Does wind speed and gusts affect descent rate?

[k_marr08 0]

Hi! Having a debate about wind speed and descent rate - I know when facing into the wind, ground speed decreases when wind speed increases, but does descent rate decrease as well? Does the added wind speed provide more lift? And, a related question, if one were to downwind a landing, would their descent rate increase, or would only their ground speed increase? And if you KNOW which answer is correct, can you explain why?

If the answer is that the descent rate is NOT effected by wind speed, then why do gusts "feel" like they affect descent rate? Is there some additional element of gusts that actually do affect descent rate?

Please and thank you :)

"I believe the risks I take are justified by the sheer love of the life I lead" - Charles Lindbergh

[wolfriverjoe 1,339]

No. It won't affect anything but groundspeed.

You are flying through the airmass. Your airspeed is the speed relative to the airmass. That will be the same no matter what the wind is doing (presuming the wind is steady). So your descent rate or stall speed or potential for canopy collapse will not change as your direction relative to the wind direction changes.

The easiest analogy I know:

If you throw a toy glider inside a larger airplane, will it matter if you throw it towards the front of the plane or the back?

Edit to add (because you added stuff):
Gusts affect how the canopy feels because your momentum keeps the speed from changing as fast as the gust changes the windspeed. It's more turbulence than actual "gusts" once you are off the ground. The wind is changing direction and speed (think of eddies in a river). Those will bounce you around a bit.

"There are NO situations which do not call for a French Maid outfit." Lucky McSwervy

"~ya don't GET old by being weak & stupid!" - Airtwardo

[JohnMitchell 14]

It's been debated for years but proven a long time ago. A flying object, such as your parachute, does not "know" which way the wind is blowing. Upwind, downwind, crosswind are all in reference to the ground below, not what the air is doing over your wing. Your rate of descent does not change. The air continues to flow straight over your canopy, from nose to tail. And the DZ continues to get farther away if you're pointing the wrong direction.

Gusty, turbulent conditions will cause changes in rate of descent. Downdrafts and updrafts will, of course, push you in those directions vertically. Changes in headwind will have your canopy diving or floating as it seeks its flying speed.

Close to the ground this can be very problematic. A little downdraft increases your rate of descent, a little tail wind from rotors coming off of obstacles makes your canopy dive, all when you want to flare to slow your rate of descent. Tough situation.

[JohnMitchell 14]

wolfriverjoe

If you throw a toy glider inside a larger airplane, will it matter if you throw it towards the front of the plane or the back?

I like that analogy.

[k_marr08 0]

Thanks! Any chance anyone with a physics background can explain this in physics terms? My friend is not convinced lol

Maybe an illustration would help??

"I believe the risks I take are justified by the sheer love of the life I lead" - Charles Lindbergh

[k_marr08 0]

Or math calculations?? He thinks wind speed MUST affect descent rate because it's energy acting upon mass.

"I believe the risks I take are justified by the sheer love of the life I lead" - Charles Lindbergh

[wolfriverjoe 1,339]

How about "frame of reference"? The only one that matters is the canopy (or airplane) relative to the airmass.
It doesn't matter which direction or how fast (presuming steady state movement - steady winds, not gusty) the airmass is moving.
That's all the airfoil cares about. The air travelling over it.

It doesn't matter if you are under canopy with a steady wind blowing at 10 mph or inside a 747 going 500+ mph. (toy glider in the bigger plane analogy).

The idea that you are going faster downwind or slower upwind is an illusion, based on using the ground as a frame of reference. It's true from that point of view, but the airfoil (canopy) doesn't care about the ground. It only cares about the air it's moving through.

"There are NO situations which do not call for a French Maid outfit." Lucky McSwervy

"~ya don't GET old by being weak & stupid!" - Airtwardo

[wmw999 2,114]

Ask him at which wind speed he thinks his canopy will begin going up in mid-air. Rate of descent in a canopy is changed by flaring or angle of attack, not by increasing the wind speed. You have to change the shape to change the speed -- it's no different from any other object in mid-air.

