The 9/11 Forum

All of which is part of the reasons I have no interest in debating the socio-political stuff of 9/11.

The technical issues are in or near enough to my areas of expertise - WTC collapses particularly.

And all the big technical questions are easy to answer. No CD at WTC; it was that plane at Pentagon and Shanksville was not a "shoot down". The main reason that confidence can be so high is that all the contributing elements of fact are yes no determinable. Very few depend on probability argument. And the primary evidence is visible so zero need to rely on other parties opinions OR on "open to adjustment" text document materials of variably defined accuracy. One rare probability example I rely on for my conclusions being the logistic/security/strategic "for all reasonable purposes impossible" status of the use of CD in Twin Towers collapse initiation. Sufficient mechanisms contributing to initiation are identifiable - inward bowing perimeter and probable strength reducing temperatures affecting core will do by themselves (well plus aircraft severed columns) - but in the context of Internet debate I cannot "prove" they are enough. So I take the lazy way out.

All the "CCC" conspiracy stuff is pretty well unidentifiable and not sufficiently definable for reasoned argument to the standards I would accept. So I don't venture into the minefield.

There is no way that the conspiracy/collusion/(in)competence stuff is resolvable. It is all fuzzy edges and probabilistic argument with most of the material at least one or two layers of fog removed from the original facts or context.

All of which is interesting but OT... My OT contribution would be that (A) the nanothermite issue has not been resolved, nor has the temperature gap issue, even though Steven Jones appears to have done his best to discredit his own research by doing other things which call his scientific integrity into question. Since I was a big supporter of his, I hope I don't have to explain that this pains me. (B) The NIST reports are demonstrably false, although that doesn't prove 'CD'. (C) There is a good case for LIHOP, although unclear who pulled the strings (suspect are the military and the CIA, as usual) (D) It's a proven fact that the 9/11 Commission Report was a cover-up, in other words a conspiracy to lie.

So elements of the 9/11 Truth Movement have been successful. I do not regard anybody as the true Truth Movement except the 9/11 family members, first responders and survivors. These people are repeatedly overlooked. They are what matters here, as well as the collateral victims of the ensuing global war on terror. Poorly informed and badly educated conspiracy theorists who feel drawn to 9/11 research are irrelevant in my opinion.

Moreover, the Poteshman paper proves with mathematical certainty that there was insider trading. The counterarguments are circumstantial and cannot debunk Poteshman's statistical analysis.

For what it's worth (and it isn't worth much) Pat Curley ("Brainster" at JREF) responds here. with the usual casual, unscientific hand waving and intellectual bandwidth-deprived ridicule we've come to expect from his ilk.

einsteen wrote:http://911blogger.com/news/2011-09-26/analysis-rocket-projectiles-wtc2

we've seen the ridiculous artifical nist collapse function of wtc#7 that had a >g double derivative. But now David Chandler used his physics toolkit for a falling part he found on a video. Has this already been analysed here? He claims a >g due to ejective force. He should provide an error margin but it is an interesting piece.

Hello, einsteen. At first this seemed ridiculous, but I gave it a wee bit of thought from one angle to see how ridiculous it actually was.

The accelerations Chandler gives are g/3 prior, 15 m/s² for 0.5 second during and "a little less" than g after. The difference between prior and during is 11.7 m/s², but take the more conservative figure of 50% greater than g, or an additional 5 m/s² due to downward force in addition to gravity.

a = 5 m/s²
Δt = 0.5 sec

increase of velocity due to this force in g-accelerated frame:

Δv = aΔt = 5(0.5) = 2.5 m/s

From the rocket equation,

Δv = v_eln(m₀/m₁)

where m₀ and m₁ are the initial and final masses, respectively, which differ by the mass of the so-called propellant. Again, being conservative, assume all propellant was expended in the half second interval of increased acceleration; this will produce the greatest thrust and velocity increment, all other factors being equal. Expressing the mass of the falling panel as m and the mass of the expended rocket propellant as m_r, the equation above can then be restated as:


Δv = v_eln((m + m_r)/m)

so

Δv = v_eln(1 + m_r/m)
Δv/v_e = ln(1 + m_r/m)
exp(Δv/v_e) = 1 + m_r/m
m_r = m(exp(Δv/v_e) - 1)

This last form expresses the mass of rocket propellant in terms of

- panel mass
- change of panel velocity over high acceleration interval due to 'thrust'
- effective exhaust velocity

For the first two, I'll use Chandler's values, four tons (=> m ~ 3600 kg) and 2.5 m/s. Effective exhaust velocity can only be estimated. From the table here, solid fuel motors are around 2,500 m/s, both turbofan jet engines and generic ion thrusters are 29,000 m/s, and the extreme high is 115 km/s.

