0
jerolim

Firebird MARD

Recommended Posts

No Collins Lanyard? I'm not going to pretend to be smart enough to judge if this system is safe and effective or not. But it could be. Unless of course you have a riser break on the RSL side. In which case you will probably die without a Collins Lanyard.

I know, riser breaks are no longer very common. But why take a chance?

Share this post


Link to post
Share on other sites
I'd like to see this test performed in the opposite direction. Hold the assembly as it would be held in place for a straight-to-reserve deployment, and show what happens if the PC launches in the direction of the two arrows (as close to 180 degrees as possible). How does the extraction force change?

Also, that's a large amount of fabric that has to be kept flat in order for the disconnect to happen as shown. If it gets folded in half, which seems likely to happen with the RSL attached in the middle, the disconnect force will go way up and may lock the assembly altogether.

Share this post


Link to post
Share on other sites
If I'm getting it right, compared to a system like the Wings Boost, this uses bridle fabric in place of a steel pin, and a bungee in place of a piece of line.

That seems to be changing towards materials that are higher friction (the bridle) or weaker & perhaps more variable (bungee). While the subtleties of any issues with MARDs can be difficult to see, I'd like to know the rationale for changing things in this way.

Share this post


Link to post
Share on other sites
mxk

I'd like to see this test performed in the opposite direction. Hold the assembly as it would be held in place for a straight-to-reserve deployment, and show what happens if the PC launches in the direction of the two arrows (as close to 180 degrees as possible). How does the extraction force change?



Assembly is not held in place in any scenario. In RPC activation scenario there is force between RPC and RSL lanyard (connected to main riser).

Angle of RPC pull is unimportant as assembly orients between RPC and RSL lanyard in case of RPC pull (in that scenario).

I will try to film this scenario for you, I did test it many times and it is under 1 kilos of force.


Quote


Also, that's a large amount of fabric that has to be kept flat in order for the disconnect to happen as shown. If it gets folded in half, which seems likely to happen with the RSL attached in the middle, the disconnect force will go way up and may lock the assembly altogether.



If you are talking about red part of bridle:
There is also small loop at the end of MARD assebmly (left of red area) it holds fold in place with red break thread.
Also I have played with many configurations and it evens it self out as it is being pulled from RCP side.

Also if you are talking about green part of bridle:
SS gromet size 0 and big loop ensures that green part of bridle will not be distorted or sucked into a size 0 hole.

Share this post


Link to post
Share on other sites
pchapman

If I'm getting it right, compared to a system like the Wings Boost, this uses bridle fabric in place of a steel pin, and a bungee in place of a piece of line.

That seems to be changing towards materials that are higher friction (the bridle) or weaker & perhaps more variable (bungee). While the subtleties of any issues with MARDs can be difficult to see, I'd like to know the rationale for changing things in this way.



It is like that as it is simpler system overall. Friction of bridle i negligible in whole story. It is important that RSL -> MARD bungee can handle forces needed for deployment (and it surley can) and yet fail before freebags safety stow (by having less stitches on it than on freebags safety stow).

RSL -> MARD bungee is replaceable.

Share this post


Link to post
Share on other sites
gowlerk

No Collins Lanyard? I'm not going to pretend to be smart enough to judge if this system is safe and effective or not. But it could be. Unless of course you have a riser break on the RSL side. In which case you will probably die without a Collins Lanyard.

I know, riser breaks are no longer very common. But why take a chance?



This is yet to be decided. Mirage took approach with moving rsl shackle on riser below usual breaking point. That is also an option.

Share this post


Link to post
Share on other sites
jerolim

It is like that as it is simpler system overall. Friction of bridle i negligible in whole story. It is important that RSL -> MARD bungee can handle forces needed for deployment (and it surley can) and yet fail before freebags safety stow (by having less stitches on it than on freebags safety stow).



That sounds like what I expected. It's hard to know what forces might be set up in the system without a lot of testing.

Indeed the red lanyard for the Skyhook system was set up to be a weak link in the chain -- strong enough to work as the MARD almost all of the time but break in case of some weird high force situation.

I wonder what the strength of the bungee is. The ultimate strength would likely be largely from the sheath. But there isn't just a particular Mil Spec style bungee out there? If I were building the thing, I'd want careful control of the bungee loop source and material and stitching, so that a bungee good for 200 lbs (or whatever it actually is) didn't get replaced by a low quality one that's good for 100 to 150 lb depending on batch. It does look like the bungee is sewn into the RSL, and not a loose part, so it isn't something a rigger would easily mess up by trying to replace.

