Posted on 11/16/2001 1:21:51 PM PST by The Magical Mischief Tour
Edited on 04/29/2004 1:59:37 AM PDT by Jim Robinson. [history]
Information from the last 28 seconds of the flight data recorder aboard Flight 587 according to NTSB reports.
(Excerpt) Read more at cnn.com ...
First of all G's are not forces, but accellerations, which are response to a force.
F=mA where F is the force in pounds, m is the mass in slugs (1 slug being 32.2 pounds-weight), and A is the accelleration in ft/sec/sec. 1 G is 32.2 ft/sec/sec.
Those are english units, and you can leave the mass in pounds (Which being a force is really the weight, not the mass, damned English units) and the accelleration in G's and get the same results for the force in pounds. Since aircraft have lots of mass/weight even a 0.3 G accelleration is the result of lots of force. But aircraft are also big, so they have lots of area to exert the force on. At low speed, the tail would normally not be encountering all that much sideforce, but if it gets hit by a 200 mile/hour vortex, that could result in a large sideforce. I would also like to know what the yaw accelleration was. Since the tail is large and flat, a vortex which pushed on the side of the aircraft would be expected to push harder on the tail, and cause the aircraft to yaw with the tail moving in the direction of the wind in the vortex. I have trouble believing that even a 0.3 G equivalent of side force would snap off the tail, rather I would expect that you could snap roll the beast and the tail would hold on OK. The tail is relatively more important to lateral, or yaw, stability at lower speeds, because at higher speeds, the body itself helps "weathervane" the aircraft into the direction of travel.
A sidewise accelleration of .3 Gs would imply a force that is .3 times the normal lift forces required to hold the aircraft in level flight, IOW 0.3 times the weight of the aircraft. But that force would be exerted over a smaller area, the wing area being larger than the side or profile area of the aircraft. The tail would bear the brunt, although perhaps not the majority, of that force. All that said, I would not expect the tail to shear off unless there were also some other problem, like loose or corrodded bolts, or an undetected delamination of the tail structure near the mounting points. I sure would like to see a picture of the mounting area.
Why are the broken places all blackened? The thing did fall in the water, not into the fireball. Could it be from friction if the attachment point was "working" against the bolts and bracket it was fastened too? That would imply loose bolts I guess, but not very loose. Something easy to miss in a quick inspection?
But I never saw any blacked areas around the section they pulledo out of jamaica bay. In fact I thought it looked like you could put the thing right back on a plane.
Loosen the bolts just a tad at the phase inspection? Don't know if that would do it, but it would be quick I would think. Perhaps over torqueing them severly followed by retorqueing to the correct value, might damage the composite, without being particularly noticible if someone else takes a quick look or even re-checks the torque on the bolts. Last A inspection was just Nov. 11, the day before the crash.
Pictures at the link from post 9.
That's how the article reads, but it may not be what the data actually show.
I suspect the data refer to lateral acceleration around the aircraft's vertical axis, i.e., the aircraft yawed left/right, as opposed to experiencing lateral displacement (which would be pretty weird).
The reported 0.3 to 0.4g lateral accelerations, if in fact they were yaw (rotation about the vertical axis of the aircraft), reversing quickly in direction, might be just what it takes to exceed the strength of an already weakened vertical stabilizer attachment structure (fatigue failure of the composite structure that attaches the vertical stabilizer to the fuselage).
Once the vertical stabilizer departed the aircraft, it probably loses yaw stability, and this could give rise to sudden yaw oscillations of substantial amplitude, which in turn might exceed the shear strength of the engine/strut attachment bolts (which are designed to shear and let the engine go before the load tears the wings off the plane), especially if the frequency of the yaw oscillation is a multiple of the resonant frequency of the engine/strut structure under reversing lateral acceleration.
I suspect the problem regarding interpreting the data as lateral acceleration versus yaw is in the reporter's lack of understanding about what the data mean.
The fact that the first reported data anomaly is the "unuseable" rudder position data two seconds prior to the end of flight data recording suggests that the vertical stabilizer was the first structure to depart the aircraft. This is further backed up by the fact that the vertical stabilizer was the first object in the debris field, which is consistent with it being the first to fall off. If, for example, a wing had come off first, I would expect the first data anomaly to have been "unuseable" aileron position data for that wing..... but it wasn't.
Just a working hypothesis....
The only blackened portion I see is not a flame or explosion but is a darkening caused by the layers of composite opening up.
Do you see something I'm missing?
Thirty seconds might have given them a better chance of encountering rough turbulence, but it still wouldn't have ripped the plane apart...unless, as I said, the plane was an absolute basket case from the gitgo. And IF they prove that, then American deserves all the grief it will surely derive from this. I just find it difficult to believe that for the FIRST time in the history of avionics, in THIS kind of atmosphere, where witnesses saw a definite intrusion or extrusion from ABOVE the wing BEFORE the tail *fell* off, the wing *broke off*, and there was no, repeat, NO damage to either engine, both of which seperated from the plane in the air, flying in two different directions; in which the flight recorder and data recorder, both housed in the same compartment ended up at such a distance from each other that one was as fresh as a daisy, and the other was damaged out of all proportion, that *turbulence* could be the lone culprit. Especially when that particular plane had just undergone a safety check just days before. There are just too many wrongs to make this right. WHAT was the *security* issue we haven't ever been given any info on?
They're made of graphite, that's the natural color.
Think back to the Helicopter full of friendlies that our A.F. shot down over Iraq about 8 years ago.
Many problems. Wrong IFF code entered by ground crew, no visual check of target as per ROE, no notification of flight plan of helo to A.F. controllers, and another that is slipping my mind right now.
Remove any one of those and no friendly fire disaster.
I suspect if this is not sabatoge then what happened was a series of events and circumstances that are not likely to happen again even without a change in any policy.
But you can bet some manufacuring processes are going to be reexamined.
I haven't heard about that before. Do you have any info for me?
I agree. The events of the past few years and more recent events, have dramatically reduce my desire to fly anywhere.
There was a Japanese 747, maybe 20 years ago or thereabouts, that somehow lost the vertical stabilizer. (Collision with another plane? I don't remember.)
Anyway, the pilots managed to keep it aloft for quite some time by gingerly handling the engines and the remaining control surfaces, but they were not able to land it.
When I looked at those pictures of the snapped-off graphite lugs, I was surprised that they'd design the tail that way. They have the thing attached at a very high-stress point, it's IMO asking for trouble. If I was desiging it (I'm not a designer but I do have some common sense), I would have the graphite panels extend through the plane's body, and then attach them to the inside/bottom of the tail end of the body. That would put the least amount of stress on the attachment points. It would transfer torque to the body (at the top of the body, where the graphite panels would extend through reinforced slots) without stressing the attachment points, and also allow a bit of "flex", with the slots at the top of the body acting as a sort of fulcrum.
IMO this design would handle excessive stress a lot more gracefully than the actual design which places the attachment at the highest stress pont.
Look at how 2x4 studs are put together -- they dovetail two pieces of wood end-to-end so that there's a lot of overlap. If the guys who designed this plane were designing 2x4 timbers, they'd just take two sticks, put some glue on 'em, and stick them together end to end.
It doesn't take a degree in rocket science to predict how quickly a 2x4 like that would fail if subjected to any lateral stress. It looks like that logic escaped the guys who designed that plane.
If I ever fly again, I will never get on one of those Airbus models. After the nightmares I've had before 9/11 (when the pilot says he thinks he'll be able to land it, after circling for an hour with a jammed slat), I tend to be a bit wary.
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