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AF 447 Thread No. 5

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AF 447 Thread No. 5

Old 12th Jul 2011, 21:09
  #181 (permalink)  
 
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"Upwards" to the tail is the opposite of UP to the wing
Maybe in your world, not in mine. If you start mixing definitions according to what part of the aircraft you are talking about you can get confused very quickly!

Positive lift is upwards (anywhere) positive attitude is nose up, positive angle of attack is nose up, positive THS setting is nose up, positive elevator is TE down (i.e. nose up) etc.
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Old 12th Jul 2011, 21:13
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Originally Posted by bearfoil
"Upwards" to the tail is the opposite of UP to the wing. Its camber is on the bottom surface, no?
Bear, do you have any aeronautical engineering background at all? Your statement/question seems to indicate you don't.
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Old 12th Jul 2011, 21:14
  #183 (permalink)  
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So.. if the tail falls off, the a/c climbs?

It seems to me that rather than trying to find fault with others, and instead donated some knowledge to the thread in one's specialty, one could help everyone in their desire for understanding.

I have never been accused of being an engineer, they do most everything by proxy.


let's see, press tail down for up.........

Last edited by bearfoil; 12th Jul 2011 at 21:29.
 
Old 12th Jul 2011, 21:33
  #184 (permalink)  
 
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Hi PJ2,
Originally Posted by PJ2
If the A330's sidesticks are the same as the A320's, the fore-and-aft movement is +/-20, the lateral movement +/- 25...
A330 sidestick travel limits are : +/-16 in pitch, +/-20 in roll.
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Old 12th Jul 2011, 21:34
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So.. if the tail falls off, the a/c climbs?
Now you are just being silly!

It seems to me that rather than trying to find fault with others, instead of donating some knowledge to the thread in one's specialty one could help everyone in their desire for understanding.
I thought that was what I was trying to do, but when the response one gets is similar to that above it seems hardly worth while
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Old 12th Jul 2011, 21:45
  #186 (permalink)  
 
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With the ongoing debate over the when, why and how of the initial climb, perhaps a few links to graphics posted earlier may help you all with your musings. If you are using a decent tabbed browser, e.g. Firefox, Chrome or Opera, then opening each link will open it in a new window. This will allow for easily jumping between the thread tab and the reference graphic tab.

Descent Angle of Attack Values

THS - Configuration plus Elevator NU/ND


Initial Stall Analysis - small


Initial Stall Analysis - large


The salient points named in the BEA Note were left off for clarity but can be added if you think they will be helpful.

Why not just leave the BEA Note open in another tab for easy reference.

Last edited by mm43; 12th Jul 2011 at 22:21.
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Old 12th Jul 2011, 21:45
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Thanks Owain,

Your explanation makes sense.
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Old 12th Jul 2011, 21:51
  #188 (permalink)  
 
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how "stable" is "stable flight" in "turbulent air"

Several posters made reference to "stable/level flight" before AF 447 "a/p disconnect"....

If my understanding is correct, for the same trajectory, the controls/adjustments performed by the "a/p" during a flight through "turbulent air" are quite different in certain aspects, from those made during a flight through "non-turbulent air".

Assuming a straight line "overall" trajectory:

a) in "non-turbulent air", the flight is "a straight line", with almost an "inertial", no significant controls/actions from the "a/p".

b) while in "turbulent air", the trajectory under the effect of the turbulences is a concatenation of a sequence of "up" "down", "left" "right" "level" segments, with a distribution as a consequence of the "a/p controls" of "up/down", "down/up", "right/left", "left/right", and "level" in between, which is at best ONLY an "approximation" of "a straight line", and thus of course NOT "a straight line".

The segments are shorter, or longer, depending on the degree of turbulence, and "a/p actions".

In terms of actions, the "a/p" "actions/controls" continuously try to counter the "up", "down", "left", "right" a/c motion driven by the turbulence, in an attempt to keep the flight level/straight.

It seems clear that before the "a/p disconnect" the "a/c" was in "turbulent air".

The trajectory the "a/c" followed immediately after the "a/p disconnect" depends on which type of segment and which position were the control surfaces of the "a/c" at the very moment of the "a/p disconnect".

My understanding is that the "a/c" would continue "level" under inertia and position of control surfaces as left after the "a/p disconnect", ONLY and ONLY if the "a/c" were on a "level" segment.

But the probability of being on a "level" segment is 1/5, which is 20%, which is quite low (maximum probability is 100%).

