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jtravis121

Recovery Arc vs. Wind Speed

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jtravis121

pchapman,

Thank you for your reply. It makes sense because what I am describing and what I started out looking for was "the messy parts" the parts in the real world with wind shear and when the wind changes.

The first part I want to address is you quoted me about the 120 canopy seeing less drag. I was comparing that to a 150 canopy, important because I feel many people responding to this thread are jumping smaller canopies than I and not experiencing the effect of the sudden headwind as much as I.

The second part is your comparison to walking in jetliner and turning 90 degrees into your chair. Not hard, until you try to do it when the plane hits turbulence and you are not buckled in and then you do bounce off the ceiling. The turbulence only hit the plane and newtons laws kicked in.

A real life example of what I am describing is messy.

I am setting up for a 90 degree front riser turn. The winds are out of the South at 15mph. I am on a cross wind leg so I am experiencing some side push but this does not affect my forward speed very much and I begin my dive and then my turn.

As I snap out of my turn, my canopy and myself are now both facing a headwind that we were previously not facing (or a sudden increase in wind force beyond what was created by normal drag that I would experience when making that same turn on a no wind day)

Once facing that new wind, with new momentum generated by the dive and the turn, the canopy will be forced to slow down at a rate much quicker than when there is no wind. (The situation that I have become consistent with)

During all of this the quick impact of the new headwind does not affect my body nearly as much as it does my canopy.

The quicker slow down of the canopy swings me under the canopy sooner than I am accustomed too, changing the pitch sooner after completion of the turn. Sooner translates to higher.



You are still thinking it with the ground as reference, forget the whole ground for a while and just keep thinking about the air mass... Canopys airspeed stays exactly the same whether you're going agaisnt headwind of flying with a tailwind, however your GROUNDSPEED does change... For the aerodynamics of the wing AIRSPEED is the only thing that matters...

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This will help you out. She's got the headwind nailed.

Otherwise, do I smell troll?
Every fight is a food fight if you're a cannibal

Goodness is something to be chosen. When a man cannot choose, he ceases to be a man. - Anthony Burgess

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The question has been well answered by some of the people in the thread. But here is the thing Flight One explain in their 101 course, to sum it up:

1. Wind is simply the air mass moving over the ground.
2. Your canopy flies through the air mass, not over the ground.

Everything else follows from that.
--
"I'll tell you how all skydivers are judged, . They are judged by the laws of physics." - kkeenan

"You jump out, pull the string and either live or die. What's there to be good at?

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jtravis121


I am setting up for a 90 degree front riser turn. The winds are out of the South at 15mph. I am on a cross wind leg so I am experiencing some side push but this does not affect my forward speed very much and I begin my dive and then my turn.

As I snap out of my turn, my canopy and myself are now both facing a headwind that we were previously not facing (or a sudden increase in wind force beyond what was created by normal drag that I would experience when making that same turn on a no wind day)



jtravis, I like the way you try to find the answers. pchapman's post was excellent - try to read it few times, maybe you'll find some more answers there.

As for the quoted part - if the wind is the same throughout the turn (not likely in real life, but let's assume so, for now ) you will not be facing any change / difference in the wind after snapping out of the turn no matter which way you've turned (downwind or upwind). You are still in the same airmass which in relation to you is acting in the same way
Imagine there's so ground below you - in this case you won't be able to notice if you're going up or down or crosswind.

Imagine a swimming pool on a jetliner, which is flying at perfectly constant speed and direction. Is it harder to swim in one direction than in the other? If you dived head first to the water, would you hit the bottom easier if you jumped one way or the other?
Answer to both is 'No' - it's the same with the wind - it's this huge constant airmass which is going in some direction.

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jtravis121

I am setting up for a 90 degree front riser turn. The winds are out of the South at 15mph.



15mph relative to what? The Ground. The ground has no relevance to canopy flight.

If you are trying to understand canopy flight in terms of the ground, you are not understanding canopy flight.

You are in that 15mph wind regardless which direction you are going. Crosswind is a reference to your movement across the ground, not your movement in the wind.

