roulishollandais

did you heard about the "attracteur etrange" (i do not know the name in english): see james gleick CHAOS. unstability has such a point that gums searched and found on.the a330. congratulations to gums, retiredF4 for the stall, and machinbird for the roll
Thanks

mm43

HN39 et al;

Lonewolf_50

jc, the court case won't contribute to aviation safety.

It may make a few wallets fatter.

Rockhound

Slats,
It is completely incomprehensible why the captain, after he was summoned back to the cockpit by his crew, made no effort to take control. Indeed, for much of the time he seemed to be little more than a rather distracted observer.
Confiture,
We will never know what the captain was referring to when he uttered "prends ça!" Otelli writes that the BEA investigators thought he meant the Flight Path Vector (the "Bird") in the PFD.
Lyman,
So what if the C Chord seemed intermittent. Surely that alarm would be the least of the crew's worries. The way that plane was rocketing up and dropping back down, it's a wonder the C Chord generator didn't burn out.

Lyman

Rock hound...

Yes, I would agree, I was curious about any failure in the a/c, not just what the pilots were doing with it. So you know the parameters of c chord burning out. Where can I find them? BEA are derelict in leaving so much information out. The general drill in a report is that data can be incorporated "by reference", leaving the reader to pore over it, after he locates it elsewhere.

Thanks

jcjeant

lonewolf_50
I think it may somehow contribute to safety .. simply by excluding some people by sentences ..
People or organizations that contribute to lower safety or not taken into account by their mismanagement
And I hope this will be those of the victims families
And it may also make a few wallets thin .....

Rockhound
I read nothing about that in the final report ...
The BEA report of course ... not the useless Otelli one

john_tullamarine

(Caveat - I have no specific FBW background)

I am a tad confused by some of the recent posts commenting on stability.

If the aircraft, in degraded modes, gets to the stage of having no computer protections, then it would appear to be unflyable for the typical pilot unless statically stable along with a dynamically stable SPO. If statically neutral or marginally unstable, still flyable if one knows what to do .. and then only for a short while until the fatigue levels take over any semblance of finesse.

However, I cannot imagine that it would have been certificated unless it were stable in the worst degraded mode ?

Has anyone any information regarding the matter ? Specifically,

(a) as modes degrade does the aircraft get to the point of having nil computer assistance ?

(b) if so, what are the stability characteristics ?

I am presuming that there is no flight test data relating the the AF447 extent of stalled flight ...

chrisN

roulishollandais, "attracteur etrange" = strange attractor in English. More at :

Strange Attractors - Chaos & Fractals

If you are interested.

Hope that helps.

gums

Yeah, JT, a good question.

Wiki has a fair explanation, but one of my original posts has a link to the Viper's design WRT static stability.

Longitudinal static stability - Wikipedia, the free encyclopedia

Have to look at my website files to get a link for our design.

Found the Code One articles on my website:

http://www.sluf.org/misc_pages/codeone_v1_n2.pdf

http://www.sluf.org/misc_pages/codeone_v1_n3.pdf

The deal with the 'bus is that what we all knew as "normal" was if you let go of the stick the plane would try to achieve the trimmed AoA ( not gee). So the cee gee was well forward of the center of aero pressure. This meant that when cruising along that the elevators were actually creating a force opposite of the main wing to keep the nose up. By moving the cee gee back and having HAL to help, you could have the elevators creating upwards lift and dramatically reduce "trim drag". In short, both the elevator and main wing were generating lift upwards.

From my A330 manuals, the thing never has an extreme aft cee gee as we had, but it does allow it to be further aft than most of the other jets. This helps for range due to reduced trim drag. Because HAL is helping, you don't feel like you are flying on the tip of a needle if you turn the AP off.

The 'bus direct law is one implementation I described. The electrons directly command control surface deflection via the actuators, just like the old days when our yokes/wheels/sticks moved a valve for the hydraulics. Because the plane has positive static stability, it is still flyable by mere mortals.

What bugs me is that the 'bus reversion sequence is not real clear as to the AoA bias on pitch. At first look, you think that you have some degree of AoA limits and actually command AoA. Then you read all the footnotes and find that some data failures do not provide the expected control response related to AoA. So the jet is still trying to achieve a gee, and the AoA can go to 40 degrees, as we now know can happen.

later from this old dinosaur...

john_tullamarine

Thanks for that .. I'll review later on today during a coffee break.

