The Five-Sided Fantasy Island

An analysis of the Pentagon crash on 9-11

By Richard Stanley  & Jerry Russell                                                   version 2.0 (3/12/2004)  Page 2 of 5

Threading a Plane through the Eye of a Needle...

This composite image shows the extent of damage to the Pentagon facade before it collapsed, and the proportional size of the Boeing as it approached. (Source: http://0911.site.voila.fr/index2.htm ).  How is it possible that the jetliner could have passed through that tiny hole?  

We will now explain how it makes perfectly good sense from a hard scientific perspective  (although we don't agree that  it actually happened this way.)

The Missing Confetti Mystery

A team of computer scientists and engineers at Purdue University ran a simulation study to illustrate the dynamics of a 757 strike against the Pentagon.  Their study showed the 757 penetrating the Pentagon facade across the entire width of the wings of the airplane, which is a surprising finding as we will show below -- and is also quite different from what actually happened, as the wings clearly did not penetrate the facade.  

As noted in the Purdue  report, there is an extensive literature regarding the effects of impact of aircraft on reinforced concrete structures.  The question is important because of the possible effects of an air crash (such as, for example, a terrorist attack) onto the concrete containment of a nuclear power plant.  The studies indicate that it is difficult for an aircraft to penetrate a blast-hardened, reinforced concrete containment.  While the construction of the Pentagon is not strictly comparable to a nuclear containment vessel, nevertheless the western wedge  had recently been rehabilitated for high blast resistance.   We attempted some basic calculations (see appendix I) and found that the Pentagon structure may well have been strong enough to resist destruction by an aircraft such as a 757 flying at speeds less than 200 to 300 mph, and at any rate that the partial survival of some columns is not totally surprising.  

A key report, Sugano et al 1992, covers a rocket sled crash experiment using an F-4D Phantom jet fighter impacting into a 10 foot thick reinforced concrete block.   Sandia notes:

The purpose of the test was to determine the impact force, versus time, due to the impact, of a complete F-4 Phantom -- including both engines -- onto a massive, essentially rigid reinforced concrete target (3.66 meters thick). Previous tests used F-4 engines at similar speeds. The test was not intended to demonstrate the performance (survivability) of any particular type of concrete structure to aircraft impact. The impact occurred at the nominal velocity of 215 meters per second (about 480 mph). The mass of the jet fuel was simulated by water; the effects of fire following such a collision was not a part of the test. The test established that the major impact force was from the engines. The test was performed by Sandia National Laboratories under terms of a contract with the Muto Institute of Structural Mechanics, Inc., of Tokyo. 

With very minimal damage to the concrete target block, the plane and its engines were easily converted into small chunks of metal confetti and shrapnel at the physical interface of the two impact objects. Upon initial impact, the follow-on rear portions of the plane yet to make contact retained their shape integrity until their respective impact. (This seriously contradicts claims by Jean-Pierre Desmoulins that the wings of a 757 would have folded forward, as well as claims in the popular press that the wings folded back before entering the "too-small" hole.) The resulting shear caused debris being spread out to the left, right, and rear of the impact locus, having no ability to proceed in their original vector path, having grossly failed the test of strength with the concrete block.  However, the wings are wider than the concrete block, so the wingtips are sheared off whole, and they tumble forward after being cleanly separated from the aircraft.

F4 aircraft impacting a solid concrete barrier.  Note that the wings and tail do not fold as the nose impacts the concrete. (source: http://www.sandia.gov/media/NRgallery00-03.htm)

Sugano (in itself) doesn't show that a 757 hitting the Pentagon would be turned into confetti and small chunks, but it does show that an F4 was completely destroyed  in arguably similar circumstances. Furthermore, it wasn't anywhere close to an even contest between the wall and the F4. The F4 started with a speed of 215 m/sec -- and the tail was still traveling at 185 m/sec when it smashed into the wall. The F4 is a very strongly build aircraft, although at 18 meters long and 19 kg, it's about a third the length and a fifth the weight of the 757. In terms of comparing what would happen to a 757 versus what happened to the F4, it would be  difficult to do an accurate calculation without detailed design information on both aircraft.  In a preliminary analysis,  the extra length of the 757 means that it has three times the distance to decelerate --  but the 757 is also much heavier, so it's more difficult for the crushing process to supply enough force to decelerate even as rapidly as the F4 did.  

