Reserve not extracting

[JerryBaumchen 1,048]

Hi John,

Quote

if it requires more than 18 pounds don't certify it.

I'm not saying yay or nay, but where did this 18 lb req'ment come from?

And I'm not saying 18 lbs, more than or less than, is OK.

JerryBaumchen

PS) And I owe you a phone call; too much going on right now, but don't give up on me.

[piisfish 135]

chemist

I have a skyhook. I don't have to worry about this.

are you SURE that your skyhook is rigged properly ?
I have seen a Skyhook "not connected"

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

[RiggerLee 61]

As I recall he bases that on air speeds following a cutaway and the average drag of a well designed reserve pilot chute. Basically he's saying that if it takes more force then that then you will not build up enough force on the pilot chute, enough airspeed, to extract the canopy in time to meet the TSO requirements on a cutaway. I can make fun of him and poke holes in some of his math but it's actually a pretty good argument. Air speed from a cutaway only builds up so fast. Short of having some monster pilot chute, and even then you hit a point of diminishing returns, you just can't exceed a certain number on the force for extraction. Any more then that and there is simply no way that you can generate enough force to extract it on a cutaway with out eating up too much altitude and time. You could try to argue a pound or two ether way on the limit but the basic primmes of what he is saying is sound.

Lee

Lee
[email protected]
www.velocitysportswear.com

[theonlyski 3]

piisfish

***
I have a skyhook. I don't have to worry about this.

are you SURE that your skyhook is rigged properly ?
I have seen a Skyhook "not connected"

They're SOOO difficult to connect, nobody at a big named loft has time for that!

For what it's worth, I'm sure mine is rigged properly. I watched my rigger do it.

I don't know if it would've mattered in an incident with 1.5 seconds between chop and impact. The only time I recall seeing a skyhook tested that low was intentional and slider down packed reserves.

"I may be a dirty pirate hooker...but I'm not about to go stand on the corner." iluvtofly
DPH -7, TDS 578, Muff 5153, SCR 14890
I'm an asshole, and I approve this message

[catyduck 0]

skydiverek

Better analysis:

http://www.youtube.com/watch?v=vaYQ6iP8zlg

(Apologies for jumping back a couple days' worth of conversation)

The video caption mentions a "low drag pilot chute."

(a) This seems like a bad idea? (with the understanding that you don't want an insta-stop at e.g. terminal head-down) Why would you do this?

(b) How do you know if your container has a low drag reserve pilot chute? Are there specific models and DOMs someone could point to?

[pchapman 261]

catyduck

The video caption mentions a "low drag pilot chute."

To get a newbie up to speed:

That is a bit of a contentious issue that isn't much talked about. Every company says they have high drag pilot chutes. Most companies don't say anything else about their, or other companies' pilot chutes. One company owner, John Sherman, who made the comments on the video about another company's pilot chute, is more vocal about things and stirs things up. There are many including myself who disagree with some of the things he says, but he is willing to talk about things that other parachute system designers don't in public, so his opinions are worth hearing.

Reserve pilot chutes vary in their size, weight, spring strength, spring length, fabric type, number of flaps they are stuck under, and proportion to which there is solid fabric vs. mesh (or open space) in the inlet to the pilot chute. You also get the same pilot chute for a given brand rig no matter whether your reserve is a 99 or 360. So there are many many variables to debate if one likes, and there's no big table online where one can go check the numbers.

Some companies have pilot chute inlet area that isn't simply pretty much the bottom half of the pilot chute, but a smaller area than that. E.g. Sunrise/Wings, VSE/Infinity, UPT/Vector. I'm not sure of the full logic but those pilot chutes are accepted as perfectly normal in the industry. One justification is that the pilot chute will be spilling a lot of air anyway, so such a huge 'inlet' isn't required. Also possibly less oscillation if there's less air spilled. And if the pilot chute is bouncing around in a burble, more solid fabric may allow the pilot chute to catch air better when it is for example sideways to the air flow. As for exactly what the effects of varying inlet size on drag are, who knows, for not much is published. (Anyone know more specifically about the justifications used?)

