reply to post by pteridine
Taking the estimated airplane mass at the point of impact to be M = 127 tons and the impact velocity of 240m/s o V = , the energy of the striking
aircraft was 3658MJ KE.
3.3 Engines and wing damage The engines are the only components of the aircraft that can be considered approximately as rigid bodies. Their
devastating power is unmatched until they encounter an object of similar weight and strength.
In the experimental study in which an engine of a transport aircraft hit a thick concrete wall, the engine itself was crashed and fractured, so it was
not rigid, [28]. However, in contact with less substantial members the engine could cut and plow through the various structural members of the WTC
Towers until all their kinetic energy is absorbed.
I don't see them calculate the mass of the whole building anywhere, where is that figured? They calculate the mass of the 747, which like a
building's mass, is just the sum of it's parts. Are they conducting an honest study? The part about the engine hitting a thick concrete wall will
help over on the Pentagon thread though...thanks. Otherwise it looks like they're setting up a whitewash study, judging by the parameters they're
limited to.
Wings of modern transport aircrafts are quite complicated structures consist of open section beams, ribs and a skin reinforced by stringers.
Together they form a very stiff and strong box-type section. Determination of the strength of the wing relative to the strength of the floor structure
will require a detailed finite element analysis, which we believe has not been performed to date. In order to retain the needed degree of simplicity,
two models were developed.
In one model the wing material is lumped into single box-type beam. In the second model, the solidity ratio are determined for both the wing and the
floor and then are compared. The main structural part of the wing is the spar – a continuous beam that extends from one tip of the wing to the
other. For modeling purposes, we assumed that the mass of the wings (excluding engine) was approximately 21300kg wing M = . This mass does not include
the mass of the fuel in the wing tanks.
Assuming that this mass is now uniformly distributed over the whole wing span
It isn't. Most of the mass is between the fuselage and the engine.
and the wing is modeled as a thin-walled square section crosssection (c ´4c ) with the thickness ( eqw t ), the equivalent thickness of the wing
beam can be found from the equation (10 ) eqw w Al wing ct l r = M (8) Taking an average height of the spar to be c = 480mm and the span of the
aircraft 47.57m w l = , the equivalent thickness becomes 34.5mm eqw t = . The wings are swept at approximately 35o so that upon impact, external
columns are contacted sequentially, one by one. However, the problem of a hollow beam striking another hollow column at a right angle and a speed of
240 m/s has not been analyzed in the literature. Therefore it is not possible, at this point in time, to give any detailed account on this
interaction, between the wings and outer column, with a higher degree of accuracy than our approximate engineering analysis.
What? Therefore it is not possible? Therefore it is not possible this report proves squat. Why would 35 degree swept wings strike the individual
columns at right angles anyway? Wouldn't the swept wing strike the corner of the first column at 240 m/s, and slow down as it hit the next column,
as the fuselage is slowing down against the lateral resistance of at least two floors? Their modeling appears to be done to explain how a plane
could do it, not how it was done. Note their language throughout the report...the plane "could" have struck here...why are they guessing?
Don't they have the Naudet footage? Aren't they the experts?
The equivalent thickness of the hollow wing beam is approximately four times larger than the
thickness of the exterior columns, 9.5mm ext t = . It is therefore reasonable to treat wings as
rigid bodies upon impact with exterior columns. By the same token, the equivalent thickness of
wings is smaller (about half) than the equivalent thickness of the floor structure (to be
calculated in the next section). Consequently it would appear that the floors will cut through
the wings without being severely damaged themselves. In actuality the wings are constructed
as a 3-dimensional lattice of open section beams, ribs and sheet metal skin that maybe of
comparable strength to the floor trusses. However, interaction between two 3-dimensional
space frames impacting each other is too difficult to carry out analytically at the present level
of approximation.
Can you explain this one to the class please? Do I see them rolling all the material that would comprise a wing into a big ball of aluminum play doh,
and reforming it all in wing shape so that the wing is now equally massive from tip to root, and all the material is equally distributed to a
thickness of 9.5 mm? Why is this model wing approximately four times the thickness of the model column? On the next page they're saying they really
don't know that either but they're guessing it's about 9.5 mm, so that one threw me for a loop, but I'm no expert so can you help me out? Isn't a
real wing's skin thickness about 2 or 3 mm at most?
So now the wing has half the mass at the tip, and is 9.5 m thick, what do they do to the building? Do they include the mass, or make a big ball of
steel play doh and reconstruct it so it will be easier to model? From what I see they take out the core and treat the model to only 40% of the
building. When they're done tweaking these things, then they start the test using a flurry of hieroglyphic gibberish sure to dissuade curious eyes.
They even try to convince their readers the wings were comparable in strength to the WTC tower floors, but my eyes glazed over at that point.
Is there any need to continue with this vaunted study from MIT?