The idealized rocket equation above assumes exhaust gas velocity is directed uniformly opposite to the direction of net thrust, so-called effective exhaust velocity. The disparity between effective and actual is quite substantial for open combustion on a surface, versus a rocket optimized to convert chemical energy into kinetic energy where the effective exhaust velocity is much closer to actual. While the hypothetical energetic substance may have higher energy density than rocket propellant, yet be unsuitable as such, the orders of magnitude reduced efficiency in propulsion suggests a somewhat unrealistic upper bound of effective exhaust velocity to consider is 2500 m/s, with no real lower bound that I can establish at this time.


I've graphed the propellant mass as a function of exhaust velocity and shaded the region from 250 m/s to 2500 m/s, in other words the upper order of magnitude of what seems even possible:



Much to my surprise, the result is not entirely outrageous. At 250 m/s, the mass expended would be 36 kg, or 1/100th the mass of the panel itself. I consider 250 m/s a more realistic upper bound, considering the inefficiencies associated with the momentum transfer, with the real value probably being considerably less. The red line on the graph represents the range 100 - 110 m/s, which verges on more like propellant being 10% of the panel mass. Even in that range, the disparity between effective velocity and sonic velocity is only a factor of 3.4; considerations of propulsive efficiency suggest the actual velocity must be higher, thus the gas at the reaction surface must be exiting at supersonic speeds.

It would have to either be really loud or else a significant mass of propellant. In the former, any trailing smoke would be observed to be going upward at a significant separation velocity then slowing rapidly (but still going up) whereas trailing smoke or dust would be seen to emanate at a net downward velocity, however small. This is one possible way to discriminate, but Chandler's video is not good enough for me to tell by looking. The former possibility - a significant mass of propellant (upwards of 10-20% of panel mass) would necessarily produce a huge volume of gas and/or particulate in the short 0.5 second interval.

So, take your pick: loud, violent smoke expulsion or a huge billow. That's what it takes to stay in a band of what's reasonable. Just common sense from conservation of momentum. The velocity change is small, but the mass of the panel is large and there's only a half second for thrust.

My conclusion at this point is it doesn't seem possible given the visual constraints, though it's not as outrageously far-fetched as I originally thought.

femr2 wrote:Yeah, Tony is talking utter tosh.

Seconded. There 's no reason to reduce sample rate. Noise can be dealt with in other ways.

On the other hand, if the velocity changes are significant and/or sustained, lower sampling rate may not be a problem. In the case of Tony's calculated magnitude of jolt, for example, the low sample rate doesn't matter if that sort of jolt were to actually occur. In looking at Chandler's graph, I'd say the excursion is of significant magnitude and duration that a higher sample rate is likely of little value unless it were to reveal the position to be oscillating about the running mean as opposed to a monotonic deviation. This would require the samples taken to have conveniently captured only the high side in an aliased manner. With the continuity and physical constraints on reasonable motion of the panel, the underlying condition of oscillation is unlikely but all sorts of artifact from visual measurement could produce non-physical error in motion tracking, therefore it is advisable to oversample and reduce.

In no case is a higher sampling rate a problem.

SnowCrash wrote:I don't understand... regardless of the descent start time, the object's velocity increment is what matters here is it not?

Yes, that's true. Its initial velocity doesn't matter. You'll see I completely threw v₀ out the window in the calculations above; g, too, only differential acceleration need be considered. Change in velocity is all that matters for deriving acceleration, but doing it well from video, especially like this, requires much care. Remember the measurement is position over time, acceleration is twice removed from the direct measurement.

I'm not at all convinced that Chandler has exercised due diligence in obtaining meaningful values of acceleration. Based on what I can see in this video and in prior work, I expect not. However, that remark applies to the precise values claimed and not a more general binary question of artificial impulse or not. There may be some merit, or not. At this stage, I wouldn't take a stand on whether the anomalous bump is real or procedural/source error without a closer look, and I'm not willing to take a closer look based on this researcher's credibility alone. Sounds pissy, I suppose, but there's more on the plate than will ever be eaten. I see no jet, I see no billowing plume; therefore I suspect artifact first until any additional work may show otherwise.

By the way, another thing is, if the panel is rotating, what is its initial orientation in this interval and what rotation occurs during the interval? The change of angle dictates the actual thrust vector, pretty much. Exhaust would have to be coincidentally directed upward with no rotation to achieve directional efficiency, and to avoid being kicked sideways by some amount.

SnowCrash wrote:All of which is interesting but OT...

Yes, let's do try to remain focused on the Chandler video.

Moreover, the Poteshman paper proves with mathematical certainty that there was insider trading. The counterarguments are circumstantial and cannot debunk Poteshman's statistical analysis.

Very interesting. I'll have to check that out.

