9/11: A Boeing 757 Struck the Pentagon

Compressibility is an important notion in aerodynamics. At low speeds, the compressibility of air is not important for aircraft design, but as the airflow nears and exceeds the speed of sound, a host of new aerodynamic effects become important in the design of aircraft. These effects, often several of them at a time, made it very difficult for World War II era aircraft to reach speeds much beyond 500mph.

en.wikipedia.org...

When an airplane is in motion at subsonic speeds, the air is treated as though it was incompressible. As airplane speed increases, however, the air loses its assumed incompressibility and the error in estimating, for example, drag, becomes greater and greater. The question arises as to how fast an airplane must be moving before one must take into account compressibility. A disturbance in the air will send pressure pulses or waves out into the air at the speed of sound. Consider the instance of a cannon fired at sea level. An observer situated some distance from the cannon will see the flash almost instantaneously, but the sound wave is heard (or the pressure wave is felt) some time later. The observer can easily compute the speed of sound by dividing the distance between him and the cannon by the time it takes the sound to reach him. The disturbance propagates out away from the cannon in an expanding hemispherical shell. The speed of sound varies with altitude. More precisely, it depends upon the square root of the absolute temperature. At sea level under standard conditions (To = 288.15 K (degrees Kelvin)), the speed of sound is 340.3 meters per second (761.2 miles per hour), but at an altitude of 15 kilometers (9.3 miles or 49,212 feet) where the temperature is down to 216.7 K, the speed of sound is only 295.1 meters per second (660.2 miles per hour). This difference indicates that an airplane flying at this altitude encounters the speed of sound at a slower speed, and, therefore, comes up against compressibility effects sooner. An airplane flying well below the speed of sound creates a disturbance in the air and sends out pressure pulses in all directions. Air ahead of the airplane receives these "messages" before the airplane arrives and the flow separates around the airplane. But as the plane approaches the speed of sound, the pressure pulses merge closer and closer together in front of the airplane and little time elapses between the time the air gets a warning of the plane's approach and the plane's actual arrival time At the speed of sound, the pressure pulses move at the same speed as the plane. They merge ahead of the airplane into a "shock wave" that is an almost instantaneous line of change in pressure, temperature, and density. The air has no warning of the approach of the airplane and abruptly passes through the shock system. There is a tendency for the air to break away from the airplane and not flow smoothly about it; as a result, there is a change in the aerodynamic forces from those experienced at low incompressible flow speeds

www.centennialofflight.gov... Compressibility becomes a problem at or very close to the speed of sound. Flight 77 wasn't flying at or close enough to the speed of sound for compressibility to rip the plane apart like you say it would have.

Originally posted by Zaphod58 Compressibility becomes a problem at or very close to the speed of sound. Flight 77 wasn't flying at or close enough to the speed of sound for compressibility to rip the plane apart like you say it would have.

I will just add that according to the flight data recorder retrieved from the Pentagon wreckage the plane was travelling at 345 mph at the time of impact - about half the speed of sound at sea level.

Originally posted by Dansker I will just add that according to the flight data recorder retrieved from the Pentagon wreckage the plane was travelling at 345 mph at the time of impact - about half the speed of sound at sea level.

9/11 Commission said 530mph. Who's wrong?

530, or 345, the point is that compressibility wouldn't be a factor for either speed. The speed of sound at sea level is 761 mph. I don't know which is the accurate speed for the plane, but compressibility wouldn't be a factor unless the plane was travelling at a much higher speed than it was possible for it to be travelling at.

Originally posted by diggs

Originally posted by Dansker I will just add that according to the flight data recorder retrieved from the Pentagon wreckage the plane was travelling at 345 mph at the time of impact - about half the speed of sound at sea level.

9/11 Commission said 530mph. Who's wrong?

Hard to say. The Commision report refers to a classified NTSB report which is under the control of the FBI and unavailable to the public, while the Pentagon annual status report to the Congress quotes unnamed federal investigators about the 350 mph. Then of course there's the Arlington County after action report that says 400 mph... Frankly I think "530" was just a typo of "350" and now they are too embarassed to issue a correction, but that's just me. Either way I'm suprised you put any faith in official reports... 9/11 Commision report: www.9-11commission.gov... Pentagon annual report: renovation.pentagon.mil... Arlington County after action report: www.arlingtonva.us...

