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branch

Required pull force for main d-bag extraction

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Hi,

I'm jumping a Javelin Odyssey RSK-1 (2018) with a NZA Crossfire 3 114 sq.ft. in it and am having a problem doing Clear & Pulls.

Packing the rig as recommended in the manual (with the d-bag rotated with the bridle attachment towards te bottom of the reserve container) I have 7 second delays doing a Clear and Pull (pulling about 2 seconds after exit). The pin is pulled immediatly but the d-bag does not lift from the container for about 7 seconds. I had my rigger check the rig, bridle and pilot chute and everything is the way it is supposed to be.

I have measured the required force to rotate and lift the d-bag from the container and when pulling the bridge at a 45 degree angle (towards the top of the container) it takes 14.8 Kgs (32.6 Lbs) to pull the bag from the container. Pulling straight up at a 90 degree angle the required force is 11.4 Kgs (25.1 Lbs). I understand the dynamics of forward and downward speed doing a clear & pull and can see why it takes a while for the d-bag to leave the container but am very uncomfortable doing clear & pulls like this. I have resorted to packing with the d-bag upright and this solves the problem but the container doesn't close nicely this way. 

Does anyone know the specifications for the maximum pull-force needed to lift the d-bag from the container? Is the required pull-force outside the specifications or should I look at the pilot chute not creating enough drag as the source of the problem?

Best regards,

Peter

Edited by branch

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Only thing I can think of is the 119 crossfire packing larger than the 120 max zp main size specified by the sizing chart. Even so I would try a new pilot chute because overcoming 32lbs of pull force should be an easy task and it sounds like it is waiting until almost terminal to lift off. I replaced mine recently due to a similar situation and no longer have the problem. 

 

Edit: thing I would consider are pilot chute size, kill line length, porosity of the pilot chute 

Edited by husslr187

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@husslr187 Thanks, its a 114 sqft and its not to big, the rig closes nicely. My rigger checked the bridle, kill-line and pilot and everything is like it is supposed to be. He asked sunpath about this issue and is waiting for a reply. I was just wondering if anyone knew the specs for maximum required pull-force for lifting the d-bag  from the container if there are such specs (or pulling the pin for that matter).

Peter

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On 4/23/2019 at 7:54 AM, branch said:

Hi,

I'm jumping a Javelin Odyssey RSK-1 (2018) with a NZA Crossfire 3 114 sq.ft. in it and am having a problem doing Clear & Pulls.

Packing the rig as recommended in the manual (with the d-bag rotated with the bridle attachment towards te bottom of the reserve container) I have 7 second delays doing a Clear and Pull (pulling about 2 seconds after exit). The pin is pulled immediatly but the d-bag does not lift from the container for about 7 seconds. I had my rigger check the rig, bridle and pilot chute and everything is the way it is supposed to be.

I have measured the required force to rotate and lift the d-bag from the container and when pulling the bridge at a 45 degree angle (towards the top of the container) it takes 14.8 Kgs (32.6 Lbs) to pull the bag from the container. Pulling straight up at a 90 degree angle the required force is 11.4 Kgs (25.1 Lbs). I understand the dynamics of forward and downward speed doing a clear & pull and can see why it takes a while for the d-bag to leave the container but am very uncomfortable doing clear & pulls like this. I have resorted to packing with the d-bag upright and this solves the problem but the container doesn't close nicely this way. 

Does anyone know the specifications for the maximum pull-force needed to lift the d-bag from the container? Is the required pull-force outside the specifications or should I look at the pilot chute not creating enough drag as the source of the problem?

Best regards,

Peter

Why do you think the manual says to pack the bridle at the bottom? Page 5-5 says lines at the bottom, as every manual since they were made by Mike Fury.  The ONLY version that should be packed bridle down is the wing suit specific Aurora.

Packing bridle down is doesn't surprise me it's not coming out. What are the specs? There are none except it shouldn't take more force than the weight of the bag.  As a indication of why your having trouble most reserve PC'S at terminal speed steady state provide less than 50 lbs of pull. 

