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AF 447 Thread No. 6

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AF 447 Thread No. 6

Old 25th Aug 2011, 18:03
  #441 (permalink)  
 
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Bear.... whatever... it is you who pulled the stunt of changing your user name, not I and then fuddled around in a smog cloud, I can only presume, with the intent to shake off those that had enough of your ramblings. But you were outed. I am not concerned one way or the other regarding how childish I may appear, because you showed all exactly how childish you yourself are - kettle, meet black pot.... Hence my renaming of your current label to "Lyingman" is simply an amusement on my part. No harm intended. As you like to note, these are anonymous forums, so it doesn't seem to matter much what I call the avatar behind the label, within the bound of politeness I grant you.

My most recent post was in response to this:

In the climb, the pilot commanded NOSE UP, and the THS did not move. The THS was responding ("not responding") per design, not part of PF's quiver, for the moment (his 'bad').

At STALL, the THS responded immediately, and to the maximum, NOSE UP.

By DESIGN. Responding to PF NOSE UP? Or to gain loading for the airframe when it was less than 1g? Both?
It is this inflammatory and incorrect statement I bring your attention. Stall had noting to do with the position of the THS, the elevator demand DID. The pilot asked for continuous NU, from 2.10.45... the THS followed, as designed. The pilot asked for NU, what else would it do it do? No trim.... justify? Oh, in this case the cheese was already lined up in a stall, also of the pilots doing, some seconds before. Perhaps some ND inputs from the PF, sufficient to get some ND from the THS might have been a good idea? But, that was not what happened, NU on the SS and TO/GA from the engines was requested, more or less the very worst possible combination at that point.

If you are suggesting in some obtuse way that the automation/protections/limits built into the aircraft should/could jump in at the point a stall is "obvious" (AoA the wrong-side of "bloody-hell" + vertical speed in the "oh, crap" region, and groundspeed in the "I can't believe it" realm), and implement a modern version of the stick-pusher, then may be we agree on something. But it is the manner you get there that is most bloody annoying. The quote above is a perfect example of inflammation, a whiff of truth and good dose of fabrication. It doesn't help your case at all.
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Old 25th Aug 2011, 18:07
  #442 (permalink)  
 
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Let me take this one...

Originally Posted by Lyman View Post
This is an anonymous forum ... you have worn only one disguise?
I know I have, because I know posting here is a privilege, not a right. And for what it's worth, the most respected posters on here have retained their original handles since they first signed up. Most forums I am aware of would have served you with an instant IP ban for doing what you've just admitted to.

The THS is inhibited >1.25, <.5. I mentioned .75. My Bad. I try attribution, and am "sowing pollution"?
Again, no - only autotrim is inhibited from adding further nose-up trim at greater than 1.25g. They didn't need nose-up trim, they needed nose-down trim. The aircraft didn't reach a g-loading low enough to inhibit autotrim completely (0.6 > 0.5), so autotrim was never offline in the direction the THS needed to go. Furthermore, even if the g-loadings are beyond the limits of autotrim functionality, manual trim is always available.

Now - either you've missed my previous post explaining this or ignored it, but I can assure you that I will raise it with the mods if you post the same incorrect information on this technical thread again.

"TRIMMABLE" HORIZONTAL STABILISER. That is not a correct designation, in design, practice, and Training. In fact, it is opposite what is trained.

What is trained is to leave the wheel alone, Only in DIRECT LAW challenge the virginity of the wheel and assault her with your palm.
Again incorrect. Svarin, back in a previous thread, claimed that his airline vehemently discouraged use of the manual trim wheel at any time other than a switch to Direct Law. PJ2 said that his airline left use of the manual trim wheel to the pilot's discretion, and indeed trained him quite extensively on it's use. So if we are to take that information at face value, then it appears to be at the discretion of the airlines as to how the manual trim wheel is to be approached.