Originally posted by Dansker Frankly I think "530" was just a typo of "350" and now they are too embarassed to issue a correction, but that's just me. Either way I'm suprised you put any faith in official reports...

Well the official story keeps changing on a daily basis, so just want to know the current version.

after all that ive seen and read i still think it was a global hawk that hit the pentagon.

Originally posted by Matthew5012 after all that ive seen and read i still think it was a global hawk that hit the pentagon.

Sources? Proof? Chain of Evidence? I mean, I could come here and say I think a UFO manned by ET's hit the Pentagon but I'd need to back it up with something.

Originally posted by Aotearoa

Originally posted by Matthew5012 after all that ive seen and read i still think it was a global hawk that hit the pentagon.

Sources? Proof? Chain of Evidence? I mean, I could come here and say I think a UFO manned by ET's hit the Pentagon but I'd need to back it up with something.

1. alot of people saw somthing fly into the building and said it was a plane, from looking at the photos most people can tell that a 757 didnt fly into the building. so if alot of people who were there did see somthing hit the building it has to be (for me) a global halw, if it was any sort of plane at all. 2. the fact that there wasnt much left after the crash and the one small engin that was found there, consistant with a global hawk engin. the global hawk is made from light weight materials and (again i think) smashed into 1000's of very small peices that you can see on the photos of the crash site. and you can see people from the FBI picking them all up with there hands. why was it all not left there for people to go over with a propper team later as ever other crash is.? 3. the hole in the building is only 16ft theres no way a 757 could have made such a small hole. the global hawk is much smaller (i do admit on this account tho i do wonder why the hole is 16th and round with no damage to the windows around it) 4. where are all the passangers and there belongings? if 189 people were identerfied then why arnt they or any of there stuff on any one picture from the crash??? NOT ONE! 5. i have seem some photos that try and say its a 757, namely the wheel (part of it) and a (yes one) seat from the 757. small things like that could have been placed at the place of the crash before hand, very easily. 6. why did the flight path almost come back on itself and crash into the building. if a terrist really is a the helm why didnt he fly right into the building as soon as he had it in his sights??? (what i love about this one is the fact it looked like it would hit donalds office area if the direction of the plane had just gone striaght) why wouod he fly around the building and crash his plane into the only part that is almost empty? he's not trying to hit a big X on the bulding is he like in a computer game of some shit like that, he's just going the fly the bastard right into the building asap!! 7. if the 757 did hit the bulding then why carnt the FBI release "PROPPER" video of the 757 hitting the pentagon from the 3 differnt angles they have. the video (more like a webcam) is a joke to say the least and has propabley made there whole situation worse as most people will admit it shows NOTHING that looks liek a plane!!! 8. why did the air traffic controlers from that day all think it was a milertry plane? Why dont you chew on what ive said there for 5mins and let me know your thoughts! Matt

2. ALL crashes turn the plane into small pieces that you can pick up and carry around with your hands. In a shallow angle low velocity crash, you get big pieces left, but the majority of the plane is in small pieces. 3. The fuselage of the 757, which was going to be the only part of the main structure of the plane capable of penetrating the wall is only something like 12 or 13' around. So why is a 16 foot hole too small? 4. What do you expect in a plane crash? Perfectly intact bodies just laying around? They find mostly body PARTS after a plane shreds itself in a crash. There are actually not many intact bodies that are found in a LOW speed crash, and I certainly wouldn't expect to see many intact in a crash like this. 5. I'd hardly say "very easily". Several of those parts are HEAVY, and they're ackward to carry around. If you put them in BEFORE the crash, then surely someone would notice this plane part suddenly laying where it wasn't supposed to be. And after there were so many people running around that again, someone would notice it. 6. Have you looked at the other sides of the building? They all have obstacles there that would make them even harder to hit. And diving a plane straight down into something isn't as easy as people think it is. That's one reason that dive bombers in WWII had such huge tails, to give them better control in the dive, because forces like the wind have a much bigger effect on the plane in a dive. 7. There MAY BE a better angle video, but how many security cameras have you seen that were pointed where they could get a look at the sky? Most of them are going to be pointed at the ground around the building. 8. They thought it was a military plane because commercial airliners don't NORMALLY operate that way. They are trying to keep their passengers comfortable, so they do make turns like that one. The 757 is capable of pulling it off, they just don't normally, so when a controller sees a plane manuver like that, they think military.

