Effect of Density Altitude on Crosswinds

Discussion in 'Flight Following' started by ebykowsky, Feb 19, 2015.

  1. taters

    taters Pattern Altitude

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    who cares just fly the plane
     
    Last edited: Feb 23, 2015
  2. Lindberg

    Lindberg Pattern Altitude

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    Well at least everyone seems to be acknowledging now that an airplane can move laterally irrespective of any turning. That's some progress. For some reason I am having flashbacks to downwind turn discussions on rec.aviation.
     
  3. RotorDude

    RotorDude Pattern Altitude

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    What happened is that IF you actually use the real unadulterated compass heading, and IF your nose points to where you flying (i.e. directly into the relative wind), THEN your wind correction angles will be correct and ATC will be happy.
    But in real life, if you mess up your unslaved DG by forgetting to correct for drift, or fly uncoordinated, or your compass calibration is off, then the above is no longer true. So to make ATC happy and fly right in general, you need to make sure you fly coordinated and verify your DG heading matches your properly calibrated compass.
     
  4. MAKG1

    MAKG1 Touchdown! Greaser!

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    The air. You have a speed and direction (in three dimensions) within the air. Unless you're flying in interstellar space or magnetic-dominated fluids, every point in space has a single well defined comoving velocity.

    Those of us who calculate aircraft physics deal with this all the time. It is not at all an ambiguous definition, and it's not different conceptually from true airspeed.

    If you wish to calculate the wind triangle in a slip, is the direction of the nose corrected for compass errors what you put into your E6-B? If you take the AFH as complete and perfect Gospel, that's the conclusion you would draw. You would be wrong by tens of degrees. In reality, the AFH is targeted at student pilots and doesn't consider the off nominal case for pedagogical reasons.
     
    Last edited: Feb 23, 2015
  5. RoscoeT

    RoscoeT Cleared for Takeoff

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    Wrong. Fly along straight and level and coordinated and then try to make the airplane move "laterally" (new flight path) without producing an intial turning (curving) flight path, slip or no slip. Cannot happen. Please post video. Have never seen this.

    Now there will be 500 more posts arguing over what lateral movement means...which of course will be different with the air mass vs. ground reference, which hemisphere you're in, which direction the Coriolis effect is going, which eye you have open, and which ass cheek you're leaning on. Might also depend on the day of the week. We will all be proven slobbering idiots.
     
    Last edited: Feb 23, 2015
  6. vintage cessna

    vintage cessna Cleared for Takeoff

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    The FAA has established certain definitions for words or phrases used in air navigation. So, if you want to communicate with and comply with ATC instructions or FAR's you have no choice but to use those definitions. And if you want to communicate with a community of pilots and use definitions contrary to what has been established and accepted ( like your definition of heading) good luck.
     
  7. MAKG1

    MAKG1 Touchdown! Greaser!

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    How do you fly slips coordinated?
     
  8. MAKG1

    MAKG1 Touchdown! Greaser!

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    It's not contrary to what ATC expects. Following your badly coordinated nose would fall into that category.

    Just like ATC wants true airspeed, not what your ASI reads. If your DG is precessed, or broken or your coordination sucks, they expect you to follow a specific direction with respect to the air when they give you a "heading" for separation. They don't know what your DG reads.
     
    Last edited: Feb 23, 2015
  9. RoscoeT

    RoscoeT Cleared for Takeoff

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    Welcome to the spin zone. :rolleyes2: You don't. People are saying the airplane starts moving laterally as soon as you slip. If you're in coordinated flight, and want to move "laterally", to me this means the airplane "jumps" to a different flight path. You cannot change your flight path without turning, either coordinated turn or slipping turn.

    If I was a more sensible person, I would not bother going in this circle for the N'th time. But I am not.
     
  10. vintage cessna

    vintage cessna Cleared for Takeoff

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    ATC was my chosen profession. When I asked a pilot for his airspeed, I wanted his indicated airspeed. If you are queried by ATC for your airspeed, you better reply with what your ASI is indicating. The only time I ever asked a pilot for his TAS is when he was air filing a flight plan. The TAS in a flight plan is only useful so that the ATC computer can apply the forecasted winds at your filed altitude and then estimate your ground speed.
     
  11. Silvaire

    Silvaire En-Route

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    If you enter a slip while keeping the nose on a constant heading are not now going to be moving laterally?

    If you enter a slip while keeping your ground track constant are you turning?

    I'm not following you, a slip is a slip, the aircraft flys laterally in reference to it's longitudinal axis. When you land in a crosswind the aircraft is flying laterally in a slip to eliminate the drift caused by the crosswind?

    It boggles my mind trying to figure just exactly what you guys think is happening when you are in a slip? Is the aircraft not flying laterally in regards to it's longitudinal axis?

