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I've been thinking about the "fish in a bowl" concept with regards to how the wind could change flight characteristics on a canopy lately. I've heard from many people that turning into or away from the wind will take the same amount of time, because your canopy doesn't know how the wind is blowing, it is just operating the same way inside of a relativistic frame. I can agree that this concept is totally valid, but I'm wondering if anyone has done any actual testing to prove and/or quantify it.

The problem I am thinking about, is that it takes time for the relative wind to interact with you. Until the wind has accelerated your reference frame to the speed of the wind, you are still experiencing external forces from the wind. In a skydive, you are (I think) obviously going to hit this velocity for your reference frame, but on a 200' freefall, where you are spending a few seconds under canopy, I highly doubt it. More than knowing that winds will have an effect on flare power and turning speed (which my intuition tells me we can be pretty sure of), I'd like to know at what jump/opening altitude will you stop feeling the effects of the wind. Just curious if anyone has done any thinking about this.

Your canopy flies relative to the air mass you are in. If it's moving laterally, you move with it and fly relative to that movement. Your net lift and drag, in terms of magnitude and direction, are relative to the air mass you are in. As in the difference between "air speed" and "ground speed".

Assuming your canopy is flying, the direction of the (steady) wind is largely irrelevant to the flight characteristics (some exceptions noted below), and hence to the time taken to turn, because your movement relative to the air mass is independent of the underlying wind - since you are joined with it, whilst your movement relative to the ground or other reference point external to the air mass is very much affected by the same wind.

The main exceptions to this rule are wind shifts (either speed or direction), wind shear, anabatic, katabatic or other air flows interacting with the air mass you are flying relative to.

Relative wind is the air flow effect off your body falling due to gravity, coupled with the actual wind(s), producing an effective wind direction and velocity (speed and direction) of air relative to your body.

Relative wind interacts with you instantaneously. It takes time for you to notice a change in the relative wind, or it takes time for any control input to effect a noticeable change in your flight. Any delays are in your perception of the change - as the magnitude of change passes some threshold that gets your attention. Experience tends to reduce the gap between change and perception, allowing more intuitive - and less severe - adjustment. Think about how a cat falls upside down but lands on its feet. You can bet it doesn't actually think about what inputs to make - it's intuitive, and hard-wired into its DNA.

What matters is knowing how intuitive (or not) you are, and leaving enough margin for error for you in the circumstances. That might be more or less than what someone else needs.

My rule of thumb is "when the fall rate exceeds the wind speed".

After canopy opening I think the transition happens pretty fast, because the canopy is big enough that it is caught into the wind block very quickly.

We've been rocking flysights on our last few jumps from nil winds, 20kt tail winds and 10kt cross winds, awesome data display, give you tons of info for analizing exit heights, speeds, delays, openings, canopy flight, landing. Too cool.

I am not convinced that concept is totally valid.

Maybe I'm wrong. It works for a hot-air balloon but not for a descending canopy.

Gravity pulls you straight down. If there are zero winds and you are under a round, then the canopy will be directly above your head. You will be moving directly downwards.

If the wind is horizontal at (for example) 5 m/s then the canopy will not be directly above your head. The wind will blow it sideways faster than you. Draw yourself a picture with the force vectors.

Eventually you will both accelerate to the wind speed, I imagine. Then you are in equilibrium, but you are still not directly below the centre of the canopy. It has more drag.

The same effect will happen with a ram air. However, you can steer a ram air. If you are going cross-wind and you turn down wind, your body will continue cross wind while the canopy is captured by the wind and accelerates downwind. The line tension increases and the load on the canopy increases. It dives. You fall faster until you pendulum and reach an equilibrium again.

If you turn up-wind, then a similar thing happens, but the canopy does not accelerate downwind as fast and the loading is less. It takes longer to reach an equilibrium.

Canopies do behave differently in relation to the wind. You are not isolated from gravity or drag. If you enter no inputs, then there is one equilibrium, and it is not agnostic to the earth.

Edit: I would also love to see some hard data proving me wrong (or right). A shuttlecock falls on an angle in wind, not vertically oriented. Anyone got any good GPS data?

I think the transition speed changes with regard to the canopy's orientation into the wind. If you open into a headwind, it is going to be capturing a lot of air, making it reach the "fishbowl state" a lot more quickly. If you open into a tailwind, a lot of that air is going to be flowing around the canopy, and not necessarily into it.

If anyone has data with windspeed included in it, I would definitely like to see it too. I think developing technology will reshape a lot of knowledge in the near future.

If the centre of mass is not directly below the centre of lift then a torque is created that will align the centre mass under the centre of lift. So when the relative wind changes the system (parachute and person) will alter so that lift and mass are not aligned, but the system will self centre after some oscillations.

It will reach an equilibrium, but that won't be vertical, due to the varying drag. The centre of mass is somewhere around your shoulders, the centre of horizontal drag is somewhere a couple meters above your head.

For example, when a roundy is deployed from a plane (think military) the relative wind is mostly horizontal so the drag forces the parachute way out to one side. As the relative wind slows, the whole system becomes more vertical.

However, the gravity is always vertical.

kerblammo, I think intuition is failing in this case. Like RichM said, after a few oscillations, a person will be suspended directly below a round, regardless of wind conditions. There is no "varying drag" at equilibrium, because you will be moving with the air mass, so there will be no horizontal drag on you or the canopy.

Yeah, I could definitely be wrong. Certainly if we had a poll amongst jumpers I would be on the losing side.

However...I'm not convinced. I think that this goldfish bowl theory is dogma and over-simplified.

An arrow has a weighted head at one end and high-drag feathers at the other. These help keep it from yawing. This is similar to someone under canopy - you tend to remain under your canopy not over it:)

However, if you fire an arrow in a crosswind, it will move downwind, but the feathers will be slightly further downwind. The moment of drag is not at the centre of mass but towards the feathers.

