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JohnnyUtah

PCA Discussion

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The jumper on the left is Johny 9lives. We did a 2-way, holding hands through opening with both of us being PCAed. The cliff was a rock quarry in Rode Island. The town locals said it was 78 feet. Our landing was into deep clear water (thank goodness). 9lives chose to prime his Velcro and that is what you're seeing. I figure since we were getting a PCA, whatÕs the point of priming my Velcro, so I didnÕt. But hey, if a man wants to prime his Velcro, then thatÕs his business.

A couple different sites and a few days later, 9lives, Danny Koon and myself made it back to Cross Keys where they were having a boogie. At the end of the boogie the local fire department came out with a ladder truck and shot up a stream of water for swoopers to swoop under. 9lives decided he wanted to jump this fire truck ladder. At full extension, the ladder is 100 feet long. They leaned the ladder out a bit over the pond, making the exit altitude close to 80 feet. The exit point was over 3 feet of water. He kept asking me what I thought. I kept telling him 50/50. So we went up the ladder. Having just done the quarry jump a few days earlier, I learned a lot about the relationship between bottom skin inflation rate and anchor point tension strength (such as break cord strength or how hard one holds on to the PC during a PCA). When we reached the top of the ladder and looked over, I figured it was possible but it would be close. He wanted to do it and I knew the only way it would work is if he had an anchor point strength almost equivalent to his weight (155 pounds). Once he climbed over the rail and got in position, I unpeeled his shrivel flap, folded it in half and gripped it so it would pull out of the bottom of my grip. I told him he was all set, and he went quickly. I held onto that shrivel flap with every fiber of strength I had and I believe that for a moment, I held his whole weight in my hand. He did get very quick bottom skin inflation, and then full canopy pressurization. The canopy flew forward for a short canopy ride, and he landed in the three feet of water standing up for the most part and walked right out of the water without a scratch. If he had landed on hard ground, he probably would have walked away as well. In the end, I had just watch the lowest real BASE jump that I have ever seen or heard of, and my hand was completely numb for a while. We do have video of it and I will post an image in the near future. If anyone knows of a lower ÒrealÓ BASE jump, IÕd like to hear about it. The part that cracks me up, is that he not only jumped from a ladder, he BASE jumped from a vehicle, a truck. Unbelievable!!!
Have Fun, Don't Die!
Johnny Utah
My Website
email:johnny@johnnyutah.com

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Hey Johnny, is that a tower is see reflecting in the water? ;)

- Z
"Always be yourself... unless you suck." - Joss Whedon

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...I knew the only way it would work is if he had an anchor point strength almost equivalent to his weight (155 pounds).



Can you elaborate?

Why did you believe that the anchor strength had to be 155 pounds?

It seems to me that such a strong grip on the PC would yield center cell strip, thereby slowing inflation. (I don't think this would have much effect on bottom skin expansion.)

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I had just watch the lowest real BASE jump that I have ever seen or heard of, and my hand was completely numb for a while.



I believe that there is video of a 63 foot jump on Fixed 2.
-- Tom Aiello

Tom@SnakeRiverBASE.com
SnakeRiverBASE.com

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Zennie, yes there was a very small tower there.

Tom,
I don't have a whole lot of time right now to go into full detail (Trevor keeps me very busy), but I'll do my best to quickly elaborate for you.

You replied,
ÒIt seems to me that such a strong grip on the PC would yield center cell strip, thereby slowing inflation. (I don't think this would have much effect on bottom skin expansion.)"

My response,
From my experience through the 12 years I've been BASE jumping, I've noticed that the harder one holds on to the PC during a PCA, the faster the opening. I believe this is due to quicker bottom skin inflation, which results in an increase in canopy inflation rate (similar to the way my Super Mushroom packing technique works with a PC). Center Cell Strip is a result of too much snatch force (such as having too big of a PC at terminal). What causes center cell striping is that the cocoon is extracted too quickly from the container. Increasing the anchor strength on a S/L or PCA jump does not increase the snatch force. It does not result in the cocoon being extracted quicker, it just puts more tension on the lines and fabric once the parachute has reached full line stretch. This tension anchors the parachute system a moment longer, giving it that moment of more time to spread out before the jumper and parachute fall away from the anchor point. The more canopy you can get to spread out before the system breaks away from the anchor point, the more bottom skin is exposed and within a small fraction of a second the bottom skins grabs air, and that is bottom skin inflation. Obviously the less altitude lost during bottom skin inflation, the less altitude lost during the whole inflation process. Further more, the decrease in loss of altitude is exponential to the bottom skin inflation rate. I donÕt know the mathematical formula yet, but it has to do with acceleration during sub terminal freefall. Every moment of sub terminal freefall you lose more and more altitude as you accelerate, and that results in the exponential characteristic of it.