The weight of the facade panels from floors 102 - 107 was 4.2 tons.
The weight of the facade panels from floors 97 - 104 was 5.9 tons.
The weight of the facade panels from floors 77 - 84 was 10.1 tons.
The weight of the facade panels from floors 68 - 79 was 11.2 tons.
The panels from the Mech floors on 74-76 weighed about 12.4 tons


If this was tower 2, I would suspect it came from perhaps floors 68-79. Obviously Chandler makes shit up and the object (facade panel) did not come from above the 102nd floor. He is very sloppy in his work. The weight might not actually matter much... I'll leave that to the physicists.. but why make up stuff? Oh I forgot... never mind...

SanderO wrote:He is very sloppy in his work.

And somewhat arrogant about it. It is for this reason that I have to take it with a grain of salt in the absence of sufficient evidence to make a firm determination. I don't mean to confer legitimacy where it's undeserved... it seems completely wacked to me at first glance, but being as objective and open-minded as possible, it can't really be ruled out on the basis of physics of motion alone - as much as I expected and even wanted it to be so. There would be other possible means of refutation, like the trailing smoke's direction of motion mentioned above, but it turns out a 2.5 m/s bump in speed over a half second may not require an obscene amount of combustible material.

Upon reflection, I wasn't even being that open minded in the calculations above. I assumed unconfined burning, therefore largely undirected exhaust, and further stretched this to mean great loss of propulsive efficiency. Neither of these are fair, the last may even be incorrect. A more conservative approach would be to postulate a cutting device with a focused jet rather than a surface coat for widespread heating. Even Chandler alluded to unconfined combustion, but why would that necessarily be so?

While there's no reason an incendiary optimized for cutting should also be optimized for propulsion, a device which utilizes a high temperature gas jet could be pretty efficient at propulsion purely by accident. With that in mind, I'll change my analysis above to be more conservative and say the most of the shaded area is within the bounds of reason. That means quantity of material is apparently not a big objection like I thought it would be.

The weight might not actually matter much...

For a given exhaust velocity, the mass of propellant required is in direct proportion to the mass of the panel. Triple the mass of the panel, three times as much stuff needed.

What strikes me odd about Chandler's finding is that the object supplying the impulse is doing it exactly in the direction of motion of the object as it apparently does not change course if I understood his claim.

I don't think it can be ruled out because of the improbability of the coincidence of alignment of the impulse with gravity but it strikes me as odd.

And then why does this impulse kick in at about floor 50 or so for only .5 sec.... what could be the mechanism to explain that?

The trace data, seems to indicate something odd and his analysis seems OK... My sense is that his data was inaccurate and so it's a garbage in equal garbage out affair.

If Chandler has accurately computed the velocity he should be able to identify the floor it came from... I'd have to look at his velocity profile but if it was in FF then he can work it right back up to where it has 0 downward velocity and I am coming to about the 75-80th floors... and the panel weight would be in the order of 12 tons.

I also would find it odd that the object was NOT rotating or twisting... the trajectory seems to be moving from east to west and so it has some lateral force applied from the beginning of its decent. And if this is the case that since it is free falling it would likely be rotating and that would or could skew his trace data.

I find the presentation similar to his others.. mostly hyping his theses.

I've gone back and looked at his video again and I even dispute his description of this being a facade panel... it looks too small when compared to the tower... and in the last clip from below the detail of other facade panels... and their scale is strikingly different. The object comes from the 75-76 mech floors or just below from the east side of the south facade and is moves SW.

I am wondering if it actually one of the columns on the mech floor just behind the facade sprung out when the top tilted to the SE... one of the first things to be tossed out when the core let go and the top came down????

SanderO wrote:What strikes me odd about Chandler's finding is that the object supplying the impulse is doing it exactly in the direction of motion of the object as it apparently does not change course if I understood his claim.

I don't think it can be ruled out because of the improbability of the coincidence of alignment of the impulse with gravity but it strikes me as odd.

Yes, this is improbable. There is also another concern raised at 911 Blogger which I overlooked, that the thrust must be directed through the center of mass otherwise it induces rotation, thus changing the thrust vector continuously. More improbability.

And then why does this impulse kick in at about floor 50 or so for only .5 sec.... what could be the mechanism to explain that?

Hard to pin down. Last spurt? Ill-timed?

The trace data, seems to indicate something odd and his analysis seems OK... My sense is that his data was inaccurate and so it's a garbage in equal garbage out affair.

That's what I think, but I won't post it on YouTube with comments disabled, and present it with certainty...

If Chandler has accurately computed the velocity he should be able to identify the floor it came from...

Slight snag with the air resistance. Non-negligible if it was falling at only 1/3g. Variable over time and incalculable due to odd shape and tumbling.

I also would find it odd that the object was NOT rotating or twisting... the trajectory seems to be moving from east to west and so it has some lateral force applied from the beginning of its decent. And if this is the case that since it is free falling it would likely be rotating and that would or could skew his trace data.

