Banneling
Geregistreerd: 2 april 2012
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Misschien dit eens doornemen. Aan het einde enkele argumenten waarom er ws geen vliegtuigen in de WTC torens gevlogen zijn. Heeft met snelheid te maken.
Citaat:
Here is some info on the fire and such (I will provide a link at the bottom):
The fire is the most misunderstood part of the WTC collapse. Even today, the media report (and many scientists believe) that the steel melted. It is argued that the jet fuel burns very hot, especially with so much fuel present. This is not true.
Part of the problem is that people (including engineers) often confuse temperature and heat. While they are related, they are not the same. Thermodynamically, the heat contained in a material is related to the temperature through the heat capacity and the density (or mass). Temperature is defined as an intensive property, meaning that it does not vary with the quantity of material, while the heat is an extensive property, which does vary with the amount of material. One way to distinguish the two is to note that if a second log is added to the fireplace, the temperature does not double; it stays roughly the same, but the size of the fire or the length of time the fire burns, or a combination of the two, doubles. Thus, the fact that there were 90,000 L of jet fuel on a few floors of the WTC does not mean that this was an unusually hot fire. The temperature of the fire at the WTC was not unusual, and it was most definitely not capable of melting steel.
In combustion science, there are three basic types of flames, namely, a jet burner, a pre-mixed flame, and a diffuse flame. A jet burner generally involves mixing the fuel and the oxidant in nearly stoichiometric proportions and igniting the mixture in a constant-volume chamber. Since the combustion products cannot expand in the constant-volume chamber, they exit the chamber as a very high velocity, fully combusted, jet. This is what occurs in a jet engine, and this is the flame type that generates the most intense heat.
In a pre-mixed flame, the same nearly stoichiometric mixture is ignited as it exits a nozzle, under constant pressure conditions. It does not attain the flame velocities of a jet burner. An oxyacetylene torch or a Bunsen burner is a pre-mixed flame.
In a diffuse flame, the fuel and the oxidant are not mixed before ignition, but flow together in an uncontrolled manner and combust when the fuel/oxidant ratios reach values within the flammable range. A fireplace flame is a diffuse flame burning in air, as was the WTC fire.
Diffuse flames generate the lowest heat intensities of the three flame types.
If the fuel and the oxidant start at ambient temperature, a maximum flame temperature can be defined. For carbon burning in pure oxygen, the maximum is 3,200°C; for hydrogen it is 2,750°C. Thus, for virtually any hydrocarbons, the maximum flame temperature, starting at ambient temperature and using pure oxygen, is approximately 3,000°C.
This maximum flame temperature is reduced by two-thirds if air is used rather than pure oxygen. The reason is that every molecule of oxygen releases the heat of formation of a molecule of carbon monoxide and a molecule of water. If pure oxygen is used, this heat only needs to heat two molecules (carbon monoxide and water), while with air, these two molecules must be heated plus four molecules of nitrogen. Thus, burning hydrocarbons in air produces only one-third the temperature increase as burning in pure oxygen because three times as many molecules must be heated when air is used. The maximum flame temperature increase for burning hydrocarbons (jet fuel) in air is, thus, about 1,000°C—hardly sufficient to melt steel at 1,500°C.
Figure 3
Figure 3. A cutaway view of WTC structure.
Figure 4--Web Link
Figure 4. A graphic illustration, from the USA Today newspaper web site, of the World Trade Center points of impact. Click on the image above to access the actual USA Today feature.
But it is very difficult to reach this maximum temperature with a diffuse flame. There is nothing to ensure that the fuel and air in a diffuse flame are mixed in the best ratio. Typically, diffuse flames are fuel rich, meaning that the excess fuel molecules, which are unburned, must also be heated. It is known that most diffuse fires are fuel rich because blowing on a campfire or using a blacksmith’s bellows increases the rate of combustion by adding more oxygen. This fuel-rich diffuse flame can drop the temperature by up to a factor of two again. This is why the temperatures in a residential fire are usually in the 500°C to 650°C range.2,3 It is known that the WTC fire was a fuel-rich, diffuse flame as evidenced by the copious black smoke. Soot is generated by incompletely burned fuel; hence, the WTC fire was fuel rich—hardly surprising with 90,000 L of jet fuel available. Factors such as flame volume and quantity of soot decrease the radiative heat loss in the fire, moving the temperature closer to the maximum of 1,000°C. However, it is highly unlikely that the steel at the WTC experienced temperatures above the 750–800°C range. All reports that the steel melted at 1,500°C are using imprecise terminology at best.