You asked,
"Why did you believe that the anchor strength had to be 155 pounds?Ó

My response,
Well, honestly, it was an educated guess at best. I actually am planning a series of test to gain some real data that will hopefully show just how much benefit is gained for every pound of increased anchor strength, and if there is a point when it doesnÕt increase the benefit (benefit being less loss of altitude).

I said,
ÒI had just watch the lowest real BASE jump that I have ever seen or heard of, and my hand was completely numb for a while.Ó

You replied,
ÒI believe that there is video of a 63 foot jump on Fixed 2.Ó

YouÕre right, there is a clip of that on fixed 2. IÕve watched it myself many times. That one is marginal. That jump could be made just as safe without a parachute. Jason noted in his video, that using a parachute was optional for that cliff jump, and if it had been over hard ground, that dude would have been seriously broken or dead. The PCA 2-way we did in Rode Island was just like that, only 78Õ. It was not a ÒrealÓ BASE jump. If the water had not been there, we would have been seriously messed up or dead, and people were jumping from the same exit point without parachutes and were just fine. So on that jump, the water was our final deceleration device. The jump Johny 9lives did from the fire truck ladder, was a ÓrealÓ BASE jump because the parachute opened and stopped his fall, completely inflated, and flew. If it had not opened, he would have been seriously injured or dead as it was over only 3 feet of water. A very ballsy move on his part. Common sense needs to be applied here, otherwise, I could static line from my roof into a pool and call that a BASE jump.

IÕm interested to know if anyone knows of a lower BASE jump using these guidelines.

Thanks for your input Tom.;)
Have Fun, Don't Die!
Johnny Utah
My Website
email:johnny@johnnyutah.com

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So, do you think that a static line would yield faster overall inflation than a direct bag?

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Obviously the less altitude lost during bottom skin inflation, the less altitude lost during the whole inflation process.



I'm not sure that's so obvious. Just for the sake of argument, picture a hypothetical deployment method that would create full cell pressurization simultaneously with bottom skin expansion, but take ten more feet than a PCA. I'd guess that cell pressurization on a PCA will take more than the ten extra feet.

Another hypothetical: Picture a canopy with a "perfect valve" bottom skin. Assume that the whole bottom skin is one giant (but perfect) one way valve. This theoretical canopy ought to expand top skin first, with the top skin pulling the bottom skin into place. I could also make a pretty good argument that it would be the fastest inflating canopy possible. But it would clearly lose more altitude prior to bottom skin expansion (which would follow top skin expansion) than a real world unvented canopy. So, this canopy would lose more altitude prior to bottom skin expansion, but still be "overall" inflated and flying sooner.

And a not so hypothetical: What about tailgates? Tailgated canopies achieve bottom skin expansion slower than non-tailgated canopies, but still achieve full inflation faster than non-tailgated canopies.

I guess what I'm driving at is that I'm not convinced that faster bottom skin expansion must necessarily lead to faster overall inflation.
-- Tom Aiello

Tom@SnakeRiverBASE.com
SnakeRiverBASE.com

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I split this discussion of PCA, altitude and opening time (and some other stuff) off from the "You're a BASE jumper when..." thread.

It looks like it's diverging in interesting (and more technical) directions. If I get a chance I'll try to replicate it onto BLiNC, as well.
-- Tom Aiello

Tom@SnakeRiverBASE.com
SnakeRiverBASE.com

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if anyone would like to see the video of the jump let me know where i can upload the file.

i swear i had nothing to do with suggesting the firetruck idea:):P
edited to add: damn i forgot i was logged in as my GF!:P -payback462

BettyAnn

Getting married? Check out my website!

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Right on Tom, I enjoy a good brain storm. IÕll quote you and then respond so the readers can follow the conversation.

