New Greening Paper on Flight 175

[pomeroo]

Dr. Greening has graciously sent me a copy of his new paper:


The Impact of Flight 175 on WTC 2

By F. R. Greening


1.0 Introduction

The behavior of the Boeing 767 aircraft, designated as United Airlines Flight 175, that struck the south face of WTC 2 on the morning of September 11th, 2001, has been the subject of much debate and on-going controversy. For example, in March 2007, Morgan Reynolds issued a letter to the National Institute of Standards and Technology (NIST) that included a Request for Correction (RFC) to the sections of the NIST Report on the World Trade Center (WTC) Disaster that purport to analyze the aircraft impacts on WTC 1 & 2. In particular Reynolds questions the validity of NIST’s conclusion that a Boeing 767 could penetrate into WTC 2, with little or no deceleration of its motion, as described by NIST on page 234 of NCSTAR 1-2B and on page 86 of NCSTAR 1-5A.

In April 2007 Gregory Jenkins published a critique of Reynold’s RFC in the Letters section of the Journal of 9/11 Studies. In his letter, Jenkins argues that the tail end of an aircraft impacting a rigid structure is quite capable of showing essentially no loss of velocity until the front section of the aircraft’s fuselage is crushed, concertina-like, against the rigid structure. Jenkins bases his argument on a video analysis of the well-known test carried out by Sandia in 1988, involving the high-speed collision of a F-4 Phantom jet and a massive concrete block. Jenkins’ video analysis shows that the tail end of the F-4 maintained a constant velocity until just before its destruction and he argues that the Boeing aircraft that hit WTC 2 would have shown the same type of behavior. From this analysis, Jenkins concludes that there is no scientific basis for Reynold’s RFC to NIST.

In this letter I wish to show that Jenkins’ analysis of the motion of the F-4 Phantom is not correct because the tail section of the F-4 in the Sandia test actually does show significant deceleration. Reynold’s argument that the Boeing 767 showed no deceleration after striking WTC 2 is also demonstrated to be invalid using video evidence showing that the aircraft’s velocity was significantly reduced during the initial stages of the impact.


2.0 The Impact of Flight 175 on WTC 2

In the context of the present discussion we need to consider a number of physical quantities related to the Boeing 767 aircraft that struck WTC 2 on 9/11. The aircraft was actually a Boeing 767-200ER with a fuselage that was 48.5 meters long and 5.4 meters in diameter at its widest cross section. NIST estimates that the mass of the aircraft, including the fuel it was carrying at the time of impact, was ~ 124,000 kg. There is some uncertainty in the impact velocity of Flight 175, (See the Table on page 173 of NCSTAR 1-2B), but NIST’s value of 242 m/s falls close to the average of impact velocities estimated by FEMA, MIT, and Hart-Weidlinger.

The length and speed of the aircraft may be used to calculate the very important parameter, Te, that is key to the following discussion. Te is the time, (after first contact of the nose of the aircraft with the face of WTC 2), for the full length of the aircraft to enter the tower assuming no deceleration occurred. The calculation of Te is straightforward because, to a very good approximation, the aircraft was moving on a trajectory that was perpendicular to the south face of WTC 2. Thus, using time = distance/velocity, where the distance of interest is the length of the aircraft, we have Te = 48.5 (meters)/ 242 (meters per second) or Te = 0.2004 seconds which we can safely round off to 0.2 seconds.

This calculated value for Te is consistent with NIST’s Table 7.1 on page 86 of NCSTAR 1-5A that lists the time for the aircraft to completely disappear inside WTC 2 as 0.20 seconds. However, the fact that the NIST Report appears to be saying that the aircraft that struck WTC 2 penetrated all the way into the structure with no apparent resistance is problematical. Indeed, it is the main reason for Reynold’s assertion that NIST “violates scientific principles” because, as Reynold’s claims in his RFC, “a jetliner must decelerate at impact due to the laws of conservation of momentum and conservation of energy.” (Emphasis added). Now it is precisely the assertion that an aircraft must decelerate on impact that is challenged by Jenkins in his letter to the Journal of 9/11 Studies. Jenkins bases his challenge of Reynold’s RFC on a video analysis of the well-studied case of a F-4 Phantom jet impacting a massive structure. Therefore, before commenting on Jenkins’ analysis, we need to first look at the Sandia F-4 impact test in some detail.


3.0 The F-4 Phantom Jet Impact Tests

In 1988, Sandia National Laboratories in Albuquerque, New Mexico, carried out a full-scale test of a high-speed military aircraft impacting a reinforced concrete target. The test results have been reported by T. Sugano et al. in Nuclear Engineering and Design 140, 373, (1993). Important details of the test derived from Sugano’s paper are as follows:

· The aircraft was a modified F-4 Phantom, mounted on a carriage running on 600 meter-long rails, driven by a pusher sled powered by a combination of Zuni and Nike rockets.

· The aircraft was 17.7 meters long, weighed 19,000 kg, and carried no fuel but included 4,800 kg of water that was added to simulate the fuel mass distribution.

· The aircraft was fitted with ten accelerometers along the length of its fuselage, and a telemetry package that allowed deceleration data to be transmitted to a receiving station.

· The target was a block of reinforced concrete, 7 meters square and 3.7 meters thick, weighing 469 tonnes.

· The target was mounted on ten air bearings that allowed for about 0.5 meters of horizontal recoil motion.

The measured impact velocity of the F-4 was 215 m/s and the aircraft was totally crushed in less than 0.1 seconds. The reinforced concrete target experienced a slight rocking motion during impact but overall was accelerated to a relatively constant recoil velocity of 8 m/s within about 0.08 seconds.

The most interesting data recorded during the F-4 impact test were the decelerations of the aircraft. Representative measurements are plotted in Figure 14 of Sugano’s Nuclear Engineering and Design report. These data show, for example, that decelerations were detectable after the first 6 meters of the fuselage had been crushed. Focusing on the tail section of the F-4, we have the following velocity reductions reported by Sugano et al.:


Time After First Contact Measured Velocity Percent Velocity Reduction
(Seconds) (m/s) (%)

0.03 213 1.0
0.04 205 4.7
0.05 196 8.8
0.06 192 10.7
0.07 179 16.7


These data are not consistent with Jenkins’ video analysis of the F-4 impact as summarized in an Appendix to his letter to the Journal of 9/11 Studies. Thus Jenkins claims that no reduction in the velocity of the tail section of the aircraft was measurable, (to within an error of 3 %), during the crushing of the front 14.2 meters of fuselage, or 80 % of the total length of the aircraft. By comparison, Sugano’s data show a 16.7 % velocity reduction after 0.07 seconds, which would be approximately equivalent to Jenkins’ 80 % crushing of the aircraft.

The reason for the discrepancy between Sugano’s data and Jenkins’ measurements is not immediately apparent. However, one point concerning the two sets of measurements is obviously key, namely that Sugano et al. used accelerometers to measure velocity changes along the length of the aircraft’s fuselage while Jenkins used displacements of the image of the aircraft relative to a fixed vertical overlay. Interestingly, Sugano et al. also mention the use of high-speed cameras to measure the velocity reduction of the aircraft and include a curve labeled “High-Seed Film” in Figure 14 of their report. Compared to the accelerometer data given above for the tail section of the aircraft, the “High-Speed Film” curve shows more velocity reduction in the time interval up to 0.03 seconds and less reduction in the interval 0.03 to 0.07 seconds. Nevertheless, the velocity reduction of the aircraft after 0.07 seconds derived from Sugano’s photographic measurements is about 12 %, not 0 % as claimed by Jenkins.

