Originally Posted by
predictorM9
What the report says is that the full deflection of the elevator down was not achieved with this input, because of the alt2b law. While the same law gives the full deflection of elevator up when the pilot was pulling the stick.
It is due to Load Factor law (aka Nz law) which applies in all Flight Laws except Direct Law not only in Alt2b. Alt2b is insofar different as all 'protections' are lost.
That said Full Nose Down command in an Nz law should correspond to a G Load Factor significantly below 1g even if the reference Speed is pretty low. This should result in a Nose Down Elevator response finally. Taking into consideration that average G Load in a developped stall will be close to 1g an Nz law should still allow ND Elevator. As there are G Load fluctuations in the dynamic evolution of the stall they might have been unlucky that during these 2s of ND input the temporary G load was on the low end of the range. Unfortunately I don't have the traces in front of me atm. I don't see why Full sustained ND input should not lead to a significant ND Elevator deflection in an Nz Law !?
And 2 seconds is not a lot, but in Quantas 72 that's exactly the time that was needed to flung the passengers up at -0.8g. 2 seconds (that's on the cvr). Granted it is not a stall and all, but the 2 seconds nose down input, at full authority would probably have improved things for them.
That was at a rather high speed and starting in a mostly neutral THS and Elevator.
I'm not a pilot anyway, but a 707 was crashed in the eighties for some fuel test, maybe they could do a similar test over an ocean with a remotely piloted airliner. After all, this might help calibrating models for simulations, and thus give an insight to all planes. It is not an A330 specific issue.
I guess no one is keen on showing crashing airliners these days. They want to convey the image that these things don't fall out of the sky...
I hope in 2013 we have the capability of simulating the unsteady flow around wings, even in the transonic regime. What is lacking is probably just some experimental data to validate the computations.
I'm not so confident. I would think there is quite some iterations between calculation and actual data required to come to a reliable prediction.
Yes but all that is easier when you have an AoA indicator. As you mentioned in your post you are probably safe below 30 degrees, which is not that much.
No disagreement here.