If there were no ground to change your (re)actions and perceptions, and you did your turn exactly the same in any stable airmass, your altitude loss and plane out would be the same each time, regardless of whether that airmass had a ground speed of 1mph or 200mph. How you hit the ground would vary considerably in those two airmasses though...

Please correct me if I'm wrong on any of the above! I'm pretty sure I'm not though...
Sky Switches - Affordable stills camera tongue switches and conversion adaptors, supporting various brands of camera (Canon, Sony, Nikon, Panasonic).

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Keep working on thinking about being in a 'block of air' that you're in. It doesn't matter if the ground is sliding by at 1, 15, or 100 mph. (In reality of course there may be some turbulence etc)

If you were in a balloon in that block of air and closed your eyes, you wouldn't know whether it was a windy day or not. Everything would be calm, with no wind in your face no matter which way you faced. The balloon would be serenely drifting in the air mass at the same speed it is moving.

If you now jumped out and opened your parachute, it wouldn't know which way the wind was blowing either. Only when you look at the ground do you notice your block of air is sliding over the ground.

What if you jumped from the balloon in a jet stream doing 200 mph?

And you open your canopy above a high stratocirrus cloud layer, so you can't even see the ground. If you turned your canopy one way, would it pitch up out of the dive crazy fast because of facing a 200mph headwind? Or super slow in the other direction?

No it wouldn't. Your canopy may be doing 170mph groundspeed flying upwind or 230mph groundspeed flying downwind, but the parachute isn't in any way affected by what the ground is doing down below.

You'd also owe beer for your first jetstream balloon jump.

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Joellercoaster

The question has been well answered by some of the people in the thread. But here is the thing Flight One explain in their 101 course, to sum it up:

1. Wind is simply the air mass moving over the ground.
2. Your canopy flies through the air mass, not over the ground.

Everything else follows from that.




First of all, I comletely agree. Groundspeed means nothing, airspeed and gravity is all the canopy "feels".

There is however one detail that makes things a bit more complex.
The wind is not constant for all altitudes; especially close to the ground the differences can be significant.
So when you descend under canopy, the wind suddenly changes, to which the canopy has to react. Just like it has to react to a gust of wind.
In theory, I can imagine this would affect the recovery during a swoop; However i do not have enough swooping experience to notice it at all.

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My original question was how/if did wind affect lift. I was wrong.

First. I want to thank everybody for not flaming me as I work through this and taking the time to discuss this.

Second. I believe everybody is stuck on two ideas that they are trying to prove to me. The idea that ground speed has no effect on the airspeed of the canopy, which I understand. And the idea that you are in a bubble of air, such as when you are in a jetliner walking down the isle and turning left.

I believe the Jetliner example (or the in-a-balloon example) are both incorrect because nobody here has mentioned the real world of momentum and newton's laws as we cannot ignore those in real life.

If a jetliner slows rapidly it doesn't matter which direction you were walking or even sitting, you will be thrown forward.

Under canopy, aerodynamic properties remain constant until a change is enacted upon them.

Example A: A bowling ball and a piece of paper are falling through the sky and then encounter a 200mph wind, the paper will change course must faster than the bowling ball.

The paper's relative velocity and direction to only the bowling ball change quicker due to the difference in mass vs. surface area the wind contacts.

With a canopy at any point, with no relation to the ground, a person is a swinging weight under the canopy that is affected differently by the wind force than the canopy.

My original question was how did wind affect lift. I was wrong. I understand that after not only asking it here, but researching it.

At somepoint yesterday it dawned on me that airspeed did not affect the lift of a canopy but the pitch did (no matter the ground speed, or wind speed, because of the moving airmass) and I was confusing the two because velocity is something you also have after a turn and I was only thinking in terms of how the velocity affected the canopy individually and not how the velocity affected the person and the pendulum affect.

My question then changed to what might be better explained from my point of view as how does wind effect pendulum dynamics (no matter what altitude).

The pendulum dynamics are a separate function of flight outside of the moving airmass.

Pendulum dynamics are what cause the oscillations of the canopy after a turn as it returns to it's normal flight path. At a high altitude, (with no ground reference, after completing a turn the drag on the light weight canopy is higher than on the heavy person who then swings under the canopy and then in front of the canopy causing the canopy to change pitch and create a moment of lift. The person then swings back under the canopy and a little bit behind it causing another pitch change and the canopy to dive. This oscillation occurs until the person is stable directly under the canopy and normal flight path is achieved.