4.0 Discussion

We now return to the question of the velocity reduction of the Boeing 767-200ER that struck WTC 2 on 9/11. Here, as we have seen, Reynolds’ and Jenkins agree that little to no reduction in the velocity of the aircraft was observed during the first 0.2 seconds of impact, the time required for an unimpeded aircraft to “disappear” into the tower. Reynold’s asserts that this is physically impossible while Jenkins argues it is “not unexpected”; a conclusion based on his video analysis of a F-4 Phantom subject to hard impact. However, given that that Jenkins’ method of motion analysis is not supported by more precise measurements, it would be prudent to look more closely at Jenkins’ claim that there was no observable reduction in the velocity of the aircraft that struck WTC 2.

A cursory survey of available information on the impact of Flight 175 on WTC 2 shows at least two instances of measurable velocity reductions: one derived from the much-discussed Evan Fairbanks video footage, and the other based on a video analysis reported by Y. Omika et al. in the January 2005 issue of the Journal of Structural Engineering. Thus the Evan Fairbanks video, when viewed as still frames ~ 0.03 seconds apart, shows a measurable velocity reduction of the tail end of the aircraft, (of about 5 m/s), when the nose of the 767 had penetrated about 16 meters into WTC 2. This increases to a velocity reduction of about 30 m/s, or 12 % of the initial impact velocity, approximately 0.15 seconds into the impact. By comparison, Omika et al. use the analysis of an unnamed video to estimate a 50 m/s velocity reduction of the aircraft after 0.15 seconds, increasing to a 100 m/s reduction after 0.2 seconds.

While it is clear that significant velocity reductions are discernable from careful measurements of appropriate videos showing the impact of Flight 175 on WTC 2, NIST remain strangely silent on this topic. However, as previously discussed, NIST certainly imply in NCSTAR 1-2B and NCSTAR 1-5A that Flight 175 entered WTC 2 with little or no deceleration of its motion. NIST do, in fact, present calculated momentum vs. time plots for the aircraft impact on WTC 2 on page 224 of NCSTAR 1-2, but fail to compare this theoretical result with observational data. This omission is regrettable because NIST show elsewhere that it’s not averse to analyzing videos to obtain aircraft velocity data. Thus on page 99 of NCSTAR 1-5A NIST presents an analysis of a video by Scott Myers showing Flight 175 approaching WTC 2. NIST’s analysis of this video has been quoted by some researchers as evidence for the proposal that the aircraft did not slow down on impact with WTC 2. However, this is not valid because the sequence of frames used by NIST in NCSTAR 1-5A covers a time interval just before the aircraft struck the tower.

5.0 Conclusions

We have looked at the proposal that Flight 175 did not slow down on impact with WTC 2 and found it to be sadly wanting. We support this conclusion with two sets of data showing velocity reductions by Flight 175 as it entered WTC 2. We also show that Gregory Jenkins’ video analysis of the impact of a F-4 Phantom jet is not consistent with previously published data based on accelerometer measurements.

F. R. Greening, Oct 2007.

[Arkan_Wolfshade]

Um, where does he show is working supporting his #'s?

[einsteen]

I remember he said that the kinetic impact energy is much larger than the NISt value, but I didn't know he was working on this. I once used a bitmap extract technique for this impact using two independent movies, that gave this

http://i16.tinypic.com/4y9cdqb.jpg
http://i16.tinypic.com/4y9cdqb.jpg

[T.A.M.]

For all of his comments on this forum, I have to admire Dr. Greening's dedication to REAL science.

TAM:)

[einsteen]

And it should also be done for the jet of course, as a anti-no-planer I've never compared it but let's do it. Here something about the Jet

http://www.sandia.gov/news/resources/video-gallery/index.html

The video was down, but found another one at

http://www.f1-express.net/perso/F4CrashTest.wmv

Converted it to avi, used good old virtualdub, extrated a cropped version (containing the tail) from frame 6723 to 6930

merged them and that gives:

http://i20.tinypic.com/153lor4.png

http://i20.tinypic.com/153lor4.png

I don't want to take any position in this discussion and I'm not sure what the purpose is but the x(t) function of the tail looks extremely linear to me.

[BenBurch]

That does indeed look tolerably linear.

[beachnut]

And it should also be done for the jet of course, as a anti-no-planer I've never compared it but let's do it. Here something about the Jet

http://www.sandia.gov/news/resources/video-gallery/index.html

The video was down, but found another one at

http://www.f1-express.net/perso/F4CrashTest.wmv

Converted it to avi, used good old virtualdub, extrated a cropped version (containing the tail) from frame 6723 to 6930

merged them and that gives:

http://i20.tinypic.com/153lor4.png

I don't want to take any position in this discussion and I'm not sure what the purpose is but the x(t) function of the tail looks extremely linear to me.
You need to plot it better, there is not a straight line in the photo of the data, it is bent. Pay more for a better screen, or please print it out and try a straight edge.

[einsteen]

I forgot that not all JREF'ers fit in the upper half part of the bell curve. And my Acer AL1751 is fine enough. Are you playing games ?

http://i21.tinypic.com/2m3lnpe.png

Even Ace Baker (with all respect) would be able to connect these dots.

[T.A.M.]

civility folks...no need for generalizing insults.

TAM:)

[BenBurch]

It is indeed bent, but the bend divides it into two linear segments, as though the aircraft decelerated briefly when it hit the building but then either the building or the airframe or both lost structural integrity and couldn't transmit force to the tail.

[gumboot]

As we explained to Ace Baker with his analysis of the UA175 impact, the resolution of images is so low that the margin of error is significant enough to make any sort of pixel-based analysis somewhat meaningless. And that's not even taking into account compression methods for the video.

-Gumboot

[beachnut]

I forgot that not all JREF'ers fit in the upper half part of the bell curve. And my Acer AL1751 is fine enough. Are you playing games ?

Even Ace Baker (with all respect) would be able to connect these dots.
Oh? Please make the red line bigger to hide the not so straight data below.

What a waste of ink. Twice. I think you need to rethink your bell curve, and forget being close to six sigma. Next time you need to edit your original photo before you try to make up a straight line story.

You could look up the definition of a straight line before implying I am an idiot. I actually finished engineering school and already printed your original data photo, and it was not a straight line. You either need a better printer, more data points that lie in your "straight line" or a better screen. Good luck getting a straight line on your not so straight diagonal challenged photo program. Funny stuff.

BTW, you know how many errors you need to correct before you can even publish your bs photo as science? I would ask, as an engineer to the person producing the work, please name 17 reasons your work is flawed; but then I doubt you understand you added some of the errors yourself and already published more than two reasons your data is flawed, and now you have tried to draw a red line, that also fails to be a straight line and you call me an idiot. Thanks

[Redtail]

I forgot that not all JREF'ers fit in the upper half part of the bell curve. And my Acer AL1751 is fine enough. Are you playing games ?

http://i21.tinypic.com/2m3lnpe.png

Even Ace Baker (with all respect) would be able to connect these dots.

