# The Flat Earth Society

## Flat Earth Discussion Boards => Flat Earth Theory => Topic started by: fisherman on April 27, 2021, 09:57:51 PM

Title: Question about the Vomit Comet
Post by: fisherman on April 27, 2021, 09:57:51 PM
Hoping one of you good people who are familiar with how the Vomit Comet works can clear something up for me.

My understanding is that during parabolic motion, thrust and drag cancel each other out and lift is reduced to zero because of the angle. That leaves just gravity working on the plane and since the plane and the occupants are falling together, there is a sensation of weightlessness.

I don't see how this could work with FE/UA.  Without any other forces to counteract it, the UA force should continue to accelerate the plane up, pushing the floor of the plane up and creating the sensation of weight.

Essentially, no different than our friend in the enclosed rocket ship that can't tell if he's being accelerated up or gravity is pulling him down.
Title: Re: Question about the Vomit Comet
Post by: WTF_Seriously on April 28, 2021, 02:22:31 PM

I don't see how this could work with FE/UA.  Without any other forces to counteract it, the UA force should continue to accelerate the plane up, pushing the floor of the plane up and creating the sensation of weight.

In essence, UA is just another form of drag.  If thrust can overcome drag, there's no reason to believe it doesn't also overcome UA.
Title: Re: Question about the Vomit Comet
Post by: fisherman on April 28, 2021, 02:58:51 PM
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In essence, UA is just another form of drag.  If thrust can overcome drag, there's no reason to believe it doesn't also overcome UA.

I was thinking more like UA is thrust...that you can never adjust or turn off like you can a rocket engine.  In order to be in free fall, thrust and drag must be equal.  Since you can't adjust the thrust UA causes, how do you equalize the drag so that the plane is in freefall?

Don't know enough about how it works, which is why I asked.
Title: Re: Question about the Vomit Comet
Post by: WTF_Seriously on April 28, 2021, 03:49:36 PM
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In essence, UA is just another form of drag.  If thrust can overcome drag, there's no reason to believe it doesn't also overcome UA.

I was thinking more like UA is thrust...that you can never adjust or turn off like you can a rocket engine.  In order to be in free fall, thrust and drag must be equal.  Since you can't adjust the thrust UA causes, how do you equalize the drag so that the plane is in freefall?

Don't know enough about how it works, which is why I asked.

Thrust/drag doesn't really matter.  Think RE.  To simulate freefall, the plane must overcome aerodynamic drag while equaling acceleration due to gravity.  In FE, the plane must overcome aerodynamic drag while equalling acceleration due to UA.  In either model, those would be the two things acting to simulate freefall, no?
Title: Re: Question about the Vomit Comet
Post by: SteelyBob on April 28, 2021, 04:19:52 PM
My understanding is that during parabolic motion, thrust and drag cancel each other out and lift is reduced to zero because of the angle. That leaves just gravity working on the plane and since the plane and the occupants are falling together, there is a sensation of weightlessness.

Nearly. Yes, thrust will be adjusted to pretty much cancel out drag - this prevents the occupants from falling forwards or backwards with respect to the fuselage.  Speed will still reduce because of the component of weight acting along the aircraft's flightpath axis - a ballistic profile. The angle of attack is controlled to give zero lift, starting at around 45 degrees nose up and ending at around 45 nose down - the pilot pushes forward on the controls until 0gz is achieved.

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I don't see how this could work with FE/UA.  Without any other forces to counteract it, the UA force should continue to accelerate the plane up, pushing the floor of the plane up and creating the sensation of weight.

Whilst I disagree with the FE/UA proposition in the strongest possible terms, of all the many things that are obviously wrong with it, this isn't it. In a FE/UA world, the earth and the atmosphere would be accelerating upwards. To fly normally, aircraft would need to generate lift just as they currently do. A ballistic flight profile would work in just the same way.

I think the point you are missing is that the UA 'force' is deemed to only act on the earth - everything else is then pushed up by the earth. You are correct, in that if UA pushed on everything, then the parabolic flight profile wouldn't work. But then nor would anything - just walking around on the ground wouldn't work.

Title: Re: Question about the Vomit Comet
Post by: c0i9z on April 28, 2021, 04:25:57 PM
You have to remember that universal acceleration is not actually universal. Only some things get directly accelerated. Specifically, all the things that it's difficult to interact with directly. Planets, stars, whatever is supposed to be under the Earth that's actually experiencing the acceleration. All the things you might have actual experience with, like rocks, plants, animals, water, air, planes, etc. aren't apparently affected, for some mysterious reason. Otherwise, you'd get rocks that hover when they're dropped, something which I don't recall ever seeing.
Title: Re: Question about the Vomit Comet
Post by: fisherman on April 28, 2021, 05:48:25 PM
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I think the point you are missing is that the UA 'force' is deemed to only act on the earth - everything else is then pushed up by the earth. You are correct, in that if UA pushed on everything, then the parabolic flight profile wouldn't work
.

Well, maybe it is the UA/FE model I don't understand.  But from other discussions, mostly about skydiving, I thought that the UA force accelerated the atmosphere along with the earth and that anything in the atmosphere accelerates along with it.  And that the reason that the earth eventually "catches up" is because drag slows down the acceleration of whatever is in the atmosphere.  It is accelerating at a slower rate, so eventually the earth is able to cover the distance between them.

The wiki defines terminal velocity as ‘When the acceleration of the falling object is equal to the acceleration of the Earth, the object has reached terminal velocity relative to the Earth.’

A “falling object” is being accelerated...by something other than gravity.  The Vomit Comet is a “falling object” what’s accelerating it? The whole concept of terminal velocity in UA makes it impossible to use the same formula in UA than gravity, but that's a different thread.

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All the things you might have actual experience with, like rocks, plants, animals, water, air, planes, etc. aren't apparently affected, for some mysterious reason. Otherwise, you'd get rocks that hover when they're dropped, something which I don't recall ever seeing.

The UA force doesn’t work directly on thing on the surface of the earth, but it does effect them.  Otherwise, the “pinning force” that is described in the wiki wouldn’t be necessary.  That’s their explanation for why we don’t see things hover.

Go back to the often used analogy used to describe the EP.  The closed box has no other force on it other than it is being accelerated up by some force and that causes whatever is in the box to become  pinned to the floor.

A plane in parabolic flight is the equivalent of the closed box.  It has no other force on it other than it is being accelerated up by some force.  If that force causes the person in the box (who isn’t being directly accelerated) to be pinned to the floor, the same thing should happen to people in the plane, who also aren’t directly effected by the accelerating force.

EDIT: Another thing to consider is that even if the plane is neither accelerating upn or accelerating down, its going to take a lot less than the 45 seconds or so that the plane is in freefall before an earth accelerating up at 1g to slams into it.
Title: Re: Question about the Vomit Comet
Post by: SteelyBob on April 28, 2021, 06:39:13 PM
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I think the point you are missing is that the UA 'force' is deemed to only act on the earth - everything else is then pushed up by the earth. You are correct, in that if UA pushed on everything, then the parabolic flight profile wouldn't work
.

Well, maybe it is the UA/FE model I don't understand.  But from other discussions, mostly about skydiving, I thought that the UA force accelerated the atmosphere along with the earth and that anything in the atmosphere accelerates along with it.  And that the reason that the earth eventually "catches up" is because drag slows down the acceleration of whatever is in the atmosphere.  It is accelerating at a slower rate, so eventually the earth is able to cover the distance between them.

