TWeeD ([info]densaer) wrote,
@ 2008-05-01 09:10:00
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Ping [info]rfrench (or other pilot types)
I remember from my training that at or below maneuvering speed (Va) meant that one could cause any abrupt control surface deflections without damaging the aircraft - the aircraft would stall before breaking.

How then to explain AA Flight 587? Overly aggressive use of the rudder (from one side full deflection to the other side full deflection) caused the rudder and tail fin to come off ... but I think most pilots prior to the accident would have said that such a maneuver would have been okay considering the speed of the aircraft.

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[info]banacheq
2008-05-01 06:27 pm UTC (link)
Yeah, that just doesn't add up to me. The wake from the 747, combined with weakened composite mounting bracket, AND moving the rudder around, seems plausible.
I was working at NCAR's RAF when they got in a B-57 (WB-57F, precisely) which had some major cracks in the composite internal wings struts. Given the amount of variation in wing level on the ground and in flight (easily a 30 degree change) plus the bouncing of the wings on landing, they took a LOT of abuse. I would suspect a lot of vertical tails on aircraft experience (thanks to things like the wake of 747's, etc) a lot of similar shear.

Witnesses say they saw the explosion and fire first - maybe the hydraulics in the tail couldn't take the sudden changes?

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[info]rfrench
2008-05-01 11:14 pm UTC (link)
Well, first of all there's no indication that the plane was at or below Va.

Secondly, Va is very misunderstood. It doesn't say anywhere (except in layman books) that a plane can handle "any control input". It's purely an indication of stall speed times sqrt(design load factor). That protects the wing against positive loads, but not against negative loads and doesn't protect the rest of the structure from anything.

See this great article for details. And here.

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