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thechutist

Rationale for AAD Cutter Location?

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The recent discussions related to the Argus lead to an obvious question that I haven't seen asked or answered: Are there any compelling reasons for a rig designer to not put the cutter under the free-bag?

Perhaps one of the rig designers to known to read this forum could comment.

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Because it makes the rig much more tolerant to things that would contribute to friction on the loop/delay of that loop pulling out. Of course it is easy to say that rigging errors are mostly what causes such a delay (too long of a loop or not lubricated, etc.), but our world is definitely not a perfect one where riggers do not make such mistakes. Even if a slightly long loop only delays the PC by a small fraction of a second, that can eat up a lot of altitude when there isn't much to spare.

If the cutter doesn't have problems cutting the loop (guillotine cutters have never failed to cut when fired, correct?) then there is no disadvantage to a top mounted cutter.
People are sick and tired of being told that ordinary and decent people are fed up in this country with being sick and tired. I’m certainly not, and I’m sick and tired of being told that I am

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If the cutter doesn't have problems cutting the loop (guillotine cutters have never failed to cut when fired, correct?) then there is no disadvantage to a top mounted cutter.



And there in lies the problem. As you said we don’t live in a perfect world. With the cutter above the pilot chute there is chance that a partial cut will lock the reserve container even if you pull the rip cord. I would prefer to take my chances with a loop clearing the grommets.

Sparky
My idea of a fair fight is clubbing baby seals

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The recent discussions related to the Argus lead to an obvious question that I haven't seen asked or answered: Are there any compelling reasons for a rig designer to not put the cutter under the free-bag?

Perhaps one of the rig designers to known to read this forum could comment.



On rigs where the pin is on top of the top flap, placing the cutter under the topmost flap most closely mimics the deployment sequence initiated by pulling the pin.

On rigs where the pin is under the bottom of the pack tray, placing the cutter at the bottom of the pack tray most closely mimics the deployment sequence initiated by pulling the pin.

When you place the cutter location 'someplace else' [eg under the PC, above PC & under several flaps, at the bottom of the pack tray on rigs with the pin on top of the flap stack, top of container for pins under the pack tray etc] you change the deployment sequence when it is initiated by the cutter.
These changes include, and are not limited to:
- a tendency for the cut loop to act as a Chinese finger trap
- a tendency for the cut loop to relieve pressure on the packed reserve asymmetrically

Delays in complete pack opening may occur because the loose end of a cut closing loop may have to unwind itself through a three dimensional stack of grommets and bags. Excessive friction, whether permanent or temporary may be experienced.
Excessive friction may be because of long closing loop, insufficient lubrication of the closing loop, incompatible container/reserve sizes etc.
Also important in these situations is whether or not the 'normal pack opening sequence' (when the RC is pulled) has the spring of the PC splaying the flaps apart.

In one situation the opening sequence is more like trying to pull your shoelaces out from the toe end of the shoe and in the other situation is more like how a towel moves when you snap it.

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DiveMaker

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And there in lies the problem. As you said we don’t live in a perfect world. With the cutter above the pilot chute there is chance that a partial cut will lock the reserve container even if you pull the rip cord. I would prefer to take my chances with a loop clearing the grommets



+1

Especially so in light of recent developments.
Personally, it appears to me that the solution created a much worse problem.
My reality and yours are quite different.
I think we're all Bozos on this bus.
Falcon5232, SCS8170, SCSA353, POPS9398, DS239

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Personally, it appears to me that the solution created a much worse problem.



Exactly that. The solution (moving the cutter above the P/C) was a band aid fix to a problem it should have never been asked to handle. The rig geometries and canopy combinations were the problem, compounded with incorrect rigging, which all should be addressed.
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You're not as good as you think you are. Seriously.

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Personally, it appears to me that the solution created a much worse problem.



Exactly that. The solution (moving the cutter above the P/C) was a band aid fix to a problem it should have never been asked to handle. The rig geometries and canopy combinations were the problem, compounded with incorrect rigging, which all should be addressed.



It was an effective fix.

The incorrect rigging should of course be addressed, but that isn't going to change the reality that it will continue to persist, just in smaller numbers than before the heightened awareness.

There is no problem with top cutter location for cutter designs that don't fail. We now know of a cutter design that seems to be poor, but that is clearly distinct from the others.

