Slider down pack job question

[JFK 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.

You might want to check out the old posts of the forum. There has been few discussions about that topic.

It doesn't seem to be such a smart thing to do...

Jul.

JFK #1013
PM Me
No Adrenalin.... No Fun!
"Minds are like parachutes the

[980 0]

that is a good point

to the poster who suggested this: if you really feel you need to tie your lines together at least be smart enough to use your bridle instead of something else

[TomAiello 25]

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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.

Am I describing a 20 years old known technic ?

Pretty much.

Some people like to use some kind of restrictor around the base of the pack job (I do this), while others are worried about leaving it on (a pretty legitimate concern). So, if you do this, I recommend using a large and brightly colored clamp, rather than a string or cord. Another reasonable option is to use masking tape, so that if you forget it, it will tear away on opening anyway.

-- Tom Aiello

[email protected]
SnakeRiverBASE.com

[tommyh 0]

"The bottom skin vents work to synchronize bottom skin expansion with cell inflation. That won't stop you moving downward any faster."

I had this exact same theory... until I jumped my new vented canopy.

A little background: I have about 95 jumps on my unvented fox 285. I am very comfortable taking 2-3 second delays with it (slider off/down(duh)).the openings were completely reasonable/tolerable. I am referring to the pain I received on opening, not any other characteristics.

I always figured that, just like some others are saying, The speed of inflation of the bottom skin of your canopy will determine how "hard" your opening is, regardless of wether you've got vents or not.

Then I got my Troll DW MDV. I did about a 1.5 second delay on it and it spanked me. Hard. I got some whiplash and had pain shooting down my arms for several days. I have never had an opening like that on my un-vented canopy.

I do understand that there are many differences between the two canopies aside from secondary inlets, but it still led me to a theory (one that I am still pretty skeptical of) regarding venting and cross porting

The theory: Since a canopy with secondary inlets starts filling with air above the bottom skin faster than an un vented one, and it seems to me that any canopies bottom skin starts "spreading out" from the center outwards, it is possible that a vented canopy will reach bottom skin inflation faster than an un vented canopy because of the cross ports. IN other words, Air will come in through the bottom skin vents and push outwards through the cross ports, thus making the wing expand faster than a non vented one. thus giving your bottom skin more surface area faster, thus giving you a faster, harder opening.

After jumping my new canopy two other times, I am frankly a little scared to take it to a full 2 seconds of freefall. Thanks for reading this far.

[TomAiello 25]

That seems like a lot of "apple v. orange" to draw any conclusions from, either way.

When I took my FOX 265 and put vents into it (the exact same canopy--I just shipped it back to BR and they sewed vents into the bottom skin), my experience was very different from yours. This suggests to me that the difference in what you are experiencing is not specifically related to the vents.

-- Tom Aiello

[email protected]
SnakeRiverBASE.com

[lifewithoutanet 0]

That's one unvented canopy from one manufacturer vs. another vented canopy from another manufacturer...and quite a bit fewer jumps on the latter than the former. I would expect some differences between the wings.

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Since a canopy with secondary inlets starts filling with air above the bottom skin faster than an un vented one, and it seems to me that any canopies bottom skin starts "spreading out" from the center outwards, it is possible that a vented canopy will reach bottom skin inflation faster than an un vented canopy because of the cross ports. IN other words, Air will come in through the bottom skin vents and push outwards through the cross ports, thus making the wing expand faster than a non vented one. thus giving your bottom skin more surface area faster, thus giving you a faster, harder opening.

I get what you're saying here and in theory, it makes sense, but I'm not sure it's that simple in terms of vents providing greater surface area yielding a faster, harder opening. I'm not convinced that the pressurization through vents and crossports will have a measurable effect on presenting more of the bottomskin of the canopy in the way you describe. Hopefully some of the aforementioned wing designers can/will weigh in.

-C.

[littlestranger 0]

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if you say which canopy will start flying first,sure your vented canopy is the answer,

i equate this as which canopy you have control of first. when i go handheld i consistently open off heading 90 left. pretty confident it's body position. having the ability to react is one thing, but you need a responsive canopy as well. my new canopy is vented for this reason.

this is an excellent thread, i'm learning quite a bit despite not understanding some of the more technical responses.
thanks.

