Originally Posted by CONF iture
(Post 8409124)
...and a stall could not have happened after clearing the trees as alpha max is not alpha stall.
Good for you ... what I was expecting is a BEA + Airbus analysis. By the way if phugoid damping was involved, they could have detailed why Bechet was miraculously spared from it ... ? As I said before, the fact that the investigation went as far as confirming the behaviour as normal, but no further, could be argued as a point that they missed an opportunity to further explore the mode switches (and consequences of those changes) involved. However, the events of the last three seconds in the context of an accident investigation could equally be considered a minor point when compared to the major systemic failures that led to the aircraft being put in that position. Namely:
The result of these failures was that the flight crew were effectively entirely reliant on their ability to improvise at short notice - which, given the inherent riskiness of the manoeuvre, should have been completely unacceptable on the face of it. Even more so when you take into account that there were pax on board. To the best of my knowledge, "Priority One" of accident investigation is working to ensure that the incident is never repeated. Now, I'm no accident investigator, but if I were I'd be inclined to consider getting to the bottom of how the aircraft was permitted to get into that position in the first place as a much higher priority than getting too far into why the Alpha Max command was complied with more slowly than it otherwise might have been (especially given the fact that the flight had been woefully mismanaged long before Asseline pulled that stick back). Put another way, if the mistakes and loopholes in the list above can be prevented and closed, then with all other things considered there should never be another aircraft put in that position again, making the assessment of precisely why the aircraft was slow to achieve Alpha Max somewhat of a moot point. Again, I said before that Asseline's best hope of being able to get the investigation to look further into the matter of what the EFCS was doing in those last few seconds would have been to take his lumps and remain positively engaged with the investigation throughout. By disengaging from the investigation and subsequently actively briefing against it, he did his own cause more harm than good. |
Originally Posted by OK465
(Post 8410400)
If I'm reading it correctly, I am guessing that what you're referring to here is the fact that in the simulation, the elevator smoothly continues to trend leading edge less down (less negative)/aircraft less nose up until the end of the plot.
|
metalanguage
Metalanguage = object formal language in semantic brackets.
Example of semantic brackets in character strings is using a special character which is never used in the object language. As the number of characters is very limited, the special character is often an unused string of characters, like : = , http://www , Ctrl Z, [/quote] and [quote], etc. Building an object language vs metalanguage may use different gramatic too but it is not mandatory. Children playing to be master or parents or king mostly build metalanguage to be considered as master, parents or king! Sometimes they forget to use the metalanguage and suddenly they are no more king, and everybody is laughing. In the simulator a hidden mistake (forget the space between ":" and "=" and you discover a smiley no-no instead of the string ": =" ) in the metalanguage semantic brackets may modify the behaviour of the simulated system (plane, inertial system, aso) without you know it, and you have a bad surprise when you do the same action on the plane, despite your aerodynamic algorithm is OK. It is always difficult to test the semantic brackets, you would mostly need a meta-meta-language! All that applies well on well structured simple systems using formal language. Graceful degradation brings a greater complexity .... KISS! |
@roulis - I've said before, the computer code is not manually keyed in in that manner. Code blocks are tested in situ against the formalised function, then assigned to an element in a graphical development environment, which then generates the logic path from those individually-tested blocks of code. Each subsystem is then itself tested against the required behaviour pattern, and as the subsystems are linked together to form an overall program "module", that module and its functions are tested individually and in conjunction with others.
These tests are run *every single time* a change is made, and the results of the tests plotted against a regression graph. Any change in that graph is immediately apparent, and will point to exactly where the program deviates from the specified behaviour. |
You clearly didn't read what I wrote, because I said they were comparing it to a *conventionally-controlled* aircraft. As HN39 said, phugoid damping is not used when in pitch command (i.e. the mode Bechet was in), only in HAP mode (which Asseline was in). |
Originally Posted by CONF iture
(Post 8410577)
Typical Dozy disinformation again - where is the quote ?
EDIT : Certainly whenever I've heard that factoid referred to in the past, I got the impression that they were talking about an unprotected (i.e. conventional) aircraft - not least because I can't see how it makes sense any other way! Speculation only from HN39 that would demonstrate how the system is inefficient but you're happy to take it for cash ... Where is the official reference ? On a different subject, I strongly recommend you have a look at OG's post #734, then look at the graphic on Annex 10 p.13. Bear in mind that what you're looking at (I think) is a simulation of how the aircraft and systems would have responded to the commands as they were prior to impact had there been no collision (114 kt being very close to the airspeed achieved just prior to impact). |
Originally Posted by Dozy
Here's a novel idea, why don't you find it and prove me wrong?
It's not inefficient, it's a necessary consequence of an aircraft being commanded to achieve or hold a specific AoA - namely a tendency to begin a phugoid motion. |
Originally Posted by CONF iture
(Post 8410654)
Assume the disinformation you're spreading around or retract it.
(Or more to the point, how is it fair that you get to make unsubstantiated claims of a "restriction" in the EFCS (and insinuate that it may have been surreptitiously removed) unchallenged, whereas I must retract any statement with which you disagree out of hand?) Knowing both are starting from identical parameters, why Asseline should be subject to it but Bechet not ... ? The difference is in pulling the sidestick back - Bechet at the same instant and Asseline 3 seconds later. So Bechet was still in pitch control law when he pulled the stick back while Asseline was in alpha-prot. |
Originally Posted by Dozy
Why?
