How could the planes wings penetrate the WTC?

derwoodii

Senior Member.
while appearing solid, WTC were mostly air glass fiber board within, at cruising speed id suggest penetration of outter wall most likely..


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It is notable that the visual representation of the airplane in your video is far larger than reality.
99a42601e59b18f02319d552ed76dd2a.jpg

Taken from https://historythings.com/final-moments-last-images-tragedy-struck/16/
I know, but I couldn't find a more close simulation from recent videos enacting such collisions. Nevertheless in that video there are at least two instances where the plane (despite being larger) doesn't penetrate fully, presumably because it is launched at a slower speed and/or too steep an angle.
 

Landru

Moderator
Staff member
I know, but I couldn't find a more close simulation from recent videos enacting such collisions. Nevertheless in that video there are at least two instances where the plane (despite being larger) doesn't penetrate fully, presumably because it is launched at a slower speed and/or too steep an angle.
Well if they got the size wrong they probably made other mistakes too.
 

JMartJr

Senior Member
Almost every building aside from warehouse... ie human occupied buildings are 95% air. All high rises are 95% air.
Yeah, but it is probably worth being reminded of just how much that is true. Seeing the pic Derwoodii posted frankly surprised me. 1 picture = 1 kiloword, and that picture brought home to me, and I would suspect others, just how penetrable those buildings (not uniquely) would be. With the old adage that you can't use logic or facts to reach somebody who built an opinion not based on logic and facts, the visecral truth of that image might be a very useful tool for practical debunking of "How could a plane punch through a solid building?" In other pics the buildings indeed look like very solid objects -- that image helps to see them in another way.
 

Landru

Moderator
Staff member
I know, but I couldn't find a more close simulation from recent videos enacting such collisions. Nevertheless in that video there are at least two instances where the plane (despite being larger) doesn't penetrate fully, presumably because it is launched at a slower speed and/or too steep an angle.
This is not a model but seems to be a video game rendering.
 

JMartJr

Senior Member
1 picture = 1 kiloword, and that picture brought home to me, and I would suspect others, just how penetrable those buildings (not uniquely) would be. ... In other pics the buildings indeed look like very solid objects -- that image helps to see them in another way.
This one might also be worth considering. A plane moving at high velocity penetrating a lot of windows might be easier to understand.

l7izkj39aum71.jpg
 

Keith Beachy

Senior Member
There was a study about what it took to break the shell and enter the WTC. In addition the study states if the shell steel had been thicker, the planes could be stopped even at high speed.

From the paper:
A numerical simulation of the aircraft impact into the exterior columns of the World Trade Center (WTC) was done using LS-DYNA. For simplification, the fuselage was modeled as a thin-walled cylinder, the wings were modeled as box beams with a fuel pocket, and the engines were represented as rigid cylinders. The exterior columns of the WTC were represented as box beams. Actual masses, material properties and dimensions of the Boeing 767 aircraft and the exterior columns of the WTC were used in this analysis. It was found that about 46% of the initial kinetic energy of the aircraft was used to damage columns. The minimum impact velocity of the aircraft to just penetrate the exterior columns would be 130m∕s. It was also found that a Boeing 767 traveling at top speed would not penetrate exterior columns of the WTC if the columns were thicker than 20mm. https://ascelibrary.org/doi/10.1061/(ASCE)0733-9399(2005)131:10(1066)

I have a copy on my computer, and can't find a free download now.
 

FatPhil

Active Member
But aren't physics oriented video game models an approximation for physical models that would otherwise be too expensive to construct and test in the real world?

Yes, but a sphere is an approximate physical model for a cow.

A handy clue that this was not a good approximation was that the distance between the porthole windows down the fuselage was about the same as the distance between the floors in the skyscraper. What is this, a trade center for ants?
 

FatPhil

Active Member
From the paper:
> a Boeing 767 traveling at top speed would not penetrate exterior columns of the WTC if the columns were thicker than 20mm.

I'd suggest that the plane would *never* "penetrate" such exterior columns - it would simply go in between them. And thus the plane and payload would end up inside the WTC anyway, just shredded slightly more quickly than it was in reality.
 
A handy clue that this was not a good approximation was that the distance between the porthole windows down the fuselage was about the same as the distance between the floors in the skyscraper. What is this, a trade center for ants?
Okay, I see how in that video, the scaling would pose a problem in accurately simulating such a scenario. Still it's expensive to construct a model to demonstrate such a scenario, so wouldn't physics simulation games be a substitute for trying to model these plane impacts? If not, what is still missing, assuming the scaling is not amiss?
 

Landru

Moderator
Staff member
Okay, I see how in that video, the scaling would pose a problem in accurately simulating such a scenario. Still it's expensive to construct a model to demonstrate such a scenario, so wouldn't physics simulation games be a substitute for trying to model these plane impacts? If not, what is still missing, assuming the scaling is not amiss?
No, it's not. It's a cartoon.
 

