Altitude loss in a swoop

[rainman 0]

I'm not sure whether this belongs here or in swooping & canopy control, but here goes:

I was having a discussion with a friend, both of us being non-swoopers, with him being more experienced than me.

His statement: Swoopers start their final turn lower in high winds, because the recovery is faster (i.e. takes less altitude).

Me: *stutter* moving airmass, no difference *cough* parachute doesn't know about wind *confused look*

What I'm trying to say is that his statement sounds like a myth to me, much like parachutes having a tendency to turn downwind, but I can't provide a coherent reasoning behind this.

Any informed opinions on this?

Rainman

[grega 0]

You're right.

The parachute doesn't feel the wind, it moves with the airmass, so it's completely the same for it if there is any wind or not.
But that applies only in constant non-turbulent wind !!!

I'm sure you'll find half of people here that won't agree with you and the other half will.

Aerodynamics is a vaaast science and it ends right at quantum physics... And most people that have an opinion about this know very little of both...

"George just lucky i guess!"

[AggieDave 6]

Well, I couldn't tell you yes or no nor have any proof to back it up...BUT, if I start the exact same turn I do on a no wind day at the exact place and altitude (as best as I can judge) on a day with 15mph wind, I come out high on my swoop (what little there would be in 15mph winds).

If I do the approach I tend to do in higher winds on a no wind day, I'd have to dig it a little bit, where I wouldn't on a high wind day.

Why? I have some thoughts and theories, but I can't prove it, I don't know enough about the science to sit down and really hash it out.

--"When I die, may I be surrounded by scattered chrome and burning gasoline."

[billvon 3,096]

>His statement: Swoopers start their final turn lower in high winds,
>because the recovery is faster (i.e. takes less altitude).

Canopies do not recover faster in high winds. Since we perceive height at least partly by relative motion (i.e. how fast things on the ground are moving) high winds do affect our _perception_ of how high we are when we start the hook.

[ramon 0]

Grega is absolutley right.

When turning altitude seems to lenthen or shorten in wind it is usually due to updrafts or downdrafts associated with turbulence.

Psychological factors also enter when pilots mess up their set up due to unfamiliar wind conditions and find them selves low or high when they want to turn.

my 2 cents.

ramon

"Revolution is an abrupt change in the form of misgovernment.", Ambrose Bierce.

[ianmdrennan 2]

I use my neptune to help gauge the initiation of my turn. I use the same alt regardless of the wind speed.

There have been many discussions regarding this just search and you'll find more info that you wanted.

The jist of the conversation goes: As long as the wind speed isn't changing (ie gusty) the turn heights are identical. The canopy has no concept of the actual speed of the wind, only the speed of the wind flowing over it.

Blue skies
Ian

Performance Designs Factory Team

[AggieDave 6]

Quote

Since we perceive height at least partly by relative motion (i.e. how fast things on the ground are moving) high winds do affect our _perception_ of how high we are when we start the hook.

Well, that would explain my world. Thanks Bill! Since I don't use my alti to swoop, that makes sense that my perception of altitude is off.

--"When I die, may I be surrounded by scattered chrome and burning gasoline."

[USPA 0]

This could also be the reason why people starting to hook downwind, mostly have the tendesy to be low...

The trouble with skydiving; If you stink at it and continue to jump, you'll die. If you're good at it and continue to jump, you'll see a lot of friends die...

[kaerock 1]

This is why often swoopers (and myself included) stab early, then plane out very high on windy days. We do this because our forward ground motion is reduced into the head-wind, tricking our brains into thinking we're about to screw in, when in all actuality, we're probably on a perfectly good recovery arc.

-Rory

Quote

>His statement: Swoopers start their final turn lower in high winds,
>because the recovery is faster (i.e. takes less altitude).

Canopies do not recover faster in high winds. Since we perceive height at least partly by relative motion (i.e. how fast things on the ground are moving) high winds do affect our _perception_ of how high we are when we start the hook.

You be the king and I'll overthrow your government. --KRS-ONE

[mnischalke 0]

I know that higher winds also cause your perceptions to change during the turn as well.

Your normal sight picture on a no-wind or light-wind day might have the ground moving at a certain speed beneath you. In those same normal conditions, if you see the ground moving less, or not at all, your mind would probably tell you that you're getting into the corner, so you alter your inputs with maybe added harness to speed up the turn while conserving some altitude.

On a windy day, I have found that I have mistakenly recognized the corner sight picture, because I am heading straight at the ground, when in fact the moving airmass is tricking me. I get around to my intended heading faster, and what do you know, I am high.

