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# AF 447 Thread No. 5

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# AF 447 Thread No. 5

13th Jul 2011, 17:04

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A33Zab, #230

Thanks for the excellent diagram. Not quite clear on the following:
2 Xdcrs(contains 4x triple potentiometers per axis).

FCPC1 & FCSC1 driven by separate linkage. (Dual Channel output 4 potentiometers, 2 unused) per axis.
FCPC2 & 3; FCSC2 driven by the other linkage (Dual Channel output 6 potentiometers) per axis
So what you are saying is that:

The system has a total of (4 x 3) 12 pots per pitch and roll axis, total 24

FCPC1 and FCSC1 each get pitch and roll, triple redundant, 12 pots (minus 2 ?)

FCPC2 and FCSC2 each get pitch and toll, triple redundant, 12 pots

Question: Why are two pots unused ?.

Looks like a clever design though, in that the redundancy even extends
disconnects or breaks, the second linkage and potentiometer set would continue to
function.

Question: What is the function of the solenoid and does that lock the
stick at any point (zero ?) in it's travel ?.

13th Jul 2011, 17:13

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Originally Posted by PJ2
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...

Indeed, the "a/c" trajectory is never really a "perfect" "straight line". It is rather a series of segments of the type I've mentioned - "up", "down", "left", "right", "level" - with the length of these segments depending on the degree of air turbulence, and how fine the control of the "a/c" is.

In non turbulent air, the 4 "non-level" segments are very short, while the "level" segments are long, or very long, and predominant.

That is different in turbulent air: the length of the 4 "non-level" type segments is a lot more significant, while the length of the "level" segments a lot shorter, possibly down to "zero", with a predominance of the "non-level" segments, versus "level" segments.

That implies more drastic or significant actions of the "a/c controls", that react to the change and transition from one type of segment, to the next, to keep the "a/c level".

Originally Posted by PJ2
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.
My understanding is that that would be the case if there is no, or little turbulence.

However in turbulent air, at an "a/p and a/thr disconnect", which can be coincidental with a change of law, and loss of certain protections, the "inertia" and the "a/c control surfaces at normal position" would keep the "a/c" level, ONLY and ONLY if the segment is "level".

Otherwise, as I understand it, if the segment is "non-level", there is a good chance/probability that "inertia" and "control surfaces" as left after the disconnect, and lack of protections, can bring the "a/c" way out of being "level" - "up", or "down", or "left" or "right". The degree of how off from "level" depends also on the time interval between the "automation disconnect" and the taking of the controls by the pilot, as well as a correct control correction coming from the pilot.

The probability of 20% and 80% I've referred to implies an equal distribution and length of the 5 types of segments, which is a stretch, for the sake of an easier explaining/understanding .

But it is a stretch in both directions!!!

Which means that for a very active turbulence, for the duration of that turbulence, the segments might be only "non-level", in which case in that time interval the "probability" goes from 80% to 100% - which makes it "a sure thing".

13th Jul 2011, 17:40

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syseng68k, the SS probably did not fail. The PF was able to achieve ND type inputs on several occasions. And if the PF pulled the stick and got NU he'd no doubt announce it and turn control over to the PNF whose stick would presumably work.

And I'd be tempted to look into "springs" and strain gauges. (The sticks gums cites very probably were based on strain gauges since they had so little movement.) Strain gauges have nothing to get dirty, noisy, or erratic. So they're a little more reliable.

13th Jul 2011, 17:41

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takata - post #235 - you accuse Bear of posting "such a load of cr*ap about a subject" and then do it yourself. I repeat - there is NOTHING in the BEA report to tell you that the pilots caused the climb. A 'nose up' input of unspecified size or duration does NOT prove that and may well have been of short duration - you do not know. As for your bit about "There is another way to change pitch attitude than pulling up on the sidestick as simply applying thrust could do the job if the amount is large enough." - you don't say? Now show me where the report tells you they increased thrust. You are making this up!

Now to TC-JDN - have another look at the trace. The a/c began pitching while the engines were throttled back, the side stick did not move but the THS did.

I note you come 'from Toulouse'.

13th Jul 2011, 17:48

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Hm.... Perhaps I've missed this.... are the variables/parameters determining the values of the Stall Warning Threshold function and thus the shape of the curve valid, for the entire time (X) axle in the graph?