Follow manual', pack lines to bottom and rotate bag in to have bridle to reserve.

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1 hour ago, councilman24 said:

Follow manual', pack lines to bottom and rotate bag in to have bridle to reserve.

That's actually what he's doing:  the "bottom" he's referring to is the bottom of the reserve container, not the bottom/BOC end of the main container.

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I thought Branch did pack lines to bottom... since it was bridle towards the "bottom of thereserve container", which is bridle towards the head.
Anyway, whatever the confusion over a lack of consistent skydiver terminology regarding directional axes, that sounds like a super tight main if one has to pull up at 25 lbs on the bridle to rotate the bag out...

Edit: ninja'd

Edited by pchapman

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On 4/23/2019 at 7:54 AM, branch said:

I have resorted to packing with the d-bag upright and this solves the problem

A side note to consider, extraction problem or not, pulling immediately out the door is begging for line twists. Even if you solve your extraction problem you should still consider taking a longer delay to generate the airspeed necessary to lift the bag quicker and cleaner than a 2 second delay will provide.

P.S. I jump an RSK 1 and an RSK .5 and have found that overly tight configurations will cause the hesitation you are experiencing. Something I have noticed to be beneficial is to ensure your closing loop is tight, the tighter the better. This will keep the canopy compressed nice a neat inside the container until the pin is extracted at which point the container will relax some making it easier for the bag to lift out.

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From what you've said, it sounds like the issue is not with pull force required to lift the bag, it is pull force required to unjam the bag from its position (rotated grommet to reserve) in the container before it can be lifted.

So you are deploying after 2 seconds and having to wait 5 more seconds for the airspeed to pick up for the pilot chute to exert the required force to do this.

Try taking a slightly longer delay (3-4), and the snatch force when the PC inflates will increase and may give you that boost you need to free the bag. As you've said the issue is not with lifting the bag as when you pack it grommet to pin there's no problem.

I agree it sounds like PC porosity could be an issue too.

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46 minutes ago, johnmatrix said:

From what you've said, it sounds like the issue is not with pull force required to lift the bag, it is pull force required to unjam the bag from its position (rotated grommet to reserve) in the container before it can be lifted.

So you are deploying after 2 seconds and having to wait 5 more seconds for the airspeed to pick up for the pilot chute to exert the required force to do this.

Try taking a slightly longer delay (3-4), and the snatch force when the PC inflates will increase and may give you that boost you need to free the bag. As you've said the issue is not with lifting the bag as when you pack it grommet to pin there's no problem.

I agree it sounds like PC porosity could be an issue too.

Sunpath insists on F-111 main PCs. They wear out. Try a ZP PC of an appropriate size. Your problem will probably go away.

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Hi @johnmatrix, you are right. The issue here is the force needed to rotate the bag, not the force needed to lift the container. I've done a lot of C&P's in the past on different rigs (used to du CReW too :-) and never experienced this problem until now. A 5 second delay will likely be enough to generate the snatchforce needed to rotate the bag. Normally that won't be a problem but I'm would not like to end up in a situation where for some reason I have to exit at 2500 ft and am forced to do at least a 5 second delay.

@councilman24 I do pack with the lines towards the bottom of the container (and therefore the bridle attachment towards the bottom of the reserve container :-)

@gowlerk The PC is pretty new and perfectly fine according to the rigger. (and does not change the considerable force required to rotate the d-bag)

The question remains: Is 25 to 32 lbs too much?

Edited by branch

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Do you have a spectra kill line PC?  

The spectra will shrink with heat from the friction with the bridle when the PC collapses.  To check it, the bridle has to be under tension.  A kill line will look correct with the load tapes taking the force until you tension the bridle, then the kill line will be taking the force and not allowing the PC to fully inflate.

Check the length of your kill line with the bridle under tension.

