> WHAT???
>
> Design maneuvering speed is "Va" and is simply and _only_
> Va = Vs * sqrt(g load limit)
>
> You can be sure that an aircraft manufacturer would have a whole lot of
> patents if they had a method to recognize all the situations that can
> cause structural overloading and recover before these are reached.
> That would be the holy grail of FCS design, and of aerodynamic modelling!

At 450+ knots a sudden full deflection elevator movement might not be so
good. (?)   Additionally, a back and forth elevator motion at a particular
frequency might not be good at all. For one thing I know the F-16 (not a
modern commercial transport, but for example) has structural filters on
most/all aerosurfaces. This might have to do with the interaction between
the hinge moments, the servoactuator, and pilot inputs (etc.) so as to
prevent a divergent oscillation that might violate some structural
constraints - I can't remember exactly what it does, except that it
attenuates control inputs of a particular frequency. I am almost sure that
commercial transports limit some pilot actions to stay within structural
tolerances.

In the case of the flight that crashed into the neighborhood in New York,
the particulars of that accident lead me to believe that given the sideslip
angle, and the yaw rate at rudder separation, the rudder command might have
been processed to eliminate the peak that stressed the rudder too far. I
could be wrong, but the thought occurred to me and I think it is plausible.
This particular accident did not appear to me to feature an obscure,
unpredictable causal manuever.

Also, I don't think that all possible permutations of pilot actions that
overstress the aircraft need to be accounted for. Given my limited
understanding of neural networks (and from the demos I have seen at work)
this tactic might be effective in filtering out undesirable pilot inputs as
far as structural limit violations go.

Jon



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