re : Jelly Fish oscillation

[Tom Aiello]

Sorry that was so brief (and essentially the e-quivalent of throwing my hands up in the air). You caught me just after I had spent a bunch of time writing that novel I posted in the vented/unvented thread.

Thanks for your thoughts. More please.

I'll try to post more later, but in short, I think that most of the pressurization waves (aka jellyfishing) I've seen have been the result of inherent canopy design.

Is it possible that you got more jellyfishing on one jump because your brakes were deeper on that one? If you jump in a stronger tailwind, your brakes will effectively be "deeper" during deployment, which could lead to jellyfishing as the canopy recovers from a slight deployment stall.

As a side note, in terms of canopy design, the killer mod to reduce jellyfishing appears to be secondary inlets.

[JaapSuter]

Wouldn't airlocks with bottom skin vents... SNIP

Are you talking about nose-airlocks?

I hope so. I'll let you know in another couple months.

Will you be prototyping something soon? What manufacturer is this? Can you elaborate?

Thanks,

Jaap

[Tom Aiello]

Are you talking about nose-airlocks?

Yes.

Can you elaborate?

Not yet.

[SideSwooper]

I'm making an assumption that the jump that you're referring to was possibly the first jump that we made last Sunday by the seaside, before I disappeared off to work.

The canopy certainly did jellyfish, but what concerned me more was the complete end cell closure that required not only releasing the brakes, but a 180 degree turn to inflate.

I suspect that on that 330' cliff, an upright body position would not be a big factor. That is a more appropriate consideration on much lower jumps, with considerably less canopy time (even taking a nice delay, you had loads of canopy time).

I think it may have already been suggested by one considerably more knowledgeable than myself, but I believe what you need for a much fuller flavour on those jumps is a vented canopy.

[Mac]

but I believe what you need for a much fuller flavour on those jumps is a vented canopy.

I have most of my jumps on an unvented canopy and found that there was some days it would jellyfish and others it would not, I cant say I ever really thought alot about it as I always put it down to the winds, brake settings and pulling off the brakes quickly (as most of these jumps were quite low) - I have since got a vented and valved (MDV) canopy and with the few jumps I have with this (only 5 before the **** hit the fan) have not experienced the jellyfishing I was so used to on my unvented - BUT I only took this from 315ft with 2+ sec delays and once from 210ft with a result I am sure you are aware of....... I can certainly rule out jellyfishing as a reason on that result!

With the minimal experience I have on a vented canopy, it only took one jump for me to notice the difference in what I had above my head (although the canopy I had before was not rated as something special) - I can only say that for the types of jumps I was doing (mainly sub300ft, but generally around the 300ft mark) then I would certainly prefer the vented canopy option.........

Saying that, I saw sabre210 have an interesting jump off that cheesy little tike one dark evening (after a perfect jump from myself), and was impressed by his canopy performance that evening, but this may have been down to skill of his fight too........... cheese in the dark anyone? not for me anymore ta!

[jupija]

i got it again... out of last 15 jumps or so i had 3 oscilations. Im getting worried with it... It happend on jumps with and without slider....
What do u think, could lines shrink - some say it can, any additional experoance?

here is the last jelly fish... from one of our newest jumping stuff http://www.skydivingmovies.com/ver2/...n=file&id=2014 and u can also c the second one i had on mexbase-death day boggie (u cant miss it - its the one from another e in mex.)

[Tom Aiello]

Jupija,

What canopy are you using and where are your brakes set?

It looks to me like you are using overly deep brakes on a vented canopy and experiencing a backsurge on opening, which stalls your canopy. The canopy then dives forward to recover from the stall. This could happen erratically if you are right on the edge of stall (especially if you are jumping at a variety of altitudes or temperatures, or in different wind conditions).

You could also be seeing this result from popping the toggles while the canopy is still pressurizing (more likely on an unvented canopy, but still possible with a vented canopy), initiating that forward dive.


Note that this video isn't, at all, what I've previously seen described as "jellyfishing".

[jupija]

[QUOTE=Tom Aiello]
What canopy are you using -- MOJO 220(no vents, and valves)

till this year i really didnt have any probl. with my brake setting, i had it made shorter, and i didnt get any weight, well maybe 2 kg.

and i poped the togles when i realised im falling bacwards, maybe i should not reacted as fast as i did, couse after deblockinthe brakes i imidiatly lift my arms ahead...

/QUOTE]
so what do u say about possibility that lines would get shorter

[Tom Aiello]

It is possible for your lines to shrink over time. To what extent this will actually effect the openings, I'm uncertain.

Have you tested for riser responsiveness? In other words if you try to initiate a hard riser turn immediately after opening, does the canopy stall (or, as it should, turn)? Of course, do this off a span, with plenty of altitude underneath you.

[sabre210]

Jupija

Interesting video but like Tom says, this isn't the Jellyfishing i believe we were thinking of. This definitely behaves like a canopy in a brief stall and then surging forward upon release of the brakes. The jellyfishing in question actually occurs to the canopy as it flies forward. Imagine a big strawberry flavoured jelly (jello) in the shape of a canopy (orange will do but definitely not blackcurrent). Take a large wooden spoon and twat it on the nose. Now watch as the shock wave ripples from front to back then back to the front, sometimes repeating the cycle. That's the general idea. Now take a spoon and some custard or whipped cream.....

ian

[jupija]

got it. It slike, let say just hipotethical situation, if u r banging a bit fatt lady from behind and when all does wrinkels r mnoving front .

[SideSwooper]

got it. It slike, let say just hipotethical situation, if u r banging a bit fatt lady from behind and when all does wrinkels r mnoving front .

That's it!

Although a Jelly Fish oscillation lady is considerably more fun, as long as your friends don't see it.

[Faber]

to me the video looks like too deep brakesettings resulting in a stall,poping the toogle and raise the hands(full speed) you´ll get the surge just after the stall.. but im not novice in this just saying what i think it looks like..

[sabre210]

got it. It slike, let say just hipotethical situation, if u r banging a bit fatt lady from behind and when all does wrinkels r mnoving front .

I like your style mate. That's precisely what it looks like.

ian