Another contrast is between the construction of the target for the Sugano experiment, as compared to the Pentagon.  While the Pentagon has only  10 inch thick brick and masonry infill walls, the facade's columns spaced 10 feet apart were concrete reinforced with spiral wound and axial steel rebar, and were supposed to have been reinforced during the building's renovation project in this very section. In the direction vector of the plane, the second story concrete floor slab was effectively contiguous for approximately 300 feet. Additionally, the plane's wings had to hit the electrical generator to the right and contractor's trailers to the left before possibly impacting the building. While (according to the ASCE report) the fuselage and core portion of the airplane were able to penetrate the facade and enter the building, the outer portions of the wings, and the tail,  definitely did not penetrate the facade -- and thus that portion of the plane (at least) should have been converted to small fragments.

Proceeding cautiously to apply the Sugano results --  we believe that the Sugano experiment may present a possible counter-argument against  two of the most widely cited arguments for the "no 757" theory at the Pentagon: the "too small" hole, and the "missing wings" and tail.  According to our detailed analysis (presented below in Appendix I), the hole appears to be too small because the wing-tips and tail were not massive enough to penetrate the facade, and in some cases the columns were also strong enough to survive (or partially survive)  the onslaught of the airplane's core.  Furthermore,  we should expect  no recognizable remnants of the wings and tail because they should have been smashed into small pieces and spread all over the Pentagon lawn.

If the wings & tail of the 757 hit the Pentagon wall, why can't we see any clear signs of impact?  The fuselage of the F4 crashing into the concrete block wall, left an indentation 2cm deep, while the engines (more heavily constructed than the 757 tail for sure) left indentations 6cm deep. But with all the smoke and foam in the photographs taken immediately after the crash, it is difficult to be confident that even this amount of damage would be clearly visible.  It is also odd that the wings didn't do more damage to the windows, although without specific data, it is difficult to know  whether the impact  would have exceeded their blast resistance capabilities.  Indeed, it is possible that the wings and tail might have missed the windows completely.

The Sugano results may also explain the bizarre appearance of videos showing the WTC aircraft disappearing into those buildings like knives into butter, without slowing down.  The force exerted backwards from the crash through the airframe is not sufficient to cause significant deceleration of the parts that haven't impacted yet, at least from a visual point of view.  In the case of the F4 experiment, although the airframe behind the crash zone experienced a 100G deceleration, this was only sufficient to slow the tail by 30 meters per second (out of 215 meters per second) during the 70-millisecond duration of the impact. 

We do not claim that the Sugano results can be used to definitively establish exactly what the hole in the Pentagon should have looked like, if it in fact had been struck by a 757.  Due to the many complexities of the structural analysis of such a crash, the exactly "correct" impact hole size and shape is simply an imponderable for both the crime scene investigator and the perpetrator alike.  What we are saying, is that the hole in the Pentagon does appear (at least in its basic size and shape) as a plausible outcome of a 757 crash, although questions do remain about the specific nature of damage to the columns and the interior features of the Pentagon offices.

We turn to the photographic record of the Pentagon crash to evaluate the evidence of a debris field sufficiently extensive to account for thousands of pounds of wing structure. 

(source: http://www.geoffmetcalf.com/pentagon/images/13.jpg)  

Probing Frank Probst 

http://fire.nist.gov/bfrlpubs/build03/PDF/b03017.pdf from page 13

http://www.militarycity.com/sept11/fortress1.html (Approx. 9/11/2002)

 

'I knew I was dead'

Exactly 60 years later, half the world was watching the World Trade Center burn on television on the morning of Sept. 11, 2001.

