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AF 447 Thread No. 5

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AF 447 Thread No. 5

Old 7th Aug 2011, 16:32
  #1741 (permalink)  
 
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Originally Posted by 3holelover View Post
Airbus will also display that on the ECAM FLT CTL page. (but you all knew that, right?)... Is the suggestion for a separate screen always displaying this?
I don't know what JD-EE intended.
The 'Icovol' was hardly a primary flight instrument, but then of course Concorde may have been FBW, but it was not a glass cockpit, so a space for it was found on the central panel.

I've refrained from commenting on the autotrim issue, because the only autotrim I know was the Concorde one.... and that was a separate computer, and an electro-mechanical actuator, that moved the neutral point (in pitch) of the stick. And autotrim also moved the manual trim wheel, with the obvious 'ping', 'ping' of the bicycle bell.

As an ancient, I'm still somewhat astonished about the lack of "feedback" from the aircraft to the pilot, which seems to have disappeared slowly....

No 'stick force', other than a side-stick spring (crikey, even MS Flight Simulator and other games now come with force-feedback joysticks).

Concorde had FBW, so no direct force feedback from rods and cables either, but it had a quite sophisticated 'artificial feel' system and I've never heard complaints about it.

No 'throttle position feedback' - on Concorde the autothrottle computer controlled an autothrottle actuator, which moved ... yes, the throttle levers themselves.

No 'bicycle bell' on the pitch trim.

Concorde of course had André Turcat..... who stuck his nose into everything, including a lot of aspects of the "pilot-aircraft interface".
For those of you who read French, read his book "Essais et Batailles" (sadly it's never been translated).

I tend to think the FBW family (A320, etc.) never had the benefit of 'ancient' pilots like him.... but I may be wrong.
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Old 7th Aug 2011, 16:33
  #1742 (permalink)  
 
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@ChristiaanJ - the A320 did in fact have Gordon Corps.

Also, MS Flight Sim provides a rough-and-ready simulation of everything from single-engined Cessnas (where feedback comes directly from the surfaces and is therefore appropriate) to the A380 (where it arguably isn't such a big deal). When the force-feedback on a computer joystick or yoke malfunctions or dies, you can hit Alt-F4, get up from your chair, go to the store and get a replacement. If force-feedback were to go wrong at 35,000ft your options are more limited.
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Old 7th Aug 2011, 16:37
  #1743 (permalink)  
 
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@Config Full:

I have a question on AOA data. The FDR records their actual values, which we get in the report. But wasn't these values fed to the ADRs, which in turn were rejected? Where did the PRIMs get the data from and how did they elect the data as correct to trigger a stall warning? (Shouldn't AOA be correlated -at least to a certain degree of incidence- with airspeed, which was unreliable?)
- The stall warning is processed in FWCs not FCPCs
- It's the ADR itself which sets AOA to 0° (SSM=NCD) if CAS is below 60 Kts.

(A. did already changed that with 'BUSS' option, AOA is always available [only SSM will be NCD if CAS <60Kts])

- In ALT/DIR LAW the AOAsw triggervalue is 10,8°, this value is modified by a value which depends on MACH (and in other flight phases by S/F Config and Speedbrake setting)
The minium AOAsw triggervalue is 3,8° @ or above M 0.82.
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Old 7th Aug 2011, 16:52
  #1744 (permalink)  
 
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Originally Posted by DozyWannabe View Post
@ChristiaanJ - the A320 did in fact have Gordon Corps.
Sorry, I know the name, but I thought he was Servanty's British counterpart. I'll do some Googling.

Also, MS Flight Sim provides a rough-and-ready simulation of everything from single-engined Cessnas (where feedback is appropriate) to the A380 (where it arguably isn't such a big deal). When the force-feedback on a computer joystick or yoke malfunctions or dies, you can hit Alt-F4, get up from your chair, go to the sotre and get a replacement. If force-feedback were to go wrong at 35,000ft your options are more limited.
I get your point.... but as I said, I can't remember any serious issues with the mechanics of the Concorde artificial feel, which was a lot more complicated than the force feedback on an MS joystick.
My point being, really, that implementing reliable force feedback on an aircraft sidestick is no more difficult than what we did over 40 years ago.
And if one 'dies', there's always the other side.....
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Old 7th Aug 2011, 17:59
  #1745 (permalink)  
 
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@DW:

Hi DW,

Quote:
he does not have the benefit Longitudinal speed stability in ALT2 Law
I'm still not sure about the argument there - the flipside is that in the case of a small-intermediate upset he has complete control of elevators and trim in one hand and can manage throttle in the other.
It depends what is understood by LLS, indeed you loose the protections but as long Nz and Nx are available there is speed stability due to thrust changes.

In fact you can see it in the 'simulated' graph in the 3rd report.