The wiki defines terminal velocity as ‘When the acceleration of the falling object is equal to the acceleration of the Earth, the object has reached terminal velocity relative to the Earth.’

A “falling object” is being accelerated...by something other than gravity.  The Vomit Comet is a “falling object” what’s accelerating it? The whole concept of terminal velocity in UA makes it impossible to use the same formula in UA than gravity, but that's a different thread.

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All the things you might have actual experience with, like rocks, plants, animals, water, air, planes, etc. aren't apparently affected, for some mysterious reason. Otherwise, you'd get rocks that hover when they're dropped, something which I don't recall ever seeing.

The UA force doesn’t work directly on thing on the surface of the earth, but it does effect them.  Otherwise, the “pinning force” that is described in the wiki wouldn’t be necessary.  That’s their explanation for why we don’t see things hover.

Go back to the often used analogy used to describe the EP.  The closed box has no other force on it other than it is being accelerated up by some force and that causes whatever is in the box to become  pinned to the floor.

A plane in parabolic flight is the equivalent of the closed box.  It has no other force on it other than it is being accelerated up by some force.  If that force causes the person in the box (who isn’t being directly accelerated) to be pinned to the floor, the same thing should happen to people in the plane, who also aren’t directly effected by the accelerating force.

The issue is that normal newtonian physics only works in an inertial reference frame. For normal everyday calculations, we can consider earth to be inertial frame of reference (it's actually not quite, but close enough), with a gravity force equal to mg acting on everything. With that in place, all the maths makes sense.

FE/UA turns that on its head. In it, everything is being accelerated by, as I understood it, the earth. It is as if we are floating in space in a spaceship which then fires its rocket engine and starts accelerating at 1g - we all squash down to the base of the spaceship for as long as it accelerates. If the cabin of the spaceship was pressurised, then there would be a pressure gradient, albeit a very small one, detectable in the 'atmosphere'.

In that environment, we would no longer be in an inertial frame of reference, because everything is accelerating. So if I throw a ball to you, it doesn't just fly horizontally with respect to the spaceship, but rather 'falls'. Terminal velocity, in that context, would be achieved when the drag force acting on the object was equal to mg - exactly the same as on the inertial 'normal' planet earth.

So FEers are correct (for a change!) on this one - were we to exist on a UA/FE world, it would be indistinguishable from our current environment.

Indistinguishable, that is, apart from the stars and planets rotating beautifully around our celestial poles, and the massive discrepancy between observed distances between known points, and all the many other things that, aside from the actual footage of our beautiful round earth viewed from afar, clearly point to it being globe shaped.
Title: Re: Question about the Vomit Comet
Post by: fisherman on April 28, 2021, 08:50:41 PM
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The issue is that normal newtonian physics only works in an inertial reference frame. For normal everyday calculations, we can consider earth to be inertial frame of reference (it's actually not quite, but close enough), with a gravity force equal to mg acting on everything. With that in place, all the maths makes sense.

Newton v Relativity has nothing to do with the point I am making.

If the plane is only subject to gravity, it will go into freefall and the occupants will “float”.  If the plane is only subject to UA, then the floor of the plane will be pinned against the occupants and they won’t float.

That’s true by Newtonian physics and also true according to relativity.

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So FEers are correct (for a change!) on this one - were we to exist on a UA/FE world, it would be indistinguishable from our current environment.

Indistinguishable, that is, apart from the stars and planets rotating beautifully around our celestial poles, and the massive discrepancy between observed distances between known points, and all the many other things that, aside from the actual footage of our beautiful round earth viewed from afar, clearly point to it being globe shaped.

A lot of Rers seem to buy into this notion as much as the Fers and its simply not true. I think it come from the belief that the EP, and relativity in general makes all motion relative. It doesn’t, It only makes unaccelerated motion relative.  Which overall, accounts for a small portion of the motion we see in real life.

So if the occupants in the Vomit Comet were being accelerated by the UA force, they’d know it, just like the guy in the closed box floating around in space.  If the floor came up and hit him or the he hit the floor, either way he knows he’s being accelerated.  He may not know why, but he knows he is.

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Terminal velocity, in that context, would be achieved when the drag force acting on the object was equal to mg - exactly the same as on the inertial 'normal' planet earth.

The difference is If terminal velocity is defined as “when the falling object is accelerating at the same rate as the earth”...then the falling object is still accelerating, which means its velocity continues to increase.  As opposed to the RE/gravity concept of terminal velocity… when an object is no longer accelerating and its velocity stops increasing. You’d have to use two different formulas to determine those two very different things.

Anyway, back to my original question.  It seems like it boils down to whether or not the UA force would cause the atmosphere to accelerate and the plane along with it.
Title: Re: Question about the Vomit Comet
Post by: WTF_Seriously on April 28, 2021, 09:03:39 PM

If the plane is only subject to gravity, it will go into freefall and the occupants will “float”.  If the plane is only subject to UA, then the floor of the plane will be pinned against the occupants and they won’t float.

So if the occupants in the Vomit Comet were being accelerated by the UA force, they’d know it,....

Here's where you're misunderstanding UA.  Someone mentioned the issue before.  Not in any way discussing the validity or possibility of the effect.

The plane and the person are NOT being accelerated by UA.  That is why they 'fall'.  Only the earth is being accelerated by UA.  The earth, in turn, pushes the atmosphere up with it.  In FE, a plane flies because the lift generated causes it to accelerate upward at the same rate as the air column, being pushed up by the earth, surrounding it.  The person inside the aircraft is pinned to the aircraft's floor because that person is not naturally accelerated upward by UA.

Once thrust is reduced, the plane loses the lift ability to maintain the upward acceleration.  When enough thrust is reduced, the acceleration of the plane upward will become zero, the same as the passenger.  This results in weightlessness.
Title: Re: Question about the Vomit Comet
Post by: fisherman on April 28, 2021, 10:38:52 PM
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The plane and the person are NOT being accelerated by UA.

Well, like i said, that seems to be thrust of the issue :).  The wiki implies that the plane and the person would be accelerated by UA.  It would be nice if an FEr would clarify.

The wiki defines terminal velocity as When the acceleration of the falling object is equal to the acceleration of the Earth, the object has reached terminal velocity relative to the Earth.  And note that it's in the "universal acceleration" section of the wiki.  To me that implies that under UA, a "falling object" is being accelerated.

I want to clarify this statement.

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With that in place, all the maths makes sense

The maths only make sense if you are considering unaccelerated motion. GR divides all motion into geodetic, unaccelerated motion that is traveling along the straightest possible path under no force and non-geodetic, accelerated motion not along the straightest possible path and under a force.

No change of perspective, manipulation of coordinates or maths can change one into the other.  Geodetic motion will always have the straightest possible worldline, non-geodetic will not.  If you plot the worldline of an earth that is not under any force, you will get the straightest possible path through spacetime. If you plot the worldline of an earth that is under acceleration by UA, you will get something other than the straightest possible line.

That is what the maths show according to GR. An earth under acceleration will follow a hyperbola. An earth not under acceleration will not.
Title: Re: Question about the Vomit Comet
Post by: fisherman on April 28, 2021, 11:04:43 PM
A question for anyone who can answer, but from an FE would be nice..

