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AF 447 Search to resume

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AF 447 Search to resume

Old 2nd Sep 2010, 18:13
  #2101 (permalink)  
 
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Originally Posted by bearfoil
HazelNuts39, do you see how the stated numbers in certification can be very "soft"?
bearfoil; I'm entirely happy with the conclusion of a long debate.
regards,
HN39
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Old 2nd Sep 2010, 18:16
  #2102 (permalink)  
 
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Hazel....

Ahhhhhh... music to our collective ears!

Thank you, thank you, thank you.

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Old 2nd Sep 2010, 20:13
  #2103 (permalink)  
 
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PBL
I am not encouraged ..... when I read of "Volumetric Area" in m^3 or "Force" given the dimensions of m.kg/sec (this is equally treated as a statement of energy where it actually has the dimensions of momentum)
Yes, and yes again, I should have been more careful with my words. Volume would have done nicely and likewise moment.

Old Engineer; Bearfoil; HazelNuts39 and others

Thanks to OE for a well thought-out description on the function of Arm 36g and the manner in which it failed. I look forward [along with I suspect others] to the notes associated with OE's summary of its failure in due course.

Cheers
mm43

Last edited by mm43; 3rd Sep 2010 at 01:04.
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Old 2nd Sep 2010, 20:15
  #2104 (permalink)  
 
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Yes! Thank you Old Engineer for your instruction and clarity about how the VS likely departed the aircraft. As with Grizzled, HN39, bearfoil, mm43, Finn47 and probably many others I, too, would love to see your detailed description. If as you say it's too large for a post on the thread, I could create a PDF file and post a link to it, if you would PM me the source.

The discourse here has sprung back to reason and reasonableness. Aaaah, relief. Only if BEA/France does NOT announce a Phase 4 search in the coming days will this thread become shrill again, if not bitter. My opinion: the CVR and FDR from AF447 are orders of magnitude more valuable to us than a few still-corked bottles of 1898 vintage Champagne lying in the Titanic's muddy debris field. Standing by...

GB
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Old 3rd Sep 2010, 00:58
  #2105 (permalink)  
 
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GB- I fear the thirst for information for all of us will go and remain unsatisfied if we expect the BEA to provide the libation we seek. Thus I humbly suggest that we will be seeking other sources for a likely explanation, probably one which in one way or another has already been offered. I hope that my previously stated suspicious will be proven incorrect, however, like you, and this is now September, standing by.
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Old 3rd Sep 2010, 08:00
  #2106 (permalink)  
 
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Comments--"Arm 36g": Implications for separation of VS

I appreciate the thanks for my study of the forces surrounding the failure of "arm 36g". Perhaps it is more a case of being glad that I was able to put together a written summary that was actually understandable. In any case the effort to do so really focused the mind.

At the time, I just concentrated on the one piece-- the aluminum arm and the immediate area around it. Its failure could be analysed without going into a lot of speculation. Well, the answer or endpoint of any analysis had to be that it broke at the bolt hole. And then a picture of the break turned up (meaning one clear enough to see almost the exact starting point of the crack). And after I'd helped the cause by having only one of the two bars break, someone commented that's exactly what had happened (while I was still checking the spelling).

By helping the cause, I mean finding the least amount of force that would explain why a part broke. Today I browsed around a bit in the qestion of how much force it would take to remove the VS. I looked at HN39's calculations and his sketch of the dimensions of the anchorage points. He is right-- the static pull to get it tumbling forward is 66 g's, perhaps even more.

That was a problem to him. It is a force that seems too high for the small damage seen to some debris. I have myself been reluctant to disagree with Bearfoil's instinct that there had to have been some damage at altitude, to the VS.

The only way that reasonably low forces (low to my mind, anyway) can remove the VS at water level is if there was prior damage to the aftmost anchorage area of the VS, making both clevises ineffective. Damage in this area is up in the carbon-composite. I think side loading from torque about the vertical axis of the fin would fit the bill here. Torque is caused by rudder action.

If that is the case, VS separation at water level could be accomplished by a forward deceleration of 16 g's, applied as an impact force to the forward four attachment points. That's kind of a nominal minimum; perhaps 16-20 is a better way to express that.

