Explained: Why flying isn't impossible on a globe

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there is no rope - the fixed link is a rigid link, attached to the person by a harness and is allowed to rotate on the upright poll by use of roller bearings

the person can only move forward or backward, along the dotted line (imagine the fixed link is a mile long)
 
there is no rope - the fixed link is a rigid link, attached to the person by a harness and is allowed to rotate on the upright poll by use of roller bearings

the person can only move forward or backward, along the dotted line (imagine the fixed link is a mile long)
But the key here is that the person WOULD have to rotate, representing the plane rotating nose down to keep up with the circle.
 
and the plane has to rotate to

the force* acting on person is the rigid pole

the force acting on the plane is gravity


*not strictly a force I suppose
 
But the key here is that the person WOULD have to rotate, representing the plane rotating nose down to keep up with the circle.
The plane will rotate, but it won't have to take any action to do so. Gravity will take care of it. Imagine transporting a pendulum from London to Los Angeles. Would you have to rotate it through 90 degrees to get it to hang straight down when you arrived?
 
I asked an actual pilot about this (who flies 777s for a large airline).

Their response:

Ah, that old argument again... I think they've heard the term 'flight level' and decided level = flat, whereas it actually means we fly perpendicular to the centre of gravity. So no, we don't 'constantly nose down', Otto* just keeps us nice and perpendicular to CoG
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*
 
There are a few problems with this.
Let's say you can take 3 steps straight forward before reaching the end of the rope. After taking those 3 steps, what do you have to do to continue your way around the circle?
Also a plane flying at 35,000 feet still has plenty "rope" left to go.

No, the "rope" is always tight. There's no slack.
 
But the key here is that the person WOULD have to rotate, representing the plane rotating nose down to keep up with the circle.

I think the crux of the problem Provemewrong, as Trailblazer has succinctly put it

is that gravity is an invisible force acting on the plane

I have just tried to replicate it in my analogy by making the "force" a visible rigid link to the upright pole

but the result is the same - the person will simply walk (straight) forward, but in fact he/she will end up going around the pole
 
representing the plane rotating nose down to keep up with the circle.
the plane is a spirit level. no matter where it goes it remains level to the center of the earth, just as the spirit level does.
Then how did the plane leave the surface of the earth?
it lifted it's nose and used "thrusters" to ascend to the desired altitude. the rigid rope analogy only works when flying level ie once the plane gets to altitude then levels off.
 
I think the crux of the problem Provemewrong, as Trailblazer has succinctly put it

is that gravity is an invisible force acting on the plane

I have just tried to replicate it in my analogy by making the "force" a visible rigid link to the upright pole

but the result is the same - the person will simply walk (straight) forward, but in fact he/she will end up going around the pole
I don't see how that is theoretically possible. That's like saying the earth doesn't curve, but is still a sphere.
 
The plane will rotate, but it won't have to take any action to do so. Gravity will take care of it. Imagine transporting a pendulum from London to Los Angeles. Would you have to rotate it through 90 degrees to get it to hang straight down when you arrived?
I really like this comparison. For me to visualize better let's replace the pendulum with the spirit level. Let's pretend there's no elevation on earth, just the smooth curved surface. You are saying it would be possible (in theory) to travel the surface of the spherical earth without the level ever changing ?
 
but the result is the same - the person will simply walk (straight) forward, but in fact he/she will end up going around the pole
the problem is the scale. walking around a maypole with a 10 foot pole attached to you is alot different then the size of the earth :)
 
the problem is the scale. walking around a maypole with a 10 foot pole attached to you is alot different then the size of the earth :)
Absolutely but a circle is a circle and you can't make one without rotation/curvature (or change in direction). If the person has to shift the way their nose is pointing to trace the circle, then so does the plane.
 
i just saw an excellant demo of the "rigid rope" analogy i think on the show Penny Dreadful, the [antique wind up] toy carriage attached to a stick went round the barn but the carriage itself doesnt need to turn. i'll look for it when i get home.

kinda this concept.

f11a9018f679e9f28ff39bcc5a320b0a.jpg
 
Absolutely but a circle is a circle and you can't make one without rotation/curvature (or change in direction). If the person has to shift the way their nose is pointing to trace the circle, then so does the plane.
i hear you, it is counterintuitive for me too. but look at the toy, the plane doesnt move or tilt. it remains in it's exact same position no matter where it is on the circle.
 
we
i just saw an excellant demo of the "rigid rope" analogy i think on the show Penny Dreadful, the [antique wind up] toy carriage attached to a stick went round the barn but the carriage itself doesnt need to turn. i'll look for it when i get home.

kinda this concept.

f11a9018f679e9f28ff39bcc5a320b0a.jpg


we had a great toy as kids - called the whirly bird (not sure if it came from the states)

a helicopter attached to a central column - it could go up and down


Source: https://www.youtube.com/watch?v=MhkRnjLxQBc
 
i hear you, it is counterintuitive for me too. but look at the toy, the plane doesnt move or tilt. it remains in it's exact same position no matter where it is on the circle.
In the pic, are the noses not pointing in opposite direction? They can't get that way without change.
 
