F111 vs ZP Pilot chute

[ftaba1 0]

I saw it at several dealer's sites that manufacturers recommend to use pilot chutes made of F111 fabric. I know for sure that Sun Path doesn't make pilot chutes of zeroP fabric for Javelins (even kill-line collapsible). The questions is what is wrong with ZP pilot chutes? As far as I understand they last longer and they are smaller in size.
Any thoughts?

[lazerq3 0]

I am by no means an expert on this but I am thinking along the lines of F-111 conapies compared to zp. Zp's slip through the air easily for, so if you think of that in terms of a pilot chute, that chutes soul purpose is to deploy your main canopy. Thats the last thing I think I would want to be "slipping" through the air. Where F-111 will grab the air and get your main out quick. I dont know I'am I wrong in this thinking?
jason

[Geoff 0]

One argument is simply that ZP is more slippery, and so potentially has more chance of a premature deployment (slipping out of the pouch when knocked or pulled).
Personally I don't really buy that - a more slippery PC is more likely to be pulled out by a flapping bridle and so less likely to result in a horseshoe mal. I'd prefer a premature to a horseshoe so that's a good thing in my book.
I know BASE jumpers don't like ZP PCs - apparently the lack of porosity makes the PC more likely to 'potato chip' and hesitate - but that only applies at VERY low air speeds, and doesn't apply to skydiving, even hopnpops.
Mirage rigs come with ZP PC as standard, I think (certainly at least an option).
Geoff

[SkymonkeyONE 4]

I own a bunch of both. There is no real reason not to have a ZP pilot chute. They last longer and you can get away with jumping a smaller one than a similar-drag F-111 variety. A ZP pilot chute has a higher snatch force than an F-111 one and as such makes a parachute open harder, assuming you are jumping a standard size pilot chute. That is obviously something you would want to avoid on an already-hard opening main. Jim Cazer is now making zero-p pilot chutes as small as 22". I jump one of those on my Cobalt 75 and it works fine.
Chuck

[DBTECH 0]

An excerpt from my "yet to be published" article, entitled--
Fast openings/Slow openings--The Real Physics of slider rebound; plus invention revealed.
(Patent Pending) By David B. Brownell
An excerpt from that article--
Another way to reduce snatch force energy and the evils resulting from it, is to go with a smaller pilot chute.
A smaller pilot chute will result in the bagged canopy reaching a slower speed relative to the jumper at last line stow release* This slower speed will result in lower slider stop line rebound energy. A smaller pilot chute will also lessen the chance of line dump.
How much smaller do you ask? Well now; I'm jumping an Atair Cobalt 135 with a 21" zero porosity (ZP) pilot chute that I made. I'm sure that this scares many of you, but please listen to my logic here. Back a few years ago we were jumping canopies that weighed eight to twelve pounds. Many of the pilot chutes used then were 30" to 32" made of F-111 fabric. If we were to go with a canopy of half the weight, say five to six pounds, "logic" should tell us that we would need a pilot chute of half the area with approximately half the drag; which, in my mind, is true. For those of you that are thinking a square function, that only applies to airspeed changes, not area changes. A 21" pilot chute has half the area and approximately half the drag of a 30" pilot chute. Also, don't forget that we are talking here about an F-111 pilot chute that degrades with use. A ZP pilot chute would not degrade. Based on the above factors and testing I have done in the field, I believe that we can go with pilot chutes made with ZP fabric under 21" for canopies under six pounds.
Dave Brownell

[ftaba1 0]

OK guys, thanks for the inputs. Now after Dave touched the subject of PC sizes here is another question. I want to buy a ZP pilot chute for a 149 sq. ft. main. What brand and size should I get? There are quite a bit of them on the market nowadays.
Blue skies, safe swoops!
Anton

[DBTECH 0]

For your reference--
This same 21" ZP PC was used on a Spectre 170 for 295 jumps with no problem, before it was put on my Cobalt 135.
Dave Brownell