[980 0]

the video is approved and available on skydivingmovies.com here: blackjack and mojo unpacked 2 way

looking at it again, it looks like I actually get line-tension before Trent does

[460 0]

The one thing I've noticed about vented versus unvented:

unvented - jumper less likely to hit the object, IMHO. jumper much more likely to incur a serious injury or die from object strike.

vented - more likely to hit the object. jumper has far lower probability of serious injury or death from the object strike.

Opinions? What's your take on it?

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

[GreenMachine 0]

I agree with "Littlestranger", this thread has been very informative, thanks to you experienced guys.
The video also helped...noticed differences in their inflation and glide.

Questions:

The Mojo & BlackJack are both 260s, was the weight of the two jumpers close to the same?

Why would an unvented canopy have a lower chance of object strike?

Thanks,

~Tom

www.Sky-Frogs.com

[HydroGuy 0]

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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.

I am also curious as to what you do differently to a very low jump packjob as opposed to any other slider down/off jump...

Get in - Get off - Get away....repeat as neccessary

[tommyh 0]

Like I said, It's just a theory that I am also skeptical of.

[TomAiello 25]

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Why would an unvented canopy have a lower chance of object strike?

The theory:

An unvented canopy takes longer to reach full inflation. Prior to reaching full inflation, the canopy is not moving forward. However, it is evident to the jumper which direction the canopy is heading. The jumper can use this lag time to correct the canopy's heading before it fully inflates, and hence before it begins moving forward.

I've met some experienced jumpers who actually put sliders up for low, solid objects, basically on this same premise.



Note that I'm not saying this is my position--I'm just trying to explain the reasoning.

-- Tom Aiello

[email protected]
SnakeRiverBASE.com

[980 0]

I checked with my buddy and the weights are like this (jumpers without gear):

Mojo 260 : 175 lbs

Blackjack 260 : 165 lbs

not a big difference, but according to the higher wingloading = faster opening theory, it would have made the Mojo open faster than if the person under it weighed 165 lbs also.

[littlestranger 0]

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The jumper can use this lag time to correct the canopy's heading before it fully inflates, and hence before it begins moving forward.

not to sound ignorant...just inexperienced, but this implies that you have some control over the uninflated canopy. i guess i just assumed that before it was inflated it would be mushy and inputs would have little effect...of course at the same time we're working in milliseconds.

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I've met some experienced jumpers who actually put sliders up for low, solid objects, basically on this same premise.

if i'm understanding this, the purpose of the slider up configuration on low cliff/building jumps,gives the jumper more time to deal with an off heading opening. but at the same time canopy inflation takes longer...how much longer? and aren't you putting yourself at risk with a sub-terminal pitch. (i appreciate the fact that you referred to 'experienced' jumpers)

[yuri_base 1]

A clean experiment would be like this:

One jumper makes two static line jumps with a vented and a non-vented canopy of the same make and size (e.g. Flik 266 vents/no vents). Static line will set the time to line stretch precisely equal in both jumps. We can shoot video both from above and below to study the pressurization.

That would be a cool little research project for the Memorial Day in TF. I'll buy beer for the jumper and the owner of the second canopy and film the jumps. I'll be in TF from Thursday to Monday. Anyone?
Yuri

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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...not to sound ignorant...just inexperienced, but this implies that you have some control over the uninflated canopy. i guess i just assumed that before it was inflated it would be mushy and inputs would have little effect...

I think that you've hit the nail on the head. Now you understand the debate.


I think the response to your point would be that if you begin giving the input before the canopy is flying, it will begin responding the very moment that it begins flying--just as it begins to move forward it will begin to turn.

-- Tom Aiello

[email protected]
SnakeRiverBASE.com

[nicrussell 0]

couldnt we use two 80lbs. bags of dog food so we can get side by side comparison?

[nicknitro71 0]

The one thing I've noticed about vented versus unvented:

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unvented - jumper less likely to hit the object, IMHO. jumper much more likely to incur a serious injury or die from object strike.

vented - more likely to hit the object. jumper has far lower probability of serious injury or death from the object strike.

