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Pros & Cons of M.A.R.D (Was: Skyhook Activation Stories)

 

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pchapman  (D 1014)

Oct 5, 2008, 6:51 PM
Post #51 of 107 (2814 views)
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Re: [eric.fradet] Pros & Cons of M.A.R.D (Was: Skyhook Activation Stories) [In reply to] Can't Post

In reply to:
As the main came out his ankle was caught in one of the lines. The main actually fully open but was in spiraling. The student cut way and had a successful reserve deployement. He landed safely[..]
I am wondering what would happen if this student had some kind of MARD ...not sure he would survive with such device

Either with a MARD or plain RSL, the reserve is being fired into a main canopy that hasn't yet departed. Roll the dice.

(The above report might imply that the main cleared completely, coming off his foot, but it isn't absolutely clear.)

But I see a point:
A MARD generally gets a reserve out quicker after risers release, than during a chop with an RSL, and a fair bit quicker than many a chop without an RSL.

Most of the time that's a good thing. It might be a bad thing if one is still attached to a main for some other reason (eg, CRW, horseshoe). A delay between cutaway and reserve activation might not help in some cases, but might in others (such as if cutting away does clear that main off one's foot).

One solution is to release the RSL (plain or MARD) before cutting away, but doing that in an emergency situation may be tricky. The 'too quick a reserve' issue is one of the reasons people may choose to have no RSL... and unless I'm mistaken, one potential risk of a MARD.


[MARD: A parachuting device named by Bill Booth. Ironically, also pretty much what Eric Fradet mutters under his breath in French whenever he thinks about Skyhooks...]



(This post was edited by pchapman on Oct 5, 2008, 6:52 PM)


eric.fradet

Oct 6, 2008, 2:09 PM
Post #52 of 107 (2703 views)
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Re: [erdnarob] Skyhook Activation Stories [In reply to] Can't Post

I put a flat hook knife with a pull cord behind the wall of the reserve floor in order to cut the loop at its very maximum length.
________________________________________________

using a hook knife is not the best way to fire test the reserve container, because the move helps the container to open.
in the last experimentation I did this year, the cutter is located ABOVE the reserve PC, the loop is lubricated, the loop length is exactly the one recommanded by the manufacturer, the reserve PC strenght is about 35 pounds force and the rig packed the day before according packing manual by one of the best rigger in France.
after firing, the reserve container is not securely locked up so you do not really have to beat on it to finally give way, means as long the skydiver pulls the reserve ripcord, it will probably open with a delay due to the time the reserve bridle will call the reserve PC to get out from the burble, but in case of a total malfunction and AAD firing it will probably be a fatality.
Now if you experiment the same on different rigs with a longer reserve loop as recommand by the manufacturer, it is also, not as difficult to lock the reserve container up on rigs like Vector, Javelin , Wings but in this last situation we speak about rigging error not a wrong manufacture design..
Attachments: Atom + Quick 3.wmv (222 KB)


eric.fradet

Oct 6, 2008, 2:28 PM
Post #53 of 107 (2695 views)
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Re: [pchapman] Pros & Cons of M.A.R.D (Was: Skyhook Activation Stories) [In reply to] Can't Post

here is an example of potential issue I see with any MARD, I found this one from an old post from someone else, sorry I cannot find the poster name, I hope he will forgive me :
The situation of a horseshoe (premature container opening with PC still in pouch) is worth looking at.
I think the SkyHook may increase the probability of a main and reserve entanglement in this type of horseshoe mal.
The SkyHook essentially shortens the reserve bridle line and uses the drag from the cutaway main to act as the drag of the reserve PC to deploy the reserve, unless the reserve pc catches air first and the SH disconnects from the reserve bridle line.
I made two little pics to show the differences.
Pic 1 shows a PC (without a SkyHook) trying to blow by the cutaway main that is still attached to a jumper via a stuck pc.
Pic 2 shows the SkyHook trying to blow by the cutaway main that is still attached to a jumper via a stuck pc.
If the reserve pc with the SH inflates, it is likely that the reserve will find clear air to inflate in, but not if the reserve pc goes through the lines of the main or something similar.
If the reserve pc with the SH does not catch air immediately, and is still attached to the SH wraps the trailing main, then I think that a main-reserve entanglement is almost a certainty. The remaining length of the reserve bridle line may provide enough drag for the reserve canopy to come out of the reserve bag, but maybe not.
You can also get more slack in the reserve deployment (from the SH point of attachment to the reserve risers) that will allow the reserve (bag and or lines) to flap around and become entangled with the trailing main. At best you could hope for the drag on the reserve lines to pull the reserve canopy out of the bag, even if the bag is attached someplace along the trailing main.
I think this is a failure mode of the SkyHook that has not been tested, not been explained and kind of glossed over. (I certainly do not recommend asking test jumpers to test this either.)
with a regular RSL, maybe the reserve has a chance to clear up
Attachments: Doc1.doc (84.5 KB)


