Chest strap question

[alan 1]

Can anyone tell me why some manufacturers use single Ty 17 webbing, others use doubled Ty 17 webbing, still others use single Ty 8, and even others use doubled Ty 8, and then some even mix in Ty 7 with Ty 8 webbing on the chest strap and then use a quick fit adaptor that is rated for a proof load of 500 lbs. or less? Look at your hardware, is it stamped MS 70101 - 1? Check out what it says about that adaptor in the Para-Gear Catalog, item #H337 and H336. Unless you have the SS (stainless stell), they are not even rated to 500#.

alan

[riggerrob 558]

Humor alert: There are a couple of sarcastic points in the following post. So before you get your shorts all in a knot, try to see my dry sense of humor.

Single or double layered webbing relates to how much they care about "filling out" the buckle.
Back when bellytive work was fashionable, you had essentially one body position per dive and a single layer of Type 8 webbing could be trusted to stay in the same place in an MS 70101 light weight, stamped buckle.
Then those heathen Frenchmen complicated the issue by inventing chute-assis, which often resulted in a dozen different boy positions per dive, all that flopping about tended to loosen that flimsy, single layer of webbing through that flimsy buckle, so manufacturers started using double layers to better fillout the buckles.
That is similar to the reason why some student rigs use Type 7 or Type 13 webbing for chest straps. They don't really need the extra strength, but the less they slide, the more secure students feel and the less they try to mess with their gear in the airplane, etc.

However - as the latest Advance/Para Fun Service Bulletin details - if you are going to neglect BOC maintenance to the point that your main pilot chute sneaks out at random and you want your harness to survive a tumbling opening - then you would be better off with a Javelin-style, double layer, Type 8 chest strap that wraps around the main lift web.

Whether your chest strap contains two layers of Type 8 or Type 17 iwebbing s purely a matter of fashion.
Which type of webbing makes your boobs/pecs look bigger?

[billbooth 10]

The MS-70101 may have a "rating" 500 lbs., but luckily it is "good for" well over 2,000 lbs. Your chest strap usually doesn't take much load. but if you jump "no-stretch" line and have a one-sided opening, it can load pretty heavily, and at an angle. I have seen MS-70101's cut half way through a single type 8 chest strap on such an opening (without damaging the hardware, by the way). That is why we have been using double type 8 for many years now.

[alan 1]

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Humor alert: There are a couple of sarcastic points in the following post. So before you get your shorts all in a knot, try to see my dry sense of humor.

Getting a little gun shy around me? Not to worry, I actually have a sense of humor.

So, if I'm reading you correctly, these people that are all concerned about Ty 17 webbing being foolish and all that is really just nonsense. The hardare is the limiting factor and it has more to do with slippage. Bill's post mentions the hardware cutting the chest strap, so it seems the hardware strenth also is not the real issue, or the webbing breaking, it seems that the hardware cuts it.

My impression now is there is a ceratin amount of marketing or "puffery" going on with rigs. Javelin for example since you mentioned them. That chest strap isn't really needed for strength and it is misleading when people associate it with better built. It is needed to make up for poor hardware, which is pretty much the same throughout the industry. Am I on track here or missing something?

alan

[alan 1]

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The MS-70101 may have a "rating" 500 lbs., but luckily it is "good for" well over 2,000 lbs.

Just a point to clarify for me, the Stainless Steel adaptor is rated to 500#, the info I have says the MS-70701 is light weight and similar to the MS22019 but is a light weight stamping and should only be used where a small amount of tensile strength is required. So, is it actually the MS-70701 that is good for over 2000# or are we confusing different adaptors?

Also, if I understand you correctly, tensile load strength has little to do with chest strap webbing choice, but rathter shear strength properties, hence you double it?

Quick question...or two. When you do drop testing for TSO, do you do it with the chest strap in various configurations of too tight, too loose, and properly adjusted? I wonder how much this would affect the failure of the harness, since there is very little in any owner's manuals I have concerning how tight the chest strap should be, RI says in their manual that all straps should be very tight. Would an overtightened chest strap on a rig with chest rings actually present a high risk of failure? I'm under the impression that rigs with articulated harnesses are designed for proper load distribution and that they pass TSO drop testing.

