Becoming unconscious under open canopy

[JohnMitchell 14]

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If a pilot wants to hold a given course and there is a crosswind component to deal with, the pilot must hold a different heading to keep the plane from drifting off down wind of the crosswind component.

A course is a certain track across the ground. If there is a crosswind, the pilot must hold a different heading to fly a given course, not to keep the plane from "drifting off downwind".

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The only thing that counts is what you or your canopy is doing relative to the ground. If you put your canopy or a plane at a 45-degree angle to the relative wind, put the controls to natural and let go, the canopy or the plane will turn down wind.

How do you put your canopy at 45 degrees to the relative wind? I can't make my canopy fly almost sideways thru the air! I can make it crab across the ground on a windy day.

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That is one of the reasons there are trim wheels on airpanes. The relative wind on the 45 degrees is greater than the relative wind on the nose of the plane or canopy. The slower the plane or canopy is moving, the greater the effect will be.

The trim wheels are there to make the plane fly straight and true, regardless of wind conditions. Once again, airplanes, unless out of trim or doing aerobatics, fly strainght into the relative wind. Their course across the ground is affected by winds aloft, but the wind flowing over the wings is not affected by what the winds aloft are doing, unless the aircraft is tied to the gound with a rope, like a kite.

Guiding airplanes is what I do for a living.

[mjosparky 3]

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Guiding airplanes is what I do for a living.

And the only thing that counts is where you guide that airplane relative to the ground. A cross wind will push you down wind of your course if you do not make control inputs to stop it. You may be able to hold you heading but not your course. Your course is your chosen line across the ground not through the sky.

Sparky

My idea of a fair fight is clubbing baby seals

[JohnMitchell 14]

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If you put your canopy or a plane at a 45-degree angle to the relative wind, put the controls to natural and let go, the canopy or the plane will turn down wind.

This was one of your original statements. I think our debate is starting to drift off course. I agree that canopies drift in the wind, and their track across the ground is affected by the winds aloft. You and I both used to jump the round canopies. If you didn't understand drifting in the wind, you learned to take long, sweaty hikes carrying parachutes.

What I don't agree with is the statement that an untended parachute will automatically turn downwind, like a weathervane will turn into the wind. That statement is wrong.

And by the way, air traffic controllers give compass headings to the aircraft to fly, and adjust those accordingly to the winds aloft to get the desired groundtrack. We do not assign an aircraft to fly a certain ground track.

[tso-d_chris 0]

I agree that weathervaning will not always turn a canopy downwind. See quote from one of my previous posts. (The stabilizer shape is a very big factor, and I initially failed to consider it.)

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There are many other factors that need to be considered that will determine whether that orientation is into the wind, or downwind; among them is where the CG is on the planform and the shape of the stabilizers.

All I'm saying is that a given canopy will weathervane in a similar, consistent manner given similar conditions.

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It's a roll of the dice as to which way you'll be facing when you land. Agreed?

I think this is being considered in Newtonian terms, not quantum. What makes it seem random is our poor ability to predict wind accellerations.

[tso-d_chris 0]

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How do you put your canopy at 45 degrees to the relative wind? I can't make my canopy fly almost sideways thru the air! I can make it crab across the ground on a windy day.

Fly with the wind line, then turn 45 degrees. Your canopy does not change its velocity instantaneously, it has to take the time to accellerate. During that time, the relative wind is not coming from straight ahead. It is during these times that any weathervaning is going to occur.

An positive average accelleration implies that the wind accellerations will not balance to zero, so neither can the weathervaning.

[JohnMitchell 14]

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How do you put your canopy at 45 degrees to the relative wind? I can't make my canopy fly almost sideways thru the air! I can make it crab across the ground on a windy day.

Fly with the wind line, then turn 45 degrees. Your canopy does not change its velocity instantaneously, it has to take the time to accellerate. During that time, the relative wind is not coming from straight ahead. It is during these times that any weathervaning is going to occur.

An positive average accelleration implies that the wind accellerations will not balance to zero, so neither can the weathervaning.