NorCal Dave

Active Member
Where would the bulk of the aircraft gone? Bounced off like a huge shotgun blast? Slid down into the streets below?
Into the building. Think of a paper shredder, the paper doesn't bounce off the face of the machine, it goes into the trash can in ribbons.

Same with the plane. IF, the above calculations are right and IF, the exterior columns we thicker than 20mm, then the building would have acted like a paper shredder and "ribbons" of the plane would have continued on their trajectory into the building. Of course the columns are wider than the knives in a paper shredder, so some debris would probably pile up on the columns and fall to the ground, but most of the plane would still end up inside the building.

And, in the case of the WTC, the columns were less than 20mm thick, so the plane simple smashed through them.
 

Mendel

Senior Member.
then the building would have acted like a paper shredder and "ribbons" of the plane would have continued on their trajectory into the building
the question is, how much energy would that consume?
once you match the initial kinetic energy of the aircraft with the energy expended to bend columns and "shred" the plane, the craft stops moving forward.
 
No, it's not. It's a cartoon.
How exactly is it no better than a cartoon if physics calculations and setting various parameters are going into creating these sandbox simulations?

There was a study about what it took to break the shell and enter the WTC. In addition the study states if the shell steel had been thicker, the planes could be stopped even at high speed.

From the paper:


I have a copy on my computer, and can't find a free download now.
This is interesting because before the attacks, the exterior columns of the WTC were thought to be quite formidable in thickness already, with most of the weight of the building lying in the exterior columns or core columns, instead of being spread out evenly across the floors like in normal, traditionally constructed skyscrapers.

If the outer steel shell columns had been thick enough to prevent the plane from entering the building, then most of the jetfuel explosion and ensuing fires would have occurred outside of the towers, meaning that multiple floors would not be ignited in an expansive traveling fire scenario, and so the towers likely wouldn't have collapsed.

If this is all true, this shows that designing buildings with strong exteriors is very important to guarding against plane crashes and ensuing fires, arguably as important as having a strong core column area that can resist disintegration and is not as flammable (for example, encasing core columns in a concrete core rather than a drywall core). As an aside, this possibly means that because the new WTC buildings have even less of a thick outer steel shell than the old WTC towers, being mostly glass on the exterior, meaning the planes would probably have an easier time penetrating the exterior of the new WTC towers in NYC than the old ones.

That would have a been a good argument for rebuilding the twin towers with thicker exterior perimeter columns and the core columns contained in a concrete core as part of the WTC site rebuilding plan, but that's just my opinion.
 
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Landru

Moderator
Staff member
How exactly is it no better than a cartoon if physics calculations and setting various parameters are going into creating these sandbox simulations?
I can find no evidence that what you say is true. It's a game engine designed to run a game. Just like Coldwaters is a submarine game and not a submarine simulator.
 

NorCal Dave

Active Member
the question is, how much energy would that consume?
once you match the initial kinetic energy of the aircraft with the energy expended to bend columns and "shred" the plane, the craft stops moving forward.
I wont argue that, as it's beyond my mathematical abilities, but I understand that at some point the plan can no longer move through the "shredder" and some of it will be left outside the building. I suppose someone could calculate how much would end up in vs out, but in the end it's a mute point, though perhaps a fun intellectual pursuit. The columns were not over 20mm thick, so the plans simply plowed right through most of them and into the building.
 
I can find no evidence that what you say is true. It's a game engine designed to run a game. Just like Coldwaters is a submarine game and not a submarine simulator.
But doesn't the game engine contain programming instructions for carrying out physics calculations to model the physics in the sandbox simulations?

What would it take for such a simulation to be more similar to the real world instead of an unrealistic game engine rendering?
 

JMartJr

Senior Member
But doesn't the game engine contain programming instructions for carrying out physics calculations to model the physics in the sandbox simulations?

What would it take for such a simulation to be more similar to the real world instead of an unrealistic game engine rendering?
Define "physics." A game needs a "physics engine" that makes stuff move in a way that works for game play -- often but not always looking sort of like how stuff moves in the real world. You drop something, it falls don, you shove something, it falls over or doesn't depending on how massive it is, you throw something against a wall, it bounces back. It does not generally need to be able to emulate the actual physcial behavior of an aircraft engine interacting with the structural member of a skyscraper at various speeds, with variables for how the building and aircraft are constructed. A game physics engine /= the laws of physics in the actual Universe. If you have reason to think this engine does more than I am assuming, please feel free to show that to us.
 
