Does a steady tailwind “push” an airplane?

Discussion in 'Flight Following' started by FastEddieB, Dec 3, 2017.

  1. FastEddieB

    FastEddieB Final Approach

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    Concerning a recent thread, “Tailwind question”, I read it too quickly and misunderstood what was being asked. My bad.

    But in my response, I mentioned that the phase “<wind> blowing from behind” alerted me to a possible misunderstanding of the effect of wind on an airplane in flight, one I’ve seen before. But my answer prompted a disagreement with jimhorner over whether an airplane in flight is “pushed” by a steady tailwind

    Oldtimers are certainly sick of it by now, but a while back I posted a compilation of what I called “Stick and Rudder Moments”. https://www.pilotsofamerica.com/community/threads/stick-and-rudder-moments-redux.79699/ I mention that now for the benefit of newbies, and to point out why I think the mental image of wind “pushing” a plane in flight can lead to misunderstandings.

    Most relevant was the thought that engine cooling can be compromised when flying with a tailwind:

    "5) I’ve heard it said cowl flaps are especially useful when flying downwind, when cooling would otherwise be compromised by the tailwind. More recently, a forum poster here thought winds affected cooling in a Seneca, possibly due to cowling shape. Then he doubled down with: "On my 206 I've notice a 5-10 degree change in CHT based on a strong wind. I am not a fluid dynamics expert, so I have no idea exactly why. Perhaps a slight pressure change in the cowl as I mentioned, or slight turbulence in the relative wind, IDK.""

    Another was a pilot’s assertion that his Flight Design CTLSi seemed to run out of nose down trim more quickly when flying into a headwind.

    Let me first stipulate the obvious - of course a tailwind results in a higher groundspeed. The question is whether the word “push” is the best descriptor for how the "wind" makes that happens. So, basically a semantic debate.

    My assertion remains that once in the air, barring gusts and shear, a plane “feels” no wind. The affects of wind - in this case the additive effect of the tailwind on groundspeed - is simply because the air mass in which the plane is moving is itself moving.

    So, in my mental construct there is no “pushing” going on. There is no wind “pushing against” the plane. To a pilot, a plane doing 50kts with a 50kt tailwind will have identical flight instrument readings as the same plane doing 50kts into a 50kt headwind. Under the hood, he or she will be unable to tell which is the headwind and which is the tailwind situation - barring instruments utilizing ground or satellite references, of course. Of course, an experiment could be set up using pressure transducers on the nose, tail and sides of a plane and again, the movement of the airmass the plane is in - the “wind” - will have zero effect on those readings.

    I want to thank jimhorner for his thoughtful response - #29 in the “Tailwind question” thread. He clearly outlines that the disagreement may be based on frames of reference: “Its <the wind’s> force most definitely IS pushing your plane, just not relative to the air. It is, however, providing a force which pushes you relative to the ground, and that force is real.”

    (italics mine)

    There are many frames of reference we could discuss. But point is that as long as we’re airmen discussing airplanes, what we should concern ourselves with is flight through the air and language that best describes said flight. I still feel references to wind “pushing” can and does lead to flawed or inappropriate mental models that can lead to the “Stick and Rudder Moments” that many pilots still fall victim to.
     
    Last edited: Dec 3, 2017
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  2. SkyHog

    SkyHog Touchdown! Greaser!

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    I think what you’re trying to say is that the concept of pushing brings to mind a 2nd law emotion of imagining that and equal and opposite push is occurring on the other side of the plane, when in reality, the entire airmass, plane included, is being pushed and the 2nd law reaction is occurring on the opposite side of the air mass instead.
     
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  3. N659HB

    N659HB Pattern Altitude

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    I definitely feel a push when the air is moving vertically.
     
  4. Velocity173

    Velocity173 Final Approach

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    What if you're hovering in a helicopter at 0 kts with a 50 kt tailwind? Being pushed or just flowing with the air mass?
     
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  5. Cooter

    Cooter Pattern Altitude

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    I didn’t read the other thread but Jim Horner seems to have expressed my thoughts. Being pushed by the winds is most often used to describe the effects when referencing the ground, or something attached to the ground. There may be some misconceptions associated with it but none that sound overly harmful. There are real effects and I think your position could also lead to misperceptions. So it really just comes down to understanding, not the language.

    At pattern altitude, the wind changes a lot more than when up at cruise and the effects can be seen and felt. It is more helpful to teach those effects in terms that are most natural to use. If you turn to final and experience a tailwind, being pushed gets the right point across. Or if you are setting you’re abeam distance and don’t account for an overshooting wind, if sure feels like your being pushed when the runway goes zipping past you.
    It seems like pedantry to refuse to call it what it is, simply because the language doesn’t hold true throughout all realms.
     
    Last edited: Dec 3, 2017
  6. Ravioli

    Ravioli En-Route

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    "Push" is an incorrect description. The IAS and TAS are relative to the fluid through which the craft is moving. The GS is relative to movement over, well the ground.

    GS will increase/decrease because of the fluids motion but IAS and TAS are not impacted.

