Slider down pack job question

[460 0]

My experience has been that I have on heading openings regardless of any details for any slider down packjob. So long as the packjob is relatively neat, symmetric, and properly tensioned, I have pretty much the same on heading openings every time. I might tailor the packjob a bit if the jump is very low, however.

Most of the critical parts of the packjob technique seem to be important when doing subterminal mesh slider up jumping.

What's your take on it?

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

[TomAiello 25]

My experience is that so long as you:

1) Maintain line tension;
2) Keep everything symmetric; and
3) Keep the lines in the middle and the fabric on the outside,

You can pretty much let the rest of the details go.

-- Tom Aiello

[email protected]
SnakeRiverBASE.com

[dmcoco84 4]

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I might tailor the packjob a bit if the jump is very low, however.

What exactly do you do to your packjob for the low jumps. I have a few low ones planned in the near future so I'm interested to hear what makes it open better/faster, besides VTEC. Planning 170-250 feet jumps.

Coco

[TomAiello 25]

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...what makes it open better/faster, besides VTEC.

Can you explain how you think the bottom skin vents are going to change the opening characteristics for low stuff?

The bottom skin vents work to synchronize bottom skin expansion with cell inflation. That won't stop you moving downward any faster. It appears to start you moving forward faster. In other words, I think that the bottom skin inlets have no effect on the first function of the parachute--as an aerodynamic deceleration device. They work primarily on the lag time between the use of the parachute as an aerodynamic decelerator and the beginning of it's use as a wing.

-- Tom Aiello

[email protected]
SnakeRiverBASE.com

[mtnlion667 0]

yeah,
I pack like shlt, basicly. but my lines are tight n' straight. n' when i'm done, i can see my D lines if i peek way in side my center cell..... right before i velcro her shut. after that, seem's to fly pretty straight so far. all without a slider of course, being in the east and all. now that i jinxed myself real good, i'm gonna go out.

[yuri_base 1]

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In other words, I think that the bottom skin inlets have no effect on the first function of the parachute--as an aerodynamic deceleration device.

With inlets, canopy is pressurized faster and starts decelerating you earlier. However, for slider down jumps the difference in pressurization time between vents and no vents is small (~0.1s, even less?). This small difference in time makes a small difference in height for low jumps: if you go-n-throw, for example, your speed at line stretch is ~50ft/s, so 0.1s difference in time makes only 5ft difference in opening height.

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

[TomAiello 25]

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With inlets, canopy is pressurized faster and starts decelerating you earlier.

Can you explain why this is so?

Won't the canopy decelerate you once the bottom skin expands, even before the cells inflate?

-- Tom Aiello

[email protected]
SnakeRiverBASE.com

[dmcoco84 4]

Oh......well I guess I was incorrect in that thought then. I was told when I bought my gear that VTEC was recommended if I was planning to do sub-250 jumps (I think that is the right number). I guess I was under the impression from that statement and reading things on the board that bottom skin inflation allowed the cells to pressurize faster and more equally which in turn would mean quicker openings on low jumps.

Coco

Example - first paragraph

http://www.dropzone.com/cgi-bin/forum/gforum.cgi?post=588189#588189

[TomAiello 25]

In my opinion (take note--just my opinion):

The canopy opens in stages:

After it reaches line stretch, the bottom skin expands outward as it catches air. In this stage, the canopy operates as an aerodynamic decelerator, and slows (greatly) your downward motion.

Then, the cells inflate, and the canopy begins to operate as a wing, flying you (and itself) forward in the direction it is facing. This generates additional lift, further slowing the downward progress of the jumper.

There is some lag between these two stages, during which the canopy has decelerated you (and/or is decelerating you) but is not yet functioning as a wing.

The bottom skin inlets tend to synchronize these two stages (i.e. they greatly reduce the lag between them, perhaps to the point where for functional purposes, they occur at the same time).

In theory, the secondary inlets would actually slightly slow the first stage (bottom skin expansion), but that effect is probably very small (so small I doubt you would notice it).

