with very high AoA the effect of the profile with his flow is becoming smaler, the center of lift and Cd and Cl approaches the forces of a flat panel with the same AoA.... with an AoA of 90 deg every different foil ends with an center of lift near 50% and an Cd near 1....

PJ2, #281

Thanks for the reply and the reference. What was interesting was the
comment about access to tech detail information and it's scarcity. At
the risk of repetition, if I were flying these machines, I would want to
study the detail. A deeper understanding of the machine can only improve
pilot skills, in the same way that knowing what goes on under the hood
of a car helps to appreciate the limitations and to get the best from
it.

Perhaps the (secrecy ?) is a european thing and wonder if boeing provide
more free access to such information.

Anyway, this is probably a bit off topic for tech log :)...

takata;

I think I basically agree with what you wrote. I just wasn't aware of it and thanks for patiently clarifying this point. However, I'm left with a few grey areas which may be relevant for what the pilots of AF447 saw.

The text you copied from the Air Caraibes memo appears on page 5 in the context of the protection named "CAS MONITORING" which in the BEA reports is the initiating event at 2:10:05 of the whole 2:10 sequence and results in the PROBE PITOT fault message after closing the one-minute correlation window.

Page 7 of the ACA memo shows pictures of the PFD speed scale in Normal and Alternate law in the context of an ADR DISAGREE message with Vsw in the Alternate Law 2 case.

While it may be unimportant whether or not a calculated Vsw is indicated on the speed scale when IAS has dropped to 60 kt or less, the intriguing question for me is whether it would be shown in the intermediate period when one or more of the indicated speeds had become valid again. EDIT:: Why should Vsw not be shown along the speed scale showing a 'valid' speed, first on PFD1, later on ISIS, and at an unknown time on PFD2?

Nope, it's a proprietary-systems-and-software-design thing. I don't think they've even publicly released the tools they use, let alone open-sourced the design and the software, and I'm almost certain that no, B don't do it either.

Bear in mind that in Redmond - a few miles away from Boeing HQ - lives the second-biggest PITA for proprietary software there has ever been!

Can't see where I suggested we were at high mach no:)

Yes, we can easily be stalled at High Mach, just as in incompressible flow (that's what the lower cruise buffet boundary and coffin corner is about, no?)

What do you mean by high Mach ? > M 0.5? transonic? or supersonic?

Right. There is two independant functions for monitoring the speed for essential systems which should be the first to detect probe errors (beside plenty of other systems self monitoring their own recieved imputs, just in case).

a) ADR monitoring at Auto Flight System (AFS) level (-> FMGC). This should also be the first one to react as the threshold is set at 0.45 seconds for a variation of 20 KT.

b) ADR monitoring at Electronic Flight Control System (EFCS) level (-> FCPC/PRIM) which is "CAS Monitoring" you refered to. Here, the threshold is a variation of 30 KT during 1.0 second. It is also responsible for changing immediately the Flight LAW to ALT2 when a variation is detected. Hence, it takes 1 second to change the flight law, but it's at first temporary. After this point, the last valid value (before change) is retained and a comparison is made with the current value 10 seconds later: if the difference is > 50 KT, ALTERNATE 2 is confirmed, whithout the possibility to revert to NORMAL until post flight reset.


This illustration is taken from the FCOM and is generic for ALTERNATE if airspeed is not unreliable. In case of UAS, What you will have instead is the red flag "SPD LIM" (see report previous page) without Vmax, VSL nor VSW and... It will last for the remainder of the flight like ALT2! (read me well: even if the airspeed come back to normal after a while, this is lost as it is displayed only when ALTERNATE low/high speed protections could work, which would not be the case after an UAS. Even if coherent, speed will always be considered spurious by the system). That is also the reason why some long haul flights turned back and landed after an UAS event which was not transient (lasted more than 10 seconds).

Quite simply, it is an EFCS function that compute all the characteristic speeds from data comming from the FE part of FMGC and ALL ADRs. This function become inoperative as soon as more than 1 ADR is rejected by the FCPC. After this point, it will consider both FMGC (1 & 2) as inop regardless if the data will be later coherent again. Hence, the display of probe data (speed) on each PFD or ISIS is directly available for the crew but it is unrelated with the function computing the characteristic speeds which is lost. Those data displayed are not what the system could use as it will need two "valid" sources, at any time, for safe operation.

