Canopy deflation

[ddircksen 0]

So here's my weekend jump story I jump a 145 ZP.exe (square from Chute Shop) main which I load quite heavily (I'm 6 feet, about 190 pounds with gear). With 100 jumps, I'm not the most experienced skydiver, but I've been jumping this canopy for the last 60 jumps or so and feel pretty confident with it. Also, I'd never hook it in and take it pretty easy when landing it.
This past weekend I was coming on final approach, about 300 feet up when I hit some turbulence. My canopy deflated (2 center cells) and I dropped a good 50 feet before it inflated again. About 100 feet up the same happened and my canopy reinflated just in time for me to get it back on course and land it safely. At the time I didn't panic, tried to fly it out and got on the ground safely.
Afterwards, quite a few fellow skydivers who had seen the incident remarked on how it had looked and I realized how serious it could have been.
The turbulence occurred over a group of trees and not over the hangar as you would normally expect. No-one else taking the same approach line experienced the same turbulence. My brakes were all the way up when this happened. The canopy's got about 300 jumps on it. I was landing against a wind of about 10mph.

Al of the above said, I've got a few questions related to discussions I had with some people afterwards:
1. If I had been jumping a bigger canopy, could it have been worse? I.e. would my canopy have taken longer to inflate again?
2. Is it just turbulence? I mean, could there be other contributing factors to this happening?
3. Anyone else with this wing loading experience anything like this?

Any comments appreciated. I'd like to avoid this happening again

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[eeneR 1]

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The turbulence occurred over a group of trees and not over the hangar as you would normally expect.

Just an FYI...Trees also can cause turbulance As well as alot of other things besides just the hanger.

She is not a "Dumb Blonde" - She is a "Light-Haired Detour Off The Information Superhighway."
eeneR
TF#72, FB#4130, Incauto

[riddler 0]

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The turbulence occurred over a group of trees and not over the hangar as you would normally expect.

I would expect turbulence over (or in the wind-path of) trees, hangers, buildings, towers and anything else that is good-sized.

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I jump a 145 ZP.exe (square from Chute Shop) main which I load quite heavily (I'm 6 feet, about 190 pounds with gear). With 100 jumps,

This loads you at 1.31. I think that's on the high side for 100 jumps. Check out the Dutch canopy regulations for a starting point.

Turbulence is tricky. It's best to play it safe until you really start to get some more experience. Ask the previous load what they thought of the winds. Watch the old-timers - are they jumping? Remember, just because you have 100 jumps doesn't mean you're no longer a student. Find good mentors to continue your education - the instructors and experienced coaches at the DZ can help you understand what winds do there, and what to watch out for.

Trapped on the surface of a sphere. XKCD

[srsand1960 0]

You certainly have more jumps and are more knowledgeable then I am... however ddircksen 3 minutes after you posted this, I posted a series of questions and one of them was about riding breaks on a turbulent path line. Page 158 and 159 of the skydiver's handbook has a great write up on the subject and page 158 of the 2006 SIM has a quick blurb about it. The flight integrity you described I believe can also happen when behind another ram air.

It doesn't matter how anyone else lives their life.... it matter how you live yours!

[ddircksen 0]

Thanks for the reply. Yes, I know you can have turbulence over trees, just kind of used to having more over the hangar.
I totally agree with your statement about "not being a student doesn't mean stop being a student".
I spoke to quite a few senior jumpers after the incident and decided to post to get some responses here, as the advice always seems reasonable.
I also agree about the wingloading being a bit high.

[MrBrant 0]

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I also agree about the wing loading being a bit high, I might be accused of being overly cautious in my flying because of it.

just a quick note, there are 2 main factors in being a cautious canopy pilot. The first is the actual canopy flying, and the second is canopy CHOICE.
You cannot consider yourself a conservative flyer without meeting BOTH of those criteria.


Note: I am not criticizing your W/L (I am in no position to do that), just pointing out the above.

Edit: This is just my opinion of course, I am not a coach of any sort

[ddircksen 0]

Yip, agreed, I edited my previous post

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[MakeItHappen 15]

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2. Is it just turbulence? I mean, could there be other contributing factors to this happening?

There is also turbulence generated from a canopy. Did you fly through the wake of another canopy?

BTW, many 100 jump wonders say the same thing you do about their canopy and how they fly. Then one day they get a long spot and have to land in a tight area. Then end up doing a low turn into the ground. Or one day someone cuts them off and they do a full toggle turn into the ground. Or one day they get some turbulance or down draft right at flare time. Or they start a turn too low and do not stop it before landing crashing. Or....