The probability of being on a "NON-level" segment - "up" or "down" or "left" or "right" - is 4/5, that is 80%. That is quite high!!!
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Old 12th Jul 2011, 21:58
  #189 (permalink)  
 
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Stall Warning curve in posted graphs

mm43:

> With the ongoing debate over the when,....


Illustrative graphs - thanks!

Question: it is unclear what the "Stall Warning" curve is. Would you please clarify? Thanks in advance.

It seems obvious it is not the "Stall Warning" message given to the pilots, as that was, afaik, not permanent/continuous.
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Old 12th Jul 2011, 22:03
  #190 (permalink)  
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Hello Garage Years. Script is an unfortunate term. It infers a drama, a fiction, something crafted from whole cloth by someone to gain interest or commercial advantage. Wait..........wasn't AB pleased to trumpet it?

It is simply not possible to know where the NU part of RL derived. In not giving up some data, by way of explanation, BEA have encouraged a result not in evidence. Or, it could be treated as you did, absence of evidence is evidence of absence. I choose to assume the input was correct as stated, and derived as one would who had some confidence in the PF. You choose another way, variety is the spice of........

Take your pick, both are conjecture. Do you not see this? OR, in seeing it, do you choose to ignore/deny it?

Can you try playing the Ball, and not the Player? Your emoticons are starting to fade from exposure to the ether.
 
Old 12th Jul 2011, 22:10
  #191 (permalink)  
 
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Thanks

Gums #179

Thanks for that pitching moment graphic, I had it in my head, of course, but didn't have a physical copy of it anymore.
For people who can interpret such a graph, it is extremely enlightening, but of course, they must be able to appreciate the differences between an F-16 and an A-330 to get to the right conclusions.

Thanks again for the picture.
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Old 12th Jul 2011, 22:18
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Originany posted by Owain Glyndwr about the downwash angle:

A ballpark range for this would be between 0.4 and 0.5 times body AoA.
Ordinarily, the downwash angle at the tail is related to the lift coefficient more than to the wing/body AoA. Would your values be more specific to a stalled swept wing?

PS: Welcome aboard!
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Old 12th Jul 2011, 22:19
  #193 (permalink)  
 
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Bear is correct about the airfoil of the horizontal stabilizer causing downward thrust making the aircraft stable. Soon after the Wright Flyer this was incorporated into most aircraft. Using the term upward lift confuses the issue because an increase of airspeed in stable flight will cause a downward force on the horizontal stabilizer bringing the nose up to stable flight. This negative lift or what ever you want to call it requires the wing to supply more lift to compensate for that effective extra weight.

Airbus used fuel transfer to get the CG as far aft as possible to eliminate some of the effective weight the wings had to carry. I have seen race planes lose their tails and they immediately dive into the ground because of the loss of down force on the tail.
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Old 12th Jul 2011, 22:20
  #194 (permalink)  
 
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Bear, all this is fun, but we have a 'limited' (and on that I think we agree) set of data that BEA have deigned to bestow upon us - clearly it is not the full story, CVR or flight data wise, but I think we can be pretty confident that the important stuff is in there. Or do you think they are holding back on some surprise? Otherwise all hell breaks loose when they DO release the rest.

I used the word "script" with purpose, because so far that is all we have - in my world a script is used to instigate a more complex set of actions "below the surface". So I meant that we have the keywords, the triggers if you like, those things that the BEA fell worth reporting at the top level, without which presumably this accident would not have occurred. There may be other less significant issues that were not so evident from a couple of weeks of looking at the CVR/FDR, but will there be great revelations from here on out....? Somehow I think all we will see is joining the dots, and those are to the majority already in front of us. That is my position. Yours appears to one that needs many other dots, simply because you don't like the picture. Your musing don't seem to achieve much aside divert useful thought on the information that is known.

Last edited by Jetdriver; 12th Jul 2011 at 23:48.
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Old 12th Jul 2011, 22:22
  #195 (permalink)  
 
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Hi BOAC,
Originally Posted by BOAC
Do we have any idea of the 'g' required for this pitch up into the climb? I see 1.75g quoted as an over-speed FCS 'increase' in applied PF input. Are we close?
Assuming that this aircraft overshoot Mach 0.86 (Normal Law), after an overspeed warning, with speed still increasing, an overspeed protection could have been ordered by the FMGC and could have added up to 1.75 g pitch load while disconnecting the autopilot, hence, this would happen at 0210:05.

The main issue with such case is that the BEA/AIB/NTSB/etc. would perfectly know it from the beginning, right after the first CVR (warnings) and DFDR tracks (speed, etc.) lectures ; then they will voluntarily hide that to us...