Frank Probst was one of them. A Pentagon renovation worker and retired Army officer, he was inspecting newly installed telecommunications wiring inside the five-story, 6.5-million-square-foot building.

The tall, soft-spoken Probst had a 10 a.m. meeting. About 9:25 a.m., he stopped by the renovation workers' trailer just south of the Pentagon heliport. Someone had a television turned on in the trailer's break room that showed smoke pouring out of the twin towers in New York.

"The Pentagon would make a pretty good target," someone in the break room commented.

The thought stuck with Probst as he picked up his notebook and walked to the North Parking Lot to attend his meeting.

Probst took a sidewalk alongside Route 27, which runs near the Pentagon's western face. Traffic was at a standstill because of a road accident. Then, at about 9:35 a.m., he saw the airliner in the cloudless September sky.

American Airlines Flight 77 approached from the west, coming in low over the nearby five-story Navy Annex on a hill overlooking the Pentagon.

"He has lights off, wheels up, nose down," Probst recalled. The plane seemed to be accelerating directly toward him. He froze.

"I knew I was dead," he said later. "The only thing I thought was, 'Damn, my wife has to go to another funeral, and I'm not going to see my two boys again.'."

He dove to his right. He recalls the engine passing on one side of him, about six feet away.

The plane's right wing went through a generator trailer "like butter," Probst said. The starboard engine hit a low cement wall and blew apart.

He still can't remember the sound of the explosion. Sometimes the memory starts to come back when he hears a particularly low-flying airliner heading into nearby Reagan National Airport, or when military jets fly over a burial at Arlington National Cemetery.

Most of the time, though, his memory is silent.

"It was pretty horrible," he said of the noiseless images he carries inside him, of the jet vanishing in a cloud of smoke and dust, and bits of metal and concrete drifting down like confetti.

On either side of him, three streetlights had been sheared in half by the airliner's wings at 12 to 15 feet above the ground. An engine had clipped the antenna off a Jeep Grand Cherokee stalled in traffic not far away.

Liquid Hammer Jet Fuel Induced Concrete Erosion, As Per Purdue? 

The Purdue simulation shows a computer modeled 757 impacting into a representation of the Pentagon. It is interesting for several reasons.

· It shows the aluminum fuselage and wings of the plane being shredded by the building's reinforced columns until those columns are eventually demolished by the mass of the fuel contained in the wings and the center tank of the fuselage. The shredding of the aluminum comports with the Sugano report, which of course is in dire conflict with the photographic evidence as discussed above.  However, the Sugano report leads us to question whether we should expect the aircraft to necessarily penetrate any part of the Pentagon wall, which was built with heavy reinforced concrete columns, thick brick and limestone infill, and steel reinforcement columns and beams for the windows.  Expecting difficulties, the Purdue authors wrote: 

"A basic hypothesis, informally confirmed with engineers knowledgeable in this subject, is that the bulk of the impact damage is due to the body of fuel in the wing and center tanks. Most of the aircraft structure is light-weight low-mass, and relatively low strength, with the exception of the wheel undercarriage."

Based on this hypothesis, Purdue built an elaborate model of the effects of fluid on reinforced concrete.  However, the Sugano paper actually did specifically  attempt to account for the effects of fuel in aircraft impacts.   The F4D fuel tanks were filled with water, which was presumed to have similar mechanical properties to jet fuel. No special damage was notably caused by this fluid, apart from the expected force of impact as predicted by the momentum equation.

· Ostensibly due to manpower and computational limitations, several aspects of the event were not modeled. This includes the effect of the column infill walls, the new blast resistant windows, and the newly added reinforcement steel, the debris containment mesh, and the second story floor slab and everything above. This allowed for the survival of major sections of the simulated 757 tail section. Also, it appears that fuel was left in the wings clear out to the extreme wingtips, as these also penetrated the simulation building in contrast to the real event. Of course, all these details that are missing, or excessive, might possibly allow for some wiggle room for when tough questions arise. It can be stated that it was not the project's scope  to create a perfect model, just enough to show the 'major' effects to the columns.