With this deceleration, the "arm 36" will have an upward lift of 10 g's required of it by the departing VS. Otherwise, if the VS attachments were undamaged at water contact, the force at "arm 36" would have been 40 g's upward. With this force, both of the pair of aluminum bars would have broken and we would be seeing a lot more damage in this area.

So the study of the aluminum bar fracture, after reflection on the total picture today, seems to compel the conclusion that the damage at the bottom rear of the VS, in the carbon-composite, had to have occurred at altitude, prior to water entry.

That is, in my previous sequence of events in the loss of the VS-- "a, b thru f"-- "a" occurred at altitude and due to side loading, likely torsional; and only "b thru F" occurred after water contact.

I appreciate the offer of help in placing some of my notes offline to save bandwidth. There is some background material on my work with fiber-composites that is more general than specific.

OE
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Old 3rd Sep 2010, 10:23
  #2107 (permalink)  
 
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old engineer, many thanks for your last 2 very informative postings, they now form for me and i am sure many others a very clear picture of just how the VS separated, and i am now in the camp with those that believe it did so on impact with the ocean. I wonder with your computational is it possible to calculate trajectory?
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Old 3rd Sep 2010, 15:24
  #2108 (permalink)  
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Old Engineer

I for one am immensely satisfied with your reasons for VS failure. I caution others not to rely too heavily on instinct, (though I may have!) It is invaluable if used appropriately. I found my inability to complete the picture frustrating, it is a bit embarrassing I took what may have appeared to be an "All or Nothing" position. I consider it less likely the assembly separated at altitude.

There is a caveat, naturally. Although the water impact is easier to "picture" as of now, there are two things. One, the Arm36 tip may have departed at altitude, if the Rudder was subject to emphatic Torsional Reversals, (perhaps even flutter). Two, to ennable the great load required to "flyaway" the VS, (diminished somewhat by your work),

Hazelnut's
figures and intuition remain, and I believe the sudden Horizontal cease of motion was ennabled by the sinking of the Nose, at the end of the "S" curve I propose is the profile of the CG from tail impact to cessation of motion (absent the final buoyancy sequence).

Let's not forget that the tip may not have been present on the a/c at Take-off. A night Walkaround would have spotted it, perhaps, then again...

bear
 
Old 3rd Sep 2010, 21:57
  #2109 (permalink)  
 
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Old Engineer wrote:-
So the study of the aluminum bar fracture, after reflection on the total picture today, seems to compel the conclusion that the damage at the bottom rear of the VS, in the carbon-composite, had to have occurred at altitude, prior to water entry.
... and

Bearfoil wrote:-
Although the water impact is easier to "picture" as of now, there are two things. One, the Arm36 tip may have departed at altitude, if the Rudder was subject to emphatic Torsional Reversals, (perhaps even flutter).
Which leads to:-
  1. How might have damage to the bottom area of the rudder occurred at altitude?
  2. Does the RTLU WNG at the beginning of the ACARS sequence have some relevance?
In the case of (1); vortex flutter due to an overspeed excursion could be possible? My eyes tend to tell me that the damage has both horizontal and vertical components??

In relation to (2); I am not sure that a RTLU WNG will normally be created on change from Normal to Alternate Law. Maybe someone with SIM experience of that situation can offer the answer. I have previously posited that the rudder must have been "booted" for the RTLU WNG to have been generated.

Old Engineer
's analysis of Arm 36g, its relationship with the rudder and the V/S, along with the impact separation sequence of the V/S has been extremely helpful. The new task (IMO) is to try and determine what if any airborne events were culpable along with the impact damage described by the BEA.

mm43
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Old 3rd Sep 2010, 22:53
  #2110 (permalink)  
 
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Old Engineer:

First of all: Really Great Work !!!

I have a careful question regarding:
I browsed around a bit in the qestion of how much force it would take to remove the VS. I looked at HN39's calculations and his sketch of the dimensions of the anchorage points. He is right-- the static pull to get it tumbling forward is 66 g's, perhaps even more.
Do you think the weakening of the mounting structure could have also happened by simply impacting the water with the tailcone first?
In other words: could it be possible that the supporting structure was damaged first by the impact and only then the VS departed ?

