Canopy Collapse

[obelixtim 100]

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"The air going over the top is accelerated, ‘cause it has to go further, to keep up with the air going under the bottom" is simply INCORRECT.

Agreed,....it doesn't make sense to me either..

Turbulence can vary greatly, both in its cause, AND effects. What saves your arse one day might be ineffective the next. The best you can do is have a standard plan of action, and be aware when conditions are such that you are ready to use it.

If you get caught in a rotor, the canopy can remain fully inflated, and not even stall.

The effect though is like a giant hand pushing your canopy straight down from above. It can pound you into the deck really hard. The canopy effectively drops out of the sky.

Flying with a lot of brake is just asking for trouble IMO. Even on half brakes, a good turb can induce an almost instant stall.

He fails to mention wake turbulence which is present behind a canopy, and has caught out more than a few skydivers who are right on someones tail on landing.

My computer beat me at chess, It was no match for me at kickboxing....

[DocPop 1]

Thank you for posting the link, and to Airtwardo for your practical experience.

Clearly there is some dispute about what is actually the right thing to do and maybe there is no one universal rule.

Still, even knowing that gives us some power, even if it is just to recognize what we don't know.

Makes me feel better about being a pussy for not jumping in higher/gusty winds! And having sat in the hospital yesterday for 7 hours due to a partial canopy collapse I am going to be even more conservative in future.

"The ground does not care who you are. It will always be tougher than the human behind the controls."

~ CanuckInUSA

[steve1 5]

About ten years ago, I was doing a demo into a football field. It was in a bowl with high cotton wood trees on one side. The wind was stiff, with some gusts. I had turned onto a final approach, when I had this sickening falling feeling. Being about a 400 jump wonder, I thought, "Oh crap, what do I do now!"

My Falcon (9 cell) had collapsed. I'm not sure how many feet I lost, but it seemed like a lot. Then my canopy reinflated, and I came in for a nice landing.

I sure don't want that to happen again! I should have been able to read some of what might happen due to the weather conditions, and the location of the field.

Maybe there's a reason why green horns, shouldn't do demos....

[obelixtim 100]

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And having sat in the hospital yesterday for 7 hours due to a partial canopy collapse I am going to be even more conservative in future.

You are going to UPSIZE??.

After your posts of the last few weeks, I can assure you the the forum sharks on here will smell blood in the water....

My computer beat me at chess, It was no match for me at kickboxing....

[DocPop 1]

Reading through that link again, I can't help thinking that it is very one-dimensional. He seems to only be considering airfoil shape or camber in the production of lift.

He does not consider that lift can also be increased for a given airfoil by increasing airspeed. Neither does he consider the need for airspeed to pressurize the cells and maintain airfoil shape - again essential to lift. The whole airplane wing analogy does not work for that.

I am not dismissing the piece totally, I just think there are some significant missing pieces in his explanation.

"The ground does not care who you are. It will always be tougher than the human behind the controls."

~ CanuckInUSA

[DocPop 1]

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And having sat in the hospital yesterday for 7 hours due to a partial canopy collapse I am going to be even more conservative in future.

You are going to UPSIZE??.

After your posts of the last few weeks, I can assure you the the forum sharks on here will smell blood in the water....

LOL - nice try!

I am talking about my wind limits, not my canopy! (Please let's not go there again - this is a great discussion).

"The ground does not care who you are. It will always be tougher than the human behind the controls."

~ CanuckInUSA

[obelixtim 100]

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LOL - nice try!

I am talking about my wind limits, not my canopy!

And you don't think there is a connection there somewhere???.

Didn't your experienced mentor point out a few things about wind, turbs etc etc.....

Sorry mate, but you put yourself in the firing line, I'm sure there's gonna be a bit of incoming....

Learn from it.......

My computer beat me at chess, It was no match for me at kickboxing....

[airtwardo 6]

I'm no rocket surgeon, just trying to understand...

