"terminal snivel" (technical)

[peek 21]

My comments here are a result of reading a few messages about someone's AAD firing after a canopy sniveled too long (or they pulled too low considering how long it normally takes for their canopy to open.)

We want our canopies to snivel for a certain amount of time so that they don't just open right away and slam us. You know, the old "force = velocity squared" formula, meaning that the slower you can make you and your canopy go just before inflation (canopy _spreading_), the more comfortable your opening.

Due to lack of understanding, I find that skydivers seem to latch on to an idea, and then go overboard on it, for example, they think that the longer their canopy snivels, the better their opening.

Well, only up to a point.

Actually, once we and our canopy reach an equilibrium, or what I would propose we call "terminal snivel", that waiting any longer for our canopy to open is a waste of time and altitude, (and could actually be dangerous too, couldn't it?). It is simply time that our canopy can use to misbehave and possibly fly itself into a turn or something.

I hear Tandem instructors in particular saying how cool it is for a canopy to snivel so long and give them a great opening, but when I jump the same canopy, I can tell that I have reached "terminal snivel" long before canopy spreading, and then have to wait and watch the damn thing start dancing, turning one way, then (thank goodness usually) turning the other way.

(By the way, how can I tell, you ask? Good question. If one is in tune with their canopy opening sequence they can feel the equilibrium by the stabilization of G forces in their harness.)

Note:
Only canopies noted for their slow opening will ever reach terminal snivel and allow you to feel this. Most canopies begin spreading before terminal snivel, (but still open slow enough to be comfortable.)

[Amazon 7]

I pack my canopy to snivel. I can certainly tell the difference when it takes just a little longer to open and I am watching it when it starts doing this slower than normal opening thing. I like it the way it is

I used to flatpack and freepack a Parafoil for a more positive opening and it would STILL snivel for way to long and then EXPLODE OPEN. It was so hard opening that about every ten jumps it would blow a steering line. That was after taking it out of the Bag that came with it . It had the BIG pilot chute and spider slider that came with it to supposedly retard the opening. It used to snivel/streamer so much that it would scare people on the ground. I only had to cut it away once. It had streamered for long enough to get me under 1500 ft when I chopped. I had deployed about 3k on that jump. but I could tell this was one to get rid of and had watched it loing enough.

I love the opening my Triathalon gives me now. I can live with it.
Amazon

[ThighMan 5]

When I had my Saber 170, I packed it to snivel. I could make it snivel from between 600 and 1000 feet. I would grab (softly) my risers and watch it open while glancing around to see if anyone was near. When I moved down to my old Samurai 150, I packed it to snivel also. Nice and slow and on heading. The same for my Samurai 136. Pack it so I won't have that "SLAM or SPANKING" on opening. So long as it is seeking a opening, I leave it alone. I have actually kicked out of line twist while it was still opening. Of course, I also kicked into more because I went the wrong way. But, I love the long openings and plan on keeping it up.

Airborne
Blue Skies, No Wind
Feet and Knees Together

[mikeat10500 12]

Quote

My comments here are a result of reading a few messages about someone's AAD firing after a canopy sniveled too long (or they pulled too low considering how long it normally takes for their canopy to open.)

Most of the old trash canopies I've jumped...opened slow, most of the new hot rods I've jumped...opened slow, almost all canopies can all will snivel at one time or another.
Now if I was jumping with an AAD that might fire as high as a grand, and a main that might eat up as much as a grand opening... I would set my main activation alt at 3000' and reserve at 2000'(if main deployment has not begun by that time). When I borrow someones fast little main, it usually comes complete w/AAD (turned on)and square reserve. I have tried to move my own pull alt's up to meet the
requirements of all the equipment I may jump. It's easy to do 'cause everyone else is braking off and pulling higher these days.
....mike

-----------------------------------
Mike Wheadon B-3715,HEMP#1
Higher Expectations for Modern Parachutists.

[billvon 3,107]

If you take a pigeon and train it to push a button when it hears a bell to get a pellet of food, it will soon learn to push the button when it hears the bell. You can even train pigeons to land on perches, walk in circles, peck at things etc in the same way.

A while back someone did an experiment. They started training pigeons this way, then started randomizing everything. They'd just randomly feed them, ring bells, etc. And rather than just realizing that they're going to get fed anyway, the pigeons started some really bizarre ritualistic behaviors, like running in circles, pecking at things in a certain order etc. They would do them, and get fed (because they _always_ get fed eventually) and that would reinforce the bizarre behavior.

I think we sometimes do the same things with our packing techniques. There are a few basic rules you have to follow - the lines have to be near the center, the slider has to be at the stops, the canopy has to come out of the bag. A lot of the packing tricks we do simply help that to happen; wrapping the tail helps control the slider and lines if done correctly.

A lot of the other things are a bit ritualistic, I think. Thinking that rolling the nose more tightly will change a 400 foot opening to a 700 foot opening doesn't make a lot of sense, for example. Just look at the video of any opening canopy. 10 milliseconds after it's out of the bag, all that careful work is gone. The wind has taken that neat pack job and turned it into a chaotic mess of flapping fabric.