This thread has been more about making the rig not too tight to pull the reserve out at some angles, than worrying about exactly how much drag the pilot chute produces.

[Southern_Man 0]

pchapman

Some companies have pilot chute inlet area that isn't simply pretty much the bottom half of the pilot chute, but a smaller area than that. E.g. Sunrise/Wings, VSE/Infinity, UPT/Vector. I'm not sure of the full logic but those pilot chutes are accepted as perfectly normal in the industry. One justification is that the pilot chute will be spilling a lot of air anyway, so such a huge 'inlet' isn't required. Also possibly less oscillation if there's less air spilled. And if the pilot chute is bouncing around in a burble, more solid fabric may allow the pilot chute to catch air better when it is for example sideways to the air flow. As for exactly what the effects of varying inlet size on drag are, who knows, for not much is published. (Anyone know more specifically about the justifications used?)

The mostly solid fabric pilot chute is referred to as a ballute pilot chute.

Here is an older thread in which Bill Booth explains his reasoning (with counter-points): http://www.dropzone.com/cgi-bin/forum/gforum.cgi?post=3842194#3842194

"What if there were no hypothetical questions?"

[catyduck 0]

Thanks, pchapman and Southern Man. Really helpful reply and link. If anyone knows of data that has been published, I would be very interested.

I did not ask earlier, precisely because the thread was about overstuffing a rig at that point. The discussion seemed to have turned more towards altitude for deployment.

Thanks again.

[JeffCa 0]

pchapman

Every company says they have high drag pilot chutes. Most companies don't say anything else about their, or other companies' pilot chutes. One company owner, John Sherman, who made the comments on the video about another company's pilot chute, is more vocal about things and stirs things up. There are many including myself who disagree with some of the things he says, but he is willing to talk about things that other parachute system designers don't in public, so his opinions are worth hearing.

This is exactly what I found when I was researching which container to buy. I went to every major manufacturer's website. Only a few mentioned their reserve pilot chute. Some had no comment at all about it. Of the ones that did mention it, all but one had just a single fluff comment like, "One of the industry's strongest pilot chutes". Only one manufacturer, Jump Shack for their Racer, gave any more information. JS has some documents about their testing published for anybody to see. As for all of the other manufacturers, they made sure that colour and pinstripe options were very prominent. The worst offender was one company that, based on my observations, I'd wager sells more sport rigs than any other company. Did you know that you can now get rig X with an extra pinstripe?! Wow, we should all run out and buy it!

The research made me think that we as skydivers are not a very bright group. I'm sure the manufacturers are just giving us what we want, and we are apparently dazzled by shiny things (pinstripes and tie-dye). If we were smart enough to rebel and demand that safety information be published, we might see some progress on this.

"So many fatalities and injuries are caused by decisions jumpers make before even getting into the aircraft. Skydiving can be safe AND fun at the same time...Honest." - Bill Booth

[RiggerLee 61]

It hasn't been totally ignored. I had a chance to glance at a report that was done by some university for sunpath on the javelin reserve PC. It was the exact same testing that racer has done. It attracted my attention because the numbers seemed a bit screwy. They were measuring their area differently. They were actually looking at the inflated area in the wind tunnel. They didn't have access to quite as nice of a wind tunnel but in essence they were able to generate the same data as Sherman. I don't think they have waved it around like he has. Sunpath has been through a couple of nasty lawsuits and they've hired some fucking lawyer and I think he's been telling them to keep all the shit like this hidden. I don't see why. Numbers looked good to me but it seems to be a legal tactic to suppress all public information to deny it the opposition. Keep the world stupid so no one can deny what you say in court. I'm not wild about the philosophy. If it's going to be like that then you will never be able to get any real information about a system beyond the color options. But my point is that it is out there. He let me hold the report in my hands and read some of the data. So just because a manufacturer doesn't wave his arms around like a crazy man screaming about these things it doesn't mean that it hasn't been addressed.