Define "physics." A game needs a "physics engine" that makes stuff move in a way that works for game play -- often but not always looking sort of like how stuff moves in the real world. You drop something, it falls don, you shove something, it falls over or doesn't depending on how massive it is, you throw something against a wall, it bounces back. It does not generally need to be able to emulate the actual physcial behavior of an aircraft engine interacting with the structural member of a skyscraper at various speeds, with variables for how the building and aircraft are constructed. A game physics engine /= the laws of physics in the actual Universe. If you have reason to think this engine does more than I am assuming, please feel free to show that to us.
The video of the plane crashing into the WTC-like tower is from the game Teardown.
According to several links I was able to find (https://www.teardowngame.com/, https://teardown-game.com/, https://screenrant.com/teardown-game-destruction-physics and https://store.steampowered.com/app/1167630/Teardown/) the simulations in the game feature a fully destructible, polygon voxel environment.

When I think of sandbox simulations these days, I assume they have the same standards as games like universe sandbox, where calculations go into simulating the movement of objects and collisions (as can be seen here).

I don't know whether the game engine in teardown does more than you are assuming, all I see is that it has destructible polygon voxel environments, ray tracing and uses a custom physics and graphics engine designed for the game itself.
What game engine are you using?
The game uses a custom physics and graphics engine built for this game specifically. It uses raytracing for lighting, but does not require an RTX GPU.

How is one able to tell whether a game physics engine is suitable for simulating the laws of physics in the actual Universe? For example, what makes a game engine like Blender suitable for simulating rigid and soft body collisions but not other simulation sandbox games?
 

Mendel

Senior Member.
But doesn't the game engine contain programming instructions for carrying out physics calculations to model the physics in the sandbox simulations?

What would it take for such a simulation to be more similar to the real world instead of an unrealistic game engine rendering?
Which physics engine was used for that video?

Game engines are supposed to look fun.
One thing that games do is compute scenes frame by frame, with e.g. 1/30 of a second elapsing between frames. Because of this, objects that move towards each other can be separate in one frame and occupying the same physical space in the next. An engine such as Havok will try to "fix" this by generating a force out of nowhere that pushes the objects apart again. In a truck driving game, you might hit a power pole fast enough, and your truck could go flying high through the air. That's obviously not happening in reality.

Game physics is constrained to be fast (computations need to complete in real time) and forward. Most game objects are treated as rigid objects because soft body physics with deformation is difficult to compute quickly and realistically (and typically simulates a soft body by simply using more connected rigid elements).
"Generally, these methods only provide visually plausible emulations rather than accurate scientific/engineering simulations" ( https://en.m.wikipedia.org/wiki/Soft-body_dynamics )
"
However, if the overall stiffness of all connected beams are too high, it will begin to vibrate, and may even explode." ( https://www.beamng.com/game/about/physics/ )

A physics package for engineering has a different purpose and is validated for that purpose. A game engine is validated by the programmer saying, "hey, this looks good".
 
Which physics engine was used for that video?
I'm not sure, it says it's a custom physics and graphics engine designed for use in the game, but doesn't name the type of game engine used, other than saying that it does not require an RTX GPU

It also says at https://www.teardowngame.com/ that
Due to the rendering technique and the heavy use of physics simulation, the game requires a modern PC to run well. We recommend an Intel Core i7 processor and an NVIDIA GeForce GTX 1070 or similar. The game will run on older hardware as well, just slower.
Game engines are supposed to look fun.
One thing that games do is compute scenes frame by frame, with e.g. 1/30 of a second elapsing between frames. Because of this, objects that move towards each other can be separate in one frame and occupying the same physical space in the next. An engine such as Havok will try to "fix" this by generating a force out of nowhere that pushes the objects apart again. In a truck driving game, you might hit a power pole fast enough, and your truck could go flying high through the air. That's obvious not happening in reality.
This was frames per second data for various graphics card that I was able to find:
https://www.game-debate.com/games/index.php?g_id=36786&framesPerSecond=Teardown
fps.png
Game physics is constrained to be fast (computations need to complete in real time) and forward. Most game objects are treated as rigid objects because soft body physics with deformation is difficult to compute quickly and realistically (and typically simulates a soft body by simply using more connected rigid elements).
"Generally, these methods only provide visually plausible emulations rather than accurate scientific/engineering simulations" ( https://en.m.wikipedia.org/wiki/Soft-body_dynamics )
"
However, if the overall stiffness of all connected beams are too high, it will begin to vibrate, and may even explode." ( https://www.beamng.com/game/about/physics/ )
I think that from how collisions are rendered in the destructible environment, the Teardown game engine mainly simulates rigid body collisions, but I don't know how to tell the difference or whether there are soft body collisions
https://teardowngame.com/modding/api.html

ParticleReset​

ParticleReset()
Arguments
none

Return value
none

Reset to default particle state, which is a plain, white particle of radius 0.5. Collision is enabled and it alpha animates from 1 to 0.


MakeHole​

MakeHole(position, r0, [r1], [r2], [silent])
Arguments
position (table) – Hole center point
r0 (number) – Hole radius for soft materials
r1 (number, optional) – Hole radius for medium materials. May not be bigger than r0. Default zero.
r2 (number, optional) – Hole radius for hard materials. May not be bigger than r1. Default zero.
silent (boolean, optional) – Make hole without playing any break sounds.

