loosening chest strap/leaning forward

[rhys 0]

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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.

...therfore pitching the parachute forward further due to a forward movement in the centre of gravity.

This is the parachute equalling out the load.

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

[JanuszPS 0]

Only when you add some input with your hands on the toggles/rear risers into the equation. Otherwise no matter what you do below the pinned connection doesn't really matter*. That's how I see it.
j.
Edit
*Excluding drag effect.

Back to Poland... back home.

[davelepka 4]

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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.

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...therfore pitching the parachute forward further due to a forward movement in the centre of gravity.

I think you're looking at it backwards. The motion of you pulling the risers back, does just that and only that, pulls the riser back. Your position in the harness is not a factor bacause regardless of your position, your weight will again center itself under the pivot.

For your assertion to be correct, you would have to find some way to both pull the risers back, and move the attachment point forward at the same time, which is impossible. The amount of force you apply to the risers is not enough to support your weight, so even if there was a way to move both yourself forward and the risers back, you could only apply as much force forward as you would to the rear, and this would be too much for the rear risers and you would stall the canopy.

When you apply rearward (or outward) pressure to the risers, the pressure is applied against line tension, which runs between the canopy and the base of the risers. So the pull against the risers uses the base of the risers as a stop, and that point remains stationary, with the risers moving relative to it.

If you're the type who pulls on their risers and slacks the riser under your grip, then of course you're not using the risers as a lever to hold yourself out of CG, you're not applying the force against anything but the canopy (such as the base of the riser).

If you were to view the application of rear risers from the side, you would see that the three ring remain in place, and the risers move relative to it. Weight continues to hang level under the attachment point, and it's realtion to the front riser remains the same.

Again, a good example of this is any freestlye move that requires a backward lean in the harness. If your suggestion is that a forward lean will produce a flatter glide, than a rearward lean should prodcue an opposite reaction, a steeper glide causing the canopy to dive into the water, but we don't see this, or any reaction from the canopy during these moves.

If I'm not mistaken, there's even a version of the lazyboy where both hands are removed from the toggle and risers. Here is a situaiton with a pronounced rearward lean, and no opportunity to apply any sort of input to the canopy. If leaning fore- or aft in the harness could indeed effect the pitch of the canopy, this move would not be possible, as the pitch change would be fully unchecked.

http://slipstreamairsports.com/wp-content/uploads/2009/07/stu-freestyle.jpg

[danielcroft 2]

Wouldn't the reduction in wind resistance at the jumper's body cause a general reduction in drag? Wouldn't that have an affect on the AoA of the canopy, etc?

[davelepka 4]

Indeed, check out post #5 in this thread, and that aspect is covered. I'm a pretty firm believer that the reduction in drag is very slight, and really only significant at higher speeds, which is another way of saying that it's not going to do shit for you unless you destroy your swoop and just wring your canopy out like dishrag.

With the Olympics on, I can make the comparison to the skin tight suits a lot of the competitors wear. At that level, yes it's an advatage, but really only at that level. You won't see many weekend skiers in one of those suits just so they can go that much faster down the hill.

Beyond that, this discussion is not about the effects of drag reduction on the canopy, but about leaning forward in the harness, and if that will effect the pitch of the canopy in any way.

I'm still going with 'no', but others seem to disagree.

[danielcroft 2]

Sorry, long posts and many days between reading.

I was thinking of a pretty serious swooper at my DZ who flies with a very long chest strap and leans forward to the point that his body is (or near) horizontal. He competes so I believe that this is having an affect on the way his canopy flies. For everyone else, I guess it's as you say, such a small difference that there really isn't any (kind of like an RDS?).

[davelepka 4]

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such a small difference that there really isn't any (kind of like an RDS?).

There is a difference, but the problem is the very nature of drag itself. There's a technical, scientific reason that the effects of drag increase at a higher rate than the increase in speed. It's a multiple or a square of something or other, but the basic deal is that if you have 'y' drag at 30 mph, you'll have more than 'y x 2' at 60 mph. The speed will double, but the amount of drag will triple (or something like that).