It is easy to know a rig doesn't have that poor cutter design. It is not possible to know that a rigger in the future won't contribute to a delay by using a slightly long loop or not lubricating it.
People are sick and tired of being told that ordinary and decent people are fed up in this country with being sick and tired. I’m certainly not, and I’m sick and tired of being told that I am

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It was not an effective fix.

The FAA states that an AAD may not negatively affect the normal operation of the reserve system.

Even the designer of the Cypres AAD admits there is an expected failure rate of cutters of ANY designe.

This means it is NEVER acceptable to place the cutter in a location that could render the system inoperable if there is a cutter failure. Period.
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You're not as good as you think you are. Seriously.

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It was not an effective fix.



Yes it is. It fixed a specific problem (delay due to loop friction...)

I understand that it opens the potential for other concerns. That is different than saying it wasn't an effective fix for an existing problem. The OP asked for the rationale for top mounted cutters, and that was the rationale. You're saying it isn't an overall good trade-off, I understand that viewpoint.

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The FAA states that an AAD may not negatively affect the normal operation of the reserve system.



If that was a concern of the FAA for guillotine cutters (or the cyrpes cutter specifically), then we can expect the FAA to soon ban their top-mounted use, right? I think not, so it doesn't really mean what I think you're suggesting.

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Even the designer of the Cypres AAD admits there is an expected failure rate of cutters of ANY design.



That isn't saying that the mode of failure will be a locked loop. There are other things that can fail. When a reliability engineer states the probability of a particular failure, for any mechanism you'd like to consider designed by a human, it will never be zero.

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This means it is NEVER acceptable to place the cutter in a location that could render the system inoperable if there is a cutter failure. Period.



Has there ever been an instance of any mfgs guillotine cutter locking onto a loop? Are you concerned about it? I think it is much more reasonable to be concerned about a slight delay that prevents the AAD from being useful when it is actually needed. There are many actual AAD activations when it is needed every year. It is unfortunately, and unavoidably likely that some of those activations will not be as effective due to delays from the loop friction. Riggers should be more careful, but rigs will have to be redesigned to eliminate that failure mode.

I find the discussion about this stuff interesting, and wish there were a solution that didn't have some downside. I just don't think that exists, and still think the top mounted cutter with an extremely reliable, proven cutter design to be the best way to go. Of course not all mfgs agree, and some made the tough decision to change things to that layout, maybe some will change back, we'll see.
People are sick and tired of being told that ordinary and decent people are fed up in this country with being sick and tired. I’m certainly not, and I’m sick and tired of being told that I am

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Where do the various pop top designs (racer/reflex/TSE) have their cutter/relative to the ripcord pins, and are they vulnerable to a locked loop?
People are sick and tired of being told that ordinary and decent people are fed up in this country with being sick and tired. I’m certainly not, and I’m sick and tired of being told that I am

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agreed. Putting the cutter in above the bag is a classic case of solving one problem and creating another. And to say it only happens, or can happen with one specific brand of cutter is silly. The potential is there with any cutter above the bag.

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My opinion is that anything that could reduce one's options for saving one's life is not a good way to go.

Blame it on riggers, blame it on cutters, blame it on whomever...the bottom line is the same.

I'm not a rigger. I'm not an innovator.
Even so, I have to think that there has to be some way to fix this problem.

-There is no way to guarantee that a rigger is going to install a closing loop with the exact right tension/length.

-There is no way to guarantee a rigger is going to lubricate the loop properly with the proper lubricant.

-There is no way to guarantee that a closing loop is going to stay in place, perpendicular to the cutter cylinder, throughout the entire life of the repack.

Pointing fingers at those issues only delays the development of a real fix...a cutter that does it's job in spite of all that.


edited to remove my suggestion for a cutter design because I'm no innovative mechanical engineer.

My reality and yours are quite different.
I think we're all Bozos on this bus.
Falcon5232, SCS8170, SCSA353, POPS9398, DS239

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Has there ever been an instance of any mfgs guillotine cutter locking onto a loop?



I worked with Roberts Research cartridge cutters; both guillotine and hammer, for around 15 years. Roberts is probably the largest manufacture of pyro cutters in the world. We used them on test items ranging from static line deployment to 20 sec. freefall deployment. I have packed them into the head box for the F-18 Hornet. And in all cases we would use at least 2 cutters on every application. I have seen a failure of every configuration of cutter out there. Al Frisby used to say “If you can imagine it, it can happen”. Good words to live by.