Return value
none

Make a hole in the environment. Radius is given in meters. Soft materials: glass, foliage, dirt, wood, plaster and plastic. Medium materials: concrete, brick and weak metal. Hard materials: hard metal and hard masonry.



MakeHole(pos, 1.2, 1.0)


ParticleCollide​

ParticleCollide(c0, [c1], [interpolation], [fadein], [fadeout])
Arguments
c0 (float) – Collide (0.0 - 1.0)
c1 (float, optional) – End collide (0.0 - 1.0)
interpolation (string, optional) – Interpolation method: linear, smooth, easein, easeout or constant. Default is linear.
fadein (float, optional) – Fade in between t=0 and t=fadein. Default is zero.
fadeout (float, optional) – Fade out between t=fadeout and t=1. Default is one.

Return value
none

Control particle collisions. A value of zero means that collisions are ignored. One means full collision. It is sometimes useful to animate this value from zero to one in order to not collide with objects around the emitter.



--Disable collisions
ParticleCollide(0)

--Enable collisions over time
ParticleCollide(0, 1)

--Ramp up collisions very quickly, only skipping the first 5% of lifetime
ParticleCollide(1, 1, "constant", 0.05)
 
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econ41

Senior Member
I've hesitated to comment with an engineering perspective on "plane penetrating" the towers. Most members seem to be treating the situation as if it was simple binary EITHER "Would penetrate" OR "Would not penetrate". And the referenced academic paper claiming the plane would not have penetrated if the perimeter columns were 20mm or thicker. (I haven't read the paper - it is blocked by a "Paywall" - but the abstract seems to indicate that the paper does make that form of abstract binary simplification.) Sorry - it is not so. There is no "magic" threshold between "would penetrate" and "would not penetrate". If the columns plates were progressively increased in thickness less and less of the plane would penetrate. The "lighter" - lower momentum - parts being left behind

Look to the "Wile-E-Coyote" silhouette which shows that in the actual impact all BUT the wingtips penetrated, cutting/tearing/shearing columns as it did so. The wingtips were too light to penetrate. IF the column walls had been a bit thicker more of the outer wings would have failed to penetrate. Thicken the columns even more and less and less would penetrate. At some thickness the engines would have bounced, as would most of the wings. Until, with thicker columns, only a circular hole of the fuselage would penetrate. (And I'm outlining a process - not guaranteeing the details.)

So these three posts are probably "near enough" for lay-person discussion EXCEPT I suspect they are adding to @investigating911's confusion.
I'd suggest that the plane would *never* "penetrate" such exterior columns - it would simply go in between them. And thus the plane and payload would end up inside the WTC anyway, just shredded slightly more quickly than it was in reality.
Probably true enough.
Where would the bulk of the aircraft gone? Bounced off like a huge shotgun blast? Slid down into the streets below?
Not until the columns were much thicker than 20mm.
Into the building. Think of a paper shredder, the paper doesn't bounce off the face of the machine, it goes into the trash can in ribbons.

Same with the plane. IF, the above calculations are right and IF, the exterior columns we thicker than 20mm, then the building would have acted like a paper shredder and "ribbons" of the plane would have continued on their trajectory into the building. Of course the columns are wider than the knives in a paper shredder, so some debris would probably pile up on the columns and fall to the ground, but most of the plane would still end up inside the building.

And, in the case of the WTC, the columns were less than 20mm thick, so the plane simple smashed through them.
Agreed most - especially the two "IF" provisos. But bending columns sideways would probably be more of a factor than knife cut shredding.

Now this speculation by @investigating911 fails for another reason - but still related to the column thickness:
If the outer steel shell columns had been thick enough to prevent the plane from entering the building, then most of the jetfuel explosion and ensuing fires would have occurred outside of the towers, meaning that multiple floors would not be ignited in an expansive traveling fire scenario, and so the towers likely wouldn't have collapsed.
The scenario is near enough impossible. Whilst it MAY have been plausible to build a stronger tower it would not have been economically viable. The lightweight steel frame was the only pragmatic way to achieve such a tall building within the engineering capabilities of its era.

The remainder of the post diverges into broader issues drifting off the focus on "penetration".

If this is all true, this shows that designing buildings with strong exteriors is very important to guarding against plane crashes and ensuing fires, arguably as important as having a strong core column area that can resist disintegration and is not as flammable (for example, encasing core columns in a concrete core rather than a drywall core). As an aside, this possibly means that because the new WTC buildings have even less of a thick outer steel shell than the old WTC towers, being mostly glass on the exterior, meaning the planes would probably have an easier time penetrating the exterior of the new WTC towers in NYC than the old ones.
The causes of deaths associated with WTC9/11 were lack of redundancy of fire limiting provisions and escape paths for occupants. Initial structural damage was not the sole problem. I'll take a rain-check on the issues of bigger picture policy.
 
