Re: Why the planes did not crumple

A reasonable response and reasonable questions. I guess this isn't a
waste of breath. Discussions continue inline:

2) Why the aeroplanes did not crumple

STATUS: resolved (any objections?)

There probably was crumpling until the first major aircraft structure
impacted the building wall. I don't know the exact leading edge flap
length of a 767 or the distance from the tip of the nose to the first
pressure bulkhead, but I'm guessing that the Leading Edge Flaps are
maybe 3-4 feet long and the distance from the nose radome to the
pressure bulkhead is 15-20 feet. At 500 MPH and a crumple distance of
20 feet, that is a time of .03 seconds. This is too fast to capture
with anything but specialized high speed cameras.

Why only this distance? Well, the forward wing spar of an aircraft is
one of the beefiest structures in an aircraft as is the forward
pressure bulkhead. The forward wing spar has to carry most of the
weight of the aircraft in flight and obviously the pressure bulkhead
has to contain the internal pressure at 40k feet. When they hit the
building at speed, the building will be the one that gives first at
that speed.

I'm NOT saying that the wing spar and pressure bulkhead survived this
first collision, at least not intact. They were destroyed as aircraft
structure. At that speed, however (and as laid out in my first post),
they went right through the building outer structure.



You obviously don't investigate very many airplane crashes. I've done
a bunch.

greaT (with a capital T ;-)

Actually, I'd prefer to never do another one again. It isn't the most
pleasant thing in the world to do.


So, even at the strongest point of the impact zone, the impact forces
were nearly 133% of the yeild strength of the structure. It didn't
matter what the material that hit the structure was.

Just double-checking...
Would not *any* crumpling of the air-frame have been visible?

Oops. Sorry, answered above. The bottom line is that at 500 mph, the
entire aircraft would enter the building in under 1/3 second. The
crumple area of the aircraft is only about 20 feet and the crumple
happens in a hair under .03 second. Your typical video camera simply
can't catch this.

So yes, the aircraft crumpled and yes, aircraft structure was
destroyed in the initial impact. It simply happened too fast for the
cameras to catch and, after the leading aircraft structure punched
through the building wall, the rest of the aircraft simply passed
through the hole and was destroyed as the aircraft exploded or it hit
interior structure.


A fully loaded 767 easily penetrates the
side of the WTC and most of the aircraft remains fully inside the
building.

fine, but would it also destroy the BlackBoxes?

Hard to say. The CVR and FDR are usually physically located in the
rear of the aircraft protected by fairly beefly structure. Further,
the actually recorders themselves are housed inside frames that are
designed to protect them in crashes. They survive when aircraft hit
mountains at full speed. Even when they are compromised, it is often
possible to pull data off the chips inside them even if the circuit
cards are badly damaged. I've seen flight recorders that I'd swear
that there is no way we are getting ANYTHING off of them that the
experts manage to get good data out of.

In this case, I highly doubt the boxes survived intact. If they could
find them in the rubble, however, I believe that getting data out of
them is possible.


Then the INCREDIBLE collapse!! The second-hit tower EXPLODED first!
.. and they neatly came down ... the massive steel core did not keep
standing
up even though it was anchored in the bedrock and had very high
vertical strength.

To be honest with you, this was what I had the hardest time with as
well. The entire collapse was related to how the WTC buildings were
constructed. Some structural engineers have even gone on record as
saying that buildings using traditional construction techniques may
not have collapsed!

As you know (based on your questions, you obviously did some
significant research here), the WTC used a design where there was an
interior core and an outer rigid shell structure with NOTHING
STRUCTURAL between the two. This gave the building a LOT of usable
interior space. When I first saw the videos, I was unclear on the
special construction and when I saw some of the aircraft parts come
out the back side of the building after impact, I was amazed that the
building was still standing. I fully expected the upper structure to
"topple" onto nearby buildings and take out half of Manhattan. If the
planes had hit lower, I still think that is what would have happened
and on a traditional building that suffered enough damage that it was
blowing aircraft parts out the back side on impact, it is certainly
what would have happened.

The WTC was a special case. Each floor was attached to both the
interior core and the outer wall by steel support brackets. When the
aircraft hit, they started firestorms burining across several floors
(they didn't hit perfectly horizontally). Remember, they were
carrying several hudred thousand pounds of aircraff fuel that pretty
much started everything on the floors burining at once. The central
core acted as a chimney making the fire even hotter.

What finally happened is that it got hot enough that the steel
supports for the floors started yielding. This created uneven
stresses around both the core and the shell causing the remaining
structure to start buckling towards the floor slabs (the core
structure buckled out, the walls in). When the first section finally
buckled, the whole thing collapsed vertically as the lower floors
couldn't hold the load of the upper floors coming down on top of them.

