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jtravis121

Recovery Arc vs. Wind Speed

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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?

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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.

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11bjohnny

wind affects ground speed, not airspeed.




Urgh. This thread is about to derail hilariously, but briefly.

Consider what happens to your airspeed when you do a 180 in high winds. If you're going downwind -> into the wind, your airspeed shoots through the roof as you complete the turn, since:

Downwind: ground speed = airspeed + wind speed
assuming ground speed stays the same through your turn, which it won't, because canopies accellerate
Into the wind: airspeed = groundspeed (Which was airspeed + wind speed) + wind speed

So you get the wind speed twice as you complete the turn. The second you start turning vectors the "wind is irrelevant" trope becomes meaningless.

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Airspeed = lift. More headwind = slower airspeed = less lift... however you can add airspeed by adding input to your canopy via a pitch change or a roll+yaw+pitch change.

It's time to get a flysight and take some canopy courses (all this is covered in depth by Flight-). The best possible feedback will come from flysight data played simultaneously as video from the ground. Those two together will show you exactly what input you are giving at exactly what altitude, for how long, and exactly what your canopy does in response. Varying any input strength or duration (including your body position) will change what your canopy does, including speed/diatance/time of recovery. The difference could be you.

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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.

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I'm not quite sure if I understand you correctly, had a good laugh, but I've got time to kill so here we go :P

Windspeed = Speed of windmass moving across the earth
Airspeed = Your speed inside the airmass and only relative to the airmass
Groundspeed = Your actual speed over the ground

First of all you need to understand that your speed inside the moving airmass under canopy will always be the same for a given input, no matter the wind strength or direction. The only thing that changes is your groundspeed and thus your perception of speed.
Lets say your canopy has a full flight speed of 30km/h within the airmass.
3 Scenarios

Nillwind: airspeed = groundspeed (30km/h)
30km/h headwind (windspeed): airspeed is still 30km/h, Ground speed is 0km/h
30km/h downwind (windspeed): airspeed still at 30km/h, groundspeed is 60km/h

Although your airspeed stays the same in all 3 scenarios your groundspeed varies greatly.
Your canopies only point of reference is the airmass it is moving through. At which speed this airmass is moving across the ground is completely irrelevant for your airspeed.

Now it's the same for swooping or any input in general. 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!

But now your perception comes into play. On nillwind days you might be able to get 60 km/h of groundspeed out of your turn which would be 60km/h airspeed inside the (standing) airmass.
Now no matter the direction relative to the wind you're landing in, your airspeed will always be 60km/h. But your groundspeed can vary greatly depending on the wind direction.

You acustomed yourself to low wind days and higher ground speeds. Now you are jumping in higher windspeeds and low ground speeds and that messes with your perception. The speed inside the airmass (airspeed) during your recovery is still 60km/h but your groundspeed is only 30km/h. So you are coming out of your turn and you don't see the speed you are used to, hence thinking you are recovering more quickly, probably giving a little different input also but that can only be judged by watching video of your landings in different conditions.


Probably any canopy design out there can create enough lift to overcome its rate of descent. But this has nothing to do with wind direction but rather with its airspeed within the air it is moving through. So a popup can happen to you no matter the wind direction you are landing in.

did I leave anything clear? :$:$
-------------------------------------------------------

To absent friends

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I understand the difference between ground speed and airspeed.



I really don't think you do. Not fully.

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



No it isn't. That sentence is literally meaningless.

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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.



And that is down to airspeed.

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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.



That is not an example of 'this' - it is an exampl of something completely different. Windspeed is important to how a kite flies because you are anchoring it to the ground. A parachute is moving freely in the airmass. That is a major, fundamental difference.
Do you want to have an ideagasm?

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A precise and correct description. However, I see no reason to laugh - The question is relevant to our forum and well posed. I've met CP competitors on, perhaps in this context, embarrassingly high levels that do not understand the basic physics behind this, and either fly on their gut feeling - or - truly believe and teach that there is a change in recovery arc depending whether it is head or tail wind.

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richoH

Urgh. This thread is about to derail hilariously, but briefly.



Yes, what you just said was hilarious.

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Consider what happens to your airspeed when you do a 180 in high winds. If you're going downwind -> into the wind, your airspeed shoots through the roof as you complete the turn



No it doesn't. It really doesn't. Go and experiment with an anemometer if you don't believe me.

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Downwind: ground speed = airspeed + wind speed
assuming ground speed stays the same through your turn, which it won't, because canopies accellerate
Into the wind: airspeed = groundspeed (Which was airspeed + wind speed) + wind speed



You a messed up mathematical fool. What is this supposed to demonstrate? Why does your canopy care what your airspeed is in relation to your groundspeed?

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So you get the wind speed twice as you complete the turn. The second you start turning vectors the "wind is irrelevant" trope becomes meaningless.



You are so much worse at this than the OP.
Do you want to have an ideagasm?