Originally posted by Matthew5012 1. alot of people saw somthing fly into the building and said it was a plane, from looking at the photos most people can tell that a 757 didnt fly into the building. so if alot of people who were there did see somthing hit the building it has to be (for me) a global halw, if it was any sort of plane at all.

The crew of a C-130 (Gopher 06) were vectored to follow the unidentified aircraft. They identified it as a 757 or 767 and the silver body as an American Airlines jet.

2. the fact that there wasnt much left after the crash and the one small engin that was found there, consistant with a global hawk engin. the global hawk is made from light weight materials and (again i think) smashed into 1000's of very small peices that you can see on the photos of the crash site. and you can see people from the FBI picking them all up with there hands. why was it all not left there for people to go over with a propper team later as ever other crash is.?

The engine was consistent with a 757 engine Source

3. the hole in the building is only 16ft theres no way a 757 could have made such a small hole. the global hawk is much smaller (i do admit on this account tho i do wonder why the hole is 16th and round with no damage to the windows around it)

You are talking about the front of the building and not the punch out hole, aren't you? The entry damage hole to the front of the building was ~96 feet. Source - Scroll down to the photo with the coloured lines.

4. where are all the passangers and there belongings? if 189 people were identerfied then why arnt they or any of there stuff on any one picture from the crash??? NOT ONE!

I suspect they are in some of the photos that have been posted on this and other sites. I haven't looked at them. I've already seen enough dead, charred bodies in this lifetime, thanks.

5. i have seem some photos that try and say its a 757, namely the wheel (part of it) and a (yes one) seat from the 757. small things like that could have been placed at the place of the crash before hand, very easily.

Charred and buried in other rubble? Okay. How about the landing strut that was found inside the building?

6. why did the flight path almost come back on itself and crash into the building. if a terrist really is a the helm why didnt he fly right into the building as soon as he had it in his sights??? (what i love about this one is the fact it looked like it would hit donalds office area if the direction of the plane had just gone striaght) why wouod he fly around the building and crash his plane into the only part that is almost empty? he's not trying to hit a big X on the bulding is he like in a computer game of some shit like that, he's just going the fly the bastard right into the building asap!!

It's been suggested that this side is one of the easier to hit, being clearer of things like parking lots, clumps of trees, etc. One point that has occurred to me recently is "how good was the terrorists' intelligence?" Technically, if not very good, they may not have realised the building was being strengthened and decided a construction site would be weaker. ( ... to be continued, I've run out of space)

( ... continued)

7. if the 757 did hit the bulding then why carnt the FBI release "PROPPER" video of the 757 hitting the pentagon from the 3 differnt angles they have. the video (more like a webcam) is a joke to say the least and has propabley made there whole situation worse as most people will admit it shows NOTHING that looks liek a plane!!!

No Court of Law is going to release information that may be used in a trial for fear of prejudicing a potential jury. The one they released was useless in a trial. We have no way of knowing how good the others are.

8. why did the air traffic controlers from that day all think it was a milertry plane?

All? I've seen the quote of one ATC. Your Source for "all" please. Edited to add Oh yes, further to your comment 2 - There are a lot of pieces of wreckage with green/yellow primer on them. This is used on aircraft that have the possibility of rust. To my knowledge, the Global Hawk is made of composite material and does not rust, therefore needing no special green/yellow primer. [edit on 6/6/06 by Aotearoa]

Originally posted by Matthew5012 1. alot of people saw somthing fly into the building and said it was a plane, from looking at the photos most people can tell that a 757 didnt fly into the building. ...

