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AF 447 Thread No. 5

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AF 447 Thread No. 5

Old 13th Jul 2011, 00:02
  #201 (permalink)  
bearfoil
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I suppose another way to put it would be, that if THS remained +/- 3 degrees all the way up, would the a/c have started THS NU to counterract the -g the a/c "felt"(up to, through, and beyond the apogee?). Aren't the accels in charge of this protection? Would the PF know that the THS was trying to reweight the airframe, not retain the Stall? If this is what happened, the THS would articulate NU to the stop, since positive g at that point would be unrelated to THS position (all the way down), Yes? Is the 'g' protection active, then? Or just preventive?

Does this question have anything to do with Perpignan at all? Was Test pilot #1 trying to exceed 2.5 gees? To Pull up and away from the water?
Was the a/c actively prevented from more than +2.5 gee? Was 447 actively prevented from recovery from Stall because the PF did not know the THS had migrated all the way UP to regain +g? At 10,000 feet, was 1g regained, and the Tail became responsive again?

thanks, and much respect, Sir.
 
Old 13th Jul 2011, 00:29
  #202 (permalink)  
 
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Hi Bear,
Originally Posted by Bearfoil
takata has entered into the log the g envelope protection which is the "only" protection left in AL2 (?).
Without valid airspeed, yes.

Originally Posted by Bearfoil
So the same question to you sir. Is this Limit actively monitored by the accels? And if so, when the a/c reached her zenith (perhaps even more than -1), would the a/c activate NU to regain some g? IOW, if essentially weightless for a short time, would 447 runup the THS to gain some "G"?
It doesn't work like that: PF imputs, on flight control surfaces, are filtered by a function that would not allow excessives g-forces to be pulled out, even in direct law with an abrupt full deflection order.
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Old 13th Jul 2011, 00:48
  #203 (permalink)  
 
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@ Bear:

I'm not sure if I understand your questions in total.
Load Factor Protection is the same in NORMAL as ALTERNATE.

Maybe you other questions become more clear with this general concept of G demand, if not we have to wait on Takata or any other to reply.


Note: (* added by me.

Flight Mode

In pitch, when an input is made on the sidestick, the flight control computers
interpret this input as a g demand/pitch rate. Consequently, elevator deflection
is not directly related to sidestick input. The aircraft responds to a sidestick order
with a pitch rate at low speed and a flight path rate or g at high speed. When no
input is made on the sidestick, the computers maintain a 1g flight path. Pitch
changes due to changes in speed, thrust and/or configuration, which in a
conventional aircraft would require the pilot to re-trim the aircraft, are
compensated for by the computers repositioning the THS. The pitch trim wheel
moves as the control law compensates for these changes. Sometimes, changes
of trim due to changes in thrust may be too large for the system to compensate,
and the aircraft may respond to them in pitch in the conventional sense and then
hold the new attitude at which it has stabilised after the trim change.
Due to its neutral static stability, the aircraft maintains the selected flight path.
Should it deviate however, only small sidestick inputs are required to regain the
desired flight path.






Load Factor Protection


On most commercial aircraft, the maximum load factor range is 2.5g/
-1g clean

and 2g/0g with slats and/or flaps extended. The load factor protection is


designed to maintain the aircraft within these limits while allowing the crew to

consistently achieve the best achievable aircraft performance, if required.
On commercial aircraft, high load factors are most likely to be encountered when
the pilot responds to a GPWS warning. Airline pilots are not accustomed to using
"g" as a flying parameter and experience has shown that, in emergency
situations, the application of "g" is initially hesitant and then aggressive. If a
GPWS alert is generated which requires an immediate pull-up, full back stick
should be applied and maintained. The load factor protection will allow maximum
"g" to be achieved in the shortest time while preventing the aircraft from being
overstressed.











Protected/Non-Protected Aircraft Climb Angle Comparison



If the pilot maintains full aft stick because the danger still exists, the high AOA

protection will eventually take over. This is one instance where load factor

protection is enhanced by the high angle of attack protection. (* Hi AOA Prot. NOT in ALT)








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Old 13th Jul 2011, 01:09
  #204 (permalink)  
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In "Flight Mode": "when no input is made on the sidestick, the computers maintain a 1g flight path."

In the zoom, we are in uncharted territory, so my questions may seem "thick". The Approach to STALL was through the back door of the Drag curve.

