I'll chuck this (2000) paper in too if it helps.
Fly-By-Wire A Primer for Aviation Accident Investigators |
Hi BOAC,
Your paper sums up in one sentence, what I've tried to say. Now for the bad news. While FBW technology could make an aerodynamically unstable aircraft flyable, it can also destabilize an otherwise stable airframe. |
It might be a good idea to return this thread 'to earth' with a brief summary of what we know.
Leaving aside what happened after the climb, what about the climb? 1) There is nothing in the BEA report to suggest that the aircraft caused it itself. The only 'query' here is the track record of system reaction to 'events', like the QF pitch anomaly and the 2001 North Atlantic altitude excursion with TC-JDN. It is worth noting that in this the crew did not trigger a climb. (There is some confusion (for me) in the AAIB report where the FDR traces suggest the TCAS RA occurred BEFORE the a/c left its cruise level). Had this crew been in the ITCZ at night and not in clear air in daylight it is worth contemplating what might have occurred. 2) There is nothing in the BEA report to suggest that the pilots caused the climb either. Until the BEA provide the full CVR transcript AND RHSS trace from the FDR for the period 2:10:05 to 2:10:51 we are all guessing. Why they have not is a mystery to me. |
Ordinarily, the downwash angle at the tail is related to the lift coefficient more than to the wing/body AoA. Would your values be more specific to a stalled swept wing? The numbers I quoted are pretty good for an aircraft like the A330, at least up to stalling AoA. When lift curves go nonlinear then I would agree with you that lift coefficient would be a better handle. I don't think anyone knows exactly what the downwash would be at 60 deg AoA, but I was using it in an argument about THS stall and as the later bit of my argument took the THS away from stall I didn't worry too much about ithttp://images.ibsrv.net/ibsrv/res/sr...lies/smile.gif Thanks for the welcome! |
Takata, #204
This is something I really don't understand about you... Those basic things are mandatory to understand how those aircraft are flying and most of this stuff, about Airbus FBW systems, is available nearly everywhere. rather than a serious technical manual and the logic that drives the transitions between the various laws is not available anywhere, afaics. Perhaps you could provide pointers ?. Sure, the fcom has bits and pieces dotted around all over the place, but nowhere can I find a flowchart or logic diagram that describes the whole process. The fact that, ergo, ab seem to think that this is not important to crew is one of the most worrying things about the whole episode. Fly the computers, not the a/c, seem to be the modern mantra and you don't need to know about the detail :eek:. Why don't you take a little time to read it, all by yourself, instead of posting daily, from two years now on this thread, such a load of cr*ap about a subject you never bothered to study a minimum? like a post, then don't read it. It's not as though you had anything constructive to say in rebuttal anyway. It's not the way that it's done here, so please, let's keep it civil... |
takata
Sorry,but I find that takata`s outbursts are unpleasant and confrontational and not really required.Everyone is doing a fantastic job here with lots of team effort to try to discover what caused the death of so many innocent people,and that includes bearfoil.Some are more qualified than others and some have other agenda`s that are not easy to see.Sometimes those from without Looking In have better vision that those inside who may not see the Wood for the Trees......pull together guys and girls.Works much better.
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BOAC, #222
2) There is nothing in the BEA report to suggest that the pilots caused the climb either. Something that occurred to me is the fact that the sidestick transducer, which translates physical input to electrical signal, could have failed in such a way as to provide a bias in it's output. Don't have enough info to know if it uses a synchro, resolver, potentiometer or optical encoder, but any but the last of those could in theory degrade to provide a bias away from zero, (ie: nose up) depending on failure mode. Probably a long shot, but it is a possibility... |
It is completely understandable that frustration surfaces when repeatedly confronted with fantasies, ignorance of facts, invention of facts, rewriting of facts and then attempting to mask it by consistent use of gobbledygook.
Loerie, What you have here is a bunch of people running in circles and they have done so for quite a while. Some have even resorted to just spin around them selves. Try this little experiment; Select at random five people who regularly posts on AF447 threads 1-5, select at random five posts from each, compare the five posts. If you can spot any difference let me know. |
Originally Posted by Loerie
(Post 6568731)
Sorry,but I find that takata`s outbursts are unpleasant and confrontational and not really required.