· The damage to the columns seen in the simulation were 'calibrated' to the actual columns by empirically adjusting the simulation parameters until a match was obtained. Of course, we are left to wonder as to how compliant the calibration is to reality considering all the possible variables that may have been omitted, and all the structural elements that actually were left out.

· By advancing frame by frame one can see the engines vanish as if being subsumed underneath the ground level floor. While it could be understood that it may be somewhat imponderable to decide on the precise lateral point of impact and the effect of the retaining wall on the mechanical integrity of the port engine (especially since it should have also hit the bed of one of the contractor's trailers first), we can see that the starboard engine has an elevation problem simply because the starboard wing has been modeled at such a low elevation so as to attempt to reproduce the actual column damage along the right side where the columns remained attached to the ceiling and bent back. Yet  the plane was supposed to still be maintaining a bank to the left such that the starboard wing impacted high enough to cross the second story floor slab.

· The simulation did not attempt to render the wire spools to 3D even though their dark 2D circles can be seen in the Space Imaging satellite photo used from 9/7/2001, 4 days before the event. The simulated plane merely flies right over them.

The aspects of the simulation which were left out lead us to an interesting question. If we are to assume that the observed bread slicing / cheese grater effect seen in the simulation is correct, then based upon the most conservative alignment of the plane with the building, a significant upper slice of the fuselage should have been sliced off by the second story floor slab as the alleged 757 made its entrance. This portion of the fuselage should be something on the order of 1/3 of the fuselage circumference. Most of this aluminum material should have then proceeded further into the building and as per the rest of the simulation, the bulk of that should have proceeded past the column 11 expansion joint collapse seam. This is important because this material would be sequestered from any fire and fuel from the plane. Protected from the ground floor fire by the effect of the concrete floor further in, and from the fuel by the fact that the port wing and fuselage tank fuel would only apply to the ground floor level as would most all of the balance of the fuel in the starboard wing (that is, any wing fuel also left over from the impacts with the generator and the trailers). Any possible hydrogen from Jean-Pierre Desmoulins' claimed chemical reaction would gravitate to the ceiling of the second floor, not to the floor where the debris would rest. There is no sign of possible fuel entry to the second floor except possibly via one or two windows impacted by the starboard wingtip, in any case too far from the fuselage debris of this scenario.  Arguably, in this scenario there should have been much more severe damage to the second floor, and at any rate large quantities of fuselage debris should have been found in the second floor.

However, we have no proof that fuselage debris was not actually found on the second floor.

APPENDIX I

Based on the Sugano et al. paper, we have attempted to calculate the forces that would be involved in a hypothetical crash of a 757 against the Pentagon. The results are tantalizing yet uncertain.

If the impact of the "757" occurred at a relatively low velocity, such as 200 mph, it seems questionable whether any part of the aircraft would have penetrated the Pentagon wall.  On the contrary,  the plane probably should have been entirely smashed and shredded. Furthermore (and perhaps this is the most important point) if we're making this calculation correctly, the planners of the operation would have been aware of the problem, which might have led to the logistical decision to use pyrotechnics and / or a missile or missiles to penetrate the facade.

At high speed (400-500 mph) penetration of the facade is much more likely (though perhaps not certain) -- yet a high-speed attack directed at the first floor of the Pentagon would have been difficult to carry out accurately with a 757, because of turbulence and ground-effect.

There are enough uncertainties in this calculation, that we would be very uncomfortable claiming that it would be *impossible* that any part of the aircraft would have penetrated the facade.  But, if  it is accepted (based on other evidence)  that 9/11 was an inside job, then this analysis may help to explain why  the planners might have decided to use missiles or pyrotechnics, rather than relying on a 757.

There is a similar situation with the WTC towers -- the planners could hardly have tolerated the uncertainty of an uncontrolled collapse -- so they would have needed to place some explosive charges, to prevent the towers from tipping sideways and destroying all of Wall Street.