If "When the acceleration of the falling object is equal to the acceleration of the Earth, the object has reached terminal velocity relative to the Earth".

doesn't mean that a "falling object" is accelerated by UA, what does it mean?
Title: Re: Question about the Vomit Comet
Post by: SteelyBob on April 29, 2021, 06:10:52 AM
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The issue is that normal newtonian physics only works in an inertial reference frame. For normal everyday calculations, we can consider earth to be inertial frame of reference (it's actually not quite, but close enough), with a gravity force equal to mg acting on everything. With that in place, all the maths makes sense.

Newton v Relativity has nothing to do with the point I am making.

If the plane is only subject to gravity, it will go into freefall and the occupants will “float”.  If the plane is only subject to UA, then the floor of the plane will be pinned against the occupants and they won’t float.

That’s true by Newtonian physics and also true according to relativity.

I entirely agree - I wasn't bringing relativity into this. I'm simply talking about an inertial reference frame - a frame of reference, or datum, that is not accelerating. So the surface of our earth is a good inertial reference point (ignoring very small error due to rotation and the centripetal acceleration towards the sun - barely measurable). You could also use a vehicle travelling at constant speed. To borrow from another thread, you and I could play table tennis on a moving bullet train, and the ball would fly just as it would if we were at rest in a station. To calculate the ball's motion we could choose the train as a reference point - a valid choice, as it is inertial (ie non accelerating),and a wise one, as it keeps things simple - we measure all velocities etc with respect to the train. We could if wished, choose the earth, but then things get complex, because all the velocities would have the motion of the train superimposed on them, meaning a negative velocity with respect to the train might still be positive with respect to the earth.

But it all breaks down if the train accelerates. If you hit the ball to me and the train brakes suddenly, then the motion of the ball with respect to the train will not be what we would expect at all - we would have to choose the earth as a datum, or perhaps compensate for the acceleration in our calculations - engineers sometimes use d'Alembert forces to do this. You sometimes see it being done with circular motion - they add a 'centrifugal' d'Alembert force, even though no such thing exists, to change an accelerating reference frame into an inertial one.

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If "When the acceleration of the falling object is equal to the acceleration of the Earth, the object has reached terminal velocity relative to the Earth".
doesn't mean that a "falling object" is accelerated by UA, what does it mean?

Again, the FEers are sort of, oddly correct here. The whole thing is nonsense, clearly, but as a thought exercise it does work.

Remember, the earth in UA/FE is not an inertial reference frame - you can't do newtonian maths with respect to the surface and expect things to work. So we have to imagine ourselves outside the earth, stationary, watching it accelerate past our fixed datum point. The earth is accelerating 'up' at 1g. The earth's atmosphere will eventually achieve a steady state whereby it ends up with a pressure/density gradient just like our atmosphere does on our beautiful, globe-shaped earth. Once stabilised in that state, it too will accelerate at 1g - every small 'parcel' of air will experience a net 'mg' force pushing it up. So we have a planet and an atmosphere accelerating upwards at 1g. If you then drop a ball from a hot air balloon or similar, the ball will initially be stationary with respect to the balloon, so it will have whatever velocity with respect to us observing that the earth/atmosphere/balloon did at the point of release. But it will retain that velocity, while the atmosphere and balloon etc keep accelerating, and so will appear to 'fall' from our perspective. As it falls it will start to experience a force, increasing with the square of the velocity difference, as the air rushes past it. At some point the drag force will reach mg, at which point the ball's upward acceleration will equal that of earth/atmosphere/balloon. However, it will retain a constant velocity difference. With respect to the earth's surface it is falling at terminal velocity. With respect to us, it is accelerating upwards at the same rate as the earth/atmosphere/balloon, but is at a slightly lower velocity. So the earth might be going at 1000m/s, and our ball might be going at 970m/s, with each adding 9.8m/s to their speed every second - the ball has a terminal velocity of 30m/s.

Note: none of the above obviates the numerous issues with the UA model, or indeed the many obvious flaws in the FE model generally.
Title: Re: Question about the Vomit Comet
Post by: fisherman on April 29, 2021, 01:28:26 PM
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The issue is that normal newtonian physics only works in an inertial reference frame. For normal everyday calculations, we can consider earth to be inertial frame of reference (it's actually not quite, but close enough), with a gravity force equal to mg acting on everything. With that in place, all the maths makes sense.

Newton v Relativity has nothing to do with the point I am making.

If the plane is only subject to gravity, it will go into freefall and the occupants will “float”.  If the plane is only subject to UA, then the floor of the plane will be pinned against the occupants and they won’t float.

That’s true by Newtonian physics and also true according to relativity.

I entirely agree - I wasn't bringing relativity into this. I'm simply talking about an inertial reference frame - a frame of reference, or datum, that is not accelerating. So the surface of our earth is a good inertial reference point (ignoring very small error due to rotation and the centripetal acceleration towards the sun - barely measurable). You could also use a vehicle travelling at constant speed. To borrow from another thread, you and I could play table tennis on a moving bullet train, and the ball would fly just as it would if we were at rest in a station. To calculate the ball's motion we could choose the train as a reference point - a valid choice, as it is inertial (ie non accelerating),and a wise one, as it keeps things simple - we measure all velocities etc with respect to the train. We could if wished, choose the earth, but then things get complex, because all the velocities would have the motion of the train superimposed on them, meaning a negative velocity with respect to the train might still be positive with respect to the earth.

But it all breaks down if the train accelerates. If you hit the ball to me and the train brakes suddenly, then the motion of the ball with respect to the train will not be what we would expect at all - we would have to choose the earth as a datum, or perhaps compensate for the acceleration in our calculations - engineers sometimes use d'Alembert forces to do this. You sometimes see it being done with circular motion - they add a 'centrifugal' d'Alembert force, even though no such thing exists, to change an accelerating reference frame into an inertial one.

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If "When the acceleration of the falling object is equal to the acceleration of the Earth, the object has reached terminal velocity relative to the Earth".
doesn't mean that a "falling object" is accelerated by UA, what does it mean?

Again, the FEers are sort of, oddly correct here. The whole thing is nonsense, clearly, but as a thought exercise it does work.

Remember, the earth in UA/FE is not an inertial reference frame - you can't do newtonian maths with respect to the surface and expect things to work. So we have to imagine ourselves outside the earth, stationary, watching it accelerate past our fixed datum point. The earth is accelerating 'up' at 1g. The earth's atmosphere will eventually achieve a steady state whereby it ends up with a pressure/density gradient just like our atmosphere does on our beautiful, globe-shaped earth. Once stabilised in that state, it too will accelerate at 1g - every small 'parcel' of air will experience a net 'mg' force pushing it up. So we have a planet and an atmosphere accelerating upwards at 1g. If you then drop a ball from a hot air balloon or similar, the ball will initially be stationary with respect to the balloon, so it will have whatever velocity with respect to us observing that the earth/atmosphere/balloon did at the point of release. But it will retain that velocity, while the atmosphere and balloon etc keep accelerating, and so will appear to 'fall' from our perspective. As it falls it will start to experience a force, increasing with the square of the velocity difference, as the air rushes past it. At some point the drag force will reach mg, at which point the ball's upward acceleration will equal that of earth/atmosphere/balloon. However, it will retain a constant velocity difference. With respect to the earth's surface it is falling at terminal velocity. With respect to us, it is accelerating upwards at the same rate as the earth/atmosphere/balloon, but is at a slightly lower velocity. So the earth might be going at 1000m/s, and our ball might be going at 970m/s, with each adding 9.8m/s to their speed every second - the ball has a terminal velocity of 30m/s.