One last thought to share along this line, wouldn't a chest strap and quick fit adaptor that is attached to the MLW via a ring, that allows it to float with the load help to mitigate the risk of the adaptor shearing the webbing on an asymmetrical shock load as well as to the anchoring stitching failing?

alan

[FrogNog 1]

Regarding the idea of a chest strap buckle attaching to the MLW via a ring, so it can change orientation to remain in line with the load:

would the buckle orient itself properly to a load coming from another direction (i.e. the asymmetric riser loading issue)? I think that would depend on how much the geometry of the buckle made the buckle "prefer" to orient to the strap.

And how much do the buckles currently attached directly to the MLW via a short loop of webbing orient toward misaligned loads? Do they do it enough in most cases? Do they only fail when a hard opening combines with a serious harness shift problem such as an undone legstrap (or an adjustable MLW that is or becomes improperly adjusted )?

Executive summary: is it really broke?

-=-=-=-=-
Pull.

[billbooth 10]

I am referring to the MS-70101. It is simply a lot stronger than its "rating". The breaking strength of most adapters never comes into play, because they slip way below their rating. I say most, because the MS-70101 is the exception. It won't slip at all. It distorts just above 2,000 lbs. and the breaks at around 2,500...with some variation between manufacturers.

When we high speed or tower drop test, we use a hard rubber dummy with all straps tightened as much as possible. Unfortunately, the dummy cannot compress and/or bend like a real human, but it's the best we can do...that is unless YOU would like to exit an aircraft at 500 feet, at 210 knots, with a few extra hundred lbs. strapped to your body.

[riggermick 6]

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The MS-70101 may have a "rating" 500 lbs., but luckily it is "good for" well over 2,000 lbs.

Just a point to clarify for me, the Stainless Steel adaptor is rated to 500#, the info I have says the MS-70701 is light weight and similar to the MS22019 but is a light weight stamping and should only be used where a small amount of tensile strength is required. So, is it actually the MS-70701 that is good for over 2000# or are we confusing different adaptors?

Also, if I understand you correctly, tensile load strength has little to do with chest strap webbing choice, but rathter shear strength properties, hence you double it?

Quick question...or two. When you do drop testing for TSO, do you do it with the chest strap in various configurations of too tight, too loose, and properly adjusted? I wonder how much this would affect the failure of the harness, since there is very little in any owner's manuals I have concerning how tight the chest strap should be, RI says in their manual that all straps should be very tight. Would an overtightened chest strap on a rig with chest rings actually present a high risk of failure? I'm under the impression that rigs with articulated harnesses are designed for proper load distribution and that they pass TSO drop testing.

One last thought to share along this line, wouldn't a chest strap and quick fit adaptor that is attached to the MLW via a ring, that allows it to float with the load help to mitigate the risk of the adaptor shearing the webbing on an asymmetrical shock load as well as to the anchoring stitching failing?

If an MS 70701-1 is side loaded or loaded at an oblique angle the 500 lb rating comes in to play, it doesn't take a whole lot of preassure to pop the slide bar out under a dynamic load when the bar is lodad in direction other than inline. This configuration, while not impossible to to attain is for all practical purposes not easy to attain either. Hence the need for the 500 rating and it's proven reliability over the years.

As far as harness adjustments in different configurations during drop tests, no. There are no requirements for this during TSO testing plus it would drive the cost of the whole process up even further than it already is, which is pretty expensive.

Mick.

[riggerrob 558]

I don't really see extra layers of webbing as "puffery" designed to compensate for poor hardware.
Good engineers always over-build stuff. They always make educated guesses about whether a particular component will still carry the load after five years of use and abuse, dragging through the sand, etc.

Much of the "puffery" is written by marketing managers after the fact and has little to do with engineering.

The military never expected a chest strap to support more than 5% of opening shock, because they believed that the primary function of a chest strap was to prevent shoulder straps from sliding off your shoulders when the harness is un-loaded.

Skydivers have bad habits of mis-using and abusing gear in ways that never crossed the designer's mind in his worst drunken nightmare.
For example, no "fashionable" skydiver significantly tightened his chest strap until head-down skydiving became fashionable a decade ago. Then they started cranking chest straps down hard to compensate for loose-fitting shoulder yokes. Those shoulder yokes fit just fine for belly flying, but few designers gave any thought to head-down until the mid-1990s.