If NOT, then, "invalid", or "non-defined values" for the variables determining the values of the function/curve, means "invalid" or "non-defined function values", which means segments of curve which would be "invalid", or "non-defined". This means that the "non-defined" portions of the curve can be represented accurately only as a discontinuity - gap - on the non-contiguous curve.

Ultimately, it does not matter much, as these curves are just an illustration to help the understanding and communications of info on this thread.

Originally Posted by HazelNuts39
The systems consider the signals coming from the AoA vanes invalid, there is no discontinuity in the SWT.

13th Jul 2011, 17:52
bearfoil
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Would the Throttle setting be cruise detent? Could the actual thrust of the engines be somewhat higher than "normal" due a/p increases to maintain straight and level? If so, at handoff, the Throttles would lock? An assumption could be that with high N1, a change in Pitch (up) might be aided by thrustline? (These are rephrasing of my earlier question, so if they seem repetitive, they pretty much are just that).

(no offense)

13th Jul 2011, 18:00

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hi everyone. could some one please explain the g loading on a aircraft in laymans terms. many thanks

13th Jul 2011, 18:21

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G is an expression of acceleration.

If you or I simply sit in our chair, we feel the normal 1 g load on our body. That is due to earth's gravity acting down toward the center of the earth.

If we are in a roller coaster car, and go racing down an incline, when we reach the bottom, and then race up the next incline, we feel more than 1 g acceleration as we go through that arc on the bottom of the track. (we feel pushed down into our seat a bit). This is like a pitch rate change in an aircraft, pitching the nose up.)

If we are in a plane flying along straight and level, we should feel 1 g.

If the plane goes into a 60 degree angle of bank turn, straight and level, the vector forces sum up to 2 g's. You'll feel that in your seat. (You'll feel a bit heavy).

If you are flying with the Red Arrows, or Blue Angels, or Snow Geese flight demonstration teams, you may do a high G turn over the field to show how maneuverable your jet is. You can induce g's up to 5, 6, 7 ... depends on which aircraft you fly. While doing such a maneuver, if you try to raise your arm, it will feel heavier to lift than when under 1 G. Under 5 g turn, your arm feels about 4 times more heavy than just sitting in your seat. (You can usually still lift it, but it feels strange to do so, much effort).

If you are in level flight, and you push the stick forward, you will tend to feel light in your seat: you are feeling < 1 g. If you fly the plane in a particular manner, beginning nose up, you can push over into a parabola shaped flight path that will induce a zero G condition, temporarily: if not strapped in, you can float a bit in the aircraft cabin. (Astronaut training used to include such events. Not sure if it still does).

If you choose to roll the aircraft inverted, and fly level, you will feel 1 G acting in the opposite direction to your sitting down: you will feel pushed OUT of your seat, not held into it. (Keep those harness straps on nice and tight). That G is typically referred to as negative G. It makes the blood rush to your head. The earth pulls on you the same, but your orientation made you experience that force differently.

A vigorous nose down push on the stick from level flight can induce negative G, and you will fall "up" toward the aircraft's cabin ceiling if you are not strapped in.

For much smaller changes, you can induce a 1.2 g or 1.1 g, or slightly less than 1.0 G (0.9, 0.8) via small pitch changes, as a result of control inputs that you choose.

G onset tends to be rate sensitive. If I make a very slow input, nose up or nose down, I induce a small acceleration, so the "g" of that maneuver, or the "change in G force" is small.

If I make a rapid input, the G tends to increase, and it is readily felt.

Does that help?

If you like a fuller article, this one is OK, more detail.
g-force - Wikipedia, the free encyclopedia

Last edited by Lonewolf_50; 13th Jul 2011 at 18:33.

13th Jul 2011, 18:39

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lonewolf 50

thanks very much for your time sir

13th Jul 2011, 18:48

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Originally Posted by airtren
.... are the variables/parameters determining the values of the Stall Warning Threshold function and thus the shape of the curve valid, for the entire time (X) axle in the graph?
As I said, in a given configuration SWT depends only on Mach. I have explained in a recent post how Mach etc. are calculated. The calculated speeds are the speeds that the airplane physically has in the simulation, and do not reflect any erroneous or 'invalid' speed that the systems may have 'thought' the airplane had. You have to consult the BEA Note for those. The SWT shown on the graph is valid for the 'simulation' Mach.