Some source for people not recognizing 757?

2. the fact that there wasnt much left after the crash and the one small engin that was found there, consistant with a global hawk engin....

Because this wasn't an ordinary crash, there was no need to investigate WHY the aircraft came down - the reason was rather straightforward.

3. the hole in the building is only 16ft theres no way a 757 could have made such a small hole....

16' round hole, no broken windows? Are you sure you're looking at the impact hole and not at the hole in the C ring? The width of the impact hole is atleast 90 feet and damage is visible. And why would be GH more suitable to cause such damage?

4. where are all the passangers and there belongings? if 189 people were identerfied then why arnt they or any of there stuff on any one picture from the crash??? NOT ONE!

You think you have all the pictures? Victim can be at this day and age identified from rather small piece of tissue or bone containing DNA.

5. i have seem some photos that try and say its a 757, namely the wheel (part of it) and a (yes one) seat from the 757. small things like that could have been placed at the place of the crash before hand, very easily.

This has been already discussed ad nauseam... In this very thread and others.

6. why did the flight path almost come back on itself and crash into the building....

hitting something in a dive flight isn't as easy as it seems. The impacted side of the Pentagon was coincidentally the only one with free path for low-level attack.

7. if the 757 did hit the bulding then why carnt the FBI release "PROPPER" video of the 757 hitting the pentagon ...

granted they have one. Only one camera picked up the first 767 hit of WTC, it was there by chance. Why there won't be similar situation in the Washington?

8. why did the air traffic controlers from that day all think it was a milertry plane?

They have only said that this kind of maneuver is UNUSUAL for the civillian because it is UNSAFE. That doesn't mean it isn't doable, just that airline pilots, concerned with health of the passangers and wear of the airframe won't usually do it. I'm afraid the hijacker didn't have neither of these two aspects in mind.

This question of whether an amateur could have flown Flight 77 into the Pentagon was also posed to a colleague who previously worked on flight control software for Boeing airliners. Brian F. (he asked that his last name be withheld) explained, "The flight control system used on a 757 can certainly overcome any ground effect. ... That piece of software is intended to be used during low speed landings. A high speed dash at low altitude like [Flight 77] made at the Pentagon is definitely not recommended procedure ... and I don't think it's something anyone specifically designs into the software for any commercial aircraft I can think of. But the flight code is designed to be robust and keep the plane as safe as possible even in unexpected conditions like that. I'm sure the software could handle that kind of flight pattern so long as the pilot had at least basic flight training skills and didn't overcompensate too much." Brian also consulted with a pair of commercial airline pilots who decided to try this kind of approach in a flight training simulator. Although the pilots were not sure the simulator models such scenarios with complete accuracy, they reported no significant difficulties in flying a 757 within an altitude of tens of feet at speeds between 350 and 550 mph (565 to 885 km/h) across smooth terrain. The only issue they encountered was constant warnings from the simulator about flying too fast and too low. These warnings were expected since the manufacturer does not recommend and FAA regulations prohibit flying a commercial aircraft the way Flight 77 was flown. These restrictions do not mean it is impossible for a plane to fly at those conditions but that it is extremely hazardous to do so, and safety was obviously not a concern to the terrorists on September 11. An aircraft flying at those high speeds at low altitude would also likely experience shaking due to the loads acting on it, but commercial aircraft are designed with at least a 50% safety margin to survive such extremes. One of the pilots summarized his experiences by stating, "This whole ground effect argument is ridiculous. People need to realize that crashing a plane into a building as massive as the Pentagon is remarkably easy and takes no skill at all. Landing one on a runway safely even under the best conditions? Now that's the hard part!" While he may have been exaggerating a bit for effect, he does raise a valid point that flying skillfully and safely is much more difficult than flying as recklessly as the terrorists did on September 11.

Source I'm not sure if I've posted that extract before in this thread or another one. One thread would have made it so much easier. By the way, some of the questions/comments you asked, Matthew5012 were in fact answered on the previous page of this thread.

Originally posted by Matthew5012 after all that ive seen and read i still think it was a global hawk that hit the pentagon.