So when you look at swoopers leaning forward as a drag reduction technique, you can see that the benefits quickly diminish at lower speeds. Of course, if you happen to build a ton of speed, and 'assume the position', I'm not advocating sitting up as you slow down, once you're there you might as well stay. In the end, unless you have that monster speed to start with, there are far more beneficial things to focus on to improve your swoop.

An RDS, on the other hand, I think is a bit more useful, and I'll tell you why. The leaning forward trick only comes into play after your dive, once you have planed out and begun your swoop. The RDS, however, is providing benefit during the entire canopy ride, and especially during the dive itself when you'll reach the highest speeds, and get the most benefit from the drag reduction.

Now if there was a way to fly your entire swoop, from set up to shut down in 'the position', that might be something, but I'm not sure how that would work.

That said, I think the RDS is a huge pain in the ass, and really just a 'look at me' deal for anyone who's not a serious competitor.

[danielcroft 2]

I'd gathered that the RDS allows the canopy to fly further forward in the window by reducing the drag on the canopy. For most people, the affect is minimal due to the size of the PC relative to the canopy and the speed of the swoop. I was just thinking that the same would be true for 'the position' based on being told to change the size of my body relative to the wind under canopy when doing clear and pulls in order to adjust speed. Being that lift increases with speed as does drag, I would have thought that the position of the body, even on just the plane out would make a difference.

[davelepka 4]

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I'd gathered that the RDS allows the canopy to fly further forward in the window by reducing the drag on the canopy.

That's correct, and that in turn allows the jumper to get further behind the canopy, and prolong the dive by taking longer to swing back under the wing. Like I stated uprthread, there are several different factors at work when you dive a canopy, which brings me to my next point...

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For most people, the affect is minimal due to the size of the PC relative to the canopy and the speed of the swoop.

Again, you are correct about the size of the canopy relative to the size of PC to the size of the canopy. Taking the bag and PC off of a 190 is only going to reduce drag by a very small percentage.

However, if you are able to dive your canopy long enough that it reaches it's 'terminal velocity' where drag equals the force of gravity, then any canopy will see a benefit from an RDS because the reduced drag will allow the canopy to reach a higher top speed.

It's true that a smaller wing would also benefit from faster acceleration to that higher top speed, but in theory if you're taking your canopy 'to terminal' the RDS will alllow you to go faster.

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I was just thinking that the same would be true for 'the position' based on being told to change the size of my body relative to the wind under canopy when doing clear and pulls in order to adjust speed

Are you saying that while under canopy, you were adived that your body position should be used to adjust your speed?

I'm not sure why anyone would tell you that, because that has to be the least efficient way to adjust your speed over a very small range. If it was intended as a learning tool, just to illustrate the effects of drag, then I can understand that, but as a normal course of action, it seems like a waste of time.

The only times I use that technique under canopy is when I'm waaay out there, and making back to the DZ is a question in my mind. In those cases, I will tuck up and streamline my body position to squeeze every last inch out of my canopy.

The problem with that technique is that it encourages target fixation, and lures pilots into focusing on making back instead of coming up with a plan B, being preparred to land off.

When I do that, I'm last out with a tandem video, and trying to get back to shoot the end of my video. I'm also generally flying back for a straight-in downwind landing, so making the turn back into the wind is not a factor. Additionally, I am very familiar with the territory surrounding the DZ, and have landed in all of the surrounding fields several times.

I would advise any jumpers using that technique to get back to the DZ abandon the idea by 1500ft, and focus your attention on making a safe landing at a location you are sure you can reach.

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I would have thought that the position of the body, even on just the plane out would make a difference.

Again, it does make a difference, but it makes less of a difference the slower you are going. I remember someone measuring speed at the gates of a swoop comp, and they found that the top guys were coming through at 90 mph.

So if the benefit of the drag reduction at 90 mph equals 'x', if your speed through the gates is reduced by 20% (72 mph), your reduction in drag is only going to be, lets say, 70% of 'x'. Even though you have 80% of the speed, the drag reduciton is only going to be 70% of what you would expereince at 90 mph.

Now, let's remember that once you blow through the gates, you're just getting into the plane out, where you immediately being to slow down, and that nobody is in 'the position' though the gates, that happens after establishing the plane out. So even a guy who goes though the gates at 90 will not be in 'the position' until the canopy is doing 80 or even 70.

