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sfzombie13

installing a drogue system on a sport rig

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Larger canopies have a larger volume than smaller canopies so fill time on a smaller canopy is less. Having worked in R&D at Para-Flite and done many test jumps and drops from small canopies to large the larger canopies opened softer. I think the hard opening problem is related to an out of sequence deployment. If that is the case the solution would be to use something like the free pack strap we used in the 1970s but still put it in a deployment bag. That would insure you are at line stretch before inflation starts and the slider is still in position.

 

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1 hour ago, accumack said:

Larger canopies have a larger volume than smaller canopies so fill time on a smaller canopy is less. 

Hi Jim,

While it has been 15 yrs since I had a nice sit-down talk with one of the major players at PD, he said the very same thing.  He said that the small canopies registered the highest opening shock loads of all the canopies that they had measured.

It is fairly simple physics.

Jerry Baumche

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Larger canopies are also heavier, which might break rubber bands prematurely. Look at all there out-of-sequence openings suffered by early tandems and all the different solutions invented by tandem manufacturers.

Strong stows most their suspension lines in standard rubber bands, the wraps an Anti Line Slump flap over the stowed lines and closes the ALS flap with a trio of bungee cords (rubber elastic wrapped in a nylon sheath) to lock the d-bag closed.

UPT uses 4 double-wide rubber bands to close their d-bags, plus a bunch of regular rubber bands to stow lines.

Jump Shack/Parachute Labs uses almost a dozen locking stows.

I vaguely remember Parachutes de France using 6 locking stows.

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(edited)
1 hour ago, Binary93 said:

Could someone please add some reference/image/more details on this one, for us, young padawans? :)

We used to roll pack the canopy and there was a strap sewn to the canopy on one of the Vee tapes for the B lines on the rib. You would roll the canopy then fold the lower portion and close the strap with one line stow and the rest of the lines were coiled in the container. It was important that the fold would open the strap after the line stow was released or you would have a streamer. I no longer have the instructions or I would post them. This was discontinued after a few people had lines grab one of the flaps. Using it with a d-bag would eliminate that problem. Dick Morgan invented the strap in the mid to late 1970's.

 

Edited by accumack

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5 hours ago, riggerrob said:

 

UPT uses 4 double-wide rubber bands to close their d-bags, plus a bunch of regular rubber bands to stow lines.

 

I recently found out that with thinner Spectra and Vectran lines UPT no longer calls for the double wide rubber bands.

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On 8/21/2020 at 1:30 PM, sfzombie13 said:

i was planning on going from my 218 to the 181 sometime when it comes back from the shop.  looks like it may indeed save my life, even if it's not a reserve any longer.

This part of your post makes me think you might be jumping Ravens (or Super Raven). Although any canopy design is theoretically capable of painfully hard openings, the Ravens have a reputation of also being practically capable for it.

If you have actual experience with painful openings on one of those canopies, I would suggest you first look into switching to another canopy type that is known for softer openings, before walking the difficult and laborious path of building a drogue system on a sport rig, or the slightly less difficult path of messing around with slider sizes.

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On 8/21/2020 at 1:30 PM, sfzombie13 said:

i wonder if the issue is something that can be fixed by using a larger slider rather than break away risers or a drogue system.  do you know of any data on it?

I don't have any specifics. But that has been the fix for some canopies well known for opening hard (ie: Sabre 1). But there are two things to consider:

 

- It is a delicate balance. If the slider is too big the opening might take too long, or never happen (the slider might hangup all the way up)

- The reason catastrophic openings happen is because the slider comes down prematurely (which could be due to a variety of reasons). A larger slider does not guarantee a proper deployment either. I can imagine it could help, but I wonder if the help is marginal

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On 8/21/2020 at 8:57 PM, accumack said:

Larger canopies have a larger volume than smaller canopies so fill time on a smaller canopy is less. Having worked in R&D at Para-Flite and done many test jumps and drops from small canopies to large the larger canopies opened softer. I think the hard opening problem is related to an out of sequence deployment. If that is the case the solution would be to use something like the free pack strap we used in the 1970s but still put it in a deployment bag. That would insure you are at line stretch before inflation starts and the slider is still in position.

