chest strap under canopy?

[pilot-one 0]

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nor at the size listed, will find significant gains by loosening your chest strap.

Really? And you know this because why? Tell me again. I guess when I was jumping a Sabre 2 210 I must have been smoking crack? Eh?

[rocketscientist 0]

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Accuracy jumpers on rounds do it so they can see DOWN a little better. My guess is you'd never seen a classic accuracy competition, but it actually has very little to do with a "normal" landing.

Now, what I'd like you to do is a little bit of a thought experiment, but first I gotta ask you; "how much do you know about triangles?"

you are correct in saying that i have never seen a classic accuracy competition, but it did not look to me, in the picture i was refering to as a round, according to your last statement it is (as you would know better than i, and i am not trying to argue that fact). i did read and understand the reply that was posted about changing from one "type" of tri to the next. i guess i will stop now, i get one saying yes one saying no, and no one can seem to agree on anything except that is does make significant gains but only when you go smaller. (of course i am also talking about pulling slider all the way down and or having a removible slider)

My inner child is a mean little fucker

[relyon 0]

For all the aerodynamic drag purists out there I'll point out that the largest source of drag in the total deployed canopy system is the suspended human. Collapsing sliders and RDS are mere window dressings until people are willing to wear full spandex/vinyl "style" suits. Allowing risers to spread can have some effect on glide performance though it's effect is often misperceived and usually overestimated. The canopy planform, aspect ratio, airfoil, number of cells, fabric type, line trim, line type, and total included anhedral angle have greater performance implications - some significantly so - than spread risers do. Loosening a chest strap beyond the point there is any tension in it is potentially unsafe and useless except perhaps in classic accuracy competitions.

Bob

[quade 4]

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I guess when I was jumping a Sabre 2 210 I must have been smoking crack? Eh?

Are you familiar with the terms "Emperor's New Clothes" and "Placebo Effect"?

quade -
The World's Most Boring Skydiver

[denete 2]

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I guess when I was jumping a Sabre 2 210 I must have been smoking crack? Eh?

Are you familiar with the terms "Emperor's New Clothes" and "Placebo Effect"?

I'm familiar with the "Elephant in the Living Room", and I've read "The Pachyderm and its Pilot".

SCR #14809

"our attitude is the thing most capable of keeping us safe"
(look, grab, look, grab, peel, punch, punch, arch)

[pwln 0]

This thread made me think a little bit. I had wondered what the big deal was.
I always deploy, check my airspace, stow slider, unstow brakes (snap toggles, no velcro) control check, then I reach down (1/4 to 1/2 brakes) and loosen my chest strap.

I know that it does not make a huge difference most of the time but that's just how I have always done it.

Your last reply, about a small "twitchy" canopy makes me see how "later on" doing what I do now could become a pain. Not that I plan on downsizing anytime soon, but that makes pretty good sense to me, I think I may re-think how I do that just in case I decide to downsize later. (BTW my other canopy is a Classic 304)

[pilot-one 0]

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I guess when I was jumping a Sabre 2 210 I must have been smoking crack? Eh?

Are you familiar with the terms "Emperor's New Clothes" and "Placebo Effect"?

Oh yea...I never thought about that. You must be right. I just made it up in my mind.
Now that's a good one.

[denete 2]

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To be honest...i'm not even looking at my chest strap when I do it. With my XF2 I can "flare" the canopy use my right hand to loosen the chest strap and not even skip a beat.

I still use two hands to loosen mine. But, I do this with the brakes still stowed, so I've got a little more time (check traffic, rear-riser turn toward my first balloon, check altitude, do the housekeeping, check traffic / altitude / position, un-stow brakes, and fly the flight plan).

SCR #14809

"our attitude is the thing most capable of keeping us safe"
(look, grab, look, grab, peel, punch, punch, arch)

[NoShitThereIWas 0]

If you do not feel overloaded, are able to multi-task and realize your priorities, I would say open it up. As a result of hanging out with some of the top swoopers in the world, I have realized some things and changed my ways.

Especially if high performance canopy landings are anywhere in your future repetoire of skydiving I would say get in the habit now of opening your chest strap. Since learning how to collapse my slider and get it out of the way behind my head, along with opening my chest strap and my wingloading; this has made a world of difference in the flight characteristics of my canopy (for the better My landings now seem smoother and more efficient. I am not a Pro Swooper by any means but I consider my small steps as part of the mechanical baby steps to higher performance. It certainly isn't going to hurt you to open that baby up

The best analogy I can give is riding a horse. You own this beautiful mustang horse who likes to run. It performs best when it is free from restraint. You want it to run so why put any tension on the reigns?

Roy Bacon: "Elvises, light your fires."

Sting: "Be yourself no matter what they say."

[relyon 0]

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... Since learning how to collapse my slider and get it out of the way behind my head, along with opening my chest strap and my wingloading; this has made a world of difference in the flight characteristics of my canopy (for the better My landings now seem smoother and more efficient. ...

While not at all directed at solely at you, in light of comments such as these I'm curious as to other people's opinions are of an earlier reply of mine.