Viper stabilators
 

For DJ77, et al:

- The stabilators, or horizontal stabilizers/elevators, moved +/- 21 degrees.
- They had a symmetrical airfoil, and...
- They were interchangeable from one side to the other
- They moved independently in order to help with roll, especially when supersonic

Harry:
You were talking about a highly separated flow regime. That's (in the context of this case) the low speed regime stall. The case under discussion isn't, as far as I understand, a high speed (and thus high mach for this airplane) stall example.
I wasn't sure what to make of your reference to high mach, honestly.
That's why I asked. I think, on reading your post again, you were comparing shapes of Cd curves at different ends of the spectrum ... as a general reference? :confused:
In the context of this class of airfoil (large transport) let's say transonic or approaching supersonic (limits of airfoil before the high speed buffet, coffin corner, etc.) would seem to me "high mach" as the airfoil isn't shaped for operations in supersonic flight. (I confess, it's been over thirty years since I studied compressible flow, and things like Prandtl Meyer flow, so it doesn't recall well from memory.)

I don't think we'd get anywhere discussing this airfoil under conditions at Mach 2, for example. :cool:

Ah yes, thanks Just covering as you say either end of the spectrum, though drag buckets due to a cruise Cl laminar regime also can have a Mach element (be a function of).

Just out of curiosity, is this a boundary layer phenomenon? (BL is an area I wasn't all that strong in when studying fluid mechanics. )

Yes, very much so...

I find there is always a lot of confusion between separated flow, turbulent flow and laminar flow. The later two are boundary layer states, the former (whilst to some extent the result of boundary layer effects) is a total flow phenomena.
Saying the flow is turbulent does not mean its separated, indeed a turblent boundary layer has a greater facility to resist negative pressure gradients (behind a body) and remain attached.. .nor laminar meaning low darg and attached (indeed again, laminar flows easily separate , the classic being a 'laminar separation bublle' at the l.e. of a thin foil at high alpha; draggy too (pressure drag)... whilst the laminar layer itself has low (frictional) drag.
So it isn't difficult to spot a lay commentator when it comes to aerodynamics, or certainly flow discussions ;)

Stall always involves the boundary layer. It wouldn't occur in friction-less flow, but there wouldn't be any lift either. To comment on the Mach involved - I noted a while back that alpha-max is defined by low-speed stall at more or less constant AoA up to M=0,275, and is defined by Mach-related buffet above that M. In AF447 stall occurred at about M=0,6 (2:11:06, 185 kCAS at FL375).

Harry/HN:

Thanks to you both, some of it's coming back to me. I am thinking that I am wrong to posit that the stall wasn't at "high mach," given the numbers HN kindly reviewed. The conversion of CAS to IAS at high altitude reminds me of how fast the plane was traveling at stall entry ~ M0.6. I can see where one can say that it was a stall at a relatively high Mach number ... depends on frame of reference for what "high" or "low" means.

(HN, I am aware that stall involves boundary layer effects, what had me curious was the Harry's pointing out the mach elements within drag ... I suspect that was once taught to me but it wasn't in long term memory).

Not always true :

http://i45.servimg.com/u/f45/11/75/17/84/fcom_110.gif


That must be part of the complexity of the system, laws, protections, stability ... In the mean time, can we presume that if under Low Speed Stability in ALT2, autotrim does not operate ?

If no autotrim never under manual flying, at least a pilot knows trim is under his watch always - No ambiguity.

henra, CONFiture.

henra's comment ( "a/p mistrimming, disconnecting and handing back", etc.), was one of the very first progenitors of passionate disagreement here on thread. I said, (roughly) that getting the a/c back under these 'unproven as yet conditions' would be like having a wet enchilada dumped in one's lap. Distracting, uncomfortable and in immediate need of a clean up.

THS as TRIM versus THS as CONTROL? How can one be separated from the other? It seems an incestuous combination of duties, and ripe to provide confusion.

As CONFiture has said, "One way or the Other". SA should be natural, intuitive, and rapidly moving. Stopping to think just to get a handle on the moment seems a dangerous waste of time.

Doesn't the Computer (FCS) take as much as TEN SECONDS to validate a LAW? In some situations, one imagines ten seconds may be an eternity, and in danger, delay is the Devil. (Unless it is appropriate, there's the rub).

takata,
Hmmm, may be the AB engineers cited in the ACA memo don't understand their aircraft, but they say explicitly on page 6: "Sur les PFD les vitesses VaPROT et VaMAX sont remplacés par Vsw".