Doesn't dropping a few degrees of flaps give you more lift?

How about when coming back from a long spot, put it in 1/4 brakes to increase lift a bit, even though the trade off is airspeed it seems to work.

I was a business major so I really don't get some of this stuff...break it down like yer talking to a 'state school' graduate

~ If you choke a Smurf, what color does it turn? ~

[pchapman 261]

Hey Twardo,

Yes, curving the airfoil more gives more lift (and drag) right away, but when you slow down because of that, then you are back to pretty much the same lift as before -- the airfoil is working harder (higher lift coefficient) but with less speed, keeping you in an equilibrium.

With an airplane flying level, lift = weight (ignoring the sometimes downwards lift of the tail to maintain balance), while with gliders and skydivers under canopy, on a descending glide path, weight is counteracted by both lift (along the flight path) and drag (perpendicular).

Talking aerodynamics can get messy because whenever one tries to say something brief, there are often a bunch of "fine print" conditions and explanations that go along with it.

I only brought up the lift issue to show how John Sherman was being confusingly imprecise when trying to teach about lift.

We all talk about "lift" and "drag" in a very non-scientific way at times, which is OK, but we have to be more careful when trying to explain things precisely.

For example, say a jumper has a bag locked main canopy. Not much drag there!, we say. But technically that's wrong. If the jumper and gear is 200 lbs, then he's got 200 lbs of drag between him and the pilot chute, just that that equilibrium exists only with him plummeting at 110 mph.

It's not that he needs more drag, because he'll have the same 200 lbs landing under a big round parachute. He just needs something that'll give him 200 lbs of drag at 10 mph or less descent rate. (Or an equivalent upwards combination of 200 lbs of lift & drag if he's got a square reserve.)

So the guy under the bag lock needs "more drag" only in a casual, you-know-what-I-mean kind of way --
more drag per unit of speed than he can achieve with a bag lock.

[obelixtim 100]

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For example, say a jumper has a bag locked main canopy. Not much drag there!, we say. But technically that's wrong. If the jumper and gear is 200 lbs, then he's got 200 lbs of drag between him and the pilot chute, just that that equilibrium exists only with him plummeting at 110 mph.

It's not that he needs more drag, because he'll have the same 200 lbs landing under a big round parachute. He just needs something that'll give him 200 lbs of drag at 10 mph or less descent rate. (Or an equivalent upwards combination of 200 lbs of lift & drag if he's got a square reserve.)

So the guy under the bag lock needs "more drag" only in a casual, you-know-what-I-mean kind of way --
more drag per unit of speed than he can achieve with a bag lock.

OK, we need a volunteer here to test this bag lock theory......I nominate DocPop....because he needs the experience.....

My computer beat me at chess, It was no match for me at kickboxing....

[airtwardo 6]

Pic of me going through some turbulance...notice the kick back on the banner.



2nd pic shows some funky wake...

~ If you choke a Smurf, what color does it turn? ~

[DocPop 1]

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OK, we need a volunteer here to test this bag lock theory......I nominate DocPop....because he needs the experience.....

OK, three things:

1. It's not a theory, it's a well-described scientific fact. If you don't understand it, get an adult to explain to you.

2. Please stop creating thread drift. You are polluting a very useful thread which some of us would like to learn from. I have already revised my simplistic view of what I thought was right based on Airtwardo's comments/experience.

2. Regarding your hidden agenda of starting another flame-fest against me - you do not know what you are talking about. Any further posts from you on that topic are going to make you look very foolish. And we wouldn't want that, would we?

"The ground does not care who you are. It will always be tougher than the human behind the controls."

~ CanuckInUSA

[Calvin19 0]

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The canopy education I have had/read all agrees that full flight is the most stable flight mode for turbulence for most modern canopies.