So you will bring this info forward and take down the true criminals?

[Shrinker]

As we explained to Ace Baker with his analysis of the UA175 impact, the resolution of images is so low that the margin of error is significant enough to make any sort of pixel-based analysis somewhat meaningless. And that's not even taking into account compression methods for the video.

-Gumboot

The supposed 5m/s slowdown after 16m of penetration amounts to about 45cm. I have a hard time believing anybody detected a 45cm displacement in the Fairbanks video. That's an even bolder claim than Ace was making.

[gumboot]

The supposed 5m/s slowdown after 16m of penetration amounts to about 45cm. I have a hard time believing anybody detected a 45cm displacement in the Fairbanks video. That's an even bolder claim than Ace was making.


Exactly. To begin with there's the simple problem of scale. A single pixel represents a considerable distance.

Then we have the issue of our shutter speed. The electronic shutter on a digital camera allows the CCD to be exposed to light for a set period of time, and in that time the object in question moves, creating blurring.

Next we have pixel bleed. Bright light will bleed into neighbouring pixels which can cause problems with determining the actual position of objects - especially bright ones such as an aircraft in sunlight with a silver fuselage.

Then there's source compression - with the exception of a few newly released specialist digital cinema cameras, all digital cameras use compression. Even High Definition Broadcast footage is compressed when it is captured. Compression means a loss of detail. If we're talking MPEG compression (which most cameras use), small high speed objects are typically the most adversely affected.

All of the above is purely some of the factors that affect the accuracy of the original recording or transmission.

But of course our intrepid truth-seekers didn't use original tapes. And for every single step of transfer, every new compression and new encoding, every change in resolution, you have to widen the margin of error.

By the time you get to a highly compressed streaming video on youtube, you could easily be looking at a margin of error that works out, in real scale, to be dozens and dozens of feet.

-Gumboot

[beachnut]

The supposed 5m/s slowdown after 16m of penetration amounts to about 45cm. I have a hard time believing anybody detected a 45cm displacement in the Fairbanks video. That's an even bolder claim than Ace was making.
But you can make it look like a straight line if you squeeze it all up in a few inches, distort it a few times, mark it up with big red dots that could be bigger than the change you are looking for...

I find it hard to believe there were calculations made by someone who actually entertains 9/11 truth as a viable group with real facts?

It is funny when I can draw, with a pencil, a straighter line than some 9/11 truth supporter with bs data.

[qarnos]

This is like the Apollo shadows all over again...

[Shrinker]

What I also find interesting about Dr Greening's paper is that regarding the Sandia test he appears to demonstrate that video analysis is incapable of capturing the deceleration effect. He states himself, the cause of the discrepancy isn't clear and therefore we infer he cannot find the source of the error. We can also see from Einsteen's image that the deceleration is simply too subtle to detect visually, even with high-speed video with good resolution. But then he proceeds to reach his conclusion by exclusively using the very method he has discredited.

The following phrase is also misleading, NIST show elsewhere that it’s not averse to analyzing videos to obtain aircraft velocity datasince, finding velocity data using video, is significantly easier than finding acceleration data. Again, refer to Einsteen's F4 image see how relatively trivial this calculation would be.

[chillzero]

Thread closed pending review

Thread reviewed, and re-opened.

[einsteen]

You think I'm faking photos in favour of the plane is real theory ? The red line is added to the first picture, here the picture below is aplying a difference algorithm (with paint shop pro) at the two images:


http://i23.tinypic.com/2qclcic.png
http://i23.tinypic.com/2qclcic.png

Is that linear or not ? You could maybe better take the first picture and rotate it about 10.5 degrees then a line is even more linear. And I refer to the contrast between the tail and the sky, the white part behaves different but that is because the video is a little bit rotated and the extrated bitmaps were not 320 x 1 but had a height which gives an optical illusion, I repeated the method with 320 x 1 bitmaps because some other serious people don't flip out immediately when something is different as expected. See

http://i23.tinypic.com/2937sk6.png
http://i23.tinypic.com/2937sk6.png (http://i23.tinypic.com/2937sk6.png)

I never talked about scientifical methods etc, but please if you want to show you find a parabole or an other continuous function go for it, I'm open for it, you produced nothing so far except some loudmouth.

[A W Smith]

I forgot that not all JREF'ers fit in the upper half part of the bell curve. And my Acer AL1751 is fine enough. Are you playing games ?

http://i21.tinypic.com/2m3lnpe.png

Even Ace Baker (with all respect) would be able to connect these dots.


when I scroll up and down I notice the building face retreat away from the plane. You wouldn't be trying to be dishonest now einsteen would you? You thought none of us would catch that? hell just compare the margin at top and bottom.

[PhantomWolf]

I wouldn't expect the plane to slow down much untill it was at least halfway into the building, mostly because until then it still has two large jet engines propelling it forwards....

[rwguinn]

For all of his comments on this forum, I have to admire Dr. Greening's dedication to REAL science.

TAM:)

While the essay is a decent analysis of the two events, it is simply an analysis of asingle, minor issue.
What Dr. G, and his unworthy opponents all miss is the fact that a non-existant target cannot exert a force. A broken spring is a non-load bearing element.
At the time of the collision of the F-4 with the reinforced concrete wall, the wall remained intact from a structural standpoint. The tower did not remain intact--it broke. It gave way.
In the F-4 test, the aircraft material failures were the primary source of resistive force. There was some momentum transfer, as the block was not anchored, and it did move some, but the buckling and rupture of the aircraft itself was the primary source.
Additionally, the target in the F-4 test was a monolithic solid. The tower was not, being comprised of primarily air, with a very thin shell around it. Additional hard points (The structural columns) would have acted more as knives than as a wall. This would effectively slice away parts of the aircraft, resulting in less loss of velocity than a solid wall would, since the main aricraft parts could follow a path already cleared by initial contact. The F-4 had no such option. It had to collapse in on itself, with increasing area as the wings made contact, and would, in fact show higher acceleration due just to that fact.
Add in that the F-4 is a considerably stronger and stiffer structure than the 767, and you have a much higher acceleration than the 767 would show.
And I would agree with Shrinker and gumboot: Anyone who thinks he can make accurate measurements from the videos with that pixel resolution is fooling himself. The F-4 was done at 5000 or so frames per second, and on film. It is very hard to detect the acceleration, even so.

[beachnut]

You think I'm faking photos in favour of the plane is real theory ? The red line is added to the first picture, here the picture below is aplying a difference algorithm (with paint shop pro) at the two images:

http://i23.tinypic.com/2qclcic.png

Is that linear or not ? You could maybe better take the first picture and rotate it about 10.5 degrees then a line is even more linear. And I refer to the contrast between the tail and the sky, the white part behaves different but that is because the video is a little bit rotated and the extrated bitmaps were not 320 x 1 but had a height which gives an optical illusion, I repeated the method with 320 x 1 bitmaps because some other serious people don't flip out immediately when something is different as expected. See

http://i23.tinypic.com/2937sk6.png (http://i23.tinypic.com/2937sk6.png)

I never talked about scientifical methods etc, but please if you want to show you find a parabole or an other continuous function go for it, I'm open for it, you produced nothing so far except some loudmouth.
Your first photo is not a straight line, and adding red dots is funny; the red dots almost hide the parts of the line that fall outside the definition of straight. Fact. Sorry.