As of this moment, we do not know what Air France's policy was or is regarding the manual trim wheel, so to state as fact that the pilots were trained to leave it alone is a falsehood, because the only thing we know for sure is that we don't know. (h/t Socrates).

Responding to PF NOSE UP?
Almost certainly.

Or to gain loading for the airframe when it was less than 1g?
Possible, but unlikely.

Both?
I doubt it.

Later, it went 'Dormant' at NOSE UP all the way down.
No, it stayed there because there was neither a nose-down SS input deflection for a sufficient period of time, nor was there any attempt to manually change the trim.

Posit. The a/c was UPSET at the loss of a/p, and LOC happened soon after ~ . With LOSS OF CONTROL, a design that trims in elevator for its retention when maneuvering is the order of the day? Hmmm.....
Sorry - that doesn't wash. Far more likely is an overcontrol response to correct the slight wing-drop at FMS disconnect, followed by PIO as the PF consistently overcorrects, possibly tensing up and inducing the nose-up attitude we see. Look at the FDR traces - now, admittedly I'm working from memory here, but most upset recovery procedures require progressive and sustained control inputs opposite the direction of the upset, until stable flight is resumed (this, incidentally, is why the 737 rudder-reversal failure mode was so deadly, with pilots thinking they were putting in correcting rudder when in fact they were controlling in the direction of the upset and inducing a spiral dive). The AF447 traces show the lateral SS movements going from stop to stop repeatedly over the space of a few seconds at most, classic PIO. Judging by the PF's remarks on the CVR, he seems primarily concerned with lateral control and unaware that he is making pitch demands at the same time - only the PNF seems to notice this ("you're going up - go down"), and reminds the PF to touch the lateral controls as gently as possible.

Above all, the magnitude of the inputs made is more appropriate for batting a Pitts around in VFR conditions at a couple of thousand feet, certainly not appropriate for a widebody at cruise in IMC at night.

The THS, as it moves, changes the flight characteristics of the airframe, it changes the ANGLE OF INCIDENCE of the aircraft, as well as its PITCH.

This is why ANGLE OF INCIDENCE is considered separate from AoA, for it is a critical component of AIRCRAFT ATTITUDE.

Until one separates these two concepts AOI, AOA, the manner of control cannot be explained.
Yes it can, and it was explained by several people not long after the black boxes had revealed their first secrets in the lab. In normal flight, autotrim trims the aircraft to maintain a g-loading (in most cases). In the case of Alternate Law with no protections, the autotrim will follow any demand made by the pilot based on the assumption that the pilot knows what he or she is doing - this feature of the design is specifically to support ease of operations in abnormal circumstances. If the pilot does not feel that the autotrim is behaving as they desire it is a simple matter of moving the trim wheel to the desired position and the aircraft will attempt to stabilise around the manually set trim, with the autotrim taking over again from there except in the case of Direct Law or Mech Reversion.

@PJ2 - I completely and unreservedly accept what you are saying and agree totally. However, what bothers me is the knowledge that some journalists are known to either paraphrase or report verbatim some of the things that are posted on here. The BEA and Airbus have spent years trying to overcome the largely undeserved reputation they garnered by the number that Michel Asseline and his enablers in the press did on them, and what worries me is that I'll open the paper one day to find one of Bearfoil/Lyman/Will Fraser's more lurid assertions reprinted as fact in an environment where the general public are more inclined to take such things at face value (which is why we still have people saying that the A320 "overrode the pilot" and hit the trees "because it thought it was landing", and other such nonsense).
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Old 25th Aug 2011, 18:46
  #443 (permalink)  
 
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Hello AR33Zab,

Thanks for the BUSS information.

I could add the following to your post, from the general perspective of compliance to an engineering, or certification specification :

If the Stall Warning announcement in a Stall approach, or Stall situation is a required - it's a MUST - then the logical formula that is at the basis of the announcement MUST calculate and deliver a TRUE or FALSE result.

If it has an "UNDEFINED" result for a certain condition, than the functioning of the formula, and the Warning announcement corresponds to a SHOULD, not to the specified MUST, and thus it fails to follow or to deliver according to the specifications.

