Some kind of autopilot?

[WindyTX]

Biggest load of tosh I have ever read.

 

But if your plane is taxying you would be exactly right.

 

Sent from my SM-G955U using Tapatalk

[David OC]

Fascinating!

 

How does it relate to weathervaning? The quoted Wikipedia article doesn't say anything about the reasons for sideslip angles.

 

To put it differently: If I fly into a headwind, will that affect the Angle of Attack the same way that flying in a crosswind affects the Angle of Sideslip?

 

 

The simplest answer I could find:)

 

Eli Cohen, BS from MIT, MS from Purdue University in aerospace eng. Aircraft Designer.

 

"Yaw is typically just the heading of the aircraft on the compass.

 

Sideslip is the relative angle between the freestream flow and the aircraft yaw vector (to simplify it somewhat). Sideslip is the analog of angle of attack, but for yaw instead of pitch."

 

https://www.quora.com/Aerospace-Engineers-What-is-the-difference-between-Yaw-angle-and-Side-slip-angle

 

To put it differently: If I fly into a headwind, will that affect the Angle of Attack the same way that flying in a crosswind affects the Angle of Sideslip?

 

Yes.:)

 

.

Edited June 29, 2017 by David OC

[Yurgon]

I dont like this word weathervaning or weathercocking as it relates to a fix pivot point, an aircrafts cg moves. More like a pendulum affect. Think of the cog when a plane loads fuel and passengers, they make sure the COG is within limits of the design. [...]

 

The ability of the aircaft's CG (the entire aircraft, actually) to move freely seems to have a pretty big influence on this whole discussion.

 

While we're in the phase of randomly throwing quotes that prove our respective points, take this! :music_whistling: :D

 

Weathervaning or weathercocking [1] is a phenomenon experienced by fixed wing aircraft on the ground and rotorcraft on the ground and when hovering.

 

Aircraft on the ground have a natural pivoting point on an axis through the main landing gear contact points [disregarding the effects of toe in/toe out of the main gear]. As most of the side area of an aircraft will typically be behind this pivoting point, any crosswind will create a yawing moment tending to turn the nose of the aircraft into the wind.[2][3]

 

It is not to be confused with directional stability, as experienced by aircraft in flight.[4]

 

I like how it repeatedly says "on the ground", and I'm particularly fond of "is not to be confused with".

 

The really funny thing is, on June 26 the article was edited to include exactly that NASA reference for weathervaning rockets that came up here around a day before. I guess if anyone was editing Wikipedia to prove their point, they did a pretty bad job of expanding the weathervane effect to mean "is similar to directional stability". :lol:

 

Edit:

 

The simplest answer I could find:)

 

Eli Cohen, BS from MIT, MS from Purdue University in aerospace eng. Aircraft Designer.

 

Seems to be a very smart guy!

 

I also agree with everything he said (as far as the above quote is concerned, obviously).

 

I just don't think it has anything to do with aircraft weathervaning while they're in flight. :smartass:

Edited June 29, 2017 by Yurgon

[David OC]

 

I just don't think it has anything to do with aircraft weathervaning while they're in flight. :smartass:

 

It's all the same thing

 

Weathervaning around COG, to the oncoming mediums flow, air in this case.

 

Directional stability around COG, to the oncoming mediums flow, air in this case.

 

Sideslip angle around COG, to the oncoming medium flow, air in this case.

 

It all comes back to...

 

"Sideslip is the relative angle between the freestream flow and the aircraft yaw vector (to simplify it somewhat). Sideslip is the analog of angle of attack, but for yaw instead of pitch."

 

Angle of Sideslip (AOS) is your "Weathervaning affect" into the wind flow direction.:)

 

Take the A10 up in a 30 knot @ 30 degree crosswind and watch it fight the AOS, the centerline of the aircraft is not aligned with flight path. There is an offset or "Angle of Sideslip" or Weathervaning because of the unsymmetrical flow at low speeds, dense air, design etc.

 

EDIT

 

It's all just in the wording here, "Weathervaning" I dont like this word once in flight.

 

All you need to do really is look up AOA here, except now looking top down.

