jtravis121

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.

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

Does wind resistance affect the pendulum action during the cycle?

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.

OK, everybody. Help me with this. Leave the jetliner and the ground out of it.

What causes the oscillation of a canopy after a turn?

CrashProne,

Regardless of wind or airspeed.

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

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.

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.

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The canopy's forward velocity relative to the ground will decrease faster against the wind. However, what causes the change of pitch is the canopy's motion relative to your body. And since the canopy and your body experience the same wind, whatever it might be, the relative motion between the two is the same.

This statement is incorrect because of the ratio of wind force to momentum that each the canopy and your body experience.

A canopy and a person are not in a protected "bubble" that does not allow them to feel the effect of outside forces. If they were then a canopy would not collapse or feel turbulence.

Along the same reasoning, a 20mph wind will kite a canopy but not blow a human away.

Momentum is velocity x weight. A person has a much higher momentum than a canopy.

Both the person and the canopy experience the same wind, if they are already moving in the same direction, a change in direction will affect the way a canopy and person experience new wind direction though, such as when you complete a turn to face into the wind. At this point the wind force on each is very different because of the different size of the wind contact area. The wind force will slow a canopy with much lower momentum much faster than it will slow a person with a much higher momentum.

This changes the relative velocity of the canopy to your body much faster (in a shorter time span) than it would without a strong headwind. The larger your canopy the more you will experience this because wind force increases with size.

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You swing under your canopy at exactly the same speed no matter what the wind.

However, you swing under your canopy in a different DISTANCE over the ground since you are moving with the airmass.

Sort of. It sounds like the way you describe it you would swing under your canopy in a shorter horizontal distance but still cover the same vertical distance. Meaning you would reach the ground and just have a short swoop distance.

You may swing the same speed under the canopy, but the canopies forward velocity has decreased much faster in a headwind, causing you to be under it and thus change the pitch sooner than you would on a no wind day. Causing less of vertical distance and your plane out to be higher.

The question still remains: What to do about it.

Billvon,

Yes, I understand. I originally confused lift with the idea of pitch and how it related to the position of the person underneath. I understand the dynamics of how it all works now.

Now I want to know what more experienced pilots do about adjusting their swoop in a high wind.

More so, I have a feeling the this experience is compounded by the drag created by the size of a parachute in the headwind. Being a heavier guy I am at 1.6 wingloading on a 150 canopy.

A 1.6 wingloading on a 120 would experience less drag and therefore less decrees in canopy velocity when entering a headwind thereby reducing the difference in momentum between the canopy and the person and reducing the speed at which the pitch changes.

This would happen even less to a highly experienced pilot on a an even smaller (sub 100) canopy further explaining why less people experience the dramatic swing that I encounter being fairly conservative with my canopy size.

After much research today, I have answered part one of my question.

Yes, wind speed does affect the point at which you "roll out" or recover from your dive.

Here is the physics as to why:

Under normal, controllable, wind conditions (not hurricane or extremely gust) the canopy does indeed move within it's own airmass. However, airspeed over the foil does not account for all lift created. Position, or specifically the pitch of the canopy does. What changes the pitch of the canopy during the recovery arc more than the airspeed is the momentum of the person under the canopy swinging forward.

This is important on a windy day because of difference between the relative velocities of the canopy and the person. After completion of a turn into a stronger wind, the canopy may still have a specific airspeed but it's actuall forward velocity decreases rapidly because of the headwind, causing the person (in my case a 205lb person) to have a much less change in velocity due to the wind and I swing under the wing faster than on a no wind day.

Restated: My momentum which is still pretty much the same as a no wind day causes a faster roll out and change in my position under the canopy causing a faster pitch change and thus a higher plane out.

The question remains, what do experienced canopy pilots do about this.

Tommy,

Thank you for seeing the question for what it is meant to be. I am trying to learn.

I ask this, if you have met CP competitors of embarrassingly high levels that believe that there is a change in recovery arc depending on the wind; what causes them to believe this?

What are the physics that cause a canopy to come out of it's dive, arc for a certain amount of time/distance and ultimately create enough lift to plane out?

Probrause,

I understand that my perception may be different due to the trained perception of a certain ground speed.

Your post however raises two more questions.

1. My perception of forward speed may be different, but I do not understand how my perception (or actual) of downward speed is different. My canopy is planing out higher and during the plain out the forward ground speed is noticeably slower (which is what you described) but the plane out height is different, why?