Mxk's suggested tests sound good to try 'just in case' although I see that you would argue that those situations shouldn't happen:

The 'pulling 180 degrees' opposite test would be interesting, although it shouldn't happen unless the MARD somehow hung up on something. Once the rig opens the MARD should be free (or only lightly restrained to a rig flap as many are), so that if one tries to pull the PC end of the bridle back 'against' the MARD, the MARD will just rotate as needed so the folded bridle acting as the pin will always pull straight out of the cloth loops.

The 'fold the MARD in half' case is also interesting to test. If the MARD can still disconnect without much force in that situation, then it isn't a problem.

Even if disconnect forces went up, some could argue whether a disconnect is needed at all when the RSL is pulling super hard. Normally people expect MARDs to disconnect if there's any light force from the PC end. Yet they also don't want it to disconnect when chopping from some weird vertical-axis spinning mal (ie, helicopter style, not a smooth spiral canopy-on-horizon) just because the PC bounced around while the RSL & main were starting to extract the reserve bag just fine. Is a MARD supposed to disconnect at 0 lbs, or 5 lbs, or is a higher value allowed in cases where it is far less than the RSL end's force?

Still, the 'folding MARD' thing could be tested. Even on the ground with a car coming to the end of a long slack rope. Maybe the MARD is light enough that even in the case of an explosive main opening just as a cutaway is performed, giving say a 20g or whatever acceleration to the MARD, it will either not fold the material, or is one of the extreme cases that will break the bungee as the deliberate weak link.

I'm just winging it here; thinking through all the possible failure cases of MARDs is tricky.

Share this post


Link to post
Share on other sites
pchapman

Even if disconnect forces went up, some could argue whether a disconnect is needed at all when the RSL is pulling super hard.



The most important case when the RSL would be pulling super hard is when it's still attached to the rig (i.e. AAD fire or straight-to-reserve deployment). I can see the fold-in-half scenario happening for an unconscious jumper falling on his back. AAD fires, RPC launches toward the red end and wraps around the body, bridle doesn't have enough time to rotate. The pull of the bungee in the center not only applies extra friction, but also causes the assembly to fold in half.

Share this post


Link to post
Share on other sites
Quote

This is yet to be decided. Mirage took approach with moving rsl shackle on riser below usual breaking point. That is also an option.



That would be a start. But its only a matter of time till someone uses the wrong risers on it. Skydivers can be very creative.

Share this post


Link to post
Share on other sites
All three MARD inventions where the D bag is pulled out/off/up by the cutaway main by means of a (Described by some as a "fold over") operate on the same principles.

OPINION: I think that, from what I've seen they could be rated as possibly good, better and best. As for myself, I wouldn't rely on a bungee. that makes the Firebird proposed invention in the video (once again, in my opinion) "possibly good". But not for me as it relies on a bungee's strength. It is good in theory, but have my doubts how it would perform under varying conditions as set forth by other posters.

The Boost = better, as it relies on a lolon cable

Best = the Peregrine ACE, as it relies on a long metal pin, with a Dyneema (Cypres loop material) loop. In my opinion, the absolute best of the "fold over" design MARD devices.

Share this post


Link to post
Share on other sites
pchapman

Wings Boost has a metal pin.
So which one were you thinking of?
(Quite a few variations out there to keep track of...)



The Strong Sky Anchor uses a yellow cable and depends on bridle extension/unfolding to pull the cable to release in case of a total malfunction.

--Mark

Share this post


Link to post
Share on other sites
mark

From the video posted on the Firebird website, it looks like the MARD is closer to the freebag than the pilot chute. Is that correct? Or is it just an illusion/perspective thing?



No, it is closer to RPC to avoid possibility of RPC wrapping around reserve lines.

Share this post


Link to post
Share on other sites
gowlerk



I know, riser breaks are no longer very common. But why take a chance?

I know a Ti who has had three over the course of his career. I was on a load with a Ti this year who had a riser failure on his RSL side and it deployed his reserve (Strong rig). I agree with the need for a Collins lanyard. Every RSL and MARD should have one. With the patent expired, there is no reason not to include one.

Share this post


Link to post
Share on other sites
PC Chapman Oops. My error.

The original one I saw at PIA (George G showed it to me on the Plexus rig) had a yellow Lolon cable. I guess Wings has improved it. My mistake. I haven't packed a Wings with the Boost. In that case, (metal pin) it would be one the best too.

Share this post


Link to post
Share on other sites
Westerly

***

I know, riser breaks are no longer very common. But why take a chance?

I know a Ti who has had three over the course of his career. I was on a load with a Ti this year who had a riser failure on his RSL side and it deployed his reserve (Strong rig). I agree with the need for a Collins lanyard. Every RSL and MARD should have one. With the patent expired, there is no reason not to include one.

Talked with Firebird yesterday, there will be Collins with this system. It just wasn't showed in this short video presentation.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

0