Piece  (A 53144)

Oct 6, 2008, 6:38 PM
Post #54 of 107 (2643 views)
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Re: [eric.fradet] Pros & Cons of M.A.R.D (Was: Skyhook Activation Stories) [In reply to] Can't Post

I've been wondering about this for a while, it seems like the main non-theoretical disadvantage to the Skyhook, though any RSL would have this problem. You would have to recognize the malfunction, disconnect the RSL, cut away, possibly clear the risers manually from the three rings and deploy the reserve, all at terminal at 3000'. That's quite a lot of work for that little time.

This made me wonder: why don't sport rigs have cutaway systems on the BOC like AFF rigs do? I mean a handle on the left side of the BOC that will cut away the entire pilot chute container. My understanding is that at least some DZs use this to give the reserve-side instructor a means to deploy the main. Wouldn't this clear a hard pull/horseshoe type malfunction, at least if the horseshoe is attached at the BOC? I apologize in advance if this is a dumb question.


riggerrob  (D 14840)

Oct 7, 2008, 10:59 AM
Post #55 of 107 (2569 views)
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Re: [Piece] Pros & Cons of M.A.R.D (Was: Skyhook Activation Stories) [In reply to] Can't Post

Modern BOCS are almost idiot-proof.
Only a true clutz can pack a modern, Spandex BOC so badly that it jams.

If you give a more-complex BOC to someone who is not bright enough to pack a standard BOC, you only increase the risk of packing errors and malfunctions.

KISS


kirkverner  (D 11059)

Oct 7, 2008, 11:39 AM
Post #56 of 107 (2550 views)
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Re: [eric.fradet] Pros & Cons of M.A.R.D (Was: Skyhook Activation Stories) [In reply to] Can't Post

A very experienced jumper using a skyhook had a malfunction on a Velocity that had him spinning into line twists while the canopy was spinning. The resulting cutaway with a skyhook had him entangled in the freebag and bridle, he sorted it out but was nearly choked out by the reserve risers caught under his chin. It produced some nasty rash. Severe spinning around your Y axis while spinning violently doesn't seem to be covered on the videos that I have seen.


dgw  (C License)

Oct 7, 2008, 11:46 AM
Post #57 of 107 (2550 views)
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Re: [Piece] Pros & Cons of M.A.R.D (Was: Skyhook Activation Stories) [In reply to] Can't Post

I jump a Dolphin AFF rig with the secondary release on the BOC pouch.

I pack the pilotchute using Brian Germains technique, specifically because it appears to minimise the chances of a pilotchute getting bunched up and jammed if the bridle tries to extract it.

That said, my 'plan' should I sustain a jammed pilotchute during a horseshoe malfunction is to open the BOC by pulling the 'reserve side' handle. This handle disconnects the pouch. Clearly, this is an altitude-dependent extra step. However, as I understand it, most horseshoe malfunctions seem to occur at altitudes higher than normal deployment altitudes, so it appears like a reasonable extra step on the rig I mainly jump.


