The 9/11 Forum

OneWhiteEye · by **OneWhiteEye** on Wed Nov 04, 2009 5:12 am

The antenna tilt stays roughly in the plane containing the optical axis until around frame 990. Then it gets a big whack.

OneWhiteEye · by **OneWhiteEye** on Wed Nov 04, 2009 6:03 am

Just had another look at it, the big whack really comes a second after that, around 1020. Before that, drift.

Dr. G · by **Dr. G** on Wed Nov 04, 2009 5:37 pm

DBB & OWE:

It is interesting to consider the tilt as a rotation about a hinge on the north face near the 96th floor. For a freely rotating upper section, of height h and width w, the angular rotation is given by:

d(theta)/dt = Sqrt{ 3wg.sin(theta) / (h^2 + w^2) }

I have used this formula and my values of theta taken from OWE's data to determine d(theta)/dt of a freely rotating upper section as a function of t from t=0 to t=3.33 seconds and compared these values to the observed d(theta)/dt data.

What I find is that the angular velocity is about half the free rotation rate. This shows, as we also observe for the vertical drop motion, there was considerable (relatively constant!) resistance to the rotational motion, at least for the first few seconds of motion.

David B. Benson · by **David B. Benson** on Wed Nov 04, 2009 6:22 pm

Algoithm 1 was used in the first post; it produced the more modest tilts.
Algorithm 2 is Dr. G's; those tilts are somewhat more modest.
Algorithm 3 produced more agressive tilts, but lacked sufficient control on the drop.
Here it is as algorithm 4 with good constraints on the drops. I'm posting just the b01 angles as this suffiices to see that the angles are less agressive then in algorithm 3 but more so than the first two algorithms.

Code: Select all: frame time after formal start: angle (degrees) 800 t= -3.637: b01= 0.000 900 t= -0.300: b01= 0.681 910 t= 0.033: b01= 1.080 920 t= 0.367: b01= 1.738 930 t= 0.701: b01= 2.939 940 t= 1.034: b01= 5.308 950 t= 1.368: b01= 5.948 960 t= 1.702: b01= 7.464 970 t= 2.035: b01= 8.088 980 t= 2.369: b01= 8.545 985 t= 2.536: b01= 9.067 990 t= 2.703: b01= 10.173 995 t= 2.870: b01= 9.106

The apparent reduction of angle in frame 995 appears in all calculations using the nw corner feature and in none of the calculations using the washer feature.

Major_Tom · by **Major_Tom** on Wed Nov 04, 2009 6:54 pm

Just had another look at it, the big whack really comes a second after that, around 1020. Before that, drift.

If we assume for the moment that the collision is between an intact hat truss/ antenna and something hidden in the smoke,

at about what floor level or elevation would the collision take place?

The 92nd floor?

What I find is that the angular velocity is about half the free rotation rate. This shows, as we also observe for the vertical drop motion, there was considerable (relatively constant!) resistance to the rotational motion, at least for the first few seconds of motion.

Interesting. It is an applied resistance in the form of torque. How do you know it was relatively constant?

David B. Benson · by **David B. Benson** on Wed Nov 04, 2009 7:35 pm

Major_Tom wrote:at about what floor level or elevation would the collision take place?

I calculate floor 85 or lower. Floors 79--83 were type 9, all above, except floor 92 were type 1; floor 92 was type 2.
However, from 2.2 seconds onwards, the antenna mast was freed from at least one guy wire. What is observed could simply be the antenna mast beginning to fall off the remaining structure.

OneWhiteEye · by **OneWhiteEye** on Wed Nov 04, 2009 9:35 pm

Dr. G, that's fascinating. An effective constant torque?

femr2 · by **femr2** on Wed Nov 04, 2009 10:00 pm

OneWhiteEye wrote:Dr. G, that's fascinating. An effective constant torque?

If so, could that be an effect of a more rapidly descending South side ? (Natural or contrived)

David B. Benson · by **David B. Benson** on Wed Nov 04, 2009 10:34 pm

Dr. G wrote: d(theta)/dt = Sqrt{ 3wg.sin(theta) / (h^2 + w^2) }
...
What I find is that the angular velocity is about half the free rotation rate. ...

Very nice! I'll use this formula to fit (and smooth) my data. I just want a decent estimate of the tilt to apply a sin(theta) correction to all of OneWhiteEye's pixel measurements.

That is, I'll use
d(theta)/dt = Sqrt{ k.sin(theta) }
for best estimated value of k to fit the data.

Dr. G · by **Dr. G** on Thu Nov 05, 2009 12:25 am

Major_Tom:

I was careful to say "relatively" constant because the observed tilts follow the calculated tilts only to some approximate degree; in fact I do see what look like periodic "wobbles" in the data which may be due to variable resistance to the rotational motion; or could be artefacts in the data!

Whatever, ..... it's hard to imagine a tilting of an upper block of WTC 1 that is completely smooth over 10 or so degrees! Forget missing jolts; worry about missing wobbles!

femr2 · by **femr2** on Thu Nov 05, 2009 4:31 pm

With the open-ended thread title, I must ask...

Is this thread to be limited to tilt over the first couple of seconds, or the full cycle ?

http://www.youtube.com/watch?v=fUFzZ3HyfXM
http://www.youtube.com/watch?v=GgnkO1SeuPU

If watched carefully, it can be seen that the entire cap tilts towards the East after the initial drop and Southward tilt.

If this thread is limited to first couple of seconds, no probs, I'll start another one, but would request the thread title be updated to clarify.

David B. Benson · by **David B. Benson** on Thu Nov 05, 2009 5:52 pm

femr2 --- As long as something can be learned from the tilt.
Watching your clip, I'll opine that the antenna mast is indeed loose at the base towards the end and beginning to fall off the rest of the structure.

femr2 · by **femr2** on Thu Nov 05, 2009 6:22 pm

David B. Benson wrote:femr2 --- As long as something can be learned from the tilt.

Indeed it can...

If watched carefully, it can be seen that the entire cap tilts towards the East after the initial drop and Southward tilt. Watch the NW corner as the antenna begins to tilt to the East.

Watching your clip, I'll opine that the antenna mast is indeed loose at the base towards the end and beginning to fall off the rest of the structure.

Please watch again carefully. I will, of course, include additional resource to confirm the behaviour, but this view is particularly clear (Or I wouldn't have chosen it)

David B. Benson · by **David B. Benson** on Thu Nov 05, 2009 6:45 pm

femr2 --- Possibly, but to my inexpert eye, less that the antenna mast.

Major_Tom · by **Major_Tom** on Thu Nov 05, 2009 7:19 pm

Femr, in your GIF of eastern antenna movement a few posts ago...

It seems as if there is sharply increased NW corner resistance about 6-7 stories into the fall.

A soft collision. Hat truss vs lower NW corner (or fl 98 vs fl 92, or fl 106 vs fl 98???) after 6-7 stories of relatively smooth descent.

Hmmmmm.

The 9/11 Forum

WTC 1 tilt

Re: WTC 1 tilt

Re: WTC 1 tilt

Re: WTC 1 tilt

Re: WTC 1 tilt

Re: WTC 1 tilt

Re: WTC 1 tilt

Re: WTC 1 tilt

Re: WTC 1 tilt

Re: WTC 1 tilt

Re: WTC 1 tilt

Re: WTC 1 tilt

Re: WTC 1 tilt

Re: WTC 1 tilt

Re: WTC 1 tilt

Re: WTC 1 tilt

Who is online