In the pic, are the noses not pointing in opposite direction? They can't get that way without change.
look at the horses then. the horses are parellel to the "earth" ie the side of the carousel. they remain in exactly the same parellel position no matter where they move on the carousel.
 
look at the horses then. the horses are parellel to the "earth" ie the side of the carousel. they remain in exactly the same parellel position no matter where they move on the carousel.
Parellel yes but there are not facing the same way. The entire time. I think what the argument is coming down to is RELATIVE direction.[/QUOTE]
 
Yes but gravity still would have to bring the nose in line with the dotted flight path. There is no way the nose can stay pointed perfectly to the right the entire circle.

does it help if you image someone on the plane holding a spirit level - level

why would the spirit level remain level when the plane has flown another qtr round the earth
 
@Provemewrong, did you try drawing a scale diagram of the problem?

I think you are getting a little caught up with the analogies of things that are much smaller. The Earth, as you know, is incredibly large compared to a plane.

Try drawing a scale diagram of 100 miles of flight over a curved earth of radius 3959 miles, then post it here.
 
Parellel yes but there are not facing the same way
they are facing the same way really, but that doesnt matter. the sides of the horses remain parallel to the carousel base, just as the bottom of the plane remains parallel to the earth surface. Turn the carosel on its side so the horses are in a plane position to better see it.
 
does it help if you image someone on the plane holding a spirit level - level

why would the spirit level remain level when the plane has flown another qtr round the earth
Only if the earth is flat lol. The horses are not facing the same direction from the cameras point of view. The camera is on the same room, which we can compare to the sky.
 
Only if the earth is flat lol. The horses are not facing the same direction from the cameras point of view. The camera is on the same room, which we can compare to the sky.
well when the plane is on the right side of the globe its tail fin is pointing right and when the plane is on the left side of the globe it's tail fin is pointing left.. if we were on the moon watching it from a still camera.
 
well when the plane is on the right side of the globe its tail fin is pointing right and when the plane is on the left side of the globe it's tail fin is pointing left.. if we were on the moon watching it from a still camera.
Correct. But in order for that to be the case the plane has change direction at some point ( at least from our perspective on the moon).
 
This is a video of control line model aircraft in action

The plane is attached to the operator by a series of chords as the plane flies the thrust of the plane wants to take it in a straight line, but due to the fact it's attached to the controller by chords it can't and is 'forced' to describe an arc around the operator.

Now imagine the operator is the earth, and the line is the earths gravity ('attached' to the underside of the plane and not the wing - obviously), as the plane flies in a 'straight' line, the control chord (gravity) makes it follow a curve around the operator (earth).

You can try this yourself, control line aircraft are fairly easy to fly and you can get them from under £30 ($40)
 
Correct. But in order for that to be the case the plane has change direction at some point ( at least from our perspective on the moon).

outside perspective, that's irrelevant. if you look at the carousel toys above. the plane, or horse, or helicopter themselves stay in the exact same position at all times.
They stay "level" .

Let it stew in your brain a bit. maybe @tadaaa can add more planes at 2o'cock and 8o'clock to his graphic above.to help you visualize more.
 
outside perspective, that's irrelevant. if you look at the carousel toys above. the plane, or horse, or helicopter themselves stay in the exact same position at all times.
They stay "level" .

Let it stew in your brain a bit. maybe @tadaaa can add more planes at 2o'cock and 8o'clock to his graphic above.to help you visualize more.
Would the perspective not be the same from the sky as the moon? ( other than size and visibility)
 
Would the perspective not be the same from the sky as the moon? ( other than size and visibility)
if you walk around a maypole with a taut 10 foot rope and keep your left shoulder exactly parallel to the maypole, would your perspective change? no. your body would be in the same relation to the pole as it was 45degrees earlier. your view (the scenery) would change.

Me watching you walk around the Maypole has nothing to do with the position of YOUR body in space compared to the maypole.


edited persons to ease visual
 
Here's a scale diagram of a plane at 36,000 feet (7 miles up) flying 100 miles in level flight.
20160930-105706-u33e8.jpg

20160930-111234-ifylp.jpg



20160930-105924-1izbs.jpg


Planes fly along slightly curved paths. They stay approximately the same height above sea level when in level flight. That's all.

https://ggbm.at/Exam7fne
 
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i think your second pic is going to throw him as he wont realize that the "flatish" 100 miles will "move" with the plane.

There was a light dashed line in the middle pic that I just removed. Is that what you meant?
 
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