Piece  (A 53144)

Oct 7, 2008, 3:43 PM
Post #58 of 107 (2490 views)
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Re: [riggerrob] Pros & Cons of M.A.R.D (Was: Skyhook Activation Stories) [In reply to] Can't Post

So you don't think that a horseshoe caused by the pin releasing with the pilot chute still in the BOC is going to bunch up the pilot chute? My understanding was that this is possible. This is mostly what I was thinking about when I made the suggestion.


erdnarob  (D 364)

Oct 7, 2008, 7:04 PM
Post #59 of 107 (2442 views)
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Re: [eric.fradet] Skyhook Activation Stories [In reply to] Can't Post

I have to be more accurate maybe by saying that when I did the experiment I was using a 1/8" thick flat stainless steel hook knife. That hook knife was placed to cut the loop under the the reserve floor (between the reserve floor and the back pad). If you look on a Vector III under the yoke you can easily see that you have access to that space. That was certainly the way to use the closing loop at its maximum length. A pull cord was attached to the eyelet of the flat hook knife and going out by the access under the yoke. I was holding the container when I pulled swiftly on the pull cord. Therefore, the motion or the shaking of the container was zero or near zero and no significant move could help the reserve container to open. It was a Vector # 348 accepting a PD 160 reserve and a Sabre 2-170. The whole story has been published in Skydiving Magazine on 2 full pages in 2005 if I remember including a picture of the flat stainless steel hook knife and a sketch of the set up.


jerolim  (F License)

Feb 24, 2011, 7:22 AM
Post #60 of 107 (1954 views)
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Re: [eric.fradet] Skyhook Activation Stories [In reply to] Can't Post

Quote:
The reserve PC cap too wide is the main issue !, when associated to the cutter location too low (on the kicker flap) it can lock up, even with the correct reserve loop length.
Which also means that moving the cutter above the reserve PC does not definetly fix this issue, even with the PIN PULLED.

Is this more pronounced on Icons with smaller reserve ? Because if there is a bigger reserve and bigger reserve flaps, more force reserve PC will with same top diameter will have against reserve flaps. Correct ?
I have 3 student Icons in Croatia (Smart 250) and 1 Icon Sport with Smart 220.

Also I belive I have on my Atom legend Quick 2 reserve PC. What is diference to Quick 3 reserve PC ?


(This post was edited by jerolim on Feb 24, 2011, 7:38 AM)


Deyan  (D 322)

Feb 24, 2011, 11:47 AM
Post #61 of 107 (1885 views)
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Re: [jerolim] Skyhook Activation Stories [In reply to] Can't Post

In reply to:
Also I belive I have on my Atom legend Quick 2 reserve PC. What is diference to Quick 3 reserve PC ?

The difference is in the shape of the cap. Quick 2's has a round shape. Quick 3's has the same cap, but the material is taken off from 2 sides giving an elliptical shape. And Quick 3.1 has a totally different spring and cap.

Blue skies


(This post was edited by Deyan on Feb 24, 2011, 3:55 PM)


riggerrob  (D 14840)

Feb 24, 2011, 2:31 PM
Post #62 of 107 (1832 views)
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Re: [jerolim] Skyhook Activation Stories [In reply to] Can't Post

The worst-case scenario has a large diameter pilot-chute cap, in a narrow container, large stiffeners in the side flaps and the cutter very low in the container (e.g. under the kicker flap like a Vector).

The more "stuff" the spring has to push out of the way, the slower the pilot-chute launch.


rapaz

Feb 24, 2011, 6:34 PM
Post #63 of 107 (1771 views)
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Re: [riggerrob] Skyhook Activation Stories [In reply to] Can't Post

Two things:

1- Horseshoe malfunction, very easy to solve if you use the PC packing Brian Germain method that permits PC goes out alone.

2- You guys..., Give some credit to Mark Hewitt, I think he was who real invent the MARD or Skyhook concept on his system Sorcerer (BASE equipment), no Mr. Booth
Wink


riggerrob  (D 14840)

Feb 25, 2011, 12:35 AM
Post #64 of 107 (1704 views)
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Re: [rapaz] Skyhook Activation Stories [In reply to] Can't Post

"... Give some credit to Mark Hewitt, I think he was who real invent the MARD or Skyhook concept on his system Sorcerer (BASE equipment), no Mr. Booth
Wink
..................................................................