 

So.

 

AOA is the angle between a reference line on a body (often the chord line of an airfoil) and the vector representing the relative motion between the body and the fluid through which it is moving.[1] Angle of attack is the angle between the body's reference line and the oncoming flow.

Same for AOS just top down right.

 

It's just not really called weathervaning / weathercocking, I relate this to ground work only.

Edited June 29, 2017 by David OC

[WindyTX]

And in the Air in balanced flight there is no side slip. Which brings us back to the fact that in the Air there is no weathervaning.

 

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[David OC]

And in the Air in balanced flight there is no side slip. Which brings us back to the fact that in the Air there is no weathervaning.

 

Sent from my SM-G955U using Tapatalk

 

There is always a side slip and angle of sideslip, unless flying perfectly straight on or away from the airflow direction, which rarely happens.

 

AOA, AOS

 

relative motion between the body and the fluid through which it is moving

 

angle between the body's reference line and the oncoming flow

 

Agian this will all change (More or less AOS,AOA) per aircraft with speed, COG, air density and aircraft design.

 

We can compare the A10, to the L-39 etc. I will video to show the AOS from top down on the A10 later tonight.

 

See the big (B) in the pic below.

 

 

 

.

Edited June 29, 2017 by David OC

[WindyTX]

There is always a side slip and angle of sideslip, unless flying perfectly straight on or away from the airflow direction, which rarely happens.

 

???

 

Pilots fly balanced with negligble sideslip. And sideslip depends on control dection and is completely independant of the wind the Aircraft is flying in.

 

At the top of climb we actually have a procedure to ensure the Aircaraft is flying balanced with no sideslip. Sideslip causes drag which costs fuel which cost money.

 

If we flew around with crossed controls to induce sideslip your airline ticket price would go up.

 

Your diagrams while perfectly correct are irelavant to the question, sideslip is never caused by the wind it is caused by unbalanced control forces and is trimmed out by the pilot. ( Again ignoring the Take off case)

 

I am on holiday right now but if you want I will take a photo of the controls Eicas page at top of climb and show you the before and after trim picture.

 

To imply that the wind in the air has an effect on sideslip is wrong , I am sorry but you are miss understanding the pictures you posted.

Edited June 29, 2017 by WindyTX
Spelling

[David OC]

Are you saying you can cancel out AOS with rudder trim, this is what this debate was all about right. :)

 

Canceling out AOS using rudder trim (Done) Will show this without trim for others to see tho in video. Pic above shows this.

 

What we sort of mixed up was Vectors and the wind triangle

Trim for AOS and set direction of air track to endup on the ground where you want to be right. The airflow makes it not very efficient or very efficient sometimes right.

 

So you are side sliping across the ground;)

 

Wind Correction Angle (WCA)

 

For example:

(a) track = 045° w/v = 075/20 kn: relative angle = 30 = 30/60 × 20 = 10 kn crosswind.

Edited June 29, 2017 by David OC

[WindyTX]

Ok you have missed the whole point of the conversation. Wind drift and sideslip are 2 completely different things. Someone was claiming that the wind caused yaw during flight.depending on what direction the wind you are flying in is coming from. It causes drift but no yaw.

 

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[WindyTX]

In fact you may have showed the actual misunderstanding.

 

Wind causes drift.

 

Unbalanced control surfaces can cause sideslip.

 

The 2 are totally independant when the Aircraft is airborne

 

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[David OC]

Ok you have missed the whole point of the conversation. Wind drift and sideslip are 2 completely different things. Someone was claiming that the wind caused yaw during flight.depending on what direction the wind you are flying in is coming from. It causes drift but no yaw.

