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I have seen multiple jumps of people jumping a 42" PC from 330' to as low as 230' with very good results. Both stowed and hand held. Yet, every base manufacture says that you need a 48"/46". After seeing the success of a 42" from those varying altitudes with varied delays as well; my question is why not use the 42" everytime? Especially when going stowed from those lower altitudes. To me is makes more sense to use a 42". It is easier to go stowed and there is less material to open up and grab air. What some other jumpers thoughts on this?

Bryan Ody

what is relevant is not the height of an object but the planned delay. 46" and 48" will pull your canopy out a little faster at 0-2 sec delay. canopy size is a factor as well. i would not jump 230 with 42. no way

well as I stated. The jumps I have seen are with varying delays. From half a second to 2 seconds. Obviously 2 seconds is good for a 42". I have seen the 42" work just as well as a 46/48" on a half second and second delays. Wouldn't there be a less chance of pilot chute hesitation with going stowed with a 42 instead of stowed with a 46/48 on shorted delays?

Bryan Ody

I have very little knowledge, but seems to me stowing a 48 might not be a very good idea.

Whattup Ody?
I can imagine the results would differ between pin rigs and velcro, as it takes a stronger force to remove velcro than to pop your pins.(I imagine there would be a heigher snatch force with a larger PC.)
>"I have seen multiple jumps of people jumping a 42" PC from 330' to as low as 230' with very good results."
~could you notice wether they were open 10,15,or 20 feet heigher with a larger PC or not?
~were they jumping pins or velcro?
....A false sense of security is better than nuthin' at all, I like my 46"
~J

I have multiple 48" stoved ones, even from 330ft , if i have had bad landingarea or something else that i have to had be extra carefull....no problem. ever. we have even compared openings with couple of friends to 42" from same spot. 42" IS SLOWER, in 0-1 delays, as 1-2 delays...
say what you want...but thats in the video

Is that a STANDARD 42" PC?

(Just answer yes or no please.)

Yo Pete !

How many really is you "multiple" stowed 48's from 330ft ? Do you really have hard comparison on video where you can clearly show that when going for a 2 sec stowed delay with 48 or 42 the one going with 48 will be open constantly higher ? With same canopy, same PC's etc ? If so I'd really be interested in seeing that video.

for example in Budapest with Tony. i had 48" all the time...Stowed...Tony had 42"....not with the same canopy but still...as you know...

Chad,

The 230 was NOT a standard PC. The rest was WITH a standard PC.

Bryan Ody

Yeah I know but my point was that when jumping a 200 jump mojo and your new and crispy MDV Troll there probably are some other variables as well as PC size that are contributing to differences in opening alti with same delay. I wouldn't start drawing any conclusions about PC size and opening alti based on few jumps in Buda where variables affecting to that alti were very different.

In Buda I jumped with OLD troll, no vents... :)

Also in Russia, Alor setar Malaysia, US, Belgium....want some more ??

Dude, I only want the video where it clearly shows that for example on a 2s delay with all variables been equal a jumper with 48" will be open significantly higher than the jumper with 42".

previous post on same subject....

http://www.dropzone.com/...rum.cgi?post=1079722

... maybe you have a 310 on your back?

but kidding aside, I know of a good few people (myself included) who have used a 42 down to the 200ishft mark (dependant on other factors like closure method / canopy size / how the head felt etc),

if you do a, search on DeeZee and BLiNC, you should find some good responses, as this has had some good and thoughtful discussions before.

Dwains writings explains a lot. thanks man.

funny shit is that 2 years ago we had a talk about this?
well i still jump the same way.. and i havnt died or got hurt from it yet

just a note i have a 48´but its broken,actualy i only used it once and it were on a SL jump as a back up

today my biggest pc is a 46´AV ZP ,floowed by a unvented 45´zp(only used on SL´s) then i have my work horse 42´av zp i also have a 38´av zp but i only use that whith a slider,so its aa bit dusty i guess

Mac,welcome back online,Mister BASE pink hat mincer #1
Also welcome back jumping below 300 you owe me a pint and it aint going to be a stella...