Mark Hewitt invented the first pin-type' Main Assisted Reserve Deployment (MARD) system and sold a few dozen in the Sorcerer BASE container.
Jerome Bunker refined the pin-type MARD and sold a few hundred in Advance skydiving containers. I never heard the full story as to why Bunker stopped selling his version of MARD.
Bill Booth invented the cam-type, Skyhook version of MARD.
A few years aback, John Sherman experimented with his "Lasso" MARD, but never worked out all the bugs????
Now Strong Enterprises is drop-testing their 2-ring riser based MARD. We wish Strong lots of success.


Premier skydiverek  (C 41769)

Feb 25, 2011, 1:53 AM
Post #65 of 107 (1695 views)
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Re: [riggerrob] Skyhook Activation Stories [In reply to] Can't Post

There is also RAX: http://www.youtube.com/watch?v=aqxjHOSKTT0

and DRX: http://www.miragesys.com/...-test-jump-pictures/


piisfish

Feb 25, 2011, 1:58 AM
Post #66 of 107 (1693 views)
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Re: [riggerrob] Skyhook Activation Stories [In reply to] Can't Post

[replyJerome Bunker refined the pin-type MARD and sold a few hundred in Advance skydiving containers. I never heard the full story as to why Bunker stopped selling his version of MARD. JEROOOOOOOME , we need an explanation, please Angelic


Premier skydiverek  (C 41769)

Feb 25, 2011, 2:11 AM
Post #67 of 107 (1685 views)
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Re: [skydiverek] Skyhook Activation Stories [In reply to] Can't Post

And there is also 'Interlock' MARD, designed by... Eric Fradet! It is using magnets and is used on Para Flite military equipment:

http://www.faqs.org/patents/app/20090127395


Rugby82  (D 705310)

Feb 25, 2011, 3:33 AM
Post #68 of 107 (1666 views)
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Re: [Piece] Pros & Cons of M.A.R.D (Was: Skyhook Activation Stories) [In reply to] Can't Post

In reply to:
I've been wondering about this for a while, it seems like the main non-theoretical disadvantage to the Skyhook, though any RSL would have this problem. You would have to recognize the malfunction, disconnect the RSL, cut away, possibly clear the risers manually from the three rings and deploy the reserve, all at terminal at 3000'. That's quite a lot of work for that little time.

This made me wonder: why don't sport rigs have cutaway systems on the BOC like AFF rigs do? I mean a handle on the left side of the BOC that will cut away the entire pilot chute container. My understanding is that at least some DZs use this to give the reserve-side instructor a means to deploy the main. Wouldn't this clear a hard pull/horseshoe type malfunction, at least if the horseshoe is attached at the BOC? I apologize in advance if this is a dumb question.

The problem with secondary releases for the BOC-pouch is the fact that the have small holes where they are attached to the harness (where the yellow cables run through the loops to connect the two). These can cause air to slip thru the BOC-pouch while freeflying and thus blow the pilotchute out of the BOC resulting in a premature opening. This is extremely dangerous while freeflying.

We had this happen to one of our student rigs when a student was freeflying with a rig that had a secondary release for the BOC. For this reason our students cannot do freefly-jumps with a secondary release on the BOC.

I think this would work for belly-flying.


Premier skydiverek  (C 41769)

Feb 25, 2011, 5:56 AM
Post #69 of 107 (1610 views)
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Re: [Rugby82] Pros & Cons of M.A.R.D (Was: Skyhook Activation Stories) [In reply to] Can't Post

RAX disconnects with zero force, not 15 or so punds needed in case of Skyhook.

Check the scene starting at 0:44:

http://www.youtube.com/watch?v=aqxjHOSKTT0

I played with RAX, and it is literally zero pounds of force needed for disconnection. Yet, it stays connected when needed. And the cost of parts to manufacture one is like $15.


(This post was edited by skydiverek on Feb 25, 2011, 5:57 AM)


jerolim  (F License)

Feb 25, 2011, 7:02 AM
Post #70 of 107 (1569 views)
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Re: [skydiverek] Pros & Cons of M.A.R.D (Was: Skyhook Activation Stories) [In reply to] Can't Post

I didn't understand how is RAX connected to reserve bridle. Can you please explain.


sundevil777  (D License)

Feb 25, 2011, 7:03 AM
Post #71 of 107 (1580 views)
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Re: [skydiverek] Pros & Cons of M.A.R.D (Was: Skyhook Activation Stories) [In reply to] Can't Post

Can you explain how the RAX is connected to the bridle - how the 2 bits of webbing and the pin work together?


