Originally Posted by takata
Now, that the weather alone would put suddendly this aircraft close to an "upset" attitude, while flying in automatic mode at Mach 0.82, would certainly disconnect everything the same way. Then, if this was followed immediately by the freezing of all the probes, ...
Any thoughts as to how (at FL350) "the weather alone would put suddenly this aircraft (in or) close to an "upset" attitude" in pitch, roll or yaw?
Regards,
HN39
PS1:: To illustrate what I have in mind, I have done a
simple sum. In its Appendix 1 to BEA Report No.1, MétéoFrance writes:
The strongest vertical movements are observed in the "tower" of the cumulonimbus in its phase of rapid growth, that is to say before the top reaches the tropopause and the anvil is formed. The upward speeds can then reach 110 km/h and the downward speeds 50 km/h. The vertical speed can thus vary very rapidly inside of the cumulonimbus while crossing its "tower":
variations of more than 70 km/h in the space of 2 km have sometimes been observed. This intense turbulence can occur at the flight level of airliners and constitute a danger for them.
As I read this, these are extremes, unlikely the fit the CB's encountered by AF447. But let's take them as written. An aircraft encountering an increasing updraft as described by MétéoFrance will pitch up, unless the pilot or AFCS opposes that with control inputs that maintain a set pitch attitude. The tail length of an A330 is about 29.25 m. Therefore the updraft velocity seen by the wing is 0.284 m/s greater than that seen by the tail. When the aircraft pitches up at 0.56 deg/sec, that difference will be nullified by the downward speed of the tail relative to the wing. At 483 kt TAS, the 'space of 2 km' is traversed in 7.45 sec, during which time the aircraft has pitched up 4.15 deg,
less the lag attributable to its mass moment of inertia in pitch (which I have no data on).
PS2:: As a result of further research into the 'mathematical model' proposed in PS1 above, I should add that, due to several attenuating factors not taken into account in the 'simple sum', such as inertia, and the natural stability that induces a pitch-down moment when AoA increases due to an upward gust, the actual pitch up will be much less than that derived in PS1. Unfortunately, I do not have the more sophisticated 'mathematical model' that would produce the correct number.