I know this perplexed me for a while until someone with a lot more knowledge pointed it out to me.

mike

Girls only want boyfriends who have great skills--You know, like nunchuk skills, bow-hunting skills, computer-hacking skills.

[mnischalke 0]

what he said...

mike

Girls only want boyfriends who have great skills--You know, like nunchuk skills, bow-hunting skills, computer-hacking skills.

[thelem 0]

Quote

The parachute doesn't feel the wind, it moves with the airmass, so it's completely the same for it if there is any wind or not.
But that applies only in constant non-turbulent wind !!!

I've thought about this one before, and come up with the constant, non-turbulent wind thing. But what you didn't mention is that the wind needs to have a constant velocity (speed and direction) in relation to the velocity of your parachute. I.E. if you don't touch your risers/toggles, then the wind could be constant, but as soon as you start a turn you will be affecting the relation between the velocity of your canopy and the wind. I think that makes sense ;)

[rainman 0]

Thanks everyone for the helpful responses!

I'm sure I can now convince my friend that 'his logic is flawed'.

Rainman

[grega 0]

Hmm i'm not sure i understood you.

What i ment to say with constant non-turbulent wind is exactly that. To apply all the statements i said in earlier post, the wind has to have the same direction and same speed/strength through whole maneuver.

Because if the wind would change, the canopy would acomodate to that speed sooner than the pilot because of way lower mass it has. it's similar, if you throw a feather with all your force away. it will decelerate in a second. but if you throw an iron ball, it will keep it's speed for much longer. same with canopy and pilot. So that's why the speed and direction of the wind needs to stay constant.
And don't let me explain it in more details when turbulences apply because only then it gets [B] REALLY complicated.

Quote

but as soon as you start a turn you will be affecting the relation between the velocity of your canopy and the wind.

if by "the wind" you ment speed at which the airmass is moving over the ground, then true. when you turn, looking from the ground it will naturally seem that your speed/direction has changed. no matter the wind, if looking from the ground the direction/speed will seem to change.
if you ment the relative wind - speed that the air is hitting the canopy at, then not. i mean of course the relative wind get's higher because you make a turn. but the realtive wind through maneuver is the same as it would be if the "ground wind" would be 0knots.

ugh complicated... for easier understanding:
If you and your buddy made 2 jumps. both jumps with same canopies. 1st jump with 20knots "ground wind", 2nd with zero "ground wind".
and your friend would make exactly the same turn both times, and you would be exactly at the same position (relative to him) under the canopy of course, when he'd do a turn. the turn would look exactly the same from you perspective.
relative to you, he would loose the same altitude, gain or loose same speed, and changed his direction exactly the same at both jumps. that of course would be from your perspective.
if a 3rd friend would be watching all that from the ground. those 2 turns in 2 jumps would look very different...

Exactly the same turns twice at exactly the same position is impossible to do in reality though. so you actually can't prove that with trying. But i hope you understood what i ment to say...

"George just lucky i guess!"

[GravityGirl 0]

That's too much math. I just land cross or down wind on windy daze!

~~~~~~~~~~~~~~~~~
Peace and Blue Skies!
Bonnie ==>Gravity Gear!

[mathias 0]

Me: *stutter* moving airmass, no difference *cough* parachute doesn't know about wind *confused look*

Hey I used to think that the moving airmass thing was correct until I talked about this HIGH WIND low TURN thing for landing with a hanggliding pilot.

He pointed out two things to me that changes a lot when you get close to the ground.
1. Gradient - a 15kt wind on the surface will be significantly higher at 200 or 300 fet. ie there is a rather large change of wind as You perform your turn for landing.
2.Coriolis - the wind turns as you move away from the surface, because of the earths rotation. (And many other factors.)

The biggest reason, in my opinion, that people (including me) turn lower on high wind days is the perception of speed, we usee the groundspeed to judge not the airspeed.

Mathias

Ingen minns en fegis!

[FrogNog 1]

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2.Coriolis ...

I thought the Earth Coriolis effect had a maximum impact of one revolution every 24 hours, and as a result was only worth worrying about when looking at airmasses at least hundreds of kilometers in size. For someone making a very short flight, this would just look like wind.

-=-=-=-=-
Pull.

[mathias 0]

http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/circulation/coriolis_and%20friction.html

I should have mentioned friction together with coriolis.

Ingen minns en fegis!

[rainman 0]

Clicky!

Rainman