I'm alway a fan of simple explanations, although sometimes reality takes a more complex path...
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Old 4th Sep 2010, 00:32
  #2111 (permalink)  
 
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OE, I still have in mind a severe tail strike situation.

I'm an EE not an ME so I could easily be all wet here. But I envision that the overall tail section design would be such that the pressure vessel would not be ripped open with a very severe tail strike. I figure it would break just aft of the cabin's end leaving the pressure vessel intact not spilling cargo. If that is the case, the stringers on the bottom break leading to a bending moment somewhere up among the clevis joints. The scenario I have in mind does not use acceleration to pull anything loose, it uses simple static stretch on the clevis joints with the front and rear of the VS as the pressure points and the clevis pins all going into varying degrees of tension. That would produce the damage to the nose of the VS that is very visible. I imagine it should have produced a characteristic damage to the rear of the VS as well.

Can that work into your analysis? And did the break on "36g" come with the force in the right direction to even entertain a scenario like the above?

(I am envisioning an attack angle closer to 10 to 20 degrees as the plan hits the water. But the wave effects might have been enough to do the trick even at 5 degrees.)
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Old 4th Sep 2010, 08:58
  #2112 (permalink)  
 
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In the answers offered to questions today (well, yesterday now), I just wanted to preface generally that I've formed a scenario of known failure events combined with the forces necessary to cause them. As I came across more clearer pictures, I had more events and had in part to modify the scenario.

My following answers or comments on the questions raised are based on making the my answer fit the scenario I put together as it now stands, slightly different from 2 days ago. If I had to change the scenario thinking again tomorrow, my answers now might wind up somewhat off the mark.

bia botal

By trajectory, I assume you must mean the angle of descent into the water just prior to contacting the water itself. I would have to say no, other than that the wings were approximately level. I had originally accepted per Report #2 that the rudder had pulled the arm downward in breaking it; only I thought the force was less. It was only when I saw that the arm(s) had pulled up on the rudder, in a later more clear picture, that I realized the break could not be the indicator of vertical deceleration on hitting the water. So any trajectory would fit, up to the point of being so steep as to cause 10 g's of vertical deceleration.

bearfoil

Yes, you are right that I am assuming that the break in "arm 36" is a fresh break. Which is to assume that the investigators did look for that, could confirm it, and would not have pointed to the break as evidence otherwise. But they didn't say that in so many words; instead they said their paragraph (I imply this from the preface) could now be put in final form. The things omitted from these reports make it awkward for the outsider.

mm43

1. It does not matter where this damage occurred.* It does matter that the damage to the fin at the rear attachments occurred at altitude.* It may matter that the rudder continued to work (the report said that it was stop-limited to 7.9 deg. IIRC) if the posited upset was such that the rudder was required to exit from it.

2. I suspect the WNG does have some significance. There has been some discussion. I had to deal with control systems and their reliability to some extent; all I can add is to say that fully testing a system with multiple states and inputs rapidly becomes very difficult. That is because each input or state increases a factorial parameter for tests. This factoral is equal to the number of machine states; plus the number of inputs, taken once for each of their individual states; plus who knows what for comparing 3 computers. Factorals increase very rapidly.

One could assume that WNG has occurred because the rudder lock has moved to not be at its most restrictive limit; and has done that at a time when the computers cannot know if speed and altitude permit that position. Obviously if fin damage at altitude is required,* it may be explained by excess rudder travel being available.

In your paragraph following these items: Flutter-- Normally one would like to have all the operating regime below the onset of flutter, analogous to the design of engine crankshafts in regard to torsional vibrations. But I have no idea what the margin is, or how it is affected by the variable configurations and attitudes of the airframe. Damage-- Agree; my eyes see lateral shift damage on one side, and tension damage on the other, both up in the carbon-composite area; and that the VS composite shell overall has not retained any obvious premanent distortion from the forces that caused this damage.

henra

I think that the scenario* I proposed is not compatible with more than 10 g's downward impact, because then the aluminum rod have broken before the VS broke loose, by the downward pull of the rudder, leading to a deformation of the standoffs different from that seen. I also am also uncomfortable imputing damage to this robust tailcone area from underneath by a slapping impact, seeing the minor damage to the recovered rack of flimsy cubicles.