Lee

Lee
[email protected]
www.velocitysportswear.com

[JeffCa 0]

Thanks for the info, but you have to understand that most of us have not seen it. I don't think I wrote that testing was never done, just that we don't get to see it, or it isn't prominently displayed on their websites. It impairs our ability to make educated choices as consumers and people who are literally trusting them with our lives. I'm pretty happy that at least one manufacturer is waving around the info like a crazy man, but if it's just one I have nothing to .... Oh, look at the pretty colours and pinstripes! Wait, what was I just talking about? Oh well, it couldn't have been important.

Sounds like you're saying that we should blame the lawyers?

"So many fatalities and injuries are caused by decisions jumpers make before even getting into the aircraft. Skydiving can be safe AND fun at the same time...Honest." - Bill Booth

[airtwardo 6]

Quote

Sounds like you're saying that we should blame the lawyers?

That's the 'easy' out..

As you've so eloquently stated...it's the consumers that drive the thing. Demand better safety and it will come...demand an extra pinstripe...

~ If you choke a Smurf, what color does it turn? ~

[JohnSherman 1]

Quote

Some companies have pilot chute inlet area that isn't simply pretty much the bottom half of the pilot chute, but a smaller area than that. E.g. Sunrise/Wings, VSE/Infinity, UPT/Vector. I'm not sure of the full logic but those pilot chutes are accepted as perfectly normal in the industry. One justification is that the pilot chute will be spilling a lot of air anyway, so such a huge 'inlet' isn't required. Also possibly less oscillation if there's less air spilled. And if the pilot chute is bouncing around in a burble, more solid fabric may allow the pilot chute to catch air better when it is for example sideways to the air flow. As for exactly what the effects of varying inlet size on drag are, who knows, for not much is published. (Anyone know more specifically about the justifications used?)

Test were conducted by NASA on 3 different pilot chutes. The Vector 1 and Vector 2 and Racer. Here,again are the results of those tests. Study the results and remember that a Cd of less than .40 is a drogue not a pilot chute. A pilot chute requires a CD of greater than .60. An MA-1, the standard for the industry, has a CD of .65.

https://www.youtube.com/watch?v=Zva4gHVX_zI

A Ballute is a Supersonic drag stablization device.
A pilot chute is a extraction drag device.
To get drag out of a ballute you gotta go fast, we don't!

The pilot chutes refered to as Ballutes by their manufacturer do not have enough drag for sport use.
It is a major reason they have trouble meeting the 3 second cutaway test.

As to getting out of the burble faster: This is good retoric for those who actually believe that things go "UP" when released in FF. They don't, we fall away from them.

John

[JohnSherman 1]

Quote

I'm not saying yay or nay, but where did this 18 lb req'ment come from?

Hi Jerry,
I wrote this some time back http://www.jumpshack.com/default.asp?CategoryID=TECH&PageID=18pounds&SortBy=DATE_D but I am presenting it here as I think it is important to this discussion..

Quote

Due to recent incidents indicating there might have been difficulty extracting the reserve free bag from its container during deployment we have initiated an investigation of the forces available and the forces required along with the mechanics of accomplishing the process. In simplest terms there are two forces involved. The drag force capability of the pilot chute and the force required to extract the bag. Certainly the ability of the pilot chute must be greater than the retention of the container. This demands that we know the capability of the pilot chute. To know this requires testing with instrumentation. However we can calculate the size requirement of the pilot chute and measure the bag extraction force without doing sophisticated testing. A rate of descent of twenty (20) feet per second defines a malfunction. If we assume this rate of descent to begin our problem we add to it the rate of acceleration due to gravity, 32 feet per second squared, which begins at cutaway. In the first second of this acceleration we travel 16 feet plus the 20 feet of the initial rate which means we traveled 36 feet. We are now traveling at a rate of 52 FPS and still accelerating. The rate of 52 FPS at 2000 feet will generate a dynamic pressure of 3 pounds per square foot. This benchmark is important as it is where a commonly used free bag and bridle will load for extraction. This means that at the point of bag extraction we have available, 3 pounds per square foot of dynamic air pressure for the pilot chute to drag. Pilot cutes are generally 36 inches in diameter which is 7.07 square feet. No parachute or flexible body will drag to its full size; the size is effectively reduced due to rigging and billow of the canopy. This is accounted for mathematically by applying a Coefficient which reduces the physical size to an “effective size”. It could be thought of as a percent of efficiency of the design. An MA-1 Military surplus pilot chute commonly found has a published Coefficient of Drag (Cd) of .65. When the Cd is applied to the physical size or plan form it identifies the “effective size” of 4.6 square feet. There are better more efficient pilot chutes. Let us assume there is a pilot chute with an effective size of 6 square feet (I don’t know of any that good). At bag extraction time there is 3 pound per square feet available dynamic pressure as explained above. 6 square feet times 3 Pounds per Square Foot equals 18 pounds drag. This is the maximum that could possibly be allowed and will be too high in some cases. Nothing over this limit should be acceptable on any rig without a letter from the manufacturer specifically allowing whatever force they specify. This bench mark should be set by National Aero Clubs as instruction to their riggers until the manufacturers provide a specification for their specific gear.