A large part of the problem is the sharp edges on the stamped MS70101 hardware.
MS70101 are one of the few pieces of hardware stamped out of sheet steel.
If they are not tumbled long enough, they can still have rough edges that cut webbing prematurely.
Back in the mid-1990s Sun Path issued a Service Bulletin to inspect a particular batch of MS70101 buckles for sharp edges that cut chest straps.
I never found any of those sharp buckles on Sun Path products, but - a few years later - found one on an R.I. product and R.I. quickly mailed me a replacement buckle and chest strap.
Just goes to show that many SBs are just reminders of good GENERAL inspection practices, that should be applied across the board to everyone's products.

The other big problem with MS70101 buckles is that if you load them assymetrically, (more tension on one edge than the other by pulling at an odd angle) they are far more likely to cut webbing.
A single layer of Type 8 webbing frays far too fast at that loading.
Last year I replaced adjustable MLWs on a couple of Student Sidewinders and 20 Student Javelins because of a similar wear pattern.

As for drop-testing chest straps at a variety of tensions ... that may be an amusing game for test engineers, but - $800 per drop test - will quickly bankrupt most fledgling parachute manufacturers.

I remember asking Sandy Reid about deliberately tumbling test dummies, and he replied that tumbling dummies were "guarranteed to tear harnesses, but teach us little." Little learning takes place because it is very difficult to determine what angle/airspeed/g-loading/etc. the dummy was at when the harness failed.
Tony Frost (Marana, Arizona) is one of the few test droppers who insists on tumbling test dummies. Since Tony did most of the early drop tests on Javelins and apparently he tore a few lateral straps while tumbling. That would explain why Javelins and Dolphins have such heavy (wrapped Type 7 webbing) lateral straps when many of their contemporaries were still using a single layer of Type 8.

[alan 1]

Thanks for the reply. I'll pass on being the test drop dummy. So, am I correct in surmising, the reason that owner's manuals are not very specific on rig adjustment (including chest straps), fully articulated harness or not, is that it just isn't a real issue?

alan

[alan 1]

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If an MS 70701-1 is side loaded or loaded at an oblique angle the 500 lb rating comes in to play, it doesn't take a whole lot of preassure to pop the slide bar out under a dynamic load when the bar is lodad in direction other than inline. This configuration, while not impossible to to attain is for all practical purposes not easy to attain either. Hence the need for the 500 rating and it's proven reliability over the years.

As far as harness adjustments in different configurations during drop tests, no. There are no requirements for this during TSO testing plus it would drive the cost of the whole process up even further than it already is, which is pretty expensive.

Thanks. Another poster in a different thread, which has been locked, seemed to be leaving readers with the impression that an overly tightened chest strap on a rig with chest rings created a high risk of failure. My silly debates have been aimed at getting factual information on the issue. I would hate to be childish and argue an untenable position.

Bottom line is it seems to be a non-issue as no one has come forth with incident reports of properly routed chest strap failures in the field due to overloading. If there were, I would suspect there would have been some sort of industry wide response.

alan

[alan 1]

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Executive summary: is it really broke?

No, I have just been trying to get that point across to to Sparky. The other thread is locked.

alan

[alan 1]

Thanks Rob. Very good info and much more appropriate for this forum than the post a pic of your new rig threads. It may be a little dry reading, but a serious rigger or anyone serious about knowing their gear can appreciate it.

alan

[mjosparky 3]

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Another poster in a different thread, which has been locked, seemed to be leaving readers with the impression that an overly tightened chest strap on a rig with chest rings created a high risk of failure.

And where did I say anything about a high risk of failure. This is what I said.

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I agree with you and JP that there is very little chance of the failure with the lateral loading. But when you say Type 17 is 2,500 lbs. the friction adapter used with it is rated at 500 lbs.

Ain't fashion a wonderful thing?

Sparky

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My silly debates........I would hate to be childish and argue

And I believe this is what got the thread locked. It might be time to move on.

Sparky

My idea of a fair fight is clubbing baby seals

[billbooth 10]

I don't know of a fatality from a broken, or too loose chest strap, so I guess it's not much of a problem. I do know of people falling out of harnesses when they don't thread strap correctly, or at all.

