6 ms·

The Turn (1993)

146 points by karzeem 16y ago

lisper 16y ago
> The bank is a condition of tilted wings, and the turn is the change in direction that results. The connection between the two is inexorable: the airplane must bank to turn, and when it is banked, it must turn. This is only true if the rudder is not being used. It is possible to turn a plane without banking it, and to bank a plane without turning it using the rudder. The former maneuver is called a skidding turn, and the latter is called a slip.
joejohnson 16y ago
The near-negligible Coriolis force can be felt (barely) at velocities which planes reach. This could tip of the inner-ear to a bank, if ever so slightly. However, this force is many orders smaller than the centrifugal force that the authors is talking about. However, I don't think it's technically correct to say the passengers "have no way of guessing the airplane's degree of bank."
- phreeza 16y ago
  If they had a gyroscope they could measure it, of course.
javanix 16y ago
The airplane could be momentarily upside down and passengers would not know. At some point I suspect gravity would override the masking sense of motion that he talks about.
- jacksoncarter 16y ago
  If the centrifugal force in the upward direction is 2g, that is, twice gravity, then passengers will feel like the plane is flying exactly upright and parallel with the earth.
  - asmithmd1 16y ago
    Or the plane could be on a zero g simulating parabolic arc and at the same time doing a 1G barrel roll. A passenger with their eyes closed would think they are flying strait and level. We have a bubble level in our heads for sensor. Not a gyro.
  - sesqu 16y ago
    Even with a centripetal force of 137N (2g, 70kg), you'd think passengers would notice earth's gravitational pull circling them.
ggchappell 16y ago
Very nice, but the description of Focault's pendulum, near the end, is incorrect. > ... though the pendulum appeared to change direction as it swung, in fact the plane of its swing remained constant .... Nope. Unless you're at one of the poles, the period of the rotation of the plane is not 24 hours; the plane can hardly be fixed. Wikipedia says a bit about this: https://secure.wikimedia.org/wikipedia/en/wiki/Focault_pendulum https://secure.wikimedia.org/wikipedia/en/wiki/Focault_pendu... And there was a nice article in the American Mathematical Monthly some years back, which I found here: http://geomsymm.cnsm.csulb.edu/courses/451/foucault_pend.pdf http://geomsymm.cnsm.csulb.edu/courses/451/foucault_pend.pdf But the basic idea is something like this: Say you're in the Northern Hemisphere. As the Earth rotates, your path essentially pushes you to the right (where "forward" is west). If you have a swinging pendulum with you, then the plane of its swing will rotate just as if you were on a flat surface, walking in a very large circle. The closer you are to the equator, the less you are moving to the right, the larger is this theoretical circle, and the slower the plane turns.
- mechanical_fish 16y ago
  Sure, but this is just the Science Writing Uncertainty Principle: You can be brief, or you can be precise, but rarely can you be both brief and precise. Langewiesche doesn't have time for a discourse on the physics of the pendulum -- which is basically just another kind of gyro. He has just a couple of sentences for his aside, and his readers are not physicists, so he grabs for the example of the Foucault pendulum, because that's a pendulum experiencing gyroscopic forces that every science museum visitor has seen.
  - ggchappell 16y ago
    Ah, but the statement "the plane of its swing remained constant" is not imprecise; it is false. And I don't mean false-but-kinda-true like "pi = 3.14" is false-but-kinda-true; I mean just plain wrong. The fixed-plane idea seems to be a common misunderstanding, even among intelligent people, but it ain't so. The plane turns, even with respect to a "fixed" frame of reference that does not rotate with the Earth. I would have been better just to say that the plane changes, showing that the Earth rotates, and leave the explanations for another time.
cma 16y ago
The article on rolls: "but if you ignore convention, you can fly them in any airplane, including a Boeing 737" or a 707: http://www.youtube.com/watch?v=Ra_khhzuFlE&feature=related http://www.youtube.com/watch?v=Ra_khhzuFlE&feature=relat...
mmaunder 16y ago
This is Bob Hoover (who he mentions) pouring iced tea during a roll. http://www.youtube.com/watch?v=pMWxuKcD6vE http://www.youtube.com/watch?v=pMWxuKcD6vE
- moolave 16y ago
  This idea was probably taken from Coca Cola the ad wherein a pilot of an F-16 had to do a full roll when the bottle got stuck in the console.
  - spitfire 16y ago