Same if you descend under canopy under a cross wind. The canopy will be shifted to downwind as the moment of drag is higher than you. Similar to if you dropped an arrow feathers down in a crosswind - it would rotate to an equilibrium with the head down but the feathers slightly downwind, not vertical.

Popular answer does not always equal correct.

I think both ideas have merit to them, but they need to be joined. There are two differences between the canopy and the jumper. First, the drag coefficient, which results in a higher force on the canopy, making it reach the "fishbowl state" more quickly. The second is the mass, which results in a smaller acceleration for the jumper, making him or her reach the "fishbowl state" less quickly.

Two concepts, same end result: the canopy is effected by the wind more quickly than the jumper.

However, once the canopy gets to the fishbowl state, it stops accelerating, but the jumper continues accelerating. Once the jumper's reference frame reaches wind speed, he or she stops accelerating too. The system is then in equilibrium.

I'm actually staring to think the line tension prevents the jumper and canopy from ever acting (in a practical sense) as two systems. If nobody has any data, I'm going to try to run some testing on this in June.

I think you are still missing a step. Once stable flight is achieved the arrow will be pointed straight down, or a jumper under a round will be directly under the canopy. The entire system is moving downwind with the airmass. An observer on the ground would see the arrow or round canopy moving downwind diagonally but the orientation of the system would be vertical(exactly parallel with gravity), descending in a straight line relative to the airmass but at an angle not perpendicular with to the ground OR parallel with gravity.

As the canopy or arrow transitions between wind layers (or exit speeds) it will temporarily weathervane until stable flight is achieved again.

Other than sheer layers, a jumper/canopy system behaves exactly as it would in dead calm air. Ground and wind do not matter, only changes in the wind matters.

I could go on with different examples for hours if we get into the complexities of transitioning between layers or the fluid dynamics of air in a valley or around obstacles but they are not necessary for safe parachuting.

One simple and interesting example that I think about a lot from soaring-
Every jumper should know that because of sheer the wind measured on the ground will be different than wind measured 50' above the ground, 100', etc.

If you are landing into the wind but are doing an accelerated 180 degree turn ("swoop"), then your airspeed(AS) at the end of the turn will be LOWER than if you did the same 180 turn in CALM air.
Why?
It's not complicated, but understanding it requires a bit of thought and will help people understand other transitions through different air masses.

Let's assume the fictional canopy starts the swoop at 20kts airspeed(AS) from 200'AGL and in stable air the AS after the turn is 50kts.

lets assume the wind on the ground is measured at 5kts and the wind at 200' is 20kts in the same direction.

This means the ground speed (GS) at the start of the turn is 40kts. (In stable air the GS would be 20kts)

With this sheer layer and wind speed, the same* diving turn has the ability to achieve an AS of only 35kts after the turn. The opposite is true for 180 degree downwind swoop where the canopy would theoretically achieve 65kts AS.

*obviously the aerodynamics of the turn are complicated and cannot be the "same" because it is flying through changing air masses, but for the purpose of this thought experiment we are ignoring this.

Hmmm... I agree the entire system moves downwind and accelerates until it reaches the speed of the crosswind. However, it also moves down due to gravity. So, the relative wind for the system is on an angle.

If the system then aligns itself somewhat to the relative wind (as suspended weights tend to), then: No goldfish bowl. It does matter which way you are flying relative to the cross wind as there is a natural relative wind angle due to your descent.

If the system was to remain vertical (which I doubt), then it would have an angle of attack due to the relative wind being on an angle. So, again, no goldfish bowl - the angle of attack will change your flight characteristics depending on which way you point your ram air and get the angle of attack.

I stumbled across this wind shear experiment:

http://www.dtic.mil/dtic/tr/fulltext/u2/809384.pdf

and they seem to agree.

I don't think I completely understand you. Gravity vector does not change no matter the wind.
I don't know what you mean by 'goldfish bowl' but I am assuming it is a metaphor for how aircraft behave in airmasses unaffected by the ground. Unless traveling through a noticeable sheer layer, an aircraft is essentially in that 'fish bowl'. Using terms like 'crosswind' infers that you mean the ground. Are you talking about crab angles?
I'm starting to think that we are talking about different things.
That experiment is pretty cool (and old, but accurate)... And everything in that article is describing what I am talking about.

This is true for a period of time. But after that period of time the jumper and parachute will both be moving exactly with the wind due to drag. Under a round the system will be falling vertically in the air, but will be crabbing in a horizontal direction from the ground as it is travelling with the moving air mass. Under a square the system will be travelling forward through that air due to canopy trim, but will still be crabbing relative to the ground.

You have to think of the moving mass of air that the system is in, and understand how that differs from the view of the static ground below you.

Think of a yacht travelling due east at 5 knots, but in a tidal flow of 5 knots going north to south. The yacht is pointed due east and its track in the water is due east. But the water it is moving through is also moving, 5 knots north to south. So its track on the static ground is actually exactly south-east and its ground speed is about 7.2 knots. If the tidal flow changes to 5 knots south north, then the ground track changes to north-east. But as far as the yacht is concerned nothing has changed, it has always been travelling only east in the water.

Scenerio:
you are on a guyed A with a good crosswind from left to right.
say you have a 180 offheading,
which way are you going to turn?

with the wind or against it?

whoever says that wind direction does not matter (headwind/tailwind) has never been in this situation or didn't think it over very well.

id much rather plow in to the wires flying against the wind than flying with it. groundspeed is a lot higher if you are flying with the wind.

I was only talking about wind and how it relates to a canopy/jumper. Obstacles definitely change the priorities.