 

 

On 8/21/2020 at 10:51 PM, JerryBaumchen said:

Hi Jim,

While it has been 15 yrs since I had a nice sit-down talk with one of the major players at PD, he said the very same thing.  He said that the small canopies registered the highest opening shock loads of all the canopies that they had measured.

It is fairly simple physics.

Jerry Baumche

 

Thanks for your input Jim and Jerry. You are way more knowledgeable than me, so I don't want to contradict you and I agree that the time to fill a larger canopy is necessarily longer than the time to fill a smaller canopy for a given airspeed. Also larger canopies tend to be "higher" (have more distance between both skins), so the volume increases significantly more than the surface. From that point of view, I totally understand that smaller canopies might have higher loads on deployment than larger ones, under normal circumstances.

But I meant a catastrophic opening scenario, where inner inflation might play a secondary role. Simply the drag of the bottom skin when spread. Imagine a slider-off deployment with a single skin canopy. The drag from a fully spread bottom skin on a large canopy is much larger than the drag from small one, so the deceleration is also larger. That was the scenario I was talking about. Fully spreading a large canopy takes longer than a smaller one, but I expect that the additional time needed to spread a larger canopy does not offset the much larger drag a large canopy can create.

That was my way of thinking to explain the trend that most folks incapacitated on catastrophic openings, had those openings on large canopies. Maybe there is something else to consider, and my reasoning is totally off.

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2 hours ago, IJskonijn said:

This part of your post makes me think you might be jumping Ravens (or Super Raven). Although any canopy design is theoretically capable of painfully hard openings, the Ravens have a reputation of also being practically capable for it.

If you have actual experience with painful openings on one of those canopies, I would suggest you first look into switching to another canopy type that is known for softer openings, before walking the difficult and laborious path of building a drogue system on a sport rig, or the slightly less difficult path of messing around with slider sizes.

yes i am and no, never had one.  i just got interested in the discussion about the break away risers and found a problem that needs solved.  i love those, but most of the ones i work on are amusements and novelties.  i figured that if it could be solved, then it may just do me some good since i'm getting old.  i had thought about the ravens openings, but have yet to jump the 181 and it is the one that is zp, so i may just be getting rid of that one sooner than anticipated.  if it opens and flies anything like the 218 i'll keep it.  thanx for the good advice.

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Fair enough, but I'm not sure that this route is the correct one to solving the problem of hard openings. Part of the success of the three-ring system (and why it superseded pretty much any other release system ever thought out) is that it is highly reliable. For skydiving equipment, reliability is a very big concern. As already mentioned, a drogue system adds quite a few failure modes which may make it too unreliable to be worth it.

In practical terms: I see more instances of tandems having drogue issues than I see instances of hard openings.

The slider already does a very good job of slowing down ram-air canopy openings. It's quite fun (in a slightly morbid way) to take a look at all the ways people tried to slow down ram-air canopy openings prior to the slider. My personal guess would be that an incremental improvement on the slider could very well be better in terms of reliability, with the same effect on reducing hard openings.

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(edited)

I had been thinking of a similiar post to Deimian's, so with him breaking the ice here goes:

One does seem to hear of more damaging openings from larger canopies, but it isn't always so.

Confounding variables may be that older jumpers traditionally have sometimes been under big canopies, and maybe are more susceptible to injury. Or that heavier jumpers are also more likely to be on bigger canopies, and thus tend to start deployment at higher freefall speeds.

As an example of a bad small canopy opening, although with a non-standard slider:   I know someone about 160 lbs, a DZ packer and thus with experience,  who broke some neck vertebrae recently on a Crossfire 2 109 with a 'slightly smaller' than normal slider. Someone else thought it was acceptable to put that particular removable slider on in place of the regular one. Worked fine for 40 odd jumps but one time it didn't.