>ÒSo, do you think that a static line would yield faster overall inflation than a direct bag?Ó<

That is an excellent question Tom! I donÕt know for sure. IÕve seen it go both ways. Of course factors like canopy type, wing loading, wind direction and velocity, air density, and other factors, might affect the opening speed. If and when I do the test jumps, I will be sure to include some S/L vs D-bag experiments. If I had to make an educated guess, it would be that a S/L with a low anchor strength would lose more altitude than a d-bag. Whereas, a S/L with a high anchor strength would lose less altitude than a d-bag.


DEFINITION
In my previous post I mentioned: The more canopy you can get to spread out before the system breaks away from the anchor point, the more bottom skin is exposed and within a small fraction of a second the bottom skins grabs air, and that is bottom skin inflation. To simplify. My definition of bottom skin inflation is: When the bottom skin has expanded and has air pressure against it. So, bottom skin expansion is essentially the same thing as bottom skin inflation, with only a very small fraction of a second difference in timeÉso small, how could we measure it?


>ÓAnother hypothetical: Picture a canopy with a "perfect valve" bottom skin. Assume that the whole bottom skin is one giant (but perfect) one way valve. This theoretical canopy ought to expand top skin first, with the top skin pulling the bottom skin into place.Ó<

For this valve to work, doesnÕt it need bottom skin inflation? Even if it doesnÕt require bottom skin inflation, and can some how allow air in with the bottom skin folded up, the more the bottom skin is open, the more air can get through to the inside of cells and the top skin.


>Ó I could also make a pretty good argument that it would be the fastest inflating canopy possible. But it would clearly lose more altitude prior to bottom skin expansion (which would follow top skin expansion) than a real world unvented canopy. So, this canopy would lose more altitude prior to bottom skin expansion, but still be "overall" inflated and flying sooner.Ó<

What I would like is a canopy that packs itself.


>Ó And a not so hypothetical: What about tailgates? Tailgated canopies achieve bottom skin expansion slower than non-tailgated canopiesÉ.Ó<

I agree.


>ÓÉ. but still achieve full inflation faster than non-tailgated canopies.Ó<

I disagree. I have seen several times, a canopy open slower due to a tailgate (like if you wrap the rubber band too tight for a no delay or short delay jump). However, the tailgate increases your chance of an on heading opening, and on heading openings seem to pressurize cleaner and quicker than off heading openings. This is probably due to less distortion of the air inlets in the nose and the increase of forward airspeed during the inflation process.


Tom, when I do the test jumps, I will need some test jumpers. Let me know if youÕre interested.
Have Fun, Don't Die!
Johnny Utah
My Website
email:johnny@johnnyutah.com

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So if you were doing a static line in this situation would you use thicker break cord? Like you figured that you should hold with 150 lbs...would you use 150 lbs break cord instead.

Tom mentioned center cell strip. BR's much maligned multi might help with that.

I think this is significant even for jumps that are over 80 feet. Say a 150 foot static line. Wouldn't you enjoy that much more saftey margin if you could work this out properly? Or how about that 150' object where you can't quit reach the landing area, you get flying higherybe you can make it...

Don't know.
BASE 853

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I think this is significant even for jumps that are over 80 feet. Say a 150 foot static line. Wouldn't you enjoy that much more saftey margin if you could work this out properly? Or how about that 150' object where you can't quit reach the landing area, you get flying higherybe you can make it...



I really disagree with that. You might be open higher with more tension on the anchor. I still doubt that, but it sounds like Johnny is going to do some empirical testing and let us know.

But using a higher tension anchor will certainly create more center cell strip, and hence degrade heading performance. If your goal is to get open and fly somewhere (as opposed to just getting open and landing), having good heading is going to be more important than having a (possibly) slightly higher opening. Any altitude you might gain from using an old school "grim death" PCA grip will, statistically, be lost in the riser and toggle corrections you need to make to fly in the correct direction.
-- Tom Aiello

Tom@SnakeRiverBASE.com
SnakeRiverBASE.com

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I have seen several times, a canopy open slower due to a tailgate (like if you wrap the rubber band too tight for a no delay or short delay jump).



Leaving aside improper application of the tailgate (i.e. too tight a rubber band, or girth hitching, or whatever), I really believe that a tailgated canopy will reach full pressurization sooner.

I don't think I am alone in this belief. Reading Dwain's Nose First Inflation article, I see that he comments: "if the canopy inflates nose first it will surge less, reach full pressurisation quicker and stress the brake lines less." (emphasis added).