    If you're in a boat the fluid is water and we describe the phenomenon as current. If you're a in a plane the fluid is air and we describe it as wind.

    [Edit] if "push" were real, then a headwind would be a "pull" since the implied point of reference on an airplane is the tail? I hope that doesn't become a thing.
     
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  7. AKBill

    AKBill Cleared for Takeoff

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    Interesting thought about being "pushed" or acted upon. I may be out to lunch on but I'll take a crack at it.

    For example take a boat with only a rudder in a fast flowing river. The boat is buoyant and is riding in a fluid and being moved with the water mass. A plane with an engine that is traveling fast enough for the wings to create lift would also be "buoyant" in a mass of air. Is the plane being carried in the mass of air as a boat is being carried in a mass of water?
     
  8. Cooter

    Cooter Pattern Altitude

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    If it’s a Zepplin, it is. ;)
    I’m sure riverboat captains don’t mind using the word “pushed” to describe the effects of the current.
     
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  9. Ravioli

    Ravioli En-Route

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    I'm not saying that the expression isn't used. Just that it is inaccurate.
     
  10. Piperonca

    Piperonca Pre-Flight

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    Among other things you're tap dancing like a madman on the pedals trying to keep the nose straight whilst placidly being stationary (not flowing or pushed) with respect to that strange air mass. Your bucking bird is headed downrange at 50 kt with respect to the ground.

    Odd things do happen when you're hovering with a really strong tailwind, and a gust picks up the stabilator and wants to pitch the nose down. Of course that is a real air mass, not the strange one.
     
  11. FastEddieB

    FastEddieB Final Approach

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    Sure. Changes in wind is not what I’m trying to discuss. Quick changes in wind direction or velocity, in the form of gusts and shear, can clearly be felt.

    Words matter. Keep saying to a student that a plane is being pushed can reinforce misconceptions.

    Lord knows I’ve said “push” when it was inappropriate. Hardly the Crime of the Century. But I really try to substitute the word “drift” to help the student correctly build his or her mental model. Rather than say, “The wind is pushing us off course”, I will try to say “The wind is drifting us off course”.
     
  12. FastEddieB

    FastEddieB Final Approach

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    Pure speculation, but I’ll speculate they’re more likely to deal in terms of drift.
     
  13. write-stuff

    write-stuff En-Route

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    The aircraft would be carried along with the moving airmass. It would appear to the aircraft that the air was not moving. So, no push.
     
  14. Cooter

    Cooter Pattern Altitude

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    Ok, I don’t want to get in the weeds here, but if you rotate into a crosswind, why does the aircraft want to “drift”? Because of increased dydamic pressure on one side of the aircraft. Increased pressure is pushing in my understanding. If the air mass is moving you away from where you want to be, I see no problem with saying it’s pushing you. Purposefully avoiding that word so that you can more easily explain the aerodynamics of it seems excessive.
     
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  15. Cluemeister

    Cluemeister Pre-takeoff checklist

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    15 posts in and nobody's mentioned the treadmill.
     
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  16. FastEddieB

    FastEddieB Final Approach

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    I think that’s exactly the type of conflation that leads to confusion.

    Of course a plane taking off will need to stabilize with the airmass. And of course this brief acceleration is caused by differential air pressure. And I think that acceleration could be properly called a “push”.

    But once established in the air mass, the “pushing” stops, and the time frame for that happening is very, very brief.
     
  17. FastEddieB

    FastEddieB Final Approach

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    Or Coriolis Effect!
     
  18. mscard88

    mscard88 Touchdown! Greaser!

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    Cardboard box lying on the ground. Wind is calm. Box isn't moving. Wind picks up, box moves to neighbors yard. What happened here? Did the wind cause the box to drift or did the wind push the box? I dunno, as both terms (push, drift) are so intertwined as to mean the same thing?

    interesting discussion, but I've had 3 cups of coffee and I feel a push coming on.
     
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  19. Lindberg

    Lindberg Pattern Altitude

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    Clearly the wind "carried" the box.
     
  20. Clark1961

    Clark1961 Touchdown! Greaser!

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    Or Eötvös
     
  21. Ryanb

    Ryanb Final Approach PoA Supporter

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    Yeah I agree. Although the explanation that Eddie teaches agrees with my beliefs, the terms (push, drift,carry.,etc) are very similar and almost synonymous. As long as the student understands how wind affects an airplane in flight and the theory behind it, that’s all that matters.
     
  22. X3 Skier

    X3 Skier En-Route

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    Are you sure it wasn’t the Amazon Driver who pooped in the yard that moved the box?

    Cheers
     
  23. Clark1961

    Clark1961 Touchdown! Greaser!

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    If wind can push an airplane in flight can I use a piece of string to push an airplane on the ramp? And then put toothpaste back in a tube? And can we work stuffing a wild bikini in here somewheres?
     
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  24. mscard88

    mscard88 Touchdown! Greaser!

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    Now you've opened another wind theory I think. If I were walking down the sidewalk in that area say, and the Amazon driver had pooped where she did, what would be causing me to increase the speed of my walk as I passed the pile of poop, and there were no wind. Why did my walking ground speed increase to the point of a trot?
     