The functional result is that the bottom skin inlets give you a canopy which is responsive to control inputs (for which it must have cell inflation) much sooner in the overall inflation sequence. The canopy can be turned, or flared, almost immediately upon bottom skin expansion (because cell inflation is happening concurrently).

This does not mean, however, that bottom skin expansion (and hence aerodynamic deceleration) happens any sooner.

-- Tom Aiello

[email protected]
SnakeRiverBASE.com

[RayLosli 11]

I am also under the same impression.
That if you take 2 identical Canopies. One Vented & one Not. Then you jump them off identical exit points under the exact same conditions.
Both will have Exactly the same (Opening Height) as far as Line-Stretch & Bottom-Skin inflation. (aerodynamic deceleration)
The Vented canopy will come to full pressurization faster. Leading to the gain of Faster Flight and the canopy reacting to Pilot Input faster.
.

[yuri_base 1]

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Won't the canopy decelerate you once the bottom skin expands, even before the cells inflate?

Yes, but the speed of inflation directly affects the speed of bottom skin expansion.

What makes the canopy expand to full wingspan is pressurization, not the line tension itself, because the span of the wing is shaped in such a way that the lines are almost perpendicular to it, so there's no component of tension force that would cause the canopy to expand (and inside pressure and lift resist the small component of this force that wants to collapse the "accordion").

If you completely close the nose and bottom skin inlets, the ram-air parachute won't assume it's square form. It will flutter much like Maggot's Mary Poppins till impact.

One-skin parachutes (rounds, Pterodactyl) keep their shape by trapping the air dynamically inside their concave shape.

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

[Lonnie 0]

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With inlets, canopy is pressurized faster and starts decelerating you earlier.

I have to agree with Tom, vents only give you a flying wing faster. They will not decelerate you any sooner. I spoke with Adam extensively about this when he was developing the Blackjack, and made a bunch of jumps on the pre-production model in 2001. As he explained it to me it will not open faster. What the vents do is give you a fully pressurized (aerodynamic wing) canopy quicker. Until it is fully pressurized it is only a decelerator similar to a round. Deceleration happens at bottom skin inflation, when the canopy expands. At this point you have an open canopy, but not a flying canopy. Without vents the canopy generally needs to move forward to inflate, even if just a little. So it will not open faster, but be a real wing quicker, therefore steerable and able to flare sooner.

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What makes the canopy expand to full wingspan is pressurization,

If you watch video frame by frame, on the non-vented canopies they do reach full span without full pressurization, then inflate.

Maybe Marty can explain, he helped develop the BlackJack

NEVER GIVE UP!

[dmcoco84 4]

Man, I start some damn good decisions! I just don’t know shit so I can add to them.

Coco

[PeteS 0]

I agree that a vented wing will give you a FUNCTIONAL ramair parachute in less distance than non vented. Bottom surface spread should happen relatively the same, all else being equal. The net loss in altitude comes from the wing accelerating to flight speed (it is not stalled, so it "dives" a bit for speed). With deep brakes both wings cannot pitch nose down steeply, so "sink" is the flight mode until a steady state pressurization and speed occurs. The "braked" configuration gives the lower surface resistance or pressure to maintain some shape while the cells are being pressurized and lifted off the lower surface.

[dmcoco84 4]

Sounds good. I stand corrected. Learn something new every day!

So what about the question of what can be done to make a canopy open faster for low jumps?

Coco

[Gaper 0]

remember Its all fluff.

Go forth now, to the promised lands, and swear much unto each other, with mighty profanity and many personal attacks. T.A.

[Faber 0]

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My experience is that so long as you:

1) Maintain line tension;
2) Keep everything symmetric; and
3) Keep the lines in the middle and the fabric on the outside,

You can pretty much let the rest of the details go.

ill second that..

I often get a notice about my packjobs(well they dont look neat) but i use the above as my packing platform,i do belive that i have no more offheaddings than others and would say that most of my offheaddings are more likely due body position while deployment,winds and pc than from my packjob.

