Canopy turning downwind?

[Icon134 0]

I occasionally stumble across statements that don't make a whole lot of sense to me and generally like to inquire about them after hearing them enough. I stumbled across this little gem (which I have heard before) in the incidence forum and I'm not picking on the poster itself since it's not the first time I've heard this...

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Take into account a down winder (canopy wants to turn down wind on its own) into an obstacle or water.

I guess my confusion is that my understanding that my canopy flying through a body of air doesn't "know" the direction of the wind relative to the ground and as such if what the poster is suggesting the canopy will turn downwind automatically how or why does this happen...

My thoughts are that the only way I know that the wind is actually blowing is through my canopies relative speed to the ground.

I suppose I'm also curious if anyone has done controled experiments to show that a canopy without any input will in fact turn downwind.

What are y'alls thoughts?

Livin' on the Edge... sleeping with my rigger's wife...

[PhreeZone 20]

You are correct, a canopy will not make any turns unless directed to by its pilot.

Yesterday is history
And tomorrow is a mystery

Parachutemanuals.com

[Icon134 0]

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You are correct, a canopy will not make any turns unless directed to by its pilot.

oh, thank goodness... It's just that I've heard it said more then once... It's good to know that I'm not losing my mind...

Livin' on the Edge... sleeping with my rigger's wife...

[billvon 3,078]

>I suppose I'm also curious if anyone has done controled experiments
> to show that a canopy without any input will in fact turn downwind.

When on final, without any input, canopies will often turn downwind.

HOWEVER, that is not because the canopy knows which way "downwind" is. It is because when you on final you are heading directly into the wind, and any turn at all will result in turning downwind - and most canopies will turn slowly with no input as a result of asymmetry, loading etc.

[livendive 8]

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It's good to know that I'm not losing my mind...

Losing? As in present tense? No, I wouldn't worry about that.

Blues,
Dave

"I AM A PROFESSIONAL EXTREME ATHLETE!"
(drink Mountain Dew)

[jcecil 0]

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>I suppose I'm also curious if anyone has done controled experiments
> to show that a canopy without any input will in fact turn downwind.

When on final, without any input, canopies will often turn downwind.

HOWEVER, that is not because the canopy knows which way "downwind" is. It is because when you on final you are heading directly into the wind, and any turn at all will result in turning downwind - and most canopies will turn slowly with no input as a result of asymmetry, loading etc.

I've always heard that the decreasing wind experienced by the canopy as it loses altitude (almost always wind speed decreases gradually the closer one gets to the ground) can make the canopy turn on its own, although slowly, as the canopy 'sees' this as an slightly increasing wind from the opposite direction the wind is actually blowing.

This is more theoretical than usually seen, I think, because the effect would be very slight and easily overcome by something like an uneven harness.

[Icon134 0]

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It's good to know that I'm not losing my mind...

Losing? As in present tense? No, I wouldn't worry about that.

Which is why I'm not worried...

Livin' on the Edge... sleeping with my rigger's wife...

[Icon134 0]

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HOWEVER, that is not because the canopy knows which way "downwind" is. It is because when you on final you are heading directly into the wind, and any turn at all will result in turning downwind - and most canopies will turn slowly with no input as a result of asymmetry, loading etc.

That makes sense...

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I've always heard that the decreasing wind experienced by the canopy as it loses altitude (almost always wind speed decreases gradually the closer one gets to the ground) can make the canopy turn on its own, although slowly, as the canopy 'sees' this as an slightly increasing wind from the opposite direction the wind is actually blowing.

I understand that the speed of the wind relative to the ground may decrease as you get closer to the ground but the canopy is flying in the body of air relative to the ground unless you are actively referencing the ground the canopy only cares about it's relative speed in the air mass.

Livin' on the Edge... sleeping with my rigger's wife...

[pilotdave 0]

I believe the theory is that a canopy will turn TOWARD a gust. So if you're flying north and you get a gust of wind from the west, the canopy will turn slightly to the left. But a decrease in wind will act like a gust in the opposite direction. So if you're heading north in a decreasing west wind, your canopy will behave like there's an increasing wind from the east and will slowly turn to the right.

