Effect of wind on IAS

[Robinson67 5]

Hi guys,

We know the effect of the wind on GS, a HW component will decrease
the GS whereas a TW component will increase the GS.

As for the IAS, I understand that flying with a HW there´s more ram air flowing
into the tube, why is there no increase in IAS?

Another point, in a turbulence the IAS goes crazy by the effect of the wind or by something else?

Thanks

[scandinavian13 5,192]

 

 

As for the IAS, I understand that flying with a HW there´s more ram air flowing
into the tube, why is there no increase in IAS?

 

Your understanding is incorrect.

 

 

 

Another point, in a turbulence the IAS goes crazy by the effect of the wind or by something else?

 

Differences in relative wind speed due to the causes of the turbulence: rapid changes in the direction and speed of the air.

[downscc 1,327]

 

 

As for the IAS, I understand that flying with a HW there´s more ram air flowing
into the tube, why is there no increase in IAS?

 

What Kyle said.  In a steady wind, the aircraft is moving in the mass of air and has no knowledge of how that air is moving without such tools as INS or GPS etc. In rapidly varying wind, turbulence, the aircraft is subject to a whole different set of influences involving acceleration and inertia and is no longer a "steady state" system. A little high school physics would be helpful in explaining this.

[ALF1 15]

What weather engine are you using ?

 

Both Dan and Kyle of course are correct but you may be getting exagerated wind shears. In cruise, if you have a severe decrease in headwind the airspeed will decrease on N1 cruise and you will have the autothrottle adding power to keep FMC SPD

[Robinson67 5]

In reference to the turbulence explanation provided by Dan and Kyle is clear. Appreciated it.

 

Although the IAS is not affected by wind I still didn´t get it fully understood.

If a plane is on ground and facing a 30kt headwind, wouldn´t  the ASI indicate 30Kt?

 

ALF1 - I´m using ASN on P3D 2.3.  Thanks

[scandinavian13 5,192]

If a plane is on ground and facing a 30kt headwind, wouldn´t  the ASI indicate 30Kt?

 

In theory, yes, but on the ground your lack of motion is "motion" relative to the air moving by you. If your aircraft had no mass and you did not hold it in place, a 30 knot wind would push you backwards across the ground at 30 knots. By holding yourself in place (with the brakes and/or mass) on the ground, it's the same as if you were able to fly forward at 30 knots, while the air blew you backward at 30 knots (lack of forward motion).

 

Similarly, when you're flying, you're part of that moving air mass. Think as if you were flying flying a long tube of air. Within that air mass, you can only see that you're moving through that mass at the indicated air speed. Now, drag that tube backwards at a constant speed. You're still moving through that parcel of air at the same speed, but that parcel of air is moving backwards.

 

In the transition from completely still air to a stronger headwind, you would initially see increased airspeed (see turbulence and wind shear), but since air is fluid in its dynamic, it's rare that you'd see such an event (see the frequency of large sheer events). You'd "ease" into the new speed of the parcel of air so gradually that it wouldn't show up in the IAS.

[ALF1 15]

The pitot tube and airspeed indicator will not provide any readings for anything under about 45 kts headwind component while static on the ground or on a ground roll.

[Alpha Floor 237]

Although the IAS is not affected by wind I still didn´t get it fully understood.

 

Picture yourself inside of a train that's moving at a constant speed. Now imagine you stand up your seat and walk "forward" along the train to the bar. Then you walk "backwards" from the bar to your seat. How does the movement of the train affect your own speed with respect to the train? Would it make a difference if the train was standing still?

 

Now replace the passenger in the train by the aircraft, and replace the train by the mass of air around the aircraft. Walking forward inside of the train is similar to having a "tailwind". Walking backward is similar to having a "headwind". Clear now?

 

The aircraft only "cares" about its speed relative to the mass of air around it. It doesn't care about how it moves relative to the ground. Naturally the pilot does care about moving relative to the ground because he intends to navigate somewhere, but that's another topic.

 

BTW: For anyone curious, this is a great explanation that's found in the book of my signature. If you haven't done it already, you should read it!

 

 

If a plane is on ground and facing a 30kt headwind, wouldn´t  the ASI indicate 30Kt?

 

Indeed. And that's exactly what the ASI does if you're on the ground with the brakes on and into a 30 knot headwind.

 

 

Another point, in a turbulence the IAS goes crazy by the effect of the wind or by something else?

 

Using the analogy of the train. Turbulence or rapid wind changes in direction and intensity is like if the train you're riding started to accelerate, decelerate and or start hitting bumps on the rails.