Stay safe
Stefan Faber

[Zoter 0]

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That if you take 2 identical Canopies. One Vented & one Not. Then you jump them off identical exit points under the exact same conditions.
Both will have Exactly the same (Opening Height) as far as Line-Stretch & Bottom-Skin inflation. (aerodynamic deceleration)

This video....by BASE864 , although POV ,shows the vented canopy is 'flying' before the unvented canopy

http://www.skydivingmovies.com/ver2/pafiledb.php?action=file&id=1850&string=vented

[Faber 0]

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the vented canopy is 'flying' before the unvented canopy

yes it does BUT both vented and unvented canopyes opens at the same time,it just takes longer to a unvented canopy to start moving forward,as its pumping more.

so if you say which canopy will start flying first,sure your vented canopy is the answer,but both canopyes will open at same hight,the difference is that as we are moving downwards always you will in a unvented canopy only move downward were a vented will start moving forward,shortly before the unvented.

i will agree whith you that i also preffere a flying canopy compared to just the open one.. its about broken bones or not

Stay safe
Stefan Faber

[obi 0]

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This video....by BASE864 , although POV ,shows the vented canopy is 'flying' before the unvented canopy

http://www.skydivingmovies.com/ver2/pafiledb.php?action=file&id=1850&string=vented

A very different question: I watched the video and thought that both wings had NO flare at all in them. And that being 322 sqft! How much experience did the jumpers have on those wings? How old where they (the wings)? I assume the jumpers did flare, right?

[Faber 0]

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I watched the video and thought that both wings had NO flare at all in them

On skydivingmovies.com 864 tells its factory brake settings.My guess would be that he/she popped toogles and flew by deep brakes probaly by the 5th line mod,looks like some landings i had before i removed the line.

Stay safe
Stefan Faber

[nec 0]

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3) Keep the lines in the middle and the fabric on the outside

As a junior base jumper, I haven't yet seen so many different packing technics.
And when looking at my own way to do, I realize that during packing, I could bind the lines close to the canopy to ensure they stay centered, and prevent them from going apart the center. And then of course remember to remove the binding cord before putting the lines in the tailgate.

Am I describing a 20 years old known technic ?

Nico

[Zoter 0]

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And then of course remember to remove the binding cord before putting the lines in the tailgate.

Right there......is the problem
Overcomplication....something 'else' to remember that if not remembered could kill you.

#94 on the List is a recent example....BSBD
http://hometown.aol.com/base194/myhomepage/base_fatality_list

[base704 0]

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I could bind the lines close to the canopy to ensure they stay centered, and prevent them from going apart the center. And then of course remember to remove the binding cord before putting the lines in the tailgate

Yeah. That's a great idea.

Wait 'til ya forget that pull-up cord.

You can get a lot more done with a kind word and a gun than with a kind word alone.

[980 0]

I agree with what Lonnie and Tom are saying and I have some video that you can see the differences they are talking about clearly.

My buddy Trent and I did an unpacked 2 way off the Perrine recently and we have video from the side, so it’s really easy to see the time and altitude taken by the openings.

He was jumping a Mojo 260 and doing a rollover, I jump a Blackjack 260 and did a TARD-over. Both slider off.

We exited really close together because with a little delay after coming around on the TARD-over, before letting the canopy go, we SHOULD have had decent vertical separation.

I rotated the TARD-over kind of fast and Trent did the rollover kind of slow, so we pretty much exited and flipped over all synchronized, then I let the TARD go after a slight pause.

Trent got linestretch first. I get linestretch very soon after. I am below Trent’s level when we both have linestretch.

Then you can see the two canopies go through bottom skin inflation.

Then you can see the differences in pressurization. I end up slowing down more than Trent at this point and now I’m the high guy. My canopy also starts moving forward way before the Mojo does.

Then there’s a difference in time-to-toggles, with me unstowing the toggles and flying the Blackjack before Trent even has full pressurization.

I am really glad that we both had on-headings, because we spent most of our deployment very close.

I will post a video clip of the whole jump on skydivingmovies soon so people do not have to depend on my description of this experience.

It is the same jump there’s a little of right at the end of the SObase2006teaser.

Cya
Sam