It would be interesting to see frame 6723 and frame 6930. That would be neat. Thanks.

[einsteen]

Beachnut you are right that the line is not straight, but what I mean is that within the error margin of the video/resolution/etc I cannot conclude that it must be a parabole, in other words we can also not conclude that straight is wrong. If even a wall that doesn't move leads to a reasonable straight line, what then if a much weaker plane collides with a building that is 90% space ? And those 911 vids are normal framerate, you will only see a few frames during the crash. Maybe even flight 175 decelerates, but with my crappy amateuristic bitmap extraction method I can only conclude that there is nothing strange with the impact of flight 175 :)

[rwguinn]

bump for Apollo20

[firecoins]

Dr. Greening has graciously sent me a copy of his new paper:


The Impact of Flight 175 on WTC 2

By F. R. Greening


1.0 Introduction

The behavior of the Boeing 767 aircraft, designated as United Airlines Flight 175, that struck the south face of WTC 2 on the morning of September 11th, 2001, has been the subject of much debate and on-going controversy. For example, in March 2007, Morgan Reynolds issued a letter to the National Institute of Standards and Technology (NIST) that included a Request for Correction (RFC) to the sections of the NIST Report on the World Trade Center (WTC) Disaster that purport to analyze the aircraft impacts on WTC 1 & 2. In particular Reynolds questions the validity of NIST’s conclusion that a Boeing 767 could penetrate into WTC 2, with little or no deceleration of its motion, as described by NIST on page 234 of NCSTAR 1-2B and on page 86 of NCSTAR 1-5A.

In April 2007 Gregory Jenkins published a critique of Reynold’s RFC in the Letters section of the Journal of 9/11 Studies. In his letter, Jenkins argues that the tail end of an aircraft impacting a rigid structure is quite capable of showing essentially no loss of velocity until the front section of the aircraft’s fuselage is crushed, concertina-like, against the rigid structure. Jenkins bases his argument on a video analysis of the well-known test carried out by Sandia in 1988, involving the high-speed collision of a F-4 Phantom jet and a massive concrete block. Jenkins’ video analysis shows that the tail end of the F-4 maintained a constant velocity until just before its destruction and he argues that the Boeing aircraft that hit WTC 2 would have shown the same type of behavior. From this analysis, Jenkins concludes that there is no scientific basis for Reynold’s RFC to NIST.

In this letter I wish to show that Jenkins’ analysis of the motion of the F-4 Phantom is not correct because the tail section of the F-4 in the Sandia test actually does show significant deceleration. Reynold’s argument that the Boeing 767 showed no deceleration after striking WTC 2 is also demonstrated to be invalid using video evidence showing that the aircraft’s velocity was significantly reduced during the initial stages of the impact.


2.0 The Impact of Flight 175 on WTC 2

In the context of the present discussion we need to consider a number of physical quantities related to the Boeing 767 aircraft that struck WTC 2 on 9/11. The aircraft was actually a Boeing 767-200ER with a fuselage that was 48.5 meters long and 5.4 meters in diameter at its widest cross section. NIST estimates that the mass of the aircraft, including the fuel it was carrying at the time of impact, was ~ 124,000 kg. There is some uncertainty in the impact velocity of Flight 175, (See the Table on page 173 of NCSTAR 1-2B), but NIST’s value of 242 m/s falls close to the average of impact velocities estimated by FEMA, MIT, and Hart-Weidlinger.

The length and speed of the aircraft may be used to calculate the very important parameter, Te, that is key to the following discussion. Te is the time, (after first contact of the nose of the aircraft with the face of WTC 2), for the full length of the aircraft to enter the tower assuming no deceleration occurred. The calculation of Te is straightforward because, to a very good approximation, the aircraft was moving on a trajectory that was perpendicular to the south face of WTC 2. Thus, using time = distance/velocity, where the distance of interest is the length of the aircraft, we have Te = 48.5 (meters)/ 242 (meters per second) or Te = 0.2004 seconds which we can safely round off to 0.2 seconds.

This calculated value for Te is consistent with NIST’s Table 7.1 on page 86 of NCSTAR 1-5A that lists the time for the aircraft to completely disappear inside WTC 2 as 0.20 seconds. However, the fact that the NIST Report appears to be saying that the aircraft that struck WTC 2 penetrated all the way into the structure with no apparent resistance is problematical. Indeed, it is the main reason for Reynold’s assertion that NIST “violates scientific principles” because, as Reynold’s claims in his RFC, “a jetliner must decelerate at impact due to the laws of conservation of momentum and conservation of energy.” (Emphasis added). Now it is precisely the assertion that an aircraft must decelerate on impact that is challenged by Jenkins in his letter to the Journal of 9/11 Studies. Jenkins bases his challenge of Reynold’s RFC on a video analysis of the well-studied case of a F-4 Phantom jet impacting a massive structure. Therefore, before commenting on Jenkins’ analysis, we need to first look at the Sandia F-4 impact test in some detail.


3.0 The F-4 Phantom Jet Impact Tests

In 1988, Sandia National Laboratories in Albuquerque, New Mexico, carried out a full-scale test of a high-speed military aircraft impacting a reinforced concrete target. The test results have been reported by T. Sugano et al. in Nuclear Engineering and Design 140, 373, (1993). Important details of the test derived from Sugano’s paper are as follows:

· The aircraft was a modified F-4 Phantom, mounted on a carriage running on 600 meter-long rails, driven by a pusher sled powered by a combination of Zuni and Nike rockets.

· The aircraft was 17.7 meters long, weighed 19,000 kg, and carried no fuel but included 4,800 kg of water that was added to simulate the fuel mass distribution.

· The aircraft was fitted with ten accelerometers along the length of its fuselage, and a telemetry package that allowed deceleration data to be transmitted to a receiving station.

· The target was a block of reinforced concrete, 7 meters square and 3.7 meters thick, weighing 469 tonnes.

· The target was mounted on ten air bearings that allowed for about 0.5 meters of horizontal recoil motion.

The measured impact velocity of the F-4 was 215 m/s and the aircraft was totally crushed in less than 0.1 seconds. The reinforced concrete target experienced a slight rocking motion during impact but overall was accelerated to a relatively constant recoil velocity of 8 m/s within about 0.08 seconds.

The most interesting data recorded during the F-4 impact test were the decelerations of the aircraft. Representative measurements are plotted in Figure 14 of Sugano’s Nuclear Engineering and Design report. These data show, for example, that decelerations were detectable after the first 6 meters of the fuselage had been crushed. Focusing on the tail section of the F-4, we have the following velocity reductions reported by Sugano et al.:


Time After First Contact Measured Velocity Percent Velocity Reduction
(Seconds) (m/s) (%)

0.03 213 1.0
0.04 205 4.7
0.05 196 8.8
0.06 192 10.7
0.07 179 16.7


These data are not consistent with Jenkins’ video analysis of the F-4 impact as summarized in an Appendix to his letter to the Journal of 9/11 Studies. Thus Jenkins claims that no reduction in the velocity of the tail section of the aircraft was measurable, (to within an error of 3 %), during the crushing of the front 14.2 meters of fuselage, or 80 % of the total length of the aircraft. By comparison, Sugano’s data show a 16.7 % velocity reduction after 0.07 seconds, which would be approximately equivalent to Jenkins’ 80 % crushing of the aircraft.