Some reports suggest that the aluminum from the aircraft ignited, creating very high temperatures. While it is possible to ignite aluminum under special conditions, such conditions are not commonly attained in a hydrocarbon-based diffuse flame. In addition, the flame would be white hot, like a giant sparkler. There was no evidence of such aluminum ignition, which would have been visible even through the dense soot.
It is known that structural steel begins to soften around 425°C and loses about half of its strength at 650°C.4 This is why steel is stress relieved in this temperature range. But even a 50% loss of strength is still insufficient, by itself, to explain the WTC collapse. It was noted above that the wind load controlled the design allowables. The WTC, on this low-wind day, was likely not stressed more than a third of the design allowable, which is roughly one-fifth of the yield strength of the steel. Even with its strength halved, the steel could still support two to three times the stresses imposed by a 650°C fire.
The additional problem was distortion of the steel in the fire. The temperature of the fire was not uniform everywhere, and the temperature on the outside of the box columns was clearly lower than on the side facing the fire. The temperature along the 18 m long joists was certainly not uniform. Given the thermal expansion of steel, a 150°C temperature difference from one location to another will produce yield-level residual stresses. This produced distortions in the slender structural steel, which resulted in buckling failures. Thus, the failure of the steel was due to two factors: loss of strength due to the temperature of the fire, and loss of structural integrity due to distortion of the steel from the non-uniform temperatures in the fire.
THE COLLAPSE
Nearly every large building has a redundant design that allows for loss of one primary structural member, such as a column. However, when multiple members fail, the shifting loads eventually overstress the adjacent members and the collapse occurs like a row of dominoes falling down.
The perimeter tube design of the WTC was highly redundant. It survived the loss of several exterior columns due to aircraft impact, but the ensuing fire led to other steel failures. Many structural engineers believe that the weak points—the limiting factors on design allowables—were the angle clips that held the floor joists between the columns on the perimeter wall and the core structure (see Figure 5). With a 700 Pa floor design allowable, each floor should have been able to support approximately 1,300 t beyond its own weight. The total weight of each tower was about 500,000 t.
As the joists on one or two of the most heavily burned floors gave way and the outer box columns began to bow outward, the floors above them also fell. The floor below (with its 1,300 t design capacity) could not support the roughly 45,000 t of ten floors (or more) above crashing down on these angle clips. This started the domino effect that caused the buildings to collapse within ten seconds, hitting bottom with an estimated speed of 200 km per hour. If it had been free fall, with no restraint, the collapse would have only taken eight seconds and would have impacted at 300 km/h.1 It has been suggested that it was fortunate that the WTC did not tip over onto other buildings surrounding the area. There are several points that should be made. First, the building is not solid; it is 95 percent air and, hence, can implode onto itself. Second, there is no lateral load, even the impact of a speeding aircraft, which is sufficient to move the center of gravity one hundred feet to the side such that it is not within the base footprint of the structure. Third, given the near free-fall collapse, there was insufficient time for portions to attain significant lateral velocity. To summarize all of these points, a 500,000 t structure has too much inertia to fall in any direction other than nearly straight down.
http://www.tms.org/pubs/journals/JOM...agar-0112.html
I have an understanding that fire CAN melt steel at about 1800-2000 degrees, but over time. Now, there are images of molten steel right after the planes hit. How did the steel in the building melt so quickly when steel melts in very hot temperatures over time? I know that at about 1000 degrees, the steel starts to expand and loses strength, but, to melt it so quickly is just not possible.
This video presents the molten steel just dripping like it was in the fire for hours to reach that melting point.
http://www.youtube.com/watch?v=OmuzyWC60eE
There is evidence that leads me to believe that it was a controlled demolition, simply because of the molten steel only minutes after the planes hit. Thermite is something that is used by demolishing experts to effectively pull a building down.
Here's a wiki link to what Thermite is:
http://en.wikipedia.org/wiki/Thermite
"In principle, any reactive metal could be used instead of aluminium. This is rarely done, however, because the properties of aluminium are ideal for this reaction. It is by far the cheapest of the highly reactive metals; it also forms a passivation layer making it safer to handle than many other reactive metals. The melting and boiling points of aluminium also make it ideal for thermite reactions. Its relatively low melting point (660 °C, 1221 °F) means that it is easy to melt the metal, so that the reaction can occur mainly in the liquid phase[6] and thus proceeds fairly quickly. At the same time, its high boiling point - 2,519 °C (4,566 °F) - enables the reaction to reach very high temperatures, since several processes tend to limit the maximum temperature to just below the boiling point.[7] Such a high boiling point is common among transition metals (e.g. iron and copper boil at 2,887 °C (5,229 °F) and 2,582 °C (4,680 °F) respectively), but is especially unusual among the highly reactive metals (cf. magnesium and sodium which boil at 1,090 °C (1,990 °F) and 883 °C (1,621 °F) respectively). Further, the low density of the aluminium oxide formed as a result of the reaction tends to cause it to float on the iron, reducing contamination of the weld."