My canopy doesn't change it's heading immediatley either. Like any wing, it banks to the side and changes the vector through lift. I'm still not flying my canopy at 45 degrees of slip. Tie some yarn tufts on your a-lines as slip indicators, then go video some turns. You'll see what I'm saying.

As far as the quantam aspects, I'm a pretty Newtonian guy, but I think I see what you're trying to say. That in the chaos of turbulence there are subtle patterns in the currents pushing the nose of the canopy downwind, right? How large are those effects compared to the more mundane factors such as canopy trim. I also think, relativistically, that the canopy is moving constantly forward in a large air mass, subject to random gust loads, and does not relate to which direction that air mass is moving across the ground. It knows not upwind or downwind.

[tso-d_chris 0]

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I also think, relativistically, that the canopy is moving constantly forward in a large air mass, subject to random gust loads, and does not relate to which direction that air mass is moving across the ground. It knows not upwind or downwind.

By and large, you are correct. But we are talking about zero pilot input. In effect, the things that on any other jump have effects so small we can counter them by leaning a tiny amount, actually make up the majority of the forces at hand controlling heading. Thus, they become significant.

BTW I was wrong about it always being downwind. But weathervaning will be consistent, all else being equal (which it never is).

Of course, the liklihood of thinking about any of this under such rare conditions is slim to none. Except for the fact that its been raining nearly every day here for several weeks now, there's no real world purpose for the discussion.

[speedy 0]

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But weathervaning will be consistent

Have you not noticed that the main difference between a weathervane and a canopy is that the weathervane is fixed to the ground?
As John said, a canopy in flight cannot see the ground and thus cannot be influenced by a wind direction that is measured relative to the ground.

Dave

Fallschirmsport Marl

[tso-d_chris 0]

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Have you not noticed that the main difference between a weathervane and a canopy is that the weathervane is fixed to the ground?

I've noticed lot's of differences, actually.

I didn't use the term weathervane first, but I have to admit it is sure a lot easier to type than "find its preferred orientation relative to the Earth due to the second derivative of the position of the air molecules, amongst which the canopy flies, relative to the Earth." (Even if a weathervane only gives us information about the air molecules' position's first derivative.)

Even without being fixed to the earth, the jumper plays the same role in keeping the canopy fixed on two axis while allowing freedom of movement on a third axis as the fixed shaft of a weather vane.

[JohnMitchell 14]

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I've noticed lot's of differences, actually.

Like what? I've never observed my canopy wanting to turn downwind more than upwind.

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I didn't use the term weathervane first, but I have to admit it is sure a lot easier to type than "find its preferred orientation relative to the Earth due to the second derivative of the position of the air molecules, amongst which the canopy flies, relative to the Earth." (Even if a weathervane only gives us information about the air molecules' position's first derivative.)

Well, you got me there. I only had a year or two of calc, and I didn't like it. Maybe my 16 year old can help me with this when she gets back from her summer internship at Sun Microsystems. Kallend, are you out there anywhere?

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Even without being fixed to the earth, the jumper plays the same role in keeping the canopy fixed on two axis while allowing freedom of movement on a third axis as the fixed shaft of a weather vane.

Well, I'll agree with that. I've never had my canopy miraculously zoom underneath me in flight. I will concede that gravity is still doing it's job. You're mixing your apples with your oranges.

[JohnMitchell 14]

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BTW I was wrong about it always being downwind. But weathervaning will be consistent, all else being equal (which it never is).

That is what we have been saying all along.

[goose491 0]

We have to 'crab' to maintain a particular flight direction when flying in a cross-wind. That in itself shows that the canopy does not turn because of cross wind... it merely 'strafes' for lack of a better word.

It is no different than any other wing. Point yourself North with a wind from the west, your canopy will fly North-East... but it will not point itself East, it will maintain it's Northern heading. You as the pilot, must point it sligthly West if you wish to continue flying North.

My Karma ran over my Dogma!!!

[pilotdave 0]

A lot of people are missing chris' point (which I still don't believe, but that's not important). He isn't talking about steady winds. He's talking about gusts. If you are flying north and a gust comes from the west, it will induce a crosswind component over the canopy. It's exactly the same as if the canopy was "skidding" through the air. He believes that, in the situation i just mentioned, a canopy will have the tendency to turn slightly to the east. Another gust from the west will turn it more to the east. Eventually the canopy will be facing east, directly downwind.