Opinions? What's your take on it?

Empirically and theoretically sound, IMHO as well.

The way I see it, someone has more time to correct from an off-heading with an unvented canopy. This correction can be made before the canopy actually starts to react to control inputs. Also the DBS on an unvented canopy can be calibrated more precisely than the one on a vented canopy.

Once the strike does occur, a vented canopy will stay more inflated and more responsive with the nose blocked by the object versus an unvented canopy.

In the end knowing well what you are jumping is far of greater importance than just what you are jumping.

Memento Audere Semper

903

[980 0]

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Empirically and theoretically sound, IMHO as well.

I'm not sure that I would agree about empirically sound.

I have personally seen 4 object strikes, 3 of which was with unvented canopies and the 1 vented canopy object strike I've seen was gross pilot error and would have happened just as easily on an unvented canopy.

To be able to draw any valid conclusions from incident reports, we need to know the ratio of vented vs. unvented canopies in the field, we need to factor in experience level of the pilots and then the type of objects and weather conditions that they will jump.

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The way I see it, someone has more time to correct from an off-heading with an unvented canopy.

maybe, but if they do, it's not a lot more and sometimes it's not enough more to make a difference

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This correction can be made before the canopy actually starts to react to control inputs.

same with a vented canopy if you are quick (and you need to be)
the difference is that the vented canopy will actually start to respond to control inputs pretty much as quickly as you can make them, whereas the unvented canopy will take longer to respond

which is better?:
-a canopy that gives you marginally more time to react and give control input, but will take longer to respond
OR
-a canopy that gives you marginally less time to react and give control input, but will respond to it immediately and tolerate far more control input before full pressurization and in deep brakes

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Also the DBS on an unvented canopy can be calibrated more precisely than the one on a vented canopy.

more precisely? I don't think so. Deeper and closer to the stall point, maybe.


Now is anyone willing to get into the heading performance of vented vs. unvented canopies??

that's a good debate too

[yuri_base 1]

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Now is anyone willing to get into the heading performance of vented vs. unvented canopies??

Do vents "amplify" the inputs from bad body position or any other initial asymmetry, since their intake depends on surrounding line tension?

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

[Zoter 0]

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I am also curious as to what you do differently to a very low jump packjob as opposed to any other slider down/off jump...

I am curious as well.....anyone experienced care to answer...?
I'm taking a guess at :-
No indirect control
Adjustment to the folds in the microreef
(Obviously) not rolling/folding any nose cells at all.
Leaving the pin protector flaps and riser covers 'open'
Priming the pins..

[hookitt 0]

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I am curious as well.....anyone experienced care to answer...?
I'm taking a guess at :-
No indirect control
Adjustment to the folds in the microreef
(Obviously) not rolling/folding any nose cells at all.
Leaving the pin protector flaps and riser covers 'open'
Priming the pins..

I do use the primary stow on low jumps. A double wrap of the rubberband with about a 2 inch or so bight of line.

Rolling the nose on slider down jumps doesn't slow it down anyway.

Micro reefing... we'll that's to be determined if it does anything either. I leave it the same way for all delays.

I do leave the flap open and prime the pins for peace of mind.

My slider down pack job is the same no matter the altitude. The only thing that changes is the pilot chute and the delay.

Slider up, it's the same pack job with the addition of rolling the nose depending on delay, and the pilot chute depending on delay.

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

[Faber 0]

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My slider down pack job is the same no matter the altitude. The only thing that changes is the pilot chute and the delay.

on ultra low freefalls and some SL(object/lz dependt) i use more shalow brakes.

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Slider up, it's the same pack job with the addition of rolling the nose depending on delay, and the pilot chute depending on delay.

dont forget the slider then

Stay safe
Stefan Faber

[brits17 0]

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Rolling the nose on slider down jumps doesn't slow it down anyway.

Could be just me... but when I was getting slammed by most of my slider down openings, I started rolling the nose fairly tight and stopped wrapping the center cell around the pack job. It seemed to help quite a bit.
Going handheld I leave everything exposed still.
Maybe I'm just special because I jump a Raven

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