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RE: more on jet engine penetration - Scott Portzline



Title: RE: more on jet engine penetration - Scott Portzline

Norman Cohen wrote:
To those of you, including Jaro, who were discussing jet engine penetration of containment:
"Scott D. Portzline" wrote:

<SNIP>
 The 4% difference Jaro mentions is virtually meaningless as he states for smaller loads. But, that difference for a jumbo jet is enourmous for destructive force.

>
> Anti-nuclear folks may find it ironic that jet engines (hardened with thorium) are the most solid part of the airliner and are likely to penetrate a containment building fairly intact (in mass) and potentially striking reactor systems.

<SNIP>
<><><><><><><><><><><><><><><><>

Comment:

"Smaller loads" ?? ...smaller than what ? by how much ?

As I said previously, according to information from Jane's All the World's Aircraft, the Phantom jet in the Sandia crash test has two General Electric J79-GE-17 turbojets (Siamese-style installation, equivalent to a single mass for the purpose of this discussion), each of them weighing 1,740 kg (3,835 lbs) and having a diameter of 992 mm (39"), with a total weight of 3,480 kg (7,656 lbs) for the two side-by-side mounted engines, and an average impact area density of 3.21 psi. Large commercial airliners like the Boeing 767 and 747 use engines with a weight of some 4,200 kg (9,200 lbs), and a diameter of 2,463 mm (97"), for an average impact area density of only 1.24 psi, which is about 2.6 times less severe than the Phantom's engines.

Actually however, much of that large engine frontal area is due to the high-bypass fan (which the military jet doesn't have), while much of the weight is concentrated in the "core" part of the engine, which contains the compressor and turbine stages. This core part of the engine has an average impact area density roughly the same as the Phantom's engines, possibly slightly higher. The shafts BTW are, in both cases, thin-wall hollow pipes, several inches in diameter.

As one colleague here wrote,
"The size of the aircraft does not matter as much as one might expect - larger aircraft take more time to destroy themselves (we're talking mili-seconds here) than smaller aircraft.  An important factor is again the peak (maximum) loading on the structure.  I would expect a large civilian aircraft would actually have a lower peak impact load on containment, than would a small compact military aircraft, because they take longer to destroy themselves and are less dense.  Remember that a civilian aircraft contain a large volume of air and soft stuff (e.g. people [sorry, but it's true], seats, luggage and fuel) which has a thin skin around it - this volume reduces the density of the aircraft and thus lowers the impact force.  A military aircraft is essentially a jet engine (quite dense) surrounded by small wings, and is designed to fly in combat (i.e. high g-forces, sustain some hits and remain flyable).  Thus by definition a military aircraft like the F-4 is a tougher, harder target than a 747.  It is also much more dense, and thus the peak loads would be higher, I would expect. Also, since a civilian aircraft is spread out, some of it would even miss the containment or strike a glancing blow.  The F-4 crash was a perpendicular (i.e. direct) strike where all the energy was concentrated on the target."

Mr. Portzline's argument is just as phoney as Mr. Resnikoff's. What he is attempting to do, is to repeal the laws of physics.

No, thank you. I think I'll stick to my good old physics text book (see below).

Jaro

[ PS. just so we don't get some sort of weird impression that airliner jet engines are a kind of unstoppable doomsday device, please recall that the engine which fell off the airliner that crashed in NYC a couple of weeks ago, did NOT cause much damage on the ground -- never mind a 100ft crater or anything like that ]

> Marvin Resnikoff  wrote on Monday November 05, 2001 7:18 PM :
>
> <SNIP>
> Our calculations for concrete penetration do not assume the structure moves.
> As must be clear to you, one cannot infer from the Sandia test that a 767
> engine moving 500 mph will penetrate 6 cm of concrete.  If the building or
> storage cask were stationary, the penetration depth of the 767 jet engine is
> closer to 4 feet, and several U.S. reactors have a thinner concrete
> containment.  Our method of calculating the penetration depth is identical
> to the method used by NRC staff and DOE contractors.
> Marvin Resnikoff
> END QUOTE>
>
> Marvin, this is pure nonsense !
>
> Whether the impact block in the 1988 Sandia F-4 Phantom crash test moved or
> not makes very little difference. I will tell you exactly how little difference.
>
> The Sandia test was performed much the same way one would do the classic
> Ballistic Pendulum experiment for measuring the impact speed of a bullet : a
> block of wood is suspended by strings, so that there is no external force,
> such as friction, acting along the line of impact -- the same was achieved
> (nearly) by putting the reinforced concrete block atop an air-bearing
> platform. Quoting from the report,
> The target consisted of a block of reinforced concrete 7 m square and 3.66 m
> thick mounted atop an air-bearing platform with a combined weight of 469
> tonnes (almost 25 times the weight of the F-4)
> .....
> Ten air bearings were installed in "pockets" in the lower surface of the
> air-bearing platform. After inflating the air bearings, a force of only 816
> Kg (less than 0.2% of the weight of the target) was required to initiate movement of the target.
> When the bullet in the Ballistic Pendulum experiment hits the block of wood,
> it stops within it and thus transfers all its kinetic energy to the combined
> block-with-bullet mass. The movement of the block-with-bullet mass can then
> be used to calculate the initial speed of the bullet, or -- and this is the
> important part -- if you know the speed of the bullet, it can be used to
> measure the amount of energy expended in different ways in the collision.
> It turns out that in the case of such an inelastic collision, its easy to
> demonstrate that the fraction of energy going into destruction of the
> colliding objects is simply the total energy (i.e. initial kinetic energy),
> minus the ratio of the mass of the bullet (or the F-4 Phantom) versus that
> of the target-with-bullet. For example, a 5-gram bullet hitting a 2000 gram
> block of wood will result in ( 1 - 5/2005 = ) 99.75 % of the total impact
> energy converted to destructive energy (mechanical crushing, heat, shrapnel spray, etc.).
> Similarly for the Sandia impact test, where the ratio of airplane mass to
> concrete block mass was 1-to-25, the amount of impact energy converted into
> destructive energy is ( 1 - 1/26 = ) 96.2 % of the total.
> This may be compared to the case where the concrete block had been fixed
> perfectly to the ground, which is exactly analogous to having a block with
> infinite mass. In this case the amount of impact energy converted into
> destructive energy is ( 1 - 1/10000000.... = ) 100 % of the total.
> Note that there is a difference of only ( 100% - 96.2% = ) 4 % between the
> case where the block is fixed to the ground (infinite mass equivalent), and
> where it is floating frictionlessly. That of course is because of the large
> mass difference in both cases.
>
> Note also that Mr. Resnikoff and other critics are telling us is that a 4%
> difference in impact energy conversion to destructive energy, makes the
> difference between the 2½" penetration of the concrete wall in the actual
> experiment, and the 4 feet ( 48") penetration calculated by them.
> A 4% difference in energy results in 19-times deeper penetration according to them.
> AMAZING !!!
>
> Just as amazing is that this is grade eleven high school physics.... the
> bullet example I cited above comes from my 1966 edition of the Physics text
> book by Halliday & Resnick, page 220.
>
> Radsafe colleagues, please make sure everyone gets the message !  ...no more
> screwing around with antinuke-motivated misinterpretations of the historic
> Sandia crash test !
>
> Thanks.
> Jaro
>