I've hesitated to comment with an engineering perspective on "plane penetrating" the towers. Most members seem to be treating the situation as if it was simple binary EITHER "Would penetrate" OR "Would not penetrate". And the referenced academic paper claiming the plane would not have penetrated if the perimeter columns were 20mm or thicker. (I haven't read the paper - it is blocked by a "Paywall" - but the abstract seems to indicate that the paper does make that form of abstract binary simplification.) Sorry - it is not so. There is no "magic" threshold between "would penetrate" and "would not penetrate". If the columns plates were progressively increased in thickness less and less of the plane would penetrate. The "lighter" - lower momentum - parts being left behind
I think it's as much the impact (be it the plane hitting the exterior columns or the floor trusses falling on top of other floor trusses ) that loosens or destroys the connections as it is severing. The columns and floors were welded together and impacts to these areas where the connections would come lose would have an effect of knocking out the columns and floors in the areas where the plane wings and fuselage impacted the building.
Look to the "Wile-E-Coyote" silhouette which shows that in the actual impact all BUT the wingtips penetrated, cutting/tearing/shearing columns as it did so. The wingtips were too light to penetrate. IF the column walls had been a bit thicker more of the outer wings would have failed to penetrate. Thicken the columns even more and less and less would penetrate. At some thickness the engines would have bounced, as would most of the wings. Until, with thicker columns, only a circular hole of the fuselage would penetrate. (And I'm outlining a process - not guaranteeing the details.)

So these three posts are probably "near enough" for lay-person discussion EXCEPT I suspect they are adding to @investigating911's confusion.
I agree the wingtips were too light to penetrate, and as such might have been part of the aluminum debris that is shown falling to the street from the impacted face.

Your continuum example where there is no binary simplification between whether a plane part or parts would or would not enter the building makes sense.

The scenario is near enough impossible. Whilst it MAY have been plausible to build a stronger tower it would not have been economically viable. The lightweight steel frame was the only pragmatic way to achieve such a tall building within the engineering capabilities of its era.
That's understandable. It's not usually economically viable to build such strong commercial office buildings.
The causes of deaths associated with WTC9/11 were lack of redundancy of fire limiting provisions and escape paths for occupants. Initial structural damage was not the sole problem. I'll take a rain-check on the issues of bigger picture policy.
Yes but people still perished in the floors below the impacted regions of the buildings when the buildings underwent a total collapse. Had it been more difficult for the plane to fully penetrate the building and spread fires across the multiple impacted floors, wouldn't a total collapse have been significantly less likely?
 

Keith Beachy

Senior Member
How exactly is it no better than a cartoon if physics calculations and setting various parameters are going into creating these sandbox simulations?


This is interesting because before the attacks, the exterior columns of the WTC were thought to be quite formidable in thickness already, with most of the weight of the building lying in the exterior columns or core columns, instead of being spread out evenly across the floors like in normal, traditionally constructed skyscrapers.

If the outer steel shell columns had been thick enough to prevent the plane from entering the building, then most of the jetfuel explosion and ensuing fires would have occurred outside of the towers, meaning that multiple floors would not be ignited in an expansive traveling fire scenario, and so the towers likely wouldn't have collapsed.

If this is all true, this shows that designing buildings with strong exteriors is very important to guarding against plane crashes and ensuing fires, arguably as important as having a strong core column area that can resist disintegration and is not as flammable (for example, encasing core columns in a concrete core rather than a drywall core). As an aside, this possibly means that because the new WTC buildings have even less of a thick outer steel shell than the old WTC towers, being mostly glass on the exterior, meaning the planes would probably have an easier time penetrating the exterior of the new WTC towers in NYC than the old ones.

That would have a been a good argument for rebuilding the twin towers with thicker exterior perimeter columns and the core columns contained in a concrete core as part of the WTC site rebuilding plan, but that's just my opinion.
Aircraft obeying the speed limit below 10,000 feet, by FAA limited to 250 knots. This means aircraft would not penetrate the WTC tower if the aircraft were operated according to FAA rules. At 250 knots, the kinetic energy would be equal to ~500 pounds of TNT. Flight 11 kinetic energy was nearly 1400 pounds of TNT, and Flight 175 had the kinetic energy equal to 2093 pounds of TNT. Both terrorists aircraft had enough energy to enter the WTC and do damage.

The terrorists ruined hijacking for all future hijackers.

Aircraft under 2,000 feet, like airliners, are usually slower than 200 knots as they get ready for landing. The WTC towers would stop an airliner going 250 knots, as seen in the study, and Robertson designed the structure to stop an aircraft going 180 mph. Not surprised a study shows the shell had more than enough strength to stop an aircraft as designed, and the design point had some over engineering itself.

