Pie Slice Pilotchutes

[base689 0]

> That's the way my specially designed 49 inch pilot chute works. Very stiff tapes to cause it spring open
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Would you mind posting (or PM) pictures and/or drawings of that special PC, please?

Stay safe out there
Blue Skies and Soft Walls
BASE #689 - base_689AT_NO_123_SPAMyahoo.com

[luv2fly 0]

There's an interesting physics problem: double pendulum. "A double pendulum is a pendulum with another pendulum attached to its end, and is a simple physical system that exhibits rich dynamic behavior. Above a certain energy its motion is chaotic."
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This is great! I think Yuri is on to something here. So to reduce the double pendulum, wouldn't it be beneficial to find a way to reduce the top pendulum (i.e. the PC) from oscillating? Of course it would! Imagine all the deaths/injureis/bruised egos that may have been prevented if this damn oscillation were to stop!

The best way to stop the oscillation can be summed up in one letter and three numbers - F111. Hello!

No need to be afraid of a little porosity

[d_goldsmith 1]

Hmm. I can tell you put a lot of thaught in to that.

[hookitt 0]

As did you. He's right actually. F-111 made pilot chutes are more stable than their ZP counterparts.

My grammar sometimes resembles that of magnetic refrigerator poetry... Ghetto

[d_goldsmith 1]

I was mainly replying to "No need to be afraid of a little porosity".

Don't you get drastically more pull force from ZP. Would you have to use a 60" F111 PC to compare to a ZP46" pull force, even if it's vented.

I'm pretty sure I have heard other benefits to ZP as well.

[crwper 7]

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I'm pretty sure I have heard other benefits to ZP as well.

The problem with going to F111 is that you gain some porosity, which makes the pilot chute more stable, but at the same time it also produces less drag. An F111 pilot chute is not optimal because it's letting air through everywhere. A better design would be a pilot chute whose porosity is controlled so that it produces a maximum of drag, but also lets air through in just the right places to stabilize. That's the idea behind a zero-p pilot chute with an annular vent.

Michael

[luv2fly 0]

lets see....
many thousands of jumps under study...hundreds of jumps of personal experience using F111...and I'm still here! Never had an object strike attributed to F111 pc. Problem is nobody has adapted it because of this fallible fear of "unwanted freefall." F111 is bulletproof! Can be evidenced by a 36 F111 I sold (it had 100+ jumps before I got it and jumped it for about 100 jumps and numerous counts of water exposure). It is fear that causes oscillation and thus death

THE DEATH MONGER

[crwper 7]

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many thousands of jumps under study...hundreds of jumps of personal experience using F111...and I'm still here!

I'm certainly not saying using an F111 pilot chute will kill you. I use them, too. I'm just saying better solutions are possible.

Michael

[tr027 0]

How about a hybrid PC with both fabrics, ideally combined in a way to capture the benefits of both? Perhaps an inner circle of ZP and outer circle of F111? Just throwing ideas out there.

"The evil of the world is made possible by nothing but the sanction you give it. " -John Galt from Atlas Shrugged, 1957

[yuri_base 1]

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but then again, its not really a double pendulum system until linestretch, is it?

You're right, until linestretch it's more like a single pendulum with the suspension point (PC) able to oscillate due to feedback from the suspended weight (canopy).

When the suspension point moves with the frequency equal to the natural frequency of the pendulum, a resonance occurs. The system begins to oscillate with high amplitude.

The period of oscillations of a L=9ft. pendulum is T = 2*Pi*sqrt(L/g) = 2*3.14*sqrt(9/32) = 3.3s.

What frequency the PC oscillates at? Although it's more chaotic motion rather than harmonic oscillation, it still has some characteristic frequencies. They depend on airspeed, size, construction, etc. If the PC oscillates with the period of 3.3s, then we have resonant coupling between the PC and the canopy, which can cause an offheading.

If we can make the PC oscillate slower than the canopy does - slower than 3.3s - than this energetic coupling will be broken and onheading performance will improve.