Why the formula failed - which the NCD or AoA zero is - matters in terms of explanation for its failure to comply with MUST, and as an element for considerations in fixing it, so it complies with the MUST.

airtren.

Originally Posted by A33Zab View Post
jcjeant:

The Stall Warning logic itself is not at fault here.
It's the 'reducing' AoA value to 0° when CAS <60Kts by the ADIRUs which stopped the warning.
(We know they have changed that, don't know if its a part of the optional BUSS mod or if it is a separate -mandatory- mod)

Anyway this will be a legal case, who's to blame?
and I think we already suspect who will be blamed (for operating outside specs) at the end.

Last edited by airtren; 26th Aug 2011 at 00:34.
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Old 25th Aug 2011, 20:08
  #444 (permalink)  
 
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Knowledge of the stall would not help

Ian W;
Quote:
From Airbus Safety First ...
"It is important to know that if such a thrust increase was applied when
the aircraft is already stalled, the longitudinal effect would bring the
aircraft further into the stall, to a situation possibly unrecoverable."


MM43
I believe that Airbus had worked out from the ACARS sequence the most likely scenario, and that statement is valid when compared with the Thrust and Pitch Attitude graphic shown on the previous page.

We now know that there was no escape as they didn't 'know' they were STALLED.
Actually that is NOT what the quote says:

It says ""It is important to know that if such a thrust increase was applied when the aircraft is already stalled, the longitudinal effect would bring the
aircraft further into the stall, to a situation possibly unrecoverable."

It does not say recoverable if the crew recognize they are stalled. It says that a thrust increase at the wrong side of the drag curve when stalled can lead to a situation possibly unrecoverable
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Old 25th Aug 2011, 20:46
  #445 (permalink)  
 
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Knowledge of the stall would not help ???

Originally Posted by Ian W
It says that a thrust increase at the wrong side of the drag curve when stalled can lead to a situation possibly unrecoverable
Ian, this is about pitching moment, the 'wrong side of the drag curve' has nothing to do with it. Let me think, where could it be 'possibly unrecoverable'? I would think possibly when the engines are capable of delivering a high thrust, i.e. at low altitude, low temperature, low speed, flaps down?

Last edited by HazelNuts39; 25th Aug 2011 at 21:01.
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Old 25th Aug 2011, 21:12
  #446 (permalink)  
 
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@ OK465
GerardC :
Do you mean you have first hand experience of (hand-)flying a 330 in ALT law2 at 35 000 feet ?
OK465
Of course not.

But I have experience that takes the observations out of the realm of pure opinion. (You're welcome to discount anything I say, that's fair, no problem.)
In this case I suggest you do some homework : ALL pilots having actually faced flying ALT law2 at high altitude reported :
"If I can make a small contribution to this thread.
I have flown the A330 in ALT 2 LAW after a twin ADR incident due to icing conditions.
What surprised me was how "twitchy" the aircraft was, especially in roll.
The handling was much harder than I had experienced in the simulator during training.
"
This is not an "opinion" but established facts. (I have more testimonies on shelf...)

Please see : post 3429 (http://www.pprune.org/rumours-news/4...found-163.html).

Last edited by GerardC; 25th Aug 2011 at 21:25.
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Old 25th Aug 2011, 22:04
  #447 (permalink)  
 
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Hi GerardC:

I personally do not act on "established facts" from an internet forum.

You're certainly welcome to fly your A330 in whatever manner you feel appropriate.

I'm sure this applies to ALL pilots.

(BTW you mean post #3249 and I may be too old for homework)
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Old 26th Aug 2011, 01:11
  #448 (permalink)  
 
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Originally Posted by Lyman
The THS, as it moves, changes the flight characteristics of the airframe, it changes the ANGLE OF INCIDENCE of the aircraft, as well as its PITCH.

