9/11 757 question
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9/11 757 question
Hello everyone,
I have always been interested to know the answer to this question:
During the 11 September 2001 tragdey, why didn't the 757 that crashed into the Pentegon blow any traffic off the roadways in its wake? I'm not sure of its exact path but the images taken at the Pentegon once it hit suggests the aircraft was pretty low to the ground. Surely, vehicles would have been scattered around? I don't think anyone has even claimed to have seen the low-flying plane.
I'd be interested to hear your comments.
Cheers!
P.S. I promise this is not a conspiracy related question. Just curious.
I have always been interested to know the answer to this question:
During the 11 September 2001 tragdey, why didn't the 757 that crashed into the Pentegon blow any traffic off the roadways in its wake? I'm not sure of its exact path but the images taken at the Pentegon once it hit suggests the aircraft was pretty low to the ground. Surely, vehicles would have been scattered around? I don't think anyone has even claimed to have seen the low-flying plane.
I'd be interested to hear your comments.
Cheers!
P.S. I promise this is not a conspiracy related question. Just curious.
Yes – people have seen the plane coming in.
The 757 generates a noticeable wake when it flies at low airspeed.
At 400 mph the amount of air encountered per minute is so large that the wing imparts only a small movement on the affected air. This entails a long and ‘thin’ wake. Think of a water skier going fast vs. slow.
Also, the big engine fans can ‘blow’ enormously when the airplane is stationary on the ground. But a fan that moves forward itself at 400 mph can’t add much ‘blow’ to the (in fact stationary) air that enters the engine at a relative 400 mph already.
The 757 generates a noticeable wake when it flies at low airspeed.
At 400 mph the amount of air encountered per minute is so large that the wing imparts only a small movement on the affected air. This entails a long and ‘thin’ wake. Think of a water skier going fast vs. slow.
Also, the big engine fans can ‘blow’ enormously when the airplane is stationary on the ground. But a fan that moves forward itself at 400 mph can’t add much ‘blow’ to the (in fact stationary) air that enters the engine at a relative 400 mph already.
Last edited by Plumb Bob; 20th Mar 2007 at 07:35.
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If you do not think anyone has even claimed to have seen the low-flying plane, then I suspect you have not bothered to look for an affirmative answer, or you have not asked the right question in Google.
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So far I have never read anything about people spotting the low-flying plane but I wasn't looking too hard either. That's not what interested me. I was really only questioning why there wasn't any debris of damaged vehicles caught in the wake of a 757, which I understand is very strong.
I was reading here on Pprune only last week about the wake of a 757 and it sparked the question that I have wondered for some time. So, instead of treating me as though I am a conspiracy theorist, Henry, why not answer my question? If you are not a professional pilot than why speak up?
When I am traveling on the motorway and a huge lorry roars past me I feel its "wake". I still don't understand why this 757 didn't do the same.
Cheers!
I was reading here on Pprune only last week about the wake of a 757 and it sparked the question that I have wondered for some time. So, instead of treating me as though I am a conspiracy theorist, Henry, why not answer my question? If you are not a professional pilot than why speak up?
When I am traveling on the motorway and a huge lorry roars past me I feel its "wake". I still don't understand why this 757 didn't do the same.
Cheers!
Hi xfeed,
What you feel while being overtaken by a lorry really is its “bow wave”.
Finely streamlined airplanes generate only a small bow wave, which is not nearly as noticeable as their wake. The wake is a consequence of the wing sucking down (and pushing down) the air that it slices through.
The wake of a 757 indeed is quite (in)famous.
However, like I said in my previous post, that applies to the airplane shortly before a normal landing, in slow flight. Like a knife going through warm butter at an angle, curling it up. The wing really ‘plows’ through the air.
High-speed flight, on the other hand, is more like the knife going through the butter with the blade nearly parallel to the direction of movement. Not displacing much butter.
So: it may seem strange, but the strongest wake is generated by airplanes flying relatively slowly. The 757 into the Pentagon was going very fast. Airplanes are designed to be able to go fast without disturbing the air a lot. Therefore no wake-induced damage there.
IF lorries were normally driven on descending viaducts parallelling the final approach within feet of the wingtips of landing airliners, THEN such vehicles falling over would be an everyday occurrence, especially if the lorries could be driven at matching speeds.
What you feel while being overtaken by a lorry really is its “bow wave”.
Finely streamlined airplanes generate only a small bow wave, which is not nearly as noticeable as their wake. The wake is a consequence of the wing sucking down (and pushing down) the air that it slices through.
The wake of a 757 indeed is quite (in)famous.
However, like I said in my previous post, that applies to the airplane shortly before a normal landing, in slow flight. Like a knife going through warm butter at an angle, curling it up. The wing really ‘plows’ through the air.
High-speed flight, on the other hand, is more like the knife going through the butter with the blade nearly parallel to the direction of movement. Not displacing much butter.
So: it may seem strange, but the strongest wake is generated by airplanes flying relatively slowly. The 757 into the Pentagon was going very fast. Airplanes are designed to be able to go fast without disturbing the air a lot. Therefore no wake-induced damage there.