    Bob was doing this before the designers of the f-16 were a sparkle in their parents eyes. Bob knew Orville Wright and Charles Lindbergh as friends. youtube up the video of him flying the f-86 sabre if you want to be stunned.
    - mrduncan 16y ago
      The F-86 video: http://www.youtube.com/watch?v=TRt6UnNzR6I http://www.youtube.com/watch?v=TRt6UnNzR6I
- jurjenh 16y ago
  I do love how he mentions that the difficult part of the tea-pouring-during-a-roll was pouring the tea back-handed... I guess it all comes down to a matter of perception, as with so many things in life.
- JesseAldridge 16y ago
  I don't really understand how this works. The article mentioned something about inertia... So gravity moves the object in a downward direction... and then, when the plane is flipped, it keeps moving in that direction -- which is now up? I guess that the effect would "wear off" after awhile? So if you kept flying upside down the tea would eventually fall, right?
  - 16y ago
chime 16y ago
> The artificial horizon is a gyroscopically steadied line, which stays level with the earth's surface. The airplane pitches and banks in relation to this steady line, which in spatial terms never moves. Of course, in airplane terms it does move -- which presents a problem, because pilots are part of the airplane: they fly it from within, strapped to their seats. In clear skies they would never misjudge a bank as the tilting of the earth, but with their view restricted to the abstractions of the instrument panel they sometimes do just that: when the airplane banks, they perceive the motion as a movement of the artificial horizon line across the face of the instrument. This causes them to "fly" the wrong thing -- the moving horizon line, rather than the fixed symbolic airplane. For example, as turbulence tilts the airplane to the left, the pilots, tilting with it, notice the artificial horizon line dropping to the right. Reacting instinctively to the indication of motion, they sometimes try to raise the line as if it were a wing. Would this be considered an example of a dangerously confusing user interface?
- rubyrescue 16y ago
  From personal experience, during instrument training this is something you get used to and a trained pilot would not normally make such a mistake; the interface is so simple it would be hard to simplify it further, and further, it's not the only instrument you have at your disposal - you get a sense of them working together (turn indicator; airspeed indicator; compass, GPS, and VOR, all are secondary indicators indicating that you're turning in a particular direction or pitching down or up)...
- jrockway 16y ago
  Not really, the UI works exactly like the thing it models. Bank the plane to the left, the horizon moves to the right. And so does the artificial horizon. I think people get confused when they see the marking representing the planes wings not moving relative to the console, but they see the blue-and-red thing inside the instrument moving. So they assume that their control inputs are causing the artificial horizon to move, when in reality, they are moving the plane and the artificial horizon is remaining still, just like the real horizon would. Presumably there is some sort of mental issue with the "size" of the horizon -- when you look out the window, it's really big, so of course you're not moving it. Newer cockpits make the artificial horizon bigger, perhaps to compensate for this effect: http://www.cockpitgps.com/VOR_magnetic_variation/G1000CBEAV-SWL.JPG http://www.cockpitgps.com/VOR_magnetic_variation/G1000CBEAV-... I know that as long as I remember "fly the little airplane, not the horizon", it's not a problem. And as the comment below mentions, you also have a turn indicator, which clearly shows "R" when you're turning right and "L" when you're turning left: http://www.unitedinst.com/images/TurnSlip9500Series.gif http://www.unitedinst.com/images/TurnSlip9500Series.gif
VictorHo 16y ago
That was an amazing article. I've always been intrigued by flight but I think I have a newfound appreciation.
- ojilles 16y ago
  Same here. Really liked the article!
sammyo 16y ago
During an aerobatic glider ride for the initiation of the first maneuver all I saw was the horizon rise then slowly drop below the edge of the cockpit. A few moments later the pilot behind me said to look straight up. Directly above me were cars on the highway. I had no sense of being upside down. Very cool. Later maneuvers were more visceral.
jeffcoat 16y ago
I have Wolfgang Langewiesche's _Stick and Rudder_, a classic book for pilots on how to fly airplanes, sitting on a shelf near me. According to Wikipedia, the author of this article is his son.
limist 16y ago
Wonderful article, as it gives more reason to smile in appreciation on the next flight. Human hubris, stubbornness and over-reliance on intuition add to the article's lessons in physics and biology.