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Tom, when I do the test jumps, I will need some test jumpers. Let me know if you're interested.



Absolutely. I'd love to help out.
-- Tom Aiello

Tom@SnakeRiverBASE.com
SnakeRiverBASE.com

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I agree that if you lose heading control of your opening and have to correct then you would indeed lose any altitude gains. BUT, don't you agree that by using a muti system you could minimze the center cell strip effect thus regaining the altitude gain?
BASE 853

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...by using a muti system you could minimize the center cell strip effect thus regaining the altitude gain?



In theory, yes. I haven't done any real research into it, but I think the theory is pretty sound. I don't see a downside to the multi on a PCA, and I can see plenty of upside.

Note for anyone reading this who doesn't know already: You should not use the multi sheath on a PCA jump, as per BR's owners manual section 4.4:

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With assisted jumps (i.e., static line or pilot chute assist) the air speed and opening forces from this type of jump may not be sufficient to open the Velcro sheath. The opening canopy will be slightly restricted as the Multi lines attempt to open the sheath. Instead of the sheath opening during deployment the sheath tends to compress. Therefore, on assisted jumps it is advisable to close the sheath around the red line only, leaving the 3 white lines unrestricted.


-- Tom Aiello

Tom@SnakeRiverBASE.com
SnakeRiverBASE.com

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aiello wrote:
>Ó I could also make a pretty good argument that it would be the fastest inflating canopy possible. But it would clearly lose more altitude prior to bottom skin expansion (which would follow top skin expansion) than a real world unvented canopy. So, this canopy would lose more altitude prior to bottom skin expansion, but still be "overall" inflated and flying sooner.Ó<

Gardner writes: Lately I've been using a ballistic spreader gun to get faster bottom skin expansion for those really low deployments.:P

utah wrote: What I would like is a canopy that packs itself.

Gardner writes: Our R&D dept. at The Uninsured Redneck Parachute Loft has been working on this recently. The R&D Director reports recent huge strides toward this goal. ...Look for future updates regarding the latest in self-packing parachute design.



With the utmost sincerity,
I remain,
Gardner

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So if you were doing a static line in this situation would you use thicker break cord? Like you figured that you should hold with 150 lbs...would you use 150 lbs break cord instead.



Some of this is new territory that needs to be safely explored further. One danger I can think of, is if you use too strong of break cord, you could end up hanging off the exit point. So, do not start out using a break cord strength close to your body weight. Some more research needs to be done first.
Have Fun, Don't Die!
Johnny Utah
My Website
email:johnny@johnnyutah.com

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When I told the story of the Ladder truck jump, I was doing just that, telling a story. Explaining how things happened and why. This has turned into a brainstorm or a debate out of control (what ever you want to call it), which can be a healthy thing. It just seems like we have strayed away from the story I was telling about one of the coolest jumps I have ever seen. I have attached some images of the jump. Please enjoy them.

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Tom said
I really disagree with that. You might be open higher with more tension on the anchor. I still doubt that, but it sounds like Johnny is going to do some empirical testing and let us know.

But using a higher tension anchor will certainly create more center cell strip, and hence degrade heading performance.



This reminds me of something you said at Petronas last December. You were saying that a line over will not make your canopy spiral. I over heard this and thought for the safety of you and other's, I should inquire. I asked you why you would think that. You said because you had a line over and it did not spiral. I told you then, ÒEvery line over has a different configuration.Ó I hope you believe that.

Time in the sport is a huge factor when considering ones experience and knowledge. Through time, one learns from all that they see and hear. This helps give them solid knowledge.

I know for a fact, that the harder you hold on to a PCA, the faster the parachute will open. I have seen it with my own eyes (real life, not video) many, many times, both as a spectator to it and the person giving the PCA.

The basis of my study is to understand exactly why and to what point of adding anchor strength you would benefit. Also, at what anchor strength will there be no more additional benefit and perhaps even a negative effect (The extreme example, would be an anchor strength that results in you hanging off the exit point).

Tom, I am impressed with the knowledge you have gained in a short time, however, you still have much to learn in this sport. You are an asset to the BASE community; just make sure you are teaching solid information. I hope my words do not offend you as you do a great job here.

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But using a higher tension anchor will certainly create more center cell strip, and hence degrade heading performance.