Bob

[billvon 2,792]

>You own this beautiful mustang horse who likes to run. It performs best
>when it is free from restraint. You want it to run so why put any tension on
>the reigns?

Right. But loosening the chest strap while not wearing a vinyl suit or using an RDS is like loosening his saddle a bit while still pulling on the reigns. The chest strap length is one of the most minor contributors to performance on a parachute system compared to, say, an RDS.

[NoShitThereIWas 0]

I agree with both statements of Relyon and Billvon. Opening a chest strap is not going to contribute tons of aerodynamic efficiency and if one wears a baggy freefly suit while flying their canopy, then this would defeat the whole purpose of becoming more aerodynamic.

But I guess it all has to do with the goals of this jumper. If he wants to develop the habits now I say good idea. I do not find it dangerous to loosen one's chest strap unless doing so takes their attention away from landing safely.

An RDS is going to make a difference and I do not have one yet because I am not at the flying level that I would require it. I already find it a pain in the ass just to stow my slider with a rubber band and bungee. I have thought about getting rid of it but I do notice enough of a difference between that and my chest strap that I keep it on there.

It seems like the RDS would be an even bigger pain so I don't mess with it, and plus they are expensive little buggers (even to make).

So yes, I do agree with both comments above, but then I also say, open that baby up and see what he thinks. If he thinks it flies better and he likes it, great. If not and it makes no difference, great too. I like flying with mine open and I learned from the best of the best

Roy Bacon: "Elvises, light your fires."

Sting: "Be yourself no matter what they say."

[virgin-burner 1]

well, in the light of aquiring the mechanics of future swoops, the person under canopy tends to lean forward as they are landing. so, done with un-loosened chest-strap thats not very cool. except, you like a little autoerotic suffocation under your wing. well, i dont!

and the noise of an unstowed slider is just pure annoying!

“Some may never live, but the crazy never die.”
-Hunter S. Thompson
"No. Try not. Do... or do not. There is no try."
-Yoda

[pilot-one 0]

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But loosening the chest strap while not wearing a vinyl suit

Huh? This makes no sense whatsoever.
It has nothing to do with the aerodynamics of the pilot. We're talking about the wing here. What loosening the chest strap and dropping the slider does is take the anhedral out of the wing to make the wing more efficient. A vinyl suit would make a difference under canopy probably but in a completely different arena.
This is really very simple to understand and anybody who thinks it doesn't make a difference in any size canopy has never tried it.
I took a Sabre 2 230 out for a test jump the other day and test the "placebo effect" or the "emperor'
s new clothing" concepts. Even on this size canopy the differece is very noticable. In fact it turns a very boring canopy into something that is reasonably fun.

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The chest strap length is one of the most minor contributors to performance on a parachute system compared to, say, an RDS.

Very wrong. Loosening the chest strap is key to flattening the wing by separating the anchor points of the suspension lines. The wider the better.
I'll agree that the RDS removes the drag from the equation but a regular slider colapsed and stowed produces very little drag compared to the benefits of loosening the strap. Actually both would be best. Maybe that's why a lot swoopers use an RDS and open their chest straps. Hmmmm.

After further thought on this thread I think we are talking about two different things. What I think billvon is looking at is improving the aerodynamic drag factor to increase speed, glide, etc. Whereas I am looking at the handling characteristics of the canopy to improve turns (toggle, harness and riser), flare, glide angle, etc.

[billvon 2,792]

>It has nothing to do with the aerodynamics of the pilot. We're talking
>about the wing here.

We're talking about the areodynamics of the SYSTEM. An F-14 has a spoiler that deploys from its body to slow its flight; effectively it makes it less efficient. You can't discount it just because it doesn't affect the wings.

Wearing a slick suit will have far more effect than flattening the canopy by a few inches on the overall performance of the system.

>Loosening the chest strap is key to flattening the wing by separating the
>anchor points of the suspension lines.

Loosening the chest strap allows the canopy to spread out a few inches, until further spread is stopped by the slider. The canopy cannot spread any farther than that. Which is why it doesn't do much without an RDS.

>Even on this size canopy the differece is very noticable. In fact it turns
>a very boring canopy into something that is reasonably fun.

Try an RDS sometime. You'll note a MUCH more significant difference.

> Whereas I am looking at the handling characteristics of the canopy
>to improve turns (toggle, harness and riser), flare, glide angle, etc.

Yep. And less drag = better glide, better flare (more energy for longer) snappier _feeling_ turns etc.

Edited to add - this is not to say you shouldn't loosen your chest strap; it does indeed add a bit of performance from the reduction of anhedral. But a few things to remember are:

1) the change will be minor
2) after the slider is under tension, further loosening doesn't do anything to improve aerodynamics.

[relyon 0]

virgin-burner:

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well, in the light of aquiring the mechanics of future swoops, the person under canopy tends to lean forward as they are landing. so, done with un-loosened chest-strap thats not very cool. except, you like a little autoerotic suffocation under your wing. well, i dont!

and the noise of an unstowed slider is just pure annoying!