@syseng68k:
 

In fact there is another (identical) set of xdcrs for the roll channel.

De redundacy is: 2 potmeters for each Flight Computer (2x roll & 2x pitch)
If 1 input rod becomes disconnected, both potmeterclusters are driven by the other crank & geartrain by means of the shearpin.
If 1 input rod/geartrain is jammend, the shearpin will break and allows free operation of the other set of potmeters.

To J T the Mod - a FBW thread?
 

I suggest we interested parties crank up a thread in the Tech Forum specifically devoted to FBW systems - philosophy, real engineering crapola, human factors, experience from several folks here when things went awry, and of course lessons-learned from AF447 and other FBW airline types.

I can't moderate, but can help.

I only suggest this as I was around when we saw the first fully-FBW system fielded in significant numbers - a charter member, if you will. My engineering background is so-so, not half as good as some here, but "adequate". I also worked with the high-tech avionics in operational jets earlier than many here due to my military experience, and most of that time I was solo.

I recall a question from a U.S. Senator at a hearing with our new Sec Def ( McNamara) who was fascinated with high-tech and other aspects of military equipment designs. He asked the Secretary, "Just what experience, if any, do you have in these matters?"

Shuttle Flight Computer
 

I apologize if this has already been posted.

For safety critical system design folks:

Spaceflight Now | STS-135 Shuttle Report | Astronauts restart computer; Obama to call Atlantis today

I don't think that is correct - I think autotrim is always active outside of direct law (or manual backup) except in abnormal attitude law. Abnormal attitude law could, I guess, co-incide with low speed stability activation, but would not automatically follow from it.

It's a good theory, but there are incidents (more than one 737 I can think of) where it hasn't held up in practice. In situations where the automatics dump the plane back in the pilots' lap unexpectedly (perhaps trimmed up to the limit) it can only add to the workload.

Also, I think autotrim is effecitively requried for C* control law, so without it you are looking at direct law, and no protections/limits whenever A/P is out. Not sure that is going to be an improvement.

You could reduce the number of laws/transitions to simplify things - as others have suggested. Go straight to direct law, and hence manual trim, when things start to go wrong. I'm ambivalent on that - I can see from a design & engineering point of view that the current laws are a nice graceful degradation, which should make things easier.... however, all the different laws, sub-laws, caveats and footnotes add up to a lot of combinations to learn and fit in training on. It's arguably little use having intermediate graceful degradation modes if pilots are never trained on them.

Be careful what you wish for though - there are reasons why non-normal laws get latched, and the A/P doesn't handle direct law, so you could be looking at hand-flying a long way when stuff goes wrong. On the other hand, maybe if the previous UASs had been a bit more of an "event" the **** pitots might have got fixed sooner (like when AB suggested it, or earlier).

Hi HN39,
Sorry, but it seems you are the one confused here.
What is quoted, with illustration, is only the manual, word for word, until the last sentence. Each part quoted is detailing a protection in NORMAL Law and what happen when mode switch to ALTERNATE (generic, as per the manual). Only the last sentence of each paragraphe is an addition which is explicitly telling what was the "real" condition in ACA case.
Read it again, it ends with "dans ce cas ... cette protection est perdue" (this protection is lost) for each of them, except for the load factor protection (no low/high speed stability after the rejection of all ADRs by the PRIMs).
Consequently, it is all taken from the manual and there is no need for one to refer to any hypotetical confusing Airbus engineers "quote".

Hi Bearfoil,
Right. The EFCS will need 10 seconds to validate that ALTERNATE LAW 2 will be irreversably maintained at PRIMs level.
But then, what you don't understand is that EFCS logic is one thing that is different from Pilots information logic.

When you are flying this machine without system failure, you are protected by the system all the time. Most of the system single failures won't change the flight laws, they are completely transparent for the Pilot Flying as everything (protection) is maintained. They will trigger ECAMs for troubleshooting purpose.

As soon as a system failure is occuring that will change the EFCS flight law (generaly dual or triple faults), by following the EFCS logic, it will be translated into a degraded mode called "ALTERNATE" or "DIRECT", from the consideration of the flight controls on each axis.