 

Derek V

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2 hours ago, branch said:

The PC is pretty new and perfectly fine according to the rigger. (and does not change the considerable force required to rotate the d-bag)

The question remains: Is 25 to 32 lbs too much?

Unless your rigger has equipment to test porosity the condition of the PC can not be accurately measured. But I guess you are correct, none of that answers your original question. Is the force required too much. There is no correct answer to your question. There is no standard except for what you find acceptable. Clearly the system will work at a higher speed, but that does not suit all the applications you want to use it for.  Also clearly you have a good understanding of the issues involved, so your solutions are obvious. Either decrease the needed force for extraction, or increase the available force. One way to increase the available force would be to change the PC to either a larger one or a ZP one. Depending on whether or not Sunpath sewed the bridle to the bag as they used to do it may be quite simple to attach a more forceful PC and take it for a test jump.

Or, ditch the Javelin and get a Racer......Not what I would do, but the required extraction force would drop dramatically.

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Sunpath really like F111 pilot chutes. Without getting into that debate (I am firmly in camp-zp-pilot chutes) you're probably going to have hella hesitations if you take super short delays with an F111 PC.

You could screw around with your gear, but 2s is a really short delay for a hop n pop. I would just take an easy 5, and I bet your problem goes away.

If you're just set on taking super short delays (This was me for a while, I had a katana with a Velo RDS and on it and the openings were.. snappy) try either a larger PC (sunpath will make you a 33", understand that this is a bad idea for terminal) or try a ZP one (personally I really like the VSE design, and did before I represented them).

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On 4/23/2019 at 9:54 PM, branch said:

I have resorted to packing with the d-bag upright and this solves the problem but the container doesn't close nicely this way. 

I reckon this your easiest and best option. Container may look a little bulkier but no need to change anything. I pack my Vector like this all the time.

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The best person to answer the question is Tom at Sunpath. I have supplied quite a number of pilot chutes to individuals and it isn't the first time I have heard of this sort of thing. SunPath calls for a larger than average PC.

Not everyone agrees to use the recommended size, but for those experiencing lazy extractions, a new PC has always resulted in the problem going away. More than once I've loaned a replacement PC when someone felt theirs wasn't worn out, and funny thing, they never ask to have their original re-installed...

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(edited)
On 4/29/2019 at 12:26 PM, gowlerk said:

Sunpath insists on F-111 main PCs. They wear out. Try a ZP PC of an appropriate size. Your problem will probably go away.

Because F111 is a superior fabric over ZP for PCs. It allows some air through and so makes for a more stable PC that reduces the chances of linetwists on your main. Mirage does the same thing (Use F111) as do other companies. The better answer is to monitor your PC and replace it when it's worn out.

Edited by 20kN

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8 hours ago, 20kN said:

The better answer is to monitor your PC and replace it when it's worn out.

That's exactly what people do. They replace them with appropriately sized ZP ones. I have never seen anyone replace a worn out F-111 pc with another one one of the same flawed item. There are many myths around skydiving. ZP P/Cs causing line twists is a new one on me. Must be a secret Sunpath and Mirage are not sharing with everyone else. 

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15 hours ago, gowlerk said:

That's exactly what people do. They replace them with appropriately sized ZP ones. I have never seen anyone replace a worn out F-111 pc with another one one of the same flawed item. There are many myths around skydiving. ZP P/Cs causing line twists is a new one on me. Must be a secret Sunpath and Mirage are not sharing with everyone else. 

It's pretty well known that F111 PCs are more stable than ZP ones. Several manufactures have made the claim. Skydiving PCs in general are trash. If you look at BASE PCs, skydiving ones dont even compare. Skydiving PCs are made as cheaply as possible. BASE PCs are made from ZP, but they have an apex vent that makes them much more stable than any form of non-vented skydiving PC. The only skydiving PC I've seen that's halfway solid is the Squirrel SkySnatch, which is basically a small BASE PC with a killline.