A canopy has to turn toward a gust to be stable. If it turned away, it'd be unstable and want to fly backwards.

Dave

[kallend 2,108]

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>I suppose I'm also curious if anyone has done controled experiments
> to show that a canopy without any input will in fact turn downwind.

When on final, without any input, canopies will often turn downwind.

HOWEVER, that is not because the canopy knows which way "downwind" is. It is because when you on final you are heading directly into the wind, and any turn at all will result in turning downwind - and most canopies will turn slowly with no input as a result of asymmetry, loading etc.

I've always heard that the decreasing wind experienced by the canopy as it loses altitude (almost always wind speed decreases gradually the closer one gets to the ground) can make the canopy turn on its own, although slowly, as the canopy 'sees' this as an slightly increasing wind from the opposite direction the wind is actually blowing.

This is more theoretical than usually seen, I think, because the effect would be very slight and easily overcome by something like an uneven harness.

The theory is quite correct. Any kind of wind shear provides a directionality to the system that can be sensed by the canopy.

Whether the effect is detectable in practice over other disturbances is another matter. Might make a nice experiment.

...

The only sure way to survive a canopy collision is not to have one.

[DJL 235]

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You are correct, a canopy will not make any turns unless directed to by its pilot.

This phenomenon to inexplicably and repeatedly turn downwind is most often seen in AFF canopies. Must be because they're large canopies or sumthin'.

"I encourage all awesome dangerous behavior." - Jeffro Fincher

[highspeeddirt 0]

for a minute there i thought we were going to open up that whole weathervaning controversy that began to take hold back in the 70's. seems national's 26 bias constructed lo po reserves,made by security (with a 4 line release) ,were SO assymetrical that lots of them had built in turns . national came out with a statement about the weathervaning effect to explain why there product was turning all by itself.

[mnealtx 0]

If weathervaning is actually NOT the issue, then would the asymmetry not cause the canopy to turn OUT of a downwind run equally as readily or as fast as turning INTO a downwind run? In fact, all else being equal, would a canopy with a slight asymmetry not turn in a (very) large circle?

Mike
I love you, Shannon and Jim.
POPS 9708 , SCR 14706

[billvon 3,078]

>In fact, all else being equal, would a canopy with a slight asymmetry
>not turn in a (very) large circle?

Yes, it would. Since most times you don't care much about which direction someone (especially a student) is flying until they are on final, you notice it most when they are pointed into the wind getting ready to land. Thus the "turn downwind" belief.

[mnealtx 0]

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>In fact, all else being equal, would a canopy with a slight asymmetry
>not turn in a (very) large circle?

Yes, it would. Since most times you don't care much about which direction someone (especially a student) is flying until they are on final, you notice it most when they are pointed into the wind getting ready to land. Thus the "turn downwind" belief.

Ok - so would the canopy then turn equally quickly OUT of a downwind situation as it seems to turn INTO one?

Looks like a good experiment for a high h&p.

Mike
I love you, Shannon and Jim.
POPS 9708 , SCR 14706

[mark 107]

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Ok - so would the canopy then turn equally quickly OUT of a downwind situation as it seems to turn INTO one?

Looks like a good experiment for a high h&p.

Tongue firmly planted in cheek:

Especially since the winds at altitude are generally much stronger than at the surface. The effect (if any) should be much more obvious in 50-knot winds than 5-knot.

Even better: a downwind jump run could add another 80 or 90 knots, so the effective wind would be in the 130 knot range. Using Scarecrow math, the rate of turn should be proportional to the square of the tangential velocity divided by the width of the hypotenuse.

Mark

[mnealtx 0]

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Ok - so would the canopy then turn equally quickly OUT of a downwind situation as it seems to turn INTO one?

Looks like a good experiment for a high h&p.

Tongue firmly planted in cheek:

Especially since the winds at altitude are generally much stronger than at the surface. The effect (if any) should be much more obvious in 50-knot winds than 5-knot.

Even better: a downwind jump run could add another 80 or 90 knots, so the effective wind would be in the 130 knot range. Using Scarecrow math, the rate of turn should be proportional to the square of the tangential velocity divided by the width of the hypotenuse.