So again, and this is the question/theory, and it will be posed with no ground reference.

When swinging into a headwind, which will have more opposing force on both objects (the canopy and the person) does the wind force/increased drag affect the speed at which a person swings under the canopy compared to turning into no wind because of the difference in the change of velocities between the two objects affected (the canopy and the person) due to their very large difference in momentum.

Please remember this is posed as a real world question, not a question of controlled airspeed, drag and momentum in say a vacuum.

Also remember, none of this has to do with ground reference.

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Wow, you've really got yourself wrapped around the axle with this one, but you're still operating on a significant piece of flawed logic.

You are not "swinging into a headwind". It's been pointed out to you numerous times, but you keep ignoring it. You are one with the airmass you are flying in, there is no headwind or tailwind until you begin to reference the ground. There is only your velocity with respect to the airmass you are flying in. Turn to the east and wait 10 seconds, you'll be flying at whatever your canopies "resting" airspeed is through that airmass. Turn back to the west, and it'll be the same. The dive and recovery will also be the same, all of this irregardless of which way or how fast the airmass is moving.

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jtravis121


When swinging into a headwind, which will have more opposing force on both objects (the canopy and the person) does the wind force/increased drag affect the speed at which a person swings under the canopy compared to turning into no wind because of the difference in the change of velocities between the two objects affected (the canopy and the person) due to their very large difference in momentum.

Please remember this is posed as a real world question, not a question of controlled airspeed, drag and momentum in say a vacuum.

Also remember, none of this has to do with ground reference.



Simply no. You still don't get it. For your canopy there is always headwind.

No matter which way you are turning under canopy the wind always does come from the front, yes?
So your pendulum in a stable airmass is always the same, no matter the direction as relative to the airmass there is no direction.

Only if you were switching between differently moving airmasses it would affect your airspeed and thus your recovery. I think this is the point you confused with a "headwind" the whole time.
If you are jumping in a fast moving airmass close to the ground you are very likely to encounter turbulence. These rapid changes within the airmass can mess with your recovery as they quickly change your airspeed and therefore the abillity of your canopy to get out of its dive/ your swoop.

When the winds at your starting point and the winds close to the ground are more or less the same without strong turbulence your recovery is not affected no matter the overall windspeed.
-------------------------------------------------------

To absent friends

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jtravis121

CrashProne,

Regardless of wind or airspeed.

What causes the oscillations of a canopy after a turn before it returns to normal flight?



Do you mean you come out of your turn and at the end of the recovery gain a few feet?

This happens because for your canopy you generated enough airspeed to create enouph lift to go up although it is trimmed towards the ground in full flight mode.

As you progress into more "high performance" wings this effect will fade away and only comes back if you want it during very fast distance rounds for example where you have enough airspeed (power in your wing) to change the pitch ange of your canopy (the trim) enough to gain a bit of altitude until you run out of airspeed.
-------------------------------------------------------

To absent friends

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>My question then changed to what might be better explained from my point of
>view as how does wind effect pendulum dynamics (no matter what altitude).

>The pendulum dynamics are a separate function of flight outside of the moving
>airmass.

Yes, they are. But once again, IT DOESN'T MATTER what the ground is doing.

Let's take another example. Let's say you jump near the equator on a no-wind day. You are flying South at an airspeed of about 20mps, and you turn East. Your airspeed is now 20mph again. But your speed relative to the center of the Earth is 1020mph, because that's how fast the Earth spins.

Now you turn West. You are now moving 20mph in terms of airspeed, but again relative to the center of the Earth you are doing 980mph.

Do you think your canopy (or your "pendulum dynamics") will care about that extra 1000 mph of speed (or momentum?) Nope, your canopy will turn like it always does. And that's true whether the ground has an extra 1000mph due to the Earth's rotation or an extra 10mph due to a moderate wind.

>When swinging into a headwind, which will have more opposing force on both
>objects (the canopy and the person) does the wind force/increased drag affect the
>speed at which a person swings under the canopy compared to turning into no
>wind because of the difference in the change of velocities between the two objects
>affected (the canopy and the person) due to their very large difference in
>momentum.

