Skyhook at terminal

[Davew 0]

A reserve pilotchute is designed to function at terminal. A cutaway main attached to a skyhook enormously improves its perfornce subterminal. It seems the Skyhook has covered both situations. There, however, scenarios where an open canopy can be cutaway and act as a super pilotchute while the jumper is still at terminal.
1. The cutaway handle is accidently pulled on exit or in freefall, the jumper deploys the main, the riser covers hold long enough for the canopy to come out of the bag and partially inflate before separating from the harness. This has happened at my DZ.
2. The jumper deplys the main, has a hesitation, goes for the cutaway handle as the pilotchute lifts off, cuts away just as the canopy comes out of the bag. This is a relatively common malfunction.
3. The jumper experiences a baglock. Just on cutaway the canopy comes out of the bag.
In these scenarios the jumper has not been decelerated by the main but it will be at least partially inflated as it lifts off. If there is a skyhook it will act as a super pilotchute with the risk of a catastophically hard opening.
Many people think that once the resrve is out of the bag the speed of the opening is determined only by the slider. The slider is critical for any opening but so is the pilotchute. BASE jumpers know this and have a variety of pilotchutes for use on different delays. RWS knows this so their drougues collapse on lift off so as to have just the right amount of snatch to lift the bag at optimum speed. If your kill line shrinks on your sport rig not only do you get slower bag lift off you get slower inflation.
A big pilotchute gives a harder opening because the bag is more rapidly decelerated. At the moment the canopy comes out of the bag the speed difference between the jumper and the canopy will be higher and therefore the load on the lines will be higher. That means the initial snatch will be harder but force on the lines also contributes to the next stage of canopy inflation.
Lets say standard bag lift off takes one third of a second. That suggests the bag is travelling at about 45 feet per second slower than the jumper. 135 ft/s vs 180 ft/s.
A fully open canopy with a suspended jumper has a descent rate of about 15 feet per second. A cutaway canopy with only a reserve freebag hanging under it will have a descent rate somewhere between 135 ft/s and 15ft/s depending on the degree of inflation. It d doesn't need to be inflated much to increase the speed difference between the jumper and the bag by a factor of 2 or 3 and possibly as much as 6 compared to a standard pilotchute.
Surely this creates the possibility of a severely hard opening. As I write there are 2 jumpers out of action at my DZ with injuries caused by hard openings with standard pilotchutes. The prospect of superhard skyhook openings has not been fully investigated.
I would like RWS to demonstrate that I am wrong by conducting a few tests along the lines of the following: Pack a main with no bag. Disconnect the risers but connect the skyhook. Throw it out with a heavy weight (please don't use a real person!) and either have a jumper or an aad dump it out. There are gadgets out there to measure the forces on the reserve opening.
To really ensure the main opens before popping the reserve try it with the slider down. Try it again with 10 or 20 pound break tie btween the risers and the harness.
The skyhook is like a wonder drug that can cure certain diseases. In this case low cutaways and unstable cutaways. The vendors of this wonder drug have an obligation to test for side effects that may be just as bad as the disease they hope to cure.
RWS's response was very poor to problems raised concerning the tandem fatalities in Guam and Tokyo where the skyhook was suspected of failing to clear the velcro running down to the RSL when bag locks were cutaway. These situations ended with main reserve entanglements.
One can only suspect that a huge investment in development and marketing won't be jeopardized by the small matter of safety

[justinb138 0]

I believe that Bill Booth has addressed this exact issue in another thread, fairly recently actually.

[davelepka 4]

It's called a freebag, and once the PC or superPC strips it off the reserve, you're in slider city. Really.

Base and tandems both keep the PC/drouge attached to the canopy as it opens, thus you need to consider it when looking at openings.