I certainly can't go against Performance Designs, but want to mention one factor among many competing ones in how canopies open.

Fill time certainly is longer for larger canopies which have larger internal volume (rising faster than the size increases, due to volume cubing when area is squared).

But what about plain old bottom surface inflation before filling?

If a 20 ft wide canopy can snap open and create as much drag as it does, then a 30 ft wide canopy might be able to snap open 20 ft wide in nearly the same time (with just a little more mass to push around)... and then continue to open fully to 30 ft, creating even more drag than the 20 ft canopy.

This only applies if the canopy expansion is very fast, so that the jumper hasn't been gradually slowing down. With more time involved, the 30 ft wide canopy won't add more pounds of drag because the jumper will be slowing rapidly before the canopy area gets too big.

So that's a scenario where I'd rather have an explosive opening on a smaller rather than a larger canopy.

As for the Para-Flite experience, I wonder if the trends in zero-p canopies are different than in F111 style ones. We never had openings quite as explosive back when the fabric would let more air through.

And just for fun and maybe just a little education, a few pics of hard openings I've seen as a PFF (~AFF) instructor with students -- where they had a largely open canopy while only a short distance away from me in freefall. Shows 5 different opening in series of 1 or more pics. [Edited to change description, as file names not shown in-line]

Some were sore but no long term injuries. A blown brake line in pic #1. The last series shows how a canopy can start inflating a lot in the middle even when the slider is at the slider stops on the stabilizers -- I haven't quite thought through the geometry issues contributing to that. (These students were on Aerodyne Solo canopies, full ZP versions. They later shipped larger sliders that helped somewhat.)  Some filling of the cells is happening, especially in the center cell in some photos, that may be driving some openings,  but there's a lot of 'squished flat' bottom surface inflation happening in many photos too. 

When your student is still within 50 feet of you and slider down, you're glad not to be them!

1 hard opening - PChapman cap.jpg

2-1 hard opening - PChapman cap.jpg

2-2 hard opening - PChapman cap.jpg

3 hard opening - PChapman cap.jpg

4-1 hard opening - PChapman cap.jpg

4-2 hard opening - PChapman cap.jpg

5-1  hard opening - PChapman cap.jpg

5-2  hard opening - PChapman cap.jpg

5-3  hard opening - PChapman cap.jpg

5-4  hard opening - PChapman cap.jpg

Edited by pchapman

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2 hours ago, IJskonijn said:

Fair enough, but I'm not sure that this route is the correct one to solving the problem of hard openings. Part of the success of the three-ring system (and why it superseded pretty much any other release system ever thought out) is that it is highly reliable. For skydiving equipment, reliability is a very big concern. As already mentioned, a drogue system adds quite a few failure modes which may make it too unreliable to be worth it.

In practical terms: I see more instances of tandems having drogue issues than I see instances of hard openings.

The slider already does a very good job of slowing down ram-air canopy openings. It's quite fun (in a slightly morbid way) to take a look at all the ways people tried to slow down ram-air canopy openings prior to the slider. My personal guess would be that an incremental improvement on the slider could very well be better in terms of reliability, with the same effect on reducing hard openings.

i'm not sure either but in know that examining more than one solution to a problem is the best way to solve it.  personally, i think the break away risers are the best idea that would prevent deaths from hard openings, and i will most likely not go further with this, but i would like to put one together to see if it would work as intended. 

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The more I noodle this idea the more I hate it. Sorry, you get points for initial creativity, but they all get taken away for not being creative enough to envision all the problem. Please don't play around with this idea, it is a problem in search of a fatality, not a solution.

If you use the system like a tandem drogue where it is deployed out the door then no one will be able to skydive with you if you intend on creating a drogue fall speed that will have any meaningful impact on max opening forces. Even at 60mph freefall speed you can still potentially have a hard opening with high g's.

Why bother with the freefall at all, or the complexity at that point, just do short delays on hop and pops and high pulls.