 

Sent from my SM-G955U using Tapatalk

 

Only once more, then I'm out:)

 

Sideslip angle

 

The sideslip angle, also called angle of sideslip (AOS, AoS, β {\displaystyle \beta } , Greek letter beta), is a term used in fluid dynamics and aerodynamics and aviation. It relates to the rotation of the aircraft centerline from the relative wind. In flight dynamics it is given the shorthand notation β {\displaystyle \beta } (beta) and is usually assigned to be "positive" when the relative wind is coming from the right of the nose of the airplane. The sideslip angle β {\displaystyle \beta } is essentially the directional angle of attack of the airplane. It is the primary parameter in directional stability considerations.[7]

 

In vehicle dynamics, side slip angle is defined as the angle made by the velocity vector to longitudinal axis of the vehicle at the center of gravity in an instantaneous frame. As the lateral acceleration increases during cornering, the side slip angle decreases. Thus at very high speed turns and small turning radius, there is a high lateral acceleration and β {\displaystyle \beta } could be a negative value.

 

https://en.wikipedia.org/wiki/Slip_(aerodynamics)#Sideslip_angle

 

And

 

Eli Cohen, BS from MIT, MS from Purdue University in aerospace eng. Aircraft Designer.

 

"Yaw is typically just the heading of the aircraft on the compass.

 

Sideslip is the relative angle between the freestream flow and the aircraft yaw vector

(to simplify it somewhat). Sideslip is the analog of angle of attack, but for yaw instead of pitch."

 

https://www.quora.com/Aerospace-Engineers-What-is-the-difference-between-Yaw-angle-and-Side-slip-angle

 

 

(AOA or AOS) is the angle between a reference line on a body (often the chord line of an airfoil) and the vector representing the relative motion between the body and the fluid through which it is moving.[1] Angle of attack is the angle between the body's reference line and the oncoming flow.

 

Agian this will all change (More or less AOS,AOA) per aircraft with speed, COG, air density and aircraft design.

 

Are you saying Eli Cohen an aerospace eng. Aircraft Designer is lying here? and there is no AOS and the Wiki Sideslip angle page is wrong too?

 

Or there is no yaw seen, because you trimmed this out when needed, in relation to the airflow at the time, angle speed, you and the air speed, and the air density.

 

.

Edited June 29, 2017 by David OC

[BigDuke6ixx]

Only once more, then I'm out:)

 

Sideslip angle

 

The sideslip angle, also called angle of sideslip (AOS, AoS, β {\displaystyle \beta } , Greek letter beta), is a term used in fluid dynamics and aerodynamics and aviation. It relates to the rotation of the aircraft centerline from the relative wind. In flight dynamics it is given the shorthand notation β {\displaystyle \beta } (beta) and is usually assigned to be "positive" when the relative wind is coming from the right of the nose of the airplane. The sideslip angle β {\displaystyle \beta } is essentially the directional angle of attack of the airplane. It is the primary parameter in directional stability considerations.[7]

 

In vehicle dynamics, side slip angle is defined as the angle made by the velocity vector to longitudinal axis of the vehicle at the center of gravity in an instantaneous frame. As the lateral acceleration increases during cornering, the side slip angle decreases. Thus at very high speed turns and small turning radius, there is a high lateral acceleration and β {\displaystyle \beta } could be a negative value.

 

https://en.wikipedia.org/wiki/Slip_(aerodynamics)#Sideslip_angle

 

And

 

Eli Cohen, BS from MIT, MS from Purdue University in aerospace eng. Aircraft Designer.

 

"Yaw is typically just the heading of the aircraft on the compass.

 

Sideslip is the relative angle between the freestream flow and the aircraft yaw vector

(to simplify it somewhat). Sideslip is the analog of angle of attack, but for yaw instead of pitch."

 

https://www.quora.com/Aerospace-Engineers-What-is-the-difference-between-Yaw-angle-and-Side-slip-angle

 

 

(AOA or AOS) is the angle between a reference line on a body (often the chord line of an airfoil) and the vector representing the relative motion between the body and the fluid through which it is moving.[1] Angle of attack is the angle between the body's reference line and the oncoming flow.

 

Agian this will all change (More or less AOS,AOA) per aircraft with speed, COG, air density and aircraft design.

 

Are you saying Eli Cohen an aerospace eng. Aircraft Designer is lying here? and there is no AOS and the Wiki Sideslip angle page is wrong too?

 

Or there is no yaw seen, because you trimmed this out when needed, in relation to the airflow at the time, angle speed, you and the air speed, and the air density.

