I answered this a few pages back which means the obfuscatiors efforts are effective.
To illustrate it I posted an animated gif,
WTC 1 animated gif of the impact.
WTC 2 animated gif of the impact.
The obfuscatiors, cried, "That doesn't show the core." and my answer was lost in what followed.
The core of Tower one was holed all the way through by the right engine of flight 11, fuel flowed it through and spread fuel through the core. The central stair and the western stair were destroyed. The engine bounced off the inside of the farside perimeter walls not exiting the tower. The left engine hit interior walls and stayed inside the core on the east half. Falling debris had partially blocked the east stairwell and the fuel exploded making the environment full of smoke and fire, uninhabitable. The core was protection from the aluminum plane but not the engine. It was about 2.5 thick at impact height.
The core of tower 2 was holed by the left engine of flight 175 which was traveling 100 MPH faster than 11 and the core was about 4 feet thick at that elevation. Smaller amounts of fuel were in WTC 2 as much of the fuel burned outside the east wall at impact. Tower 2 had 2 functioning stairwells and little smoke in the core.
Flight 11 made a solid hit and only the engines penetrated. That is pretty good protection, but the fire issue made the environment uninhabitable.