The two will be exactly the same. Your canopy does not feel headwinds or tailwinds when it is flying in those winds. It just sees air.

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As others are pointing out, you're still having an issue with the "swinging into a headwind" thing.

You aren't swinging into any sort of wind as you are already in the same wind no matter which direction you face.

Now if you were to talk of different layers of wind, so that there's a change during your flight, of course there will be different effects. If you are descending in still air and suddenly drop below a shear layer into a sudden headwind, or sudden sidewind, certainly all sorts of things can happen to your parachute. There it is more like the feather and bowling ball example you gave where there's no wind, then suddenly they "encounter" a 200 mph wind. Just that airfoil aerodynamics are more complex.

(If you are flying your parachute along and DROP INTO a layer with a headwind, you need to do a vector analysis of the change in relative wind. You'll likely get increased lift coefficient from increased airspeed coming at the canopy, but a reduction in angle of attack which is also needed for lift. The net result could be more lift on your canopy ... or less lift ... or even the nose of the canopy folding under. Depends on the details.)

But we're supposed to be still working with the basic situation of you flying in a constant wind situation.

As for momentum:
Quote

I believe the Jetliner example (or the in-a-balloon example) are both incorrect because nobody here has mentioned the real world of momentum and newton's laws as we cannot ignore those in real life.

If a jetliner slows rapidly it doesn't matter which direction you were walking or even sitting, you will be thrown forward.



The jetliner slowing has nothing to do with some notion of momentum, although you might use the term. You could be standing in the jetliner when it is stopped on the ground. A ground tug suddenly pushes the plane backwards out of the gate, and you fall towards the front of the plane.

Exact same result, whether you are standing still with zero "momentum" or flying 600mph. So "momentum" doesn't matter. It is just an acceleration of one object affecting another.

Ok, I'm finished lunch, so that's enough for now.

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Oscillation of canopy.

After flying in breaks, upon returning the toggles to full flight position, a canopy dives. Then it recovers, then it dives again, then it recovers, then eventually it returns to the normal flight path.

Each dive and recovery of the parachute is shorter than the one before it.

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The "oscillations" are covered in PD's Flight-1 101 course, the entry level course. You should take it, then 102, then 201... that will leave you with a 300 jump checklist of skills to perfect before you even start to work on turns, which are covered in 202 after you've completed that 300 jump checklist of successful maneuvers used for landing.

Canopy cycles (what you call oscillations) occur after all canopy input as the pendulum (person hanging under wing) returns to balance. Think of a swing on s swing set. Push it forward, it swings back a bit less, then forward even less, then back, etc until it comes to a stop. You do the same thing under canopy, every canopy, whether you perceive it or not. If you do a maneuver too low to the ground for your canopy to recover fully and your body is in the backswing portion of the pendulum arc, your landing input will be a mushy flare = either a crappy landing or similar to landing from a braked position.

The Flight-1 course progression works through understanding these dynamics and using them to anticipate what your canopy is going to do. 102&102 courses illustrate these basic canopy principles and applying them (including proper debrief methods so you can continue to learn). The 201 course specifically deals with adding airspeed using pitch only, no turns.

You say you have a swoop coach but you don't have the basic concepts of canopy flight dynamics... Get a new coach. Personally I recommend Performance Designs Flight-1 coaches because they have the long track record of winning competitions along with an established curriculum of how to train the next winners. Get a Flysight and you can see the oscillations after canopy input and see your exact path over thr ground to use during debrief (and clear up any wind/distance/lift/airspeed, etc confusion). Get a few PD courses and talk to the instructor about getting 1:1 coaching.

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You just described a pendulum. Canopy surges forward, picks up speed, generates more lift than its build in sink rate, gaines a few feet, swings you forward, canopy surges forward again and so on and forth until it stops because of wind resistance.
Pendulum or overcompensating effect is highly dependant on your canopy design and linetrim. Some canopies have such a short recovery, that you literally swing forward when it pulls out, some have a more natural, some even a negative recovery, that dont swing you back forward anough to create a noticeable pendulum effect.

