Dr J as if I haven't posted enough proof have a look at this picture of the engine wreckage.
http://www.photolibrary.fema.gov/photodata/low/va_pentagon_0901_135.jpg
This photo clearly shows the engine wreckage on the outside of the pentagon and to the left of the hole in the wall. Various people including Longspaugh and viallis have claimed this to have come from either a F-16, a Global hawk, a cruise missile or the Aux power unit of a 757.
In all these cases these are mounted centrally towards the rear of the aircraft. If the aircraft came in at a 45 degree angle from the right of the building this would put the engine on the right hand side of the hole in the wall and not the left. But lets ignore this convenient FACT for the time being.
I have already given evidence with links for the size of the engine hub of a F-16 but just to repeat so all the info is together it works out at about 9"
A cruise missile is only 20" in diameter
Source So for starters it would be impossible to fit a 1m hub into it never mind the fan blades that attach to the hub. The engine in a cruise missile is a F107
Dimentions of the fan diameter are given as 12" the hub being approx 4" (judged from photos of the engine)
Global Hawk uses the AE3007H engine.
Source From the picture of this engine the hub is approx 1/3 the diameter of the engine which is stated elsewhere as 43" giving a hub diameter of about 14"
Engine pic
Aux power unit can be seen in this
pic This appears to be only 2 - 3 foot in overall diameter and from the exploded view the hub is approx 1/4 the size so this would be only 6" - 9". Note it also has a flat not rounded end to the shaft.
So NONE of the engines above are big enough to have left this piece of debris. Also surely with a centrally mounted engine, the engine would have followed on it's flight path and dissapeared into the hole in the wall during the crash.
This leaves the Pratt & Whitney engine fitted to the 757 or the alternative Rolls Royce engine
RB211-535 This states that the diameter of the fan is 74". The hub appears to be 1/4 of this giving a hub diameter of 18". The hub also has a pointed not rounded end.
Alternate engine type came from this
article
Longspaugh also claims that the security camera photos proove that whatever hit the pentagon was doing well over 1000Kmh. From the above links
Global hawk speed = 640Kmh
Cruise Missile speed = 880Kmh
So if Longspaugh is correct about the speed of impact then NONE of his suggested alternatives apart from the F-16 are fast enough. Either that or he has mis-calculated the speed of impact.