It is not entirely clear how the system calculates SWT in the event of erroneous or invalid airspeed. BEA#2 says that the system then sets it at the low speed value of 10 degrees. But several UAS incidents show that that does not occur. Maybe we just need to have better understanding of 'erroneous' and 'invalid'. For the NCD condition it doesn't matter where SWT is, or does it?

Last edited by HazelNuts39; 13th Jul 2011 at 19:25. Reason: Last sentence added

13th Jul 2011, 18:50

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@A33Zab

Thank you for your posts #202 & 230.

I just love the way theories seem to gain momentum in the ether, only for them to be dashed by the cold FACTS.

13th Jul 2011, 18:56

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pitch moments, gee and tranducers

I welcome the "fresh blood" to the fray. Attaboy.

- Although the pitch moment chart I posted is for another aircraft, it illustrates two points ( one positive, one negative) that result in little or no pitch control authority for the existing HS/elevators/stabilators in either positive or negative direction.

My main point presenting that chart was to counter all the folks that think a deep stall is only a concern for the T-tail designs. I also wanted to show the c.g. of the Viper, and point out that under some instances the 'bus has a very aft c.g. The reduced trim drag of the main wing is reduced if we can fly with a more neutral longitudinal stability. Simple, really, as the HS doesn't have to induce a nose up moment, and can basically "float". The big savings are the reduced AoA of the main wing and associated reduced induced drag.

In my case, we had a great cruise drag reduction, but we also had the HS and the wing contributing to lift when in a turning fight. Yeah, I can just see the 'bus in a turning fight with a Sopwith Camel, heh heh. Except for the inital HS movement, our HS (stabilators) usually was "limiting" the nose up tendency. So when we got to the deep stall scenario, out HS were commanded full nose down. Turned out there was a small AoA/c.g. range that allowed the jet to settle into a classic deep stall.

- The gee and roll rate are two physical phenomena that pilots can sense instantly ( as opposed to the drone pilots at Creech AFB and other places). We tried pitch rate for the longitudinal axis, but seemed to most pilots that the gee was easier to sense and control. Rates are still involved to prevent overshoots of pitch commands and to "smooth things out" for the SLF's. No big deal.

'bus takes into account actual pitch attitude, so at a 30 deg climb angle you get a 0.87 gee command, not one gee. With a constant one gee command you would continue to pitch up once a few degrees greater than level. Because we weren't worried about the SLF's, we normally let the basic one gee trim setting alone and just manhandled the sucker. But many pilots would trim for zero gee and simply hold back pressure. Would be willing to bet that the Thunderbird slot pilot trims for slightly less than one gee, and prolly the wingies.

The Viper concept was that we flew around in something close to the 'bus "direct law", but we could never command actual physical movement of the control surfaces. Only exceptions were rolling down the runway and if we wound up in a deep stall with AoA above 30 degrees. Even then, we had no rudder control, as HAL cut us off, heh heh.

All of our "sub-laws" were due to things like gear down while airborne, special setting for carrying external ordnance and "standby gains" in case we lost air data. Interesting, that last feature, ya think?

- Our stick employed piezo-electric transducers - 4 of them for pitch and roll, Rudder pedals moved one half an inch and were linear voltage tranducers. After a few jets, we had 1/8 inch of movement and some springs or whatever could be felt. Initial jets had zero stick movement - all pressures.

As with every fighter built from the mid-fifties, there was no feedback from the control surface pressures. Some jets had bellows to provide a "stiff" stick at high speeds. Some had bobweights to help pulling too many gees too quickly. But zero actual physical feedback. The feedback was from your butt and inner ear.

13th Jul 2011, 19:00

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Hi Dozywannabe,

There has been no such thing as real "elevator feel" since the '60s, and Direct Law does not provide it.
You keep telling me that and I've tried to explain it to you before.
Would it help if I called it "sense of longitudinal speed stability"? The aircraft has it naturally by design concept.

Normal Law removes it, but adds Alpha Prot & Alpha Max.
Alternate Law removes it and has no such "protection" or "Limit".
Direct Law would restore it. Ask any conventional aircraft pilot - they would understand it.