IF lorries were normally driven on descending viaducts parallelling the final approach within feet of the wingtips of landing airliners, THEN such vehicles falling over would be an everyday occurrence, especially if the lorries could be driven at matching speeds.
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Thanks Plumb Bob. That was the information I was looking for. That's very interesting about the strongest wake being at the plane's slower speed. I'm not sure how the airframe is designed but would (did?) the wings shear off at this speed? Perhaps the tail as well?
Thanks for taking the time to answer.
Cheers,
xfeed
Thanks for taking the time to answer.
Cheers,
xfeed
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xfeed: I do not need to be a professional pilot to comment on your statement "I don't think anyone has even claimed to have seen the low-flying plane".
Here is just one link which will show you that witnesses did see the low flying plane hit the Pentagon, it took me about 30 seconds to find it using Google.
http://911research.wtc7.net/pentagon...ses/sgydk.html
Here is just one link which will show you that witnesses did see the low flying plane hit the Pentagon, it took me about 30 seconds to find it using Google.
http://911research.wtc7.net/pentagon...ses/sgydk.html
xfeed, you may want to clarify what you mean by “this speed”.
The airframe, more particularly the wings, can stir up a strong wake at low speeds, because we are talking of a strong wake over a short distance travelled per minute (compared with a long ‘thin’ wake at high speed).
Should a large sudden gust then occur, at a slow flying speed, the wing would simply temporarily lose some of its grip on the air – without breaking.
However, above a certain high speed, a sudden large gust (or, for that matter, a sudden large control input by the pilot) MAY be able to overload and in extreme cases bend or break the wing. That’s why such circumstances are avoided.
Flying into a strong and heavy building shears off any protruding parts like wings and tailplanes (which also are not really built to withstand great backwards forces), while the fuselage, acting with a lot of mass all concentrated on a fairly smal round spot, will try to force its way through the wall like some giant sort of spear.
The airframe, more particularly the wings, can stir up a strong wake at low speeds, because we are talking of a strong wake over a short distance travelled per minute (compared with a long ‘thin’ wake at high speed).
Should a large sudden gust then occur, at a slow flying speed, the wing would simply temporarily lose some of its grip on the air – without breaking.
However, above a certain high speed, a sudden large gust (or, for that matter, a sudden large control input by the pilot) MAY be able to overload and in extreme cases bend or break the wing. That’s why such circumstances are avoided.
Flying into a strong and heavy building shears off any protruding parts like wings and tailplanes (which also are not really built to withstand great backwards forces), while the fuselage, acting with a lot of mass all concentrated on a fairly smal round spot, will try to force its way through the wall like some giant sort of spear.
Last edited by Plumb Bob; 20th Mar 2007 at 23:46.
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I have not looked or searched into this. But with it being the Pentagon - a high security building of National security and importance to the US of A, then surely there would be security camera's on every road leading upto it, on every corner of its five sides, at every check point and various positions on the rooftop. Also buildings around the Pentagon must have cameras.
So why has no camera footage been released.
Do correct me if I'm wrong.
So why has no camera footage been released.
Do correct me if I'm wrong.
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Plumb Bob, I was referring to the high speed that the plane would have been traveling whilst low to the ground. I would imagine that the wings would have been sheared off and perhaps the tail if they were at a very high rate of speed. I don't know what their ground speed might have been but perhaps 300-350kts? Also, how difficult would it be to control a 757 at that presumably high rate of speed?
Henry Crun, I will concede that I made a poor choice in words in that quote. I hadn't read anything about anyone seeing the low-flying plane while driving along the nearby roadways but I wasn't trying to state fact. What I meant was someone testifying about how the plane nearly blew them off the roadway but Plumb Bob has explained already why that didn't happen. I was defensive because I didn't want to be labled a conspiracy nutter. My apologies.
Cheers!
Henry Crun, I will concede that I made a poor choice in words in that quote. I hadn't read anything about anyone seeing the low-flying plane while driving along the nearby roadways but I wasn't trying to state fact. What I meant was someone testifying about how the plane nearly blew them off the roadway but Plumb Bob has explained already why that didn't happen. I was defensive because I didn't want to be labled a conspiracy nutter. My apologies.
Cheers!
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Originally Posted by Brian Fantana
So why has no camera footage been released.
Do correct me if I'm wrong.
Do correct me if I'm wrong.
Unless of course it's actually a missile/car bomb/alien death ray etc.
Well, xfeed, I had vaguely in my memory that the 757 approached the Pentagon at high speed, so I readily accepted the 400 mph I found somewhere. About the same speed you mention.
The difficulty of controlling the airplane near max speed mainly depends on one’s practice, I would think. It is quite standard to go fast during part of the descent. Usually on autopilot.
Doing this at low level and manually is not on many people’s repertoire.
BTW, I 'll soon be offline for the rest of the week, between two 100 mph cruises at 100 feet below sea level.
The difficulty of controlling the airplane near max speed mainly depends on one’s practice, I would think. It is quite standard to go fast during part of the descent. Usually on autopilot.
Doing this at low level and manually is not on many people’s repertoire.
BTW, I 'll soon be offline for the rest of the week, between two 100 mph cruises at 100 feet below sea level.