Aircraft vs Building was a concern because an aircraft hit the Empire State building with the kinetic energy equal to ~30 pounds of TNT. It easily entered the Empire State Building, killing 11, one engine went through the building, and the fires were put out. The port authority for the WTC complex bragged how a fully loaded 707 at 600 mph was studied. However, this appears to be the Port Authority bragging - where as Robertson, the structural engineer for the towers, said it was a low on fuel, like landing, lost in the fog, configured to land, 180 mph.

The aircraft on 9/11 were speeding, I doubt the terrorist pilots thought about the 250 below 10 rule. The Boeing jets fly well at 300 knots. When we let down we slow at 10,000 feet to 250 knots, the terrorist did not slow down. Flight 175 was going well past Vmo, the maximum speed to ensure airframe long life. As it turns out, 175 was only slight over the test pilot limits past Vd at impact. Flight 11 was at a moderate speed. I guess you could plan on terror attacks and overengineer everything, but under normal conditions the towers would still be standing.

Most of the NYC buildings if hit the way the WTC towers were hit, would have killed hundreds if not thousands, and maybe the buildings may have NOT globally collapsed. The planes delivered 10,000 gallons of jet fuel and instantly ignited it, the 10,000 gallons of jet fuel did double duty, bringing 66,000 pounds of mass, adding to the Kinetic Energy helping destroy structure, then starting massive office fires.

Velocity squared, brings speed kills to the energy equation.

If you do build a new WTC tower, you could specify the design to stop aircraft at certain speeds/energy levels. You could have the floor connections to the core and shell beefed up to possibly stop a Serial large expanse workspace floor connection failure due to mass overload, aka SLEWFCFDTMO... or, Serial Mass overload of large expanse workspace floor connections, SMOOLEWFC

Should we recommend retrofit for the Empire State Building to stop aircraft from entering the building to save lives if an aircraft hits. The ESB failed to stop a tiny impact.
 
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Aircraft obeying the speed limit below 10,000 feet, by FAA limited to 250 knots. This means aircraft would not penetrate the WTC tower if the aircraft were operated according to FAA rules. At 250 knots, the kinetic energy would be equal to ~500 pounds of TNT. Flight 11 kinetic energy was nearly 1400 pounds of TNT, and Flight 175 had the kinetic energy equal to 2093 pounds of TNT. Both terrorists aircraft had enough energy to enter the WTC and do damage.
According to others on this thread and others about this similar topic https://www.metabunk.org/threads/debunked-demolition-“squib”-is-visible-at-top-of-wtc-north-tower-before-flight-11-crash.11997/) like @econ41 @Jeffrey Orling

even at normal speed for that height, the plane wings would still penetrate the facade. So I'm not sure what to believe at this point, unless you are meaning that by not penetrate, the wings of the airplane flying at such a speed would not enter the building and instead snap off and fall to street level. That's what I initially thought would happen in the "lost in fog, wanting to land" scenario that Leslie Robertson said the towers were designed in mind for. However, people on this thread and the other thread said that the wings would still penetrate the facade even at that slower speed because of the fuel tanks (that were near full fuel capacity) in the wings, the strength of the connections in the wings to the fuselage, and mass and momentum of the airplane.
The aircraft on 9/11 were speeding, I doubt the terrorist pilots thought about the 250 below 10 rule. The Boeing jets fly well at 300 knots. When we let down we slow at 10,000 feet to 250 knots, the terrorist did not slow down. Flight 175 was going well past Vmo, the maximum speed to ensure airframe long life. As it turns out, 175 was only slight over the test pilot limits past Vd at impact. Flight 11 was at a moderate speed. I guess you could plan on terror attacks and overengineer everything, but under normal conditions the towers would still be standing.
The intent of flying the airplane at near top speed was to cause as much damage to the building as possible upon impact and kill everyone aboard the airplane as part of the hijacker's murder suicide mission. Some eyewitness accounts of both impacts recalled that the plane appeared to be speeding up and making a dive for the towers in the last moments (much more so for the south tower impact, but also occurring to a lesser extent in the north tower impact). The last minute tilting of the airplane was in the case of both towers to probably take out as much floors as possible, although the UA175 airplane was also probably tilted at the last moment supposedly either because hijackers feared they'd otherwise miss the south tower altogether, or because there was the beginning stages of a passenger revolt in place and the hijackers were trying to ward off any possible revolt or successful entry or breach into the cabin by flying the plane erratically like they did on UA93. The first possibility is much more likely, but we will never know what the true intent of the hijackers to steeply bank the airplane at an angle before hitting the south tower was.
If you do build a new WTC tower, you could specify the design to stop aircraft at certain speeds/energy levels. You could have the floor connections to the core and shell beefed up to possibly stop a Serial large expanse workspace floor connection failure due to mass overload, aka SLEWFCFDTMO... or, Serial Mass overload of large expanse workspace floor connections, SMOOLEWFC
The curtainwall of the new WTC being mostly glass is arguably very bad, but the thicker and stronger concrete used (in addition to concrete instead of drywall housing the core) and lack of lightweight steel trusses being used as the floor decking (instead opting for more traditional, thicker steel beam decking) is a positive, so there are tradeoffs of the new buildings in how they would be able to withstand (as far as damage and preventing global collapse) such plane impacts that the old WTC experienced.
Should we recommend retrofit the Empire State Building to stop aircraft from entering the building to save lives if an aircraft hits. The ESB failed to stop a tiny impact.
Not only the ESB but also the new WTC buildings, which have an exterior of mostly glass instead of dense, thinly spaced hollow steel columns like in the original WTC.
 
