Rationale for AAD Cutter Location?

[mxk 1]

Deimian

The comment about cord tension makes a good point, I didn't think about it, but I am not sure it is true. There are plenty of videos around of AAD cutters cutting Cypres cord without tension on it. If the cutter is working as designed, that shouldn't be an issue. But even if it was, if the top cutter pinches the closing loop, the bottom of it is not attached to the container anymore (because it has been cut by the bottom cutter), so it should open anyway.

No, the flaps would still be held closed between the top cutter and the pin. I would also expect the cutter to do its job without any tension, but if we're entertaining the possibility of a pinched loop with a single cutter, removing the tension is probably going to increase the chances of failure, however small they might be.

[gowlerk 2,190]

I get a headache trying to think of all the possibilities here. But my opinion is simple. Less complex is better than more complex. If there is a cutter effectiveness question the answer is a better cutter, not another cutter.

Always remember the brave children who died defending your right to bear arms. Freedom is not free.

[Deimian 43]

mxk

No, the flaps would still be held closed between the top cutter and the pin.

That's true unless the cutter is installed in the outermost flap. I didn't picture that situation correctly. In the rig I was looking that is not the case, so thank you for that thought. Are all the rigs with the cutter on top like that (cutter not in the outermost flap)?

gowlerk

I get a headache trying to think of all the possibilities here. But my opinion is simple. Less complex is better than more complex. If there is a cutter effectiveness question the answer is a better cutter, not another cutter.

Generally speaking, I agree. But assuming a perfect cutter, another perfect cutter on the bottom might outdo perfection . Also, assuming a perfect cutter, the best place for it is on top, which some people don't like (rightfully so, because perfection doesn't exist), and that was the situation I intended to address, for extra peace of mind of those that don't like the location on the top of the reserve tray, because it might prevent the user from opening the reserve tray manually.

As mxk pointed out, if the top cutter fails and pinches the loop, the bottom cutter doesn't matter, as the flaps between the cutter and the pin are trapped, unless the cutter is installed in the outermost flap. However, if you pull the ripcord, the bottom cutter operates correctly, and the top cutter pinches the loop, it will open. A container without the bottom cutter wouldn't open if the top cutter pinches the loop, regardless of what the user does with the ripcord.

So I still see some potential benefit. A failure of any cutter in such a design still gives the user the possibility to save his/her own life, not like single cutters placed on top pinching the loop. Even though I wouldn't bet on the user saving his/her life below AAD activation altitude. Whether it is good enough for research and implementation or not is still debatable

[Unstable 9]

Quote

So I still see some potential benefit. A failure of any cutter in such a design still gives the user the possibility to save his/her own life, not like single cutters placed on top pinching the loop. Even though I wouldn't bet on the user saving his/her life below AAD activation altitude. Whether it is good enough for research and implementation or not is still debatable

This is a very interesting debate. I've enjoyed just reading and soaking up this thread. So let's say the cutter activates but the result is a delayed launch of the reserve PC. (For the sake of the argument, let's leave out the cutter failing). You can draw a line and look at the possible condititions that may have lead to the end result. They are (I think MMX listed these out a page back):

a. Loop length (finger trapping effect between unalilgned grommets)
b. Condition of the loop (Silicon or no silicon)
c. Design of the reserve container (corners, fit, staging of the PC launch through freebag extractions, etc)
d. Comparability of components (main size, reserve size, aad present)
e. Tension on the loop itself
f. Condition of the rig (grommets, especially)
g. Placement of the cutter (Above or below reserve PC)


So possible effects a, b, d, and e are the result of the rigger who does the most recent reserve inspection and repack. Effect c and g are governed by rig design, and condition f deals primarily with long-term maintenance (which an average field rigger may or may not address.

So the rig manufacturer in question is going to have a few options: Address the rigging effects (SB, training, awareness campaign), adjust their design to be more mistake-proof. In the given case, it makes sense to move the closing loop.

From SB12-04

Quote

MIRAGE SYSTEMS, INC.
PRODUCT SERVICE BULLETIN 12-04
December, 2004
SUBJECT: AAD CUTTER LOCATION CHANGE
DESCRIPTION: The location of the AAD cutter assembly must be changed from below the #1 flap (below the reserve PC) to below the #3 flap (above the reserve PC). This reduces the cut length of the
reserve closing loop and isolates it from the effects of poor field rigging, such as misplaced bulk, undercompressed or worn pilot chutes and overly long and/ or unlubricated loops. By reducing and standardizing loop cut length, reserve pack opening functionality and reliability in the case of AAD activation are
improved.

(emphasis added)

Real-world, however, must address conditions of cutter reliability. Seems to me that the correct issue to address would be poor field rigging.

*edited for spelling

=========Shaun ==========

[riggerrob 643]

Pinching a closing loop is difficult.
You would need to stack all the variables on the wrong side of the equation: dull blade, weak pyrotechnic charge, loop too thick, etc.

[piisfish 140]

riggerrob

Pinching a closing loop is difficult.
You would need to stack all the variables on the wrong side of the equation: dull blade, weak pyrotechnic charge, loop too thick, etc.

or get an Argus

scissors beat paper, paper beat rock, rock beat wingsuit - KarlM

[Deimian 43]

Unstable

Seems to me that the correct issue to address would be poor field rigging.

Absolutely! However, I don't see how poor rigging can be addressed at design and manufacturing time. The manufacturer has no control over the professionalism of any rigger. The other effects are more under the manufacturer control.

[JerryBaumchen 1,354]

Hi Deimia,

Quote

because perfection doesn't exist

And almost every piece of your gear comes with a disclaimer.

This reminds of one of the guys I jumped with back in the mid-60's. When the piggyback rig came out, he thought he would get one so he could wear two reserves, one on the back & one on the front. He was worried about 'what if' his only reserve did not work.

As to the cutter not doing its job, I would be more concerned about the reserve container not doing its job, or the reserve canopy not doing its job.

IMO the odds of the container or reserve not doing their jobs is far more likely than the cutter not doing its job.

YMMV

Jerry Baumchen

[Unstable 9]

Quote

IMO the odds of the container or reserve not doing their jobs is far more likely than the cutter not doing its job.

I would agree, especially with some of the popular trends regarding rig design and common field rigging questions. Tight rig + closed corners + poor part comparability = excessive extraction forces, which we have seen more than enough.

=========Shaun ==========

[Deimian 43]

Unstable

Quote

IMO the odds of the container or reserve not doing their jobs is far more likely than the cutter not doing its job.

I would agree, especially with some of the popular trends regarding rig design and common field rigging questions. Tight rig + closed corners + poor part comparability = excessive extraction forces, which we have seen more than enough.

I agree as well. The reason I was suggesting a double cutter is not because I think the chances of the cutter failing are too big, but because I can't see a downside to it, besides the price, of course.

The point made about tight containers is a very good one. That's the reason why I changed my reserve to another of the same size but lower pack volume. It bothered me because the design of my current rig seems to be prone to that problem. I think it is a good idea to start another thread about that topic.