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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.

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?

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.

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

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.

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.

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.

Can you explain why this is so?

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

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/...i?post=588189#588189

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.

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.
.

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.

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.


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

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

Coco

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.

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

remember Its all fluff.

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.

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

http://www.skydivingmovies.com/...50&string=vented

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

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?

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.

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 ?

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/...e/base_fatality_list

Yeah. That's a great idea.

Wait 'til ya forget that pull-up cord.

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

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.

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

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.

"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.

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.

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.

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

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?

 

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...

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

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.

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.

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.


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)

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

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.

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

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


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.

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.



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



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



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

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

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.

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

dont forget the slider then

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

Tim,
is that for vented or unvented?

Both. I have a bunch of jumps on Ace canopies but both my current canopies are Black Jacks.