Why was the hole in the Pentagon on 9-11 so small for an airplane?

I'm watching a doentary on the National Geographic Channel and it's showing the size of the hole the aircraft made when it flew through the wall and it's only about 10 feet wide in the shape of a circle with no wings. that protrude outward and none of the gr in front of it had been disturbed and no airplane could be seen anywhere. Where did it go and how did it get through such a smal hole?