DonÕt take me the wrong way Tom, but you should know that what you are saying here makes no sense (unless you are using a hypothetical 40 foot static line). Let us define what Òcenter cell stripÓ is. I said the following in a previous post (post#4).

{Center Cell Strip is a result of too much snatch force (such as having too big of a PC at terminal). What causes center cell stripping is that the cocoon is extracted too quickly from the container.
Increasing the anchor strength on a S/L or PCA jump does not increase the snatch force. It does not result in the cocoon being extracted quicker, it just puts more tension on the lines and fabric once the parachute has reached full line stretch.}

In other words, that last two sentences mean: You will have the same snatch force using 40 pound break cord as you will using 100 pound break cord. Now if you had a hypothetical spring-loaded static line that will spring upward as the jumper exits, then you would have a higher snatch force.

Perhaps you think that any distortion of the center cell after full line stretch is the same thing as Òcenter cell stripÓ. It is not. Center cell strip is just exactly what it saysÉwhen the center cell is stripped off the packed canopy (cocoon). This happens when the opposing forces between the bridle and the jumper are high during container opening. The bridle yanks (snatches) the attachment point away from the jumper so fast that the heavier part of the packed canopy (cocoon) cannot keep up. In other words, the majority of the packed canopy stays in or closer to the pack tray, as the center cell is stretched vertically by the attachment point being yanked upward by the bridle. Whew!!! That was a mouthful.

To simplify:

Let us define an anchor, as that force, which pulls against the jumperÕs fall, causing the canopy to come out and play.

Let us create and define a new term called, Òextraction speedÓ. Extraction speed is how fast the anchor pulls the canopy out of the container. This speed is determined by the total force downward (jumpers fall rate and exit weight), minus movement of the anchor (like in the case of a pilot chute). If you got extra time on your hands Tom, how about figuring out a math formula for this.

My definition of Center Cell Strip is: When the center cell is stripped off the packed canopy (cocoon), as a result of an extraction speed that is too fast.

Whether you are falling away from 40 pound break cord or 100 pound break cord, the canopy is pulled out at the same speed and has the same amount of tension all the way up to full line stretch (even all the way up to the point where the 40 pound break cord gives.)

I do agree that higher anchor strength may cause some extra distortion to the noseÕs air inlets at full line stretch, but this is not the same thing as center cell stripping. It happens later in the opening process so the canopy is already spreading out and approaching bottom skin expansion.

A go and throw, would cause the slowest extraction speed (that I can think of right now). Its extraction speed is only slower than that of a S/L or PCA because the pilot chute moves with the jumper. A S/L or PCA also have a very slow extraction speed (unless you are using a hypothetical 40 foot static line or bridle).

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Tom said
Any altitude you might gain from using an old school "grim death" PCA grip will, statistically, be lost in the riser and toggle corrections you need to make to fly in the correct direction.



I disagree with you. Based on my personal experience, a stronger anchor point (such as holding onto the pilot chute harder) will give the jumper significant altitude gain, which will far surpass the small amount of altitude lost in a minor toggle correction. The various combinations of variables will make it very difficult to determine at what point, with what configurations, the altitude gain is cancelled out by altitude lost from a heading correction. More testing needs to done to even give us an idea.

I would like to see those statistics and how they prove your point.
Have Fun, Don't Die!
Johnny Utah
My Website
email:johnny@johnnyutah.com

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Tom said
Leaving aside improper application of the tailgate (i.e. too tight a rubber band, or girth hitching, or whatever), I really believe that a tailgated canopy will reach full pressurization sooner.



Tom, Johny 9lives had a tailgate for the ladder truck jump. We are using tailgates on all slider down/off jumps, so I do not understand why you are still debating this. I am all for a healthy debate, but you are going in circles. In post #8 the rest of my paragraph says:

{However, the tailgate increases your chance of an on heading opening, and on heading openings seem to pressurize cleaner and quicker than off heading openings. This is probably due to less distortion of the air inlets in the nose and the increase of forward airspeed during the inflation process.}

I do not disagree with the point you are trying to make. You are just skipping some factors in between. The tailgate promotes nose inflation first -- which promotes on heading opening -- which promotes less distortion in the nose and cleaner, more direct airflow into the cells -- which promotes faster pressurization of the canopy. Do we both agree here? Your statement is almost accurate but not quite. You would be more correct to say (which is safer in this case), A tailgated canopy has an increased probability of reaching full pressurization sooner.