2. I think, (think) you contradicted yourself in your statement about the canopy not being affected by outside sources stable airmass .

"If the airmass is stable and doesn't create down and updrafts because of underlying terrain or obstacles a given turn will always eat up the same amount of altitude and generate the same amount of AIRSPEED as your canopy doesn't care which direction you're going because its only POR is the airmass. The recovery stays the same! "

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? Please explain if I am way off base.

Jakee,

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

Which is why my question asked how/if wind speed effects lift during the recovery arc. If the wind speed does not effect lift, then why does it seem that my recovery is sooner (implicating more lift) than on low wind days.

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. 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.

This is also why I asked for explanations of given answers, which you have not provided at all.

How does more headwind = slower airspeed?

In easy to explain numbers; If your canopy has a forward speed of 10mph in zero wind then your canopy is "experiencing 10mph airspeed" and the entire system (canopy, lines and person) are contributing to 10mph worth of drag (whatever that number may be for the given situation)

If the same canopy was flying into a headwind of 10 mph then the canopy is experiencing 20mph of airspeed and everything in the system is contributing to 20mph worth of drag. But the airspeed is still higher not lower.

Please explain your math so that I am better able to understand it.

What you are saying makes sense in terms of windspeed can effect airspeed "felt" by the canopy.

However it does not address if the windspeed actually does effect the lift of the canopy and thus how quickly it pulls out of it's recovery arc to a flatter glide.

Yes and no.

I understand the difference between ground speed and airspeed.

However, windspeed is airspeed with respect to a certain wing loading.

Given a wing loading a canopy will always descend at the same speed no matter the wind speed (whether tail wind or head wind) until a certain speed is reached where lift created is enough to lift the load under the wing. This is the basis of swooping. Generate enough airspeed to create lift allowing for a plane out of the wing.

Another example of this is "kiting" during a windy day. You are standing on the ground and not creating airspeed because of your descent. Yet the wind creates the airspeed that causes the canopy to lift off the ground showing that it only takes a certain amount of wind to create enough lift to lift an unloaded canopy.

Meaning, there must be a point where a canopy always has a descent rate no matter how fast the airspeed is, until the very moment it has enough airspeed to overcome the descent.

This is why I ask. The above statements are my current understanding and I would like a factual answer that states one of the following:

Your logic/understanding is correct regarding lift and recovery arc and I do the following to compensate for it.

Your logic is inncorrect, here is why, here is what you are really perceiving and this is how to compensate for it.

I do not completely understand the facts behind what you are experiencing, but I understand the experience and this is how to compensate for it.

Why, wow?

Just the facts ma'am (or science)

I am explaining what seems to be happening or rather my perception/feel and would like the science behind what is actually happening so I am able to make the proper adjustments.

I have been working (with a mentor) on 90 degree front riser turns to final.

On a no wind or light wind day I have become consistent with my turn speed, dive, recovery and plane out across the ground.

On days where the wind is stronger than say 14 mph, my canopy seems to recover quicker, meaning higher off the ground. At which point it feels like an "airball" That feeling when you start everything too high and your plane out happens to high and then the canopy starts oscillating before it returns to normal flight and you end up landing like that with a very mushy flair.

1. What is the science behind what brings a canopy out of a dive, through the arc and into level flight?
Answered : The position of a person under the canopy changes the pitch of the canopy thus creating lift as the person swings forward due to the momentum difference between the canopy and the person.

2. Does a canopy (at a given wingloading) have an airspeed at which point lift is created?
Answered : Canopies are trimmed to always 'go down' and will no matter the airspeed, unless pitch is changed

3. Does a head wind effect that airspeed at which lift is created? Meaning, if a given canopy/wingloading will create lift at an airspeed of 50mph which is normally achieved after a dive of a given altitude thus causing the plane out.
Answered: No the airspeed of the canopy is not affected but the actual velocity is affected thus reducing the momentum and causing the person (with a still high momentum) to swing under the canopy faster and change the pitch faster

4. Will a 20 mph headwind cause the the canopy to come out of its dive sooner (because you would have reached an airspeed of 50mph earlier in the dive) causing you to "airball"
Answered above

The final question is what can be done to adjust for this to prevent the "airball" and thus potentially landing with a mushy flair?