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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.

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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.

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Zero difference for canopy.

What is different is your perception of the rollout point. You have a different visual picture, as your ground speed is different

When you get more experienced, you will build up your sight picture in different conditions. Trust your turn mechanics (assuming you have a good one), your heights should not change (nor timing of turn).

E.g. at the last world meet with mega headwinds there were some competitors turning over the gate and I vaguely remember someone going from the 2nd marker (e.g. behind the course)
"Don't blame malice for what stupidity can explain."

"In our sleep, pain that cannot forget falls drop by drop upon the heart and in our despair, against our will comes wisdom" - Aeschylus

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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?

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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.

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>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.

The first part of that sentence is correct. A canopy will descend at the same rate (given the same loading, control inputs and density altitude) no matter what direction the wind is coming from.

The second part is not. A canopy is ALWAYS generating lift. If it does not, it collapses.

>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.

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.

>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?

Their path through the wind is exactly the same.

Their path along the ground is different since they are moving with the wind. Since they are judged by things like swoop distance, this means that the wind affects their performance quite strongly.

>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?

The difference in drag between the canopy and your body after you disturb the free flight equilibrium by (for example) turning rapidly.

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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.

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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.

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jtravis121

Quote

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



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.

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. Causing less of vertical distance and your plane out to be higher.

The question still remains: What to do about it.



I think you should revisit that assumption. It goes against very basic principles, and that should be a clue that your informal observations show a subjective feeling and not an actual effect.

At this point the question should still be: "why is the plane out higher?". And one possible answer is: because of different input.

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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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Oh this has indeed become a mess.

It takes time for people to get their head around some of the basic concepts of canopy flight combined with basic physics. Once one has in incorrect framing of the whole issue it can be tough to get into a new more correct framework. Unfortunately we haven't got there yet. It's like every time someone posts, you now say "I understand now!"... but still come up with a wrong conclusion. :)
I'll address a few issues for you jtravis:

-- I think that generally the difference you feel between windy and less windy days is just from the different visuals, with more or less movement over the ground, which in turn might make one's behaviour different -- slightly different altitude used for the turn to final, different recovery, whatever.

Just what the visual illusions or changes of perception are, I'm not sure, and I don't know of anyone spelling them out. A possible example is that the pull out from the dive feels slower in high wind as the ground isn't moving as fast so judging speed and distance is easier so everything seems easier and slower. But that's just guessing.


-- Try to avoid thinking about "momentum". A dangerous word as using it so often messes up any clear understanding about canopy flight and swooping. Different momentums upwind or downwind don't matter to the speed of the canopy or how quickly the canopy recovers, pitching out of the dive. The latter was something you were thinking.

eg,
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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.



You're not 'entering' a headwind, you're already in the same airmass. 'Momentum' doesn't matter, whether you're in a 20 mph wind or 100 mph wind. Even if you're walking down the aisle of an airliner at 500 mph, whether facing the nose or tail, there's no 'momentum' that makes it easier or harder to turn 90 degrees to climb into your seat.

So you and your canopy will pitch the same rate whatever the wind or wind direction. Certainly your wing loading and canopy design will have an effect, as will whether you are still turning (penduluming yourself outwards) or not.

-- Stable air mass:
All the basic discussions are about an air mass without changes during one's canopy flight.

You quoted pobrause and then commented:

Quote


"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.



So we're talking about an airmass where there are no changes. Of course if there are gusts or changes in the wind (up, down, sideways, whatever) then the canopy will behave differently. Pobrause is saying IF there are no wind changes, then yes the wind speed doesn't matter.

-- In reality, at one level of detail beyond the stable, constant airmass, one does get some wind shear. This is common. Wind speed typically decreases with altitude.

You still need to understand the basics that the whole thread has been about, before getting to that next level.

When there is shear, then yes there may be some difference in effect between windy and less windy days. If there's almost no wind, then that's likely the same all the way to landing. But on a windy day, if a jumper were doing a 180 turn, the wind when starting the swooping turn might be 30 mph, but only around 15mph near the ground when about to touch down.

So yes then there will be some change in how the canopy behaves in the two wind conditions. Exactly what happens gets messy, and depends on what the canopy is doing, whether it is in a steep dive or just gliding normally. If one is gliding normally and the headwind suddenly decreases, the canopy will suddenly have less airspeed until it can adjust to the new conditions, so it may pitch forward and mush downwards. (There's more to it, that gets messy, with angle of attack and pitching moment and overall lift changes.)

(If one is in a 90 degree dive, things are different again, as the suddenly changed airflow is coming at the canopy from a different direction relative to where the canopy is facing.)

Don't focus too much on this part yet. You still need to understand the basics for a situation in in an ideal unchanging air mass. Just be aware that wind shear, which exists to some degree in general and especially if there are obstacles upwind, will have some generally undesired changes on a canopy's flight.

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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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