The Turn (1993)

146 points by karzeem 16y ago

> The bank is a condition of tilted wings, and the turn is the change in direction that results. The connection between the two is inexorable: the airplane must bank to turn, and when it is banked, it must turn. This is only true if the rudder is not being used. It is possible to turn a plane without banking it, and to bank a plane without turning it using the rudder. The former maneuver is called a skidding turn, and the latter is called a slip.

joejohnson 16y ago

The near-negligible Coriolis force can be felt (barely) at velocities which planes reach. This could tip of the inner-ear to a bank, if ever so slightly. However, this force is many orders smaller than the centrifugal force that the authors is talking about. However, I don't think it's technically correct to say the passengers "have no way of guessing the airplane's degree of bank."

phreeza 16y ago
If they had a gyroscope they could measure it, of course.

javanix 16y ago

The airplane could be momentarily upside down and passengers would not know. At some point I suspect gravity would override the masking sense of motion that he talks about.

jacksoncarter 16y ago
If the centrifugal force in the upward direction is 2g, that is, twice gravity, then passengers will feel like the plane is flying exactly upright and parallel with the earth.
- asmithmd1 16y ago
  Or the plane could be on a zero g simulating parabolic arc and at the same time doing a 1G barrel roll. A passenger with their eyes closed would think they are flying strait and level. We have a bubble level in our heads for sensor. Not a gyro.
- sesqu 16y ago
  Even with a centripetal force of 137N (2g, 70kg), you'd think passengers would notice earth's gravitational pull circling them.

ggchappell 16y ago

Very nice, but the description of Focault's pendulum, near the end, is incorrect. > ... though the pendulum appeared to change direction as it swung, in fact the plane of its swing remained constant .... Nope. Unless you're at one of the poles, the period of the rotation of the plane is not 24 hours; the plane can hardly be fixed. Wikipedia says a bit about this: https://secure.wikimedia.org/wikipedia/en/wiki/Focault_pendulum https://secure.wikimedia.org/wikipedia/en/wiki/Focault_pendu... And there was a nice article in the American Mathematical Monthly some years back, which I found here: http://geomsymm.cnsm.csulb.edu/courses/451/foucault_pend.pdf http://geomsymm.cnsm.csulb.edu/courses/451/foucault_pend.pdf But the basic idea is something like this: Say you're in the Northern Hemisphere. As the Earth rotates, your path essentially pushes you to the right (where "forward" is west). If you have a swinging pendulum with you, then the plane of its swing will rotate just as if you were on a flat surface, walking in a very large circle. The closer you are to the equator, the less you are moving to the right, the larger is this theoretical circle, and the slower the plane turns.

mechanical_fish 16y ago
Sure, but this is just the Science Writing Uncertainty Principle: You can be brief, or you can be precise, but rarely can you be both brief and precise. Langewiesche doesn't have time for a discourse on the physics of the pendulum -- which is basically just another kind of gyro. He has just a couple of sentences for his aside, and his readers are not physicists, so he grabs for the example of the Foucault pendulum, because that's a pendulum experiencing gyroscopic forces that every science museum visitor has seen.
- ggchappell 16y ago
  Ah, but the statement "the plane of its swing remained constant" is not imprecise; it is false. And I don't mean false-but-kinda-true like "pi = 3.14" is false-but-kinda-true; I mean just plain wrong. The fixed-plane idea seems to be a common misunderstanding, even among intelligent people, but it ain't so. The plane turns, even with respect to a "fixed" frame of reference that does not rotate with the Earth. I would have been better just to say that the plane changes, showing that the Earth rotates, and leave the explanations for another time.

cma 16y ago

The article on rolls: "but if you ignore convention, you can fly them in any airplane, including a Boeing 737" or a 707: http://www.youtube.com/watch?v=Ra_khhzuFlE&feature=related http://www.youtube.com/watch?v=Ra_khhzuFlE&feature=relat...