13th Jul 2011, 19:10

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Originally Posted by BOAC
I repeat - there is NOTHING in the BEA report to tell you that the pilots caused the climb. A 'nose up' input of unspecified size or duration does NOT prove that and may well have been of short duration - you do not know.
Well, this is quite authoritatively expressed... but also quite illogical as for addressing the fact that any pilot nose-up imput (whatever duration and amplitude) could not have caused this aircraft to climb (at whatever rate, as this is likely proportional).
Considering this high speed profile, manual flight and elevators sensibility, what would be the illogical part about me mentioning that?

The BEA is providing this information about a pilot imput in the same direction as the trajectory followed by the aircraft, what would be the logic to affirm : the climb wasn't related to this imput?
Obviously, you are taking the possibility (that I'm also sharing) that this full climb rate could not have been fully achieved by pilot imput alone by translating it into "nothing in the BEA is telling us that the pilot caused the climb".

Hence, you are rhetorically jumping into the breach of us lacking the full detailed picture of this imput as making an illogical point by saying that there is absolutely no causality between a pilot imput nose up and a following climb.

For my part, I'm saying that whatever else could have been added to the climb rate (turbulences, initial pitch rate at AP off, whatever else you'll like more...), this single imput "nose-up" was certainly part of it because, of course, the system would have taken it as a commanded +x g maneuver order, translated it into pitch attitude increase and, once achieved, would maintain the trajectory in climb (1 g).
What we'll need to know is the value of "x", the resulting maneuver g-load, adding/substracting possible turbulence impact, as to verify if something else was not a factor of the climb rate achieved... which is certainly what the BEA would have to acertain before mentioning, as a fact, that climb was entirely due to pilot imput.
Saying otherwise (it was unrelated) seems fallacious.

Originally Posted by BOAC
As for your bit about "There is another way to change pitch attitude than pulling up on the sidestick as simply applying thrust could do the job if the amount is large enough." - you don't say? Now show me where the report tells you they increased thrust. You are making this up!
I'm just looking at the joined DFDR tracks of N1 % thrust and read that, when autothrust kicked off, N1 was already auto-throttled back at ~70%, then moved to 100% during the climb sequence.
You should know that thrust would freeze where it was (~70%) when autothrust disconnected; Hence, this increase was manually applied, even if not reported in the narative, which include an incoherence about "alpha-floor" kicking which is not available at such speed (inactive above Mach 0.53). This is based on AIB interpreted pilot confusion about "Alpha-lock" corrected by "Alpha-floor", while it certainly was "Thrust-lock" alarm (when ATHR disconnected).

Look by yourself if I'm making up this stuff:

Originally Posted by BOAC
Now to TC-JDN - have another look at the trace. The a/c began pitching while the engines were throttled back, the side stick did not move but the THS did.
The system will use every surface control and thrust to maintain 1g flight. Changes in THS trim were very limited during the whole sequence (much less than 0.5 deg), including a "zoom climb", "apogee", "descent"... while elevators moved in both sense with a much larger amplitude. Nonetheless, the system trimming THS seems to have not been "pitch up", but the other way as there is no such 5ND in the range of THS.

Originally Posted by BOAC
I note you come 'from Toulouse'
Right, I was there some time ago. I also note that you come from "Per Ardua ad Astraeu", but who cares?

Last edited by takata; 13th Jul 2011 at 20:04. Reason: typos

13th Jul 2011, 19:13

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syseng68k

The voluminous fcom looks to me like a user guide,...
No, it's just an insurance if something goes wrong......

13th Jul 2011, 19:27

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@syseng68k:

Question: Why are two pots unused ?.
No more computers to connect. (5 in total)

Question: What is the function of the solenoid and does that lock
the stick at any point (zero ?) in it's travel ?.
The solenoid is activated by the A/P and add's a force threshold in neutral stick to prevent any unwanted switching to manual control, while keeping
the possibility to override the A/P if required.

simple schematic of xdcrs:

13th Jul 2011, 19:27

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Originally Posted by rudderrudderrat
Normal Law removes it, but adds Alpha Prot & Alpha Max.
Alternate Law removes it and has no such "protection" or "Limit".
Direct Law would restore it. Ask any conventional aircraft pilot - they would understand it.
I've been asking a few people about it behind the scenes, but the answers I got back were too technical for me to comprehend easily (my brain has an annoying habit of shutting down when presented with algebra)... there's a pile of emails/PMs looking suspiciously at me as I type.