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(edited)
On 5/26/2019 at 2:57 AM, 20kN said:

It's pretty well known that F111 PCs are more stable than ZP ones. Several manufactures have made the claim. Skydiving PCs in general are trash.

That makes it a theory I suppose. Several other manufacturers don't see it as a problem.  Lots of people get satisfactory results from ZP PCs though. I will agree that they are slapped together and not particularly well made. But that generally is not causing a problem because as a rule the PC will outlast the high wear bridle and kill line assembly. Unless it is F-111 and becomes too porous. The OP is not asking about what is causing his linetwists. He is asking about his problem with slow sub terminal deployments. A ZP PC would help with his problem simply by increasing the force. It would seem that the Sunpath supplied part is not doing the job for some reason, even though his canopy and container combination is well within their guidelines.

Could it possibly, just maybe, be that Sunpath has not tried every combination in the situation of a sub-terminal deployment and that the F-111 PC is not up to the job? I'm sure there are other possibilities, but given the description of the problem, and the clear detailed report of the condition of the gear, it would appear that most likely more drag is needed to produce a satisfactory result.

 

Edit to add:

             The OP did say he was waiting for an answer from Sunpath. I wonder what they told him?

Edited by gowlerk

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(edited)
6 hours ago, gowlerk said:

 The OP is not asking about what is causing his linetwists. He is asking about his problem with slow sub terminal deployments. A ZP PC would help with his problem simply by increasing the force. It would seem that the Sunpath supplied part is not doing the job for some reason, even though his canopy and container combination is well within their guidelines.

Could it possibly, just maybe, be that Sunpath has not tried every combination in the situation of a sub-terminal deployment and that the F-111 PC is not up to the job? I'm sure there are other possibilities, but given the description of the problem, and the clear detailed report of the condition of the gear, it would appear that most likely more drag is needed to produce a satisfactory result.

 

Manufacturers compensate by making F111 PCs larger than ZP ones. For example, if you have a larger container (Say 170 - 230) and you order a ZP PC, you're probably getting a 26 - 28" PC. If you order F111, you're likely getting a 30" PC.  Same as with smaller containers. Typically a 24 - 26" ZP or a 28" F111. When brand new, a F111 PC option from the factory will typically produce more extraction force than a ZP option because the F111 PC will be larger. Both Mirage and Aerodyne ship 30" pilot chutes with their larger containers if you select the F111 option (and the Aerodyne one is closer to 32" IMO).

Regarding the PC not extracting the bag fast enough, to comment without more info is a bit difficult as there are many possible causes.Yes, the PC could be worn out. That's common. The kill line could be too short. The PC could not be cocked sufficiently. The PC could be getting stuck in his burble. There are many possible causes and the best option here is to wear a camera pointed back and see what's actually happening as opposed to just guessing.

Edited by 20kN

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(edited)
On 5/28/2019 at 12:18 AM, gowlerk said:

Edit to add:

   The OP did say he was waiting for an answer from Sunpath. I wonder what they told him?

Sunpath wants the rig back for testing. (will do that at the end of the season)

Edited by branch
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You cannot have a perfect PC for a 2s delay and terminal..... simply will not work.  Physics...

If you can lift the dbag out of the container without lifting the rig from the floor you should be fine.

Take a longer delay.

 

My 2 cents

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Funny this came up when it did, I was just reading along these lines in the riggers handbook. Anyway, you can get a pdf copy online for free. Read through Ch4. Deployment and inflation characteristics, page 4-9 there is a section on the main pilot chute. A few folks mentioned replacing your pc with a new one. That is part of what this section covers, as well as F-111 and ZP types, so all around good info. As mentioned in other post there is no firm guidance in terms of force required for the main bag pull out. However on page 4-14 there is the topic of reserve bag extraction force, which incidentally is 18lbs. So I would say that you would want your main to be close to that but you are only 7lbs from that number. Besides like also has been said wait a couple more seconds and your main will probably come right out. 

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