Physics Response to Flight 77 Trajectory Speculation

[jaydeehess]

Are there any eyewitnesses supporting this part of the flight path and the maneuver the alleged pilot made before leveling off?

There are no eyewitnesses to the plane in reference to it proximity to the VDOT antenna. This thread is concerned strictly with the calculations that arise from the P4T contention that the plane would have been over the antenna.

In that it has been shown over and over again that the P4T 'team' did not do a very good, indeed did a very bad, job of calculating the forces on the plane in any trajectory that would put it over the VDOT antenna.

In another connotation of your question you would seem to be asking if there are any eyewitnesses to the changes in desent of the aircraft.

While the graph posted shows wide fluctuations in the aircraft desent rate this would not be immediatly obvious to an eyewitness on the ground. Eyewitnesses would have no visual reference behind the aircraft (that is to say as a backdrop to the aircraft) while the plane was still greater than about 50 feet overhead. Someone farther away who could see a skyline and the aircraft may have been able to see these changes readily, just maybe, if they watched the plane come in from far away. Anyone who was watching only for a few seconds would not have time to make this determination unless they have been involved with aircraft a lot.(ie. tower ATC)

 

[jaydeehess]

Yes the g was recorded every 1/8 of second. Here are the last seconds.
[qimg]http://www.beachymon.com/photo/gs.jpg[/qimg]
There is data missing at the end of the flight. Not sure how much. The final trend was increasing descent rate, and would most likely be followed again by a pullup of 1.4 to 1.7 gs again.

I have one question;


A g of "1" on this graph would be be level flight, correct?

 

[rwguinn]

I have one question;


A g of "1" on this graph would be be level flight, correct?

That would be the correct answer, yes.

 

[Dave Rogers]

I have one question;


A g of "1" on this graph would be be level flight, correct?

No, presumably a g of "1" would be a constant rate of climb or descent. In the special case where this constant is zero, that would be level flight.

Not meaning to be pedantic, but the truthers might pick up on this one.

Dave

 

[rwguinn]

No, presumably a g of "1" would be a constant rate of climb or descent. In the special case where this constant is zero, that would be level flight.

Not meaning to be pedantic, but the truthers might pick up on this one.

Dave

I beg to differ.
The accelerometer in the aircraft has a 1g DC offset.
When sitting on the ground it reads 1.0

 

[Reheat]

Not meaning to be pedantic, but the truthers might pick up on this one.

No, I disagree. 1G should be unaccelerated flight. All G Meters (Accelerometers) and I'm sure FDR's are the same are 1 G in normal unaccelerated flight, same as when you're sitting in your easy chair watching TV or typing on your keyboard.

Based upon the graph it appears Hani was in a minor PIO (Pilot Induced Oscillation). It was quite rapid and would not have been discernible from outside the aircraft, but it would have been quite noticeable inside the aircraft. He was what is known in the trade as "ham fisting" the controls or in layman's terms over controlling pitch, maybe roll to but we don't see that here.

The accelerometer in the aircraft has a 1g DC offset.
When sitting on the ground it reads 1.0

Correct.

 

[Corsair 115]

No, I disagree. 1G should be unaccelerated flight. All G Meters (Accelerometers) and I'm sure FDR's are the same are 1 G in normal unaccelerated flight, same as when you're sitting in your easy chair watching TV or typing on your keyboard.

Yes, but isn't a constant speed change in altitude the same thing? In other words, a steady descent rate of, say, 500 feet per minute throughout the descent should read 1 G since it isn't an accelerated rate of descent, where the descent rate is increasing in value each second.

 

[Anti-sophist]

1-G corresponds to 0 acceleration. This means a g-force is technically the 1+ (acceleration / accelerate due to the earth).

A "g-force" is really meant to measure stress on the human body. Therefore, it's really a measure of how much force your body has to endure from direct contact with your surroundings. At 1-g, or no acceleration, in order to keep from accelerating, you need to exert enough force to overcome 1*gravity. So all your bones and joints and muscles and tendons have to work together to exert your own weight worth of force to "hold you still". At 2g, your body needs to exert twice your body weight on its surrounding to keep you together. And so on.

Zero g is when you exert no force at all, and thus, are in free-fall.

 

[Anti-sophist]

Yes, but isn't a constant speed change in altitude the same thing?

The word 'speed' confused me, at first. A "constant speed change" sounds like a constant change in velocity. That's not what you meant, though.

A constant rate of change in altitude represents a constant velocity. A constant velocity means 0 acceleration, which means 1-g.

 

[Reheat]

Yes, but isn't a constant speed change in altitude the same thing? In other words, a steady descent rate of, say, 500 feet per minute throughout the descent should read 1 G since it isn't an accelerated rate of descent, where the descent rate is increasing in value each second.

Yes, partly correct. In a 500 fpm rate of descent or ascent at a constant speed there is no acceleration (accept initially) and the decent/ascent rate does not increase unless the pitch or power changes. How can the descent rate change in value without other corresponding changes in either pitch or power? Am I understanding you correctly?