One way to make the PC oscillate slower is to use a vented PC. It inreases the "effective mass" of the PC and slows down the latteral motion.

Will a longer bridle make the PC oscillations slower? Yes, but the canopy oscillation will be proportionally slower, too, so it won't kill the resonance, although the onset of resonant oscillations will be slower and the canopy will twist less.

Anyone have experience using substantially longer bridles, e.g. 15ft?

Android+Wear/iOS/Windows apps:
L/D Vario, Smart Altimeter, Rockdrop Pro, Wingsuit FAP
iOS only: L/D Magic
Windows only: WS Studio

[base935 0]

Don't we all at least agree that there is a lot of improvement that we can find with current pilot chutes? And PCs are a current weak link to a relatively solid modern setup?

Gravity Research Institute

[avenfoto 0]

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Anyone have experience using substantially longer bridles, e.g. 15ft?

ask the real yuri base... or do some more equations

[460 0]

Yuri (outrager) used to use a 25 foot bridle! There are more potential problems with this setup than there are advantages.

Looks like a death sandwich without the bread - Steve Deadman Morrell, BASE 174

[TomAiello 25]

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Don't you get drastically more pull force from ZP.

No, I don't think so.

Properly made F-111 and ZP PC's will exert almost exactly the same drag force. The air has to vent out of both of them--it just vents out differently. With an F-111 PC, it vents out through the skin of the PC. With a ZP PC, it vents around the skin of the PC (over the skirt or through the vents).

I once took a couple of F-111 and ZP PC's and tested this (I had doubted that it was true when Anne Helliwell told it to me), and it really did turn out this way when I drag tested them with spring scales.

-- Tom Aiello

[email protected]
SnakeRiverBASE.com

[RayLosli 11]

" Don't WE ALL Agree " - The PC is the Current WEAK LINK. to a relatively solid modern setup?
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NO, WTF , have you not been reading what I wrote ? I am just to tired tonight to get into this Biggest conceived piles of shit tonight & one of the most fucked-up statement I have ever read. so I will stop this right there.

"Fact" The Pilot-Chute is one of the MOST reliable things that ALWAYS Works. Next to. The Canopy will ALWAYS Inflate after extraction.
You might want to re-think and get back to the Web. BASE jumping in a few years.
(just my opinion) There is NOT Ever to be a huge breakthrough in PC's like the perfect magical Sky-Hook. There is not much more improvement left you Can & Will do to the modern BASE PC. The only thing left to be done is small refinements in design. That will maximize and capture what little efficiency is left in drag and balance of movement.
The Pilot-Chute is not the weak-link, the most important thing, the biggest key piece of equipment, The one thing to FEAR the most in BASE. All PC's now & in the future. Will work and Look and Act just like the PC you though out into the Air yesterday. All a PC has to do is One-Short-Quick-Job. To pull-open and Drag-Out a big pile of fabric to inflate in a half-assed orderly fashon. After that it is up to the Pilot, "YOU" the BASE jumper to do his/her job.
.
Some of the BEST Pilot-Chutes I got. Are the oldest & most used over my life. I have a firm belief that all New pilot-chutes must be broke-in. Life of the PC does not start on the first Pitch after it leaves the Loft. They must be used and forced to form and take shape after they come off the Sewing Machines. Thread and fabric weave must be slowly forced to take shape/stretch to a flowing end result over some PC packing & free-falls. After you get some jumps on the PC then you can judge how it tows and feels. Its got to be broke-in SLOW. You got to get to know them.
Don't be Scared. Take some slow quality time & Have a long and lasting relationship over many years with your PC. ...
.
.

[DexterBase 0]

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Don't be Scared. Take some slow quality time & Have a long and lasting relationship over many years with your PC.

Holy hell, Ray... You finally lost it.

