Originally Posted by
bearfoil
I think a picture is worth at least a thousand words. Given that the shackles and pins look as they do, reasonably untouched, and the hoops have broken away, burned, and exposed the Hardy mounting bed, I can't understand why these metallic beds are "Battleship engineered" bomb proof, and the Stabiliser is "frangible".
I agree on the composites - I suspect we still have much to learn there. It took some painful lessons before we figured out how to make aircraft (safely) out of aluminium...
I agree on the rudder attachment vs. VS attachment as well - seems like a good fail-safe has been missed there in favour of "strong enough" (and probably right across the industry - a few 737s would have been better off without the rudder). I do wonder why this is, since the extra strength (of the rudder hinge) implies extra weight which is rarely there without reason. Is it possible that as a moving part the rudder hinge has a cycles-to-failure requirement that leads to it being stronger in static load than the VS attachment ?
Now those VS attachments - again are they much stronger and hence heavier than required ? Maybe they were originally designed to hold a heavier metal VS - possible I suppose. Or maybe they aren't so much different in strength to the composite VS (after all, the overloaded joint always has to fail one side first) ?
A couple more thousand words:
First one is those same attachment lugs (I believe) from AF447. This time the composite didn't break, and the mountings were ripped out of the fuselage - by the VS. If the composite strength was a lot lower than the mounting, then we'd expect the same failure mode under the same loading.
Second image is the VS from the NZ airbus at Perpignan. It looks as though, again, the VS took attachment & some fuselage with it (I admit there isn't enough detail in the image to be sure - best image I could find). Now, in this case we
know that the VS was from a high speed water impact and an intact aircraft that disintegrated on impact.
Conclusions:
- It is definitely possible for the VS to float away in one piece and good condition from a high speed water impact of an intact a/c
- The failure mode was different to 587 (different model, but I believe the attachment design is the same)
- If (and this may be your bias and mine) the metal attachment points are stronger than the composite VS, then the forces leading to VS failure must have been significantly different in 587 and 447.
My thoughts are that the metal attachments
are stronger in normal circustances, but the fuselage was already being crushed, by impact with the water, as the VS departed.