Last edited:

econ41

Senior Member
I think it's as much the impact (be it the plane hitting the exterior columns or the floor trusses falling on top of other floor trusses ) that loosens or destroys the connections as it is severing. The columns and floors were welded together and impacts to these areas where the connections would come lose would have an effect of knocking out the columns and floors in the areas where the plane wings and fuselage impacted the building.

I agree the wingtips were too light to penetrate, and as such might have been part of the aluminum debris that is shown falling to the street from the impacted face.
Sure but those are all details that we can never be sure about. My main point was as you say in this next part of your post:

Your continuum example where there is no binary simplification between whether a plane part or parts would or would not enter the building makes sense.
Thanks. That was the main point I wanted to explain. The thread seemed to have a lot of presumptions about binary "yes <> no" - specifically "would penetrate OR would not penetrate". The full details we will never know and it is a very difficult area of forensic engineering to be sure about details.

That's understandable. It's not usually economically viable to build such strong commercial office buildings.
Which is a complex topic in its own right. I suggest "Don't go there" because it takes us way off the theme of this topic and thread.
Yes but people still perished in the floors below the impacted regions of the buildings when the buildings underwent a total collapse. Had it been more difficult for the plane to fully penetrate the building and spread fires across the multiple impacted floors, wouldn't a total collapse have been significantly less likely?
Yes. But.... Ain't 20/20 hindsight wonderful. Remember that strength of the building wasn't the main problem. Occupant escape paths were. So was provision for fire resistance and active fire fighting. And the actual decision at political policy levels - agree or not - was to minimise opportunities for repeated similar attacks. Hence all the changes to cockpit security and baggage inspections etc etc....

Better to prevent aircraft hi-jacks from happening rather than build all buildings to withstand them. BUT better the combination of the important parts of both of them. So prevent hi-jacks AND ensure that building occupants can escape via redundant multiple paths. AND redundant fire sprinkler systems....
 

FatPhil

Active Member
what is still missing

Name one thing that you can prove *isn't* missing, and provide the evidence to support that claim.

I suspect it simulates ballistics (so momentum and gravity) and a naive simplification of thrust and lift, and has elementary bounding-box collision detection, and nothing more. Heck, we have at least one game writer on the site - why would you bother implementing more than that - what would an insider do?
 
Name one thing that you can prove *isn't* missing, and provide the evidence to support that claim.
The disintegration of the airplane into smaller pieces upon impact with another object isn't missing. This is evident by how the airplane in Teardown breaks into smaller pieces when impacting another object at a nonzero speed.
I suspect it simulates ballistics (so momentum and gravity) and a naive simplification of thrust and lift, and has elementary bounding-box collision detection, and nothing more. Heck, we have at least one game writer on the site - why would you bother implementing more than that - what would an insider do?
An insider meaning what exactly?
 

benthamitemetric

Senior Member
It's pretty obvious that the video game engine "simulation" from post 158 wasn't built using a detailed engineering model of the building or the plane and does not simulate any material deformation or connection behavior in a rigorous, physically accurate way. For example. the outer part of the wings exhibit no movement at all in some scenarios after the body of the plane strikes the building and stops. It looks like parts of the building and plane and building are simply jerry-rigged to break off at certain predetermined points in the event that some force threshold is exceeded. In any case, there is nothing useful anyone can say about the video without knowing the assumptions behind it. I thus don't think it adds anything to this thread or the 4-5 other threads in which it was posted.

(For what it's worth, however, the video game simulation posted here is seemingly superior to Hulsey's completed hand-rigged animation for the collapse of WTC7, but that's a very low bar.)
 
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Landru

Moderator
Staff member
Even if this was a physics based engine, the plane is too big so the input is not accurate.
 

Mendel

Senior Member.
Sure, let's look at that.

MakeHole​

MakeHole(position, r0, [r1], [r2], [silent])
Arguments
position (table) – Hole center point
r0 (number) – Hole radius for soft materials
r1 (number, optional) – Hole radius for medium materials. May not be bigger than r0. Default zero.
r2 (number, optional) – Hole radius for hard materials. May not be bigger than r1. Default zero.
silent (boolean, optional) – Make hole without playing any break sounds.