To take that one step further, the guy who hits the gates at 70, won't be in 'the position' until they're doing, potentailly, 50 mph, which is almost a 50% redcution in speed from 90 mph, so the reduction in drag will have lost 60% or 70% of it's usefulness.

Of course we all know that speed is constantly diminishing throughout the swoop, so you can see that the benefits will drop off quickly.

[danielcroft 2]

Ok, fair enough. I'd hazard a guess that there aren't many people who get their canopies to terminal who aren't pretty serious swoopers and already on a pretty small canopy.

Sorry, I was advised to use this technique when flying with other people to make small adjustments to speed in order to keep proximity. I haven't had any need to use this technique when attempting to get back from a spot, as you said, if it's that close to the line then I land out. I wouldn't recommend anyone use this technique for getting back on a long spot either for the same reasons. It is however worth remembering when flying with others or in the instance that you're trying to make a safe landing area and don't have other options.

You know a lot more about this than me of course, I was looking for other explanations given that the CoG argument had seemingly been dismissed. I know BG recommends leaning forward (not to the extent of lying flat mind) but I would like to hear comments from people who actually do this and what difference they feel it makes.

[davelepka 4]

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I was advised to use this technique when flying with other people to make small adjustments to speed in order to keep proximity.

Got it. When you mentioned that you did this on clear and pulls, I was thinking of a low pass, and that you were alone in the sky trying to controm your speed with your body position.

It is useful when flying with others because sometimes those slight adjustments are all you need.

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I know BG recommends leaning forward (not to the extent of lying flat mind) but I would like to hear comments from people who actually do this and what difference they feel it makes.

See post #3 for a what I believe to be a quote from BG on the subject of leaning forward in the harness.

His basic premise (and mine) is that it's matter of putting your body in a posture similar to running/walking, so when you do need to start running/walking you're in a more natural position to do so.

I went on to thoerize that leaning forward became the de-facto swooping 'position', so everyone started doing it because it was the thing to do.

The aerodynamic benefits came last when guys really started leaning waay out there. In addition to the diminishing returns discussed above, I also think that tyring to utilize that posture too soon in a progression could do more harm than good, because if that extreme posture has any effect on your ability to efficiently fly the canopy, you're taking one step forward with your body position, and two steps back with your inability to fly the canopy from leaning that far forward. Just another reason it should be the very last thing on your 'to-do' list when learning to swoop.

Maybe second last, with a skin-tight rubber suit like the style jumpers wear being last. Thank god nobody has made it that far.

[danielcroft 2]

Heh, I really should go back and re-read the thread.

I'm really not even thinking about using 'the position' for my 90s, I just didn't think there was any point.

The free fall speed guys wear them too right? They're classy. It's only a matter of time.

[JanuszPS 0]

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***I think you're looking at it backwards. The motion of you pulling the risers back, does just that and only that, pulls the riser back. Your position in the harness is not a factor bacause regardless of your position, your weight will again center itself under the pivot.

For your assertion to be correct, you would have to find some way to both pull the risers back, and move the attachment point forward at the same time, which is impossible. The amount of force you apply to the risers is not enough to support your weight, so even if there was a way to move both yourself forward and the risers back, you could only apply as much force forward as you would to the rear, and this would be too much for the rear risers and you would stall the canopy.
[....]

In my opinion it is not true and I will explain why later on.
But shortly - by pulling down the risers you are bypassing the pinned connection - three rings, so the point of rotation is no longer in that place as all forces are not crossing the same point. Point of rotation is a place against which the system (body) under external forces and internal reactions rotate. Simply by pulling down the rear risers "theoretically" you can fully unload the rear risers from the three ring point to your hands and forget about that part of the risers. I'm saying theoretically as I don't know what sort of forces we are talking about. By removing or limiting that connection the point of rotation is moved thus the centre point of mass can be moved forward/backward in respect to the canopy. I might prepare some drawing when I find some free time.
j.
I advice to look into some mechanics book to understand what I'm talking about.
Edit:
the change might be very small (due to high loads) or very limited due to the no-rigid nature of the wing "wasting" all effort - I don't know.

Back to Poland... back home.