Note: none of the above obviates the numerous issues with the UA model, or indeed the many obvious flaws in the FE model generally.

Would quibble with a couple of points,  but none are relevant to this discussion.  The important point is that you acknowledge that an object in the atmosphere of an earth accelerating upwards, will also accelerate up. And it will accelerate up at 1g.

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Remember, the earth in UA/FE is not an inertial reference frame - you can't do newtonian maths with respect to the surface and expect things to work.

I’m not using Newtonian maths.  In relativity, the worldline of an accelerating earth (or anything accelerating at relativistic speeds) will be a hyperbola. The worldline of an an object accelerating at less than relativistic speed will not be a hyperbola, but it will be diagonal.  The worldline of an object that is not accelerating will follow tbe straightest possible path through spacetime.  In flat space spacetime, the worldline will be vertical, as an object at rest is moving through time but not through space. In curved space time, it will follow the curve of time, but won’t travel in space.

Frame of reference is irrelevant.  First of all, the occupants in the plane are in the same frame of reference as the plane, so if the plane is accelerating in its own frame, the occupants will experience that acceleration.  But more importantly acceleration is not relative .  If something is accelerating, it has a force on it.  Changing frames of reference doesn’t make that force go away.  It’s either there or it isn’t and objects and if its there, people being accelerated will experience the effects of the acceleration.  The perception of the force and the resulting velocities may be different in a different frame, but the fact of the force and the fact of acceleration doesn’t change.  Something is either accelerating due to a force or its not.  That is an absolute. No change in frame of reference changes that.  Clear enough?

So if, no matter what frame of reference you are in, the atmosphere is accelerating the plane up, at 1g, and is the only force on the plane how is it that the floor of the plane is not pushed against the occupants?
Title: Re: Question about the Vomit Comet
Post by: SteelyBob on April 29, 2021, 06:03:09 PM
I’m not using Newtonian maths.

I think that's the issue. Keep it simple - there's no need at all to invoke relativity at all to demonstrate that this works.

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Frame of reference is irrelevant.  First of all, the occupants in the plane are in the same frame of reference as the plane, so if the plane is accelerating in its own frame, the occupants will experience that acceleration.
It's enormously relevant. If it's accelerating, then it isn't an inertial reference frame. You either need to pick an inertial reference point to measure displacement and velocities from, or you need to correct for the acceleration by means of d'Alembert-style inertial 'forces' that correct the errors.

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But more importantly acceleration is not relative .  If something is accelerating, it has a force on it.
Agreed...but if the object is stationary and the earth is accelerating towards it then there's no force on it...

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Changing frames of reference doesn’t make that force go away.

But this discussion is about the thought experiment of a permanently accelerating flat earth versus what we know and (I think?) agree to be the truth, which is a globe earth exerting a force on everything around it equal to mg. The question is whether objects would behave the same in the two systems - would they trace, for example, the same flightpath in ballistic flight? Would objects have the same apparent terminal velocity? These things require us to measure the displacement, s, relative to a fixed point on the earth's surface. So a ball dropped from height above our accelerating FE would experience no force at all - viewed from afar it would actually be stationary. And yet it would appear to accelerate towards the earth, despite having no force acting on it. The displacement between the earth and the ball would change at the same rate - it matters not whether the ball is accelerating, or the earth.

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So if, no matter what frame of reference you are in, the atmosphere is accelerating the plane up, at 1g, and is the only force on the plane how is it that the floor of the plane is not pushed against the occupants?

Because, like the dropped ball above, in the FE/UA case, viewed from a fixed point off the earth, the aircraft would be stationary (or rather, at a constant velocity) and the earth would be accelerating towards it. The atmosphere wouldn't be pushing on it, as the pilot is not demanding lift from the wings.

Make sense?
Title: Re: Question about the Vomit Comet
Post by: fisherman on April 29, 2021, 07:16:21 PM
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Make sense?

No.  Because of the point I keep making and you keep ignoring is that frame of reference is irrelevant

From a fixed point on the earth the plane would not appear to be stationary or at a constant velocity because acceleration is not relative .  From a fixed point on the earth, the plane would appear to be accelerating at 1g because acceleration is not relative.  I can’t make it any clearer than that.  For your explanation to make sense, then acceleration must be relative, and its not.

Even, if it was.  That wouldn’t change what the plane and its occupants are experiencing.  So what if someone else on the surface doesn’t perceive that the plane is accelerating? What matters is whether or not the occupants experience acceleration.  Someone else’s perception of what they experience doesn’t change what they experience.

If someone in another frame of reference can’t perceive the plane’s acceleration, then according to you the acceleration doesn’t exist. By that logic, if the observer closes his eyes and can no longer observe the plane, the plane doesn’t exist. Not to get all philosophical, but it is fascinating to me the way people, FE and RE alike seem to think that someone's perception of your reality, changes your reality.
Title: Re: Question about the Vomit Comet
Post by: WTF_Seriously on April 29, 2021, 07:40:05 PM
So if, no matter what frame of reference you are in, the atmosphere is accelerating the plane up, at 1g, and is the only force on the plane how is it that the floor of the plane is not pushed against the occupants?

That's exactly what happens when the plane is in level flight and the occupants feel weight.  Just like a plane flying on RE.

During FE weightlessness, the thrust of the plane is such that it is forcing itself through the accelerating atmosphere in order to remain motionless just like the passengers.

Step outside the dome for a moment and position yourself stationary as you watch the approaching earth.  Earth plane and passenger are all approaching you at acceleration = G. Plane is in level flight and it's passengers are pinned to the floor experiencing weight.  This occurs because only the earth is affected by UA, not the plane and passengers.  At the moment the plane is level with you, the pilot slams the plane downward at acceleration = G.  You will see the plane and passengers stop motionless as the earth continues to rise to meet them.  At this time, the passengers will not feel pinned to the floor as neither they nor the plane is accelerating upwards any longer.

Edited to add:  Had to change my thought slightly.  When the pilot thrusts the plane downward, the plane and passenger will continue at constant velocity not stop entirely.  The key is that they will cease accelerating thus the weightless feeling.
Title: Re: Question about the Vomit Comet
Post by: fisherman on April 29, 2021, 08:13:26 PM
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During FE weightlessness, the thrust of the plane is such that it is forcing itself through the accelerating atmosphere in order to remain motionless just like the passengers.

There is no thrust in parabolic flight.  Thrust and drag cancel each other out.
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This occurs because only the earth is affected by UA, not the plane and passengers.

I already showed how that is not the case according to RE theory.  A falling object accelerates.  It says that plainly on the wiki.
Title: Re: Question about the Vomit Comet
Post by: SteelyBob on April 29, 2021, 08:17:43 PM
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Make sense?
No.  Because of the point I keep making and you keep ignoring is that frame of reference is irrelevant
No, that's not fair - I'm certainly not ignoring it. I'm disagreeing with you, and that's fine - this is a debating forum, after all. Again, frame of reference is enormously important - if it's accelerating, it ain't inertial.

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From a fixed point on the earth the plane would not appear to be stationary or at a constant velocity because acceleration is not relative .  From a fixed point on the earth, the plane would appear to be accelerating at 1g because acceleration is not relative.  I can’t make it any clearer than that.  For your explanation to make sense, then acceleration must be relative, and its not.

Even, if it was.  That wouldn’t change what the plane and its occupants are experiencing.  So what if someone else on the surface doesn’t perceive that the plane is accelerating? What matters is whether or not the occupants experience acceleration.  Someone else’s perception of what they experience doesn’t change what they experience.