The reason for the discrepancy between Sugano’s data and Jenkins’ measurements is not immediately apparent. However, one point concerning the two sets of measurements is obviously key, namely that Sugano et al. used accelerometers to measure velocity changes along the length of the aircraft’s fuselage while Jenkins used displacements of the image of the aircraft relative to a fixed vertical overlay. Interestingly, Sugano et al. also mention the use of high-speed cameras to measure the velocity reduction of the aircraft and include a curve labeled “High-Seed Film” in Figure 14 of their report. Compared to the accelerometer data given above for the tail section of the aircraft, the “High-Speed Film” curve shows more velocity reduction in the time interval up to 0.03 seconds and less reduction in the interval 0.03 to 0.07 seconds. Nevertheless, the velocity reduction of the aircraft after 0.07 seconds derived from Sugano’s photographic measurements is about 12 %, not 0 % as claimed by Jenkins.

4.0 Discussion

We now return to the question of the velocity reduction of the Boeing 767-200ER that struck WTC 2 on 9/11. Here, as we have seen, Reynolds’ and Jenkins agree that little to no reduction in the velocity of the aircraft was observed during the first 0.2 seconds of impact, the time required for an unimpeded aircraft to “disappear” into the tower. Reynold’s asserts that this is physically impossible while Jenkins argues it is “not unexpected”; a conclusion based on his video analysis of a F-4 Phantom subject to hard impact. However, given that that Jenkins’ method of motion analysis is not supported by more precise measurements, it would be prudent to look more closely at Jenkins’ claim that there was no observable reduction in the velocity of the aircraft that struck WTC 2.

A cursory survey of available information on the impact of Flight 175 on WTC 2 shows at least two instances of measurable velocity reductions: one derived from the much-discussed Evan Fairbanks video footage, and the other based on a video analysis reported by Y. Omika et al. in the January 2005 issue of the Journal of Structural Engineering. Thus the Evan Fairbanks video, when viewed as still frames ~ 0.03 seconds apart, shows a measurable velocity reduction of the tail end of the aircraft, (of about 5 m/s), when the nose of the 767 had penetrated about 16 meters into WTC 2. This increases to a velocity reduction of about 30 m/s, or 12 % of the initial impact velocity, approximately 0.15 seconds into the impact. By comparison, Omika et al. use the analysis of an unnamed video to estimate a 50 m/s velocity reduction of the aircraft after 0.15 seconds, increasing to a 100 m/s reduction after 0.2 seconds.

While it is clear that significant velocity reductions are discernable from careful measurements of appropriate videos showing the impact of Flight 175 on WTC 2, NIST remain strangely silent on this topic. However, as previously discussed, NIST certainly imply in NCSTAR 1-2B and NCSTAR 1-5A that Flight 175 entered WTC 2 with little or no deceleration of its motion. NIST do, in fact, present calculated momentum vs. time plots for the aircraft impact on WTC 2 on page 224 of NCSTAR 1-2, but fail to compare this theoretical result with observational data. This omission is regrettable because NIST show elsewhere that it’s not averse to analyzing videos to obtain aircraft velocity data. Thus on page 99 of NCSTAR 1-5A NIST presents an analysis of a video by Scott Myers showing Flight 175 approaching WTC 2. NIST’s analysis of this video has been quoted by some researchers as evidence for the proposal that the aircraft did not slow down on impact with WTC 2. However, this is not valid because the sequence of frames used by NIST in NCSTAR 1-5A covers a time interval just before the aircraft struck the tower.

5.0 Conclusions

We have looked at the proposal that Flight 175 did not slow down on impact with WTC 2 and found it to be sadly wanting. We support this conclusion with two sets of data showing velocity reductions by Flight 175 as it entered WTC 2. We also show that Gregory Jenkins’ video analysis of the impact of a F-4 Phantom jet is not consistent with previously published data based on accelerometer measurements.

F. R. Greening, Oct 2007.
Oh good! The new Greening paper! I can relax now.:faint:

[Apollo20]

Follow-up Comments to Flight 175 Impact Article (Based on Initial Feedback)

1. It appears that many of the videos showing Flight 175 entering WTC 2 were taken with cameras operating at 30 frames per second. It follows that these videos provide a series of still frames separated by 33.3 milliseconds. Given that Flight 175 was traveling at about 250 m/s, the aircraft moved about 8 meters between frames or 1/6th of the length of the fuselage. This also means that each video record of the impact, from the moment the aircraft made contact with WTC 2, to the moment the aircraft disappeared into the building, actually consists of only six images of the aircraft. Thus only six velocities, and, if the aircraft was being slowed, only six velocity decrements may be extracted from any particular video of the impact of Flight 175 on WTC 2. Nevertheless, the precision and accuracy of these velocity measurements is not limited by the paucity of video frames but by the photographic resolution of each frame.
2. An inspection of selected frames from some of the better quality videos of the impact of Flight 175 indicates a photographic resolution of about 0.5 meters. It appears that the effective shutter speed of the cameras that were used to record the videos must have been at least 1/500th of a second since very little motion blur is apparent in the still frames. Based on these estimates I would argue that a velocity decrement of about 10 m/s, (as opposed to the 5 m/s mentioned in my article), would be detectable in the best available videos. Omika’s data show a velocity decrement of almost 100 m/s about 0.2 seconds after first contact of Flight 175 with the south face of WTC 2. This means the tail of the aircraft was about 6 meters short of the position it would have reached if the building had offered no resistance to the impact.
3. Morgan Reynolds, in a written response to my article, suggests that I should “admit my contention that Newton’s Laws of mechanics are defunct … (because) … the aluminum plane cuts right through steel and disappears inside the Tower. This is impossible. Structural steel is far stronger than aluminum… and would suffer only light damage compared to complete and utter destruction/rejection of an aluminum airplane, with most of its debris scattered outside the building, especially wings, tail section and a majority of the shattered fuselage.” All I can say to this is that a number of specialists in the field of engineering mechanics, such as T. Wierzbicki, H. Astaneh and M. Karim have published independent analyses of the aircraft impacts on the Twin Towers and concluded that the facile and complete penetration of the perimeter walls of WTC 1 & 2 was to be expected for a Boeing 767 aircraft traveling at over 200 m/s. Wierzbicki’s calculations also show that only 3 % of the initial kinetic energy of Flight 175 was expended by the aircraft cutting through the perimeter wall of WTC 2.
4. High-speed impacts of aircraft flying into buildings may be classified as “hard” or “soft”. In a hard impact some portion of the stationary target is crushed by the moving projectile, which itself remains undamaged. In a “soft” impact the projectile is crushed while the target remains largely undamaged. The Sandia test of the impact of a F-4 jet into a concrete wall approximate a “soft” impact because the aircraft was totally pulverized and the concrete was relatively undamaged. Only in a purely “soft” impact would the motion of the tail of the aircraft be totally decoupled from the motion of the nose of the aircraft. In the impact of Flight 175 on WTC 2, the aircraft had sufficient kinetic energy to penetrate the open, cage-like, structure of the building. This gave the Flight 175 impact some “hard” characteristics so that the entire aircraft should be slowed to some degree as it penetrated the building.
5. Let’s estimate the deceleration of an aircraft striking a massive structure. We will follow the methodology of J. Riera as published in Nuclear Engineering and Design 8, 415, (1968). In this classic paper on aircraft impact Riera showed that the deceleration of a large commercial aircraft striking a building is governed by the aircraft’s mass distribution. In the case of a Boeing 767 weighing 124,000 kg, the average mass per unit length is 2557 kg/m. However, because the massive engines, fuel tanks and undercarriage assemblies are located near the center of the aircraft, about 75 % of the aircraft’s mass is confined to a relatively short section starting approximately 16 meters from the nose of the aircraft. Because of this mass distribution, the reaction load and deceleration of a fuselage section at the rear of the aircraft will be very small during the initial stages of an impact. Following Riera’s approach, I would estimate that the peak reaction load on Flight 175 was about 250 MN at about 0.1 seconds into the impact, (dropping to zero at 0.2 seconds). Very roughly this means there was an average reaction force of 125 MN acting on Flight 175 for 0.1 seconds. Using Newton’s 2nd Law, (Yes Morgan, I haven’t abandoned it!), this implies a deceleration of about 100 g’s! From these numbers we may calculate the velocity of Flight 175 when it was 0.2 seconds into its impact with WTC 2 to be about 150 m/s in good agreement with Omika’s result.

