Does a steady tailwind “push” an airplane?

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

  1. Cooter

    Cooter Pattern Altitude

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    We have had different experiences I guess. Because of all the problems I’ve seen students have, confusion over being pushed has never been one of them. You can avoid that language to preclude misunderstanding if you wish, I don’t see it as a problem. Bottom line is that a push is responsible for the momentum. The same way that a 100mph fastball hurts the catchers hand because the pitcher threw it.

    I see your point and don’t really disagree. But the areas where it may cause confusion are minimal based on my experience.
     
  2. PaulS

    PaulS Final Approach

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    The airmass is moving relative to the ground, which in the end is important to you in that you want to get to your destination. The air is always moving relative to your plane, that's how you fly. If you fly coordinated at 100 knots, it is moving straight ahead relative to the air, it doesn't care which way the wind is blowing. Look at it this way. If you fly due north at 100 knots in no wind for an hour, your airplane will end up 100 nautical miles north of where you started. If you do the same thing, fly pointed due north, with a wind, from the east at 5 knots, then after an hour you will end up 100 miles north and 5 miles west of where you started .
     
  3. injb

    injb Pre-takeoff checklist

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    OK Eddie/PaulS, I think I'm beginning to get it now lol. What I was missing was that when you're crabbing into the wind, you're not really banking, you're just flying a certain heading. I still haven't figured out why that works. Why isn't there a bank angle? I need more crosswind practice!
     
  4. upstateny

    upstateny Line Up and Wait

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    Now in SW Florida
    On another note...
    We were all taught that lift is produced by the airflow over the wing. But let's take the air's point of view. The air is just sitting there fat, dumb and happy (perhaps being moved around by high/low pressure) when suddenly this object (wing) appears out of nowhere. Since two things can't occupy the same place at the same time the air moves up (or down) to get out of the way. As quickly as it showed up, the object (wing) is gone and the air returns to roughly where it was, but it now has some momentum and swirls around for a while. How did that create lift?
     
  5. Clark1961

    Clark1961 Touchdown! Greaser!

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    Good old Newton. Forcing the air down provides the lift.
     
  6. upstateny

    upstateny Line Up and Wait

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    But some of the air went up, forcing the plane down (according to Newton.)
     
  7. Clark1961

    Clark1961 Touchdown! Greaser!

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    Did it?
     
  8. injb

    injb Pre-takeoff checklist

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    Some of it may go up, but more will go down because of the angle of attack. For more air to go up than down, you'd have to have a negative angle of attack. At least that's my understanding of it...
     
  9. Cooter

    Cooter Pattern Altitude

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    The acceleration of the particles above the wing means that some their “pressure”is directed parallel to the wing. That acceleration reduces the amount of pressure exerted on the upper surface and imparts a force to the wing itself.
     
    Last edited: Dec 3, 2017
  10. Stewartb

    Stewartb En-Route

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    This thread is in the running for today's Virtual Lobotomy award.
     
  11. Clark1961

    Clark1961 Touchdown! Greaser!

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    A fair bit of research suggests all effective lift is Newtonian.
     
  12. Clark1961

    Clark1961 Touchdown! Greaser!

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    Only for folks that fail to understand that wind does not push aircraft in flight...
     
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  13. PaulS

    PaulS Final Approach

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    Lift cannot occur without an AOA indicator.
     
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  14. GlennAB1

    GlennAB1 Ejection Handle Pulled

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    It's magic. NACA extensive wind tunnel tests (from the '30's) showed that differential pressure causes lift.
     
  15. FastEddieB

    FastEddieB Final Approach

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    Nope.

    Try it some time.

    Go up on a windy day. Fly perpendicular to the wind in one direction with an appropriate WCA and take a photo of the panel. Reverse direction and do the same. Then try directly into and with the wind. With proper coordination, the four panel photos will be identical as to the flight instruments. They have to be, since the plane has no way to “sense” the wind. It’s just flying along straight and level in whatever direction you choose to point it.

    If you see a wind correction as a constant “turn into the crosswind”, I think that’s the root of the problem - it’s not.
     
    Last edited: Dec 3, 2017
  16. GlennAB1

    GlennAB1 Ejection Handle Pulled

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  17. Clark1961

    Clark1961 Touchdown! Greaser!

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    lol. They proved what they wanted to prove. It's all Newton and downward airflow.
     
  18. FastEddieB

    FastEddieB Final Approach

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    Think back to your ground reference maneuvers. Rectangular pattern, for instance.

    Once the turn was made in each corner, you did not hold a bank for the straight and level part, did you? You just rolled to wings level flight and made small corrections in either direction to maintain your desired ground path.

    Right?
     
  19. FastEddieB

    FastEddieB Final Approach

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    Surely that deserves a thread of its own?
     
  20. GlennAB1

    GlennAB1 Ejection Handle Pulled

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    NACA proved Bernoulli's principle, and it did in fact cause lift.
     
  21. Dan Thomas

    Dan Thomas En-Route

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    Lift cannot occur without lots of money.
     
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  22. Clark1961

    Clark1961 Touchdown! Greaser!

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    Oh lord....there is lift and then there is enough lift to actually lift an aircraft...
     