"Although the reactants are stable at room temperature, they burn with an extremely intense exothermic reaction when they are heated to ignition temperature. The products emerge as liquids due to the high temperatures reached (up to 2500 °C (4500 °F) with iron(III) oxide)—although the actual temperature reached depends on how quickly heat can escape to the surrounding environment. Thermite contains its own supply of oxygen and does not require any external source of air. Consequently, it cannot be smothered and may ignite in any environment, given sufficient initial heat. It will burn well while wet and cannot be extinguished with water. Small amounts of water will boil before reaching the reaction. If thermite is ignited underwater, the molten iron produced will extract oxygen from water and generate hydrogen gas in a single-replacement reaction. This gas may, in turn, burn by combining with oxygen in the air."
So, i would suspect that something like this was used to create that molten metal so quickly.
There were explosions according to firefighters and people who were there when the buildings were struck by the planes.
Here's a video on the firefighters:
http://www.youtube.com/watch?v=tlAkF7E2nCs
Another one:
http://www.youtube.com/watch?v=cZ4dVo5QgYg
To me, witness testimony is more credible than someone adding numbers and doing complex physics equations. Science isn't perfect, to my knowledge:
http://www.youtube.com/watch?v=X3uFv......=PL&index=4
Firefighters talking about the explosions they heard.
http://www.youtube.com/watch?v=SXD3bAbZCow
If you watch Zeitgeist, there is a part that explains all of this. And clearly shows the lights going off in the building exactly like a controlled demolition.
Here's an interview with a FEMA videographer:
http://www.voltairenet.org/article160636.html
Another interesting to note is that there was no building sway. It's weird to look at a big ol' plane that weighs tons of pounds coming in at about 400mph and not make the building sway.
http://www.youtube.com/watch?v=Q_jIFN3jkJc
Did you see this one?
http://www.youtube.com/watch?v=_0eC3uns3pA
Another thing to note is the velocity of the plane when it hit. It's not supposed to go that fast. A Boeing 767 cannot exceed 360 knots at any altitude without incurring aerodynamic stress. Source: How Airliners Fly, Page 59 By Julien Evans(767 pilot)(1999).
But, if i am not mistaken, the "official report" stated that the plane flew in at 512 knots...wow. To me, that's a big difference.
I asked a well-known pilot (John Lear) to explain to me the difference between IAS and TAS, (Indicated Air Speed and True Air Speed) this is in his own words:
TAS or true air speed is indicated airspeed corrected for altitude and temperature.
Indicated airspeed is what the pilot sees on his airspeed indicator and it is the measure of the air molecules going into the pitot tube, that tube on the front of the airplane. The faster the airplane goes the more air molecules are rammed into the pitot tube pushing the airspeed indicator to indicate more airspeed.
At sea level, the indicated airspeed equals the TAS in other words at sea level 360 kts. indicated on the airspeed indicator is 360 kts. true air speed.
The UAL Boeing 767 allegedly hit the WTC at about 540 mph which is 470 kts. (Multiply kts by 1.16 to get mph.)
Lets look at some of the reasons a Boeing 767 could not possibly achieve 470 knots at sea level.
When the airspeed of the Boeing 767 reaches 360 kts. Which is its Vmo or Velocity Maximum Operating a very loud clacker starts clacking in the cockpit. Its goes, CLACK-CLACK-CLACK-CLACK-CLACK. The clacking is designed at a rate and volume intensity to be very irritating. It is telling the pilot, "Hey you dumb s***, slow this mother down RIGHT NOW."
The clacking effectively destroys the pilots thinking process so that he has no choice but to pull the throttles back instantly. In the UAL Boeing 767 (2001) there was no circuit breaker the pilot could pull to silence the clacker.
Circuit breakers for the clackers were installed in 2004 in all 757's and 767's mainly because of 3 major accidents involving clackers. The biggest one was February 6, 1996 a Boeing 757 which took off from Puerto Plata, Dominican Republic (Birgenair (Alas Nacionales) 757-200).