[mnealtx 0]

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Many people think that once the resrve is out of the bag the speed of the opening is determined only by the slider. The slider is critical for any opening but so is the pilotchute. BASE jumpers know this and have a variety of pilotchutes for use on different delays. RWS knows this so their drougues collapse on lift off so as to have just the right amount of snatch to lift the bag at optimum speed. If your kill line shrinks on your sport rig not only do you get slower bag lift off you get slower inflation.

You're talking about pilot chutes that are staying attached to the main, not reserves - that's a big (and important) difference, I would think. Once the freebag is off the reserve, it's no different than a terminal reserve opening. I can see where the attached main could cause a higher initial snatch force due to a higher initial deceleration, but that's all I can see it doing.

I am not a parachute or harness designer, so I could be wrong...

Mike
I love you, Shannon and Jim.
POPS 9708 , SCR 14706

[nicknitro71 0]

I don't quite agree.

A larger PC does not equal harder openings.

In BASE we do not chose the size of the PC because we want to tame the openings.

The size is dictated by the delay taken. We also want to avoid center-cell strip because we do not use a free-bag.

In skydiving the reserve is free bagged, so no center cell strip to worry. Also the PC or main canopy (in the case of the skyhook), once the reserve is out of the bag, flies away leaving the canopy to open normally in slider up territory.

I'd had no problem using the main as a terminal PC to open my reserve because I know the opening is not going to be much harder than with a normal PC.

Maybe harder snatch force but not opening.

Memento Audere Semper

903

[billbooth 10]

RWS's response was very poor to problems raised concerning the tandem fatalities in Guam and Tokyo where the skyhook was suspected of failing to clear the velcro running down to the RSL when bag locks were cutaway. These situations ended with main reserve entanglements.
______________________________________________________

First off, the Tandem rig in Guam DID NOT even have a Skyhook on it. Secondly, in the Japan fatality, the reserve was pulled without ever releasing the drogue, much less cutting away. So obviously, the Skyhook was NOT a factor in either of these fatalities.

I investigated both fatalities, and have reported everything I know about both. Here it is again:

In Japan, the reserve pilot chute entangled with the drogue bridle, an extremely rare occurrence. There was nothing wrong with either drogue release handle or the drogue release mechanism itself. The handles simply weren't pulled.

The Guam incident started with a main baglock about 18" from the ends of the risers. The tandem pair then seemed to tumble into the mess. The reserve was pulled before breakaway, then sometime later, the breakaway handle was pulled. The main canopy somehow got completely out of the bag. Every stow but the first (baglock causing) stow eventually released. The reserve never even got out of the bag. This is my best guess about both incidents, because there was no video nor eyewitness accounts from either. I didn't even get to look at the Guam rig for several months after the incident. We have always released any information that might be of help in preventing future fatalities..and we always will.

About the Skyhook: When we breakaway from a fast spinner (say a stiletto 97), it is a breakaway from a "fully open" canopy at "high speed". Guess what? The reserve deployment speed (to line-stretch) is exactly the same (1/2 a second) as when we break away from a large stable main (or for that matter from a bag lock at terminal). It really seems like that spinner would put a lot more load on the Skyhook lanyard, but it doesn't. I don't fully understand why, but I think it is because the canopy "breathes" (un-loads) for split second after breakaway, and before it can re-inflate and start pulling hard again, the Skyhook has the reserve out of the bag. Also remember, the Skyhook is only connected to one side of the canopy, and the Skyhook lanyard is designed to break if you put too much load on it. I hope this answers your question. If not, give me a call me at Relative Workshop, and I'll tell you everything I know about either situation. I talk much better than I type.

[Davew 0]

Thank you for your reply. This is the first time I have seen your response to those two Sigma accidents and I applologize for any false assumptions I have made. There are two point about wich I am not quite satified.
The report I saw of the Guam accident stated that both risers were released but the RSL was still attached. It is this aspect of the RSL, not the actual skyhook that concerns me. A collapsed drogue/baglock is a very low drag malfunction and the velcro may provide enough resistance to keep one riser attached. I have picked up a Sigma by the rsl and had to shake it about to free the velcro. By exercising it a couple of times this 50 or 60 pound resistance is reduced to insignificant levels. It is really only brand new rigs that have this problem.

