there as long as he likes (more or less, sooner or later the wing will stall).

A canopy has no such 'hard' attachment to the jumper, nor does it have the solid framework around the wing like a hang glider.

The entire concept of the C of G finding it's own center can also be illustrated by the entire canopy/jumper system, and how it reacts to the position of the jumper under the wing.

In this example, the hinge point is actually the canopy itself.

If you were to pull both toggles down, you would slow the wing and the jumpers momentum would carry him forward, out ahead of the wing, causing the canopy to ptich up. We know that you cannot sustain this change in pitch, because the jumper will run out of forward swing, and return to a position under the canopy (of course you can hold brakes, and maintain a lesser degree of pitch up, but the majority of the change is only sustained as long as the jumper is in the forward swing).

The way that the complete canopy/jumper system will return full flight, as the load returns to the C of G, is the same way your body (the load) will simply return to the C of G about the three ring if you were attempting to shift it.

You are hanging under the canopy at a flexible point, and there is nothing you can do to shift the load away from the C of G. Gravity will always pull the load back to the C of G.

As a reminder to all, this discussion is limited to the effects of fore and aft weight shifts on the pitch of the canopy. Many of the comments I made only apply to this one specific situation, and are flat out wrong when discussing other areas of canopy flight, and pointing all of them out isn't going to help anyone.

[rhys 0]

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You can indeed pull down on the rings with various movements in the harness, but any input to one ring is going to effect both the front and rear risers equally on that side. By applying different amounts of force to the left or right, you can induce a harness turn, but becuase the front and rear risers are connected above the ring, you cannot apply force exclusive to one or the other.

That I understand , but lying flat and extending your upper body forward, while bending your knees will mover the centre of gravity forward (keeping your legs straight 'might' not move the C of G). Even though the pressure is on each riser is essentially the same (we'll assume no control input), the movement in the centre of gravity will achieve forward pitch in itself.

This was what I took as Jays point, and one I am inclined to believe.

Our ability to change our form and use leverage and our muscles allows us to do something a uniform dead weight could never do. Change our centre of gravity.

"When the power of love overcomes the love of power, then the world will see peace." - 'Jimi' Hendrix

[davelepka 4]

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Our ability to change our form and use leverage and our muscles allows us to do something a uniform dead weight could never do. Change our centre of gravity

I agree with that 100%. The problem occurs when you take that leveraged form, and hang it from a flexible attachment point. When you do that, gravity will take advantage of that flexible point, and return the form a 'neutral' position, with equal amounts of weight fore and aft.

This tendency of gravity to want to balance out whatever form you happen to be holding is exactly what would cause unequal pressure if you had some sort of hard attachment point to the canopy.

Have you ever seen the trick strippers do on the stripper pole, where they grab the pole with both hands about shoulder width apart, and then hoist their (naked) bodies into a horizontal position? That is a great example of using leverge to shift your center of gravity. The catch is that the ploe represents a 'hard' attachment point, and this is what they lever against.

What you are suggesting is possible is the equvilant of a stripper doing that same trick on a rope. It is not possible. No matter how hard they push on the rope, it will flex and their body will swing under them from the force of gravity. No pole, no leverage.

[genghis 0]

While gravity will take advantage of that flexible point, so will lift, providing a counter force and thus allowing the system to stay out of the "neutral" position it would be in were it not for lift. What the argument comes down to is whether the center of forces in the entire system of the jumper and parachute is in the three ring (reasonable as the sources of lift are all above them and the forces of weight are all below) or at some point near the parachute (also reasonable based of the arguments presented; since the swing effect of any input on the parachute is focused at a pivot point of the parachute). Depending on which it is, it changes the way the moment arm of the shift in body weight affects the flight of the parachute.

[JanuszPS 0]

I'm just a simple engineer and didn't spent lots of time thinking about that, but for me it looks quite simple - no matter what you do (if there is no additional input such rear risers) the system tends to equalize the forces, which means that the center point of gravity will be exactly on the line from the attachment point.
That's how I understand that.
For the suspended weight the point of rotation is the three rings, however it is one of the points in the chain of the connections.
j.

Back to Poland... back home.

[davelepka 4]

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While gravity will take advantage of that flexible point, so will lift, providing a counter force and thus allowing the system to stay out of the "neutral" position it would be in were it not for lift.

