Does a steady tailwind “push” an airplane?

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

  1. injb

    injb Pre-Flight

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    Only if you correct for it. If you do nothing, you'll move along with the wind.

    But that's my whole point - when you're moving along with the wind, it doesn't exert a force on the plane! It only does that if there is relative movement between the plane and the wind. For example:

    * the plane is on the ground so it can't move with the wind - the wind exerts a force on the plane
    * the plane is in the air but the pilot turns into the wind to correct - the wind exerts a force on the plane

    In either of these cases, the plane can "feel" wind. But when you're not correcting for a crosswind, or when you have a tailwind, the plane cannot "feel" it. In other words, the air pressure is the same on the upwind and downwind sides of the plane.
     
  2. N659HB

    N659HB Pattern Altitude

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    When I plan a flight it is not in relation to the air I am flying in. It is in relation to the ground, where I am going. If my ground speed is faster than IAS, I'm getting a push. If my ground speed is slower, the wind is pushing against me, even though my IAS through the airmass is the same. Call it what you will. We navigate in reference to the ground.
     
  3. Clark1961

    Clark1961 Touchdown! Greaser!

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    We fly through the air.
     
  4. N659HB

    N659HB Pattern Altitude

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    That's a given. Suppose I was in a hot air balloon, not an airplane. How do I move if the wind is not pushing me?
     
  5. PaulS

    PaulS Final Approach

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    The way I was taught as an engineer and a pilot and the way I look at it, is that when you are flying, you're movement is relative to the airmass you are travelling in. You are part of the airmass you are in. In other words, if your true airspeed is 120 knots in a stationary airmass, (0 wind) then your groundspeed is 120 knots. If you are flying at 120 knots with a 20 knot tail wind, your gs is 140 knots. That airmass is moving in the same direction as you at 20 knots. Your airplane is moving relative to that airmass at 120 knots. The speeds add and your gps will say 140 knots. The key to understanding it in my opinion is to not think of it as wind in this case, but as the airmass, which you are in when you fly, moving relative to the ground. We feel this as wind on the ground.
     
  6. Stewartb

    Stewartb En-Route

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    Ground based references also are key to the downwind turn discussion. Most guys will say the airplane doesn't know the wind is blowing so there's no problem with a downwind turn. I call those guys theoretical pilots. In my world I may take off a 600' strip that has a big hill in front of it. Maneuvering distance is fixed. How I manage the takeoff largely depends on wind. What if there's a 90* crossing wind. I have a big hill in front of me and clear sky left and right. The wind is blowing 30mph from the left. Take off, the hill's close.... which direction are you going to turn? Into the wind or away? Why?
     
  7. injb

    injb Pre-Flight

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    Pushing - i.e. force - isn't necessary for movement. It's only necessary for acceleration. When the balloon is first exposed to the wind, the wind exerts a force on the balloon (it "pushes" the balloon) and the balloon accelerates until it's moving at the same speed as the air. At that point nothing is pushing the balloon. It keeps moving because there's nothing to stop it.
     
  8. mscard88

    mscard88 Touchdown! Greaser!

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    Did the plane tell you that? I thought only Dale Earnhardt could feel the wind. :)
     
  9. Clark1961

    Clark1961 Touchdown! Greaser!

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    Flatulance.

    (translation: the only appropriate response to absurdity is more absurdity)
     
  10. FastEddieB

    FastEddieB Final Approach

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    Even if you correct for it, you simply choose a new wind correction angle. The plane still flies along unpushed, with the new heading and path through the air compensating for the movement of the air mass to result in the desired ground path.



    Nope. You can turn into the wind or away from the wind and never have the wind push the plane in a way that can be felt. I defy anyone to do 360’s under the hood in a steady wind and to “feel” when the plane is turning into the wind and when away from the wind.

    The last part of that is right. But the same applies while correcting for a crosswind.
     
  11. N659HB

    N659HB Pattern Altitude

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    I really don't know much about physics, but I disagree. If the force changes, i.e. speed of the airmass decreases, the balloon will slow down, it will not continue at the same speed. If the airmass direction changes, so will the path of the balloon. Force = push, until equilibrium is obtained.
     
