Sign in to follow this  
Robinson67

Effect of wind on IAS

Recommended Posts

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

Share this post


Link to post
Share on other sites
Help AVSIM continue to serve you!
Please donate today!

 

 


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.

Share this post


Link to post
Share on other sites

 

 


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.

Share this post


Link to post
Share on other sites

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

Share this post


Link to post
Share on other sites

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. :fool:

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

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

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. 

Share this post


Link to post
Share on other sites

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

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

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! ;)

Share this post


Link to post
Share on other sites

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

Share this post


Link to post
Share on other sites

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. 

Share this post


Link to post
Share on other sites

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?

Share this post


Link to post
Share on other sites

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

 

Both. The copy that I got as a present when I was studying for my Private Pilots license  back in the late 70's   was given to me by a B-52 instructor in the Air Force. The next time its was mentioned to me as a must read , which of course I already had twice, was by a Check Pilot for Delta Airlines prior to spending 5 hours with him in a CAE 767-400ER full motion sim at the Delta Training center in Atlanta. . I also had an aerobatic instructor pilot, Dave Holland, who also told me it was a must read. One of Dave's students was William Shatner. That was good enough for me.  :wink:

  • Upvote 1

Share this post


Link to post
Share on other sites

Both. The copy that I got as a present when I was studying for my Private Pilots license  back in the late 70's   was given to me by a B-52 instructor in the Air Force. The next time its was mentioned to me as a must read , which of course I already had twice, was by a Check Pilot for Delta Airlines prior to spending 5 hours with him in a CAE 767-400ER full motion sim at the Delta Training center in Atlanta. . I also had an aerobatic instructor pilot, Dave Holland, who also told me it was a must read. One of Dave's students was William Shatner. That was good enough for me.  :wink:

 

Thought so. Do note that I at no point called it worthless. In fact, I specifically stated that it has a good perspective on flying. The post simply called it boring. Anything else was incorrectly inferred.

Share this post


Link to post
Share on other sites

I didn't read stick & rudder either....

 

Give it a try then, it won't do you any harm :)

Share this post


Link to post
Share on other sites

The Flight Manual Series by Kershner were my go to books for commercial pilot study.  The basics are here: http://www.amazon.com/Student-Pilots-Flight-Manual-Certificate/dp/156027719X/ref=sr_1_11?ie=UTF8&qid=1461765511&sr=8-11&keywords=aviation+study+books

 

However, the Stick and Rudder is a classic from the 1940s when aviation was booming and everybody was going to have an airplane. An important contribution to aviation.

Share this post


Link to post
Share on other sites

Give it a try then, it won't do you any harm :)

No longer interested.  Over the years, I probably heard or read references to about every paragraph.  There are also a few items I wouldn't agree with........................such as the power/pitch debates.  Stick & Rudder was written when excessive climb power wasn't the norm.  I'm well known around here, for saying baloney to the pitch for speed & power for climb ----------- as being the the total fact of flight.  This is why the U.S. Air force, Navy, &  FAA have different views on the subject, these days.  Years ago, there were some good arguments on this forum, regarding pitch/power.  But then...........it's been to long in my mind, to quote the exact words in the book.

Share this post


Link to post
Share on other sites

such as the power/pitch debates

 

Yeah, there's opposing views regarding this debate within pilots.

 

I personally "revert" to thrust on speed and pitch on vertical speed during approach/landing, otherwise making corrections would take too much time, time you don't have when in final for instance.

 

But for the purpose of this thread Stick&Rudder fits in perfectly :)

Share this post


Link to post
Share on other sites

Kershner uses "performance = pitch + power" to avoid the chicken and egg argument over power/pitch. I guess I really liked his books, which include private, commercial, instrument and instructor levels.

Share this post


Link to post
Share on other sites

Kershner uses "performance = pitch + power" to avoid the chicken and egg argument over power/pitch. I guess I really liked his books, which include private, commercial, instrument and instructor levels.

 

Dan, thanks a lot for the reference and the Amazon link.

 

This reminds me a little of the "Bernoulli vs Newton" arguments when trying to explain Lift. The truth is, both are true in their own way!

Share this post


Link to post
Share on other sites

But for the purpose of this thread Stick&Rudder fits in perfectly :)

 

Absolutely!

 

But in this day and age of IFR flying and Controlled Airspace when you are given instruction to maintain a given heading, given speed and a given altitude  - if you are not relying on a sophisticated autopilot you will apply changes in  both power and pitch to comply. And depending on the phase of flight, the particular aircraft, and meteorological conditions you may be using both tabs and flaps to control pitch, such as during a level approach.

 

While wind direction does not affect IAS, it does affect lift!

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this