[jaydeehess]

Ok, I haqve no idea where in the NIST reports I read it but I am sure that in the FEA they had the debris of the aircraft having passed the perimeter, at 100 MPH slower than at initial impact an reduction of about 20%.

there are two items also pointed out by BenBurch, and Phantomwolf.
First that the perimeter columns were severed and that as they were severed they would offer less resistance and less decelleration to the aircraft which was also being broken up and less able to slow its rear sections. This involves what Greening refers to as a hard impact where the impacted surface suffers a great deal of damage and yeilds to the impact.
Secondly, the 767's engines would still be putting out thrust until they were destroyed themselves. This is not then a case of simple ballistic impact, it is powered, a condition which would allow less decelleration during impact.

Greening illustrates his point with evidence to back him up whereas Reynolds does not.

[Myriad]

5. Let’s estimate the deceleration of an aircraft striking a massive structure. We will follow the methodology of J. Riera as published in Nuclear Engineering and Design 8, 415, (1968). In this classic paper on aircraft impact Riera showed that the deceleration of a large commercial aircraft striking a building is governed by the aircraft’s mass distribution. In the case of a Boeing 767 weighing 124,000 kg, the average mass per unit length is 2557 kg/m. However, because the massive engines, fuel tanks and undercarriage assemblies are located near the center of the aircraft, about 75 % of the aircraft’s mass is confined to a relatively short section starting approximately 16 meters from the nose of the aircraft. Because of this mass distribution, the reaction load and deceleration of a fuselage section at the rear of the aircraft will be very small during the initial stages of an impact. Following Riera’s approach, I would estimate that the peak reaction load on Flight 175 was about 250 MN at about 0.1 seconds into the impact, (dropping to zero at 0.2 seconds). Very roughly this means there was an average reaction force of 125 MN acting on Flight 175 for 0.1 seconds. Using Newton’s 2nd Law, (Yes Morgan, I haven’t abandoned it!), this implies a deceleration of about 100 g’s! From these numbers we may calculate the velocity of Flight 175 when it was 0.2 seconds into its impact with WTC 2 to be about 150 m/s in good agreement with Omika’s result.


Perhaps a little too roughly. If I'm not mistaken, a sustained deceleration of about 60 gs would have brought the airplane to a stop in its own length in about 0.4 seconds. So, might you be spreading out the peak reaction load too broadly, by modeling it as a linear increase from 0 at 0.0 seconds to 250 MN (peak 200 gs, mean 100 gs) at 0.1 seconds? Unless the reaction load immediately dropped to zero after 0.1 seconds, you'd get more than 100 m/sec of deceleration by 0.2 seconds.

Still, these are interesting figures. Thanks!

Respectfully,
Myriad

[uruk]

In the F4 video How far did the F4 penetrate the wall? Would there not be some sort of deaceleration of the tail due to the fact that the F4 did not penetrate that far into the wall?

How far did the airliners penetrate the WTC Towers. Would not the the tail section of the airliner undergo less deacelleration due to the greater amount of penetration?

Am I off on this?

[einsteen]

I would say that a homogeneous structure, for example a stick decelerates much more than a plane. But if you have an inhomogenous structure where the energy to crush a part of it is dependent on x it totally differs. In general the parts that have more mass also require more energy to crush, a fuselage is relatively weak, take an extreme example of this nonuniform object

()-----()-------------()-----()

the energy to crush the weak parts is low and wil not really affect the velocity, the heavy parts will have more effect, but since the length is short it will also not really affect the speed of the tail. And an other possibility is that a shockwave weakens the whole plane then we have in fact noninterating parts. Also remember that the building is an open structure and further I think Jenkins's work is relevant. If the small F4 hardly decelerates in that situation, then what about a weaker jet on a open building structure.

ps. Uruk the block moves a little bit to the right and the camera gets a shock I guess, it is not meant to be scientifically :-)

[Apollo20]

Wow, I am very impressed by the last four posts! You guys/gals all made very interesting points.....

I am only trying to grasp the essence of the no-plane argument.

But I am glad to see this level of serious scientific discussion/debate at JREF.

I am especially glad to see (i) Jaydeehess asking the question: exactly when was the engine's driving force cut off... this is important in the F-4 example AND in the Flight 175 example. (ii) Myriad question my numbers..... I agree, they are probably only good to about 50 % but this is my first try! I am sure they can be refined.

[cmcaulif]

Secondly, the 767's engines would still be putting out thrust until they were destroyed themselves. This is not then a case of simple ballistic impact, it is powered, a condition which would allow less decelleration during impact.

Wiki (http://en.wikipedia.org/wiki/Boeing_767) lists the max thrust of one engine of a 767-400ER at 282 kN as well, so this would indeed be significant compared to Apollo's calculated reaction. I think it would be quite difficult to know exactly how much thrust the engines were putting out and for how long after impact however.

[3bodyproblem]

Out of curiousity does anyone know if a 767 at full thrust could crumple the nose section against a wall? If so, at what point would the instrumentation be sufficiently damaged and cut off fuel to the engines. I'm guessing that over pressure in the fuel system at the time the throttle was cut would be sufficient to maintain maximum thrust for the brief period it was cut till the engines made contact with a solid (or relatively solid) object. I never really thought about this aspect before, thanks for the insight jaydee and phantom.

[apathoid]

I think it would be quite difficult to know exactly how much thrust the engines were putting out and for how long after impact however.


I'm no expert on jet engine theory, but I do know that once airflow is disrupted(or cut completely off), the compressor will stall, go boom, and stop producing thrust. I would guess that there is some residual thrust after the loss of intake air, but not very much. No idea how long it would take to go from 50,000 lbs of thrust to zero. I'm also not sure what thrust would be left when the LP compressor(which produces 80% of the thrust) was smashed to elementary particles when it impacted the tower - probably not much.