  12. N659HB

    N659HB Pattern Altitude

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    OK. So you're farting your way across the sky? :D

    Bet you'll go faster if you ignite it.
     
  13. Clark1961

    Clark1961 Touchdown! Greaser!

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    That's what jet pilots do.
     
  14. N659HB

    N659HB Pattern Altitude

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    Where's Eddie? He started this nonsense.
     
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  15. PaulS

    PaulS Final Approach

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    AKA crop dusting.
     
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  16. SkyDog58

    SkyDog58 Final Approach

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    I thought the same vacuum source that was sucking the air towards it thereby creating wind was also sucking the airplane towards it.
     
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  17. coloradobluesky

    coloradobluesky En-Route

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    Yes, but even a bigger effect is the air is moving at 1000 miles per hour at the equator because the earth is spinning that fast and the air is moving with the earth. So that negates any small wind effect :)
     
  18. FastEddieB

    FastEddieB Final Approach

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    This is precisely the key!

    In the balloon, once aloft things are always dead calm.

    No anemometer, no candle flame, nothing could tell you the direction of the wind without looking at the ground or using a GPS or equivalent.

    Barring gusts, there is no wind in a free balloon. It’s simply floating free in an air mass which is itself moving. Much like a plane in flight, the difference being solely that the plane has forward speed.
     
  19. mscard88

    mscard88 Touchdown! Greaser!

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    That's my thought too 'Dog. Sounds like we be knowing our shet!
     
  20. N659HB

    N659HB Pattern Altitude

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    It is still exerting a force against the balloon, is it not? The balloon is in equilibrium with the airmass. If the force lessens, the balloon slows down.
     
  21. mscard88

    mscard88 Touchdown! Greaser!

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  22. FastEddieB

    FastEddieB Final Approach

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    And the earth is moving around the sun at about 19 miles per second.

    And the solar system moves within the galaxy. And the galaxy itself moves.

    But since we’re airmen flying airplanes, the air mass we’re in is probably our best frame of reference!
     
  23. Clark1961

    Clark1961 Touchdown! Greaser!

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    Add an engine and propeller to the balloon. Now what force is the airmass exerting on the balloon?
     
  24. Cooter

    Cooter Pattern Altitude

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    I guess you don’t bother checking the winds before landing then.
     
  25. N659HB

    N659HB Pattern Altitude

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    My frame of reference is still located on the ground.
     
  26. Clark1961

    Clark1961 Touchdown! Greaser!

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    yabut the movers picked it up tuesday and won't deliver it until thursday next. HTH and HAND
     
  27. Rgbeard

    Rgbeard Pre-Flight

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    The flat-earth folks are happy to point out that with our errant spherical view of the planet, a trip from East to West would be much faster than it is, and a trip from West to East would be nearly impossible at sub-sonic speeds.

    Not my view. Just posting it here for entertainment.
     
  28. injb

    injb Pre-Flight

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    I think you're mistaken about this, but maybe I'm missing something. I think if you turn the plane to establish a crab angle to correct for crosswind, you are effectively flying into the wind. That means the wind is pushing back at you.

    Think about it like this: you take off heading north. There's a 5mph wind from the east. You do nothing to correct for it. Soon, you'll be moving north west. Mostly north, but your westward speed will be 5mph. The pressure on the east side of the plane is identical to the pressure on the west side - no pushing.

    Now repeat, but this time you turn the plane slightly to the east to maintain a perfectly northerly heading. You're still pointing mostly north, just a little to the east. At this point, air is pushing the plane from the east. The pressure is higher on the east side of the plane than it is on the west side. It's just not having the same effect as before because your engine is exerting an equal and opposite force.

    Another way - maybe a simpler way - of putting it is like this: we know the wind is moving to the west at 5mph. Therefore, if you're in the wind and you're not also moving west at 5mph for any reason, there must be relative movement between you and the air. Hence, the air is pushing at you.
     
  29. PaulS

    PaulS Final Approach

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    But until you are touching the ground your frame of motion is the air you are moving in.
     
  30. Cooter

    Cooter Pattern Altitude

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    Let me think about some of the times reference to the air mass in relation to the ground might come up.