Mark

Tongue NOT in cheek:

If, in fact, the canopy *cannot* tell what direction the wind is coming from, it *should* be an easy experiment from a normal opening altitude as well - the high H&P just gives you more time to experiment. If the canopy takes (for instance) 15 seconds to go from flying into the wind to flying downwind, it should be flying back UPWIND in another 15 seconds...not so?

Mike
I love you, Shannon and Jim.
POPS 9708 , SCR 14706

[livendive 8]

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Tongue NOT in cheek:

If, in fact, the canopy *cannot* tell what direction the wind is coming from, it *should* be an easy experiment from a normal opening altitude as well - the high H&P just gives you more time to experiment. If the canopy takes (for instance) 15 seconds to go from flying into the wind to flying downwind, it should be flying back UPWIND in another 15 seconds...not so?

In which case, all you need to do is figure out a sample rate. In your above example, if you kept your eyes closed for 29 of every 30 seconds, you'd always be pointed into the wind.

Blues,
Dave

"I AM A PROFESSIONAL EXTREME ATHLETE!"
(drink Mountain Dew)

[mnealtx 0]

I already *do* that... was I not supposed to!!


Smartass!!!

Mike
I love you, Shannon and Jim.
POPS 9708 , SCR 14706

[mark 107]

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If, in fact, the canopy *cannot* tell what direction the wind is coming from, it *should* be an easy experiment from a normal opening altitude as well - the high H&P just gives you more time to experiment. If the canopy takes (for instance) 15 seconds to go from flying into the wind to flying downwind, it should be flying back UPWIND in another 15 seconds...not so?

You know that, and I know that. On the other hand, the folks who believe the downwind myth will not be persuaded by any experiment.

Mark

[billvon 3,078]

>Ok - so would the canopy then turn equally quickly OUT of a
>downwind situation as it seems to turn INTO one? Looks like a good
>experiment for a high h&p.

Yes, and I've watched such experiments. When we droptest rigs, the reserves open and (generally) have a gentle turn built in, because the dummy isn't good at sitting straight in the harness. The canopy turns slowly until impact, and will land randomly in just about any location and direction (except, of course, the locations that are easy to get to with the truck.)

[mnealtx 0]

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The canopy turns slowly until impact, and will land randomly in just about any location and direction (except, of course, the locations that are easy to get to with the truck.)

Interesting - thanks!

Mike
I love you, Shannon and Jim.
POPS 9708 , SCR 14706

[jumper03 0]

so if you put a kayak in a stream, with no other input, it will turn down stream right?

I'm trying to figure out the difference here... is it because the canopy actually has a forward speed and the kayak is just drifting? shape of the vehicle?

Scars remind us that the past is real

[mark 107]

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so if you put a kayak in a stream, with no other input, it will turn down stream right?

I'm trying to figure out the difference here... is it because the canopy actually has a forward speed and the kayak is just drifting? shape of the vehicle?

Shape of the flow. Velocity is fastest at the center, slowest at the banks. If the flow was uniform, the kayak would just be an oblong raft.

Mark

[kallend 2,108]

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so if you put a kayak in a stream, with no other input, it will turn down stream right?

I'm trying to figure out the difference here... is it because the canopy actually has a forward speed and the kayak is just drifting? shape of the vehicle?

In a constant wind a canopy has no idea which way the wind is blowing.

If there is a wind shear, the canopy may well turn as it descends through the shear, and the turn direction would be downwind if the wind is decreasing as altitude decreases, which is usual. I wouldn't expect it to be much of an effect.

Example: say the canopy is flying on a north heading in a crosswind from the west at 20kt. Due to the wind the canopy is actually drifting sideways to the east at 20kt and the relative wind is from straight ahead.

Now let the canopy descend through a shear to where the wind is only 5kt (same direction). Newton's 1st law says the canopy and skydiver are still going east at 20kt, so the canopy now feels a (20-5) = 15kt wind from the right. The canopy will turn right into this relative wind until the system comes to equilibrium again. Seen from the ground, this is a turn downwind.

...

The only sure way to survive a canopy collision is not to have one.