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bodypilot90

w/ or w/o d bag

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Interesting - I never tense my body - I just relax. I'm going with the theory that the drunk driver never gets hurt cuz they're too relaxed!

(That and unconscious people under canopy do pretty well cuz they're not scared of pounding in!)

I can only think of 2 times in my CRW career where I had openings hard enough to feel the next day (and both times it was my back - not my neck.) One was when our Cessna pilot had the plane in a dive as we left, and the other was when I foolishly took 10+ second delays last year at Perris because the trail pilot was lost ;-)

W

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In my opinion some of the hard openings crew jumpers may experience are because of the slider traveling down the lines in the first stage of deployment (everything that happens before linestretch).

Basejumpers use a rubber band on the center C-line attachement point to ensure the slider stays all the way up until linestretch.

I don't get why crew jumpers rely on the center stow of the tailpocket for this?

Cheers

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T wrote

"Basejumpers use a rubber band on the center C-line attachement point to ensure the slider stays all the way up until linestretch.

I don't get why crew jumpers rely on the center stow of the tailpocket for this?"

good question. some answers follow;
1. not all CReW jumpers use a tail pocket, many use a standard D bag for deployment.
2. very few CReW jumpers understand the benefits / drawbacks of direct slider control VS indirect slider control,
because as strange as it may seem, there isn't much cross over between CReW and BASE.

consider entering the BASE section and search for direct slider control or indirect slider control, for further information.

be safe
kleggo
BASE 93

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<<<<>>>

Yes, this is a discussion that we've had for many hours in the BASE fraternity. I think most CRW guys do the tail pocket stow because that is how their equipment is set up and that is how they have been taught. i.e. its out of habit. Regarding your comment above, my thoughts are:
- not all BASE jumpers do this, there are basically 3 main options. They are: tail pocket stowage, slider stowed in c line band, and no stowage at all. I have not gathered data but I think that the order of popularity is : c line stowage, tail pocket stowage, no stowage. And I don't think that the result is like an election run by a dictator, more like the most recent US elections. If you get my drift.

r.e. your point about slider travel and comparing the two techniques. In both cases, the slider is usually within reason, hard up against the stabiliser grommets and quartered in the centre. Usually in both cases, the centre material is pushed up the centre of the canopy. The difference then is that the line stowage method keeps the slider up against the stabiliser grommets by locking it in place ABOVE the slider. The tail pocket method does not lock it into place at all, the stow is what keeps the slider there until line stretch. This is where the debate begins.

With the tail pocket stowage - the only way that the slider can actually travel down the lines prior to achieving line stretch, is if the tail pocket stow fully unstows and the slider moves down. If you look at the location around the slider on 99.99% of jumps, when the stow is being pulled out of the rubber bands, there is an instantenous microsecond and maybe an inch or two of lines that MAY be loose allowing the slider to drop an inch or so at the point of line stretch. So, in theory, there may be a small, partial line dump scenario occuring here. The fact that there is a locked in loop means that the slider will probably not be inflating until after the stow is unstowed. There is a slight possibilty that the other canopy material may be pressurising in the instant prior to the slider releasing and quartering. This may increase the chance of a harder opening due to what I call "micro line dump". The other factor is that any stowed lines have a greater length of lines on the outer part of the loop, and shorter on the inner. This "may" promote uneven line dump and air flow getting to various sectors of the material at different times. This may be what you are referring to.

r.e. the c line stowage method. With a traditional line dump situation, I beleive this is not the preferred configuration to have as MOST people stow the slider with less friction (i.e. looser bands) than a tail pocket stow. Hence, in most cases, the affect of traditional line dump may be worse.

IMHO - In theory though, I beleive that the c line stowage method sounds a little cleaner overall when all things are working OK. But I would rather have the tail pocket stow and sacrifice a little one inch dumper more often than a full 6 to 10 foot dumper once in a blue moon. Ouch.

- - - - -

Further discussion.