Wendy P.

There is nothing more dangerous than breaking a basic safety rule and getting away with it. It removes fear of the consequences and builds false confidence. (tbrown)

[Squeak 17]

k_marr08

Or math calculations?? He thinks wind speed MUST affect descent rate because it's energy acting upon mass.

he's r7ght it is energy acting on a mass.
Buts it's acting front to back (or vice versa)
Ts not acting from below (unless it's an up draft)

You are not now, nor will you ever be, good enough to not die in this sport (Sparky)
My Life ROCKS!
How's yours doing?

[format 0]

Wow. I never questioned that the wind will decrease descent rate.
So many times I've seen a low wing load student in higher wind, just floating up there "for ages".

Say.. girl 75lb, Navigator280, 16kts wind - FIFTEEN minutes flight from 3000ft!
All others finished repack.
That's how I recall it... talking about eye witness estimation accuracy

edit: sry, I meant girl 60 kilos or 132 pounds.. which would make WL 0.6:1

What goes around, comes later.

[k_marr08 0]

well I GUESS gravitational forces might come into play as well

"I believe the risks I take are justified by the sheer love of the life I lead" - Charles Lindbergh

[pchapman 261]

1. As pretty much noted already: Steady winds in themselves won't change descent rate, and gradual transitions between different wind speeds at different levels will basically do the same.

2. As pretty much noted already: Up and down drafts, whether thermals or just short term gusts, will of course change descent rate while affected by them, until the canopy is out of them and regains its equilibrium glide.


Now the new bit, which is messy because I haven't had time to state it more succinctly:


3. Descent rate will however be affected by sudden wind shears, or by a horizontal gust.

Consider an airplane flying horizontally that goes from a no wind condition to a sudden headwind. (Or some wind to more wind). One could equivalently have an airplane descending at a very shallow angle through some idealized shear layer, going from no wind to sudden headwind.

In any case, since the airplane has plenty of inertia relative to the aerodynamic forces on it, and isn't a dandelion seed that almost instantly changes speed with the wind, the airflow over the wings will suddenly change.

So the plane will go from some equilibrium cruise condition to suddenly having a higher airspeed through the air (with no change in ground speed.) The airplane has suddenly been given extra energy to work with. The natural stability of a normal aircraft will make it pitch upwards, trying to regain its original airspeed. Depending on the stability characteristics of the plane, it might just gradually and smoothly regain its original aispeed and horizontal flight path, or it might pitch up and down a few times in smaller and smaller increments until back to normal.

Because the airplane caught the gust, it picked up the extra energy from the high speed air, and climbed. So it changed its descent rate from zero to a climb for a while until flying level again.

This is the exception to the normal "wind doesn't matter" scenario: Usually wind changes are fairly gradual, or in the long run things even out with gusts from different directions, so then wind changes don't matter. But if a flying vehicle that creates lift is suddenly hit by a horizontal gust or shear, it will pick up energy that changes the descent rate.

Similarly, if there's a suddenly tailwind, there's suddenly less airspeed for the wings, lift is lost, and the aircraft pitches down and descends faster until it regained speed.

I used the example of an airplane flying horizontally or nearly so, because that simplifies the math. With a parachute that is descending at a significant angle, it gets a little messier and the results depend on a mix of factors. A horizontal gust from the front does increase the speed of the wind felt by the canopy -- increasing its lift suddenly, so that like an airplane it would tend to pitch up, slowing its descent rate until back at equilibrium.

But on the other hand, because the parachute is descending, the gust also reduces the angle of attack. (Consider the extreme -- if the head wind suddenly jumped by 200 mph, whatever the canopy type in a normal glide, it would suddenly have the relative wind coming from above the chord line, "hitting the front top of the canopy" so to speak, a negative angle of attack.) The reduction in angle of attack will reduce lift and cause the canopy to start to drop and pitch down. (And if extreme enough reduction in angle of attack, have the nose collapse downwards.)

So the net result of the horizontal headwind gust may be a pitch up and reduced descent rate, or a pitch down and increased descent rate, depending on the vector math of the canopy flight and gust.