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Make It Happen
Parachute History
DiveMaker

[agent_lead 0]

i actually saw this taking place and i held my breath for him as soon as i saw it deflating..

he had told me earlier tha tit was his first jump with this canopy in a while and i wished him good luck..thank god for my luck!

lol not to make light of a serious situation or anything but im guessing it was just due to the fact that the winds were gusting over those trees all day..

anyways...you lived to tell the tale...see you sunday for freezefest

--------------------------------------------
www.facebook.com/agentlead

[skybytch 259]

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I'd like to avoid this happening again

Don't jump when the winds are gusty.

Don't jump when it's turbulent. You can tell if it's turbulent or not by watching other canopies land. If they appear to be "accordioning" under 1000 feet it's not a bad idea to stay on the ground.

Choose a landing area that doesn't require you to fly over or be downwind of obstacles that can create turbulent air. Note that trees and buildings are not the only culprits. Turbulent air can also exist where the ground changes from dirt to grass (that one about got me one day at Perris), over tarmac, and over water. It can also be "bumpy" on hot days in the desert.

Don't fly in another canopy's burble.

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Also, I'd never hook it in and take it pretty easy when landing it.

If you have to fly a canopy conservatively to feel safe and/or confident with it, it's too small for your current ability level.

[TheMannequin 0]

I jump a ZPexe 170 and have learned that if you keep slight pressure on the toggles, it can handle the worst of turbulance!! I learnt it the hard way, with the canopy also collapsing at ~150ft on finals.

And also...fly your canopy until you are standing still on the ground...

Blue skies!

[Guest 1010]

my last jump (mid Dec, weathered out since) I got bounced around on the downwind and less so on the crosswind legs, sounds like a different kind of turblence than you experienced. I flew my Spectre 190 (@1.2 w/l) in both full flight and half brakes and still got bounced around, so I went with full flight. Folks at the dz agreed it was pretty turblent up there, but nobody stayed on the ground. We had fast uppers (35?) but light/var at the ground.

As an aside, I always wince when I see "conservative canopy pilot," even though that is also what I aim to continue to be close to the ground. Billvon speaks to it in this incident post better than I could. That person's w/l was erily close to yours. Be safe out there!

You can have it good, fast, or cheap: pick two.

[porterhouse 0]

Try setting up your final approach so that there is nothing below you once you get under 1000 feet (no trees, hangers, runways, swoop ponds, etc.). A general rule an instructor told me was to assume any object can produce turbulace up to 10 times its height. So if those trees are 100 feet, assume they can produce turbulance up to 1000 feet. Also, be even more careful where the terrain changes (i.e. over the swoop pond, and where the runway/tarmack meets the landing area). The runway reflects heat more than the ground (that's why you can't walk barefoot on a hot runway in the summer, but you can walk barefoot on the grass with no problem). Because the runway reflects more heat than the ground, it obviously becomes hotter. This creates a bubble of hot air that sits above the runway. Every once and a while this hot air bubble gets disturbed by something (a plane, a car driving by, whatever) and it releases upwards (hot air rises). As the bubble of hot air rises, it displaces the other air around it (kind of like a bubble moving upwards in a lava lamp). As the hot air bubble moves upwards and the other air is displaced, it can cause nasty turbulance and even create enough downward pressure to deflate a canopy.......(I'm such a f*ckin' pathetic geek!!!...why do I think that this is interesting!!?!?! ...there is something sooo F*ckin' wrong with me! AAGGHHH!)

[BrianSGermain 1]

There are many variables to consider when looking into a canopy collapse:

1) What was the pilot doing?
2) How fast was the canopy flying when it collapsed?
3) Where was the pilot flying?
4) What is the canopy design?
5) What is the wing-loading?
6) Was there any re-active solution employed?


These are the principle considerations, but not the only ones. I will take each one separately.

1) The way in which a parachute is flown can increase or decrease the "G" loading on the lines. A rapid release of one or both brakes significantly increases the chances that the canopy will collapse. This allows the parachute to surge forward to a lower angle of attack, decreasing the lift of the parachute. This reduces the amount of energy exerted by the parachute away from the suspended load, allowing the "negative" portion of the lift to take over and allow the wing to fly towards the jumper.

2) Airspeed is what creates lift. Lift is what causes the wing to strive to fly up and away from the jumper. This is the formula for line tension and therefore stability. The slower you are flying, the more likely your parachute will collapse due to low internal pressure and low line tension.

3) Was the wing flying in clean air when the collapse occurred? This is an important part of the question. All parachutes can collapse in "bad" air. We must always fly considering the invisible dangers that the sky presents us. If you wouldn't fly a kite there, don't fly or land your parachute there.