This is why ANGLE OF INCIDENCE is considered separate from AoA, for it is a critical component of AIRCRAFT ATTITUDE
So, now there are (4) different angles of interest in the pitch plane...? when only 2 are needed. Pitch and AoA

Correct me if I'm wrong... please
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Old 26th Aug 2011, 01:25
  #449 (permalink)  
 
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Oh yes, another thing...

Originally Posted by D.P.Davies
So be gentle with the aeroplane at high altitude . Make control movements slowly and smoothly and recover from divergences in the same manner.
one good reason for this, is the reduced aerodynamic damping at altitude.

whether this is still taught, explicitly, or left to the control laws to sort out today, would be interesting
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Old 26th Aug 2011, 01:47
  #450 (permalink)  
 
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Harry Mann. You are not joking I think? I would further explain, but first, do you take exception to the comparison of the HS to a VIW? I think one or the other of us should elaborate, lest some one miss the point? I am concerned that pilots of this a/c are not Trained in the potential dangers of the THS re: PITCH response?

I get this from the apparent lack of care the PF showed in his responses to mere Pitch requirements at the onset of LOC?

None of the Three, (apparently) monitored the Trim Wheel?

Certainly, an alternate to THS would be a TMP? ('TRIMMABLE' MAIN PLANE?)

I don't say the THS is inherently unwise, of course! Perhaps the builders need the discussion?

Also, are you sure mere mention of reduced aerodynamic damping is sufficient to convey the caution needed in handling?

Perhaps an elaboration?

It has dawned on me why some folks aren't particularly concerned re: AutoTrim in recovery/AL2, when some pilots here have voiced some strong exception to the concept?
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Old 26th Aug 2011, 02:05
  #451 (permalink)  
 
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@AZR:

By Joelle Barthe

Flight Operations Engineer

Published on SafetyFirst #5
December 2007

----
5 Back UP Speed Scale (BUSS)
In order to dedrease the crew workload in case of unreliable speed, Airbus has developed the Back-UP Speed Scale (BUSS) that replaces the pitch and thrust table. The BUSS is optional on A320/A330/A340. It is basic on A380, being part of the ADR Monitoring functions.
This indication is based on angle of atack (AOA) sensor information, and is therefore not affected by erroneous pressure measumements.
The BUSS comes with a new ADIRU standard (among other new system standards), where the AOA information is provided through the IRs and not through the ADRs. This enables selecting all ADRs off without loosing the STALL WARNING PROTECTION.

EDITmeans actual AoA is always available whatever CAS)

The AOA information provides a guidance area in place of the speed scale. When the crew selects all ADRs OFF, then:
- The Back-Up Speed Scale replaces the PFD speed scale on both PFDs,
- GPS Altitude replaces the Altitude Scale on both PFDs.

The Back-Up Speed Scale then enables to fly at a safe speed, i. e. above stall speeds, by adjusting thrust and pitch.
The BUSS will be displayed once all ADRs are switched OFF. Therefore, on aircraft that have the BUSS, when the flight crew cannot identify the faulty ADR(s) when performing the troubleshooting, or when all ADRs are affected, the flight crew will switch OFF ADRs, and will fly the green area of the BUSS.

However, if the safe conduct of the flight is affected, the memory items must still be applied before troubleshooting.
As the BUSS is associated to the ADR monitoring funcitions, some unreliable speed situations can be automatically detected (e. g. new ECAM warning "NAV ADR 1+2+3 FAULT"), and some ECAM procedures will lead to the BUSS activation by requesting to switch OFF all ADRs.
----


And this why AF didn't installed the BUSS option:

The "Backup Speed Scale" or BUSS is a tool which pilots use when speed indications cannot be used.
To use the BUSS, the crew must first disconnect the three ADRs (air data reference - anemometric stations). Once these have been disconnected, the crew can no longer use them during the flight.
With the BUSS system, speed is no longer calculated by the Pitot probes, but by the aircraft's incidence probes. The speed indication, which is less precise, is presented in the form of green, ambre and red stripes. In a high turbulence situation at high altitude, the speed indication given is very unstable and difficult to use.
On its A330s and A340s, Air France considered installing the BUSS system offered by Airbus and carried out tests on its flight simulators These tests did not lead Air France to adopt this system.
This is because it has the incovenience of depriving the crew of anemometric data during the flight once the BUSS system is activated, whereas experience has shown that the loss of speed indication is generally for a short time only. Moreover, the system is difficult to use at high altitude.
This has been confirmed by Airbus which recommends in a FOT (Flight Operations Telex) dated 9 September 2009 not to use this system at an altitude higher than 250, i.e. 7,600 metres (25,000 feet).
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Old 26th Aug 2011, 02:19
  #452 (permalink)  
 
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Frankly, I don't entirely disagree with AF' decision not to fit this kit.

What is frustrating, though unproven, is that had AF installed it, the glaring lack of altitude skills would probably have gone unaddressed.

Horse gone, corral closed.
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Old 26th Aug 2011, 03:02
  #453 (permalink)  
 
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Thanks A33Zab.

Can anyone comment on:
- the relative precision of the AoA "from an ADR" and "from an IR"?
- the relative failure rate (whatever reason) of an ADR vs an IR?

I'm trying to understand why the ADR AoA was used on planes, if IR AoA is/may be available too, and the latter not being subject to AoA probes icing (Perpignan), nor speed problems "pollution" (AF447).
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Old 26th Aug 2011, 03:37
  #454 (permalink)  
 
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Concur on the thanks to A33Zab.

It's a step in the right direction, and acknowledgement that something needed be done.

But with a use limited to FL250, it seems improvements are in order.

Further on the question of ADR AoA and IR AoA on the same plane:

Why not to have a compound formula, a logical summ of the two formulas/calculations, and use the result which is most efficient if it is valid, and fall back to the other, if the first result is not valid.

Originally Posted by AlphaZuluRomeo View Post
Thanks A33Zab.
I'm trying to understand why the ADR AoA was used on planes, if IR AoA is/may be available too, and the latter not being subject to AoA probes icing (Perpignan), nor speed problems "pollution" (AF447).

Last edited by airtren; 26th Aug 2011 at 04:28.
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Old 26th Aug 2011, 03:46
  #455 (permalink)  
 
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Can anyone comment on:
- the relative precision of the AoA "from an ADR" and "from an IR"?
Aren't they the same probes, just piped through the aircraft systems differently?

Compared to an airspeed system, an AOA system is significantly more accurate at low (approach) speeds and much less accurate at cruise speeds.(Assuming proper calibration and design.)
Remember that your approach speed is used primarily to infer an angle of attack for the approach.
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Old 26th Aug 2011, 09:23
  #456 (permalink)  
 