  25. unsafervguy

    unsafervguy Cleared for Takeoff

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    It's a simple matter in physics and math know as frame of reference. An aircraft flies in the airmass. In a stable airmass there is no push or drift on the aircraft in reference to the airmass. Referencing it to the ground, there is drift or push. The aerodynamics affecting the aircraft doesn't care about the reference to the ground. However, as we are trying to navigate over a fixed reference in that frame of reference it appeares to have push or drift. By the way that also explanes why the plane will take off on the treadmill.

    Bob
     
  26. injb

    injb Pre-takeoff checklist

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    "Push" implies force. In fact someone explicitly said that the air exerts a force on the plane:

    I don't think this is correct. When the air first meets the plane, it pushes the plane, causing the plane to accelerate in that direction...until the plane is moving at the same speed as the air. At that point, the air isn't exerting a force on the plane any more. The plane continues to move in that direction simply because there's nothing to stop it.

    We know there can't be a force because forces make things accelerate, and if there was a force, there'd be acceleration - unless there was an equal force pushing from the opposite direction, like drag (which is why you need a constant force from your engine or from gravity to fly though air at a constant speed). But if there was such an opposite force, that would mean that the air is pushing equally hard from opposite directions, which makes no sense. That's my interpretation of it anyway.
     
  27. Tantalum

    Tantalum Pattern Altitude

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    You could float down a river in a canoe motionless relative to the water but 5kts over the ground.. planes are no different. My Cherokee will see about 120 TAS regardless of the wind. It's the groundspeed that changes

    When you fly into clouds, turbulence, or climb/descend through different as altitudes you'll feel sheer. But the idea that cowl flap are needed with a tailwind is absurd
     
  28. Clark1961

    Clark1961 Touchdown! Greaser!

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    If it is sheer can it be sheared?
     
  29. FormerHangie

    FormerHangie Pattern Altitude

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    Did someone say "push it?"

     
  30. cgrab

    cgrab Cleared for Takeoff

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    I explain this phenomenon to non-aviators this way: the plane is like a sailboat that uses it's engine instead of a sail. A boat in the gulf stream is moving north at 5-10 knots while the sails are trying to move it in whatever direction the crew wants. The two velocities add together to get the boat to its destination.

    BTW, In 1976 the boat I was crewing won a Bermuda to Newport race by making our first leg due west and when the wind died we past the rest of the fleet riding the current.
     
  31. Stewartb

    Stewartb En-Route

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    Park your plane with a good wind on the tail and a new Ferrari a couple of feet in front of it. That'll make a believer out if you.

    The notion of "push" is relative to a stationary point. Go land on a short strip with a 20mph tail wind. Explain why you ran off the end into the trees.
     
  32. FastEddieB

    FastEddieB Final Approach

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    Would anyone here explain it by saying the wind pushed them off the runway?

    I don’t think I’ve ever heard it expressed that way.
     
  33. Stewartb

    Stewartb En-Route

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    If you use the exact same power settings to land into and away from a 20mph wind? What is the variable? The prop didn't pull you faster on the downwind landing, right?

    We're ground based creatures. We pilot airplanes off of fixed surfaces and back onto fixed surfaces. Does the wind push on the plane? I'd say that's a correct statement. Not important in normal cruise but darn important when transitioning between ground and air.
     
  34. Clark1961

    Clark1961 Touchdown! Greaser!

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    What color is the Ferrari?
     
  35. FastEddieB

    FastEddieB Final Approach

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    The variable is the movement of the air mass you are flying in. Which in this case would mean a 40kt difference in groundspeed throughout the landing process. All with no aerodynamic “push” involved.

    But to discuss takeoff and landing is to get away from my original point, which was air pushing on a plane in flight. Bring the ground into the equation and of course thing change.
     
  36. mscard88

    mscard88 Touchdown! Greaser!

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    Only one color for a Ferrari IMO - RED.
     
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  37. injb

    injb Pre-takeoff checklist

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    It's not that it's not important in cruise - it's that the wind doesn't push on the plane during cruise. It does push on the plane when transitioning between ground and air because the plane is accelerating or decelerating relative to the air.
     
  38. Cooter

    Cooter Pattern Altitude

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    It seems to me that you are trying to use the truth about one category, and force it to hold true across all categories. I don’t hear the word “push” being used except to describe the effect in its relation to the ground. Or, in relation to a previous position.

    So some people think they need to open cowl flaps on downwind. They are ignorant and thankfully rare. But it should only take a few words to set them straight.
     
  39. Cooter

    Cooter Pattern Altitude

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    If I shove you out into traffic, can I argue that it wasn’t the shove, it was your momentum that caused you to get hit?;)
     
  40. N659HB

    N659HB Pattern Altitude

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    Well, how about a quartering wind? Does that not "push" the airplane? Flying sideways is fun!

    Let's stop with the push and just say it exerts a force which affects the airplane's path and/or speed relative to the ground.