I'm not sure how you come to that conclusion. Of course lift is the counter-force to gravity, but each of those forces work do not only work in the absence of each other, they work in concert.

While the canopy may provide lift that counters gravity, gravity is still present, and pulling the jumper straight towards the earth. Any attempt to deviate from being pulled straight down, such as an attempt to alter your C of G will result in a rotation about the three ring attachment point returning the load to being pulled straight down.

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What the argument comes down to is whether the center of forces in the entire system of the jumper and parachute is in the three ring (reasonable as the sources of lift are all above them and the forces of weight are all below) or at some point near the parachute (also reasonable based of the arguments presented; since the swing effect of any input on the parachute is focused at a pivot point of the parachute).

No it doesn't. Those are two seperate situations you've outlined, and they co-exist without conflict.

The entire canopy/jumper system does indeed rotate around a point up near the canopy itself, and this is the result of the jumper swinging around at the bottom of the lines.

In looking at that system, the lower pivot point made up by the three ring attachment is of no consequence. As previously disussed, gravity maintains the load directly under that pivot point, so that pivot point, in essence doesn't even exist. If there was a way to 'hard mount' the harness to the risers, it would not effect the pendulum effect of the jumper swinging under the canopy to effect attitude changes.

(Note - the jumper will indeed deviate from being pulled straight down while in a turn or dive. At that point the jumper will remain centered and balanced under the three ring attachment point, but for off of straight down. During those manuvers gravity is overcome by the force of the turn.

However, this discussion is surrounding fore and aft weight shift in the harness while not in a turn or dive, so that situation is not a factor.)

The issue being discussed here is of a smaller system, that of the jumper in the harness, and how they move in relation to the risers. As I mentioned several times, any attempt to alter your C of G while hanging from the three ring attachement point will result in the load rotating about that point, and returning to a balanced state hanging from that point.


The concept that a different body position will apply input to the pitch of the canopy is the same as trying to push on a rope.

Because your weight will always 'find it's own level' due to pivoting about the three ring attachment, and the fact that both risers are attached to the three ring, you cannot apply force from below the three attachment point that will have an individual effect on either the front or rear risers. You simply have no load path on which you can apply a force in that direction.

It's like having a rope attached to a wagon. You can pull on the rope all day long and effect a change on the wagon, but the second you attempt to push the rope, the system becomes useless. There is no load path on which you can apply a force in that direction.

[JanuszPS 0]

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***As I mentioned several times, any attempt to alter your C of G while hanging from the three ring attachement point will result in the load rotating about that point, and returning to a balanced state hanging from that point.

Agree.
That what is show on my simplify drawing. Upper: perfectly symmetrical object in balance. Lower: unbalanced object moving to balanced position.

It is possible by moving the body's/object's forward/backward to move the CG point out of the centre position with the condition that additional force is introduced to the system (such as arms pushing down the rear risers which means "slightly lifting up"/unloading or simply supporting the body at some point and keeping the pilot in balanced position).
I'm not a swooper so I might be wrong...
j.
Edit: to load the picture.
The semi-rigid connection needs to balance eccentrically located load which is the object with moved centre point of gravity. (In fact that could be described in equation)

Back to Poland... back home.

[JanuszPS 0]

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***Because your weight will always 'find it's own level' due to pivoting about the three ring attachment, and the fact that both risers are attached to the three ring, you cannot apply force from below the three attachment point that will have an individual effect on either the front or rear risers. You simply have no load path on which you can apply a force in that direction.

Exactly. It is the basics of mechanics/static rule that all forces applied at one point do not generate momentum and the forces are balanced, the sum of all forces is equal 0. Otherwise the system is in movement (which is not the case in this situation as the body is in stable position in respect to local coordinate system). So without applying additional "connection"=force between the body and the upper system bypassing the original connection point (pinned connection - a hinge) there is no possibility to act on the upper system - risers (above the pinned connection point - three rings).
That's why when loosing the chest strap and moving upper body forward swoopers use the rear risers not only to steer/plane out the canopy but also to support themselves/to keep balance - they have to introduce additional force to keep suspended body in "initially imbalanced" position.
That's how I understand that.
j.

Back to Poland... back home.