They're not starting from identical parameters. Note that on this particular run, Bechet snaps the stick back almost immediately approximately 3 seconds prior to when Asseline did the same. Bechet's action is just prior to when the mode switched from pitch command to HAP mode. Asseline's motion is also more gradual. |
Originally Posted by CONF iture
(Post 8410709)
according to the graph at the remise des gaz, except that Bechet is 10ft lower ...
Then if I had to guess the one who could be more prone to phugoid motion I would go for Bechet not Asseline. |
Originally Posted by Dozy
Not quite 10ft
How? Asseline was in HAP mode when he pulled full-aft, Bechet was in pitch command. Still waiting for the reference stating phugoid damping under high AoA protection but none under pitch command ... |
Originally Posted by CONF iture
Speculation only from HN39
Originally Posted by CONF iture
Still waiting for the reference stating phugoid damping under high AoA protection but none under pitch command ...
Originally Posted by HN39 #707
Phugoid damping is a feature of the alpha-protection mode, because an airplane is prone to develop phugoid motions when constrained to a commanded angle of attack. Flying an airplane to a commanded pitch attitude does not result in phugoid motion, and therefore pitch-command mode does not require phugoid damping.
Secondly, I explained in post #707 why phugoid damping is necessary in alpha-prot and unnecessary in pitch command mode. I showed a phugoid motion that results from maintaining AoA after a disturbance of a steady flight condition. On the AF447 thread I showed similar simulations of airplane motion at constant pitch attitude after a pitch change, for example: http://i.imgur.com/mYVPqZz.gif?1 |
Originally Posted by HN39
If you have a reference stating that it is a feature of the pitch command mode then please provide that reference.
In other words, by which subterfuge Bechet is not subject to phugoid damping as he is obviously hitting high AoA protection too ? The point has been brought here but you did not comment. |
OK465
What's at play here? Is this solely due to the engine's increasing thrust pitching moment? Why wouldn't the elevator show reversals of direction or at least pauses during the pitching to stabilize AOA, if AOA is truly the driver? |
Originally Posted by OK465
BTW I notice on HN39's presented graph that what is referred to as alphamax is actually higher than alpha SW, I assume that reference is to alphaCLmax and not the conceptual protection alphamax which is lower than alpha SW.
P.S. I forgot to mention that we know one point of the alphaCLmax vs Mach curve: AF447 stalled at 10° AoA / M.67. |
Originally Posted by CONF iture
Not my point - What makes phugoid damping a feature of high AoA protection but irrelevant when high AoA protection is activated from pitch command initially ?
In other words, by which subterfuge Bechet is not subject to phugoid damping as he is obviously hitting high AoA protection too ? Bechet pulls the sidestick abruptly fully back at an AoA where the FCS is in pitch command mode and there is no phugoid damping. Therefore the airplane starts to pitch up achieving a rate of 2.5°/second one second later. About again one second later the AoA exceeds 14.5° and the FCS goes into alpha-protection mode. The elevator then moves to more nose-down positions in a way that is quite similar to the accident sequence and the rate of rotation starts to decrease. However, the inertia of the airplane pitching up at 2.5°/second and the nose-up pitching moment of the thrust increase allow the airplane to continue pitching up to about 16.5° while it begins to climb. That is what I see in that plot, although the resolution of the plot is not sufficient to show the AoA that is achieved. |
Originally Posted by HN39
"Not my point"? IIRC you made it a point.
What makes phugoid damping a feature of high AoA protection but irrelevant when high AoA protection is activated from pitch command initially ? In other words, by which subterfuge Bechet is not subject to phugoid damping as he is obviously hitting high AoA protection too ?
Originally Posted by HN39
However, the inertia of the airplane pitching up at 2.5°/second and the nose-up pitching moment of the thrust increase allow the airplane to continue pitching up a few degrees while it begins to climb.
You just confirm here that everything was in the aerodynamics but only the FCS restricted Asseline at 2.5 deg short of alpha max and deprived him the opportunity to survive the poor situation he initially put himself in. |
Originally Posted by CONF iture
(Post 8411872)
but only the FCS restricted Asseline...
Asseline wasn't restricted by the EFCS, he was restricted by his own actions in the previous 30 seconds or so - chopping back too much thrust, and then seeming indecisive about whether to actually go for Alpha Max (while constantly bleeding off airspeed). The EFCS doesn't know there's an obstacle three seconds away, it just tries to comply with the commands as best it can, and in this case both the TOGA thrust and full back-stick came too late. The A320 and its systems were designed for ferrying passengers between airports, and the protections were designed to fit that function - it was not designed for "playing chicken" with forests at low altitude and low speed! |
OK465
If I'm reading it correctly, I am guessing that what you're referring to here is the fact that in the simulation, the elevator smoothly continues to trend leading edge less down (less negative)/aircraft less nose up until the end of the plot. If we accept (as I think you do) that this simulator was a 'high fidelity' representation of the aircraft then these figures must mean something in terms of the actual aircraft behaviour on the day of accident. One might conclude that the EFCS was carrying out the pilot's command, but that the physics of the flight conditions were such that it would have needed around 7 or 8 seconds to complete the task. |
Originally Posted by CONF iture
You just confirm here...
|
All times are GMT. The time now is 17:57. |
Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.