But the Pilot Flying doesn't need to follow the same logic as EFCS : what he first needs to know is what protection remains available, or better, which one of the protection is removed. Remember that this is not linked with those LAW, sub-LAW modes, but to the specific nature of each failure => anything "NORMAL" that can be maintained is kept, anything affected is removed.

In fact, this information is displayed on his PFD where he can see what protection is working or not, it is all that will matter for him at this point. Any protection removed (flags or reconfiguration on each PFD) will mean something lost. following computer logic, a single protection lost is called "ALTERNATE" mode... you will know it immediately if any part of your PFD will get amber crosses or red flags instead of usual values.

Now, following computer logic, this translate also into ECAMs triggering and other warnings if an action is to be expected immediately. But most of this is not aimed at the PF (beside auto flight controls). This is for PNF troubleshooting and it doesn't really matter if an ECAM saying "ALTERNATE LAW (PROT LOST)" is delayed by 10 seconds or more.

The reason is that the PF is not taking this information from the ECAM console. It is taken on his PFD where he can see directly what is really affected. Then, it will be obvious for him as soon as ALT2 mode logic is triggered by EFCS in one second when CAS becomes monitored following a sharp variation: his PFD will be reconfigured without displaying any of those protection function nor those characteristic speeds. If he also get the red warning flashing on his PFD : "use manual Trim", he'll know immediately that DIRECT law (computer logic) was also triggered.

"ALTERNATE" by itself means nothing for the PF as to what is possible or not, being related to specific failures. His PFD would tell him everything needed (at least, it "should" tell him everything).

I did. We're not discussing any protection, but the indication of Vsw on the PFD. But thanks anyway.

No, that's not what i'm asking for. Things like inputs required for
transition between the various laws would not be proprietary and would
be expected to be available, as some of that is already in the fcom.
Just not the level of detail needed for analysis.

What i'm looking for might be covered by a technical training level
manual, but have only managed to find bits here and there for other a/c.

Found this title from a search, but not a download link, as yet :E:

A330 Technical Training Manual, Mechanics, Electrics and Avionics Course

As for the tools, some are known, but it would be a bit of a stretch to
expect sources to be available, let alone open source. Now that would be
proprietary:suspect: ...

takata, merci.

I truly appreciate your response. In it alone, I have gained (finally!) an (basic) understanding of the "duality" of ProtLoss flight.

So, then, as things get challenging, the a/c keeps the Pilots informed, and the Pilots "adjust" as to the new parameters. Friends, then.

I'll keep reading, the last two or so pages have been most edifying. If Manual Trim is necessary, why would it be annunciated in two separate colors, AMBER, or RED?

bon chance

Agreed. But then, you should read this paragraphe as something informative about the system but unrelated to this specific case as the last sentence proves that it doesn't apply to it => you can't have Vsw displayed both with Speed Limit Red Flag.
About what I wrote previously, I've got also a conflicting note saying that a dual FMGC reset was attempted in flight in order to remove the Speed Limit Red Flag after UAS event (and having Vsw, Vmax indications back), but I don't know if it was successful. I'm still looking for more info about that anyway.

"Use Man Trim" doesn't mean that manual trim is "necessary" but that autotrim is not working in this flight law => direct.
At first it is displayed flashing during 5 seconds, and later stay normal on the display, about its color, I'm saying that from memory. If one read "Use manual trim ONLY", hence big trouble, EFCS is not working anymore (mechanical back up) and you are left with trim only as pitch control.
Amber is the color of the crosses on the PFD removing the bank, pitch, roll limits. Red is the color of the Speed limit Flag (meaning no speed limits, no speed protection).

Sorry takata,

I am unclear which 'last sentence' you are referring to. I quoted from the section on "High Angle of Attack Protection", which ends with "Pour terminer, ... givrage des sondes PITOTS... entraine ... F/CTL ADR DISAGREE qui engendre ... ALTERNATE LAW 2 ... avec ... perte de ... LOW SPEED STABILITY."

Doesn't that 'prove' that this section deals with the consequences of ADR DISAGREE caused by PITOT icing?