We can fix that by broadening your reading list:

http://www.jumpshack.com/default.asp?CategoryID=TECH&PageID=Turbulence&SortBy=DATE_D

Yeah, It has been said before in this thread, but that article is INCORRECT in it's explanations of lift and turbulence. anyone who has read that article, DISREGARD the information.

[Calvin19 0]

The best thing to do in turbulence is to pay attention to your glider/parachute. Try to keep it directly overhead (in pitch and roll) and more importantly keep it flying the DIRECTION YOU WANT IT TO GO, usually straight ahead of you. This is especially important low to the ground.

If ANY size/loading and style of ram air, suspended wing collapses it will use EXPONENTIALLY more altitude to recover to un-accelerated flight if it loses it's directional heading before re-inflation.

[obelixtim 100]

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OK, three things:

1. It's not a theory, it's a well-described scientific fact. If you don't understand it, get an adult to explain to you.

2. Please stop creating thread drift. You are polluting a very useful thread which some of us would like to learn from. I have already revised my simplistic view of what I thought was right based on Airtwardo's comments/experience.
[
2. Regarding your hidden agenda of starting another flame-fest against me - you do not know what you are talking about. Any further posts from you on that topic are going to make you look very foolish. And we wouldn't want that, would we?

You obviously missed the two in my post....

My computer beat me at chess, It was no match for me at kickboxing....

[Calvin19 0]

DIFFERENTIAL AIR MOVEMENT OF ANY KIND CAN BE CONSIDERED "TURBULENCE" thus, turbulence has a spectrum.
There is "sharp" turbulence, where two air masses are moving in different directions very close to each other. (examples- wake turbulence[burbles], rotors off of buildings and mountains, and thin shear layers. Then there is "Soft" turbulence, where air masses are moving in different directions, but the changes are over longer distances. A shear layer can have a soft boundary, or a very sharp, sudden one.

Another variation is the speed that you move through these different air masses, as well as the size of the air mass.

Another variable is the transit time from one airmass to another airmass of a different speed and velocity.
Explanation-If you are flying at Mach one through wind shear, even if it is a very "soft" shear layer, you will fly through it so fast it would 'jerk'[actual physics word] or jolt you pretty hard and feel like sharp nasty turbulence. If you are putting along at 15mph in a parachute, it would not even be noticeable other than the slight change in ground track.
It is also important to remember that these air masses could have any moving direction relative to eachother, one can be moving up, the other sideways, and another on diagonally. Or, be a rotor and be turning all over the place. It also can be a stream of air like cold-air "drainage" coming out of a canyon.

(note-it is important for pilots to understand that the second they leave the ground, no matter how close or far, they are part of the AIRMASS and the ground has no effect on the way the wing flies)

A ram-air canopy(paraglider or parachute) collapses because the angle of attack of the airfoil decreases until no lift is produced, and the fabric is at the mercy of the relative wind, whatever direction that may be. If this happens for a long enough period of time (a matter of fractions of a second), the lines will unload and the wing can fold under itself, "ball up", or even tangle in itself. The worst is if only half of it collapses, and the pilot allows the wing to turn toward the collapsing side before it re-inflates, thus, inducing a VERY sharp diving turn.

(collapses are NOT caused by the boundary layer being "blown off" or from the little lift fairies being pushed away)

For skydivers, we usually only care about the sharp, high speed turbulence (like nasty wind shear layers close to the ground, or sharp thermals, or wake turbulence from another parachute or an airplane)

In AVOIDING a low altitude collapse, MY recommendation is
1- don't fly in areas of known turbulence
2- keep the canopy speed a little slower (about 1/4 brakes) if you have to fly through turbulence. The reason for this is, for example, if there is a sharp layer of downward moving air that you are about to fly through and you are going slow, you might just slowly start sinking with this air instead flying quickly into the downdraft causing the AOA of the parachute to exceed its "neutral" lift angle and collapse.
3-MOST IMPORTANTLY, keep the parachute flying the direction you want it to fly. EVEN IF IT COLLAPSES, while it is inflating, keep the parachute facing the direction you want it to go, ESPECIALLY if you are low.

