Does wind speed and gusts affect descent rate?

[unkulunkulu 0]

Why so long posts. Will headwind affect the vertical speed of said aircraft a couple seconds after takeoff or not? yes or no?

[Di0 1]

unkulunkulu

Why so long posts. Will headwind affect the vertical speed of said aircraft a couple seconds after takeoff or not? yes or no?

Yes, from an absolute point of view *.

Long post was trying to explain what "affect" means. In a certain frame of reference, people that say it does not, are correct. In another, they are not, hence the confusion.
Headwinds helps steeper climbs, therefore they affect the triangle and composition of velocities from a ground perspective (this can't be disregarded by analyzing only relative speeds).

And why what happens to an airplane might not directly transfer 1:1 to a parachute.

When potatoman said equal relative speeds means equal everything else he is also correct, 100%. But to me, that's not the whole picture. IMHO.
Problems are a little complicated and hard to explain sometimes.

* Absolute here meaning Earth Reference.

However, I have to say that what is true from the point of view of an engineer (which sits on the ground) becomes less important from the point of view of the PILOT, whose ass is on the plane/canopy, once you reach a certain equilibrium point (w.r.t airspeed), things don't change anymore.

If horizontal winds would not affect lift, then kiting stuff would not be possible.

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.

[billvon 2,435]

>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".

No, it won't. Your rate of climb is exactly the same in any wind once you are off the ground.

>That is why airplane always want to takeoff and land INTO the wind.

It has nothing to do with lift - and aircraft can take off in any direction they like without any difference in their lift. Planes like to land into the wind (and take off into the wind) because they can use shorter runways, since the runway and the air are moving at different speeds.

>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 . . ..

True. But whether you are facing into the wind or facing away from the wind, your airspeed is exactly the same.

Consider the following. Imagine a jump at the equator. If you fly east you are flying at around 1000mph compared to the rest of the Earth. Do you go rocketing skyward, or get your ears blown off? Nope - because the air around you is hitting you at about 20mph.

[unkulunkulu 0]

Quote

Yes, from an absolute point of view *.

So you're saying that when taking off into the a headwind, the aircraft climbs faster? (you see, I ask _climbs_, not takes off, we start timing once the wheels are in the air, not when the engine is warming up)
So let's say we'll get to 300ft in less time? You really believe that?

[billvon 2,435]

>If horizontal winds would not affect lift, then kiting stuff would not be possible.

AIRSPEED affects lift. You can kite by standing on the ground in a 10kt wind, or by driving a pickup at 10mph through still air. They are exactly the same to the canopy.

[pchapman 262]

unkulunkulu

Why so long posts. Will headwind affect the vertical speed of said aircraft a couple seconds after takeoff or not? yes or no?

Ok, shorter:

A steady headwind will not affect the climb speed of an aircraft.
(Of course, with less ground speed, and same climb speed, the angle over the ground will be steeper.)

A very sudden change in headwind will affect the climb rate for a short time, when the speed of air over the wings (and thus the capacity for lifting) suddenly changes, before inertia and aircraft stability have the chance to return the flight to normal.


@ Di0:
Kites are a different situation because you are anchoring them to the ground, allowing different forces to be applied to them. They aren't free to move with the air mass.

[Bufobufo 0]

A fictional cessna 150 taking off with a 27,5knots tail wind will have to accelerate through -27,5knots wind(stand still on runway) to +55knots before it can take off forcing it to accelerate 82,5knots in order to compensate for the wind.

Same plane taking off in 27,5 knots headwind will need another 27,5 knots in order to reach 55knots before reaching take off speed. A shorter runway in less time since it had a free 27,5knot (31,5mile/h 50km/h) head wind to generate lift before even releasing the brakes.

A canopy that flies 10m/s in full flight will fly 10m/s through the air no matter what direction the pilot choose to fly in, if no input is made on toggles or whatever. The pilot will spend the same time under canopy flying back to an imaginary DZ after a bad spot as his friend following a cloud away from the DZ, where they end up and the distance relative ground they travel will vary though

[Di0 1]

billvon

>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".

No, it won't. Your rate of climb is exactly the same in any wind once you are off the ground.

>That is why airplane always want to takeoff and land INTO the wind.

It has nothing to do with lift - and aircraft can take off in any direction they like without any difference in their lift. Planes like to land into the wind (and take off into the wind) because they can use shorter runways, since the runway and the air are moving at different speeds.


>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 . . ..

True. But whether you are facing into the wind or facing away from the wind, your airspeed is exactly the same.

Consider the following. Imagine a jump at the equator. If you fly east you are flying at around 1000mph compared to the rest of the Earth. Do you go rocketing skyward, or get your ears blown off? Nope - because the air around you is hitting you at about 20mph.