So the result is, like for the airplane flying horizontally, that a sudden horizontal gust (or dropping through a sudden wind shear) can temporarily change the descent rate of a canopy.

SUDDEN horizontal changes in wind can thus affect the vertical speed of a canopy, creating temporary decreases or increases in descent rate, by temporarily increasing or decreasing the canopy's lift.


Under a canopy one might get a thermal or upwards gust that makes the canopy pitch back and slow down until returning to normal. After hitting the up gust, you may then reach the end of it, or a downward gust too, and suddenly pitch down.

You might feel pretty much equivalent motions if you hit a horizontal gust -- pitching up, slowing down, then pitching down, and speeding up, until all returns to normal.


Edit:

So to clarify, responding to the original post:

Quote

Does the added wind speed provide more lift?

No, when talking about different winds in general, or flying up or downwind.

Quote

If the answer is that the descent rate is NOT effected by wind speed, then why do gusts "feel" like they affect descent rate?

Yes, sudden gusts, even if only horizontal gusts, will change descent rate temporarily.

[riggerrob 558]

wolfriverjoe

How about "frame of reference"? The only one that matters is the canopy (or airplane) relative to the airmass.
It doesn't matter which direction or how fast (presuming steady state movement - steady winds, not gusty) the airmass is moving.
That's all the airfoil cares about. The air travelling over it.

It doesn't matter if you are under canopy with a steady wind blowing at 10 mph or inside a 747 going 500+ mph. (toy glider in the bigger plane analogy).

The idea that you are going faster downwind or slower upwind is an illusion, based on using the ground as a frame of reference. It's true from that point of view, but the airfoil (canopy) doesn't care about the ground. It only cares about the air it's moving through.

.................................................................................

The parachute only knows that it is flying through a block of air.
The parachute does not know whether that block of air is sliding across the ground, ergo, it does not know whether it is facing upwind, or downwind, etc. ... ergo rate of descent does not change with heading.

[riggerrob 558]

Vertical gusts change rate of descent.
Some gusts are even rotary ... try to picture roll clouds downwind of a mountain.
If you fly your parachute into the descending part of a roll gust, your rate of descent will increase.

[unkulunkulu 0]

Quote

Any chance anyone with a physics background can explain this in physics terms? My friend is not convinced lol

It's called the relativity principle, for example http://en.wikipedia.org/wiki/Galilean_invariance
Basically: if the wind is uniform and steady, you can take an inertial frame of reference that moves with the wind. In this frame of reference the canopy flies the same as in no wind conditions.

Wind (the wind you talk about when you say "downwind landing") is flow of air masses relative to the ground (every motion is relative). If there was no ground, there wouldn't be any wind to talk about. Your canopy is not bothered with ground, it flies in the air!

That was uniform and steady. The changes in the wind (be that temporal or spatial) can provide some dynamic effects. To reason about those, you must first understand the basic stuff about steady winds and the relativity. All that matters to the canopy is the relative wind (wind relative to the canopy). For example if you fly into the wind and descent from stronger winds to an altitude where the wind drops momentarily, the canopy will surge, because it lost some speed relative to the wind => the lift is lost as well! If you catch a frontal gust, you will sense an increase in lift.

But all those are dynamic effects. If you fly in a steady wind without giving any inputs to the canopy, the rate of descent will be the same no matter what your heading is. Downwind the same as into the wind.

[potatoman 0]

Does a plane climb faster flying into wind, or with the wind?

Climbs exactly the same.

Keyword: Relative, not cousin.

You have the right to your opinion, and I have the right to tell you how Fu***** stupid it is.
Davelepka - "This isn't an x-box, or a Chevy truck forum"
Whatever you do, don't listen to ChrisD.

[rehmwa 2]

k_marr08

Thanks! Any chance anyone with a physics background can explain this in physics terms? My friend is not convinced lol

Maybe an illustration would help??