[pchapman 261]

I don't myself have a 'perfect theory for what to do in turbulence', although I've tried to teach about it in a few small canopy related courses. Calvin 19's ideas look generally good to me too, although I'm not absolutely sure what the best brake position to use is.

To expand on the idea of transit time from one airmass to another:

If the transition between air masses is sudden, with a large shear in vertical air movements in a short distance, then a faster canopy will be better, because a given down draft will create a smaller angle of attack change relative to the faster forward speed of the canopy.

But if the shear happens over a larger distance, a slower canopy will be better, as there will be more time for the canopy, despite its inertia, to change its flight path to restore a normal angle of attack with normal lift.

In between those two cases, it will be a mix of those factors at work.

So there is no one canopy or flight style that is inherently "the best" by some physics calculation.

It depends on what kind of conditions exist out there, with what probabilities, and whether you are flying in those conditions.

I recall one time when I was flying a 1.9 loaded crossbrace on a turbulent day. When I flew it to an accelerated landing, it felt ok although there were some sharp 'hits' from turbulence. When I then flew a conservative unaccelerated pattern on another jump, it bounced around a lot more, the wingtips getting softer at certain points, and it all felt scarier. But which was actually safer? High speed was probably further from any canopy collapse limits and safer in that way, yet if something had folded, flying at lower speed probably would have been better -- more time to react, less sudden canopy dive if one side folded, and a lower descent rate to begin with.

Things will depend on the canopy too.

A highly loaded canopy might like to be flown to an accelerate landing, while landing straight in leaves less flare power -- especially if hit by a down gust while about to plane out. So being a bit slow in a little brakes reduces safety at landing, whether or not is helps when up higher against turbulence.

I like the idea of loading the canopy up a bit by a gradual turning descent, something that Germain describes. But that works best with a ground hungry canopy. It might be awkward to do in a pattern with a short recovery arc canopy, as one would have to start very low even to do a gradually descending 180 from downwind to landing.

There's no one perfect answer for all conditions and all canopies.

[phoenixlpr 0]

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2- keep the canopy speed a little slower (about 1/4 brakes) if you have to fly through turbulence.

Why 1/4? I don't agree.

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The answer comes to us from our sisters and brothers in the paragliding world. They teach their students to hold a touch of tension on the brakes when flying through turbulence. The goal here is not to put on the brakes and deform the tail, but to simply take up the slack on the brake lines, in preparation for a 12-24 inch strike on the toggles to prevent a collapse. Some teach their students to hold about 5 lbs of pressure on the brakes, while others teach that we should hold no more than two inches below the “Feel Point”. Either way, taking the slack out of the brakes is like standing ready in the door, even when you can't see the count.

See Big Canopies in Turbulence By Brian Germain

So not half or 1/4 breaks, just no slack and ready to prevent your canopy surge forward.

[Calvin19 0]

Where do you think I got my aerodynamic knowledge? (Extensive paragliding flight and research, as well as my own modest stint in a wheelchair). Brian Germain has significantly more experience in parachute design than I do, and I feel that his contribution to the skydive community is paramount.

To quote the man more completely, Brian Germain-

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The answer comes to us from our sisters and brothers in the paragliding world. They teach their students to hold a touch of tension on the brakes when flying through turbulence. The goal here is not to put on the brakes and deform the tail, but to simply take up the slack on the brake lines, in preparation for a 12-24 inch strike on the toggles to prevent a collapse. Some teach their students to hold about 5 lbs of pressure on the brakes, while others teach that we should hold no more than two inches below the “Feel Point”. Either way, taking the slack out of the brakes is like standing ready in the door, even when you can't see the count.