Oh really? A Global Hawk has a maximum takeoff weight of only 28,700 pounds, less than a quarter of the empty weight of a 757 and about one ninth of the 757's maximum takeoff weight. It can only carry 2270 gallons of fuel as opposed to the 11,000 gallons of flight 77. It's wings are narrow and far weaker than a Boeing 757's. The wing of a global hawk would have a hard time clipping lightpoles not to mention knocking a huge diesel generator askew and destroying reinforced concrete columns. A Boeing 757 looks pretty much like any other large jetliner. The Global Hawk on the other hand is an odd-looking and very characteristic plane that doesn't really look like anything else most witnesses would previously have seen in the skies. Yet no witnesses describe anything like that, while most of them describe a twin engine passenger jet. Including a national guard pilot sharing airspace with the plane and someone on the ground who jumped out of the way because he was afraid the left engine would hit him. [edit on 6-6-2006 by Dansker]

Hi guys, thanks for taking the time to answer my questions. and you do have some very good points of view. its really made me think about my global hawk idea and have now put it aside in favor for a bigger air craft. BUT i still dont think in anyway that 9/11 wasnt anything other than an self inflicted wound, every topic has coverup writen all over it, the pentagon crash, twins towers, building 7, and the flight 93 events. there just seems so much that people can say for and against these arguments. this world is just so sick at times and i find it hard to belive how easy it is to cover up massive events with lies and get away with it. even if 100's of people were at the event if the offical story goes aginst this and the new media (where are they in all this mess about 9/11, they report of anything...pop stars babys, record transfer bills between football teams, IRAQ...IRAQ...IRAQ) report what the goverment say the rest of the world is ignerant to the truth. you only have to read the "rebuilding americas defences" document to see whats "sort off" going on, i somtimes wonder to myself what side are we really on? good or bad. if that even exsists in our day and age of back stabbing and lies. knowone can ever know. Whats your personal opinion on what happend, without sorses and proof for a minute just what you really think with all that you have looked into. Cheers Matt

Originally posted by Matthew5012 Whats your personal opinion on what happend, without sorses and proof for a minute just what you really think with all that you have looked into.

What do I think really happened? I've only looked into Flights 77 and 93. I don't need more emotional baggage by looking into the WTC events. I'm far removed (geographically) from the US, I don't watch the news (actually I don't own a television), I don't read newspapers. I occasionally get news from the net. My first inkling about all this came from another forum where I put some of my reading in aircraft disasters into use in a thread regarding the movie about Flight 93. From there, it just took off. I started reading, researching, finding out all the things I didn't know were out there about CT's, coverups, etc. From reading, studying and collecting data from around 50 websites, I've come to the conclusion that Flight 77 hit the Pentagon as reported and Flight 93 ended up in the ground in Pennsylvania.

I think it's impossible to prove what actually hit Pentagon (based on all available information). However, i find some other circumstances extremely suspicious. Second plane hi WTC at 9.03am. At 9.38am, Pentagon was hit. USAF is considered to be world's best airforce. But they failed to protect the Capital, 35 minutes after the second WTC strike. Andrews air force base is very close to Washington, and there is's not only home of the Air Force One/VIP transports; there is also a wing of F-16 fighters. So, 35 minutes after it was clear that that something really sinister is going on, there wasn't a signle US fighter over Washington. Incompetence? Bad luck? I find that hard to belive...

Originally posted by Duby78 Andrews air force base is very close to Washington, and there is's not only home of the Air Force One/VIP transports; there is also a wing of F-16 fighters.

But without fighters at the readiness level it takes an hour to prepare planes for takeoff. Andrews wasn't airguard base that day, as usually, total of 21 readiness fighters were available in the entire USA. The system doesn't need more against conventional threats as any attacker has to cross ocean to get in range, giving enough time to arm and launch fighters.

Yes, it takes a some time to prepare a fighter for action. But I know that even Croatian air force has at least a pair of fighters ready to scramble within minutes on 24/7 basis (that was case even before 9/11). Now, Croatia would have fighters ready (shitty Mig-21), and US would not?? I just can't belive that