@ 00:09:14 THS 3.0° @02:10:09 THS 2.8°
@ 02:10:09 THS 2.8° thrust went down & THS moved to 3.1°
@ 02:10:30 Thrust is going up again and THS retrimmed to 2.9°
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Old 7th Aug 2011, 19:09
  #1746 (permalink)  
 
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Cool

Hi,

If force-feedback were to go wrong at 35,000ft your options are more limited.
IMHO .. it's not a way to argument for justify the non presence of an artificial feedback
If the brakes go wrong when landing your options are more limited
This can be an argument for no brakes at all ?
So .. as usual .. more we are .. more fun
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Old 7th Aug 2011, 19:11
  #1747 (permalink)  
 
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About Planes and "flying Systems" Design

We could imagine his leadership and role, to the (technical) success of the fantastic bird.

As an ancient, I'm still somewhat astonished about the lack of "feedback" from the aircraft to the pilot, which seems to have disappeared slowly....
When the crew in some machines (by design) are considered almost an accessory* to it's operation why they should invest in interfaces and feedback?

An "accessory" also convenient after "multiple design faults" allowing the publishing of "operator error" (citing lack of training, etc).

(*) Just exaggerating to express how i feel after reading AF447 published "circonstances" reports.
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Old 7th Aug 2011, 19:18
  #1748 (permalink)  
 
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THS speed rate:

I’ve got these figures of THS rate.

The THS itself (the ballscrew) is driven by 2 hydraulic (B & Y) motors.

Max. Operating Load and Max. Speed (2 motors)

18940 daN (42578.81 lbf) ----- 0.4°/s
16950 daN (38105.11 lbf) ----- 1.0°/s
6770 daN (15219.56 lbf) ---- 1.2°/s

Limit load (both compression as tension) is 32500 daN (73062.9 lbf).
I assume this limit load is mentioned as being the limit for the Hydr.
motors to drive the THS.

Half speed for 1 motor (1 hydr. B or Y system failure) operation.

The rate for the BEA mentioned 1 minute to go from 3 to 13 ANU was 10°/60 = 0.16°/s.


For going back to the 3° ANU position:
The hinges are on the trailing edge and therefore the aerodynamic
load on the drive spindle is in the AND direction it would take 12 sec. to travel from 13° back to 3° ANU.

The manual trim wheel THS displacement is ~0,65° a stroke, if one need
1s to complete the stroke and 1s to re-grab the wheel, the rate will be 0,325°/s.

All of this didn't need to be known, just a hand on the moving handwheels would have been sufficient to cancel the autotrim orders.
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Old 7th Aug 2011, 19:48
  #1749 (permalink)  
 
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active artificial feel.

I understand that the mixed mode (PITCH NZ / ROLL DIRECT ) will not be easy to handle but wasn't the idea behind Nz to use the SS more or less as a toggleswitch?
toggle NU > release > toggle ND to cancel the order?

So no need for an active artificial feel for a toggle switch.

From own experience it requires considerable force to move and keep SS to full aft and fwd stop.

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Old 7th Aug 2011, 20:27
  #1750 (permalink)  
 
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A33Zab

Could the limit load be structural? It is suspiciously similar to K/2, a common critical failure constant?

Could you clarify "toggle"? There are many types. A bump toggle would satisfy your meaning here (above)?
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Old 7th Aug 2011, 20:57
  #1751 (permalink)  
 
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A33Zab,

Let's not confuse the issue.

IIRC, the AB SS provides a 'proportional' signal, from either pots or resolvers, and NOT a 'toggle' signal like the ancient Atari joysticks (LOL).

So your graph and post may be somewhat misleading to the uninitiated....
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Old 7th Aug 2011, 21:11
  #1752 (permalink)  
 
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CJ

Thanks, that was close call. I came very close to almost understanding what he wass saying.
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Old 7th Aug 2011, 21:19
  #1753 (permalink)  
 
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@DozyWannabe.
DW, I understand your point that in ALT2 the computers are missing some handles but to lose s/w would require triple AoA sensor failure or triple ADR failure or double FWC failure (and btw the UAS check list asks to respect stall warnings) so I still cannot see in what way preventing up-trim based on s/w AoA could be harmful.
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Old 7th Aug 2011, 21:26
  #1754 (permalink)  
 
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Test pilots

PuraVida post # 1726

Perfect analysis! Totally agree.
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Old 7th Aug 2011, 21:43
  #1755 (permalink)  
 
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@ChristiaanJ:

Let's not confuse the issue.


IMO a non A. FBW and even the FBW insiders are already confused.

Sometimes a simplified approach can explain a lot i.s.o. confuse.

I know there are potmeters involved (hey, did post the SS diagram myself)

BTW, the graph is from A330 FCTM...surely not intended to confuse the Flight Crew.