It doesn't matter. It's excessively weird how closed mentally people are to things like this. They refuse to believe it. Yet it's so simple/basic. the wing always see the airspeed it's designed to fly in. (It's a free flying craft. Not a KITE tethered to the surface - that's where they get confused)

Until he's open over a cloudy and socked in day (with wind) and can't see anything but the cloud layer below him, he won't get it. (the clouds are moving with him, so he can face any direction and it won't matter one bit, the view will be identical).


Now, the fact that people will 'CHOOSE' to fly their brakes different on final approach depending on whether they are upwind or downwind, etc is a totally different thing.

...
Driving is a one dimensional activity - a monkey can do it - being proud of your driving abilities is like being proud of being able to put on pants

[erdnarob 1]

The vertical component of the speed of a parachute thru an air mass is the rate of descent. And it is not affected by the wind speed which is horizontal nor by the horizontal speed component of the parachute

Take a flat moving walkway in an airport going at constant speed. Suppose now that an ant on the right side of the walkway wants to go the other side by following a line drawn perpendicular to the edge, then the motion of the ant is not affected by the motion of the walkway. The ant travel will be the same using a walkway at rest. ie. The ant will follow the drawn line.

Is that better ?

In mathematics now : If two speed vectors perpendicular to each other represent the motion of an object, any of the vectors will keep the objet motion in the direction of this vector whatever is the presence or not of the other vector.

However, most of the people do the mistake. Common sense can lie to us sometimes.

Learn from others mistakes, you will never live long enough to make them all.

[chuckakers 369]

k_marr08

Thanks! Any chance anyone with a physics background can explain this in physics terms? My friend is not convinced lol

Maybe an illustration would help??

A boat is in a river going 20 mph. It doesn't matter if the boat is traveling upstream, downstream, or sideways to the flow of the river. The speedometer will read 20 mph.

It doesn't matter if the canopy is flying upwind, downwind, or crosswind relative to the movement of the air mass. It is a mass within a mass so it only cares about that relationship.

Picture sitting in a hot air balloon 500 feet off the ground. The wind can be blowing 20 mph yet it will be still in the balloon because the balloon has zero relative speed to the air around it, even though both the balloon and the wind are moving at 20 mph across the ground.

Chuck Akers
D-10855
Houston, TX

[Remster 24]

Quote

And it is not affected by the wind speed which is horizontal nor by the horizontal speed component of the parachute

In a static wind situation, correct.

The point of turbulence is that it's rapidly changing wind speeds and direction. The canopy will try and keep a study wind speed (assuming no input from the jumper) during that change. That means, if the winds slow down dramatically in reference to the canopy, it will speed up. This will have an effect on both groundspeed, V and H.

Why do you think we don't like landing in turbulence?

Remster

[chuckakers 369]

Remster

Quote

And it is not affected by the wind speed which is horizontal nor by the horizontal speed component of the parachute

In a static wind situation, correct.

The point of turbulence is that it's rapidly changing wind speeds and direction. The canopy will try and keep a study wind speed (assuming no input from the jumper) during that change. That means, if the winds slow down dramatically in reference to the canopy, it will speed up. This will have an effect on both groundspeed, V and H.

Why do you think we don't like landing in turbulence?

I think folks were trying to keep it simple for the OP but now that you've mentioned the canopy trying to maintain a study wind spreed, well....

Chuck Akers
D-10855
Houston, TX

[Remster 24]

It's the OP who mentioned gusts.

Remster

[Di0 1]

potatoman

Does a plane climb faster flying into wind, or with the wind?

Climbs exactly the same.

Keyword: Relative, not cousin.

Wrong analogy. A plane will have to push into the wind to create lift, therefore -fact well known to a pilot - going against the wind will increase the horizontal component of the speed and, leaving all other factors untouched - generate lift "faster". Although we might disagree on what we mean with the word "faster" (in general language, I see how it could both mean steeper ascent or fastest ascent).
That is why airplane always want to takeoff and land INTO the wind.