Wiki (http://en.wikipedia.org/wiki/Boeing_767) lists the max thrust of one engine of a 767-400ER at 282 kN as well, so this would indeed be significant compared to Apollo's calculated reaction.


A slight correction, UA 175 and AA 11 were -200's which uses engines in the 48,000~52,000 lb class; the -400 engine is rated 63,300 lb

[gumboot]

1. It appears that many of the videos showing Flight 175 entering WTC 2 were taken with cameras operating at 30 frames per second. It follows that these videos provide a series of still frames separated by 33.3 milliseconds.


The cameras would have been operating at 59.94 fields per second

-Gumboot

[uruk]

ps. Uruk the block moves a little bit to the right and the camera gets a shock I guess, it is not meant to be scientifically :-)

My bad. I thought it was a sequence from the WTC impact.

[Shrinker]

Follow-up Comments to Flight 175 Impact Article (Based on Initial Feedback)

1. It appears that many of the videos showing Flight 175 entering WTC 2 were taken with cameras operating at 30 frames per second. It follows that these videos provide a series of still frames separated by 33.3 milliseconds. Given that Flight 175 was traveling at about 250 m/s, the aircraft moved about 8 meters between frames or 1/6th of the length of the fuselage. This also means that each video record of the impact, from the moment the aircraft made contact with WTC 2, to the moment the aircraft disappeared into the building, actually consists of only six images of the aircraft. Thus only six velocities, and, if the aircraft was being slowed, only six velocity decrements may be extracted from any particular video of the impact of Flight 175 on WTC 2. Nevertheless, the precision and accuracy of these velocity measurements is not limited by the paucity of video frames but by the photographic resolution of each frame.

Thanks for your response. As stated by Gumboot the cameras were most likely operating in fields, which gives a whisker under 60 images per second. However, field by field analysis can be problematic due to the nature of the interlacing, so it would be best to use just the odd or even fields. This may in fact be what happened here.


2. An inspection of selected frames from some of the better quality videos of the impact of Flight 175 indicates a photographic resolution of about 0.5 meters. It appears that the effective shutter speed of the cameras that were used to record the videos must have been at least 1/500th of a second since very little motion blur is apparent in the still frames. Based on these estimates I would argue that a velocity decrement of about 10 m/s, (as opposed to the 5 m/s mentioned in my article), would be detectable in the best available videos. Omika’s data show a velocity decrement of almost 100 m/s about 0.2 seconds after first contact of Flight 175 with the south face of WTC 2. This means the tail of the aircraft was about 6 meters short of the position it would have reached if the building had offered no resistance to the impact.


I think a more in-depth discussion of possible error is required, including analysis of the cameras involved, and their practical resolving power. Note that despite 768px (or sometimes 640px) being a common width of digital NTSC images, the cameras do not necessarily achieve this resolution. Here's a still cropped from a truther site, with a 1 metre square added. (ETA: I don't know the original source of this frame.) If there's a better quality grab from the Fairbanks video I'm sure it would help. Note how despite theoretically being able to resolve 1 metre distances, the camera appears unable to do any such thing. Considerable measurement errors are possible.

http://forums.randi.org/imagehosting/36174716010851767.jpg

Plus, despite claims that the paucity of video frames is not an issue, a much greater number of frames might have helped smooth out measurement errors. Instead we have to plot a trend based on very few, and potentially unreliable data points.

[ellindsey]

Out of curiousity does anyone know if a 767 at full thrust could crumple the nose section against a wall? If so, at what point would the instrumentation be sufficiently damaged and cut off fuel to the engines.

Throttle control on most Boeing airplanes is by mechanical linkages, with cables running from the cockpit through the plane to the engines. In theory, if those cables are severed or go slack the engines will keep running at their previous throttle setting until fuel flow is cut off. And the fuel pumps are directly powered by the engines, and fed from the tanks in the wings directly above them, so they should remain at full power until they hit the building or are torn off the wings.

[tsig]

Wow, I am very impressed by the last four posts! You guys/gals all made very interesting points.....

I am only trying to grasp the essence of the no-plane argument.

But I am glad to see this level of serious scientific discussion/debate at JREF.

I am especially glad to see (i) Jaydeehess asking the question: exactly when was the engine's driving force cut off... this is important in the F-4 example AND in the Flight 175 example. (ii) Myriad question my numbers..... I agree, they are probably only good to about 50 % but this is my first try! I am sure they can be refined.

Hi Dr. Greening.

I am trying to understand your second sentence.

I say this because I do not see how there can be a no-plane argument.

The fact that there were planes seems to to be the only possible conclusion given all the evidence.

Anyone who wants to assert no-planes has a burden of proof bigger than the towers themselves.

Being skeptical does not mean one can never reach a reasoned conclusion based on the best obtainable facts.

Having reached that conclusion only the same or more facts to the contrary should change it.

Thanks for writing yours and reading mine.

Oh.

Good conduct medals all around

[Apollo20]

Tsig:

Morgan Reynolds appears to be basing his no-plane thesis on his belief that many videos of the impact of Flight 175 on the south face of WTC 2 appear to show no deceleration of the aircraft. From this, (incorrect belief), Reynolds apparently concludes that the videos must be showing an unphysical "ghost-plane" and are therefore most likely faked.

I gather that MR feels that NIST is in some way party to this alleged deception and hence needs to "fess-up" and correct its WTC Report.

Interestingly, as far as I can tell, NIST does not come right out and say there was no measurable deceleration of Flight 175, but if you take NIST's estimate of the time for the aircraft to enter the building (0.20 seconds) and the length of the aircraft, you get a velocity that is identical with NIST's best estimate for the ENTRY velocity of Flight 175. This certainly IMPLIES there was no slowing of the aircraft in the 0.20 second entry interval.

Anyway, I decided to take a closer look at this question. After a lot of digging I found Omika's paper and saw his plots (Figures 4 and 15) showing measured velocity reductions of Flight 175 up to 100 m/s. I also noticed that Omika's velocity vs. time plot has SIX points after the t = 0 point, and up to the t = 0.20 second point. This shows that the video Omika used was shot at 33 frames per second, although I thank those posters who talked about 60 f/s videos - nevertheless, most still-frame sequences of the impact have only SIX frames. (Oh, and by the way, on the question of video resolution, may I suggest folks look at the images from Scott Myers' video as shown on pape 98 of NIST NCSTAR 1-5A. Here I would say that the photographic resolution is about 1 meter !)

I have also attempted my own (crude!) analysis of some impact videos, and like Omika, I see a measurable velocity reduction in the last 2 or 3 frames.

This tells me that Reynold's argument is based on a false premiss. The WTC 2 impact videos do actually show some degree of slowing of Flight 175 and therefore show a REAL aircraft striking a REAL building... That is, they are NOT FAKED!

Furthemore, Newton's Laws are still obviously in control of the universe and Dr. Reynold's needs to find a new rationale for his no-plane thesis....

[rwguinn]

Will the real Dr. Greening please stand up?

Which one is posting here? That last post sounded a lot like the scientist we know and love. It madesense, and was logical--even "Nistian"
Previous posts by the same user name have had a strong twoofer/susspension of disbelief aura about them.
Is it part of some nefarious scheme to drive us nuts trying to figure out what is happening

[CHF]

Frankly, I can't believe anyone spends more than 5 seconds on the no-planers.