The Pilots and pax experienced a climb, one that when it came to an end, engendered up to or even more than -1g. As she decelerated, g was diminishing, the SS may have not been active, even if it was, it was likely ineffective, and at -g the computer will try to regain +g, Yes? Of course at this point they are aerodynamiclly STALLED, but the computers would still roll in THS (NU) to regain g? No other protection is available, and AoA would be an iffy way to regain aerodynamic flight.

From the dark side of the drag curve, STALL warn would not recognize the attitude re: STALL anyway, and the THS is the preferred method for reloading the airframe. The computers would have no interest in stopping the Stall, or recovering Flight, in AL2 they do not speak STALL RECOVERY.

When the PF made his ND inputs, the a/c reacquired sensible Warnings, but the a/c would sense ND as reacquiring -g, and keep rolling in more THS. So when the final STALL activated, the elevators may have signalled to PF a climb, rather than a ND, and he relaxed ND to think of something else.

I'll stipulate that the PF may have elevated the a/c into the climb, but once STALLED and even before, would not the computers be "protecting" "g"?

You know, after two years, I have to put on a serious thinking cap to prep for this thread, and PF PNF and Captain had seconds.

What was she doing? My understanding of the last seconds of Perpignan have the PF pulling everything to gain gee, and miss the sea. The computer would not allow >2.5. She kept her slippers on, right into the drink.
 
Old 13th Jul 2011, 01:14
  #205 (permalink)  
 
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Originally Posted by Bearfoil
I suppose another way to put it would be, that if THS remained +/- 3 degrees all the way up, would the a/c have started THS NU to counterract the -g the a/c "felt"(up to, through, and beyond the apogee?). Aren't the accels in charge of this protection? Would the PF know that the THS was trying to reweight the airframe, not retain the Stall? If this is what happened, the THS would articulate NU to the stop, since positive g at that point would be unrelated to THS position (all the way down), Yes? Is the 'g' protection active, then? Or just preventive?

Does this question have anything to do with Perpignan at all? Was Test pilot #1 trying to exceed 2.5 gees? To Pull up and away from the water?
Was the a/c actively prevented from more than +2.5 gee? Was 447 actively prevented from recovery from Stall because the PF did not know the THS had migrated all the way UP to regain +g? At 10,000 feet, was 1g regained, and the Tail became responsive again?
Bearfoil, you should stop dreaming that you will be able, any day soon, to rewrite the history of every "Airbus" already resolved crash without having a single idea of what you are talking about.

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.

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?
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Old 13th Jul 2011, 01:21
  #206 (permalink)  
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No problem. Adios.
 
Old 13th Jul 2011, 01:26
  #207 (permalink)  
 
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C* (PITCH) Law, continued

Quote from DJ77:
"Please, what is this transition from g-control to pitch-control you are talking about and where is it described in the FCOM? Does it apply to A-330?"

Sorry for the sluggish response. If you thought you detected some hesitance or vagueness in my glossed-over references to C* (PITCH) law, you were right. The reason is quite simple: my only source of information is an extract from an A320 FCOM dated August 1987, six months before A320 type-certification, headed "British Caledonian" (joint launch-customer with Air France), which I obtained a few months later for my type conversion. That admitted, I doubt the fundamentals of C* law will have changed much in the meantime. But it amounts only to a brief introduction for us line pilots.

To answer the second part of your question first, Airbus have deliberately provided all their FBW aircraft with similar handling characteristics. A330 and A320 speeds are, I think, broadly similar. For example, on the A320, 210kt IAS is a typical "clean" holding speed below FL200, which has to be increased by 10kt or so at maximum landing weight. I doubt the A330 is greatly different. So the speed criteria used in C* are likely also to be similar.

My old FCOM says that C* law uses "normal acceleration as the basic parameter. At low speed, pitch rate is mixed with load factor [i.e., normal acceleration] 'G' such that at less than 150kt the effect of both G and pitch rate is [sic] equal. Above 210kt pitch-rate effect on the flight path is zero."