Calculations

According to Sugano et al, by far the most important determinant of the impact force is the term F=alpha*V^2*u, where u is the mass (per unit of length) of the airframe which is abruptly smashed against the wall, and alpha is a correction factor equal to 0.9. So if we use the figures in the ASCE report for the weights and dimensions of the 757 aircraft, and apply some reasonable assumptions about the distribution of mass within the wings, we can estimate the impact forces fairly accurately.

The wings of the 757 are tapered from the roots to the tips; from the drawing in the ASCE report, we estimated a chord length of 8 meters at the roots, 5 meters at 7 meters out, and 3 meters at the tip. The thickness of the wing is tapered proportionately, so the mass of the wing's structure should be roughly proportional to the square of the chord. The ASCE report says the mass of the wing structure is 13,500 pounds in each wing. If  this mass is distributed as the square of the chord length, then 8750 pounds of this is located within the first 7 meters of the wingspan, while the remaining 4750 pounds are in the tips. Furthermore, the engines weigh 11,900 pounds each, and the landing gear weighs 3800 pounds. The fuel mass is 14,600 pounds for each wing, and since the tanks were partly empty, most of this mass would have run towards the lowest part of the tanks (that is, towards the center).  Thus,  we have a total of as much as 39,050 pounds in each of  the wing roots, and only 4750 pounds in the tips (the outer 10 meters of the wingspan.) This should make it clear that the penetrating power of the extremities of the aircraft should be quite limited compared to the penetrating power of the core portions.

Using F=alpha*V^2*u, alpha=0.9, we can estimate the force loading for each linear foot along the width of the airplane. We used a velocity of 90 meters/sec (200 mph) although it's very possible the "aircraft" was traveling much faster. We can also calculate the pressure in psi, using estimates for the cross-sectional area of each part. We obtained the following values: wingtips, 21,000 lbs / ft (152 psi); wing roots, 200,000 lbs / ft (413 psi); fuselage, 111,000 lbs / ft (83 psi); engines, 200,000 lbs / ft (221 psi).

All of the psi loading values are well below the yield strength of concrete, which is about 3000 psi. We also need to look at the overall loading of forces onto the columns of the structure. This is much more difficult to estimate, since it's hard to say how much of the load bearing on the limestone and brick infill would be coupled into the columns, and how much would be directly transferred into deflection of the limestone & brick. But if we assume that the force on the columns comes only from the portion of the aircraft bearing directly on those columns, then we can use the values for lbs / ft directly, for our load estimates on the columns.

We found an on-line calculator for the "moment capacity" of reinforced concrete beams, at

http://www.strucsoft.com/applets/BeamStrength.htm

For 12" square beams with 8 square inches of rebar-cross-sectional area, 1" cover, concrete cylinder strength=3000psi, steel yield strength=45000psi (values estimated from the ASCE report) the calculator returns a moment capacity of 1812 in*kips.

According to this source

http://www.ce.memphis.edu/1112/notes/beam/reinforced_concrete_beams.pdf

the load-carrying capacity of a beam loaded at the center, is equal to the moment capacity divided by 4. If this is correct,  then the capacity of the Pentagon columns, treated as beams for a horizontal load, would be 450,000 pounds. This is greater than any of the estimated loads per linear foot, by more than a factor of 2. And, it is far greater than the estimated wing-tip loading.

If the "aircraft" were traveling at 400 mph, all the load figures would be quadrupled, indicating that the beams would be unlikely to survive, except at the wingtips.

http://www.sandia.gov/media/NRgallery00-03.htm - Scroll to the bottom of the page for video and stills

http://www.sandia.gov/media/images/jpg/f4_image1.jpg - F-4D impact into concrete block

http://www.sandia.gov/media/images/jpg/f4_image2.jpg

http://www.sandia.gov/media/images/jpg/f4_image3.jpg

http://www.nci.org/01nci/09/npp-planecrash-quotes.htm industry claims that nuclear containments can withstand air crashes

Confetti Summary from Eric Bart