[airtwardo 6]

Quote

...equals 18 pounds drag. This is the maximum that could possibly be allowed and will be too high in some cases. Nothing over this limit should be acceptable on any rig...

Why is that John?

I 'think' I know, but would rather 'really' know....

Thanks

~ If you choke a Smurf, what color does it turn? ~

[RiggerLee 61]

I have never understood this. I've heard his lectures, I've seen his video, I still don't get it. It's a burble. the body is shedding vortices. Depending on the renalds numbers this can happen in one of several modes. I don't recall the break down on them off the top of my head but it's a rolling vortices characterized by the air actually flowing down wards towards the back of the jumper. The air is flowing down wards towards you. How does making the pilot chute draggier on it's side help other then to have it sucked harder towards your back? Yes I've seen his video. We even changed out the spring loaded pilot chutes on our student rigs to vector II pilot chutes. They still just flopped around there just like all the others. If they were so great why did the instructors still have to reach in and grab them in the burble to hand deploy them as a courtesy to the students. I will say this. They did pack up nicely and had fewer tares then the mesh ones. But I wouldn't hold my breath on it launching till the student ether looked over his shoulder or set up in which case the pilot chute didn't "fly it's way" out of the burble it just got blown out of it when the burble went away. I hate to set here and call him a fucking liar but I can not comprehend ether in theory or in practice what he thought he was doing. Further more I am apparently not smart enough to see any other advantage or motivation for the change in design. If it's easier or cheaper to manufacturer I don't see it. And the losses in terms of drag are significant. Some times I wish I could see what is going on inside peoples heads. Other times I'm glad I can't.

Just for fun, can we brain storm and try to come up with an explanation for this change.

Lee

Lee
[email protected]
www.velocitysportswear.com

[gunneroy 0]

irishrigger

it is a Javelin NJK, reserve is a optimum 143 and main is a Vel96.I believe sunpath recommend optimum126 as max.

Could the findings be replicated using the correct maximum size reserve canopy as according to the manufacturers sizing guide?

[Skydivesg 6]

piisfish

***
I have a skyhook. I don't have to worry about this.

are you SURE that your skyhook is rigged properly ?
I have seen a Skyhook "not connected"

When you find something like that (Skyhook not connected) what do you do?

Tell the owner?

Tell the last rigger? Hopefully it wasn't you.

This is exactly why I always pull my reserve before giving it to my rigger and pull out the canopy in stages- checking everything as I go. And now there is no reason not to video the process.

Having faith in your rigger is kind of like raising kids -- trust but verify.


Be the canopy pilot you want that other guy to be.

.

Be the canopy pilot you want that other guy to be.

[irishrigger 31]

Dont know yet, i am awaiting for the owner to get me a new reserve. once i have that we will see what the outcome is. although i doubt with the correct reserve in there that it will not be a problem anymore.

[gunneroy 0]

I'd be really interested cuase if the problem doesn't repeat with the correct size reserve than this is just a case of someone not listening to manufacturer recommendations and putting them selves in danger.
If the problem does occur with a correct size of main and reserve than this is a whole other ball game.

[pchapman 261]

It is an interesting question: In the case of a Jav NJK with an OP 143 in it, is the owner a total idiot, or just someone who overstuffed the rig a little? And what of the original rigger?