[alan 1]

Sparky, you contradict yourself so often, how can anyone take anything you say seriously?

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If you have read it, then you should know that if the chest strap is loaded during deployment there is a real good chance it will fail. You MLW is designed to take the load during deployment that is why it is called MAIN LIFT WEB.

Try reading PPM on harness design.

Door, I gone.

Sparky

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I agree with you and JP that there is very little chance of the failure with the lateral loading. But when you say Type 17 is 2,500 lbs. the friction adapter used with it is rated at 500 lbs.

Ain't fashion a wonderful thing?

Sparky

Please accept my apology for confusing "high risk" with "real good chance." I assure you I will be more careful in the future.

And BTW, Bill has been kind enough to share with us that Ty 17 webbing rated at 2500# IS compatible with the friction adaptor it is used with since it distorts at 2000# and doesn't fail until 2500#. Slippage of the adaptor is a more common occurance, but not with the MS70701. As a rigger, I am appreciative of the information shared in this thread by Bill and Rob and Mick. You however, have jumped in and added nothing. Aren't you supposed to be standing in your corner?

alan

[JerryBaumchen 1,046]

Hi Bill,

I have some memory of a failed chest strap that occured 20+ years ago; I think the stitching failed/pulled out. My memory (getting worse by the moment) is that it was a Racer; if I'm wrong my apologies to John & Nancy.

Something appeared in PARACHUTIST on the fatality and I contacted USPA to find out more. I was told that the chest strap is not a structural part so they would not release any further info.

I always found their response interesting; it failed during opening but it is not structural. Hmmmm?????

That's a marketing type trying to appear as an engineer.

[skydiverek 54]

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I don't know of a fatality from a broken ... chest strap

It happened on Racer two years ago in Italy. Here is the thread: http://www.dropzone.com/cgi-bin/forum/gforum.cgi?post=512835#512835

[CrazyL 0]

Summer '04 a fella brought me a Parafun or Parafin rig. 1st I had seen one , the chest strap stitching was totally ripped apart on the long side. I was told the person stayed in the rig. Believed to be a misrouted chest strap. Routed around MLW then to hardware. The rig was grounded till more info was presented. As far as I know the rig is still on the ground.

[billbooth 10]

You're right. I remember that now. The Racer chest strap back then (I don't know how they do it now) was just wrapped around the main lift web like a confluence wrap (not doubled around it like Vectors or Javelins). So it simply unwrapped on a hard opening.

[mjosparky 3]

Are you done yet?

My idea of a fair fight is clubbing baby seals

[alan 1]

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Are you done yet?

Please, you'll have to be more specific. I'll be happy to address your questions and issues as always with quotes from the best available sources.

alan

[slotperfect 7]

To everyone - let's get the thread back on topic please.

Thanks,

Arrive Safely

John

[alan 1]

Great info Rob, I was one of those guys with the stylishly loose chest straps before the fully articulated harness came out.

As I recall RI was one of the first and actually marketed the VooDoo as the first rig designed to be freefly friendly from the ground up. They used a new flat #8 Style Ring as one feature and the manual had instructions for proper adjustment. Not the most complete, but they do say tight for the chest strap. Photos MLW above the chest ring being parallel and angled below it to the hip ring.

So, did Sandy engineer this rig for load paths that could better withstand the loads that may be encountered with freeflying? Do you think a rig configured like the VooDoo may have saved the fatality mentioned in this thread? No way to tell for sure, lots of other variables I guess.

I'm getting the impression that the RI type fully articulated harness is actually better, even if overtightened, for withstanding the loads of a head down premie.

alan

[riggerrob 558]

There are some detailed photographs of the damage in the latest Service Bulletin issued by Parafun/Basic Air Concept.
Oddly, their chest straps look like Javelin style wrap-arounds at first glance, but photos of the damage reveal that they are not continuous.
Odd that they would go to the hassle of doubling webbing, but not wrap it around the MLW. ???
That is as odd as the way Racer "sort of" wraps their chest straps around their MLWs.
But John Sherman has always been an odd bird!
Hee!
Hee!
However, their primary recommendation is to replace Spandex BOCs every 500 jups, before they become loose enough to dump a main pilot chute at random.