mmaunder 16y ago

This is Bob Hoover (who he mentions) pouring iced tea during a roll. http://www.youtube.com/watch?v=pMWxuKcD6vE http://www.youtube.com/watch?v=pMWxuKcD6vE

moolave 16y ago
This idea was probably taken from Coca Cola the ad wherein a pilot of an F-16 had to do a full roll when the bottle got stuck in the console.
- spitfire 16y ago
  Bob was doing this before the designers of the f-16 were a sparkle in their parents eyes. Bob knew Orville Wright and Charles Lindbergh as friends. youtube up the video of him flying the f-86 sabre if you want to be stunned.
  - mrduncan 16y ago
    The F-86 video: http://www.youtube.com/watch?v=TRt6UnNzR6I http://www.youtube.com/watch?v=TRt6UnNzR6I
jurjenh 16y ago
I do love how he mentions that the difficult part of the tea-pouring-during-a-roll was pouring the tea back-handed... I guess it all comes down to a matter of perception, as with so many things in life.
JesseAldridge 16y ago
I don't really understand how this works. The article mentioned something about inertia... So gravity moves the object in a downward direction... and then, when the plane is flipped, it keeps moving in that direction -- which is now up? I guess that the effect would "wear off" after awhile? So if you kept flying upside down the tea would eventually fall, right?
- 16y ago

chime 16y ago

> The artificial horizon is a gyroscopically steadied line, which stays level with the earth's surface. The airplane pitches and banks in relation to this steady line, which in spatial terms never moves. Of course, in airplane terms it does move -- which presents a problem, because pilots are part of the airplane: they fly it from within, strapped to their seats. In clear skies they would never misjudge a bank as the tilting of the earth, but with their view restricted to the abstractions of the instrument panel they sometimes do just that: when the airplane banks, they perceive the motion as a movement of the artificial horizon line across the face of the instrument. This causes them to "fly" the wrong thing -- the moving horizon line, rather than the fixed symbolic airplane. For example, as turbulence tilts the airplane to the left, the pilots, tilting with it, notice the artificial horizon line dropping to the right. Reacting instinctively to the indication of motion, they sometimes try to raise the line as if it were a wing. Would this be considered an example of a dangerously confusing user interface?

rubyrescue 16y ago
From personal experience, during instrument training this is something you get used to and a trained pilot would not normally make such a mistake; the interface is so simple it would be hard to simplify it further, and further, it's not the only instrument you have at your disposal - you get a sense of them working together (turn indicator; airspeed indicator; compass, GPS, and VOR, all are secondary indicators indicating that you're turning in a particular direction or pitching down or up)...
jrockway 16y ago
Not really, the UI works exactly like the thing it models. Bank the plane to the left, the horizon moves to the right. And so does the artificial horizon. I think people get confused when they see the marking representing the planes wings not moving relative to the console, but they see the blue-and-red thing inside the instrument moving. So they assume that their control inputs are causing the artificial horizon to move, when in reality, they are moving the plane and the artificial horizon is remaining still, just like the real horizon would. Presumably there is some sort of mental issue with the "size" of the horizon -- when you look out the window, it's really big, so of course you're not moving it. Newer cockpits make the artificial horizon bigger, perhaps to compensate for this effect: http://www.cockpitgps.com/VOR_magnetic_variation/G1000CBEAV-SWL.JPG http://www.cockpitgps.com/VOR_magnetic_variation/G1000CBEAV-... I know that as long as I remember "fly the little airplane, not the horizon", it's not a problem. And as the comment below mentions, you also have a turn indicator, which clearly shows "R" when you're turning right and "L" when you're turning left: http://www.unitedinst.com/images/TurnSlip9500Series.gif http://www.unitedinst.com/images/TurnSlip9500Series.gif

VictorHo 16y ago

That was an amazing article. I've always been intrigued by flight but I think I have a newfound appreciation.

ojilles 16y ago
Same here. Really liked the article!

sammyo 16y ago

During an aerobatic glider ride for the initiation of the first maneuver all I saw was the horizon rise then slowly drop below the edge of the cockpit. A few moments later the pilot behind me said to look straight up. Directly above me were cars on the highway. I had no sense of being upside down. Very cool. Later maneuvers were more visceral.

jeffcoat 16y ago

I have Wolfgang Langewiesche's _Stick and Rudder_, a classic book for pilots on how to fly airplanes, sitting on a shelf near me. According to Wikipedia, the author of this article is his son.

limist 16y ago

Wonderful article, as it gives more reason to smile in appreciation on the next flight. Human hubris, stubbornness and over-reliance on intuition add to the article's lessons in physics and biology.