As for the parachute, I am sure a round canopy would not be affected in its descent by horizontal wind speed whatsoever, as all its lift (or rather, "vertical drag") is purely a matter of shape factor and passive air resistance, as said by pretty much everybody, there is no way for a round canopy to know which direction it is going with respect to the ground, it's just "carried around". It's a completely passive object that would act the same and always have a 0 relative component to the wind, as in itself it does not produce any forward speed and there is no ROTATION of air flow around a profile moving forward in the wind.
The opposite is true for square canopies, I think.
I am not so entirely sure the same is true for a square canopy, which also uses its profile to create lift, in that case more air passing around the canopy should create more lift, similarly to when a bigger mass of air passes around an aircraft rigid wing (more lift is produced at bigger relative speeds, again leaving all other factors untouched).
Now, is the effect secondary compared to others, namely to the main effect of a steady head wind, which is to slow down your horizontal speed, rather than affect your vertical one?
Probably.
But my intuition tells me that for any body that generates lift using a wing profile (as modern canopies do, although very partially), a small effect from head wind vs tail wind on the descent rate should be theoretically present (although maybe not enough to make a difference from a piloting point of view).

I'm standing on the edge
With a vision in my head
My body screams release me
My dreams they must be fed... You're in flight.

[potatoman 0]

Nope, I disagree, and ask any pilot when back at the DZ.

When you are flying, your prop turns a certain speed, hence you are moving through a mass of air at that speed, minus drag offcourse.

Now, when you flying with wind, you are travelling the EXACT same speed through the mass of air. Relativity.....my key word.

So, you land into wind and take off into wind, purely cause you have ground that is not part of the relativity.

You will NOT climb faster into wind than in a downwind.

The only way you can climb faster, is if you have updrafts, cause then it will change your angle of attack as you go through it. Again, relativity.

You have the right to your opinion, and I have the right to tell you how Fu***** stupid it is.
Davelepka - "This isn't an x-box, or a Chevy truck forum"
Whatever you do, don't listen to ChrisD.

[Di0 1]

Your take off run will be shorter (i.e. another word for faster), since you already "start" at a windspeed of 10mph (let's say) instead of 0. (that's why I said that in general speaking, faster could both mean steeper ascent of faster ascent, they are two different concept in aircraft dynamics).

But I see what you mean when you say "relative speed" you're right, if the relative speed is the same, then the lift and the mechanics are exactly the same.
It's just that a word like "faster" usually is meant in an "external" and absolute reference of frame, to me faster means less time or less runway space.
"Faster" is not relative, that's where the confusion comes from. I do agree that doing 0mph ground speed into an 80mph front wind or doing 80mph with no wind are to a good degree the exact same thing from the plane point of view, however from an external point of view the ascent with head wind is much steeper (i.e. the downward slope is reduced by head wind).
Imagine this: a plane with 0 wind and doing 80mph (ground speed) is flying on a straight line.
The same plane with 40 mph wind still doing 80mph is able to climb because of the head wind, now the relative speed is 120mph so it has an excess of lift, we all agree with this, right?
Yes, you might say: relative speed just changed, but this is EXACTLY the effect of wind and you can't ignore it by saying that it does not affect horizontal and vertical speed of the plane.
That is what I mean when I say that on a plane head wind changes the equilibrium point of flight.

I don't need to ask a pilot, I'm an aerospace engineer.
A pilot might not notice because all he reads is airspeed, but wind speed will change its trajectory w.r.t. to the rest of the world, quite a lot, both vertically and horizontally.




EDIT:
Maybe a site written in proper english will make it more clear, I forgive if my writing kind of sucks, but just google "effects of wind on take off" or something like that:

http://www.experimentalaircraft.info/flight-planning/aircraft-performance-4.php

"Headwind
By taking off into the wind (the wind will generate part of the required lift) the aircraft lifts off sooner and this will result in a lower ground speed and therefore a shorter take-off run for the aircraft to become airborne."

... etc. etc...

Bring this to an extreme, a kite horizontal speed is affected ONLY by headwind.

I'm standing on the edge
With a vision in my head
My body screams release me
My dreams they must be fed... You're in flight.