Return value
none

Make a hole in the environment. Radius is given in meters. Soft materials: glass, foliage, dirt, wood, plaster and plastic. Medium materials: concrete, brick and weak metal. Hard materials: hard metal and hard masonry.

This function is for making holes. In reality, the size of the hole would depend on the speed of the object and the precise properties of the material being impacted. All of that is irrelevant here, the hole is one of 3 preconfigured sizes. There is, for example, no continuum between "weak metal" and "hard metal" as there would be in real life. (And "hard masonry" is somehow sturdier than "concrete".) Hole creation in this engine is not simulated from physical principles, these holes are scripted to look good.

ParticleCollide​

ParticleCollide(c0, [c1], [interpolation], [fadein], [fadeout])
Arguments
c0 (float) – Collide (0.0 - 1.0)
c1 (float, optional) – End collide (0.0 - 1.0)
interpolation (string, optional) – Interpolation method: linear, smooth, easein, easeout or constant. Default is linear.
fadein (float, optional) – Fade in between t=0 and t=fadein. Default is zero.
fadeout (float, optional) – Fade out between t=fadeout and t=1. Default is one.

Return value
none

Control particle collisions. A value of zero means that collisions are ignored. One means full collision. It is sometimes useful to animate this value from zero to one in order to not collide with objects around the emitter.
The fact that particle collisions can be turned off is a clear indication that this engine thinks nothing of ignoring physical laws if they stand in the way of looking good.
 

Mendel

Senior Member.
There are buildings designed for aircraft impacts:
Article:
Each applicant listed in paragraph (a)(3) shall perform a design-specific assessment of the effects on the facility of the impact of a large, commercial aircraft.

They look like this:
2-image-Barakah-nuclear-power-plant.jpg
There's been quite some effort spent on analysing these types of impacts; I'm just going to quote two bits from one, but skimming the paper gave me the impression that there was quite a bit more effort involved than the game engine's "when things collide, stuff breaks".
Article:
Sadique et al. showed that global failure occurred in the Indian BWR Mark-III-type nuclear power plant when it was hit by Boeing 747-400 and Boeing 767-400 aircrafts, while only local damage was observed when it was hit by A320 and A707-320.

Article:
SmartSelect_20211022-161002_Samsung Internet.jpg
Figure 13​

Snapshot from analysis of Boeing 767-200ER crash on the containment (wing tank case). (a) 0.10 s. (b) 0.15 s. (c) 0.20 s. (d) 0.25 s. (e) 0.27 s. (f) 0.30 s. (g) 0.40 s.

If you now think you've found a safe building for your next office, note that the regulations are not concerned with human survival.
 
It's pretty obvious that the video game engine "simulation" from post 158 wasn't built using a detailed engineering model of the building or the plane and does not simulate any material deformation or connection behavior in a rigorous, physically accurate way. For example. the outer part of the wings exhibit no movement at all in some scenarios after the body of the plane strikes the building and stops. It looks like parts of the building and plane and building are simply jerry-rigged to break off at certain predetermined points in the event that some force threshold is exceeded. In any case, there is nothing useful anyone can say about the video without knowing the assumptions behind it. I thus don't think it adds anything to this thread or the 4-5 other threads in which it was posted.

(For what it's worth, however, the video game simulation posted here is seemingly superior to Hulsey's completed hand-rigged animation for the collapse of WTC7, but that's a very low bar.)
Even if this was a physics based engine, the plane is too big so the input is not accurate.
Okay, so for now to simulate such a plane impact according to the actual laws of physics, it's probably only rendering software like Blender that could be used to model what exactly would occur in different plane impact scenarios with a WTC-like building?
 

derwoodii

Senior Member.
Okay, so for now to simulate such a plane impact according to the actual laws of physics, it's probably only rendering software like Blender that could be used to model what exactly would occur in different plane impact scenarios with a WTC-like building?

save your time as id suspect there be many known plane crashes that have analysed the impact & break up eg into trees buildings water where the plane size weight design plus air speed angle and the wings penetration damage done data seen and recorded


look here one

september-11-pentagon-design-gettyimages-1328633.jpg
 

Mendel

Senior Member.
There was a study about what it took to break the shell and enter the WTC. In addition the study states if the shell steel had been thicker, the planes could be stopped even at high speed.

I have a copy on my computer, and can't find a free download now.
You are referring to this paper, which is openly available at ResearchGate:
Article:

Impact of the Boeing 767 Aircraft into the World Trade Center


Okay, so for now to simulate such a plane impact according to the actual laws of physics, it's probably only rendering software like Blender that could be used to model what exactly would occur in different plane impact scenarios with a WTC-like building?
"Rendering software" has the purpose of producing graphics that look good.

Both the paper I cited (plane vs. power plant) and the paper Keith Beachy cited use finite element analysis software that has the purpose of allowing professional engineers to reliably evaluate the strength of real structures.

Blender is a toy when it comes to physics.
 
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