Everyone is doing a fantastic job here with lots of team effort to try to discover what caused the death of so many innocent people,and that includes bearfoil. some have other agenda`s that are not easy to see. (I hope this won't be construed as being "personal", this is just my observations from the last day or so) @rudderrudderrat : There has been no such thing as real "elevator feel" since the '60s, and Direct Law does not provide it. The only difference between Normal/Alternate and Direct Law when it comes to tail surfaces is that the trim movement becomes manual-only in the latter, and the elevator command directly affects deflection rather than commanding a rate. @KBPsen - some of us have been effectively forced to repeat ourselves because of the drip-feeding of misinformation that you are describing - in fact quite a few genuinely knowledgeable people have got fed up and only pop in occasionally, if at all. That's probably a major source of the frustration right there, because if some of us don't fight to keep the discussion to the facts then we could end up with some of the misinformation quoted in a newspaper somewhere, and that's how fallacies like "The plane thought it was trying to land and overrode the pilot" get spread around. |
FBW Investigation Primer
BOAC posted an intressant link; Fly-By-Wire A Primer for Aviation Accident Investigators
I have enjoyed reading the short description of how FBW systems operate and about C, C*, and G*U. In principle it looks almost like normal PI controllers and not PID ones. What strikes me is that all is written with the assumption that the controllers are analog and not digital. From my own experience - writing well performing digital controllers and their real-time performance is a very different story. Regards |
@ syseng68k:
2 Xdcrs(contains 4x triple potentiometers per axis).
FCPC1 & FCSC1 driven by separate linkage. (Dual Channel output 4 potentiometers, 2 unused) per axis. FCPC2 & 3; FCSC2 driven by the other linkage (Dual Channel output 6 potentiometers) per axis. The sidestick is placed in a polycarbonate container to prevent entrance of foreign matter. The sidestick design is such that rupture, disconnection or jamming of any of the parts can't cause the loss of total A/F loads on one axis or block free movement of a set of a potentiometer group related to one axis. Transducer output is monitored and compared, if any difference F/CTL L(R) SIDESTICK FAULT ECAM message is triggered. Schematic: http://i474.photobucket.com/albums/r.../SideStick.jpg |
Stall Warning Threshold curve
Thanks for your clarifications
Originally Posted by mm34
Have a look at HN39's post #70 where he explains the how the data was constructed.
Originally Posted by HazelNuts39
The curve shows the stall warning threshold. .... Except for the NCD condition explained by mm43, stall warning begins when AoA exceeds the stall warning threshold, and continues until the AoA has decreased below that threshold
As I looked again at the graph, I thought it would be helpful to see the corresponding curves/data that were available to the "a/c systems" and "a/c pilots" in the context of "loss of data", and showing the discontinuity in the SWT (stall warning threshold) curve, due to NCD - was there such a graph already made available?
Originally Posted by mm34
No valid data has resulted in the SW turning off, .... but the application of NU commands to the SS has resulted in the SW stopping again. Result is an inappropriate action was rewarded.
Is the calculation/equation used for determining the providing of the Stall Warning relying on too few parameters? "Vertical acceleration", or "vertical speed", perhaps "no lift"? Is any of the existing sensors, and parameters available on the "a/c" able to provide info, so that a Stall Warning could have been clearly brought to the knowledge of the pilots for the entire duration of the Stall? |
syseng68k;
Re your post #224, good observation. The FCOM is a need-to-know user's manual and indeed does not explain the aircraft. I think this is one of the underlying issues. FBW and C-star law are not in and of themselves problematic but unlike complex hydraulic or electrical systems, the differences in "the how" of control are materially different and require understanding, as do the more bread-and-butter areas of high altitude, high Mach number flight and even some jet transport aerodynamics. I did not know and did not understand until a lengthy and patient exchange with HN39 that the stall AoA for my aircraft was much lower at high Mach numbers in cruise flight than what Davies had expressed in his wonderful book, which was the approach and landing case with high-lift devices extended. Big, big difference and, even in retirement, I learned some fundamentals. These are not taught very thoroughly in initial ground schools at least in my experience, and if one wasn't in the air force one's knowledge was increased largely through one's own efforts. The frustrations of not knowing and not being able to find things out easily have been endemic - while easy to fly and a joy to hand-fly, "automation" has become as much a marketing tool as it has a way of solving the problems of flight. The resistance to knowing more than the "NTK". need-to-know, ground-school curriculum requires, comes first from how expensive it is to train well, and next from a lack of knowledge in those who must do the teaching, always of course, with wonderful exceptions from those memorable instructors who's passion takes them, and their students beyond NTK. Learning is expensive and NTK and automation are assumed to "solve" that "problem" for a cash-strapped, (de-regulated) industry. This isn't "THE" problem, because clearly the aircraft and the design's record is no worse in terms of fatal accident rates than conventional types - in short, the airplane and the design work extremely well but one should never be in a position to not understand and not anticipate what his airplane is doing. Below is a nuts-and-bolts schematic of the pitch-basic loop. I hope it is of some service in understanding the pitch control of the A330. http://www.smugmug.com/photos/i-RvKW...RvKWdbv-XL.jpg |
Takata: When the g load is less than 0.5g then the THS is frozen. Perhaps this is not known to Bearfoil?