[beachnut]

Who cares about the deceleration of flight 175? As an engineer I would just want a rough idea of the speed if I was studying buildings and how to make them better. It was sufficient to prove the towers meet current building codes, and any one who can do some energy impacts studies can see the building was doomed at impact; with a little work.

Your paper seems to be in the same NISTian type endeavor you relish teasing JREF posters with. Ironic. You write a paper due to an insane conclusion by someone who seems to be nuts when it comes to 9/11.

But you are showing Reynold is not able to be real in a real way. The video stuff is cute.

[tsig]

Tsig:

Morgan Reynolds appears to be basing his no-plane thesis on his belief that many videos of the impact of Flight 175 on the south face of WTC 2 appear to show no deceleration of the aircraft. From this, (incorrect belief), Reynolds apparently concludes that the videos must be showing an unphysical "ghost-plane" and are therefore most likely faked.

I gather that MR feels that NIST is in some way party to this alleged deception and hence needs to "fess-up" and correct its WTC Report.

Interestingly, as far as I can tell, NIST does not come right out and say there was no measurable deceleration of Flight 175, but if you take NIST's estimate of the time for the aircraft to enter the building (0.20 seconds) and the length of the aircraft, you get a velocity that is identical with NIST's best estimate for the ENTRY velocity of Flight 175. This certainly IMPLIES there was no slowing of the aircraft in the 0.20 second entry interval.

Anyway, I decided to take a closer look at this question. After a lot of digging I found Omika's paper and saw his plots (Figures 4 and 15) showing measured velocity reductions of Flight 175 up to 100 m/s. I also noticed that Omika's velocity vs. time plot has SIX points after the t = 0 point, and up to the t = 0.20 second point. This shows that the video Omika used was shot at 33 frames per second, although I thank those posters who talked about 60 f/s videos - nevertheless, most still-frame sequences of the impact have only SIX frames. (Oh, and by the way, on the question of video resolution, may I suggest folks look at the images from Scott Myers' video as shown on pape 98 of NIST NCSTAR 1-5A. Here I would say that the photographic resolution is about 1 meter !)

I have also attempted my own (crude!) analysis of some impact videos, and like Omika, I see a measurable velocity reduction in the last 2 or 3 frames.

This tells me that Reynold's argument is based on a false premiss. The WTC 2 impact videos do actually show some degree of slowing of Flight 175 and therefore show a REAL aircraft striking a REAL building... That is, they are NOT FAKED!

Furthemore, Newton's Laws are still obviously in control of the universe and Dr. Reynold's needs to find a new rationale for his no-plane thesis....

Dr. Greening.

Thanks for the clear answer.

I have nothing further just wanted to ackowledge your reply and assure you I have seen and read it.

[T.A.M.]

Will the real Dr. Greening please stand up?

Which one is posting here? That last post sounded a lot like the scientist we know and love. It madesense, and was logical--even "Nistian"
Previous posts by the same user name have had a strong twoofer/susspension of disbelief aura about them.
Is it part of some nefarious scheme to drive us nuts trying to figure out what is happening

Shhh...if you say that to loud you'll frighten him away, and Dr.Jeck...I mean Dr.Greening the Curmudgeon will return.

TAM;)

[apathoid]

Throttle control on most Boeing airplanes is by mechanical linkages, with cables running from the cockpit through the plane to the engines. In theory, if those cables are severed or go slack the engines will keep running at their previous throttle setting until fuel flow is cut off. And the fuel pumps are directly powered by the engines, and fed from the tanks in the wings directly above them, so they should remain at full power until they hit the building or are torn off the wings.


I don't know how much difference it makes because on open wire may act similarly to a broken cable, but 767 engines are controlled electronically. The throttles change engine speed through an LVDT and the electronic engine control(also called a power management computer on some powerplants) which is out on the engine. However, even if the broken wires commanded an engine speed change, the engine would take many seconds to spool down, so in a fraction of a second I'd only expect to see maybe a 5% fan speed change after the throttle quadrant was destroyed and before the engines themselves struck. I think the more relevant question would be: how long would it take the powerplant to stop producing thrust after the moment the compressor blades were destroyed. Should be close to instantaneous, but at 800 feet/second, close to instantaneous may still be a couple hundred feet of travel...

[PhantomWolf]

Hmmmm, could that be why the engine passed through the building while NIST's modellings didn't show the same? They would likely have done a straight Newtonian collision, they may not have allowed for the possiblity that the engine was still generating thrust for the split second it took to pass through the building.

[3bodyproblem]

apathoid: thanks for the info. If this is the case then it would stand to reason that the engines may have had more momentum during the collision, than say the landing gear. Just a thought.

[gumboot]

2. An inspection of selected frames from some of the better quality videos of the impact of Flight 175 indicates a photographic resolution of about 0.5 meters. It appears that the effective shutter speed of the cameras that were used to record the videos must have been at least 1/500th of a second since very little motion blur is apparent in the still frames.


I doubt that very much. I would be willing to bet that most, if not all, of the 40-odd recordings of UA175 hitting WTC2 were captured at a shutter speed of 1/60. One or two very clued on news cameramen might have racked the shutter speed up, but even then it's very unlikely. Even if you did crank the shutter right up, you'd then have to open right up on the aperture which produces its own issues as far as accuracy to the pixel.

As for resolution, below is the highest resolution video of UA175's impact that I'm aware of:

U90ySUwX-xA

Now if we look at the frame, it's about 2 1/2 times the width of a tower wall. Assuming the original footage is NTSC (a reasonable assumption) that gives us a width for one tower wall of 288 pixels, so we have a resolution of about 22cm.

That's not bad, right? But watch what happens when they zoom in on the image. They zoom in enough that the original pixels are clearly visible, despite the hideous compression of YouTube. As I've covered many times, physical image resolution is only one of numerous factors that determine image accuracy.

-Gumboot

[3bodyproblem]

gumboot: I'm glad you weighed in on that. I'm not familiar with video cameras, at all. But as a fairly avid photographer, 1/500 shutter speed to catch an object travelling at 250m/s would be hard. Even with ISO 1600 film and a fast lens, say 1.2 aperature, I'd be shooting at 1/250 and praying for the resolution we are talking about. And that's a fixed focal 50mm.

[gumboot]

gumboot: I'm glad you weighed in on that. I'm not familiar with video cameras, at all. But as a fairly avid photographer, 1/500 shutter speed to catch an object travelling at 250m/s would be hard. Even with ISO 1600 film and a fast lens, say 1.2 aperature, I'd be shooting at 1/250 and praying for the resolution we are talking about. And that's a fixed focal 50mm.


One thing to bear in mind is that most of the footage captured was amateur stuff, and the overwhelming majority of average consumer camera users don't even know what shutter speed means, let alone how or why you'd change it.

The last thing is at a shutter speed of 1/250 or higher, footage takes on the frenetic quality that you see in films like Saving Private Ryan (with a film camera the effect is created by changing the shutter angle from 180 degrees to 90 degrees). This is especially noticeable when there's camera movement or fast moving objects in the frame. None of the footage I have seen displays this quality.

-Gumboot