what injurys have u had?...what did u learn?

[phoenixlpr 0]

Skydiving related?

broken ankle(fib): don't ever go from 1/2 ..1/3 brakes to full flight on 15-20m.

[bert_man 0]

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When you turned 90 deg from downwind, your canopy was probably angled to one side. The wind was previously behind you. Now the wind is pressing on the top skin of the canopy.

Considering the fact that you have 8 times the number of jumps that I do, I am not in any way trying to be an expert.

That said, I have to disagree. The direction of the wind across the ground should have absolutely no effect on the way your canopy flies, until your feet touch the ground (excluding turbulence, etc).

Since your canopy is flying through the air, the only direct physical relationships that may act upon your canopy must come from the air itself. If the air as a whole is moving across the ground, it has no different bearing upon your canopy. It as if the air is still, and the ground is moving independently beneath the air.

If I'm wrong, feel free to let me know why.

-Ghetto
"The reason death cannot frighten me, is because life has cured me of fear."
Web Design
Cleveland Skydiving

[airtwardo 6]

Since your canopy is flying through the air, the only direct physical relationships that may act upon your canopy must come from the air itself. If the air as a whole is moving across the ground, it has no different bearing upon your canopy.

***

My .02
That might be true if you were on a round parachute that would turn with the apex as the axis. A square parachute turns with a non symmetrical pivot point, the outside of the canopy is going faster than the inside part relative to the turn.
If you stop the turn just right...90* to the wind, the inside part of the canopy was moving slower and has a lower pressure in the cells that are now being 'pushed' by the 'crosswind' against the stiffer more pressurized cells that were going faster.

That's one reason canopies are crossported these days, back when we use to jump rocks for gear...
the big old & slow 7 cell canopies use to do the accordion thing quite a bit turning downwind to base.

Different parts of the canopy are moving through
the air at different speeds, so the effect that wind has on the canopy will not be the same.

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

[bert_man 0]

All good points.

I just don't see where the crosswind is coming from. The pilot's inertia, causing him/her to swing out from the canopy, would keep tension on the entire system resulting in the relative wind always coming from somewhere below the bottom surface of the wing. Keep in mind that the pilot had been moving through the air at, say, 20mph before initiating the turn.

If a crosswind did push against the topskin of the canopy, wouldn't line tension be compromised?

I understand what you are saying about each cell moving through the air at different speeds, hence necessitating the use of crossports, etc, but I'm still not sure how the wind would act differently upon a canopy that was turning upwind than one that was turning any other way.

In both situations, the canopy begins the turn with the same airspeed, angle of attack, and angle of incidence, and is given the same control input. The only thing that I see different is the groundspeed, which has no bearing until the jumper or the canopy (hopefully not before the jumper) contacts the ground.

-Ghetto
"The reason death cannot frighten me, is because life has cured me of fear."
Web Design
Cleveland Skydiving

[bert_man 0]

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Okay...how about this,

Imagine the canopy is a cardboard box...cell dividers and all.
it's submerged in the water, and you're swimming behind it going downstream, pivot the box 90 degrees left...the inside of the pivot will have little or no 'new' water going into it where the outside section is pushing loads of it. The inside of the soggy cardboard wants to collapse even though the whole thing is still going downstream at the same relative speed to the shoreline.

Now turn it around and swim upstream...and do the same pivot, the inside lower pressure side of the 'box' is protected by the 'stiffer' outside of the box pushing all the water to make the turn.

Now think about tilting the box in the water as well.

...Jeeze I'm bad at trying to explain this stuff, where is Dr.K when ya need him?!

If you tried this exercise while drifing with the current without letting your feet touch the bottom of the stream, I think you'd see the same results no matter which way you turned, upstream or down. The stream itself would be completely stationary relative to you unless you started to swim in it.

[airtwardo 6]

The stream itself would be completely stationary relative to you unless you started to swim in it.

***

right..but you are swiming in it...the canopy has forward speed in addition to the windspeed..or current of the stream so to speak...

(You can't sleep either huh)

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

[bert_man 0]

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the canopy has forward speed

This is the airspeed

Quote

the canopy has forward speed in addition to the windspeed

Forward speed plus the wind vector = groundspeed. The ground has no effect on our canopy while it is in the air, so groundspeed can't be a factor that acts upon our canopy.

If we are flying upwind, our groundspeed is our airspeed - windspeed.

Let's say that my canopy, weighted as it is, has a full-flight forward speed of 25mph, under standard temp/pressure conditions. The wind is traveling south at 25mph as well.

If I fly downwind, my groundspeed will be 50mph, and my airspeed will be 25mph. If I fly upwind, my groundspeed will be 0mph, and my airspeed 25mph. if I fly facing due west, I will be traveling southwest at ~35.4mph, and my airspeed will be 25mph.

Every variable that I know of that affects canopy flight will be constant in each condition (relative wind, angle of attack, angle of incidence, stagnation point, static/dynamic pressure, drag, thrust, weight, temperature, density etc.)