Later, it continues: "The overall effect of the law is that with the [sidestick] controller at neutral, the aircraft will maintain 1G and zero pitch-rate at low speed and 1G at high speed. As a result the aircraft is short-term attitude-stable."
[my hyphens, and my comments in square brackets]

In relation to AF447, I commented yesterday:
"The other unclear factor is how the C* pitch-function of the EFCS would treat the invalidation of CAS (IAS) data, when determining the crossover from g-control to pitch-control. As I understand it, that crossover is normally a gradual transition as the airspeed falls below a certain figure in routine flight. Understanding how the UAS affected this will be the other key step in solving the relationship between sidestick position, elevator/THS position, and the achieved trajectory."
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Old 13th Jul 2011, 03:28
  #208 (permalink)  
 
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Not big brother - no voting others off

Takata doesn't speak for me when he tells you to get lost.
This is not big brother so he doesn't get to vote you off.
JT has that right yet has chosen not to do so.
So, please, bear, keep probing, asking, seeking truth. I for one enjoy your contributions.
Sorry if I overdid the smileys.
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Old 13th Jul 2011, 03:49
  #209 (permalink)  
 
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Cool

Hi,

bearfoil
My understanding of the last seconds of Perpignan have the PF pulling everything to gain gee, and miss the sea. The computer would not allow >2.5. She kept her slippers on, right into the drink.
Unfortunately you can't refer to the Perpignan final report about gee
They released a bunch of graphics and tables but no one about the "gee"

http://www.bea.aero/docspa/2008/d-la...a081127.en.pdf

If anyone find one .. post here .......
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Old 13th Jul 2011, 04:12
  #210 (permalink)  
 
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Unfortunately you can't refer to the Perpignan final report about gee
They released a bunch of graphics and tables but no one about the "gee"
Please "andianjul" don't encourage bear... see above. Yet MORE imaginary b/s from bear. There's a limit to what makes meaningful sense to extrapolate - but to simply make sh!t up seems shamefully self-fulfilling. We have facts, we have holes between those facts, but they mostly line-up to tell the story. There are those that want to believe that "the plane did it", but the facts (limited as they are) don't seem to tell that tale. That doesn't mean there can't be improvements related to the aircraft - every accident is an opportunity to learn and change things (if warranted) - but that also applies to pilot training, company procedures, etc.

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Old 13th Jul 2011, 04:16
  #211 (permalink)  
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Hi Chris;

I'm not sure this helps but there are two documents, (rare) on C-star laws and fbw - they can be found at:

https://dspace.lib.cranfield.ac.uk/b...report9303.pdf
and,
http://www.raes.org.uk/pdfs/2989.pdf

They're really technical and I found them difficult but there were a few nuggets in there for a non-engineer retired Airbus pilot!
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Old 13th Jul 2011, 04:26
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Bearfoil 13 july 00:09
Quote
The Pilots and pax experienced a climb, one that when it came to an end, engendered up to or even more than -1g. As she decelerated, g was diminishing, the SS may have not been active, even if it was, it was likely ineffective, and at -g the computer will try to regain +g, Yes? Of course at this point they are aerodynamiclly STALLED, but the computers would still roll in THS (NU) to regain g? No other protection is available, and AoA would be an iffy way to regain aerodynamic flight.
Unquote

Bearfoil, please get some education on flying before you spout more of this nonsense.
A zoom climb is not any uncharted territory.

In the most extreme case, when you decelerate to zero airspeed, you will have no more lift, so you will enter a free fall. How many G do you encounter in a free fall? Zero!

The minus 1 G that you conjure up could only be achieved by PUSHING FORWARD a large amount on the sidestick, yoke, steering wheel or whatever pitch control your aircraft has, while it still had enough airspeed to generate minus one G with a negative angle of attack.

I hope that this minus one G story of you, so that the computer would definitely roll in max THS up, yes? will make it clear to all how far off the mark you are. Please pay attention when people are politely trying to educate you.

As far as the lack of information from BEA is concerned - didn't they convey clearly that they have just put out a note:
"The BEA has decided to publish a note with information on the first facts established, based on analysis of the data from the flight recorders."

This note is not yet a final report, they need more time to analyse information.
Just imagine, they might first want to run a number of wind tunnel tests to check whether at 60 degrees of AOA there is enough nose down authority available to unstall the wing and recover the aircraft to normal flight. If they would not present proof about that in the final report, PPRUNErs would forever keep discussing about the point whether the a/c was recoverable or not.
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Old 13th Jul 2011, 04:31
  #213 (permalink)  
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airtren;
Originally Posted by airtren Post #187
My understanding is that the "a/c" would continue "level" under inertia and position of control surfaces as left after the "a/p disconnect", ONLY and ONLY if the "a/c" were on a "level" segment.