 

The frame of reference (train) would stop being inertial (that is, non-accelerated) and would become a NON-INERTIAL (accelerated) frame of reference. This means that there will be inertial forces affecting you. The erratic accelerations (turbulence) of the air mass around the aircraft will be "sensed" as when you're riding in a train over lots of bumps.

[Bobsk8 12,489]

Picture yourself inside of a train that's moving at a constant speed. Now imagine you stand up your seat and walk "forward" along the train to the bar. Then you walk "backwards" from the bar to your seat. How does the movement of the train affect your own speed with respect to the train? Would it make a difference if the train was standing still?

 

Now replace the passenger in the train by the aircraft, and replace the train by the mass of air around the aircraft. Walking forward inside of the train is similar to having a "tailwind". Walking backward is similar to having a "headwind". Clear now?

 

The aircraft only "cares" about its speed relative to the mass of air around it. It doesn't care about how it moves relative to the ground. Naturally the pilot does care about moving relative to the ground because he intends to navigate somewhere, but that's another topic.

 

BTW: For anyone curious, this is a great explanation that's found in the book of my signature. If you haven't done it already, you should read it!

 

 

 

Indeed. And that's exactly what the ASI does if you're on the ground with the brakes on and into a 30 knot headwind.

 

 

 

Using the analogy of the train. Turbulence or rapid wind changes in direction and intensity is like if the train you're riding started to accelerate, decelerate and or start hitting bumps on the rails.

 

The frame of reference (train) would stop being inertial (that is, non-accelerated) and would become a NON-INERTIAL (accelerated) frame of reference. This means that there will be inertial forces affecting you. The erratic accelerations (turbulence) of the air mass around the aircraft will be "sensed" as when you're riding in a train over lots of bumps.

 

I wish every person that flies or is learning to fly  would read Stick and Rudder. It would save many lives... You can get it on Amazon. 

[Alpha Floor 237]

I wish every person that flies or is learning to fly  would read Stick and Rudder. It would save many lives... You can get it on Amazon. 

 

Agreed. I would make it mandatory reading for every PPL. In fact, if I were the examiner, I would check the student's copy of Stick & Rudder and evaluate its wear

 

Just joking of course, I'm remembering a teacher who would do that in September to check if the students had read the summer assignment book, haha

[Robinson67 5]

Thanks all for helping me out with this train (the place I was born the word 'train' in some contexts means 'problem')

I´ve just bought the book and reading it on page 90 'Motion is Relative', found the answer there and here too.

[Alpha Floor 237]

Thanks all for helping me out with this train (the place I was born the word 'train' in some contexts means 'problem')

I´ve just bought the book and reading it on page 90 'Motion is Relative', found the answer there and here too.

 

Glad to hear that! Enjoy reading that book, it's a very good one!

[scandinavian13 5,192]

I've always found Stick and Rudder to be more of a dissertation on how to repeat oneself, how to be verbose, how to use the most obscure metaphors using your 'kid brother' as a subject, and how to use those in combination to put people to sleep. Man...maybe that's where I get it from...

 

Seriously, the number of times I fell asleep while reading that book outclasses all books read while I was at university, and flying books usually keep me awake...yes, even the Gleim and Jepps.

 

It has some good perspective on flying, I'll give it that, but prepare yourself to struggle through it. The language used is so dated (granted, it was written written in 1944) that this is the voice I read it in:

 

https://www.youtube.com/watch?v=NHOGkZapbbU

[Bobsk8 12,489]

I've always found Stick and Rudder to be more of a dissertation on how to repeat oneself, how to be verbose, how to use the most obscure metaphors using your 'kid brother' as a subject, and how to use those in combination to put people to sleep. Man...maybe that's where I get it from...

 

Seriously, the number of times I fell asleep while reading that book outclasses all books read while I was at university, and flying books usually keep me awake...yes, even the Gleim and Jepps.

 

It has some good perspective on flying, I'll give it that, but prepare yourself to struggle through it. The language used is so dated (granted, it was written written in 1944) that this is the voice I read it in:

 

https://www.youtube.com/watch?v=NHOGkZapbbU

 

That is a shame you feel that way. I have known  some  career pilots for the US Air Force and Airlines as well as two CFII's  that disagree with your opinion. Oh well, different strokes for different folks as they say. 

[scandinavian13 5,192]

That is a shame you feel that way. I have known  some  career pilots for the US Air Force and Airlines as well as two CFII's  that disagree with your opinion. Oh well, different strokes for different folks as they say. 

 

What are you disagreeing with here? The fact that I called it boring, or the supposition that I'm calling it worthless?