4) Certain parachute designs do better in turbulence than others. I must avoid pointing fingers here, as this is a volatile industry that can be taken down by non-skydiving lawyers. Nevertheless, certain wings have an increased propensity to go "negative" when presented with adverse condition, while others bump around a bit and keep on flying. This is a complex issue, and the best way to decide which parachute to buy and fly is to listen to the actual statistics, and to your own experience when flying a particular design. I have not experienced any kind of collapse on the parachutes I fly, ever. If you have on yours, you may want to reconsider what is over your head.

5) Parachutes perform differently at different wingloadings. The lighter the wingloading, the slow it will fly. This means that the internal pressurization of the wing will be less on larger canopies. In general, lightly loaded parachutes experience more small collapses than heavily loaded ones. Not only is there less internal pressure in the wing, but the dynamic forces area also less with decreased airspeed. This means that the average line tension tends to be less on a lightly loaded wing, and the wing tends to have a increased propensity to surge forward in the window when flying at low airspeeds. This is why very small, highly loaded parachutes tend to experience fewer distortions, especially when flown at high speed. Flying at high speed increases the drag of the canopy itself, relative to the jumper, so the relative wind holds the parachute back in the window and at a higher angle of attack. This is why I make carving, high “G”, high speed turns to final approach heading, especially in turbulence. The speed actually reduced the chances of a collapse by increasing the forces that keep the parachute at the end of the lines. I am literally increasing my wingloading by flying fast and at high “G’s”, and the increases velocity reduces the amount of time that I fly in bad air. I am not saying that you should downsize just to increase your stability. I am saying that until your skills and knowledge are ready to fly smaller, faster parachutes, you should stay out of the sky until the winds come down. I still haven’t been hurt by a jump I didn’t do.

6) If you are flying a good design with lots of airspeed and significant line tension, and in a reasonable location that has no obvious precursors for collapse, you can only deal with a collapse in a re-active manner, as you have addressed all of the relevant variables up to this point. This is all about "Pitch Control". If your wing tries to aggressively surge forward in the window, you must notice it and quickly stab the brakes to bring it to the back of the window. A collapse always begins by a surge to a low angle of attack, but there is very little time to deal with the problem before I folds under. Here are the signs:

a) The first sign is a change in Pitch. The wing moves forward in the window.
This is the limited flying space over your head. Too far forward and it collapses. Too far back and it stalls.
b) The "G" loading drops dramatically and almost instantly. In other words, your apparent weight in teh harness drops because the wing is producing less lift.

This is the time to jerk on your brakes: quickly, sharply, but not more than about 50% of the total control stroke. This action is to pull the wing back in the window, not to stall the parachute. By putting the wing further back in the window, we are increasing the angle of attack. This increases the lift, and forces the wing to fly away from the suspended load and thereby increase the line tension. This can prevent a collapse entirely, or cause the wing to recover to stable flight before things get really out of control.

If the wing is allowed to collapse, it may recover quickly on its own. This is why the more modern airfoils have the fat point (Center of Lift) so far forward. It causes the wing to pitch nose-up when it begins to fly again, bringing it back to the end of the lines. Nevertheless, parachutes can still collapse fully, which often involves significant loss of altitude and possibly a loss of heading.

If your wing goes into a spin because of a collapse, your job is to stop the turn first, as you increase the angle of attack. If it is spinning, there is less chance of recovery until the flight path is coordinated and the heading stable.

Conclusions:
1) Don't fly an unstable parachute. If it is prone to collapse, ground the parachute. Do not sell it to an unsuspecting jumper at another drop zone. These people are your brothers and sisters.

2) Don't fly in crappy air. Land in wide open spaces, in light winds, and never directly behind another canopy.

3) Practice stabbing your brakes in response to forward surges on the pitch axis. This must become a "learned instinct" that requires no thought at all. Like pulling emergency handles, pulling the wing to the back of the window when the lines get slack is essential for safe skydiving.

4) Keep flying the parachute. If your parachute does something funny near the ground, don't give up. If you keep your eyes on YOUR ORIGINAL HEADING, you will unconsciously do things that will aid your stability and keep you from getting hurt. Looking toward what you don't want is how you make it occur.

I hope this little article helps you understand the phenomenon of collapses a bit better. I know as well as anyone how painful a collapse can be. I do not want to go back to that wheelchair, and I don't want anyone else to have to experience that either. You morons are my family, and if information can help protect you, I wil give it until my lung are out of air.

Blue Skies, Sky People.

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Bri

Instructional Videos:www.AdventureWisdom.com
Keynote Speaking:www.TranscendingFEAR.com
Canopies and Courses:www.BIGAIRSPORTZ.com

[Orange1 0]

Excellent answer Brian!

I think this gets added to the DZ.com quotable quotes list:

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I still haven’t been hurt by a jump I didn’t do.

Skydiving: wasting fossil fuels just for fun.