I don't have a problem if the box is still helping out sensibly as what is important is what the pilot is presented with in the worst certification degraded mode ...

However, some of the posts appear to be suggesting that the degradation can extend to nil box assistance and a statically unstable aeroplane.. that's my problem at the moment.

Either such

(a) isn't the case

(b) wasn't considered because the estimated MTBF suggested the probability of occurrence was up there with the other very small numbers .. ?

I probably should have bid onto the A320 when I had the opportunity rather than staying on the FLUF.

OK465

Actually, if you go by the anti-bus crowd around here, the modes degrade as you add FC computers.

With only one secondary FCC (of possible 5 total FC computers) available to connect SS/rudder inputs to the flight control surfaces you have a 727.

With either no computers, or no electrical power, you have mechanical control, thru hydraulic actuators, of the THS using the trim wheel, and the rudder using the pedals. Though set up to provide control while resetting computers, as others have said, you can actually land the aircraft, if necessary, in this condition. Complete electrical failure, you've got no choice but to land it this way. Challenging and satisfying.

It is never divergent around any axis, regardless of the level of computer assistance or lack of.

The wonderful world of FBW.

gums

Thanks, Okie, you nailed it.

There might be more dependence upon electrons than you suggest, but the aero characteristics of the 'bus seem really good to this old fart.

I am not anti-bus. I am bitching about all the reversion sequences and such, which seem very confusing to me. I want something to hang my hat on, and if various sensors are FUBAR, and HAL doesn't use them, I still want to know what I am playing with. I also have a problem with the THS still in operation once outta Normal law. Another thread topic.

I joined the fray here to show that some knew about unexpected aero problems over 30 years ago that the cosmic FBW systems could not fathom. It's why I detest the term "protections". Although our system had different mission requirements than the 'bus, it was the first one fielded with a fully FBW system and had several hundred jets flying within two or three years. We initial cadre were afraid that the newbies would forget how to fly a "real" jet. And I can't help but see that fear realized in the AF447 disaster.

Turbine D

@ JT,

From what I have read about the A330/340, IMHO, both possess static and dynamic stability to the point that in the worst situations, the aircraft is flyable. If it were not, I don't see how it could of been certified in the first place. I think the Airbus folks, designers, engineers, aerodynamicists and software folks thought of virtually everything to enable this, complicated as it may seem or be.

The worst two cases would be Direct Law and/or complete loss of electrical power.

Direct Law - In pitch direct law, elevator deflection is proportional to stick deflection and, in all configurations, max elevator deflection is a function of CG. This should be a transitory phase prior to PRIM reset and re-acquisition of Alternate Law. There is NO automatic trim meaning you have to use manual pitch trim. The yaw damper still provides yaw damping but gives minimal turn co-ordination. So protections of g, pitch attitude (manual pitch trim is required), high alpha, high speed, bank, MLA, turbulence, low energy and AP are all lost. But, the aircraft is flyable with care.
Should a complete electrical failure occur, mechanical pitch control is through the THS using the trim wheel. There should be caution here as if the CG is back there is a pitch up bias, if the CG is forward there is a pitch down bias. Manually operating the trim wheel requires gentle and smooth movement as the THS is a large aerodynamic surface. Mechanical lateral control is the secondary effect of rudder pedal inputs. The BYDU provides Dutch roll damping.
An example of an event which would put you in Direct Law would be a double engine failure, which at high altitude cruise, would probably mean that you will need to descend in a controlled manner to a lower altitude to initiate engine restarts.

I would say a good example of a unstable large aircraft without FBW computer controls would be the B2 USAF bomber. If the computers quit, IMHO, the aircraft would not be hand flyable.

Just some thoughts and opinions from a non-pilot, engineering type.

rudderrudderrat

Hi Turbine D & JT,
Direct Law would occur only after putting the Landing Gear down. Up until then, you'd be in Alternate Law.

The aircraft is only statically neutral with the aid of the FBW computers. In Direct Law (stick deflection proportional to control surface deflection) they are (beautifully) dynamically stable.

AlphaZuluRomeo

OK thanks again
As I said earlier, I'm not that fond of maths. Would you be so kind as to "translate" what impact will a different 'a' value have (in AF447 scenario, and/or in general)?