A few thoughts about PC inflation:

When you toss your PC, it has to do two things.

1) Inflate itself
2) Pull--opening the container and moving the canopy to line stretch.

These two functions are both essential to the role of the PC in the parachute deployment, but they are different things, and are influenced by different factors. Some of these factors overlap, some have no effect on the others, and some actually work against each other.

Note also that:

(a) a PC must (1) inflate, prior to (2) pulling, and;
(b) (1) inflation is fairly complex, and subject to far more variation than (2) pull


The most important characteristic of (1) inflation is not top speed. It's consistency. It matters little if you can make the PC fully inflate in 2 feet on 1 jump in 100, if the second jump it takes 200 feet. Far better to have it inflated in 10 feet on every single jump. (These numbers are obviously just made up for purposes of illustration.)



(1) What can impact inflation?

(a) Presentation: The biggest determinant of time to PC inflation is the manner in which it is presented to the airflow. If you toss a tightly wadded, inside out PC into the air, it will likely hesitate noticeably, if it inflates at all. If you pre-inflate the PC by holding it at the bridle attachment point and "lofting" it into the air, it will already be mostly inflated and will likely reach full inflation and begin pulling almost immediately. There are numerous small steps between these states, and lots of debate about various folding methods, which I won't go into here. But the bottom line appears to be that more you can present the PC in the correct orientation, and the fewer folds you put into it, the quicker it will become inflated, and more importantly the more consistent the inflation will be (meaning that it will inflate in approximately the same time in repeated pitches).

(b) Air speed: Faster air will inflate a PC faster, and more consistently.

(c) PC construction: PC's of different designs experience variance in inflation, most importantly with regard to consistency of inflation. Without delving too deeply into various construction features of pilot chutes, note that features impacting inflation include (a) fabric used (so much so that a set of PC's were recalled from one fabric lot), (b) weight on the apex (handles or caps), (c) reinforcement tapes and the ability of the PC to maintain it's shape under load, and (d) wear of the PC itself.

(d) PC size: larger PC's tend to inflate slower and with greater variance, simply because there is more fabric and a longer process to reach inflation.

It's important to understand that the biggest goal here is to increase the consistency of repeated inflations--not the overall fastest single inflation. Since we have no way of predicting which inflation is going to be the fast one, it's foolish to "play Russian Roulette" with PC's. If you can find a technique that allows you to predict with great accuracy the altitude consumed by your PC inflation, you will be ahead of the game.


2) What can impact pull?

(a) Air speed: PC's pull harder with more air blowing into them.

(b) PC Size: Bigger PC's exert more pull force.

(c) PC construction: Some PC's, by nature of their design, will yield more pull force per size, and some less.

(d) Less oscillation: When a PC orbits around the jumper, the pull force is directed at least partly to the side. Any force used in driving sideways reduces the overall "straight up" component of the pull force which is the most "usefuly" (from a jumpers perspective) element of the pull.

Our goal here is basically to match the pull force to our requirements, without overly distorting the pack job as it moves out of the pack tray (a phenomenon generally referred to as "center cell strip" but which includes various other causes as well).



Some interesting things to note in the context of this discussion:

1) A larger PC can exert more force (reducing the time to move the canopy to line stretch), but also be more prone to hesitation (increasing the average overall time to inflation). To say that "smaller/larger PC's get you open faster/slower" is a gross oversimplification at best.

2) If you can use a presentation that will sharply reduce your inflation time and variance, you can easily (and should) increase your PC size to take advantage of greater pull force.

3) If your presentation method is one with a greater variance in inflation time (say, a stowed mushroom), you may wish to reduce your PC size to try to (to whatever extent) try to counteract this.

4) PC size (the original topic) works on both sides of this equation. A larger PC works to make your overall opening both faster (more pull force) and slower (more time to inflation and greater variance). More is not necessarily better or worse--the issue is more complex than that.


This is a huge topic, and, in my opinion, a poorly understood one. I'd love to write a six volume treatise on this (I think this post is already stretching the limits of acceptable volume), but I'll refrain for now.