Lets delve a little more deeply. Speaking physics, hard openings are basically a relatively high negative acceleration (deceleration). In laymans terms, you go from falling very fast to very slow in a very short period of time (& distance). This can be due to a number of factors that must all be considered both seperately and together. Some factors that may promote harder openings are:

1 - airfoil design that promotes rapid pressurisation and inflation.
2 - packing techniques that promote rapid pressurisation and inflation.
3 - configuration of equipment (& type) that promote rapid pressurisation and inflation.
4 - relative airflow when initiating the deployment sequence (consider prop wash, freefall speed, burble dimensions, etc).
5 - etc.

p.s. Also throw in the speed of the deployment sequence to actual pressurisation and inflation.

Modern CRW canopies and BASE canopies have a number of major differences in design that give clues as to why CRW blokes "seem" to have harder openings.

Airfoil design is a biggy. One of the requirements of CRW canopies is the ability to catch lots of air as often as possible whilst actually performing CRW (ignroing openings and landings for now). What happens when you do CRW? - often components of the nose are blocked off by other parachutists (i.e stack docks), the affective canopy aspect ratio can be very variable during a jump (i.e. if you are the bottom of an unperfect diamond, your canopy will often resemble a piano accordian as the wings pulsate left and right), your nose may be folded down a little by the brake lines of the canopy above when you have just completed a plane dock, you may have been dropped from a wrap, etc, etc. So you need to promote air flow into the cells as much as possible. Compare the distance between top & bottom skins on a CRW and BASE canopy and factor in the actual canopy size. I think you'll find the CRW canopies are HUGE. The downside is on opening. More airflow in the nose means the canopy will probably want to pressurise faster, which in turn means that it wants to push that slider down ASAP. As a comparison, I find that Vtec BASE canopies open harder at terminal than non Vtec - why - the design promotes more airflow into the canopy during deployment!!!

Sliders - both sports use mesh, but I think that you will find on average CRW slider configurations promote faster openings, spider sliders, smaller sliders, less material so you can see what you are doing, etc.

Suspension line length and material. CRW canopies have shorter lines. The angle between the stabiliser and suspended load is greater. This probably translates to more force pushing the slider down.

Many CRW jumpers deply nearer to prop blast. None of that on a BASE jump.

My point is, there are many factors that contribute to hard openings.

Thoughts anyone?

Stay Safe
Have Fun
Good Luck

:)
Stay Safe - Have Fun - Good Luck

The above could be crap, thought provoking, useful, or . . But not personal. You decide.

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Quote


2. very few CReW jumpers understand the benefits / drawbacks of direct slider control VS indirect slider control,



What is meant by direct vs. indirect slider control? And what _are_ the bennies/drawbacks? :)

Only a CRWDog for now but looking to do first BASE sometime in the next year... :O
"You guys should just do CRW. There are so many more ways to get killed, it makes a CYPRES seem safe." -Kevin Keenan

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Why do you ask??

Crimson Mist 2003 & 2004 - Australian 4 Way Rotations. Crimson Mist did USA 1998 with other team members. Hairspeed were at Spain in 2001. No Aussies at the 2000 World Meet. No $$$$$$.

Xtermin8 1996 - Australian 8 Way Speed.

+ I spent time with most of the British CRW guys briefly at the start of 1999 when I passed through London for a BASE / IT trip. I'm in communicado with Fielding, Marshall, etc occassionally.

FYI - picture of tvpb

& yourself??

:)
Stay Safe - Have Fun - Good Luck

The above could be crap, thought provoking, useful, or . . But not personal. You decide.

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yes, we have met, when you were passing through in 99 you turned up at netheravon i was on team-x with fielding and marshall, left after world meet in 2001.

it just confused me when you talked of attending world meets, but you location in your profile says europe\croatia and i thought i knew most of the european competitors.

it is all clear now. also nice to know what past competitors are up to these days as the number of people at competitions seems to decline year on year.

regards
plastic

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What is meant by direct vs. indirect slider control? And what _are_ the bennies/drawbacks? :)


please see tom begic's cogent reply above and consider that

C line stowage = direct Slider control = slider is directly fastened to a c line via a rubber

Tail pocket stowage = indirect slider control = slider cannot come down the lines, ( very far :P), until the last tail pocket stow releases.

be safe

kleggo

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