The tailgate is one way to get the nose to inflate first. Another way, is to shut down the tail. I have video of some openings of mine, back before I used tailgates, that look like there is a tailgate being used. Either way, this results in a higher chance of an on heading opening. A canopy opening on heading should have a more direct airflow going into the nose than a canopy going off heading. Also, on heading openings will usually result in less distortion to the nose, which will allow more of that direct airflow into the cells.

I agree with Dwain's article. Especially the part where he says:

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However, it must be remembered that you donÕt determine how your canopy will open by the way you pack it. Your packing technique merely encourages the canopy to open in a certain way, it does not control it.



Dwain and I are on the same page, like we were on most things we discussed. I can think of a time when we disagreed on an issue. It was at the last Petronas event, concerning a jumper who spiraled onto the roof of the mall. After watching the video one time, I said it looked like he had a tension knot. Both Dwain and Slim adamantly disagreed with me. They thought because the slider had come down, it could not be a tension knot. I listen to their response, and quickly determined that a tension knot can occur within a single riserÕs line set. After explaining this to them, they still disagreed. Later that day, a zoomed in photograph, taken from another building, showed without a doubt, that it was indeed what I said it was (a tension knot).

My point is, even the best are not always right.

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I said
Tom, when I do the test jumps, I will need some test jumpers. Let me know if you're interested.



Quote

Tom replied
Absolutely. I'd love to help out.



OK, I would love to have you there...you are on the load.
Have Fun, Don't Die!
Johnny Utah
My Website
email:johnny@johnnyutah.com

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Blah, blah blah...OK Guys....Enough with the theories

Location: Moab

Date: Turkey Boogie

Object: 100ft cliff

Method: TARD vs DBAG vs Johnny's PCA vs Tom's PCA vs (if we can find a decent anchor point) static line single 80 lb breakcord vs double breakcord vs 3 wraps electrical tape Aussie style...

Let's play!

Spence:P


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Definitely picking up an extra battery for my camera before then... Guess I should throw in a traction splint as well.

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From the pics it looks like Johnny 9lives had almost a 90 offheading opening - was this right? Any idea why? Looks like he was in a position not to have to correct it anyways, so could fly in that direction for landing...
\
Rob Price
If some old guy can do it then obviously it can't be very extreme. Otherwise he'd already be dead.
Bruce McConkey 'I thought we were gonna die, and I couldn't think of anyone

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From the pics it looks like Johnny 9lives had almost a 90 offheading opening - was this right? Any idea why? Looks like he was in a position not to have to correct it anyways, so could fly in that direction for landing...



Very observant Rob. He had a right 70 degree off heading opening. He did a normal pack job for a slider down/off jump, using a tailgate, which normally promotes an on heading opening...on this jump it didn't. From what I saw in real life and from watching the video, there is no apparent center cell distortion. Yes, his off heading put him in a perfect landing spot. That was luck.

IMPORTANT NOTE:
You cannot completely control the opening due to random chance. (There is a way to steer the opening on a slider up jump, but that should be saved for another discussion.)

RANDOM CHANCE Ð Say you fold and pack your parachute absolutely perfect, and during opening your pack tray is absolutely flat and still, and the wind conditions are totally calm; you can still have an off heading opening (or tension knots) due to random chance. This is why. The way the air hits the fabric and lines of your parachute, and the way the fabric and lines react to that air is completely random.

We pack the way we due in this sport to encourage the fabric and lines to respond to the air a certain way, but the air is random and the response is random, and we cannot control it.
Have Fun, Don't Die!
Johnny Utah
My Website
email:johnny@johnnyutah.com

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One more question. Can't tell from the pics - was this canopy vented? valved?
If some old guy can do it then obviously it can't be very extreme. Otherwise he'd already be dead.
Bruce McConkey 'I thought we were gonna die, and I couldn't think of anyone

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"IMPORTANT NOTE:
You cannot completely control the opening due to random chance. (There is a way to steer the opening on a slider up jump, but that should be saved for another discussion.)

RANDOM CHANCE Ð Say you fold and pack your parachute absolutely perfect, and during opening your pack tray is absolutely flat and still, and the wind conditions are totally calm; you can still have an off heading opening (or tension knots) due to random chance. This is why. The way the air hits the fabric and lines of your parachute, and the way the fabric and lines react to that air is completely random.