ETA: I presume you're talking about a constant Indicated Airspeed. If you're speaking of True Airspeed or Ground Speed that changes things....

 

[Myriad]

Everyone is correct, up to a point. The ambiguity comes from the fact that acceleration is a vector quantity.

If you're in an elevator, and the elevator is rising or falling at a constant velocity, then you're at exactly 1 G, the same as if the elevator were standing still.

However, planes don't just go up and down like an elevator. If the plane were climbing or falling at a constant rate, and also managed to remain completely level (as in horizontal), then as with the elevator you'd feel exactly 1 G, and the instruments would measure that as well.

However, planes don't typically remain completely horizontal when they climb or descend (nor even when they're flying "level" in the sense of not gaining or losing altitude). So, whether an accelerometer on a plane that's climbing or descending at a constant rate would still measure exactly 1 G depends on whether it's measuring acceleration in the direction straight down to the ground, or in the direction perpendicular to the plane's axes. The former remains constant during a constant-rate climb or descent, but the latter is affected by the pitch. (And in terms of stress on the airframe during maneuvers, the latter is the more important to know.)

This difference is small, though, as long as the plane's pitch angle is small.

In an airliner, it does feel a little different when the plane is climbing, flying level, or descending, because you can feel the difference in pitch even when the rate of climb or descent is constant. An accelerometer measuring the acceleration in the direction, say, perpendicular to the seat of your chair would also "feel" that difference due to the tilt.

Some simulators (including many movie-rides) simulate forward acceleration by tilting your seat (and everything else in your field of view) back. You feel more pressure against the back of your seat because of the tilt, and because you're given no visual cues of the tilt but instead a movie view of you rushing forward, you feel it as forward acceleration. (There's also a reduction in pressure against the bottom of your seat, but you don't notice that as much.) An accelerometer measuring in a direction that's fixed relative to your chair would be fooled in the same way, because they can't distinguish between acceleration and the earth's gravitational pull.

Respectfully,
Myriad

 

[Reheat]

This difference is small, though, as long as the plane's pitch angle is small.

Even with large changes in pitch an accelerometer essentially measures the acceleration perpendicular to the earth. This is most important in maneuvering as this is the most significant stress on an aircraft. The most significant longitudinal stress would be from engine power and even in an F-15 or F-22 in full afterburner this would not produce anything even close to excessive stress.

In an airliner, it does feel a little different when the plane is climbing, flying level, or descending, because you can feel the difference in pitch even when the rate of climb or descent is constant.

This is because the best accelerometer in the world is the human inner ear. The cilla (hairs) in the inner ear indicate balance and they detect the most insignificant changes in acceleration. In fact they can be fooled very easily too, as is the case in spatial disorientation, which is another subject entirely.

Even tho' this may not be directly related to the OP it is a good discussion for education and not a total waste of time as we're all interested in learning and this is, after all, the purpose of this forum.

 

[GregoryUrich]

Even with large changes in pitch an accelerometer essentially measures the acceleration perpendicular to the earth. This is most important in maneuvering as this is the most significant stress on an aircraft. The most significant longitudinal stress would be from engine power and even in an F-15 or F-22 in full afterburner this would not produce anything even close to excessive stress.

This is because the best accelerometer in the world is the human inner ear. The cilla (hairs) in the inner ear indicate balance and they detect the most insignificant changes in acceleration. In fact they can be fooled very easily too, as is the case in spatial disorientation, which is another subject entirely.

Even tho' this may not be directly related to the OP it is a good discussion for education and not a total waste of time as we're all interested in learning and this is, after all, the purpose of this forum.

Cilia aside, do you know what the time scale is in Beachnut's graph? It would seem that the negative Gs at the end of the data put the quash on Mackey's constant pull out.

 

[Myriad]

Even with large changes in pitch an accelerometer essentially measures the acceleration perpendicular to the earth. This is most important in maneuvering as this is the most significant stress on an aircraft. The most significant longitudinal stress would be from engine power and even in an F-15 or F-22 in full afterburner this would not produce anything even close to excessive stress.

I don't know how it's actually measured in practice, but I guess that what you're referring to is the equivalent of an accelerometer on weighted gimbals, so as to measure the maximum force in whatever direction that maximum happens to be relative to the earth or the airframe. In normal commercial flight, that would indeed be perpendicular to the earth most of the time, and so it wouldn't be affected directly by the pitch of the plane.

In more extreme aerial maneuvers, the maximum G forces would not remain perpendicular to the earth's surface, but would still (due to the ways a plane generates the G forces in the first place) tend to be more or less aligned with the yaw axis of the plane (and the pilot's spinal column), which as you point out is the direction of concern. For instance in a tight high-bank turn or halfway through an Immelmann, the instantaneous maximum G forces would be more or less parallel with the earth's surface.

Does that make sense?

Respectfully,
Myriad

 

[Reheat]

I don't know how it's actually measured in practice, but I guess that what you're referring to is the equivalent of an accelerometer on weighted gimbals, so as to measure the maximum force in whatever direction that maximum happens to be relative to the earth or the airframe.