So, on larger canopies, it appears that a light touch on the brakes may help prevent collapses. However, it is not because the canopy is more stable in this configuration, but simply that the pilot is more prepared to prevent the wing from surging forward in the pitch window. Once the wing has passed through that parcel of turbulent air, however, the job remains to regain the full flight airspeed, while maintaining positive G's. Letting the wing surge back into full flight too quickly can send the wing out of the frying pan and into the fire. Get it back to speed gently, but get back there as quickly as possible. These are opposing goals, so the actions of the pilot once again become pivotal, calling upon trained skills and acute attention to sensation.

Ultimately, the best way to handle turbulence is to deny it battle. Despite what your ego is telling you, you already have enough jumps. I know you want more, but sometimes the best way to go is to sit on the ground and watch the inexperienced jumpers get experienced.

Live to fly another day.

Brian Germain

I feel that my recommendation is very similar to BG's, if not identical, only a little more in depth. "keep the wing overhead" is at the same time controlling the surge/stopping the collapse. Remember that the "surge" is usually what causes the "neutral" pitch situation in the first place. First and foremost, fly the wing. Keep it above you. If it surges, STOP IT. if it drops behind you, LET IT FLY.
ABOVE ALL- keep it flying the direction you want it to go. and once you get low, there is only ONE direction you want it to go, and that is straight ahead.

-SPACE-

[jjudd 0]

Thanks for all the posts guys. Alot of good information and thoughts out there. I strongly believe that there is no 100% right way but there is what makes you feel comfortable and in control and like Calvin states keeps the wing over your head.

Justin

[theplummeter 14]

One more thing to throw on the fire:

Most aircraft that are bigger than a very light piston have a variable turbulence penetration speed that increases with gross weight. Last week I was flying a Pilatus that has published speeds varying from under 130 knots at very light weights to about 160 near max gross.

While these numbers are there to prevent structural damage and overspeed during a turbulence/windshear encounter, they do seem to demonstrate a correlation between wing loading and safe speeds that may translate to skydiving, although wing deflation is not a concern with airplanes.

[phoenixlpr 0]

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While these numbers are there to prevent structural damage and overspeed during a turbulence/windshear encounter, they do seem to demonstrate a correlation between wing loading and safe speeds that may translate to skydiving, although wing deflation is not a concern with airplanes.

Structural damage and overspeed during a turbulence/windshear encounter are not appliable to airfoils used in Skydiving.

[billvon 2,396]

>Structural damage and overspeed during a turbulence/windshear
>encounter are not appliable to airfoils used in Skydiving.

Sure they are. While canopies are almost (for our purposes) infinitely strong in the positive-G direction, they have almost no strength in the negative-G direction. Wind shear that causes negative G loading in an aircraft will cause severe turbulence and knock people around the cabin, but usually the airfoil will survive. Our airfoils will collapse.

[Calvin19 0]

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>Structural damage and overspeed during a turbulence/windshear
>encounter are not appliable to airfoils used in Skydiving.

Sure they are. While canopies are almost (for our purposes) infinitely strong in the positive-G direction, they have almost no strength in the negative-G direction. Wind shear that causes negative G loading in an aircraft will cause severe turbulence and knock people around the cabin, but usually the airfoil will survive. Our airfoils will collapse.

Agreed, that was where my 1/4 brakes penetration method came from. Slower penetration equals less violent turbulence.

-SPACE-

[phoenixlpr 0]

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>Structural damage and overspeed during a turbulence/windshear
>encounter are not appliable to airfoils used in Skydiving.

Sure they are. While canopies are almost (for our purposes) infinitely strong in the positive-G direction, they have almost no strength in the negative-G direction. Wind shear that causes negative G loading in an aircraft will cause severe turbulence and knock people around the cabin, but usually the airfoil will survive. Our airfoils will collapse.

Agreed, that was where my 1/4 brakes penetration method came from. Slower penetration equals less violent turbulence.

Wrong. More speed, more pressurization and keep your lines under tension. Do not give up your speed...