If someone in another frame of reference can’t perceive the plane’s acceleration, then according to you the acceleration doesn’t exist. By that logic, if the observer closes his eyes and can no longer observe the plane, the plane doesn’t exist. Not to get all philosophical, but it is fascinating to me the way people, FE and RE alike seem to think that someone's perception of your reality, changes your reality.

Ok let's try putting some numbers on it to see if it helps.

Imagine we're on a spaceship, that isn't accelerating, just floating in space, watching the earth, atmosphere and plane accelerate past us, from left to right. Let's say, for the sake of argument, that the acceleration hasn't being going on for very long, and the whole system is travelling at 1000m/s, increasing by 9.8m/s every second. The earth is being pushed by some mysterious force, the atmosphere is being pushed by the earth, the wings are being pushed by the atmosphere, the fuselage by the wings, the seats by the fuselage, the passengers by the seats. And so on.

From our position, we see an accelerating earth/atmosphere system whizz by at an ever increasing velocity. So far so good - agree?

Then, let's imagine that at the precise moment earth hits 1000m/s (relative to our datum on the spaceship) the pilot pushes forward on his controls until the accelerometer on his instrument panel reads '0g'. He throttles back to keep a roughly constant speed. The plane, from our position, retains its 1000m/s velocity. The earth continues to accelerate. After 1 second, the earth is now doing 1009.8m/s, increasing constantly, but our plane remains at 1000m/s left to right. The passengers feel weightless, because there is no force acting on them. From the viewpoint of a person on earth, the aircraft would appear to be ballistic, in a descending parabola, until the pilot recovers from the dive or the aircraft crashes.

And this is the key point - from the point of view of somebody in the earth/atmosphere/plane system, there is no discernible difference between a stationary earth exerting 1g and an ever accelerating earth - all the forces, all the relative velocities - it's all the same. That doesn't of course mean the earth is flat.
Title: Re: Question about the Vomit Comet
Post by: WTF_Seriously on April 29, 2021, 08:27:51 PM
There is no thrust in parabolic flight.  Thrust and drag cancel each other out.

No.  There is thrust.  Thrust = Drag that is how they cancel each other out.

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I already showed how that is not the case according to RE theory.  A falling object accelerates.  It says that plainly on the wiki.

We're not talking about RE theory.  We're talking about UA/FE theory.  In UA/FE theory, UA doesn't act upon the plane and passenger.  If it did then each would naturally float.  'Falling' in FE is earth accelerating to meet object as opposed to object accelerating to meet earth.  The two are equivalent.
Title: Re: Question about the Vomit Comet
Post by: fisherman on April 29, 2021, 10:22:06 PM
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In UA/FE theory, UA doesn't act upon the plane and passenger.

Yes it does.

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When the acceleration of the falling object is equal to the acceleration of the Earth, the object has reached terminal velocity relative to the Earth.

https://wiki.tfes.org/Universal_Acceleration#Terminal_Velocity
Title: Re: Question about the Vomit Comet
Post by: WTF_Seriously on April 30, 2021, 02:16:41 AM
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In UA/FE theory, UA doesn't act upon the plane and passenger.

Yes it does.

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When the acceleration of the falling object is equal to the acceleration of the Earth, the object has reached terminal velocity relative to the Earth.

https://wiki.tfes.org/Universal_Acceleration#Terminal_Velocity

If UA acted on the passenger, when a parachutist steps out of a plane they would float under UA.  Even FEers know a parachutist 'falls'.  The only way this happens is if the parachutist isn't acted upon by UA.  It's really not that difficult a concept.
Title: Re: Question about the Vomit Comet
Post by: fisherman on April 30, 2021, 03:05:59 AM
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If UA acted on the passenger, when a parachutist steps out of a plane they would float under UA.  Even FEers know a parachutist 'falls'.  The only way this happens is if the parachutist isn't acted upon by UA.  It's really not that difficult a concept.

Then maybe DuncanDoenitz can clear it up for us.

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Aerodynamic lift is maintaining the aircraft at a constant altitude, so it (and its occupants) are supported by the atmosphere (atmosplane - yuk!), which is supported by the Earth.  Thus, the aircraft and its occupants, by implication, have identical acceleration and instantaneous velocity as the Earth, so are accelerating upward at 9.81 m/s/s due to UA (also yuk!).

When you leave the aircraft you have the same instantaneous velocity as Earth and atmosphere, hence feel no windrush.  However, as you are now not being accelerated, the earth continues to accelerate towards you at 9.81m/s/s.  In a vacuum, you would remain at constant velocity until the Earth (because it is still accelerating) hits you.

In practice because you are in the, still accelerating, atmosphere you start to accelerate upwards again and begin to feel windrush as aerodynamic drag takes effect, until you reach terminal velocity. (And that's terminal velocity downwards in RE, but terminal velocity upwards in FE!).

At this point your body's acceleration is identical to Earth's but, because of the period when you had reduced acceleration, your velocity is less than Earth's so it still hits you.

https://forum.tfes.org/index.php?topic=17742.msg237132#msg237132

He seems to be interpreting the what the wiki says the same as I am.  The falling object is accelerated up by the atmosphere.  If that causes a contradiction with anything else that FE proposes, is that really a surprise?  The whole theory is full of contradictions.

But actually, it doesn't contradict it. The parachutist does "float", for awhile anyway. He accelerates up at a slower rate than the earth because of drag.  Since the parachutist is accelerating up at a slower rate than the earth is accelerating up, the earth eventually closes the gap.

Title: Re: Question about the Vomit Comet
Post by: DuncanDoenitz on April 30, 2021, 07:15:59 AM
@ Fisherman; Yes.

Putting aside the "celestial" objects (who's various FE philosophies I completely fail to understand), all "worldly" matter only feels the effects of UA either directly, or indirectly, from the acceleration of Earth.  If you sit on a chair, you are accelerated second-hand by the chair, which is being accelerated by the floor, which is being accelerated by Earth.  A plane in flight, by the atmosphere, because that it is supported by the Earth.

The other thing that baffles me is this;

Everything on Earth is ultimately made from Earth.  You, me, the chair (wood is a biological product of Earth-bound elements, carbon, nitrogen and so on), the house the chair is in (sand, rock), the plane is made of aluminium (smelted from bauxite, mined from the Earth).  Why does all this crap stop feeling the direct effect of UA once we give it a name?

Maybe the only things to feel UA directly are the turtle and the elephants.
Title: Re: Question about the Vomit Comet
Post by: WTF_Seriously on April 30, 2021, 01:08:01 PM
@Fisherman, @DuncanDoenitz

I finally think I see my confusion on your side of the discussion.  Admittedly, I've never took the time to actually try to understand the details of FE terminal velocity.  The majority of what you've both been saying is correct.

Back to the vomit comet.  I'm going to coin two new FE terms for purpose of discussion: Aerodynamic pull and Terminal Acceleration.

Aerodynamic pull is simply the ability of the air passing by you to impact your velocity and acceleration.  Aerodynamic pull is a verifiable 'force' witnessed everyday in skydiving simulators across the world.  Terminal acceleration is simply the acceleration reached due to the effects or aerodynamic pull and has a value of g.

For the vomit comet to work it must place itself and the passenger in a state of zero acceleration.  To do this, it simply has to be able to overcome aerodynamic pull in order to overcome terminal acceleration.  Voila, the FE vomit comet.  Simple as that.