DAMN, DO I LOVE THIS DISCUSSION!!!! Seriously.
Thank you!!!


I agree with what you say and that's why I always used the word "faster" with commas, and try to use the word steeper, which is more proper.
When you say "it won't affect anything but groundspeed", you are correct. But groundspeed is what I care about! Ground speed is what determines your glide angles etc.!
I think part of the confusion comes from the fact that glide performance are usually thought for minimum gliding angle, I'll explain. Glide performance are always, for obvious reasons, relative to the ground.

Let's talk about gliding performance alone for a second, since it's what more closely relates to a parachute. And it's easier.
Now, any good glider pilot knows what a hodograph (or polar curve) is for a glider. And how wind affects it.
The wind will move your hodograph up and down (upward/downward wind) or left/right (head/tail wind).
Go to page 21 here:
http://www.beknowledge.com/wp-content/uploads/2011/02/8f14eAirplane%20Aerodynamics%20and%20Performance%20-%20Chapter%208%20-%20Fundamentals%20of%20Flight%20Performance.pdf

It's the first example I could find (although it's not super clear, maybe this one is better:
http://www.aviation.org.uk/docs/flighttest.navair.navy.milunrestricted-FTM108/c8.pdf and maybe the discussion is easier, anyway, same conclusions...)
Anyway just google gliding performance, gliding hodograph or speed polar for a bunch of those.
You can see that up and down wind affect your gliding path A LOT, to the point that upward draft in the example causes a negative gliding angle (i.e. you have a negative descent, you go up), head and tail wind affect your gliding path less, but they still do the same way, they still change your equilibrium points in your hodograph.
The difference between point 3,0 and even 1 on the vertical speed component is minimal, although the angle changes, the vertical components not so much (this is a common approximation for small glide angles), the big difference is for point 2 (of course, point 2 is the down draft, a downdraft will make you go down faster, no arguing there).

Nonetheless, you can see that also an headwind will: reduce your glide angle, reduce your total speed, reduce your horizontal component (all obvious effects) but therefore reduce your vertical component (yes, only with respect to the ground! Not with respect to the air! But we are interested in the absolute speed with respect to the ground, if we are trying to land softly and with minimum glide angle and minimum velocity).

Also, what I think it's causing confusion is that a pilot gliding in a plane will try to minimize the glide angle by keeping a constant CL/CD (maximum possible), therefore should try to keep a constant speed (relative speed, this time), that's where the hodograph comes into play.... I really don't know if you can do that for a canopy, which is trimmed at a certain angle, but in theory you should be able to change the angle of attack with rear risers, right? So the same discussion might apply and you might be able to minimize your glide angle, total speed, horizontal and vertical speed by using a combination of headwind and rear risers, as shown in the hodograph for a glider? Not 100% sure.

From a canopy pilot perspective, I'd LOVE to see some real hodograph and flight performance chart, I wonder if there is a way to obtain them.
Those charts you'll find are true for glider/aircraft and drawn using certain approximations on the formulas (see the chapter before), I honestly don't know if they're true for canopies as well and how much of them it can be transferred, I'd love to know it or to talk with a person that studied the problem of a modern square canopy glide performance from an engineering point of view.

I really-really-really-really want to see and hodograph for a canopy or know if somebody studied the problem with that approach, I'm not kidding here, this topic made my engineering curiosity go totally wild. .

But I agree with what your guys say, if there is an effect, it's secondary and airspeed is what matters from most aspects of the problem.

++++++++++++++++++++++
Let's leave alone the equator example for a second, we all agree that rotation of Earth has a minimal effect on flight (it does though, it's the Coriolis effect, but anything slower than an SR-71 should not worry about it...).
We are assuming everything is an inertial frame of reference here, thankfully!

The only two reference frames we are interested right now are: a) the one centered on the ass of the pilot ant that moves with him b) the one centered on a point on the ground that remains stationary and we assume a fixed point in the whole universe.

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.

[Di0 1]

Ok, I see part of the problem. To me, faster and shorter had the same meaning during the discussion.
This is clearly not the case, I think in english they mean something different: faster with respect to time, shorter with respect to space? Is that right?
In that case, I agree. Headwind will make the climbing "shorter", not "faster".

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.

[craddock 0]

WTH?? The question was about rate of decent the way I read it. Obviously the trajectory relative to the ground changes.

You take off and land into the wind to use less runway and have a lower ground speed.

That spot isn't bad at all, the winds were strong and that was the issue! It was just on the downwind side.

[unkulunkulu 0]

Oh, man. Now I get what you're trying to say :)

You mean, it will ascend like this
...*..........
..*...........
.*............
*.............

versus
..............*......
.........*........
....*...........
*.............

Well, sure :) So height versus horizontal distance travelled will increase.