You should definitely get some professional canopy coaching...
-------------------------------------------------------

To absent friends

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I understand the cycle, I wanted someone else to explain it, but nobody explained why it happens.

It happens because of a combination of the lift created and due to the momentum of the weight at the bottom of the pendulum being larger than the momentum of the object that is the fulcrum point.

Quote

and so on and forth until it stops because of wind resistance.



Does wind resistance affect the pendulum action during the cycle?

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Guess a simple explanation is that as with most flying vehicles, a parachute (with jumper) has speed stability. If it is flying faster than its equilibrium trim speed, it will slow down. And vice versa.

How it does that is partially a function of basic aerodynamics of the airfoil (in which we get into pitching moment coefficients, aerodynamic centre etc), and of course for a parachute, a jumper hanging down below, which adds a bunch of pendulum stability. Lift being created up above, weight down below.

As for what is dampening the oscillations, its.... well.... just the overall aerodynamics and dynamics of the system. I at least can't explain it better on short notice. How quickly a parachute swings out of a dive will depend on airfoil design, trim angle, line length, speed, etc. If it swings out faster, it is more likely to overshoot (leaving you at less than normal speed for a bit), before settling down to steady flight again. As a jumper one generally only needs to know a little about the various factors. What really matters is getting used to the speed and altitude lost in coming out of a dive, on whatever canopy you fly.

(If you want to check out equations galore, and some simulations of dynamic response to gusts etc, look at the paper Ram-Air Parachute Design by JS Lingard 1995, available somewhere on the web free.)

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>Does wind resistance affect the pendulum action during the cycle?

Yes - but the primary effect is on the canopy, not the person, since your canopy has a lot more surface area (and a lot less mass) than you do. This is most obvious during opening, but is always a factor.

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Wind resistance, drag, affects the canopy cycle but it does so irrespective of your heading relative to the ground.

The canopy is trimmed to a certain equilibrium (glide ratio), any input will disturb that equilibrium and depending on the specifics of the system (including drag on it's different components) the response can be a smooth return to the normal or a series of overshoots. This pendulum effect doesn't explain the fact you're coming out high (which I've noticed too btw) but I don't buy into your hypothesis of "turning into the headwind", the canopy "doesn't care about groundspeed".

Explanations such as a different sight picture and slower windspeeds at low vs. high altitudes (wind shear) seem correct but I wonder if it's more to do with your setup.....if you're crabbing at 45 degrees on your base-leg and doing a 90 relative to the ground then aren't you actually doing a 45 and that's why we're coming out high?

[Edit: we're coming out high not you are!]

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jtravis121


No, I really do understand the difference between airspeed and ground speed.



Then why did you say "windspeed is airspeed with respect to a certain wing loading"? Airspeed has nothing to do with windspeed, and windspeed has nothing to do with airspeed.

Windspeed does however have a lot to do with groundspeed - hence, again, why I relly don't think you understand the concepts as well as completely as you think you do.

Quote

Kiting is actually a correct example and has nothing to do with whether the canopy is anchored to the ground or not. Because if for some reason you were to experience hurricane force winds while kiting your canopy it would lift you up and blow you away. Lift is caused by the pressure difference between the bottom and top of any object.



Well now you're talking about flying in turbulence or gusts rather than steady winds. Those are two different things. Gusty conditions can just as easily give you more lift, less lift, or anything at all depending on what's happening.

Quote

Being blown away by a strong blast of wind is an example of uncontrolled lift. A wing and it's control systems is an example of controlled lift.



In terms of the physical explanation you are seeking for the phenomenon you believe is present - how is that in any way a relevant distinction? Lift is lift.
Do you want to have an ideagasm?

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Quote

If an updraft or downdraft affects a canopy then so does a side draft or front draft. If the airmass of a canopy was not affected by drafts (winds) then they would not collapse due to turbulance or dust devils, right?



Absolutely - but what you call a side draft or front draft would be when the windspeed changes. ie. A gust of wind. It could be equally helpful or detrimental to the recovery arc depending on where it came from. In steady wind the canopy feels no 'draft' apart from its own airspeed, just like in calm conditions.
Do you want to have an ideagasm?

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