Come visit us down here and we can arrange some... therapy. Lots of cool objects to play with.[;)

[base689 0]

> You're right, until linestretch it's more like a single pendulum
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No. You are wrong. BEFORE line stretch there no pendulum nor anything else. BEFORE line stretch there is no physical connection between jumper and parachute. BEFORE line stretch, non-stretched-lines CANNOT and DO NOT transmitt anything, nor forces nor movement nor momentum nor anything else. BEFORE line stretch, parachute is "simply" a piece of cloth trailing up there, completely indipendent from jumper's body.
Immediately after line stretch, I agree that exist two pendulums, parachute (through stretched lines) transmits forces to jumper etc etc.

Stay safe out there
Blue Skies and Soft Walls
BASE #689 - base_689AT_NO_123_SPAMyahoo.com

[gweeks 1]

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> You're right, until linestretch it's more like a single pendulum
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No. You are wrong. BEFORE line stretch there no pendulum nor anything else.

What about bridle stretch? As soon as the pilot chute reaches bridle stretch the system seems like a single pendulum until line stretch when it becomes a double pendulum. Especially when you watch some bridge day videos of a dbag coming out.

[katzurki 0]

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The period of oscillations of a L=9ft. pendulum is T = 2*Pi*sqrt(L/g) = 2*3.14*sqrt(9/32) = 3.3s.

Nerd.

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Anyone have experience using substantially longer bridles, e.g. 15ft?

One unfortunate person did, see the list.

[RayLosli 11]

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Don't be Scared. Take some slow quality time & Have a long and lasting relationship over many years with your PC.

Holy hell, Ray... You finally lost it.

Come visit us down here and we can arrange some... therapy. Lots of cool objects to play with.[;)

-
What ? . you don't talk to your pilot-chute ? I know your smarter than that.
I suppose next you will be telling you don't have an intimate understanding and long-tem relationship with any working mechanical BASE component in Either Hardware or Fabric ?
No relationship what so ever in the way that each mechanical part works and interact with each other. As well as the way those parts treat and interact with you on any given BASE jump ?
.
.

[outrager 6]

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Yuri (outrager) used to use a 25 foot bridle! There are more potential problems with this setup than there are advantages.

Huh? I don't recall anything THAT long, even though some of the gear of my first couple of years was rather interesting
bsbd!

Yuri.

[RayLosli 11]

Don't worry. That is his usual response. He has many days-weeks that he can not remember and account for.
short-term memory loss.. 'cough cough' buzzzzzzzzzzzzzzzzz. .....
.
.

[Bernt 0]

I just don't get it… Why should we settle and believe that the PC cannot be improved?!?
Of course, jumper skills are more important than improving the PC, but why not improve the PC if possible??

The parameters we have to play with are atleast these:
Porosity of the topskin fabric (F-111/ZP), vents, diameter of topskin vs. diameter of mesh.

We need some facts on the table, and I don't have enough jumps to know, so to you with experience on this:
1. At what airspeeds does the oscillation mostly occur? 0-2s? 2-4s? 4-7s? 7+s? Let's pick the corresponding size(s) PC and experiment with that one.
2. I think what Tom Aiello said about the drag of F-111 vs. ZP is very interesting. Anyone want to measure the drag at various windspeeds for similarly sized F-111 and vented ZP PC's? If F-111 really makes a more stable PC, then this would be one of the first things to find out.

[outrager 6]

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Don't worry. That is his usual response. He has many days-weeks that he can not remember and account for.

How do you know??? I don't seem to remember you...

bsbd!

Yuri.

[wwarped 0]

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I just don't get it… Why should we settle and believe that the PC cannot be improved?!?

hmmm...
what problems do you want corrected?

at some point in becomes a cost/benefit situation.
what knarly situation exists such that you want to pay 3x as much to correct?

(every additional seam on a pc can create dissymmetry and consequent oscillation.)

so what needs fixing? are they too expensive?
please define a problem to solve before requesting facts.

DON'T PANIC
The lies in learning how to throw yourself at the ground and miss.
sloppy habits -> sloppy jumps -> injury or worse