Premier skydiverek  (C 41769)

Feb 25, 2011, 7:17 AM
Post #72 of 107 (1567 views)
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Re: [jerolim] Pros & Cons of M.A.R.D (Was: Skyhook Activation Stories) [In reply to] Can't Post

In reply to:
I didn't understand how is RAX connected to reserve bridle. Can you please explain.

Frankly, I do not remember the details... Here is the original thread - the first post is from the inventor of RAX:

http://www.dropzone.com/..._latest_reply;so=ASC


(This post was edited by skydiverek on Feb 25, 2011, 7:17 AM)


NovaTTT  (D 17887)

Feb 25, 2011, 7:27 AM
Post #73 of 107 (1558 views)
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Re: [sundevil777] Pros & Cons of M.A.R.D (Was: Skyhook Activation Stories) [In reply to] Can't Post

In reply to:
Can you explain how the RAX is connected to the bridle - how the 2 bits of webbing and the pin work together?


I think Jerry might explain his system, but as I've handled it I can give my observations. This isn't intended to be a detailed explanation or even a complete one - I'll leave that to Jerry if he so chooses.

The RAX device looks rather like a toggle, complete with a grommet. A small pouch is sewn to the reserve bridle and one end of the RAX device is inserted therewithin. Next to the pouch a white loop, such as is found at the 3-rings, is attached to the bridle and inserted through the grommet in the RAX device and held in place by a straight ripcord pin.

That pin is attached to the other end of the RAX device which is inserted into a pouch sewn to one of the reserve flaps. A length of suspension line connects the RAX device to both the RSL and the reserve ripcord (via a ring).

When the RLS pulls the reserve, the RAX pin keeps the bridle attached to the main. When the reserve pin is pulled, the RAX pin releases from the bridle.

It's a simple and elegant device which is made completely of common materials.

Sorry, Jerry, if my explanation stinks. Angelic


phoenixlpr  (D 3049)

Feb 25, 2011, 7:38 AM
Post #74 of 107 (1549 views)
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Re: [NovaTTT] Pros & Cons of M.A.R.D (Was: Skyhook Activation Stories) [In reply to] Can't Post

Any one has a picture about it?


(This post was edited by phoenixlpr on Feb 25, 2011, 7:38 AM)


riggerpaul  (D 28098)

Feb 25, 2011, 7:58 AM
Post #75 of 107 (1541 views)
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Re: [NovaTTT] Pros & Cons of M.A.R.D (Was: Skyhook Activation Stories) [In reply to] Can't Post

In reply to:

It's a simple and elegant device which is made completely of common materials.

Sorry, Jerry, if my explanation stinks. Angelic

But (and do please correct me if I am wrong), it still suffers from the same deficiency as the Skyhook - that being, if the reserve pilot chute gets enough air from the side, it would release the pin when you would still like it to remain attached to the main.

The system that I'd like to see would not allow the main to release if there was tension on the RSL.

But at long as the release is controlled by the reserve pilot chute getting some inflation, we will still have to live with the possibility that the main releases when we'd prefer to keep it as the reserve pilot chute.

I've considered making a skyhook-type hook with a latch gate that would not allow the red loop to come off. During setup, you don't put the red loop past the gate. If the deployment begins from the RSL, then the red loop would snap past the gate, and the main would be unable to release.

The problem with this type of system is that rough handling on the ground on the part of a jumper could possibly snap the loop over the gate. This would be a BAD THING if there was then a total where only the reserve pilot chute is deployed, as the red loop would tie the whole thing to the main that is not being chopped.

But, as I see it, if we have to worry that a side force from the reserve pilot chute can disconnect the MARD, then we cannot really rely on the MARD performing in the worst down-low canopy collision situation. And if you aren't down and dirty in the first place, you didn't need a MARD to begin with.


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