I think what happens very often is that, when we start packing, we get slammed a few times because we don't stow lines well, or let the slider creep down. So we start trying tricks, like sticking the sides of the nose into the center cell (an old favorite to slow down Sabres.) Then, one day, we get more control over the pack job and the slider doesn't move down the lines any more. We get softer openings. Our conclusion - that rolling the nose thing really works!

This isn't to say that we don't have to worry about packing, because there's a lot to doing it well. But I think that a lot of the tricks we hear about when it comes to packing are more ritualistic than real.

[nightjumps 1]

Quote

Actually, once we and our canopy reach an equilibrium, or what I would propose we call "terminal snivel", that waiting any longer for our canopy to open is a waste of time and altitude, (and could actually be dangerous too, couldn't it?). It is simply time that our canopy can use to misbehave and possibly fly itself into a turn or something.

Perhaps I'm too old school. After purchasing a canopy, I "learn" my canopy's "opening characteristics" (by opening high several times), I simply do a count (one thousand, two thousand, three thousand...) every time I pitch out.

Open religously at 3,000 and count - on my current canopy, its a six thousand count for ~800'. If I get to eight thousand... its gone. No sense getting near AAD altitude.

[John4455 0]

I hear Tandem instructors in particular saying how cool it is for a canopy to snivel so long and give them a great opening, but when I jump the same canopy, I can tell that I have reached "terminal snivel" long before canopy spreading, and then have to wait and watch the damn thing start dancing, turning one way, then (thank goodness usually) turning the other way.

I've seen tandems snivel for 2000ft. I'll just watch it. keep an eye on my students hands and watch my altitude, thinking okay, any day now.

How do ya like it Johnny?

[d604 0]

Reading this has reminded me…
You know it has always amassed me to here a skydiver after an extra long snivel say, “I knew it was going to open, every thing was looking good...” meanwhile their audible is flat lining at 1500’. I always try to convince these jumpers that they didn’t really know what was going to happen. Sure there is a good chance the slider will come down, but are you sure it will be flying correctly you just don’t know, now its probably too late to deal with it safely.

Don’t be afraid to hit the handles, your reserve isn’t your last chance its your best chance!

Sean

[b1jercat 0]

Ya, what billvon said!

[nightjumps 1]

Quote

Don’t be afraid to hit the handles, your reserve isn’t your last chance its your best chance!

I really, really, REALLY like this. You'll forgive if I steal it for training purposes.

[Deleted 0]

Isn't it possible that some canopies snivel a safe amount of time for one instructor, but longer for another? An experienced base jumper told me that the bigger the canopy(i.e., wing loading) the faster the opening. Perhaps you need a larger canopy? Would this make a difference?

[PhreeZone 20]

Openings are based on a lot of things, shape of the nose, shape and size of the slider, trim angle, taper of the nose, break settings....

Size really does'nt have much to do with it.

Snivel is only safe as long as the jumper and the canopy decellerate at the same rate, if they have equaled out then the canopy needs to continue opening, not just sit there and dance.

Yesterday is history
And tomorrow is a mystery

Parachutemanuals.com

[Deleted 0]

And you get your info from...? Size does make a difference. It can affect the snivel...the snatch force...I play with a lot of canopies just to check things out.A heavier loaded canopy can open slower, as a rule of thumb, particularly if it is known to snivel anyway.

[billvon 3,107]

>Size does make a difference.

I agree, but the main thing there (I think) is that larger canopies are generally jumped by larger jumpers; larger jumpers fall faster and even the exact same opening (in terms of time to fully open) feels harder to someone falling faster; they have to decelerate more.

I also agree that the exact same system may give you different openings on two different canopies. A 32" PC may work fine for that Tri-220 but cause problems on a Stiletto 120.

[andy2 0]

[QUOTE] >Size does make a difference. [/QUOTE]

Ok, was looking for an oppurtunity to ask this question. Does wingloading effect opening strength? I was trying to figure it out in my head as I dozed off last night, and I came up with good reasons that a big canopy would open hard on a light person, and alternately why a small canopy would open hard. Given the same characteristics, model, and packjob (I know impossible, just hypothetically) which would open harder? A .75 WL, or a 1.25 WL?

---------------------------------------------
let my inspiration flow,
in token rhyme suggesting rhythm...

[AggieDave 6]

Those Sigma Tandem canopies are pretty big (370) and loaded pretty lightly...and I can pack those to take over 1000ft to open.

What's your point again?

--"When I die, may I be surrounded by scattered chrome and burning gasoline."

[billvon 3,107]

>Does wingloading effect opening strength?

Aside from the effect I mentioned above (heavy people have harder openings) I think it completely depends on the canopy. I've had very soft openings under 400 sq ft tandem canopies, and nasty slammers under 120 sq ft Sabre 1's.

[jerm 0]

Quote

When I moved down to my old Samurai 150, I packed it to snivel also. Nice and slow and on heading. The same for my Samurai 136. Pack it so I won't have that "SLAM or SPANKING" on opening. .

i really think it has more to do with the canopy..... i've had 1 "snappy" opening on my samurai in over 400 jumps and even that was not what i would consider "hard"

leave the nose open and not pushed in all you like.. it'll still open nicely.

YMMV, of course... but this is what i've heard from most every samurai pilot i've spoken to -- they just open great, now matter how badly i pack it

Landing without injury is not necessarily evidence that you didn't fuck up... it just means you got away with it this time