I just don't think it's true. If it was, I believe the canopy would be unstable in yaw and basically be uncontrollable.

If it was true, at least the way I see it, the turn induced by each gust would increase the crosswind component and therefore increase the tendency to turn. The canopy would want to fly backwards. Or more likely the sideslip angle would increase until the canopy depressurized and collapsed. Throw one of those balsa wood glider toys backwards and see what it does.

Dave

[goose491 0]

A gust is no more than a significant and sudden change in wind speed.

Flying North when a sudden increase in the winds from the west is observed will not turn you to the East any more than flying North with steady winds from the west.

It's like a Kayak placed perpendicular the flow on a river. It's got a roll stabilizer at the back which is no more than a fin. If the kayak had a pole passing right through it's center (top to bottom) which went right to the bottom and into the ground, the fin would catch moving water and would spin the boat about said pole to face upstream much like a weathervain into wind. However, without anchoring it's vertical axis like this, the boat will simply travel downstream, remaining perpendicular the river.

This holds true if you slow the rivers flow down, if you stop and start it again. It does not matter the speed or consistency of speed of the moving water.

Note that a weathervain turns into wind by pivoting around an anchored vertical axis. In the absence of this anchored vertical axis, the weathervain will merely fall over in the direction the wind is blowing.

My Karma ran over my Dogma!!!

[billvon 2,396]

>Flying North when a sudden increase in the winds from the west is
> observed will not turn you to the East any more than flying North
> with steady winds from the west.

Actually, it will do the opposite.

A canopy cannot fly sideways with respect to the relative wind. If it did, it would deflate and all sorts of bad things would happen. It is therefore designed so it weathervanes; it always points into the wind, and will change heading to maintain that if wind direction changes suddenly. This is part of what makes it hard to land in turbulence, because the canopy is constantly 'seeking' the relative wind.

So if a gust from the east comes along, and you're flying north, the canopy will turn _into_ the gust and keep flying. When the gust goes away then it will turn back, because that will be seen by the canopy as a sudden gust from the west. It probably won't turn back to exactly north since there are so many variables.

[tso-d_chris 0]

Let me try this from a different approach...

Why is there a necessity for auto pilot on commercial jets. Why can't the pilot just take of from LA, point the plane towards New York, and then go catch the inflight movie?

Or...

Why won't you jump on the front of a storm? Is it not because the extreme accelerations of the air that you are flying in will make your canopy do some really effed up things?

Now, imagine that same turbulence, with the intensity turned way, way down, such as might be found on a typical summer day.

If the winds are increasing, then the second derivative of a function modeling the position of the air molecules relative to the earth is going to be positive. If the winds are decreasing that same second derivative will be negative. The important point is that, in both cases, the second derivative of the position function, aka accelleration, is not zero.

The reason this is important is because it implies that at any given time, the velocity of the canopy relative to the airmass in which it is flying, is constantly changing, either in direction or magnitude. This is do to the jumper/parachutes inertia, and the asymetrical surface area being exposed to any crosswind component.

This asymetrical surface are allows the force of the air molecules that are colliding with the canopy to be applied diferentially, which will change the heading ever so slightly. So slightly that any input on the part of the pilot is going to be huge by comparison.

But, the scenario at hand does not allow any pilot corrections. That is what makes the tiny heading changes accumulate predictably.

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Maybe my 16 year old can help me with this when she gets back from her summer internship at Sun Microsystems.

She'll be probably be able to do a better job than me. Sounds like you area justifiably proud papa.

For Great Deals on Gear

[cchandler 0]

Arrgghhhh.

OK enough about this old aviation myth. The "downwind turn" in flying was dispelled many, many years ago.

Imagine this scenario and you will see that the wind direction relative to flight in an airmass doesn't mean squat.

Envision that you've opened at 14,000 feet above a solid undercast at 2,000. You have no reference to the ground so will not be confused by ground speed or ground track.