I stated "Loosening a chest strap beyond the point there is any tension in it ...", not that the chest strap shouldn't be loosened at all. Also, there are more ways that one to quiet a flapping slider. Stowing it is one way, a RDS is another way, and there are other ways too.

pilot-one:

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... What loosening the chest strap and dropping the slider does is take the anhedral out of the wing to make the wing more efficient. ...

There are other ways to do this as well. Longer lines, longer risers, and wider riser attachment points all affect the anhedral geometry in the same way (ie. make the angle smaller). I'm not suggesting these are desirable for a given application, just that they're possible.

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... This is really very simple to understand and anybody who thinks it doesn't make a difference in any size canopy has never tried it.

While admittedly not simple, so does comparing the cos(A1) to the cos(A2) where A1 is the anhedral angle before loosening the chest strap and A2 is the same angle after loosening it. Anybody who thinks it makes a big difference has never done the calculation.

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... In fact it turns a very boring canopy into something that is reasonably fun.

So does shortlining, though that brings with it undersirable characteristics as well and is probably not the sort of fun a swooper is looking for.

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The chest strap length is one of the most minor contributors to performance on a parachute system compared to, say, an RDS.

Very wrong. Loosening the chest strap is key to flattening the wing by separating the anchor points of the suspension lines. The wider the better. ...

It's physically impossible to make the canopy wider than it is completely flattened out, but even that point can't be reached. The more a canopy flattens, the more the spreading force provided by the anhedral geometry diminishes. Well before it reaches the optimum flat geometry is will collapse; the internal pressurization alone in a ram air canopy is completely insufficient to keep it open.

Bob

[JerryBaumchen 1,318]

Hi relyon,

Waaaaay back in the late '60's Ted Strong built a canopy that had unequal lines so that the end result was a flat canopy ( when viewed from the front ).

IRRC, he even jumped it at a Nationals.

I think that the construction costs did not justify continuing with the idea. Or it just didn't work.

JerryBaumchen

[rocketscientist 0]

would anyone happen to have pics of canopy jerry is referring to?

My inner child is a mean little fucker

[pilot-one 0]

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It's physically impossible to make the canopy wider than it is completely flattened out, but even that point can't be reached.

I'm not referring to making the canopy wider. That is physically impossible.
What needs to be wider are the anchor points of the suspension lines.
There is no way the angle of dihedral won't change if you move the 3 rings apart from each other. By doing this you are effectively lengthening the suspension lines by removing or reducing the angle created by the restriction of the slider or chest strap. The further out the line is attached to the canopy the more the effect is.
Further more this makes a more direct link to your leg strap. The point where you are really connect to your canopy. This in turn makes harness turns much more effective.
All I have to say is "try it" and you will see.

[billvon 2,792]

>By doing this you are effectively lengthening the suspension lines by
>removing or reducing the angle created by the restriction of the slider or
> chest strap.

Correct. And as soon as you hit the limit of the slider, the canopy cannot get any wider without an RDS. That limit is hit pretty rapidly with most canopies, which is why you get only minor improvements from chest strap lengthening without an RDS.

[relyon 0]

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There is no way the angle of dihedral won't change if you move the 3 rings apart from each other. By doing this you are effectively lengthening the suspension lines by removing or reducing the angle created by the restriction of the slider or chest strap. The further out the line is attached to the canopy the more the effect is.

All true, but the actual amount of that effect is overestimated and it does less than it may seem, even though it may feel like it's doing more. On a stock Velocity 75 with 18 inch risers the distance from the top of three rings to the bottom skin is just over 120 inches. Moving the three rings apart 6 inches (3 inches each side) results in less than one tenth of one percent difference in effective span. That's with no slider (RDS) and a competely loose chest strap. The higher lift performance gain is minor compared to the lower drag performance gain that could be realized if the jumper is willing to do what that entails. Alas, RDSs are cool and vinyl suits are geeky ... or so it appears by comparing the relative numbers of each.

That is not to say there is no effect on control, since loosening the chest strap does have an effect on that in the way of harness turns. But performance and control are two different topics, albeit interrelated.

Bob

[pilot-one 0]

All theory and formulas put aside and considering most of us in this discussion actually do what we're talking about I propose this challenge:
On your next jump leave your slider up and your chest strap tight and then report back on the performance of your canopy ride in general. My guess is won't like it.

[pilotdave 0]

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On your next jump leave your slider up and your chest strap tight and then report back on the performance of your canopy ride in general. My guess is won't like it.

That's how I usually do it! I seem to like it ok... put over 1000 jumps on my canopy.

Dave

[billvon 2,792]

>On your next jump leave your slider up and your chest strap tight and
>then report back on the performance of your canopy ride in general. My
>guess is won't like it.

A better test:

1) Chest strap normal, slider down and killed.

2) Chest strap out as far as it will go, slider down and killed.

I think you'll notice a very small difference (although you might well feel more comfy and in control.)

[mnealtx 0]

I don't have a dog in this fight (Type 8 risers, so no slider pull-down for me), but loosening the chest strap under canopy does make harness inputs easier for slight corrections.

Mike
I love you, Shannon and Jim.
POPS 9708 , SCR 14706