If you are given two identical sets of conditions, and respond with two identical inputs, shouldn't the result also be identical?

What am I missing?

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(You can't sleep either huh)

No, because I'm stuck here typing shipping information for 150+ customers into MS access.

[bert_man 0]

work sucks

[bert_man 0]

Oh yea, didn't mean to hijack the thread. Here's my extensive list of lifetime injuries:

-Shattered thumb (playing baseball as a kid, swung at an inside pitch with my long, lurpy arms, and hit a line drive with my thumb)

Yep, I guess that's the list. I learned that breaking bones isn't all that fun, so I have tried to refrain from doing so again

[outlawphx 1]

1) Round reserve + 20mph winds + low pull + line over + spot over a residential area = broken ankle

Lesson learned: many, but at least breaking my ankle by kicking the top of a powerline pole kept my torso from being impaled on it. Forking out the cash for a square reserve was an easy decision after this.

2) Night jump + only one car's headlights illuminating the landing area + swooping my Nova + one piece of jagged PVC pipe sticking out of the ground = 25 stitches to my lower leg

Lesson learned: don't swoop through the middle of the desert with no illumination

3) Flaring a Sabre two feet to low on a hot day = four stitches to my knee

Lesson learned: although I stood up the landing, I dragged my knee for a couple feet on the rocks before popping back up. Heat definitely affects density altitude.

[billvon 2,400]

>and has a lower pressure in the cells that are now being 'pushed' by
> the 'crosswind' against the stiffer more pressurized cells that were
> going faster.

Nope. Airplanes turn in 120mph jet streams all the time. Doesn't affect them. All the airplane (or parachute) can see are relative winds; they can't see crosswinds or tailwinds or anything. Those terms only have meaning to someone standing on the ground.

[BillyVance 34]

broke my radius bone in at the wrist going out the door of the Otter on a 5 plane formation load (100+ way). Started to lose my balance running to the door, stuck my hand out so I wouldn't bang my shoulder on the doorframe. The line of skydivers just surged forward. You're either in sync with the flow or you're not.

Lesson learned: shit happens...

"Mediocre people don't like high achievers, and high achievers don't like mediocre people." - SIX TIME National Champion coach Nick Saban

[airtwardo 6]

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>and has a lower pressure in the cells that are now being 'pushed' by
> the 'crosswind' against the stiffer more pressurized cells that were
> going faster.

Nope. Airplanes turn in 120mph jet streams all the time. Doesn't affect them. All the airplane (or parachute) can see are relative winds; they can't see crosswinds or tailwinds or anything. Those terms only have meaning to someone standing on the ground.

***

I understand that...
but the airfoil remains constant during the turn, not necessarily so with 'some' canopies.

I have an old paraplane that I can collapse at will when doing a downwind to crosswind turn...
I'm not an engineer as you are...but to my thinking
one of the many variables that causes that to happen is the lower pressure / less lift on the turning side deforming the airfoil integrity to the extent that the 'slip' is causing it to temporarily collapse....

Doesn't seem to happen during upwind turns..


I understand the leaf in a stream thing...but something else is happening in there somewhere.
I've had it happen and seen it happen to many times to be a rare anomaly...
(on older slower canopies)


Or something like that?!

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

[uponone 0]

Wouldn't your canopy react differently depending on the difference in speed of yourself and the wind speed? For instance, if your traveling at 30mph and your going downwind and windspeed is only 10mph it wouldn't have as much effect, but if the wind was traveling at 30mph or more....

edited to make more sense

[bert_man 0]

Maybe the pilot is expecting the downwind->croswind turn to be different, so they are subconsciously doing something to compensate?

Or, more likely, the pilot is being hit by a gust during the turn. What billvon and I are speaking about is referring only to a static breeze, but if you are hit by a gust during the turn, it would have the 'crosswind' effect. In this case, everything you've been saying about the cell dynamics in the turn would be correct, and the downwind->crosswind turn would be the most susceptible to this gust.

[bert_man 0]

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Wouldn't your canopy react differently depending on the difference in speed of yourself and the wind speed? For instance, if your traveling at 30mph and your going downwind and windspeed is only 10mph it wouldn't have as much effect, but if the wind was traveling at 30mph or more....

edited to make more sense

the wind speed itself shouldn't matter at all, once you and the parachute are moving in equilibrium with the wind. You could be flying your canopy blindfolded in hurricane katrina and if you flared your canopy in the air, right up to the stall point, you would feel very little wind at all. You wouldn't know you were even in a hurricane until you smashed into the side of the superdome at about 120mph+ (except for the whistling of the wind around the buildings below, of course)

If you were at 2000ft in hurricane katrina, traveling downwind, and there were (magically) no gusts at all, you could still make a downwind->crosswind turn just like you would on a sunny sunday at the DZ.

Then you would probably begin begging the wind goddess for some type of miracle as you watched the ground race past your feet as you slowly descended into nature's meat grinder.