Title: Re: Question about the Vomit Comet
Post by: WTF_Seriously on April 30, 2021, 02:08:52 PM

The other thing that baffles me is this;

Everything on Earth is ultimately made from Earth.  You, me, the chair (wood is a biological product of Earth-bound elements, carbon, nitrogen and so on), the house the chair is in (sand, rock), the plane is made of aluminium (smelted from bauxite, mined from the Earth).  Why does all this crap stop feeling the direct effect of UA once we give it a name?

Maybe the only things to feel UA directly are the turtle and the elephants.

Just thinking out loud I would say that the reason is that the earth acts as a UA shield.  Someday, as the plethora of evidence becomes overwhelming, FEers are going to have to admit that satellites exist.  When this happens, they'll have to come up with another ridiculous Parsifal like equation to determine how UA comes back into play the further an object is from the surface of the earth.
Title: Re: Question about the Vomit Comet
Post by: fisherman on April 30, 2021, 03:24:51 PM
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Everything on Earth is ultimately made from Earth.  You, me, the chair (wood is a biological product of Earth-bound elements, carbon, nitrogen and so on), the house the chair is in (sand, rock), the plane is made of aluminium (smelted from bauxite, mined from the Earth).  Why does all this crap stop feeling the direct effect of UA once we give it a name?

It doesn't stop feeling the direct effect of UA. They use what amounts to a “reverse normal force” to explain that.  With gravity, we are always being pulled down.  If the surface of the earth wasn’t in the way, it pull us down to the center of the earth.  In response to force of gravity pulling us down to the surface, the surface pushes back up on us and equalizes the force and keeps us from being pulled down.  That’s the normal force.  FE claims it works in reverse with UA. The surface of the earth pushes objects up, and in response the object pushes down.  Equal force means we don’t fly off.

Seems like there is a flaw in that somewhere, but can’t quite put my finger on it.  With gravity, a surface can only respond with so much normal force before it breaks. With the differences in mass between the earth and individual objects on the earth, it seems like at some point an object wouldn’t physically be able to push back. Haven’t really thought it through, though.

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For the vomit comet to work it must place itself and the passenger in a state of zero acceleration.  To do this, it simply has to be able to overcome aerodynamic pull in order to overcome terminal acceleration.  Voila, the FE vomit comet.  Simple as that.

There’s no forces on the plane that would account for overcoming the acceleration. That was the whole point of my question.  Thrust and drag cancel each other out and lift is eliminated by the angle.  The only force on the plane is the acceleration caused by UA.
Title: Re: Question about the Vomit Comet
Post by: WTF_Seriously on April 30, 2021, 04:08:07 PM

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For the vomit comet to work it must place itself and the passenger in a state of zero acceleration.  To do this, it simply has to be able to overcome aerodynamic pull in order to overcome terminal acceleration.  Voila, the FE vomit comet.  Simple as that.

There’s no forces on the plane that would account for overcoming the acceleration. That was the whole point of my question.  Thrust and drag cancel each other out and lift is eliminated by the angle.  The only force on the plane is the acceleration caused by UA.

There is no force on the plane due to UA.  That's the point you continue to not see.  The force on the plane is aerodynamic pull.  Duncan's explanation you just quoted applies to the plane no different than a skydiver.  Turn off a planes engine and it ceases producing lift.  It's upward acceleraction begins to slow.  This can only happen because UA is not acting on the plane.  Eventually, aerodynamic pull begins to accelerate the plane upward but at a slower velocity than the earth.  Terminal acceleration will eventually be reached even with a plane but the plane now has a slower velocity so it eventually crashes.  IF the plane was being accelerated by UA you could turn off the engines and it would maintain altitude.

Even in RE you have to fly the plane downward in order to overcome terminal velocity.  Thrust must be provided to cause the plane to exceed terminal velocity.  FE is not different.  Thrust cancels drag means that enough thrust is provided to cancel the pulling force of the atmosphere to achieve zero acceleration of passenger and plane.  That's the only force that needs to be canceled.
Title: Re: Question about the Vomit Comet
Post by: fisherman on April 30, 2021, 04:19:07 PM
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There is no force on the plane due to UA.

Then why does the plane need to overcome "terminal acceleration"?  If it isn't being accelerated, there is nothing to overcome.

Again, I point you back to the wiki definition of TV.  It PLAINLY says that the falling object is accelerated.  Gravity isn't accelerating it so what is?

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IF the plane was being accelerated by UA you could turn off the engines and it would maintain altitude.

It would continue to accelerate, but at a slower rate than the earth because of drag.  Eventually, the earth closes the gap.

EDIT:  Curious as to your resistance to the idea that UA would effect an object that is not on the surface of the earth.  Gravity effects things that aren't on the surface, and if gravity=UA, why wouldn't UA effect things not on the surface?
Title: Re: Question about the Vomit Comet
Post by: WTF_Seriously on April 30, 2021, 04:32:16 PM
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There is no force on the plane due to UA.

Then why does the plane need to overcome "terminal acceleration"?  If it isn't being accelerated, there is nothing to overcome.

Again, I point you back to the wiki definition of TV.  It PLAINLY says that the falling object is accelerated.  Gravity isn't accelerating it so what is?

I just told you.  Objects are accelerated upward by aerodynamic pull.  In the case of the plane, it not only maintains equal upward acceleration due to aerodynamic pull, but lift allows it to also maintain equal velocity with the earth.

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IF the plane was being accelerated by UA you could turn off the engines and it would maintain altitude.

It would continue to accelerate, but at a slower rate than the earth because of drag.  Eventually, the earth closes the gap.

If the plane was being accelerated by UA there would be no drag.  The plane would be traveling vertically at the same rate as the air around it.  It would never begin to 'fall'.
Title: Re: Question about the Vomit Comet
Post by: fisherman on April 30, 2021, 05:30:50 PM
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I just told you.  Objects are accelerated upward by aerodynamic pull.  In the case of the plane, it not only maintains equal upward acceleration due to aerodynamic pull, but lift allows it to also maintain equal velocity with the earth.

There is no lift in parabolic flight.  It disappears because of the angle.

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If the plane was being accelerated by UA there would be no drag.

Unless it's in a vacuum, acceleration always causes drag.

It just dawned on me what point I am failing to make clear and why we are talking past each other.  The question isn't whether or not it would be possible for the Vomit Comet to be a thing in a UA environment.  The question is "would it be possible according to how the Vomit Comet actually operates?"

The way I understand, the vomit comet could work with UA if the pilot allowed for more drag than thrust and thereby "cancel" the UA effect.

I don't know this for 100% certainty, which is why I asked, but my sense is that if you asked a pilot of the Vomit Comet whether or not they allow for more drag than thrust in parabolic flight, the answer would be no.  They would tell you that drag and thrust are equal.
Title: Re: Question about the Vomit Comet
Post by: WTF_Seriously on April 30, 2021, 06:12:30 PM
Unless it's in a vacuum, acceleration always causes drag.

Yes, but UA provides enough force to overcome it.  The plane and air around it are feeling the same drag due to acceleration.  If UA acts on the plane, there is no net drag between air and plane.

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It just dawned on me what point I am failing to make clear and why we are talking past each other.  The question isn't whether or not it would be possible for the Vomit Comet to be a thing in a UA environment.  The question is "would it be possible according to how the Vomit Comet actually operates?"

The way I understand, the vomit comet could work with UA if the pilot allowed for more drag than thrust and thereby "cancel" the UA effect.