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Yes it is. It fixed a specific problem (delay due to loop friction...)



And it created a far worse potential problem. It can remove from the jumper the ability to save his own life by pulling the ripcord, a component that was tested and TSO’d with the system. That is not a fix it is a mistake in my opinion. I think people forget that there is not a rig made that was tested and TSO's with any brand of AAD.

Sparky
My idea of a fair fight is clubbing baby seals

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Where do the various pop top designs (racer/reflex/TSE) have their cutter/relative to the ripcord pins, and are they vulnerable to a locked loop?



On the Racer it goes pin, grommet in the bottom pack tray panel, cutter, bag, side, side then either the top flap or bottom flap then the PC.
The PC does not push on any of the flaps (ie no Chinese finger trap issue).

.
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Make It Happen
Parachute History
DiveMaker

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In one situation the opening sequence is more like trying to pull your shoelaces out from the toe end of the shoe and in the other situation is more like how a towel moves when you snap it.



This analogy makes a lot of sense to me. Thanks.
Owned by Remi #?

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Where do the various pop top designs (racer/reflex/TSE) have their cutter/relative to the ripcord pins, and are they vulnerable to a locked loop?



On the Racer it goes pin, grommet in the bottom pack tray panel, cutter, bag, side, side then either the top flap or bottom flap then the PC.
The PC does not push on any of the flaps (ie no Chinese finger trap issue).

.



So the racer also is vulnerable to a locked loop. I thought John Sherman was against implementation of the AAD in a way that could do that. Just my memory of what has been discussed recently since all this came about.
People are sick and tired of being told that ordinary and decent people are fed up in this country with being sick and tired. I’m certainly not, and I’m sick and tired of being told that I am

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>Even the designer of the Cypres AAD admits there is an expected failure rate of
>cutters of ANY designe. This means it is NEVER acceptable to place the cutter in a
>location that could render the system inoperable if there is a cutter failure. Period.

There is an expected failure mode of lithium batteries; they can short, get very hot and melt nylon. Does that mean use of an AAD in the reserve tray is NEVER acceptable, period?

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Pointing fingers at those issues only delays the development of a real fix...a cutter that does it's job in spite of all that.



The CYPRES cutter is expected to do its job even if all the errors you mentioned are made, ie it will cut the loop. But the whole system may not work as expected. Perhaps some standard test procedures should be developed first?

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Ive been thinking of something lately, and maybe its re-inventing the wheel but here goes, dont flame too hard lol.

What about designing a cutter and reserve pin that are one in the same. Maybe have a guilotein style cutter that is placed through the loop on top of the flaps, then a ripcord pin that rests right on top of the cutter and goes through the loop. I wish I could draw what I was thinking but it seems like it would be a good solution for those of us that jump AAD's.

has anyone ever discussed this before?

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So if you "pull the pin" (manual reserve deployment) you are also then, simultaneously in effect, also pulling the whole loop-cutter from the loop? Do I read what you are saying correctly?

Sounds in principal like an interesting idea.
However, what would the cutting mechanism have/use as a "back-stop" if it were cutting outwardly, from itself? I can think of several additional failure-modes that could occur as well with such set up. Seems almost anything (and everything?) has its variables/risk/reward benefit trade-off's inherent in them.
coitus non circum - Moab Stone

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>What about designing a cutter and reserve pin that are one in the same. Maybe
>have a guilotein style cutter that is placed through the loop on top of the flaps,
>then a ripcord pin that rests right on top of the cutter and goes through the
>loop. I wish I could draw what I was thinking but it seems like it would be a good
>solution for those of us that jump AAD's.

You'd have the same problem. If the cutter trapped the loop it would being the same as having the pin not pulled.

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his means it is NEVER acceptable to place the cutter in a location that could render the system inoperable if there is a cutter failure. Period.





what are racer/reflex users supposed to do then?



......................................................................

Racer and Reflex users are expected to continue with the factory-recommended packing procedures, loop length, etc.
We have not heard of any Racers or Reflexes - with AADs - failing to open when needed. Any time you change one variable, you mess with a dozen other variables, and it will take you years to figure out all the new malfunction modes.
Don't mess with success.

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