We'll finish by falling in agreement.
YES, I'm refering to this specific sentence. What it means is that everything above doesn't apply to ACA case : pitots fault => ADR Disagree => Low Speed Stability lost.
All the paragraphe above is quoting the FCOM's explanation of High AOA PROT in NORMAL, then its replacement by LOW SPEED STAB in ALTERNATE (hence Vsw displayed) and conclude that they had none of these protections because being in ALT2 with ADRs rejected.
Do we agree?
Yes it does... by detailing that those High AOA/Low Speed Prot above explained... were lost due to this current PITOT fault!!!
French is not your primary language, is it?

Hi takata,

Thank you again for your patience with me. I'm quite happy to let the matter rest, simply because the available documentation apparently doesn't provide the answers we are looking for. I do not agree with "All the paragraphe above is quoting the FCOM's explanation" because the explanations contain a number of details that are specific to this incident.

Please, explain which part (words) of the paragraphe before the sentence "Pour terminer,..." is related to this specific incident?
I really can't see anything related to current flight and I'm struggling to understand what is confusing about this way of reviewing every system protection that were not available for ACA. My reading is 100% clear.

takata.

one last, then I promise I'll leave you alone for awhile.

Why is "USE MANUAL TRIM ONLY" (I have no quote function, so if I misquote you, please understand). "Big Trouble". ? Why is this TRIM only for Pitch control?

iF EFCS is inop, and mechanical back up only, are you saying the elevators are inop also? Pitch must be managed by Trim Wheel alone?

If that is telling of my ignorance, so be it, but shouldn't an a/c in trouble have elevators? Not a slow, massive Tailplane alone?

When "USE MANUAL TRIM ONLY" appears on the PFD, you are effectively in big trouble as, either you have lost both elevators (L+R) or EFCS is not powered anymore (see basic schematic posted above about flight controls). They could be other failures but I'm just pointing that in order to illustrate that what is related to critical F/C faults should be displayed on the PFD directly to the PF without the need to wait further for PNF ECAM troubleshooting sequence.
Beside, the correct wording is USE MAN PITCH TRIM, displayed in amber, while MAN PITCH TRIM ONLY, is displayed in red. See below:http://takata1940.free.fr/reconf.jpg

That's about the size of it, pitch trim and rudder become your primary controls.

Think of this mode as the equivalent of total hydraulic failure on a previous generation jet (like, say, a DC-10). In the previous generation jet you'd have had no control other than thrust, but in this case you have thrust, pitch trim and rudder. I haven't heard of this mode coming into play outside of simulator training (thankfully, like total hydraulic failure it is expected to be an extremely rare occurrence), but it is indeed what you've got.

Don't you think Airbus trim and rudder need hydraulic too ... !?

No, read what I'm saying - the *equivalent* of total hydraulic failure, only in this case it's the electronics that have failed. I'm well aware that the control surfaces are hydraulically actuated.

And just to be crystal clear (and not that ANYONE has said this or even hinted it) this is NOT the control mode that AF447 found itself in. Just in case any casual observer or passerby should get the wrong impression.

Flag on capt (f/o) pfd
 

HazelNuts39,
Check 01.31.40 about Flags on PFD.
(Still not up to date infos):

http://takata1940.free.fr/flagon0.jpg

http://takata1940.free.fr/flagon2.jpg
http://takata1940.free.fr/flagon3.jpg
http://takata1940.free.fr/flagon4.jpg

Dozy

I get that. But hydraulics haven't failed. They have been disabled (by design? A lack of alternate actuation?). With APU, Alternators and or Battery or even RAT, and hydraulics, why throw away the standard, (elevators), to struggle along like Al Haynes had to? (just a metaphor, I suggest it is not the same thing, exactly).

Rare or no, why not go for non-existent?

I sense a high level of agreement on the potential for THS TRIM WHEEL as the ignored resource, here. THS is large, powerful, and slow moving, not my first choice in Turbulent air, where TRIM (traditional) is not a primary resource in a conventional a/c recovery?

Powerful TRIM TABS as a default no/fail?

aside. Please don't think I am suggesting bellcranks, tensioned cables, and bellows to replace ECFS. :eek:

Bear,
Take it easy. This (mechanical) back-up law may be ultimately useful in case of electrical reconfiguration when the power switch from one source to another (something very transient, to begin with). As you say in about every post, the THS is powerful, and all FBW aircraft are fully certified to be flown with THS trim instead of elevator pitch control.
Design is based on FBW (electrical control), whatever you can say about that won't change this fact. Anyway, they have provided a mechanical back-up, just in case, in a very remote situation, it may be needed at one point for the pilot to use it.