FastEddieB
Touchdown! Greaser!
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Fast Eddie B
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.
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.
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