It had been sitting for weeks, undergone some maintenance and a wash job before which the static ports were taped over with masking tape. When it was being readied for flight someone forgot to untape the static ports on the side of the airplane. The static air from the static ports are compared with the indications from the pitot tube. But if the static ports are accidentally taped then there is no comparative air and the pitot tube is sending full, uncompared information to the airspeed indicator.
On a night take over a black sea the crew was given erroneous airspeed and altitude readings which caused them to believe they were going too fast which caused the clacker to come on. They kept pulling back on the controls to reduce the speed which was erroneously reading high.
The clacker could not be silenced as there was no circuit breaker. There was no circuit breaker because in the past, as difficult as it may to believe, pilots were known to have pulled the circuit breaker on the clacker in order to cruise at a higher airspeed.
Eventually the airplane stalled and crashed into the sea killing everybody on board. A contributing cause to the accident was the incessant clacking noise which made it difficult for the crew to think clearly.
In 2004 the FAA required circuit breakers installed on all 757/767 aircraft.
Now lets look at the reasons that it is aerodynamically impossible for a Boeing 767 to achieve 470 knots. indicated airspeed.
Several uninformed individuals have found that in the type certification data information that the VD or "Dive velocity" of the Boeing 767 is 420 kts. They think that VD or Dive Velocity is an airspeed limitation that he FAA imposes and that the airplane can be safely 'dived' at 420 kts. They then propose that since it is can go 420 kts. then it ought to be able to exceed that speed by a few more knots to equal 470 kts. This is a false assumption and here is why.
The "Dive Velocity" VD is 420 kts. CAS (calibrated airspeed) is a speed that is a maximum for certification flight tests accomplished under 14 CFR Part 25.253 High Speed Characteristics and has not necessarily been achieved but is far above VFC (390 kts. 450 mph) which is the maximum speed at which stability characteristics must be demonstrated (14 CFR 25.253(b)).
What this means is not only was VD not necessarily achieved but even if it was, it was achieved in a DIVE demonstrating controllability considerably above VFC which is the maximum speed under which the stability characteristics must be demonstrated and by very experienced test pilots.
Further, as VD is considerably above VFC a alleged hijacker who is not an experienced test pilot would have extreme difficulty in controlling the airplane which would be similar to flying a buffeting bucking bronco, much less hitting a 208 ft. wide target dead center at 800 feet altitude. A remote controlled airplane would have similar problems.
Also, lets consider the aerodynamics of your proposed 470 kt. airplane.
First drag vs. power ratio. Drag is the effect of the air pushing against the frontal areas of the fuselage and wing and horizontal and vertical stabilizers. Drag also includes the friction that is the result of the air flowing over these surfaces. There are 2 types of drag: induced and parasite. We do not have to consider induced drag because induced drag is caused by lift and varies inversely as the square of the airspeed. What this means is the faster you go the lower the induced drag.
What we do have to consider in parasite drag. Parasite drag is any drag produced that is not induced drag. Parasite drag is technically called 'form and friction' drag. It includes air pushing against the entire airplane including the engines, as the engines try to push the entire airplane through the air.
The parasite drag varies with the square of the velocity so to double the speed the drag doubles.
Commercial air transport wings began using supercritical or 'aft loading' technology about 20 years ago. The supercritical wing was the idea of Dr. Richard T. Whitcomb (Langley Research Center) and what he was trying to achieve was less drag before buffet onset. Without going into extreme detail what they were trying to do was design the wing so that it would cruise the most efficiently at the highest speed. Their second goal was to insure that the drag rise occurred as soon as possible after this highest speed. The reason for this is that during flight test you tell the FAA what is the maximum speed you want to cruise at. Then the airplane is flown to this speed and 'upset' or placed into a dive for 30 seconds or so. During the recovery, which must be accomplished with the use of aerodynamic controls only, the airplane may not achieve a speed any higher than VD (420 kts. CAS). What the designers of the wing are trying to accomplish is to place the 'drag rise' right after the top speed so that the airplane will not achieve VD. If it does go over VD then the max cruise speed has to be backed off, until it complies.
To propose that a pilot could exceed 400 kts. in level flight is to ignore the aerodynamic facts of life.
We have 2 other things to consider for your 470 kt. airplane: induced power and parasite power.
Induced power varies inversely with velocity so we don't have to consider that because we are already going fast by assumption and it varies inversely.