[cobaltdan 0]

at the ccs boogies a few months ago i spoke to derek (sun path) and took exception to their policy of no zp pilots as well as their sizing.
when i asked why are you dead against zp-pilots derek gave me several reasons:
1)-zp pilots pull more and therefore will create wear and tear on your canopy.
2)-because zp material does not leak air the pilot will fill up and then air must spill over the lip causing instability.
i replied that 1) a zp pilot can pull with however much force you like. size it properly. this is definately not a valid an issue. as to 2) by the same logic zp canopies should be unstable...this is false and easily tested....and we already did:
we had pilots manufactured for us in 28", 24", 22", & 20" by jim cazer. we tested them with a digital load sensor/data logger and threw them out of a pickup truck at 70mph. we collected data on the force vs time and graphed it later on a computer. from performing these tests i got to watch the deployment of many pilot chutes, dozens of times. zp pilots are not unstable and do not waffle.
as a result this testing and other testing measuring opening shock on canopies we recommend very different pilots then sunpath. do not get me wrong i love javelins, i have jumped one since i became a skydiver, but their opinions on pilot chutes are wrong and based on wives tales, not one bit of scientific theory or testing.
my javelin rs (smallest javelin made) came stock with a 30" pilot. this is not right. this container fits a maximum of a 95 sq ' canopy. and yet you get the same pilot as you would use for a canoipy more than double the size and weight. on a graph of opening shock you see a peak from your pilot chute then your canopy. the peak with this stock javelin pilot is as high as the peak caused by stage 1 of a cobalt 95 deploying. the opening shock that pilots were noticing was from the pilot chute snag instead of the canopy. we recommend a 22" zero-p which is almost 100% less surface area than the stock javelin pilot.
when i pointed out the scientific testing we performed and showed graphs on our laptop to derek he responded well then it is dangerous to use smaller pilots because they will be loose in your spandex pocket.
...make smaller pockets....
and if anyone is switching to a smaller pilot have your rigger modify your pouch if it is too loose.
(you can also pack your pilot mesh out as it creats more friction on the spandex, but best to have a proper fitting pouch).
sincerely,
dan
atair

[Krishan 0]

Dan, I have a 26" Mirage factory pc that came with my mirage. I'll be jumping a 150 when I get it, what do you think as far as that size? Should I look for a smaller pc? I have had many hard openings that I thought were due to my sabre, but now I have doubts.
blues

[Geoff 0]

I'm not Dan, but here goes....
I also have a Mirage with the standard ZP PC, and I've jumped 3 different mains in it - Sabre 135 (100 jumps), Spectre 135 (50 jumps), Safire 129 (150 jumps).
The Sabre opened generally hard (once VERY hard) until I fitted a bigger slider.
The Spectre always opened VERY gently.
The Safire always opens gently - not quite as soft as the Spectre, but NEVER too hard.
Your PC may play some part in your hard openings, but I'd place most of the blame on the Sabre.
If the 150 you mention is also a Sabre, and opens hard, I'd strongly recommend you get a larger or 'pocket' slider - ask your rigger or PD for details. I'm sure this will have more effect than a smaller PC.
Hope this helps,
Geoff

[pyke 0]

since we're on the topic...
would a zp p/c cause a F111 to open more harshly than a F111 p/c? I have noticed since changing p/cs that my openings have been a little harsh (could also have something to do with the fact that I am jumping a converted reserve, but still)
Anyone got any sugg's??
Kahurangi e Mahearangi,
Pyke
NZPF A - 2584

[cobaltdan 0]

i agree with geoff.
the pc is just one variable. some parachutes by sake of their design variables definately open harder than others.....although i kind of view pocketed sliders as a fudge fix for a hard opening canopy. better to design the canopy so that it opens with acceptable force..... (don't mind me, i am biased towards sabres as i broke my neck on opening while jumping one.)
anyway on cobalts our pc recommendations are as follows:
170: 24" jim caser zero-p collapsable pc
150: 22-24" """"""
135 and smaller: 22" """"""
currently we are testing 20" pc for use with our 65-85 but at present we still recommend the 22" as we have tested that size thoroughly..
sincerely,
dan
atair

[weid14 0]

Dan, is that data available for public veiwing - on your website maybe? I'm curious to see it (not to disagree with it, I truely am interested). Also, did you do a literature search on the same topic, what did you find, did your results correlate with previous ones? There is urban myth surronding many things in our sport, it is good to see some science (data) behind designs/theories/.

[cobaltdan 0]

yes, we intend to post tons of data on our web site.
we just hired a new programer to update and expand our site. (this has been a huge sore point as we have strugled with several programers over the last 8 months and our flash forms still do not work the way we want).
as far as published papers on pc testing. i do not know of any.
sincerely,
dan
atair