Your analysis of a cutaway from a spinning mal does not exactly correspond with the scenarios I am describing. If a super pilotchute is not a problem at terminal why not put a 60 inch pilotchute on your reserves?

[mjosparky 4]

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If a super pilotchute is not a problem at terminal why not put a 60 inch pilotchute on your reserves?

Size?

Sparky

My idea of a fair fight is clubbing baby seals

[diablopilot 2]

Your logic of a large or "super" pilot chute doesn't work.

A larger or "super pilotchute will only produce a harder opening IF it remains connected to the canopy and does not collapse, thus producing a stripping effect.

Your logic assumes that the P/C has a decelerative effect on the jumper prior to linestretch. That just doesn't happen.

Once the canopy is out of the bag, nothing is different, and the speed at which the bag reaches linestretch is not an issue.

----------------------------------------------
You're not as good as you think you are. Seriously.

[billbooth 10]

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Thank you for your reply. This is the first time I have seen your response to those two Sigma accidents and I applologize for any false assumptions I have made. There are two point about wich I am not quite satified.
The report I saw of the Guam accident stated that both risers were released but the RSL was still attached. It is this aspect of the RSL, not the actual skyhook that concerns me. A collapsed drogue/baglock is a very low drag malfunction and the velcro may provide enough resistance to keep one riser attached. I have picked up a Sigma by the rsl and had to shake it about to free the velcro. By exercising it a couple of times this 50 or 60 pound resistance is reduced to insignificant levels. It is really only brand new rigs that have this problem.

Your analysis of a cutaway from a spinning mal does not exactly correspond with the scenarios I am describing. If a super pilotchute is not a problem at terminal why not put a 60 inch pilotchute on your reserves?

When I finally got to look at the Guam rig, the RSL lanyard was was simply lying across its velcro bridle path...the velcro cover was open. I agree with you that some low drag malfunctions will not generate enough force to even open tuck tab riser covers. So I was somewhat surprised to see that this one had indeed opened the riser covers and the velcro bridle path. I suspect that the TM help this process while trying to untangle himself from the mess. This could also explain how all the locking stows (except the bag-lock-stow) came loose. In every other bag lock I've seen, the locking stows were always more or less intact.

You are right, pilot chute size can affect opening shock...mostly on mains where it remains connected, but also on free-bagged reserves. But as I said above, every Skyhook breakaway, from every malfunction we have recorded, takes the same 1/2 second to line stretch. From this I must deduce that exactly the same force is being applied by all malfunctions.

One test jumper, spinning on a tiny main, recorded a VERTICAL velocity of 84 mph just before breakaway...with a normal (quick, but not hard) reserve opening. His body's actual airspeed around the outside of the spin-arc (which is what the canopy would "see" during deployment) must have been well over 100. His canopy, though spinning was "fully open". Yet no bag strip, higher than usual snatch force, or hard opening was noted...and this guy was one of my original Skyhook test jumpers with dozens of Skyhook cutaways...so he knows what "normal" feels like. As I said above, this is somewhat of a mystery, but that is how it seems to work.

No device is perfect, so I cannot promise that a Skyhook will function "perfectly" in every conceivable scenario. However, with 3 years, hundreds of test jumps, and about 2,000 actual rigs in the field...so far so good.

[Freeflysmiley 2]

I'd say you owe the man an apology. Especially cast aspersions,to incidents when the skyhook was not involved.

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Practise the 6 P's!
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[Davew 0]

I think you are wrong. The difference in speed between the canopy at the moment it leaves the bag and the jumper is a critical component of opening shock. It is not the only factor. Slider is a big one. The idea that a freebag rather than an attached pilotchute makes a difference is relevant only to the question of central cell stripping in BASE.