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"> I thought hard about the wisdom of posting this, but in the end decided to take the plunge. This chart takes the AOA values listed as valid in the notes accompanying the CVR transcript together with some additional data read off a digitised version of the traces and combines them with elevator and THS deflections. It has been said several times on this thread that the THS is more powerful than the elevators, usually with a ‘much’ adjective. In fact, for the A330 geometry and using standard aerodynamic calculation methods it turns out that 1 deg of THS is roughly equivalent to 1.5 deg elevator. So if we multiply the THS deflection by 1.5 and add that to the elevator deflection (with appropriate signs of course) we get an ‘equivalent elevator deflection’. This is what I used to get the graph.">">
I have plotted it with the AOA as the X axis because in that way it doubles as a qualitative pitching moment curve – if the aircraft is in equilibrium then the tail pitch will be equal and opposite to the wing/body contribution. Obviously, this hides any pitch damping or thrust contributions to pitching moment. We can’t do much about the damping, because the scale of the traces doesn’t allow one to get anything like credible values of pitch rate and we know nothing at all about pitch damper gains. One can try to assess the thrust effects, although without access to actual engine thrust variations with rpm, altitude and airspeed it is going to be rather rough and ready. Don’t shoot the messenger – he is only trying to get a ROM. The second line on the chart shows such a ROM. Beyond the AOA limit shown the thrust effect increases sharply, due to a combination of increased thrust as a result of altitude changes and the drastically reduced airspeed which makes thrust effects much more powerful. Unfortunately, this is an area where the speed indication becomes unreliable.
Apart from the fact that this graph gives some indication of the AOA you can expect for a given set of tail deflections, the important thing for me is that there is no indication of any stall. OK, there is the faintest trace of a pitch break at 30 deg AOA, but in no way can that be considered as “ a nose down pitch that cannot readily be arrested” since it was clearly possible to go to even higher AOAs by the application of more NU commands. There is another possible pitch break at around 19 deg AOA, but just before this point there was a lot of sidestick activity and pitch response, so the damping terms may be important. also the same comment that it was not a nose down pitch that could not be arrested.
So when we talk of the PF not recognising that he was stalled, one of the classic indications was missing.
The other criterion specified in the rule book [and incidentally the A330 was not certificated to CS25, but to JAR25 Change 13 – similar but not exactly so] is buffet. If you look at the plot in 1.16.5.2 of the BEA report the main change at the stall seems to be the appearance of a 5 Hz component. The report does mention that the ‘g’ at the cockpit would be significantly greater than that at the CG, but this must also be true to some extent for the turbulence generated accelerations. Both relationships will depend on the fuselage structural modes, but from what I remember of mode shapes it would be primarily the first bending mode that generates high motions up front and that would not be a 5 Hz mode.
I will bow to any pilot opinion that differs, but it seems to me to be perhaps expecting too much for a pilot to distinguish a change in frequency content of cockpit motion when he has been experiencing turbulence and was expecting more severe turbulence to come shortly. I note that the AI Chief Test Pilot has said that it is very difficult, even for experienced test pilots, to distinguish the transition into stall.
If there is no pitch break and the buffet is difficult to interpret, he would have been thrown back on symptoms that do not appear in the JAR description of stalls – high attitude and inability to arrest the rate of descent – but over to pilots to evaluate those.
One other thing that is hardly rocket science either but will probably surprise many people is the THS behaviour. THS AOA is just the body AOA less downwash and THS setting. The downwash is usually expressed as a value at zero AOA plus a downwash gradient relating downwash and AOA. I have used 1deg and 0.4 if anyone cares.
The aircraft first went into the final stall at about 02:11:55 at which time the AOA was around 10 deg and the THS at -3.4. Downwash was 5 deg, so the THS angle of attack was 1.6 degrees positive. The THS arrived at -13.6 at 02:12:27, when the AOA was over 40 deg. With the above assumptions the downwash would have been 17 deg and the THS angle of attack 9.5 deg positive. There are arguments to suggest that this is an overestimate of downwash behind a stalled wing, so the THS AOA would have been at least this positive value.
For virtually the whole of the event, and certainly for the whole time the aircraft was stalled, the THS had a positive AOA so that it was generating upwards lift and a nose down pitching moment despite the fact that it was set at -13.5 degrees!. This is consistent with it being a stable aeroplane as shown by that pitching moment curve.

Of course the net HS lift was negative and the net pitching moment positive (nose up), but this was made up of a very large downwards lift from the elevators partly offloaded by the positive lift from the THS itself. If the elevator had been returned to neutral the THS lift would have given a ND pitch and attitude reduction. Look at the traces - that is exactly what happened!

The nose was being held up by the application of elevator.

Of course, the THS setting made the elevator’s job easier, and if the THS had been (sensibly in my view) restricted to 3 deg the eventual AOA would have been lower, How much lower you can get from the first chart – with 3 deg THS and 30 deg elevator you could expect to arrive at 35 deg AOA – big deal! – you are still well stalled and although the descent would have been shallower the end would have been the same unless he had recognised early on that he was in a stall.