 

.

 

Why are you lecturing windy? He is 777 pilot with 10,000hrs. Please show some respect to pro pilots and the laws of physics. I bet you $1,000US that if you took your conclusions to an instructor at any flight school they would 'just laugh'. Want to put your money where your keyboard is?

Edited June 29, 2017 by BigDuke6ixx

[David OC]

Not lecturing anyone, having a discussion, if you can change my mind I will.;)

 

I'm only doing research here BigDuke6ixx and quoting aerospace engineers and Wiki pages.

 

Are you saying all these references are no good too? There is no AOS same as AOA?

 

AOS has no effect on yaw in flight?

 

If you have references, I would like to see them, I do like this aero stuff. :)

 

 

.

Edited June 29, 2017 by David OC

[BigDuke6ixx]

Not lecturing anyone, having a discussion, if you can change my mind I will.;)

 

I'm only doing research here BigDuke6ixx and quoting aerospace engineers and Wiki pages.

 

Are you saying all these references are no good too? There is no AOS same as AOA?

 

AOS has no effect on yaw in flight?

 

If you have references, I would like to see them, I do like this aero stuff. :)

 

 

.

 

What does the wind do?

 

The crosswind does not push harder against the tail. Ask any instructor. And I don't see why the word of a 777 driver isn't good enough for you. Anyway, you email a flying school and ask them.

[David OC]

Let's re cap the start of this debate / discussion.

 

Yep, correct. In the air the effect is called "directional stability", it does the same as weathervaning on the ground, just not so pronounced.

Anyway I wanted to help the guy by pointing to the likely cause of his issue. The wind and the aircraft's tendency to put the nose into the wind.

 

Sorry to push the point, but there is zero tendency for an aircraft in flight to point its nose into wind. The only wind the aircraft sees is the relative wind (airspeed over the wings).

 

I was thing like this too BigDuke6ixx, not now after reading about angle of sideslip (AOS), directional stability, etc.

 

 

 

.

Edited June 29, 2017 by David OC

[BigDuke6ixx]

Are you saying you can cancel out AOS with rudder trim, this is what this debate was all about right. :)

 

If he put in some rudder trim he would also have to put in opposite ailerons to stay wings level. No one flies like that accept while landing etc. There is no need to use these control corrections because there is nothing to correct against. Go email a flying school about this and they will put you right.

[shagrat]

I can not say for sure what the cause of this is, but you are not flying level, you are constantly banked a bit to one or the other side. But it almost seems as if this is happening in some sort of oscillation, perhaps induced at the very start.

 

Imo this flight does not prove anything as the aircraft's behaviour is too random...

Mind that I never touched the controls.

 

You can rest assured, the roll oscillation can be neglected.

 

Just monitor the HDG and TRK carefully.

 

That was why I said 3-4 degrees to the left, as the oscillation causes a variation in the heading of roughly 0.5-0.7 degrees, leaving 3+ degrees of nose turning into the wind compared to where the plane is flying from about 3-4 sec into the flight, while the plane still flies a 359.8 to 0.2 ground TRK.

 

I still wait for an explanation for that.

[shagrat]

Yes, that is all undisputed.

 

 

 

Thanks for the track! I guess that answers how aircraft are spawned in relation to the wind. :smartass:

 

After an initial bump, I see the aircraft oscillating in the roll axis at a rate of maybe two oscillations per minute, with a net roll rather to the right.

 

 

 

Yeah, the TacView plays for me pretty much like the track did (except that the headings are off because of magnetic variation, to be expected). I see the aircraft oscillating and slowly heading towards 011° true north at the end of the 3 minute recording.

 

I'm completely clueless as to how this is supposed to prove your point.

 

 

Now explain to me, if the laws of physics command weathervaning into the wind, seeing as the vertical stabilizers are more affected by the wind than the nose... why does the aircraft actually turn away from it?

I told everyone were to look (TRK and HDG) and the relevant timeframe 3-4 seconds in flight to about 1 min.

 

I also explained why it is different, than what you expected (mid-air spawn which is impossible IRL).