Another issue is that it doesn't fit either with all the known flight conditions (~Mach 0.81 = 275 kt), neither with all the known (and clearly acertained) system faults at 0210:05 which are all linked with an Unreliable Airspeed event.

In fact, there is not a single doubt that this aircraft entered ALTERNATE 2 at 0210:05, right after an UAS check took place during the previous second (airspeed incoherence detected). It is acertained that the system confirmed the already applied ALT2 ten seconds later -> 0210:14/15; hence, it is also proved that it was not a transient fault, meaning that NORMAL LAW was lost for the remainder of the flight.

Consequently, from 0210:05, autopilot, autothrust, several systems/functions, and all the flight envelope protections were lost, excepted the envelope g-load factor protection that will limit the PF imputs into the range of -1 g to 2.5 g in clean configuration.

Last edited by takata; 13th Jul 2011 at 01:10.
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Old 12th Jul 2011, 22:35
  #196 (permalink)  
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thanks bub.

Fuel cheat was a hidden art in the olden days, when wings were fat and safety came first. At the outset, if the chief found you squirreling fuel away aft of cg you caught Hell. Then the beanbags caught on, even that long ago, when fuel saved was minute, they said "hold on, what's this tail loading thang"

Whether negative lift or no, I always looked at it as a drag nullifier. To load the tail aft means some of net lift to carry the a/c is shifted to the tail. A heavy tail, carrying some weight, "flies" with less induced drag, which instead converts to lift, to obvious advantage in fuel savings. win/win, except when you lose. And when the cg is too far aft, to lose is to die.

This is from a non-engineer, maybe I should drag it across Chris' desk before posting.....

not now, nor have I ever been an engineer. Quick question for

takata. You say PF input is limited to 2.5 g with inertially derived g envelope prot in ALT 2. Is that separate from what the a/c will bear, or a total. As in. the Pilot can not ask for/get more than 2.5g? Does the a/c compute a "g" at all in AL2? Except for its limits? G is not "damped"?
 
Old 12th Jul 2011, 22:40
  #197 (permalink)  
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Thanks very much takata, IIRC those are familiar numbers from the A320 as well...how quickly one forgets. PJ
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Old 12th Jul 2011, 22:42
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Originally Posted by airtren
The trajectory the "a/c" followed immediately after the "a/p disconnect" depends on which type of segment and which position were the control surfaces of the "a/c" at the very moment of the "a/p disconnect".

My understanding is that the "a/c" would continue "level" under inertia and position of control surfaces as left after the "a/p disconnect", ONLY and ONLY if the "a/c" were on a "level" segment.
The Question is not so much what the positon of the control surface are upon AP disconnect but rather how the change from Roll Normal Law (Rate command) to Roll Direct Law (Deflection) is handled in that regard. I haven't found any reference to that but would assume that control surfaces return to normal at that point.
If Roll Normal Law was compensating for a constant Air Mass movement (vertical? lateral?) that could lead to a certain amount of roll in that case.
Anyone here knowing how this is done exactly?
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Old 12th Jul 2011, 22:45
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recover from stall.

IMO there was an escape from this stall but it did require the THS.

From the events (BAE) and *not official* but excellent calculations by HN39, the A/C needed TOGA + Full Elevator Up + THS 6 (ANU) to increase the pitch from 6 to 15.
More THS (ANU) travel didn't had any influence on the pitch axis, it seems to be stabilised at this value.

Later in the sequence (after 2:12:00), engines at idle '55% N1' + THS in 13 (ANU) the brief ND elevator input reduced the pitch to ~ 5 (ANU).
thereafter pitch went to stabilize @ 15 again.

With a travel of 15 THS (13 + 2) available and the ND elevator authority (10 Pitch AND in this stalled situation) it should be theoretically possible to get the nose down and regain speed.

But then again, I do most 'everything' by 'proxy'.

@mm43:

It's a pity this is not visible in your very enlighten graph, would it be possible to extend the timeframe to 02:13:00 at the least?

Last edited by Jetdriver; 12th Jul 2011 at 23:49.
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Old 12th Jul 2011, 22:58
  #200 (permalink)  
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A33Zab

Just a poor jab, Sir. Not meant in malice at all.

takata has entered into the log the g envelope protection which is the "only" protection left in AL2 (?).

So the same question to you sir. Is this Limit actively monitored by the accels? And if so, when the a/c reached her zenith (perhaps even more than -1), would the a/c activate NU to regain some g? IOW, if essentially weightless for a short time, would 447 runup the THS to gain some "G"?

Hope it is not a stupid question. If any, what would be PF's authority over such a command by the a/c?
 

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