JD-EE

Your suggestion of the lower longerons in the tailcone being broken by the pull of the VS fin on the attachment points, with resultant release of those points is interesting. There may be a substantial wedging action there. I don't see any conflict there with the senario I am using, which only requires that the pull from the fin pulls the attachment clevises loose.

My scenario* would only limit the attack angle such that the impact at the tail would not exceed 10 g's.

*Note for all comments: Means "scenario" as described in the second paragraph. That is, possible but not necessarily what actually happened. Omitting to qoute the question immediately above my comment or answer (to save bandwidth) is, on rereading, a little awkward in 2 or 3 spots. But the questions are right above in order on the same page & I am too tired to re-do the post.

OE
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Old 4th Sep 2010, 12:31
  #2113 (permalink)  
 
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Flutter-- Normally one would like to have all the operating regime below the onset of flutter, analogous to the design of engine crankshafts in regard to torsional vibrations.
A moot point maybe, but possibly a bad analogy in this context - engine crankshafts usually run through their torsional vibration speeds, sometimes work near their 2nd harmonic (I think!). Torsional dampers (metalastic bushed pulley wheels etc) control their worst effects on NVH and crank fatigue life.

The crank is simply made strong and stiff enough to have a sufficient fatigue life - one 4-cyl in-line engine I knew well had an easily recognised resonance at 5500 rpm, smoothing beautifully above that. Overdrives would in the early days help one avoid sitting at that rpm, their use often being ascribed solely to reducing fuel conusmption

Whereas as you say, flutter speds have to be a known margin above placarded safety speeds.

====

Thanks for your analysis OE... it might be worth reflecting that the VS could well have been the one major component that had no counter-balancing drag (hydraulic) to it's forward inertial forces under this hypothesis - sticking up high as it does?

Last edited by HarryMann; 4th Sep 2010 at 12:42.
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Old 4th Sep 2010, 13:48
  #2114 (permalink)  
 
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Originally Posted by bearfoil
Machaca; First, Sir, let me catch my breath. That pic is exquisite. (...) How is this wonder accepted by the Fuselage?
Some readers may not be aware that the A400M has a large rear-loading cargo door, and it is shown here:
A400M Cargo hold

Originally Posted by henra
... could it be possible that the supporting structure was damaged first by the impact and only then the VS departed ?
In my imagination the impact can be divided in two phases: vertical, then horizontal. The rear fuselage has just the perfect shape for minimizing resistance to forward motion, and hence impact forces are initially mostly vertical, pushing the light tailcone aft of frame 91 upwards against the rudder, crushing the rear fuselage structure while pushing the V/S upwards, causing the vertical acceleration that breaks arm 36g, and causing the fuselage break-up illustrated in mm43's #2067. Then large horizontal forces get into the act, as the water hits the blunt face of wing center section, engines, and wing, and rushes at high speed into rear freight hold and cabin open at the front.

BEA concludes from examination of the V/S that it separated in a forward motion relative to the fuselage. The frames were bent backwards, assembly 86-87 was slammed backwards against the V/S root rib, breaking the lateral load pick-ups in compression, and assembly 84-85 slammed backwards and broke its pick-ups in tension. Finally 86-87 was slammed forward against 84-85.

regards,
HN39

EDIT:: From BEA#2:
1.12.3.5.6 Examination of the fuselage parts (remains of the skin, frames and web frames)
The fuselage was sheared along the frames and centre and aft attachment lugs by loads applied bottom-upwards.