    Again, I feel as though I am at Cheers listening to multiple Cliff Clavens tell us all about Air Traffic Control and the intricate complexities of the simple aerodynamic slip. :rolleyes:
     
    Last edited: Feb 23, 2015
  12. FastEddieB

    FastEddieB Final Approach

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    They do???

    On a flight plan, maybe, but where else?
     
  13. RotorDude

    RotorDude Pattern Altitude

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    That's right, ATC want TAS on flight plan, IAS in flight.
     
    Last edited: Feb 23, 2015
  14. Lindberg

    Lindberg Pattern Altitude

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    Sorry, I'm all out of videos. And this thread. Fly safe.
     
  15. RotorDude

    RotorDude Pattern Altitude

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    I am thinking this thread might belong in the "Slip Zone". Admins? :)
     
  16. vintage cessna

    vintage cessna Cleared for Takeoff

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    If a pilot hears a controller say "say airspeed", the pilot must reply with what the ASI reads. If the controller says " say heading" , the pilot must comply with what his compass or DG indicates. There is no wiggle room or ambiguity in any of this. That is why everyone in the system has to use the same definitions.
     
  17. RotorDude

    RotorDude Pattern Altitude

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    The "wiggle room" is that if ATC asks for your heading, you must first check your (unslaved) DG against your (properly calibrated) compass and correct if off, and be sure you fly coordinated. Then you follow your (now corrected) DG.
     
  18. Silvaire

    Silvaire En-Route

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    Are you saying there is such a thing as "flight path through the air" referenced on air molecules? I'm not following you, the air is fluid and in motion, how can you define a path through it and what reference would you use to navigate?
     
  19. RotorDude

    RotorDude Pattern Altitude

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    Your flight path through the air is your flight relative to the air mass surrounding your aircraft. Your direction through that airmass would be always pointed into the relative wind, if you fly coordinated.
    Your TAS is measured relative to that airmass.
     
    Last edited: Feb 23, 2015
  20. FastEddieB

    FastEddieB Final Approach

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    Of course.

    A good reminder for new pilots is that many here flew for decades where the only way to know your TAS at any moment was to dig out your E6B. Or maybe if you had really good eyes and the right kind of airspeed indicator, you could dial temp opposite PA and read it there.
     
  21. vintage cessna

    vintage cessna Cleared for Takeoff

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    Well, I've seen a lot of confusion on some peoples part by the ATC instruction " fly runway heading" . If one understands the definition of "heading" , there would be no confusion. But some people think ATC wants or expects the pilot to track to track the runway alignment. Yeah, and before you say it, I know ATC will be disappointed with the pilot if he side slips like some kind of crazy ape.
     
  22. RotorDude

    RotorDude Pattern Altitude

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    Re "fly runway heading", you are right, if they use that phrase, after clearing obstructions you should turn to the runway numbers on your DG, which should be verified to match the compass (if unslaved), as always. Obviously any crosswind will drift you off, but ATC expects that.
     
  23. vintage cessna

    vintage cessna Cleared for Takeoff

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    If a controller instructs you to fly runway heading, that means as soon as you are flying. If you feel you can't do that because of an obstruction, you need to reject the instruction and state why prior to departing.
     
  24. FastEddieB

    FastEddieB Final Approach

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    I believe we've established that when told to maintain runway heading, they really want you to maintain runway track.

    Pretty sure someone produced a source for that interpretation.
     
  25. vintage cessna

    vintage cessna Cleared for Takeoff

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    See what I mean. They don't use the phraseology " maintain runway heading". The say "fly runway heading". If you just use what the FAA says is the definition of heading, you don't need to attempt to deduce what is meant. Of course, a certain level of airmanship is expected in flying the heading. If a controller is doing his job, anything he says has been clearly defined by the FAA so that a pilot would understand what it means.
     
  26. RotorDude

    RotorDude Pattern Altitude

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    p. 2-35 of the Instrument Procedures Handbook (my bold):

     
    Last edited: Feb 23, 2015
  27. RoscoeT

    RoscoeT Cleared for Takeoff

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    The spin is epic.

    You call it moving laterally, I call it turning...slipping turn, curving flight path. You can then stop the slipping turn and slip along a new flight, but you have TURNED to that new flight path via curing flight, not instantly jumped to a new "lateral" flight path as many seem to imply. If you hold the precise inputs that made you move "laterally" off your flight path, you will turn in circles until you stop it.

    Of course not. I'd ask why this was so hard, but it would only make it harder.
     
  28. Silvaire

    Silvaire En-Route

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    I'm not sure who established that but in reality, as you climb through possibly shifting air currents how do you maintain this "track" other than continually peer out the back window?