Yes. This concern has also been brought to his attention at 911 Blogger.

I find the presentation similar to his others.. mostly hyping his theses.

What I see is a quick and dirty analysis presented without consideration for basic possible sources of error and misinterpretation. As I note, some valid issues have been raised in posts at 911 Blogger and Chandler's only response thus far is to post:

DavidSChandler at 911Blogger wrote:Doing your own analysis

I am not the only one capable of doing this kind of analysis. All the software is out there and free. If you try some of this on your own you would get a much better feel for the power and limitations of the technique. Here is a tutorial I put together for my students:

...

which conveys an attitude of "I'm the teacher and you're the student" and "if you don't agree, do it yourself" which in itself erodes my confidence because the proper response is to address the concerns. And this is par for the course for these presentations. They are delivered as lectures, no discussion is indulged.

OK, some discussion is indulged. Not much. There was a rebuttal to one post towards the top. I note that Chandler's rebuttal underscores the 12 m/s^2 difference, where my calculations are for 5 m/s^2 increase. That's proportional, too. If it's really 12 tons and 12 m/s^2, it's that much more propellant mass.

It's very much one-way communication. Knowledge flows downhill from me to you, you know?

DavidS wrote:In any measurement it is important to have an idea of the magnitude of the noise. Even if you feel the noise is insignificant compared to your signal, it is still important to include it, usually in the form of error bars.

Without error bars, it is very difficult for someone reviewing your work to determine whether the different slopes are measurement error or actually a result of different accelerations. The need for error bars in the graph you have presented is particularly strong since only 3 data points (the bare minimum) were used in determining the slope.

Cluttering up the graph with more noise (by using additional data points) is okay, because it will also give a better idea of the amount of noise in the measurement.

Ignored.

Now, the bit about 3 points was a little off, because I believe the video depicts a velocity graph so 3 points represent four (most likely) position points. That's OK, it's a minor thing, no reason to ignore the rest.

Haze wrote:But I'd like to learn more about these issues:

- An estimate of the error bars for the measurement of larger than g acceleration.
- Some thought into whether vertical/horizontal rotation can explain the change in motion and downward acceleration
- An estimate of vertical and horizontal rotation
- Some kind of thought into whether the object started rotating vertically due to an asymmetrical downward force, or whether somehow the force acted symmetrically on the girder in which case one should wonder why smoke apparently appears only on one side.

All these points are not clear to me and I only raise them in order to help provide some humble "peer review".

Thanks David!!!

Ignored. Thanks David!!!

possibilities of original location




falling





fell earlier because it was already detached during early movement.

Q1: Why is a single perimeter column falling alone while others fall as 3x3 panels? (because it was already broken off from the building due to aircraft impact.) The next leading panels:





Q2: How can anyone claim collapse propagation is at or near free-fall when a free-falling object is clearly leading the collapse front by a considerable margin?

Q3: Why does the "rocket" propel downward when the object is changing orientation while falling??

Good comments everyone.

I'm waiting till someone (femr2??) either confirms or disproves Chandler's measurement of over G.

...because if it is confirmed I will really have to do some thinking.

Whilst if he is wrong I can sit back in complacency.

PS Just to show that I am thinking a little bit.

How do you get an accidentally created rocket to apply thrust through the Centre of Mass so it can create linear acceleration without causing a Catherine wheel spin? (Yup - I understand that the origins of "Catherine Wheel" may not be suitable for kids.)

PPS Now if I could just do the comparison of linear inertia/momentum to rotational inertia/momentum it could be that they are orders of magnitude different....At my age I cannot even remember the formulas reliably. And I ustawas pretty good at the mechanics/applied maths

Good catch Tom.... You've probably ID's the piece of steel depicted and it's likely only a piece of a single 36 foot length column not an entire facade assembly and from just above the plane strike on floor 79. If Tom is correct the weight would be less than a ton.

DC's piece seems to fall just ahead of the collapse and so the we might assume if it's MT's piece it hung on and was sprung off at the first movement of the upper section as perhaps as part of the initial rotation/descent. It does seem to be thicker at one end as if part of the spandrel is attached. Wouldn't that cause some sort of rotation?

I'm also a bit confused.... His claim is it was falling at 1/3 G... The how is it so far ahead of everything else? It appears to be 20-30 floors ahead of the collapsing debris which WAS falling at about G I believe. How is this possible? Was it, *exploded* off the facade well in advance but fell at 1/3G and managed not to be caught by the collapsing canopy of debris... some of which had to be falling at close to G?

Also the outburst of smoke appears to be coming from the FACADE not the object. But if this is so how could this burst of escaping gas and debris cause a downward component as opposed to a horizontal one? What outburst is DC referring to?