Last edited by Owain Glyndwr; 27th Aug 2011 at 11:33. Reason: additional explanation
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Old 26th Aug 2011, 11:09
  #457 (permalink)  
 
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OwainG,

Thanks for a truly fascinating analysis, and particularly for expressing it in a manner which we ordinary mortals can understand. In my case, most of it. Could you clarify a couple of points?

(1) Downwash assumptions

Quote:
THS AOA is just the body AOA less downwash and THS setting.
Should that read "... body AoA LESS downwash PLUS the THS setting? (Given that the THS angle is negative.)

Quote:
The downwash is usually expressed as a value at zero AOA plus a downwash gradient relating downwash and AOA. I have used 1deg and 0.4 if anyone cares.
Is the 0.4 multiplied by the degrees AoA?

(2) Effect of sidestick fore/aft on elevator position (dq)

Can you confirm that, with stick neutral in the descent phase, Pitch Alt law would still have provided substantial up-elevator (i.e., a minus dq)? Any idea how much forward stick would have been required to neutralise the elevator? I also wonder how much down-elevator could have been achieved by full forward stick, and if that might have been enough to stall the THS.

You make a particularly significant point when you state that, elevator authority being two-thirds as much as THS, stopping the THS running beyond (say) minus-3 would probably not have made any difference until the AoA reached +35.
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Old 26th Aug 2011, 11:56
  #458 (permalink)  
 
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'Locked' THS

Bear, you lost me. The "locked" descriptive seems not to mesh with the design feature that leaves open control of the THS, to move up or down, via the trim wheels regardless of elevator position or AoA. (If that isn't the case, it means my understanding is deficient).
I believe that Lyman was trying to say somewhat less than concisely, was that with the aircraft established in the stall and dropping at over 100 kts, that the g could have been less than .75g leading to the THS software logic locking in position.

or to put it another way

If the software driving the THS uses g sensimg
and moves the THS with the intent of maintaining 1 g then
0.9 g would be enough for the software to continue commanding full NU.
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Old 26th Aug 2011, 11:59
  #459 (permalink)  
 
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airtren, "Being disruptive once, or twice, to gain attention is perhaps enough."

Me, "Perhaps a two day old pizza across the face is needed in some cases where there is a persistent lack of attention."

You need to be persistent until a randomly chosen acknowledgement is performed. Then you know you have their attention, however briefly.

The object is not to avoid distraction. Sometimes one must distract the over focused attention of people ignoring warnings.
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Old 26th Aug 2011, 12:08
  #460 (permalink)  
 
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Quote:
THS AOA is just the body AOA less downwash and THS setting.
Should that read "... body AoA LESS downwash PLUS the THS setting? (Given that the THS angle is negative.)
Yes, sorry for any confusion.

Is the 0.4 multiplied by the degrees AoA?
Again yes.

Can you confirm that, with stick neutral in the descent phase, Pitch Alt law would still have provided substantial up-elevator (i.e., a minus dq)? Any idea how much forward stick would have been required to neutralise the elevator? I also wonder how much down-elevator could have been achieved by full forward stick, and if that might have been enough to stall the THS.
I think so. As I understand it, with neutral stick the system would have tried to maintain the 'g' present at the time the stick was neutralised, on the assumption that the pilot was satisfied with the situation at that time. Trouble is that there were periods of time (02:11:06 to 02:12:06 for example) where the 'g' was less than 1.0 but quite a lot of up elevator was being applied (and presumably needed). Since stick movement even in Alternate is a 'g' command not a direct elevator command I don't see how to easily translate that into how much stick would neutralise the elevator. Given though that even in the worst case that the THS AOA was only 9 or 10 deg I don't think that full down elevator would have stalled the THS.

You make a particularly significant point when you state that, elevator authority being two-thirds as much as THS, stopping the THS running beyond (say) minus-3 would probably not have made any difference until the AoA reached +35.
I didn't think I said that in quite that way, but yes, I agree
Owain Glyndwr is offline  

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