One thing to remember is that modern buildings are DESIGNED to be
taken down by implosion. They are DESIGNED to collapse vertically
like this.

Now, the sad part. Pretty much all of the structural engineers agree
that the aircraft impacts did NOT critically cripple the structure of
the building. It probably couldn't have been repaired, but running
two empty (or largely empty) aircraft into the buildings would not
have been engough to bring them down. The heat from the fires is what
caused the buldings to collapse.




Was the energy from the top-floors coming down sufficient for the
pulverization of concrete into the finest dust?
http://911research.wtc7.net/wtc/evidence/dust.html

Quite definitely. Heck, I'm sure you've seen cement before it is
mixed. It is a very fine powder. There was a heck of a lot of force
in that collapsing building, more than enough to pulverize concrete. I
was fortunate enough to be in Las Vegas a couple of years ago and
watch them implode an old casino. Even something that small created
massive amounts of dust over a several block area. When something the
size of the world trade center comes down...well, I have no problem
with the dust generated.

I'll admit that I'm an aerospace engineer, not a civil engineer (my
dad was a CE), but my experience with buildings and large structurs
coming down (as a spectator) leaves me with no doubt that the dust
from the collapse was a perfectly reasonable by-product of the
collapse.


Could the trajectory of the rubble be achieved with just the
air-pressue?
http://www.saunalahti.fi/wtc2001/soldier5.htm

Well, the buildings would move a lot of air and, near the ground with
all of the surrounding buildings limiting where the air can go, there
was probably a pretty good wind down the surrounding streets as the
buildings collapsed. I think that most of the debris was probably
thrown away from the scene on ballistic trajectories generated by the
force of the collpase (the same forces that crumpled the steel and
pulverized the concrete). I've found aircraft wreckage in amazing
places after high speed impacts. I don't have a map of where
everything was found, but I haven't seen anything that makes me shake
my head and say, "No Way". There was a whole lot of energy created
when those buildings collapsed, Just taking ONE of those wall sections
and crumpling it is going to release a bunch of energy. Taking two
buildings worth and all of the potential energy of tons of buildings
dropped hundreds of feet. No, I don't think air pressure was the
primary means of carrying debris (although the airflow is what carried
most of the dust).

BTW, this last website is a crock. Yes, the building was designed to
take the impact of a 707. However, at the time the building was
designed, the largest 707 was a max weight of only about 250,000
pounds and the cruising speed was about 485 mph. The 767 is 1.5 times
the gross weight and 10% higher design cruising speed (the cruising
speed of a 767 is about what the max rated speed was for an original
707). Still, as I said earlier, the impact is not what brought the
buildings down. The buildings were never designed for massive fires
like this. It never entered into the designer's minds that this could
happen. I saw in interview with one of the original structural
engineers. The poor guy was going nuts trying to figure out what they
could have done to protect the building against a fire like this but
he was having a hard time coming up with a workable method even using
today's technology.

When they started digging through the rubble trying to figure out what
had happened, they found something interesting. In both buildings,
most of the structure failed in tensile overstress or column buckling.
Small sections of both buildings, however, were found to have yielded
and failed in ductile buckling or ductile overload and the metal, when
looked at carefully, was found to be partially annealed (the weakest
form of the metal and something that happens only when exposed to high
heat). The floor brackets in these areas were found to have bent from
a 90 degree section to nearly flat and the wall sections were found to
have buckled in towards the core and the core was found to have
buckled out towards the shell. These sections did not show column
buckling nor did they show tensile overload. They did show evidence
of high heat.

Remember, the major building structure was only 1/4 to 5/8 inch. Even
the core was rarely more than 13/16 thick. It simply doesn't take a
good, hot fire that long to heat this structure.


Thanks in advance for engineering a proper explanation!

I don't claim that it is all absolutely proper. I have my calculator
out so the numbers are all about right, but the detailed civil
engineering stuff I'm a bit weak in. I know aircraft structure and
have gotten to see and tour a number of pretty cool building
structures, but I don't claim to be an expert in exactly how buildings
are built or how they collapse.

One absolutely key thing to remember when reading the websites you've
been searching out. If it was really bombs that caused the building
collapse, why are all of the structure in the collapse initiation zone
buckled towards the CENTER of the floor area and why is it all ductile
flow of annealed metal? A bomb creates forces AWAY from the point
where it explodes and the metal in the are fails in tensile overload.
The only way for bombs to create the forensic evidence if for there to
have been two rings of them, one OUTSIDE the building and one INSIDE
the core that all went off at the same time and all created some kind
of massive heat source that annealed the metal. I'm not entirely sure
how you get the bombs to cause the damage found to the floor
attachement brackets. I'll think on that one.

I guess my point is that the bomb theory doesn't fit the story that
the metal tells.
.

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