But the OP was asking about descent rate. Rate is per unit of time, not per unit of distance. Height/time. Height/distance -- glide, height/time - rate, ok? :)

[wstcstcmtr 0]

So he wants you to have physics and calculations... But all he has is a feeling?

[billvon 2,435]

>Nonetheless, you can see that also an headwind will: reduce your glide angle,
>reduce your total speed, reduce your horizontal component (all obvious effects)
>but therefore reduce your vertical component (yes, only with respect to the
>ground! Not with respect to the air!

Definitely. But the important thing to remember is that all your canopy cares about, ever, is what's happening to it with respect to the air.

That means that when you are landing, and returning to the ground, wind speed and direction definitely matters. Not because your canopy cares (it will turn and flare exactly the same whether you are landing into the wind, crosswind or downwind) but because when your feet touch the ground, your _feet_ care very much about what the ground is doing with respect to the air.

[craddock 0]

Just for those who repeatedly say in these threads "ask any pilot" as to offer validity to their claim, there are highly experienced Professional pilots over at Pprune.org that can not agree on these principles.
There is one guy that had at the time over 1200 public helicopter demonstration displays to show capabilities of aircraft that believed that wind does matter. Now to be fair they are primary talking about an aggressive unbalanced turn but there are plenty on there that will never to a wing over turn into the wind. Interesting discussions. Talks about inertia, loss of IAS, ect.

I only mention because I think it is funny when someone says "ask any pilot" like it is that cut and dry among all pilots

That spot isn't bad at all, the winds were strong and that was the issue! It was just on the downwind side.

[ianyapxw 0]

This is also what I've been thinking. No one's seemed to mention the fact that a ram air canopy is not a perfect rectangle but tilted downwards towards the ground.

Shouldn't flying downwind/into the wind affect lift then? Though I think how much it affects will be pretty insignificant anyway.

[unkulunkulu 0]

It can be whatever, if it satisfies the laws of physics, the rate of descent will not be affected by steady horizontal wind.

[Quagmirian 40]

Reading this thread, I am feeling much more confident about my knowledge of how to design a parachute.

As said previously, the only way a canopy's descent rate can be affected is by sudden gusts, turbulence, wind shear or updrafts/downdrafts. Flying upwind or downwind doesn't mean shit to a canopy or any other untethered flying machine, because it's flying through the airmass.

[pchapman 262]

ianyapxw

This is also what I've been thinking. No one's seemed to mention the fact that a ram air canopy is not a perfect rectangle but tilted downwards towards the ground.

I did
As usual, steady state winds have no effect.

Gusts will have an effect. Just that with a downward flight angle of a ram air parachute, the effect of horizontal gusts can vary compared to for an aircraft flying horizontally. What the effect is depends on the vector addition of the canopy's flight vector and the wind gust and lift characteristics of the canopy. A sudden headwind may increase lift (if the gust is not that fast) or decrease lift (if the gust is faster.)

Edit: To clarify, the smaller gust's increase wind speed will have more effect on adding lift than the loss in angle of attack will reduce lift. A very large gust could reduce the angle of attack enough that theoretically one could lose almost all lift, or go further to a negative angle of attack and collapse the canopy.

[billvon 2,435]

>No one's seemed to mention the fact that a ram air canopy is not a perfect
>rectangle but tilted downwards towards the ground.

Doesn't matter.

>Shouldn't flying downwind/into the wind affect lift then?

Nope. The only thing that affects a wing is a change in the airspeed it sees.

Important note - the one effect the ground CAN have on airspeed is that obstacles are on the ground. This is, of course, an issue with landing (don't want to run into obstacles) but they can also affect the canopy while it is still in the air. If you land near trees, for example, those trees can cause turbulence in the wind flowing over them, and the canopy will see that turbulence.

In an ideal case this _might_ cause the canopy to care about wind direction. If, for example, you are landing downwind and go below the treeline - and the wind change is smooth and continuous from, say, 15mph to 5mph - then your canopy will see a sudden increase in airspeed of 10mph. This will tend to cause it to "float" and seem to fly forever, since it's bleeding off that extra airspeed. Again the reason that the canopy cares is that the airspeed, not the groundspeed, changes.

On the other hand, if you are landing into the wind and you go below the treeline - and the wind change is smooth and continuous from 15mph to 5mph - then your canopy will see a sudden DECREASE in airspeed of 10mph. This will tend to cause it to drop or even stall in extreme cases. And since trees generally occur in the last few hundred feet, a stall would be a bad thing.

However I have never seen a treeline generate such a smooth transition; the turbulence is always pretty bad when the winds are high. Thus it's basically never OK to land downwind of a tree line no matter which direction you are flying.