 

What it proves is, that the laws of physics according mass, inertia and action vs. reaction work in the air as well.

[Frederf]

If he put in some rudder trim he would also have to put in opposite ailerons to stay wings level. No one flies like that accept while landing etc. There is no need to use these control corrections because there is nothing to correct against. Go email a flying school about this and they will put you right.

 

I did notice he was in a cross-control situation by looking at the controls indicator. That sort of "forward slip" flight is not normal.

The crosswind does not push harder against the tail.

 

Sorry to push the point, but there is zero tendency for an aircraft in flight to point its nose into wind. The only wind the aircraft sees is the relative wind (airspeed over the wings).

 

Certainly the offset of the relative wind is entirely due to the crosswind. Without the crosswind the relative wind would be directly opposite the motion. Since an airplane will have a yaw moment into the relative wind and the direction of the relative wind is determined by the crosswind isn't it correct to say that the airplane has a tendency to point its nose toward the source of wind?

[David OC]

1) This is the aircraft trimmed state, the ball was still in the center.

 

10,000 feet, 20 Knot wind @ 45 degrees, video coming.

 

3 degrees of AOS

2.5 degrees AOA

 

 

 

This is the best way to think about all this from an aerospace engineer.

 

Eli Cohen, BS from MIT, MS from Purdue University in aerospace engineer. Aircraft Designer.

 

"Yaw is typically just the heading of the aircraft on the compass.

 

Sideslip is the "relative angle" between the freestream flow and the aircraft "yaw vector"

(to simplify it somewhat). Sideslip is the analog of angle of attack, but for yaw instead of pitch."

 

It is the same as AOA, called AOS, angle of sideslip

 

 

 

.

Edited June 29, 2017 by David OC

[Donnerblase]

I told everyone were to look (TRK and HDG) and the relevant timeframe 3-4 seconds in flight to about 1 min.

 

I also explained why it is different, than what you expected (mid-air spawn which is impossible IRL).

 

What it proves is, that the laws of physics according mass, inertia and action vs. reaction work in the air as well.

 

Nobody claimed otherwise. Yet you must not mix things up:

 

- what we are seeing here is the aircraft's reaction to sudden change of wind forces (so from nothing to cruise in an instant). The result can be seen as seemingly random oscillation (from the diagram I saw posted earlier it looked like dynamic modes in action, see also HERE)

 

- once a steady state is reached, the aircraft MIGHT have a sideslip (dependent on external storages and induced drag, for example), but that does not mean it will change direction, as it gets trimmed by the pilot.

 

- we have to understand that in steady flight (keep that in mind), the observer (the plane) is moving only relative to the medium surrounding it, and if that medium moves at a steady rate in any direction, no additional force is applied.

 

In essence, a sideslip angle might be present, but as soon as we are airborne, it will not come from the wind, as the aircraft basically becomes part of the wind, as seen from the ground. What is important is making the distinction between what medium the aircraft is acting upon. I got this wrong before when I thought about sideslip angle induced by wind for example after takeoff or in gusts.

[BigDuke6ixx]

I did notice he was in a cross-control situation by looking at the controls indicator. That sort of "forward slip" flight is not normal.

 

 

Certainly the offset of the relative wind is entirely due to the crosswind. Without the crosswind the relative wind would be directly opposite the motion. Since an airplane will have a yaw moment into the relative wind and the direction of the relative wind is determined by the crosswind isn't it correct to say that the airplane has a tendency to point its nose toward the source of wind?

 

The relative wind is always opposite to the direction of flight. A crosswind does not change the relationship between the direction of flight and the relative wind. The wind correction angle is added to take account of drift in relation to the ground caused by the crosswind. A crosswind does not push harder against the tail and no cross control inputs are required to counter this. This is an issue that only exists in some people's minds.

Edited June 29, 2017 by BigDuke6ixx

[BigDuke6ixx]

Nobody claimed otherwise. Yet you must not mix things up:

 

- what we are seeing here is the aircraft's reaction to sudden change of wind forces (so from nothing to cruise in an instant). The result can be seen as seemingly random oscillation (from the diagram I saw posted earlier it looked like dynamic modes in action, see also HERE)

 

- once a steady state is reached, the aircraft MIGHT have a sideslip (dependent on external storages and induced drag, for example), but that does not mean it will change direction, as it gets trimmed by the pilot.