[Davew 0]

Yes I do indeed apologize for any false or misleading allegations. My motive is imrovement of equipment and saving lives. I've seen plenty of carnage and it's a lot worse that chewing the fat over real or imaginary gear problems.
Our DZ has had 2 deaths that may have been saved if the jumpers in question has had skyhooks. It would be great if everyone had one so long as there are so serious side effects.
I still see two problems.
1. The velcro on the Sigma RSL has too much resistance to clear on a low drag mal.
2. The super pilotchute theory. On this one I appear to be the only concerned person in the skydiving world. Let's hope I'm wrong.

[billbooth 10]

2. The super pilotchute theory. On this one I appear to be the only concerned person in the skydiving world. Let's hope I'm wrong.

[DiscoStu 0]

Ok may be I am wrong here but the idea of a super pilot chute at terminal, I just don't get. I am assuming you mean the main being fully open and acting as a super pilot chute on the reserve at terminal. A main has a slider so I don't see how it could be fully infalted at terminal when the reserve gets pulled out by the skyhook. Therefore the superpilot chute at terminal must be the equivilent pilot chute size of the slider. I wouldn't think the drag from the slider would be so excessively greater than that of a pilot chute that it will rip you on opening.

Just my thoughts, I may be wrong.

[RossDagley 0]

It wont rip you up at all - regardless of the reserve pilot chute size (right up to a fully inflated main canopy) the dbag may well left off quicker, linestretch may occur quicker, the canopy may leave the dbag quicker, but the reserve canopy wont *inflate* any quicker - thats dependant on the slider and packjob.

Pretty much the only thing that will happen using the departing main (partially inflated for example) will be the freebag will come off the reserve canopy quicker than with a regular sized pilotchute. Theres absolutely nothing wrong with that.

Remember the super-pilotchute isn't 'attached' to the reserve canopy in the same way as the dbag is attached to the main canopy. It might cause a problem (centre cell stripping) if it were, but its not.

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[billbooth 10]

We've been doing quite a lot of testing with direct bag static line ram air systems for the military lately...many of these tests are done at over 120 mph. In this case, the "super pilot chute" is the aircraft, which I will guarantee you pulls a lot harder than any main parachute could. While opening shocks are often a bit harder than a normal terminal freefall deployment (due mainly to the angle at which the relative wind first hits the canopy), we are not killing people or tearing up canopies.

[RossDagley 0]

Thanks for that Bill - as usual, you're over engineering everything!

[mjosparky 4]

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but the reserve canopy wont *inflate* any quicker - thats dependant on the slider and packjob.

The opening time of a canopy is dependent on the size and design of the slider and the fill time of the canopy. Fill time can be altered by packing but not much. It is mainly dependent on size and design.

Sparky

My idea of a fair fight is clubbing baby seals

[skydiverek 63]

The only "theoretical problem" I can come up with is "slider rebound" theory. What I mean by this is the situation where:

The jumper has a bag-lock. He cuts-away. The SAME moment the main inflates. The now "super pilotchute" pulls/decelleretes the freebag extremely fast. The line stretch is reached. The freebag slides off. At THAT time the reserve pack job is abruptly stopped by the now stretched lines (and accelerated back to the jumpers sped). This jerk discrupts the pack job and makes the slider bounce off the slider stops and travel some inches down the lines BEFORE the inflation. That causes the reserve to inflate faster.

End of scenario.

Any comments

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[RossDagley 0]

but your describing it like the main inflates instantly - it doesn't. as it comes out of the bag, its barely bigger than the slider, which in turn is bearly bigger than the pilotchute.

I just cant picture it being a problem.

[DJL 235]

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...slider rebound theory...Any comments ?

Yup. I saw a peanut stand, heard a rubber band, I saw a needle that winked its eye, I saw a front porch swing, heard a diamond ring...

"I encourage all awesome dangerous behavior." - Jeffro Fincher