I don't know this for 100% certainty, which is why I asked, but my sense is that if you asked a pilot of the Vomit Comet whether or not they allow for more drag than thrust in parabolic flight, the answer would be no.  They would tell you that drag and thrust are equal.

OK.. Definitely something to think about.

Just thinking out loud here.  In RE, the amount of thrust required is that which pushes the plane through terminal velocity and achieves acceleration at the rate of gravity, no?

In FE, the amount of thrust required is that which pushes the plane through terminal acceleration to reach zero acceleration.  Wouldn't those two quantities be equal?

In other words, drag to TV = drag to TA and drag to get to g = drag to get to 0 in the two different systems. This yields overall drag in both cases to be equal.
Title: Re: Question about the Vomit Comet
Post by: DuncanDoenitz on April 30, 2021, 11:41:16 PM
A couple of posts ago I thought we were getting somewhere, but now I'm not so sure.  Part of the problem here, and I say this with the greatest respect, is that the whole FE/RE thing deals with many concepts which, in isolation, can take a career to get your head around, and you can't expect to get the same level of understanding from a few hours or days on the interweb.  I'm happy to concede that Einstein, relativity and bendy space are completely outside my comfort zone, so I don't even go there.  I do, however, have a background in aviation.

First of all, what's the obsession with Terminal Velocity?  Its just a speed (downwards or upwards, depending on your take) at which the force of aerodynamic drag equals the accelerating force of gravity or UA.  (And please stop referring to gravity and suchlike as "drag"; drag is a specific force only caused by aerodynamics).  There is no single "Terminal Velocity", it is dependent on the mass, size, shape and orientation of the object, and upon air density.  So, for instance, in air;

TV of a one Metre sphere of styrofoam is less than a one metre sphere of iron (mass)
TV of a one kilogram sphere of styrofoam is less than a one kilogram sphere of iron (size)
TV of a one kilogram cube of iron is less than a one kilogram sphere of iron (shape)
TV of a 500lb Mk 82 bomb minus its fins, is less than that of one fitted with fins (orientation)
TV of anything dropped from 1000 metres above the sea is less than the same object dropped from 1000 metres above Mount Everest (air density).

So our typical human has a TV of around 300 kmph at typical skydiving heights, due to sea-level air density.  Felix Baumgartner on the other hand achieved over 1300 kmph on his dive from 39 km, due to the reduced air density at altitude.  The WW2 Tallboy bomb achieved a TV of around 1200 kmph, due to its shape and orientation.  So; TV is just a number.

Lets look at the Wiki on TV;

"In the Round Earth model, terminal velocity happens when the acceleration due to gravity is equal to the acceleration due to drag. In the Flat Earth model, however, there are no balanced forces: terminal velocity happens when the upward acceleration of the falling object is equal to the upward acceleration of the Earth".

OK, happy with the RE bit.  FE part; why are the forces not balanced?  What is causing the "upward acceleration of the falling object"?   Wouldn't it make more sense to say that aerodynamic drag of the rising atmosphere is accelerating the falling object?  Therefore the forces are balanced.

Everyone happy with the concept of a windtunnel?  You stick aerodynamic models in it and switch it on, and you can see how they will react in flight.  In other words, static-object, moving-air, gives identical results to moving-object, static-air.  Surely this is analogous to falling object-static air, and static-object, rising-air.

Finally, lift, drag, thrust and weight.  Don't run away with the idea that all these forces are working at 90 degrees to each other; they aren't.

Thrust is always aligned along the axis of the engine so, in conventional aeroplanes, can be considered (more or less) to be along the longitudinal axis of the aircraft, regardless of its orientation.
Weight is always vertically down, regardless of orientation of the aircraft.
Drag is always in line with the relative airflow on the wings.  If the aircraft has an angle of, say, 15 degrees nose-up to the relative airflow, drag will not be aligned with thrust.
Lift is always at 90 degrees to the relative airflow, so is only ever directly opposing weight if the aircraft is in straight and level flight, and almost never when flying a parabolic zero-g flight.

The flight of a Vomit-Comet (and there are several), requires a complex balance of entry speed and orientation (typically at 45 degrees nose-up), thrust and lift-management by the use of flying controls to ensure that the aircraft follows the exact free-fall trajectory of its occupants.

Terminal Velocity has nothing to do with it.

(Oh yes, and acceleration does not cause drag.  Velocity causes drag).
Title: Re: Question about the Vomit Comet
Post by: fisherman on May 01, 2021, 12:11:14 AM
A couple of posts ago I thought we were getting somewhere, but now I'm not so sure.  Part of the problem here, and I say this with the greatest respect, is that the whole FE/RE thing deals with many concepts which, in isolation, can take a career to get your head around, and you can't expect to get the same level of understanding from a few hours or days on the interweb.  I'm happy to concede that Einstein, relativity and bendy space are completely outside my comfort zone, so I don't even go there.  I do, however, have a background in aviation.

First of all, what's the obsession with Terminal Velocity?  Its just a speed (downwards or upwards, depending on your take) at which the force of aerodynamic drag equals the accelerating force of gravity or UA.  (And please stop referring to gravity and suchlike as "drag"; drag is a specific force only caused by aerodynamics).  There is no single "Terminal Velocity", it is dependent on the mass, size, shape and orientation of the object, and upon air density.  So, for instance, in air;

TV of a one Metre sphere of styrofoam is less than a one metre sphere of iron (mass)
TV of a one kilogram sphere of styrofoam is less than a one kilogram sphere of iron (size)
TV of a one kilogram cube of iron is less than a one kilogram sphere of iron (shape)
TV of a 500lb Mk 82 bomb minus its fins, is less than that of one fitted with fins (orientation)
TV of anything dropped from 1000 metres above the sea is less than the same object dropped from 1000 metres above Mount Everest (air density).

So our typical human has a TV of around 300 kmph at typical skydiving heights, due to sea-level air density.  Felix Baumgartner on the other hand achieved over 1300 kmph on his dive from 39 km, due to the reduced air density at altitude.  The WW2 Tallboy bomb achieved a TV of around 1200 kmph, due to its shape and orientation.  So; TV is just a number.

Lets look at the Wiki on TV;

"In the Round Earth model, terminal velocity happens when the acceleration due to gravity is equal to the acceleration due to drag. In the Flat Earth model, however, there are no balanced forces: terminal velocity happens when the upward acceleration of the falling object is equal to the upward acceleration of the Earth".

OK, happy with the RE bit.  FE part; why are the forces not balanced?  What is causing the "upward acceleration of the falling object"?   Wouldn't it make more sense to say that aerodynamic drag of the rising atmosphere is accelerating the falling object?  Therefore the forces are balanced.

Everyone happy with the concept of a windtunnel?  You stick aerodynamic models in it and switch it on, and you can see how they will react in flight.  In other words, static-object, moving-air, gives identical results to moving-object, static-air.  Surely this is analogous to falling object-static air, and static-object, rising-air.

Finally, lift, drag, thrust and weight.  Don't run away with the idea that all these forces are working at 90 degrees to each other; they aren't.

Thrust is always aligned along the axis of the engine so, in conventional aeroplanes, can be considered (more or less) to be along the longitudinal axis of the aircraft, regardless of its orientation.
Weight is always vertically down, regardless of orientation of the aircraft.
Drag is always in line with the relative airflow on the wings.  If the aircraft has an angle of, say, 15 degrees nose-up to the relative airflow, drag will not be aligned with thrust.
Lift is always at 90 degrees to the relative airflow, so is only ever directly opposing weight if the aircraft is in straight and level flight, and almost never when flying a parabolic zero-g flight.