[ddircksen 0]

Thanks so much for the post, Brian. I have learnt so much from this thread about canopy flying, turbulence, safety and wing loading I feel like a better skydiver already :)

[BrianSGermain 1]

Knowledge counters Gravity!!!
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Instructional Videos:www.AdventureWisdom.com
Keynote Speaking:www.TranscendingFEAR.com
Canopies and Courses:www.BIGAIRSPORTZ.com

[JumpRu 14]

I had canopy collapse at 150ft on conventional design and switched to air-locked canopies. I did not have any problems with turbulence ever since. I’ve done many (well over hundred) downwind landings at 15+ mph (not recommended!) and I have complete trust in Big Air canopy design. Thanks Brian!

[riddler 0]

Another excellent post Brian - every time you do a write-up like this, I learn at least 10 new things. On this:

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If your wing goes into a spin because of a collapse, your job is to stop the turn first, as you increase the angle of attack.

Would you suggest application of the front riser on the side opposite the turn?

Trapped on the surface of a sphere. XKCD

[BrianSGermain 1]

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Another excellent post Brian - every time you do a write-up like this, I learn at least 10 new things. On this:

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If your wing goes into a spin because of a collapse, your job is to stop the turn first, as you increase the angle of attack.

Would you suggest application of the front riser on the side opposite the turn?

Nope. Here's why:
Front risers DECREASE the angle of attack on one side of the wing. What you need to do in order to recover from a collapse is INCREASE the angle of attack accross the entire span of the parachute, but in a manner asymetric enough to maintain your heading..

Front risering on the opposite side of the wing will bring the canopy forward in the window, and thus make the problem worse. You may exacerbate an asymetrical collapse into a full frontal collapse. You might stop the spin by doing this, but you may also increase your descent rate dramatically as you deflate the remaining cells.

The best way to increase the angle of attack while efforting to stop the spin is to hit a toggle on the opposite side of the parachute. This pulls the wing back in the window quickly, and since the input is primarily YAW axis control, it helps coordinate the flight path. In other words, it is like stepping on the rudder pedal of an airplane in a spin. You align the fuselage with the relative wind, and therefore begin to regain control of the aircraft. Once you are aligned to the relative wind with respect to the YAW axis, you can increase the angle of attack of the wing to pull out of the dive by adding collective brake pressure.

Besides, toggles are already in your hands, while front (or rear) riser application requires a separate step. You don't have much time in a collapse situation, so applying the correct input quickly is essential.

Practice this up high, as often as possible. If you are ready for this kind of thing, you may even want to fly in the turbulent air behind another canopy to try to induce a collapse at high altitude. This way the unpleasant feeling of momentarily loosing control over your wing will not freak you out so much if it happens down low.

Panic is the enemy.
Calm, decisive input is the solution.
+

Instructional Videos:www.AdventureWisdom.com
Keynote Speaking:www.TranscendingFEAR.com
Canopies and Courses:www.BIGAIRSPORTZ.com

[darrenspooner 0]

I had canopy deflation on a ZP. I was jumping a 170 about about wl 1.1, with 80 jumps. At about 200 feet 3 end cells folded under and it just recovered in time for me to land. Freaked me out. I asked my instructor what to do and he said "chuck it in the bin". I now jump a Sabre 2.

I'm just a novice too, but your wl seems a bit high to me. We all say we'll never hook it or turn too low. We all lie about our weight when we're trying to justify having too small a canopy. Be careful. Its just not worth trying to kid yourself. Of course, jump number doesn't equate to ability, but nevertheless, I'd fly that thing like you were driving your car on ice. And in gusting winds, whoa, think twice.

[porterhouse 0]

Whoa!!.....Yeahhh....OK....You're pretty smart.

On a serious note, Thank You! The thing I like most about this sport is that I always learn something new. You're post just taught me something that could potentially save my life. And that's just a post! Thanks Brian! It's good to know that after everything you've accomplished, your still sticking to the basics of using your knowldege to make the sport safer and more enjoyable for all those involved. After reading this, I'm thinking I would be an idiot if I don't buy your book, read it, and memorize it cover to cover.

What's the link where I can order "The parachute and its pilot?"

[BrianSGermain 1]

It is here:

www.BrianGermain.com

Instructional Videos:www.AdventureWisdom.com
Keynote Speaking:www.TranscendingFEAR.com
Canopies and Courses:www.BIGAIRSPORTZ.com

[bob.dino 0]

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I'm thinking I would be an idiot if I don't buy your book, read it, and memorize it cover to cover.

That's some good thinking you're doing there boy.

[KNewman 0]

I just received a copy of your book today, and will enjoy reading it over and over again. Thanks for passing on your knowledge to all of us who enjoy this wonderful sport!!

Blue Skies and Stand-up Landings!!!!!!