[superstu 0]

To answer the original question, the effects of loosening the chest strap on both HP canopies and non-HP canopies can be noticed. Most people don't consider many of the CRW canopies to be high performance, however they will actually loosen and re-tighten their chest straps depending on the performance they want (ie if they need to go slower/ be less effecient they will re-tighten the chest strap).

For me personally there are a couple of things I notice when i lean forward during a swoop and they are not all physics oriented. For example, mentally when i lean forward it gives me a more aggressive mind set which helps build confidence during a distance run. When i'm in my roll out i will lean forward to help the recovery arc out. When you flatten way out it does help reduce drag, which in effect helps lift because you'll be able to maintain your speed longer and speed=lift.

On the flip side, even at the top level, most people who lean way forward are "dirty" in the harness, meaning to much movement in the harness, thus scrubbing speed. i've seen everyone do this from Nick Batch, to Jay Mo, to Marat, to GW, to everyone. if you ever watch Kaz Sheekey do a distance run, once she gets on roll-out she does not move in the harness...at all. she picks up her feet as she goes through the gates and that's it and little Kazzie can go BIG.

Those are just my thoughts, whether leaning forward effects the CG in the harness or canopy or whatever is debatable in my book because there are too many variables that can't be calculated. I mean you have a non-rigid wing, and harness that is flexible, and so many pivot points within the system i don't know if you could ever calculate it out.

Slip Stream Air Sports
Do not go softly, do not go quietly, never back down

[davelepka 4]

You're on the right track with your thoughts, but also on the right track when you state that the degree of change would be nil, or even just theoretical.

Yes, you can 'remove' the lower connection of the rear risers by pulling down on them. You can pull them in such a way that the riser below your grip will be slack. However, you can also apply outward input (spreading) to the rear risers, which maintains tension along the riser down to the attachment point.

Your next suggestion, that unloading the lower portion of the rear riser could cause the entire attachment point to move forward, effecting a change on the canopy might technically be right , but there are two caveats.

The first is that applying input the rear riser, be it with or without maintaining tension between the riser and attachment point, will cause the load to move forward, as that it the very purpose of that input. Applying the input causes the wing to slow down, and allows the pilot to move forward under the wing causing the nose to pitch up. To assert that adding rear riser input will casue a forward weight shift is a foregone conclusion.

The other problem is that I, for one, and others have found that spreading the rear risers makes for better performance than pulling them straight down (where slack between the riser and attachent point would occur). If slacking the risers would allow for additional forward movement, above and beyond the movement induced by the input itself, this is something that would have been addressed, or at least given the technique of slacking the lower riser equal billing with spreading the risers, but this is not the case.


You have to remember that the amount of force you can apply to the rear risers is very low, especailly compared to the force of gravity holding the jumper squarely under the three ring attachment point. As such, the rear risers are not an effective point with which to lever the load in any direction.

Of course, the overall ruling factor in this situation is that while discussing fore and aft weight shift, and it's ability to effect pitch changes to the canopy, you cannot include any input to the rear risers as that in itself effects a significant pitch change to the canopy, and creates an entirely new set of circumstances.

[davelepka 4]

All good poitns.

If you check out post #28, I used the pic from your avatar to illustrate my point.

I think I used goolge image search for 'freestlye swooping' or 'lazyboy swooping' or something like that to come up with that pic. It was also interesting to see the other random, non-swooping, images the search came up with. The internet is a wild place.

[rhys 0]

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if you ever watch Kaz Sheekey do a distance run, once she gets on roll-out she does not move in the harness...at all. she picks up her feet as she goes through the gates and that's it and little Kazzie can go BIG.

I just met her today training for the aussie swoop nationals. I’ll take heed of that and watch her tomorrow. Your other points are very interesting and insightful too, thanks.

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Those are just my thoughts, whether leaning forward effects the CG in the harness or canopy or whatever is debatable in my book because there are too many variables that can't be calculated. I mean you have a non-rigid wing, and harness that is flexible, and so many pivot points within the system I don't know if you could ever calculate it out.

This subject interests me immensely and I have thought of an experiment to see if I can find out...

I'm doing the nationals for the next 4 days and after that I will conduct the experiment to see if the centre of gravity moving forward 'could possibly' pitch the canopy slightly forward.

Not to argue a point, but because both scenarios seem feasible to me, and I would like to know.

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