Parasite power however varies as the cube of the velocity which means to double the airspeed you have to cube or have three times the power. So to add 100 kts. to the velocity of the aircraft we figure one quarter of the cube of the power. Lets say the power is 120,000 pounds of thrust (this is unachievable at 470 kts at sea level but let us make the assumption) take the cube of that and divide by the difference between 360 kts and 470 kts and you can see the impossible of the amount of thrust required to achieve 470 kts.
One more consideration is the impossibility of the PW4062 turbofan engines to operate in dense air at sea level altitude at high speed.
The Boeing 767 was designed to fly at high altitudes at a maximum Mach of .86 or 86/100ths the speed of sound. This maximum speed is called MMO, (Maximum Mach Operating). Its normal cruise speed, however, is Mach .80 (about 530 mph) or less, for better fuel economy. (The speed of sound at 35,000 feet is 663 mph so 530 mph is Mach .7998 see http://www.grc.nasa.gov/WWW/K-12/airplane/sound.html.)
The fan tip diameter of the PW4062 which powered UAL 175 was 94 inches, over 7 feet in diameter making it, essentially a huge propeller.
This huge fan compresses enormous amount of air during takeoff to produce the thrust necessary to get the airplane off of the ground and into the air.
At high altitudes, in cruise, where the air is much thinner and where the engines are designed to fly at most of the time, the fan and turbine sections are designed to efficiently accept enormous amounts of this thin air and produce an enormous amount of thrust.
But at low altitudes, in much denser air, such as one thousand feet, where the air is over 3x as dense as at 35,000 feet, going much faster than Vmo or 360 knots, the air is going to start jamming up in the engine simply because a turbofan engine is not designed to take the enormous quantities of dense air at high speed, low altitude flight. Because of the much denser air the fan blades will be jammed with so much air they will start cavitating or choking causing the engines to start spitting air back out the front. The turbofan tip diameter is over 7 feet; it simply cannot accept that much dense air, at that rate, because they aren't designed to.
So achieving an airspeed much over its Vmo which is 360 knots isn't going to be possible coupled with the fact that because the parasite drag increases as the square of the speed and the power required increases as the cube of the speed you are not going to be able to get the speed with the thrust (power) available.
It can be argued that modern aerodynamic principles hold that if an aircraft can fly at 35,000 ft altitude at 540 mph (Mach 0.8), and for a given speed, both engine thrust and airframe drag vary approximately in proportion to air density (altitude), that the engine can produce enough thrust to fly 540 mph at 800 ft. altitude.
That argument fails because although the engine might be theoretically capable of producing that amount of thrust, the real question is can that amount of thrust be extracted from it at 540 mph at 800 ft.
To propose that a Boeing 767 airliner exceeded its designed limit speed of 360 knots by 127 mph to fly through the air at 540 mph is simply not possible. It is not possible because of the thrust required and it's not possible because of the engine fan design which precludes accepting the amount of dense air being forced into it.
There were no planes on 911. No planes went 540 mph. That is impossible. No planes crashed into the WTC. It was a gigantic illusion. The WTC was destroyed by space based orbiting weapons platforms operated by the U.S. Navy using molecular disassociation technology.
Conclusion: A 767 cannot fly at that speed without suffering structural damage.
Another thing to point out is the nose-dive that the second plane made. If a human did that, he is obviously super human. It is physically impossible for a pilot to make that dive, in that plane, at that speed, and recover and keep flying that plane into the building. Proof? Here:
This is page 250 from Mechanics Of Flight By AC Kermode Published by Prentice Hall (1996)
Not only did that plane dive, but it was turning at the same time.
http://img166.imageshack.us/img166/1...ejoinedcb3.gif
Vishttp://img240.imageshack.us/img240/1309/wb11li1.gifit My Website
Now, how is it that a plane that is not supposed to fly faster than 360 knots, do 590 knots of a impossible turning nose dive into a plane without breaking up in the air or the pilot losing control? And all of this happens by diving at 300 knots. That plane did it at 590 knots...incredible.
Alleged hijackers of the planes are still alive...wow.
http://www.youtube.com/watch?v=f7ixuf236Dk
http://news.bbc.co.uk/2/hi/middle_east/1559151.stm
Now, let's say the big guys got their info mixed up....could that happen once more? Did it happen before? Did it happen then? I mean, if they admit that they were misled with their info, then they would lose credibility. They wouldn't want that, now would they?
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Laatst gewijzigd door DeProf_eet : 9 april 2015 om 02:35.
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