    Which runway I’ll use
    which departure
    Taxi controll inputs
    Take-off roll inputs
    Departure tracking
    Radial intercept and tracking
    Fuel calculations
    Inbound and outbound heading for holds
    Timing for hold
    Descent point
    Lead radial
    Turn point for arc intercept
    VSI calculation for glide slope
    Landing rwy
    Abeam distance
    Turn point off downwind
    Descent rate to/on final
    Power setting on final
    Capturing centerline
    Control inputs on final
    Control inputs on roll out
    Control inputs on taxi

    Those are some things that come to mind. I think reference to the ground should have a place in the pilots mind.
     
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  31. PaulS

    PaulS Final Approach

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    Nope, if you are flying coordinated the wind isn't "pushing you" the "pressure" all sides is the same as if you are flying in still air. The only difference is the airmass is moving in a different direction than your airplane is pointing. So the motion of your airplane is the summation of the direction and velocity your airplane is moving in relative to its longitudinal axis (coordinated) and the direction the airmass is moving.
     
  32. PaulS

    PaulS Final Approach

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    Yep, very important to get where you are going.
     
  33. FastEddieB

    FastEddieB Final Approach

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    I’m certain you are incorrect on this. (Edited to add: ninja’d by PaulS)

    It seems reminiscent of the Stick And Rudder Moment where the demo pilot suggested the Cirrus autopilot was flying right wing low due to a right crosswind.

    I’m not being condescending, but you need to think about this some more*.

    An airplane flying with a wind correction angle is flying straight and level, ball in the center with equal pressure on both sides. It just so happens that it’s path through the moving air mass results in the desired ground path.


    *Have you read Stick and Rudder? I read it very early on - it was my first aviation read - and I think it really helped cement some fundamental basics as to how an airplane flies.
     
    Last edited: Dec 3, 2017
  34. injb

    injb Pre-Flight

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    Moving relative to what? I am saying that if the air is moving in a certain way relative to the ground and your plane is not, then the air is moving relative to your plane. If that is true then I can't see how the air would not be exerting a force on the plane.
     
  35. injb

    injb Pre-Flight

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    No worries, I don't take it as condescending at all. I'm happy to have the chance to learn something. I will think about it some more :)

    I have Stick and Rudder but haven't finished it yet.
     
  36. FastEddieB

    FastEddieB Final Approach

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    You think?

    Obviously, and no one suggested otherwise.

    My discussion was about how to verbalize the effects of the wind on an airplane in flight. Specifically whether the concept of the plane being “pushed” by the wind can be problematical.
     
  37. Clark1961

    Clark1961 Touchdown! Greaser!

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    Century autopilots in our old spam cans are ancient technology but at least they correctly explained the wing low resulted from a rudder trim condition. And yes the ball supported the Century manual explanation.
     
  38. FastEddieB

    FastEddieB Final Approach

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    Whew! Good on you. Stay with it and I can almost guarantee an AHA! moment coming!

    As a thought exercise, from under a hood do you think any of the flight instruments, or “feel”, could give you any hint as to the wind direction? Barring navigational instruments, of course.
     
  39. injb

    injb Pre-Flight

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    The attitude indicator? I have never flown with a really strong crosswind, but I presume that since you have to turn into the crosswind with the ailerons, there must be some bank angle?
     
  40. PaulS

    PaulS Final Approach

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    Eddie, I love this stuff, sorry for butting in, and it does hurt the brain to understand sometimes. My 2 cents, I think the concept of the plane being pushed is problematic in that it falsely gives the pilot the feeling that it is something else to deal with when it really isn't, at least when the wind is steady, once you are in it the plane behaves as it does in still air.

    To get from point a to point b you fly the plane in a coordinated fashion and point the nose in a the direction that gets you to your destination, the nose may not, in fact probably will not point in the direction you are moving because of the moving airmass. If you think about it, it's really the same situation when you line up on final, you do what's necessary to travel in the required direction. You can make the nose point in the direction you want to go and travel in that direction on final if you fly uncoordinated (meaning you point the nose straight, but you also travel sideways relative to the airmass to compensate for the cross wind component), but that's uncomfortable. Much more comfortable to point the nose so that the combined motion of the airmass and your motion take you right down the centerline.

    The issues come up with the airmass is moving erratically, that makes it a little more fun.