    Heading is one and only one thing - what you see on your compass. Again, there is no alternate definition to that.
     
  29. Silvaire

    Silvaire En-Route

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    Once again, if you are "turning" why does your heading remain constant? Hold that slip for 10 minutes, you are still on the same heading. Why do you want to call it a "turn"?
     
  30. RoscoeT

    RoscoeT Cleared for Takeoff

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    Here's what you're missing - If you hold the exact inputs that caused that initial flight path change, that is a slipping turn that will continue in circles until you adjust your inputs. To keep your NEW "lateral" flight path constant, you must STOP the slipping turn before you've turned so far that you can no longer hold the nose on the original heading. All you've done is a slipping turn a few degrees to a new flight path, stopped the slipping turn, and then proceeded to slip along a constant new flight path with the nose still on your original heading. You have a limited angle at which you can turn onto a new flight path before your nose cannot stay on the original heading with a slip. For lots of airplanes, it might not be much more than 10 degrees. Depends on control surface effectiveness.

    Think of the runway drill. Fly aligned and tracking the runway, and then angle your flight path in a 10 degree angle toward the runway. You could do that without changing your heading. You did it with a slipping turn though. Now try to make that "lateral" angle 70 degrees. You won't come close to keeping the nose on heading while changing your flight path to that degree.
     
    Last edited: Feb 23, 2015
  31. RotorDude

    RotorDude Pattern Altitude

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    If you start in a coordinated flight down a straight road (zero wind), and start a bank, keeping the the nose on the road, you'll enter a slip, and drift off that road. If you keep your slip balanced (non-turning), you will start forward-slipping into a new straight course, away from the road. The slight change in direction, from down the road to the new course at some angle to it, is your turn. After that brief turn you'll be in a non-turning forward slip.
     
  32. Vance Breese

    Vance Breese Line Up and Wait

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    From the 2015 AIM.
    RUNWAY HEADING− The magnetic direction that corresponds with the runway centerline extended, not the painted runway number. When cleared to “fly or maintain runway heading,” pilots are expected to fly or maintain the heading that corresponds with the extended centerline of the departure runway. Drift correction shall not be applied; e.g., Runway 4, actual magnetic heading of the runway centerline 044, fly 044.
     
  33. RotorDude

    RotorDude Pattern Altitude

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    That's actually correct, if you use the compass itself (which you know is properly calibrated) and not an unslaved DG that's off. But ATC also expects heading to be your flight direction in coordinated flight, so if you slip you'd be confusing ATC, just like an error due to uncorrected DG drift or uncalibrated compass.
     
  34. RoscoeT

    RoscoeT Cleared for Takeoff

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    You got it, and you must STOP that turn also...and you can't turn very far until you can no longer hold the nose on heading. Maybe only around 15 degrees in lots of airplanes. Very limited window. Again, try changing your flight path by 70 degrees in a slip and see if you can hold the nose on heading. Not.
     
  35. FastEddieB

    FastEddieB Final Approach

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    Guess I misremembered.

    It is, in fact, what I always thought and taught, but I thought somewhere along the line I was corrected.
     
  36. RotorDude

    RotorDude Pattern Altitude

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    True.
     
  37. RoscoeT

    RoscoeT Cleared for Takeoff

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    I know you knew that- my comments weren't even directed toward you since you never had any issues on this subject. You are a winner of the comprehension award in this thread. :lol:
     
  38. Silvaire

    Silvaire En-Route

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    So you're saying it's a turn because my track over the ground has changed? What about in straight and level flight as you fly through shifting and changing winds. With no intervention on your part your track over the ground will change. Are you going to call that a turn too? Because back before gps if you weren't flying along a VOR radial and there were sparse landmarks it might take you awhile to discover that you're now 3 miles off course.

    I'm telling you that if you cross the aileron and elevator controls you are going to enter a slip. Now there is no force on Earth or in flight, there is no law of physics that says when you do that your nose has to shift off to the right or left or your heading must be altered so that your ground track doesn't change. You may purposely cause that to happen in a forward slip on final to lose altitude but you are manipulating the controls to make that happen.

    Forget about the ground, you are not physically attached to the ground, you are flying in the air. With the controls crossed and heading constant you are in a slip, not a turn.
     
  39. Silvaire

    Silvaire En-Route

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    Again? Where did altering your course by 70 degrees come from? We are talking about a slip where the aircraft is flying through the air laterally in respect to the longitudinal axis. If you are doing a forward slip on final to lose altitude can you kick the nose off 70 degrees?

    So what are you talking about?
     
  40. RoscoeT

    RoscoeT Cleared for Takeoff

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    It was an extreme example to make a point that is lost on you. Some get it, some don't. Such is life.