I've never actually seen one I don't remember the details of one outside of an aircraft, only used them operationally for most of my adult life. I think there is some gimbal type movement, but I believe it's limited. They move enough to do the job. But, I believe your discussion is valid and correct.

But, it's no where near the type of gimbals mount that INS accelerometers use, for example.

Does that make sense?

Of course, it does. You do understand what you're talking about. It's just that neither of us have seen or remember details of one. Well I think I did once, but it's been so long I don't remember details.

 

[Reheat]

Cilia aside, do you know what the time scale is in Beachnut's graph? It would seem that the negative Gs at the end of the data put the quash on Mackey's constant pull out.

The small dots (each recording) are 1/8 sec, he said. I don't know the scale of the numbers below, but I don't believe they are seconds.

Don't even try to guess the position of the aircraft for the period depicted on the graph. There is missing data and Beachnut's last few seconds comment was referencing the last few seconds of recorded data not the last few seconds of flight.

 

[beachnut]

Cilia aside, do you know what the time scale is in Beachnut's graph? It would seem that the negative Gs at the end of the data put the quash on Mackey's constant pull out.

NO, negative Gs! Negative Gs are below 0! No, Mackey's work is outstanding and could be used by pilots to plan for a maneuver like the fantasy maneuver p4t are trying to make up and can not figure out the Gs.

The time is each sample 1/8 of second; and the data is the last 168 or so 1/8 of seconds. (8 samples a second).

See the video by p4t with real dumb statements mixed in!
Gregory, Mackey made assumptions to show it is possible to do with much less than 11.2 gs (as in the real loading required to do it), which was made up by p4t (p4t divided feet by acceleration to come up with seconds squared, which they call gs, and add 1 g to show the loading on the aircraft as 11.2 gs).
The terrorist aimed and hit the Pentagon, without worrying about the posts et al. That is why the Gs were all over the place. I will have to post the control column setting as seen on the video.

The data, as Reheat said, was the final data from the FDR, 168 or so samples - 21 final seconds from the FDR.

((If you see the final push over the pilot may of tripped off the GENERATORS ending electrical power to the plane. Therefore the FDR stopped. Some planes will loose generator power when you go below .2 to 0 G. ))) NRFPT

Stick postion 0 to -9 for the last 44 seconds. You can see the stick position is increasing down. He is pushing forward on the stick (yoke/control column). Final recorded seconds on FDR for stick position, the terrorist is pushing on the control column. The animation shows the same with the control column, these are the raw values. (last 44 seconds, recorded on FDR)

The faster the plane goes, the more lift you get, the more you have to hold the nose down all things remaining the same. –3.3 control column was holding level fight when 77 first leveled off at FL290 (29,000 feet).

 

[Horatius]

It would seem that the negative Gs at the end of the data put the quash on Mackey's constant pull out.

You have to remember the purpose of Mackey's analysis. He never intended this to be accepted as a prediction or analysis of how the plane actually flew. It was simply to demonstrate that any of several possible flight paths were well within the capabilities of the plane, contrary to the assertions of the PfTers. They are the ones who argue that the numbers they've come up with make anything even approaching the "true" flight path physically impossible, and all Mackey has done (and all he intended to do) is demonstrate that their assertions are without merit.

We're all comfortable with the reality that no one will ever know with absolute precision the true final flight path. It's the CTists and PfTers who are can't accept the uncertainty. In their demands to know everything perfectly, they end up producing absolute nonsense, as anyone should be able to see from the several available critiques of their "calculations".

 

[celestrin]

The calculations below used for the purpose of this article are in error. We are currently reviewing the calculations and will publish a revision with the proper formula(s)/calculations consistent with the premise of this article. We apologize for any confusion and thank you for your understanding.

Salutations, brothers in shill! Mission accomplished. Report to nearest HQ to pick up a bonus check.

Are there any eyewitnesses supporting this part of the flight path and the maneuver the alleged pilot made before leveling off?

There are no witnesses per se, but one of the CIT star witnesses did find it strange that the repair crew was on the tower on 9/12. It was one of the Paik brothers (Edward, IIRC) who noticed this and assumed that the plane did some damage. Lyte didn't think this was enough of a smoking gun, so he's not talking about it too often. Or it might just be because the plane at the tower destroys his north path fantasy. I wonder what would CIT make of it if their fantasy required the plane at the tower.

Regarding accelerations - what would vertical acceleration show if the plane was flying upside down?

 

[uk_dave]

The calculations below used for the purpose of this article are in error.

Buggeration! Why do people insist on spoiling our fun?

We are currently reviewing the calculations and will publish a revision with the proper formula(s)/calculations consistent with the premise of this article.

We're going to try to spin this so that we don't look like total idiots, but we might just have to bin it and try to sell.... provide another 'smoking gun' which, hopefully, those liars on JREF won't be able to demolish.

We apologize for any confusion and thank you for your understanding.

We just hope we haven't lost too many customers....... fellow truthers with this almighty cock-up

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