Now point your canopy in any direction. It will fly straight (excluding rigging or jumper induced inputs) regardless of the wind direction. Feel free to toggle turn as many degrees in any direction as desired and stop the turn. Once again, the canopy will fly straight.

Canopy airspeed, rate of turn, rate of descent and stability are NOT affected by the wind direction. However, ground speed and ground track are affected by the wind. This common misunderstanding is proven wrong by accurate observation and calculation.

TSO-d Chris, please give it up dude. Major flaws in your analysis.

[goose491 0]

I understand that a canopy cannot fly sideways. lol. But that has nothing to do with it deflating. A solid wing cannot fly sideways either. Remember a wing flies within a box of air and does not care what that box of air is doing. My point is, it never experiences a "Push" from the side if there is a crosswind. It merely travels sideways with the wind, if said wind is coming from the side.

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A canopy cannot fly sideways with respect to the relative wind.

Careful here, the "relative wind" will always be equal the airspeed of the canopy and opposite it's direction of flight. What the winds are doing relative the earth is irrelavent. As canopy pilots, we can only mention a "cross-wind", when we know the winds to be acting perpendicular the desired flight path. At this point, pointing the canopy into said crosswind is very much a deliberate act to keep on your desired flight path.

Don't unstow your breaks. Don't do a thing. Point yourself in one direction. You may not continue to fly in a straight line, towards say a fixed target on the ground, but your canopies heading will not chage when your crosswind component does.

Just like that boat in the river, I was not stating that it would be traveling sideways along the water... it travels sideways with the water and relative the shore. Changing the speed of the waters flow will not alter the heading of the boat. That's all.

My Karma ran over my Dogma!!!

[pilotdave 0]

Chris, you're talking steady winds. A twin otter has more surface area in the back than the front (because it has a tail). A gust from the left (non-steady wind) will cause it to turn to the left...weathervaning. A better example is if you kick the right rudder pedal then let go, the plane will be sideslipping to the right (ie there will be a crosswind component from the left). The tail, without pilot input, will cause the plane to yaw left, back into the relative wind.

If you had a plane with the tail on the front, it would fly just fine until there was any yaw disturbance. A tiny sideslip would cause a yaw moment in the same direction as the yaw, causing further yaw, causing further moment, causing further yaw, etc. The plane would "groundloop" in the air.

A canopy would do the same thing IF it really did have a tendency to turn "away" from a sideslip component.

It's not about WIND, it's about RELATIVE wind. An unsteady crosswind is just one way a canopy will see a relative wind from an angle other than straight ahead. Turning (by pilot input) is another.

Dave

[billvon 2,396]

>Canopy airspeed, rate of turn, rate of descent and stability are
>NOT affected by the wind direction.

They are indeed affected by _changes_ in wind direction.

Try the following experiment. Go flying on a windy day near mountains. Trim up the aircraft and let go of the controls. You will find that the aircraft will turn left and right as changing winds hit it. An airplane cares very much if the relative wind, formerly right off the nose, changes so that it's hitting the side of the vertical stab instead. The aircraft will immediately point into the new relative wind.

I agree, though, that in a steady wind, the canopy (or airplane) doesn't care what the wind is doing with respect to the ground.

[tso-d_chris 0]

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Major flaws in your analysis.

Feel free to elighten us.

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Envision that you've opened at 14,000 feet above a solid undercast at 2,000. You have no reference to the ground so will not be confused by ground speed or ground track.

Now point your canopy in any direction. It will fly straight (excluding rigging or jumper induced inputs) regardless of the wind direction. Feel free to toggle turn as many degrees in any direction as desired and stop the turn. Once again, the canopy will fly straight.

If there is no reference to the ground, you have no way of knowing whether your claim is true or not.

All you experiment shows is that the canopy maintains a constant position relative to the jumper.

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The "downwind turn" in flying was dispelled many, many years ago.

Kindly explain, then, exactly how the myth was dispelled. What experiments were conducted? How were they conducted? Were people used to fly the canopy, or dummy weights? How many different canopy models were used? How many jumps per canopy? How were the wind conditions changing? What was the air density observed for the experiments?