Let me see if I understand what you're getting at, and if I'm wrong please correct me. Prior to this I got the impression from your post that it related to the presence of autotrim - that is, when manually trimmed (with the THS at a fixed angle), the aircraft will tend to stabilise at a certain pitch angle and speed will remain more-or-less in the required ballpark. The presence of autotrim means that the THS is correcting itself based on sidestick input, and as such the trim angle is changing. In Normal Law, Alpha Prot and Alpha Max keep the trim settings within certain limits, but in Alt 2 those are not there, so there's nothing to stop the trim getting the aircraft into difficulty if the sidestick input is on the aggressive side.

Am I following you OK?

If I am, I think it's important to recognise that it takes a significant amount of input to cause the THS to get itself to such an extreme angle, and it's also important to recognise that autotrim has other benefits as well. It's pretty clear that Airbus FBW training at a basic level instructs pilots to be more careful with their sidestick inputs when law degradation has occurred. It's also worth bearing in mind that if you're in that situation and don't like what the trim is doing, all you have to do is set the manual trim as desired and avoid making large and consistent pitch inputs on the sidestick - this should cause the autotrim, when it kicks back in, to maintain a pitch angle at or near where you've just manually set it.

If I've read the "note" correctly, this isn't a case of a slight back-stick input in combination with (presumably corrective) roll input causing the THS to move to the 13deg nose-up angle in a matter of seconds, this is a case of the elevators causing the zoom climb in response to input, followed by the THS moving over the course of around a minute as repeated full or near-full backstick was held on the way down. From what I've read, THS movement from the autotrim is not particularly sensitive, nor is it likely to come into play with inadvertent sidestick deflection - the pilot *really* has to command it to be at that kind of angle for it to have got there, which is why the initial nose-down commands weren't enough to get the THS moving.

13th Jul 2011, 19:45

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Hi DozyWannabe,

You are getting closer.

It's also worth bearing in mind that if you're in that situation and don't like what the trim is doing, all you have to do is set the manual trim as desired and avoid making large and consistent pitch inputs on the sidestick
In Alternate Law, even with the stab trim wheel held stationary, longitudinal speed stability is not restored. The elevators will be held at a displaced position in order to satisfy the pitch stable law. (as in Loss of G & Y Hyds on A320, (or G & B I think on A330)). With UAS, the pilot would still not "feel" the aircraft getting slower and heavier in pitch.

13th Jul 2011, 19:49

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Hi Rudderrudderrat,
Originally Posted by Rudderrudderrat
Normal Law removes it, but adds Alpha Prot & Alpha Max.
Alternate Law removes it and has no such "protection" or "Limit".
Direct Law would restore it. Ask any conventional aircraft pilot - they would understand it.
This is not entirely true.
In Normal Law (pitch), some feedback is artificialy maintained.
In Alternate Law (pitch), same, but there is less gain and feedback.
In Alternate Law (general), Valpha_prot is changed by Vstall_warning (g sensitive) There are still speed limits and speed protections available... but, of course, only if the system still have some valid airspeed sources.
In Direct Law (pitch), feedback is direct as you said (but artificial, as electric).
In Back up Law (no power for computers), pitch is changed using the mechanical THS trim.

13th Jul 2011, 20:12

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Originally Posted by takata
Quote:
Originally Posted by BOAC
As for your bit about "There is another way to change pitch attitude than pulling up on the sidestick as simply applying thrust could do the job if the amount is large enough." - you don't say? Now show me where the report tells you they increased thrust. You are making this up!

I'm just looking at the joined DFDR tracks of N1 % thrust and read that, when autothrust kicked off, N1 was already auto-throttled back at ~70%, then moved to 100% during the climb sequence.
You should know that thrust would freeze where it was (~70%) when autothrust disconnected; Hence, this increase was manually applied, even if not reported in the narative, which include an incoherence about "alpha-floor" kicking which is not available at such speed (inactive above Mach 0.53). This is based on AIB interpreted pilot confusion about "Alpha-lock" corrected by "Alpha-floor", while it certainly was "Thrust-lock" alarm (when ATHR disconnected).
- er - my bit refers to 447, not TC-JDN..............................