The related text:


As the flight mode is always aiming to achieve the selected flight path, avoid the
temptation to over-control. The recommended method to avoid over-controlling is
to make a small sidestick input, hold for a short period and then return the

sidestick to neutral. Even in turbulent conditions, the control law resists the

disturbances well without pilot inputs. The pilot should try to limit his control
inputs to that necessary to correct the flight path trajectory and leave the task of
countering air disturbances to the flight control system. If the pilot senses an
over-control, the sidestick should be released.
In climb, cruise, descent and approach, all these basic rules remain in effect.





How much time was the SS released to give the flight control system the
opportunity to stabilize the upset?




Last edited by A33Zab; 7th Aug 2011 at 23:39.
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Old 7th Aug 2011, 21:58
  #1756 (permalink)  
 
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Trimming Is Not Hard

Dozy:
Fair enough, that's your opinion - but have you ever actually flown a FBW Airbus? Plenty that have state that the autotrim is completely unobtrusive when hand-flying and that the aircraft as a whole handles rather well.
No, I have not flown an airbus. My problem with autotrim when hand flying any aircraft is that I may not want it to follow my control inputs. Unfortunately, this crew seems not to have known anything about trim. Maybe having the trim announce to the crew that it is moving would have been a wake-up call and someone would have said, "oops we don't want that," but I doubt it. It certainly would have got my attention. Sadly, the men seated in the cockpit were completely out of their element.

Quote:
You have stated that there are good and sufficient reasons for the design of the software in the hand-flying mode, but AFAIK you have not offered any reasons why that design is preferable to my reasons for disconnecting autotrim when hand-flying.
In fact I did, but it's several threads back - one of the reasons was the ability to have hands on throttle and stick in a pilot incapacitation scenario.
Pilot incapacitation is not much of an issue in a multi-seat cockpit. Trimming is not difficult and, for a pilot worthy of being called a pilot, it is a natural activity which is so routine that it is done almost unconsciously. I have flown aircraft with the pitch trim on the yoke, on the stick, and on the console. I never found it a burden to activate any of them. I prefer it on the stick or yoke since that does free up the other hand, but the difference is really not material. What I don't want is having the system changing the trim when I want to remain trimmed for a particular speed or AoA. In the case of AF447, the system gave up and turned it over to the people seated in the cockpit, except they didn't turn over everything and I believe that situation makes it more difficult to hand-fly. Autotrim has its place, but not in my cockpit when I am trying to hand-fly.
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Old 8th Aug 2011, 01:18
  #1757 (permalink)  
 
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airtren, you can lose lift without stalling.

Try it sometime.

Fly along with your flaps down. Then, raise the flaps. You'll lose lift, but you don't necessarily stall. You'll probably also descend, if you were flying level previous to the flap raising, unless you take the time to also add power ...
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Old 8th Aug 2011, 02:24
  #1758 (permalink)  
 
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You only lose lift if you maintain attitude. If you pitch up with flap retraction you maintain the same lift until you stall.
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Old 8th Aug 2011, 13:25
  #1759 (permalink)  
 
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Originally Posted by ChristiaanJ View Post
I get your point.... but as I said, I can't remember any serious issues with the mechanics of the Concorde artificial feel, which was a lot more complicated than the force feedback on an MS joystick.
My point being, really, that implementing reliable force feedback on an aircraft sidestick is no more difficult than what we did over 40 years ago.
And if one 'dies', there's always the other side.....
Did the artificial feel include airspeed as input ? - intuitively I feel it must do (and I believe B777 does), but deltas are very different so maybe it wasn't needed ?

If so, what did the system use in the event of uAS ?

On a vaguely related note, did Concorde ever suffer from pitot icing / similar uAS or at FL60+ was it simply not a problem ?
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Old 8th Aug 2011, 14:10
  #1760 (permalink)  
 
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Originally Posted by DJ77 View Post
@DozyWannabe.
DW, I understand your point that in ALT2 the computers are missing some handles but to lose s/w would require triple AoA sensor failure or triple ADR failure or double FWC failure (and btw the UAS check list asks to respect stall warnings) so I still cannot see in what way preventing up-trim based on s/w AoA could be harmful.
S/W can be spurious, particularly in uAS, but also, I believe, with one AOA broken (it would be outvoted by the other two for the PRIMS, but would still trigger SW - think Perpignan but other way round).

Stall warning is a warning to the pilots to asses the situtation and take action. It is not a certainty based on which the plane itself should take action or restrict the pilots action - the FBW Bus has all that in normal law, but if you get as far as s/w then this has already failed. Or in other words, if you get a s/w on a bus, the plane is already uncertain of its data.

The logic running through is that automation doesn't act (or restrict pilot actions) on known-bad data - but it may still warn pilots. Sadly in this case, I think the pilots believed the stall warning to be spurious due to uAS, and possibly believed they were overspeed and acted to correct that instead.
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