Yep, read that too. A/P issues deflection orders directly, sidesticks issue manoeuver demands which are translated into deflection orders by the flight controls computers/laws.

Regards.

rudderrudderrat

Hi AZR,
I've only ever flown in ALT LAW in full motion simulators which do not simulate realistic g loads. (constant 1 g felt in turns & TCAS events with smart pull or push etc. The pitch attitude of the box changes to simulate horizontal accelerations; and the box moves up and down within the travel length of the jacks to simulate turbulence).

There is no perceptible difference in pitch control when flying in ALT LAW v Normal Law. Roll control is however noticeably different - if feels like a conventional aircraft.

philip2412

Sometimes i`m going really mad here.Although my english is good enough for the daily talk, i`m not really able to explain the psychlogical aspects i see in this crash like i could do it in german ; and that drives me crazy.
I´m no pilot etc. so why is he posting in the tech log,some may ask ,among all these profs and not in rumours % news ?
I can tell you. I`m feeling well here,because all in all it`s a serious discussion.
and no, i`m not here because there is a need for me to lift up my selfconfidence among the gods of flying and others.
So i can`t say much about the tech.aspects,but i comprehend what is said.
Thank you for your patience with me and sometimes recognizing my posts !

Back to business.

I´ve read a few hundred accident invest.reports and there was always a chapter about the prof.career of the pilots and what they were doing in the 48-24 hours before the flight and their behaviour with colleagues in duty.
This i miss here. so why ? Bad talking about gone people not allowed.The others were also mostly dead.
So why it is missing here,quite unusual.

RetiredF4

When discussing the different laws and its effect to the flight control system it is imho important to know and accept, that there are different Alt Laws available . In the last few post those differences didn´t get any attention (see my last post).

ALt Law 2B differs substantially from the other alt Laws, as all protections except load factor protection is lost. The biggest difference being, that in this Alt2b law the FCS works along the Nz law with no high speed stability (VMO2) or low speed stability protection (Vc prot) present.

Here the details of those protections in ALt Law (not in Alt2B):

Both those limited protections had not been available.

When discussing the the stability and control issues as well as the stall entry of AF447 that point makes quite a difference. It´s the cause, that a SS in neutral on the way up to the apogee would have changed nothing, as the Nz-Law would have been active all the way into the stall. It may also be the reason, that in Dozys experiment in the A320 simulator a permanent stick force was required to maintain the pitch into the stall, or that the THS trim stopped, as VCprot worked against it or that PJ2 couldn´t achieve the same pitch as AF447 did in his simulation.

It might also make the difference between some of the other UAS flightpath excursions gone well.

If i would have to grade the handling in the different laws from a theoretical standpoint, it would be kinda

- Normal Law (artificial neutral stability with full protections)
- Alternate LAw except ALT 2b (artificial neutral stability with limited protections)
- Abnormal law (artificial neutral stability with limited protections without autotrim)
- Direct Law (natural positive stability)
- Alternate Law 2b (artificial neutral stability without protections except g-load protection)

But again, i didn´t fly that aircraft, but i doubt that all pilots are familiar with the consequences of all the different laws, as graceful as they may be (gums i´m with you on that one).

Edit:
It would be interesing to know, if the law Alt2b changed intermittently when the speeds came back on line or the above limited protections reactivated itermittently.

HazelNuts39

Again my understanding, and I may be wrong. With stick free the Nz law tends to maintain essentially the current trajectory at approximately 1 g (nz=0). If that trajectory is such that the airplane decelerates, it will have to pitch up to maintain approximately 1 g at decreasing airspeed. The pitch rate q depends on the rate of deceleration dV/dt. It will not quite maintain 1g but it will settle for nz = - q/a, i.e. an incremental load factor that is slightly negative, depending on the value of 'a'.

P.S.
For example, at FL350, M.6, 205t and decelerating at 2 kCAS/second, the pitch rate maintaining 1g is 0.27 degrees/second.

jcjeant

The answer at your question is in the BEA meeting with the press (the day they released the final report)
One journalist asked same question as yours..
Answer BEA:
They made researches about what made the crew in Rio
They find nothing interesting or related to the crash ..... so nothing of value to put in the final report ......