If instead you use it to slow down at the bottom end of a jump you have basically created a high speed malfunction, and PCIT, which will then need a second deployment action. So you pitch the drogue, you wait for a decrease in speed, then you pull a drogue release. All at the bottom end of a jump.

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Not sure if maybe different "classes" of hard openings should be considered when talking about this?

  1. Sudden inflation (either due to slider getting down/being down, small or ripped slider, "act of God"...)
  2. Rubber bands breaking early, canopy starts inflating before lines are stretched (line dump)
  3. Riser covers too stiff, canopy starts inflating before they release so when they finally do it hits you (similar to line dump, just at the risers)
  4. High speed opening (failing to slow down sufficiently after FF for example)
  5. ...

I guess noone has any statistics (don't know how would one get it) on how often which cause happens?

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(edited)

What troubles me is canopy opening distances today are hundreds of feet longer than in the past and some are killing people. The shape of the deceleration is important. At Para-Flite we had firm but consistent openings. I don't believe any reserve currently manufactured really meet the opening requirement of the TSO! I believe every manufacturer fudges the numbers. The reason most likely is the canopy cannot with stand the openings without destruction on the high speed test thus slowing deployments on cutaways the most common type of malfunction. Some of the requirements for militaries of various countries mandated documented drop tests with openings from 400' with zero airspeed. I don't think there are many current canopies if any that can meet that spec. Also we drop tested and TSO'd every size canopy in a family as opening characteristics are different and I'll guarentee most manufacturers only test one size and claim it is a minor modification (it is not) some even are using a TSO from an earlier canopy and saying it is a small modification. If the FAA ever looked into it most reserves would be grounded (it was a dirty little secret)! We made zero P canopies and didn't have a problem. There quite a number of proprietary design concepts to control the openings that I can tell a lot of manufacturers have no Idea what is going on. Let me throw this out there. A major manufacturer swore that the nose angle is what made hard opening canopies. The nose angle has very little to do with it. At Para-Flite we did so much R&D work to understand what happens.

 

 

Edited by accumack
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18 hours ago, DougH said:

The more I noodle this idea the more I hate it. Sorry, you get points for initial creativity, but they all get taken away for not being creative enough to envision all the problem. Please don't play around with this idea, it is a problem in search of a fatality, not a solution.

If you use the system like a tandem drogue where it is deployed out the door then no one will be able to skydive with you if you intend on creating a drogue fall speed that will have any meaningful impact on max opening forces. Even at 60mph freefall speed you can still potentially have a hard opening with high g's.

Why bother with the freefall at all, or the complexity at that point, just do short delays on hop and pops and high pulls.

If instead you use it to slow down at the bottom end of a jump you have basically created a high speed malfunction, and PCIT, which will then need a second deployment action. So you pitch the drogue, you wait for a decrease in speed, then you pull a drogue release. All at the bottom end of a jump.

it's not a point system.  it's called learning.  why do you suppose i proposed an idea like this in this forum?  maybe because i don't know about some things and want others who do to inform me of the things i may be missing?  like all the ideas of things i learned, such as a drogue in tow messing with a reserve deployment.  that seems like a problem that should be solved, or maybe it has, but i will find out.  i got that information from talking to a guy at strong. 

i looked at the numbers and speed is definitely correlated to high g forces.  slowing down will reduce them to a survivable force.  i just have to find out what the speed is and how big of a pilot chute it would take to get there.  it would change with different weights, but i suspect there is a happy medium somewhere.  maybe not.  and yes it would mean another action on deployment, and at least 500-1000 extra feet of altitude to get that action.  it's not for everyone, it is a niche project that will probably never make it past the drawing board.  it is a very much needed solution and we need to talk about it along with any other ideas and modifications we can figure out to prevent the high g forces from killing jumpers.  since we don't know exactly what causes them we can't prevent them.   i would love for the uspa to grab some data on hard openings, like sending out a request for incident reports to gather information on them.  that would be something we can all use.

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