  23. Lindberg

    Lindberg Pattern Altitude

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    Coordination has nothing to do with it. The story's the same if you're slipping or skidding.
     
  24. PaulS

    PaulS Final Approach

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    True, but being uncoordinated brings the apparent wind from the nose to the side facing into the apparent wind of the airplane comparatively speaking which results in a "pressure" change from one side of the airplane to the other.... which is why I said it. But in the grand scheme of things you are right, the AP is still part of the airmass it is travelling in. I think.
     
  25. Lindberg

    Lindberg Pattern Altitude

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    The apparent wind comes from the airplane's motion through the airmass.
     
  26. PaulS

    PaulS Final Approach

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    Yes, that's why I said it, flying uncoordinated moves the nose off the apparent wind, exposing the side of the airplane, a larger area of the plane to it.
     
  27. GlennAB1

    GlennAB1 Ejection Handle Pulled

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    You need to do a little math. Figure the square inches of a wing and figure out how much average psi differential is required to lift that plane. Clue: It isn't very much.
     
    Last edited: Dec 3, 2017
  28. GlennAB1

    GlennAB1 Ejection Handle Pulled

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    Take a Cessna 172R for example. Numbers taken from Wikipedia. Wing area: 174 sq ft. That's roughly 25,000 square inches. Gross weight 2,450 lb., use 2,500 for convenience.
    2,500 lb. ÷ 25,000 sq. in. = .10 lb./sq. in.

    That's 1/10 of 1 psi average differential required to lift the aircraft.

    A Boeing 747 works out to just over 1 psi average differential required at MTOW.

    That's how damaged aircraft can be lifted, very easily, with airbags.
     
    Last edited: Dec 4, 2017
  29. GlennAB1

    GlennAB1 Ejection Handle Pulled

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    Ok, please explain how, on the famous beach at St. Martin, when a 747 lands, it's downward airflow of over 500,000 lb force doesn't blow everyone and everything off the beach, yet that same aircraft on the runway with engines at takeoff power producing 200,000 lb force blows everything away?
     
  30. Clark1961

    Clark1961 Touchdown! Greaser!

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    Are you really asking about the difference between 4 point sources and a continuous system?
     
  31. FlySince9

    FlySince9 Pattern Altitude

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    Nope... that would be a wrong assumption...you haven't been paying attention:fingerwag:
     
  32. N659HB

    N659HB Pattern Altitude

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    Well, we all know it's money that makes airplanes fly. :p
     
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  33. FlySince9

    FlySince9 Pattern Altitude

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    money? what's that?
     
  34. exncsurfer

    exncsurfer Pattern Altitude

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    Just don't confuse crosswind landing practice with the concept Eddie is discussing. When you come in to land you start to compensate for the air mass in different ways(uncoordinated on purpose) than you would in cruise. When you put in the rudder input for landing in a crosswind, you will need bank angle to maintain your path over the ground. So don't confuse that with wind correction angle in cruise. Maybe that is what is confusing you? I mean you could do that(slip with a wing low) in cruise to make your nose point your track over the ground but it would be pointless and slow you down.
     
  35. injb

    injb Pre-takeoff checklist

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    No what was confusing me was that I thought that you had to maintain constant aileron correction to crab into the wind, and therefore it's the same as a constant turn. Now I'm learning that that's not the case, but I could have sworn that I had to maintain pressure in this situation. I've never done a rectangular reference maneuver but I've done the circular one. I will pay closer attention next time I fly with a crosswind...
     
  36. PaulS

    PaulS Final Approach

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    Ok, I am far from an expert here, especially on flying technique, but my instructor says your airplane should only be turning when you want it to turn, otherwise wings level, once you are pointing where you want you shouldn't have to keep constant pressure to keep it there. Maybe the plane you are flying is out of trim or out of rig causing this.

    Also keep in mind that our discussion above assumes a constant wind, which usually doesn't happen too often. Except on the smoothest days there is always some perturbation that makes you have to adjust, just part of flying.
     
  37. exncsurfer

    exncsurfer Pattern Altitude

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    To demonstrate what Eddie is saying you wouldn't perform a reference maneuver, he is saying do the 360 without ground reference(under a hood) and you will not 'feel' the wind at all. When you are doing a 360 ground reference you are compensating with aileron for what you are seeing out the window based on the ground and wind blowing across it. When you're doing a rectangular pattern you'd be doing this in the turns but once you come out of the turns you'd be setting up a coordinated(no bank or slip) crab on the straight sections.
     
  38. PaulS

    PaulS Final Approach

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    Pointless, slow you down and empty one tank before the other on some airplanes.
     
  39. FastEddieB

    FastEddieB Final Approach

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    I gave thought to this just now while walking the dogs.

    Apparently, it’s not an uncommon mental construct to view correcting for a crosswind as making a constant turn into the wind. It snagged both you and that previously mentioned Cirrus demo pilot.

    But how is “turn” defined? Most commonly it would relate to a change in direction, or in our case heading.

    So, by definition, if you’re flying along on a constant heading, you can’t be turning. Right?

    Hopefully that helps, though I see others have scooped me a little - again!
     
  40. Lindberg

    Lindberg Pattern Altitude

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    A standard traffic pattern is a rectangular reference maneuver.