Variables, variables, variables. Forget to keep track of any of them, and things which aren't random will appear to be.

For Great Deals on Gear

[cchandler 0]

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Chris, you're talking steady winds. A twin otter has more surface area in the back than the front (because it has a tail). A gust from the left (non-steady wind) will cause it to turn to the left...weathervaning. A better example is if you kick the right rudder pedal then let go, the plane will be sideslipping to the right (ie there will be a crosswind component from the left). The tail, without pilot input, will cause the plane to yaw left, back into the relative wind.

If you had a plane with the tail on the front, it would fly just fine until there was any yaw disturbance. A tiny sideslip would cause a yaw moment in the same direction as the yaw, causing further yaw, causing further moment, causing further yaw, etc. The plane would "groundloop" in the air.

A canopy would do the same thing IF it really did have a tendency to turn "away" from a sideslip component.

It's not about WIND, it's about RELATIVE wind. An unsteady crosswind is just one way a canopy will see a relative wind from an angle other than straight ahead. Turning (by pilot input) is another.

Dave

Ahhhhh, and the confusion continues. In an effort to avoid a technical discusion I used my previous post as an example. I thought it would be adequate.

Dave, sorry dude, but you are confusing wind (caused by Mother Nature) with relative wind which is a term used to describe the airflow which is opposite the direction of flight. And now don't confuse flight with ground track
If an airplane, or parachute, is exposed to increased wind velocity (gust) from a particular direction, the airplane, or parachute, will move in the opposite direction (or decrease it's velocity) an amount equal to the velocity of the gust. The aircraft will NOT turn. Additionally, this movement is only relative to the ground, not the air that the aircraft is flying in.

As far as having a "tail" in the front and it not working, let's keep it our secret and not tell the Wright Brothers.
http://www.nasm.si.edu/exhibitions/gal100/wright_flight.jpg

[evh 22]

Perhaps my previous post was too long, too complicated or whatever.....so I'll try again.



>So if a gust from the east comes along, and you're >flying north, the canopy will turn _into_ the gust >and keep flying.

Yes, this is called stability. If a canopy did the opposite it would be very annoying.


>Canopy airspeed, rate of turn, rate of descent and
>stability are NOT affected by the wind direction.

Agreed. Wind direction or windSPEED have no effect on the wing.

Accelaration however HAS some effect, as clearly explained by BillVon.
In his example he used gusts of wind, i.e. an acceleration followed by an equal decelleration turning the canopy left then right (or vice versa), so the endresult would be roughly the same heading.

But what if there is only an acceleration, NOT followed by an equal decceleration?? The canpopy would constantly turn in 1 direction, which is towards the direction from where the air accelerates!
Unlikely scenario?

My point: this is exactly the environment in which we fly our canopies:
When we get closer to the ground, windspeed decreases.
in other words: the air deccelarates in the downwind direction (right?)
In other words: the air accelarates in the upwind direction.
The canopy still turns towards the drection from where the air accelerates, which happens to always be......downwind!!

[evh 22]

gee I should learn to type faster... 6 new replies already

[tso-d_chris 0]

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If an airplane, or parachute, is exposed to increased wind velocity (gust) from a particular direction, the airplane, or parachute, will move in the opposite direction (or decrease it's velocity) an amount equal to the velocity of the gust.

True, but this change will not occur instantaneously, and that is the key in this scenario. The "flies at a constant velocity relative to the airmass" theory is only completely true if the airmass has a constant velocity. Change the velocity, and you intoduce new forces to the system.

Of course, with a conscious jumper these forces are going to cause minute changes that are easily corrected without toggles. But without any pilot input, those minute changes will accumulate, and could substantially affect heading over the course of the descent.

And, to clarify, I WAS WRONG ABOUT IT ALWAYS PREFERRING A DOWNWIND HEADING. There are factors of the canopy design which will affect whether a canopy "prefers" a downwind or into the wind heading. I initially failed to take all these factors into consideration. The fact remains, however, that an asymetrical surface area of the airfoil profile + stabilizer will result in predictable heading changes in known, changing wind conditions.