 

- we have to understand that in steady flight (keep that in mind), the observer (the plane) is moving only relative to the medium surrounding it, and if that medium moves at a steady rate in any direction, no additional force is applied.

 

In essence, a sideslip angle might be present, but as soon as we are airborne, it will not come from the wind, as the aircraft basically becomes part of the wind, as seen from the ground. What is important is making the distinction between what medium the aircraft is acting upon. I got this wrong before when I thought about sideslip angle induced by wind for example after takeoff or in gusts.

 

You got it. And fair play for being man enough to hold your hand up.

[shagrat]

Nobody claimed otherwise. Yet you must not mix things up:

 

- what we are seeing here is the aircraft's reaction to sudden change of wind forces (so from nothing to cruise in an instant). The result can be seen as seemingly random oscillation (from the diagram I saw posted earlier it looked like dynamic modes in action, see also HERE)

 

- once a steady state is reached, the aircraft MIGHT have a sideslip (dependent on external storages and induced drag, for example), but that does not mean it will change direction, as it gets trimmed by the pilot.

 

- we have to understand that in steady flight (keep that in mind), the observer (the plane) is moving only relative to the medium surrounding it, and if that medium moves at a steady rate in any direction, no additional force is applied.

 

In essence, a sideslip angle might be present, but as soon as we are airborne, it will not come from the wind, as the aircraft basically becomes part of the wind, as seen from the ground. What is important is making the distinction between what medium the aircraft is acting upon. I got this wrong before when I thought about sideslip angle induced by wind for example after takeoff or in gusts.

I am not talking about sideslip (that is someone else). I am not talking about a trimmed state, either.

 

The plane is clean (no loadout other than gun ammo and at max fuel). I do NOT control, or trim the plane the WHOLE track.

 

What the track shows is the fact that while the aircraft is settled after 3 seconds its ground track (TRK) is more or less north (with a little oscillation of 0.4°).

While it follows this ground track for quite a while over 40 seconds minimum it yaws the nose (HDG) left into the wind by at least 3° (actually 3-4° but the oscillation may swing the nose by 0.5-0.7° so lets subtract 1° for good measure).

 

Only after one minute of flight the plane starts really drifting and subsequently rolling right, where I am sure the exponential increase is related to the roll, so lets ignore the later part of the track.

 

According to the discussion here the plane should not(!) turn its nose, while in the air, as it is moving with the relative wind (thrust vector and crosswind combined).

 

So what is pushing the nose to the left by 3° ?

 

EDIT Keep in mind that the plane starts mid-air, with its inertia not overcome by the crosswind, yet. Thus it isn't travelling with the airmass, when the track begins!

Edited June 29, 2017 by shagrat

[BigDuke6ixx]

I am not talking about sideslip (that is someone else). I am not talking about a trimmed state, either.

 

The plane is clean (no loadout other than gun ammo and at max fuel). I do NOT control, or trim the plane the WHOLE track.

 

What the track shows is the fact that while the aircraft is settled after 3 seconds its ground track (TRK) is more or less north (with a little oscillation of 0.4°).

While it follows this ground track for quite a while over 40 seconds minimum it yaws the nose (HDG) left into the wind by at least 3° (actually 3-4° but the oscillation may swing the nose by 0.5-0.7° so lets subtract 1° for good measure).

 

Only after one minute of flight the plane starts really drifting and subsequently rolling right, where I am sure the exponential increase is related to the roll, so lets ignore the later part of the track.

 

According to the discussion here the plane should not(!) turn its nose, while in the air, as it is moving with the relative wind (thrust vector and crosswind combined).

 

So what is pushing the nose to the left by 3° ?

 

EDIT Keep in mind that the plane starts mid-air, with its inertia not overcome by the crosswind, yet. Thus it isn't travelling with the airmass, when the track begins!

 

 

The is no yaw to the relative wind once direction stability has been reached.