As a rigger you don't normally start looking up rig and canopy sizes before a repack. Indeed, if the original rigger were handed the reserve and rig and manuals, there would have been no guidance in there. I just had a look and sizing info for the Javelin isn't in the manual. One has to go online to find anything.

Online, Sunpath mentions a 113-120 reserve for that rig, with the next larger sized rigs holding a 126 or more. Now the OP 143 is a low bulk canopy and PD says it packs roughly like a PD 126. But there's no law that says that since 126 > 120 so you can't pack it. And indeed a google search easily finds people on DZ.com comparing an OP 143 to a Tempo 120 or PD 113, although opinions certainly differ and some say that the OP 143 isn't that small at all!

So on the one hand, it does sound like the canopy is probably bigger than what is recommended for the rig -- the rig is likely overstuffed (which means a lot when one is starting with a tiny rig). Some people say it would be, yet some more optimistic ones don't think it would be.

On the other hand, there isn't anything clearly saying that the canopy combination is incorrect or disallowed or just plain evil. (Low bulk canopies aren't specifically mentioned in Sunpath's list.)


In any case riggers are starting to pay more attention to how overstuffing affects functionality, and not just the brick factor, reserve shape, and ability to close flaps and tuck tabs.

Note also irishrigger's point that the issue with reserve extraction force on this rig may relate to rig design at least as much as reserve sizing.

[Southern_Man 0]

pchapman

As a rigger you don't normally start looking up rig and canopy sizes before a repack. Indeed, if the original rigger were handed the reserve and rig and manuals, there would have been no guidance in there. I just had a look and sizing info for the Javelin isn't in the manual. One has to go online to find anything.

Perhaps it is just because I am a new rigger (and came of age with an awareness of the issue) but I look up the recommended canopy size with each rig I pack.

"What if there were no hypothetical questions?"

[ChrisD 0]

gunneroy

I'd be really interested cuase if the problem doesn't repeat with the correct size reserve than this is just a case of someone not listening to manufacturer recommendations and putting them selves in danger.
If the problem does occur with a correct size of main and reserve than this is a whole other ball game.

Thanks for the reminder....


There is variation in rigs, everything varies a little bit. It is perhaps more important to recognize too tight fit's by that observation alone!

As compared with the published catalog manufacturers specifications etc.

There is the possibility of doing everything buy the book and still missing the point about these issues.

C

The picture's from all of the various individuals showing a rig being held up in the air by the reserve tape SHOULD be enough to keep most all of us up a night!!!
Your observation about the manufacturers, is understood, but it's your life on the line here not there's. They do the best they can, but sometimes its not enough....

Unless of course your Ron,

And you would also be correct when you point out that this issue may extend even to properly sized rigs, there is much heated debate on this subject for a full understanding of this you might want to visit the >>>>>>>>>>>>

Wait for it, wait for it>>>>>>>>>>>>>

The RACER web site and start reading, if you want to that is....AKA Jumpshack. Or whatever name they are calling themselves now a days....

But what do I know, "I only have one tandem jump."

[JohnSherman 1]

Quote

equals 18 pounds drag. This is the maximum that could possibly be allowed and will be too high in some cases. Nothing over this limit should be acceptable on any rig...

Why is that John?

I 'think' I know, but would rather 'really' know....

I don't know of any pilot chutes, including the Racer, which will lift 18 pounds, 1 second after cutaway. The Racer will only lift 17.9 pounds at that point. Therefore anything over 18 pounds is Taboo. Remember we are lifting the weight of the reserve plus any additional container restriction.

JS

[JerryBaumchen 1,048]

Hi John,

Quote

It is a major reason they have trouble meeting the 3 second cutaway test.

This is really not for you, but for other people on this site.

There is no cutaway test in TSO C23b.

My internet is down at home so I am using the local library and do not have TSO C23c/d in front of me. 23b I know almost from memory.

IMO we should not use terms like 'meeting the 3 second cutaway test' when none is req'd.

And I would like to think that any rig could do this.

Just to be clear,

JerryBaumchen