But the probability of being on a "level" segment is 1/5, which is 20%, which is quite low (maximum probability is 100%).

The probability of being on a "NON-level" segment - "up" or "down" or "left" or "right" - is 4/5, that is 80%. That is quite high!!!
I think there are different meanings of the term "level" at work here - one for an engineer and one for a pilot, . Yes, the chances of it not "being on a "level" segment may be 4/5 or 80%, especially if nobody takes over the aircraft after the autopilot and autothrust has disconnected. But as you say, it is going to remain more or less level out of it's own inertia and the position of the control surfaces, etc. The pilot takes over and maintains cruise level and speed, (pitch and power), as I know you know.

By "stable, level flight" is meant maintaining an altitude while accepting small excursions above and below the exact altitude to maintain and not climbing or descending. It's never going to be "level" in the exact sense.

Is this what you meant? Tx...
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Old 13th Jul 2011, 04:37
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Cool

Hi,

GarageYears
Please "andianjul" don't encourage bear... see above.
Maybe .. but why not encourage the BEA to release a graphic of the "gee" for the Perpignan case
Maybe it can be interesting.
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Old 13th Jul 2011, 05:06
  #215 (permalink)  
 
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Hi andianjul,
Originally Posted by andianjul
Takata doesn't speak for me when he tells you to get lost.
I'm speaking for nobody else than myself. I'm just feeling now like I'm feeding the troll for too long. If you are a member of the same fanclub, here is a good place to start reading about the aircraft: SmartCockpit - Airbus 330
and another good place to post and discuss whatever theory your imagination can elaborate without the need to read anything remotedly well documented on the subject: http://www.pprune.org/rumours-news/4...age-found.html
Now, my personal opinion is that a "technical" thread is not the best place for a conspiracy theorist (see above), but I may be wrong.
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Old 13th Jul 2011, 05:12
  #216 (permalink)  
 
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Originally posted by airtren ...
Question: it is unclear what the "Stall Warning" curve is. Would you please clarify? Thanks in advance.

It seems obvious it is not the "Stall Warning" message given to the pilots, as that was, afaik, not permanent/continuous.
Have a look at HN39's post #70 where he explains the how the data was constructed.

With regard to the stall warning, it is designed to warn of an approaching stall and works on the basis that a stall is then avoided. When in ALT2 LAW the AoA value and the CAS must be within prescribed limits for the system to calculate, and when they fall outside, e.g. AoA > 30 and/or CAS < 60 KTS, the system determines there is No Calculated Data (NCD). No valid data has resulted in the SW turning off, and it appears that when the data became valid the SW resumed, but the application of NU commands to the SS has resulted in the SW stopping again. Result is an inappropriate action was rewarded.

Looking at the AoA curve in the graphic, it bounces along the SW line as the aircraft pitches up into the climb, briefly triggering the SW. The Stall Warning sounds at 2:10:51 and continues sounding until shortly after the Capt. enters the FD. Though not shown on the graphic, it later sounds when the aircraft is established in the stall and the data is once more valid following ND inputs to the sidestick. NU inputs stopped it!
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Old 13th Jul 2011, 05:39
  #217 (permalink)  
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A little in the way of personality clashes creeping in, folks.

If you or I, as in individual, disagree with what someone else is saying, then we should just ignore the detail or the post as you prefer. I will only censor if a post is blatantly outside our reasonable expectations.

Please don't get into the gutter and engage in tit for tat - not becoming for this forum and just moves the individual combatants down the respect ladder a rung or two.
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Old 13th Jul 2011, 09:10
  #218 (permalink)  
 
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C*

Thanks Chris Scott for your detailed answer about C*. I wil take some time trying to uderstand it better.

Thanks also PJ2 for the references to C* docs.
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Old 13th Jul 2011, 09:25
  #219 (permalink)  
 
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Originally Posted by airtren
Question: it is unclear what the "Stall Warning" curve is. Would you please clarify? Thanks in advance.
The curve shows the stall warning threshold. It varies with Mach number according to a schedule that has been posted by A33Zab a few weeks ago. 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.
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Old 13th Jul 2011, 09:49
  #220 (permalink)  
 
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Hi Takata,

I think Bear was asking something like:
During the apogee when sensed g is less than 1, and stick free, will the FBW logic increase pitch in an attempt to hold 1 g?

Some of my students use the term "g" when they meant to say "delta g".
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