We pack the way we due in this sport to encourage the fabric and lines to respond to the air a certain way, but the air is random and the response is random, and we cannot control it. "

I have to respectfully disagree with you there, Johnny. The voodoo involved in "random" off headings initiated by the packjob is due to variation from the ideal configuration within our pack jobs. We vary slightly each time we pack. The way that the physical system (jumper, packjob, conditions, timing etc.) reacts is not random. It is very precisely defined by the laws of physics but the system is so large and complex that we haven't fully figured out the levers and triggers yet. I believe that the factors are indeed controllable. We just haven't found out how (yet). As the sport progresses and we reduce the variation we will inevitably move to a time where the configuration of a packjob is so consistant that it is no longer a contributor to an off-heading opening.

I'd hate to call off the dogs in the search to discover the perfect packjob. We're not there yet by any means. We're just a hell of a lot better than the old boys used to be.

Skin

On a side note...Why is it that every time I see a photo of you the pic is of your ass?

Stay safe.
$kin.

Prizes to anyone who gets to read my posts before Mr Aiello's son, Tom deletes them.

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The tailgate promotes nose inflation first -- which promotes on heading opening -- which promotes less distortion in the nose and cleaner, more direct airflow into the cells -- which promotes faster pressurization of the canopy.



While I see no reason to dispute what you're saying here, I thought the tailgate was developed as a reefing mechanism to prevent slider down/off lineovers.

- Z
"Always be yourself... unless you suck." - Joss Whedon

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I thought the tailgate was developed as a reefing mechanism to prevent slider down/off lineovers.



You might be interested in reading this old post of Dwain's.

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The primary purpose of using a tail gate is to achieve nose-first bottom skin expansion (versus tail-first bottom skin expansion). There are many benefits of nose first bottom skin expansion – just ONE of which is the minimal chance of a line over or tail inversion.

The relationship formula is not:
LINE OVER is avoided by TAIL GATE

It is:
LINE OVER is avoided by NOSE FIRST BOTTOM SKIN EXPANSION which can be achieved by using a TAIL GATE

A deploying slider down/removed canopy will have a tendency to achieve bottom skin expansion tail first. This is because the air hitting the angled bottom skin will pool where the tail is pulled back down by the deep brake settings (similar to how a round canopy inflates from the apex downwards). This in turn will force the tail to expand first resulting in large amounts of stress on the brake lines.
When the tail expands prior to the nose it will make the canopy surge forward prior to cell pressurization. This surge forward usually only shuts of the nose (due to the fact that the canopy hasn’t yet acquired sufficient internal pressure to stay inflated against the external pressures) which in turn results in slower and uneven cell pressurization (and subsequently more altitude loss). Also when the tails gets a head start on the nose, the danger exists that the brake lines will flip in front of the nose and a line over will result.

However, if the bottom skin expands nose first it will stress the brake lines less , surge less and subsequently reach cell pressurization faster. There is also significantly less chance that a line over or tail inversion will occur.

BASE jumpers have known the benefits of nose first bottom skin expansion for many years prior to the introduction of the tail gate. In order to encourage a nose first inflation two main areas were focussed on: increasing the speed the nose will inflate (by opening it up when packing) and secondly, trying to slow down or inhibit tail inflation so the nose can get a head start on it.
Many techniques have been used to achieve tail inhibition such as micro reefing (placing more folds in the tail than the nose), the differential stow (only placing the C, D and brake lines in the tail pocket primary stow), and masking tapping the brake lines together.
In late 1996(?) Basic Research introduced to the general BASE community what has become the most widely used and successful method of achieving nose first bottom skin expansion; the Tail Gate.

I have heard some jumpers express concern over using the Tail Gate for jumping low objects. They were worried that by inhibiting the tail, the canopy would take longer to open. Although the Tail Gate does inhibit the tail, it results in a faster pressurization of the cells. In short, you will most likely open slightly higher with the Tail Gate than without (and with less potential problems as well).

In summary, use the tail gate (or some other method of achieving nose first bottom skin expansion) with Direct Bag slider down deployments (especially if you are exiting low without a Vtec canopy).

BSBD,
Dwain


-- Tom Aiello

Tom@SnakeRiverBASE.com
SnakeRiverBASE.com

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