[Rdy2skydive 0]

Lets see.....
Jump 100 - a concussion, cuts on my face, torn muscles in my chest, whiplash and bruises everywhere.

Lesson Learned: Object fixation is a bad thing and don't forget to flare!

[jsaxton 0]

I had a sizeure while taking Zyban. Luckily I was on the ground.

[happythoughts 0]

quote]the wind speed itself shouldn't matter at all, once you and the parachute are moving in equilibrium with the wind.

He was not moving in equilibrium with the wind. The wind continued in one direction. He said that he turned at a 90 degree to it. In effect, he has now stopped and the wind is now pressing on the topskin of the canopy.

The forward motion of the wing is what creates internal pressurization. Internal pressure is what maintains the wing shape. Slowing down and change in direction and could reduce it.

A low internal pressurization and a pressure on the topskin could cause the canopy to collapse.

He said that he had a canopy collapse.

Jump numbers don't mean that I'm a canopy expert, I'm not. I'm a very cautious canopy pilot.

When I had 80 jumps, I had a similar experience to the one described over a chain link fence at 30 ft on a windy day.

[headoverheels 291]

Severe injury to my checking account. Every time it starts getting better, I re-injure it.


Sprained ankle, landing on a large dirt clod. Out from jumping for 6 weeks.

[bert_man 0]

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***the wind speed itself shouldn't matter at all, once you and the parachute are moving in equilibrium with the wind.

He was not moving in equilibrium with the wind. The wind continued in one direction. He said that he turned at a 90 degree to it. In effect, he has now stopped and the wind is now pressing on the topskin of the canopy.

The forward motion of the wing is what creates internal pressurization. Internal pressure is what maintains the wing shape. Slowing down and change in direction and could reduce it.

A low internal pressurization and a pressure on the topskin could cause the canopy to collapse.

He said that he had a canopy collapse.

Jump numbers don't mean that I'm a canopy expert, I'm not. I'm a very cautious canopy pilot.

When I had 80 jumps, I had a similar experience to the one described over a chain link fence at 30 ft on a windy day.

When I said 'equilibrium with the wind', I meant only at the instant that he started the turn. No matter your heading in relation to the wind, if you are at full flight, you have the exact same airspeed and angle of attack.

After the 90 degree turn, he has not stopped, and the wind is not blowing on the topskin of his canopy any more than it might if he were turning downwind. He has slowed down relative to the ground, but that is irrelevant. He is part of the atmosphere, not the ground.

If you thoroughly read this document, you will notice that none of the equations (other than the ones calculating groundspeed) ever actually take into account the speed/direction of the wind across the ground. The only factors that are taken into account are, correctly, the atmospheric conditions within the block of air surrounding the canopy, relative wind conditions at various points on the canopy's surface, and the attitude of the wing itself in relation to the relative wind and the horizon.

If he is moving downwind and turns crosswind, he does not stop moving, he keeps moving with the wind that he was already moving in. He has turned crosswind, yes, but now he is moving sideways with the wind. The wind has affected him in the exact same way it did before the turn, and that is only to change his speed/direction across the ground.

Does anyone else agree?

(edited to fix quote tags)

[happythoughts 0]

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The only factors that are taken into account are, correctly, the atmospheric conditions within the block of air surrounding the canopy, relative wind conditions at various points on the canopy's surface, and the attitude of the wing itself in relation to the relative wind and the horizon.

Right. If you were going downwind and turn right, the relative wind is now coming from what direction ?

If you turn to the right, the right side of your canopy may dip to the right. Attitude of the canopy is now angled to the right and exposes the top surface to the relative wind.

If you slow down enough, and lose pressurization, it's not an airfoil anymore, it's just a sail with wind blowing against the top (and collapsing it).

All this aside, that is my theory on why his canopy may have collapsed. This thread was all about mistakes and what to learn from them.

[ryoder 1,384]

You are correct.

"There are only three things of value: younger women, faster airplanes, and bigger crocodiles" - Arthur Jones.

[bert_man 0]

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Right. If you were going downwind and turn right, the relative wind is now coming from what direction ?

If you turn to the right, the right side of your canopy may dip to the right. Attitude of the canopy is now angled to the right and exposes the top surface to the relative wind.

I italicized the word 'relative' 3 times in my post. relative wind is the wind moving in relation to the canopy. If you fly in full flight downwind (or any direction), the wind is coming from the front of the canopy to the back (and up), if you make that 90 degree turn, the relative wind is still coming from the front of the canopy! (or diagonally across the topskin, depending upon the aggressiveness of the turn). The wind never pushes on the topskin, because the relative wind is ALWAYS going to come (generally) from in front of and beneath the wing in a simple 90 degree turn.

You can't slow down enough and lose pressurization in the manner that you speak, because you will always be moving forward relative to the air, which is what keeps the cells pressurized. If you were to have a breeze hit the top of the canopy, the canopy would simply lose altitude fast while staying pressurized.

See? Ryoder knows what I'm talking about