The flight of a Vomit-Comet (and there are several), requires a complex balance of entry speed and orientation (typically at 45 degrees nose-up), thrust and lift-management by the use of flying controls to ensure that the aircraft follows the exact free-fall trajectory of its occupants.

Terminal Velocity has nothing to do with it.

(Oh yes, and acceleration does not cause drag.  Velocity causes drag).

Thank you for this...its the kind of input I was looking for.  The only reason I brought up the concept of TV is to demonstrate that UA does in fact effect a "falling object" in FE.  Having to detour around that issue took us down a rabbit hole.

I'm not aeronautical engineer, obviously ::) but intuitively, it seems to me if during the free fall stage only gravity is effecting the plane, then with UA, only UA would be effecting the plane.  And if UA is effecting the plane during "freefall", then the occupants would be pinned to the floor.

Could the vomit comet work with UA?  Maybe, maybe not, but as I tried to clarify the question really isn't whether or not it could work, but could it work the same way.
Title: Re: Question about the Vomit Comet
Post by: DuncanDoenitz on May 01, 2021, 02:01:30 PM
This is important; the plane is not in free-fall, although its occupants are.  The plane is in aerodynamic flight.

Of the 4 forces, gravity is trying to pull the aircraft in free-fall, but it still has drag, so the pilot has to balance controls (ie lift), thrust and starting trajectory such that drag can be compensated for as if the aircraft was in free fall.  As I see it, the same would occur if the aircraft was in a rising mass of air in FE; the Earth/atmosphere's 1g acceleration would appear identical to RE gravity.

Couple of other things to point out.  The algebraic multiple of time/g-force during the flight has to remain at 1g.  In very simple terms, for 1 minute at zero-g, you might need another minute at 2g, starting and ending the manoever.  Due to structural and aerodynamic limits on the size of aircraft needed for a workable weightless environment (eg an airliner), the zero-g duration is normally less than a minute.

Remember the parachutist-guy leaving the plane and feeling zero-g for an instant?  He then immediately started feeling g due to drag as his airspeed increased.  All the Vomit Comet does is to provide him with that starting altitude, and then a cocoon of still air so that he is only affected by gravity, not drag.
Title: Re: Question about the Vomit Comet
Post by: stevecanuck on May 01, 2021, 02:26:17 PM
So our typical human has a TV of around 300 kmph at typical skydiving heights, due to sea-level air density.

Clarification: Skydiver TV is about 195 kmph (120 mph) when falling in the "frog" position belly to earth. Greater speeds occur when diving head first.
Title: Re: Question about the Vomit Comet
Post by: fisherman on May 01, 2021, 02:53:08 PM

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Of the 4 forces, gravity is trying to pull the aircraft in free-fall, but it still has drag, so the pilot has to balance controls (ie lift), thrust and starting trajectory such that drag can be compensated for as if the aircraft was in free fall.  As I see it, the same would occur if the aircraft was in a rising mass of air in FE; the Earth/atmosphere's 1g acceleration would appear identical to RE gravity

Would those adjustments be the same in UA? Again, intuitively...thrust on RE would only be whatever the engine provides, but on FE, thrust would be whatever the engine provides plus the "thrust" that UA provides.  So it seems like adjustments to make thrust=drag would be different for FE and RE.
Title: Re: Question about the Vomit Comet
Post by: DuncanDoenitz on May 01, 2021, 05:00:32 PM
Not sure why you would think that UA would augment thrust.

Thrust always acts along the longitudinal axis of the aircraft so, as the aircraft climbs it would have a vertical component driving the aircraft up.  Conversely, in the dive phase, thrust has a downward component.  A vertical force of some kind from UA could not augment both phases.

On top of that, and I'm 100% not an advocate for FE here (perhaps someone from that camp could chime in), I don't think UA directly acts on any worldly matter apart from the planet (disc?) itself.  I think the only effect of UA on flight is that the atmosphere is supposed to be accelerating upwards at a rate equivalent to (what everyone else calls) gravity.
Title: Re: Question about the Vomit Comet
Post by: fisherman on May 02, 2021, 03:38:09 AM
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Not sure why you would think that UA would augment thrust.

LOL, I just realized the mental image I have been carrying in my head is a rocket, going straight up...not a plane.

So I guess what I meant was “lift” not “thrust”.  The accelerating atmosphere creates “lift” in that it accelerates the plane vertically, independent of any lift created by how the pilot manipulates the controls.

I found a good article linked below. One of the points that stood out to me was this.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2598414/

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Contrary to popular misconception, the 0 g freefall phase of flight begins as the aircraft climbs, and does not occur solely as the aircraft descends. Although the aircraft has upward velocity during the initial 0 g phase, its acceleration is downward: the upward velocity is decreasing.

Seems to me that at that point, the upward velocity would be decreasing at a different rate in UA than with gravity alone.

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This is important; the plane is not in free-fall, although its occupants are.  The plane is in aerodynamic flight.

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Essentially, if the aircraft and its occupants "fall" together at 9.81 m/s2, "0 g" is achieved, where there is no reaction force on the occupants by the aircraft.

Also here...

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At this point, the only unbalanced force acting on the plane is weight, so the plane and its passengers are in free fall. This is what creates the zero-g experience.

https://sitn.hms.harvard.edu/flash/2018/free-falling-the-science-of-weightlessness/

EDIT:

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On top of that, and I'm 100% not an advocate for FE here (perhaps someone from that camp could chime in), I don't think UA directly acts on any worldly matter apart from the planet (disc?) itself.

That really seems to be the heart of the matter.  To me, the way TV is explained, UA does effect a "falling object".  Perhaps not directly, but in some what that it causes a falling object to accelerate.  And one must assume that is accelerate up and not down.

But you're right, it would be nice for an FE advocate to chime in.  Seems like it would be an easy enough clarification to make.
Title: Re: Question about the Vomit Comet
Post by: fisherman on May 02, 2021, 04:35:42 PM
I was thinking about the issue of whether or not UA force effects objects on the surface and the penny dropped.  (or maybe be the earth rose up to meet it). The whole question about how the Vomit Comet would work on UA is answered by how the weight force works.

Unless UA does effect objects on the surface, there would be no way to perceive weight.  When we step on the bathroom scale, it isn’t measuring the gravitational force.  It is measuring the reaction force, the normal force. Gravity causes us to produce a downward pull on the surface of the scale, and the surface of the scale pushes back up.  That “push up” reaction is what the scale measures.  UA would have to work the same, except in reverse.  The scale would be measuring the reaction force of your feet pushing down on the scale, as UA pushes the scale up.  Without contact with a solid surface, we can’t perceive or measure weight.

But here is the whole key...weight is a force with both magnitude and direction.  On a RE, a 200 lb. Person would generate 1962N of weight force.  On an FE, that same person would generate -1962N of weight force.

The article I linked shows the formula for the amount of acceleration necessary to generate 0g is

(https://i.imgur.com/5XGn5oU.png)

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2598414/#:~:text=During%20such%20parabolic%20flight%20an,aircraft%20vertical%20(z)%20axis.

You don't have to look at that formula very long to realize that if you reverse the direction of the weight force, you are going to get a very different result.  The vertical acceleration would have to be in the opposite direction on FE with UA, than what it is on RE with gravity.