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Meikleour
It was not known to me, and I appreciate rudderrat's rephrase. I'll be brief with my next question. Of course it may (is) in the FCOM, but may I see any answer in the thread? If frozen, the THS would be unavailable for Trimming, (or Pitch changes), until what point? When does it become available again? So the original question remains: If less than one g, does the THS move independently of Pilot's inputs? Does it try to regain 1g or satisfy itself that anything greater than -1g is acceptable? Does it "Unfreeze" if the g becomes <-1g? And then input NU? The limits are intriguing to me, until I have a better picture of what the THS may have been doing in <1g, who can say what the a/c's behaviour was? To expand on BOAC's #2, BEA have not assigned the climb to the pilots, that is true, and they affirm that by specifically stating, "ONE" (a) Noseup, left roll input. That apparently happened prior to the "climb", as I read it. |
Hi BOAC,
Originally Posted by BOAC
Leaving aside what happened after the climb, what about the climb?
1) There is nothing in the BEA report to suggest that the aircraft caused it itself. The only 'query' here is the track record of system reaction to 'events', like the QF pitch anomaly and the 2001 North Atlantic altitude excursion with TC-JDN. It is worth noting that in this the crew did not trigger a climb. While I agree that QF event remains a mystery, TC-JDN case is showing that, right after autothrust disconnection, manual thrust was applied and increased from N1 below 70% to 100%. Sidestick (ND?!) imputs were not applied until the top of the climb 30 seconds later, hence nothing contraried TC-JDN to change its level flight. Someone also posted a revised chart of DFDR control imputs but, as far as I remember, it did not include any thrust track.
Originally Posted by BOAC
(There is some confusion (for me) in the AAIB report where the FDR traces suggest the TCAS RA occurred BEFORE the a/c left its cruise level). Had this crew been in the ITCZ at night and not in clear air in daylight it is worth contemplating what might have occurred.
Originally Posted by BOAC
2) There is nothing in the BEA report to suggest that the pilots caused the climb either.
|
Originally Posted by airtren
naming of that curve "SW threshold" would make the graph clearer/self explanatory, while adding a "SW" curve (non-contiguous curve) would be the curve representing on the time scale the intervals when the Stall Warning was (should have been) active.
... and showing the discontinuity in the SWT (stall warning threshold) curve, due to NCD ... You pose more valid questions, but I regret not being in a position to answer them. |
HeavyMetallist, "Why some people persist in believing that stalled == totally ineffective is a mystery."
gums has posted some graphs that show an actual inversion of control for a totally different kind of aircraft when in a bad enough AoA configuration. Somebody else posted a graph I believed was for the A330 produced by calculations that indicated an AoA of 61 was sufficient to put the A330 into a realm where the tail was not particularly effective. That said, it appears from the release, in a part I'd forgotten (take your own advice, Joanne), that there still was some authority from the tail surface. Unless the PF pulled up again after the stall warning the tail surface did not have enough authority to pull them out in the remaining 2 minutes. So it was basically ineffective or marginally effective. |
Stick mechanism
A33Zab
Thanks for a nice and illustrative picture of the stick mechanism. I wonder if a very strong force on the stick to the left could force some undesired nose-up if the enclosing structure is not sturdy enough. I am also a little surprised that potentiometers are used - even with two (or more) in parallell for each axis. Regards |
bearfoil, you'd best concentrate on something you know somewhat better than law. I can think of several instances off the top of my head wherein people who are not parties to a contract or any other record do not have access to the data.
One is when a settlement is reached and both parties insist it be kept secret as a part of the settlement. |
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