[Di0 1]

billvon

>Nonetheless, you can see that also an headwind will: reduce your glide angle,
>reduce your total speed, reduce your horizontal component (all obvious effects)
>but therefore reduce your vertical component (yes, only with respect to the
>ground! Not with respect to the air!

Definitely. But the important thing to remember is that all your canopy cares about, ever, is what's happening to it with respect to the air.

That means that when you are landing, and returning to the ground, wind speed and direction definitely matters. Not because your canopy cares (it will turn and flare exactly the same whether you are landing into the wind, crosswind or downwind) but because when your feet touch the ground, your _feet_ care very much about what the ground is doing with respect to the air.

Oh yeah, absolutely agree!!
Let's put it this way, to me it's a matter of apples with apples, when talking about reference frames.
So most people say flying 10 mph in 0mph wind is the same as flying 20 mph in 10 mph wind and I say true. Relative speed is 10mph in both cases.
But to me that's not comparing apples and apples, because with a glider (no engine) or a canopy (no engine) you have limited control over approach speed (for the sake of arguments, let's assume an "uncontrolled" approach, you just let that thing fly an trim itself according to its own aerodynamic characteristics). So you see, I say that "wind" changes your approach speed, because I always reason with respect to the ground, when studying glide performances.

I agree that the canopy will fly absolutely blind to what the wind is, but I think a canopy will also automatically "trim" itself to a certain relative speed (please, correct if I'm wrong), so wind do matter a lot, because wind will determine your absolute velocity wrt the ground.

Actually, now that I think, most classes about flight mechanics use ground-fixed references, most classes of aerodynamics use wing-fixed reference frames, there must be a reason!! :)

Problem with these things, they are tricky to understand (sometime counter-intuitive) and hard to explain and communicate, especially without drawings.

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.

[kallend 1,651]

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??

I am a physics professor, and this topic was discussed AT LENGTH many years ago in the canopy control forum on DZ.COM, to include the effects of gusts and wind shears.

You could do a search.

...

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

[DocPop 1]

billvon

Important note - the one effect the ground CAN have on airspeed is that obstacles are on the ground.

There is also the effect that differing types of ground can have on the formation of updrafts, or thermals. These can certainly affect descent rate.

Quote

In an ideal case this _might_ cause the canopy to care about wind direction. If, for example, you are landing downwind and go below the treeline - and the wind change is smooth and continuous from, say, 15mph to 5mph - then your canopy will see a sudden increase in airspeed of 10mph. This will tend to cause it to "float" and seem to fly forever, since it's bleeding off that extra airspeed. Again the reason that the canopy cares is that the airspeed, not the groundspeed, changes.

Actually, in this example groundspeed will change until the system regains equilibrium under the new conditions

Quote

On the other hand, if you are landing into the wind and you go below the treeline - and the wind change is smooth and continuous from 15mph to 5mph - then your canopy will see a sudden DECREASE in airspeed of 10mph. This will tend to cause it to drop or even stall in extreme cases. And since trees generally occur in the last few hundred feet, a stall would be a bad thing.

I think you mean if there is a sudden change in wind speed??

"The ground does not care who you are. It will always be tougher than the human behind the controls."

~ CanuckInUSA

[mjosparky 3]

In ram air parachutes you have 3 basic elements, wing shape, trim and loading. The first 2 are determined by the manufacture and the last by the jumper. Only one of the three can change the rate of decent without changing canopy design factors and that is loading.

The reason you take off and land into the wind is that is the time you transition from running along the ground and flying in the air and vice versa. You want to make this transition with slowest possible ground speed possible. That is the reason you flare, you lose ground speed while maintaining lift.

Tell your friend he is a moron and owes you beer.

Sparky

Read up on canopy design.

My idea of a fair fight is clubbing baby seals

[billvon 2,435]

>There is also the effect that differing types of ground can have on the formation
>of updrafts, or thermals. These can certainly affect descent rate.

Definitely. But this is another example of the canopy caring about airspeed (i.e. the speed and direction of the wind in the thermal) rather than the ground. In that case, of course, the thermal was originally _caused_ by the ground but the canopy doesn't know that; it just sees the winds inside the thermal.

>I think you mean if there is a sudden change in wind speed??

No, because a sudden change in wind speed might well cause a collapse, and I wanted to distinguish a change in wind speed from turbulence*. However, if the change is slow enough, the canopy will "see" it as a decrease in speed.

(* - at the end of the day all turbulence is changes in wind speed - but we tend to define turbulence as _rapid_ changes in wind speed.)

[format 0]

kallend

***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 am a physics professor, and this topic was discussed AT LENGTH many years ago in the canopy control forum on DZ.COM, to include the effects of gusts and wind shears.

You could do a search.
Dude, this is the wrongest place to pull out your diploma.

What goes around, comes later.