Last edited by HazelNuts39; 4th Sep 2010 at 22:47.
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Old 4th Sep 2010, 16:03
  #2115 (permalink)  
 
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Old engineer;

Thank you for your extensive and elucidating analysis. There are however a few details that I don't fully understand. For example:
The only way that reasonably low forces (low to my mind, anyway) can remove the VS at water level is if there was prior damage to the aftmost anchorage area of the VS, making both clevises ineffective. Damage in this area is up in the carbon-composite.
Could you perhaps elaborate on this? The mid and rear attachments were all recovered with the V/S and no damage to the carbon-composite parts was reported (*). The only damage to composite parts was in the back-up structure of the front attachments which separated from the V/S and presumably remained attached to the fuselage.

regards,
HN39
EDIT:: (*) Except the damage caused by the rearward rotation of the frame assemblies.

Last edited by HazelNuts39; 4th Sep 2010 at 17:20.
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Old 4th Sep 2010, 17:49
  #2116 (permalink)  
 
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, and hence impact forces are initially mostly vertical, pushing the light tailcone aft of frame 91 upwards against the rudder, crushing the rear fuselage structure while pushing the V/S upwards, causing the vertical acceleration that breaks arm 36g,
HazelNuts,
that's exactly the scenario that crossed my mind as well.

OldEngineer:
I was thinking that maybe the tip of the tailcone hit first, starting to cause damage to the cone especially when the HS starts to enter the water and the vertical drag in the water increasing enourmously, basically rupturing the entire tail structure.
In case of the middle and aft mounts it was the supporting structure that broke and not the clevisses. Maybe the aluminum structures surrounding the massive mounts had already been weakened by these forces.
That was my idea how the VS could have broken loose at a rather low decelleartion.
This sceanrio could also fit with the deformations of the frames in the tail (which seemed to show longitudinal compression in the upper parts) described by BEA, if I understood their description of the damage patterns correctly.
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Old 5th Sep 2010, 00:31
  #2117 (permalink)  
 
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HN39, keep in mind that once the fuselage cracks open OR the elevators hit the water drag goes up astronomically. That would tend to further rip things apart as well as bend the tail feathers upwards violently. Now that I think on that visualization I am not sure the tears in the clevis joints would match what is seen on the recovered VS.

I still think it is worth considering. It IS a way to impart a huge upwards force on the joints and perhaps on the rudder itself depending on its position at impact.
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Old 6th Sep 2010, 00:47
  #2118 (permalink)  
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mm43 I believe the a/c was in Aternate Law almost immediately, and #II at that. RTLU is auto at reversion, and will not release more sweep until Flaps/slats aiui. It also is not possible to reacquire Normal Law until landing and re program. A complete failure of all tail components is entertained at impact. Consider the Crew Rest capsule. (treated below) If sufficiently left un snubbed by hydraulics, Rudder flutter could happen at almost any speed above the Stall. The definition of flutter would be strained at lower speeds, consider for now that the Rudder "vibrated" rapidly from max. aero pressure then back again.

JD-EE The "tail breaking just aft of the cabin's end, leaving intact the pressure vessel". The vessel is quite strong in resisting higher pressure inside. Failure would involve failing the longerons in tension, and the skin in shear combination tension. The aft bulkhead is a threat in reversal of pressure, as the vessel is not necessarily purposely considered in collapse. It is a stout "plug" if subjected to positive outside pressure, or a combination with aerodynamic and high outside pressure. It is difficult to consider the tail being thoroughly corrupted, and the Aft bulkhead remaining integral to the Fuse.

OE In the salt water long enough to muddy the fracture, a clean break is certainly possible, but perhaps not conclusively demonstrable. Follow me here. For the tip of the Arm to break in its intended fashion is to imply a specific stress path. This path is more indicative of vibrational or fatigue loss, rather than fracture, to wit: Vertical load imparts a tension on the Arm via a "pull" from the Hinge tower. this enters the Bolt, which must then push on the tip. Some dimensional leeway is assumed prior to fracture, yet again, the seal/resin, seat of the bolt on the Spar side appears ignorant of great stress. The Bolt would be the architect of tip fracture, but as I say, there doesn't appear to be any evidence of "movement". Hence the vibration or corrosion/fatigue model would apply. (subject to metallurgy and much closer inspection.) Your statement that you see evidence of lateral movement damage is what I claimed earlier, when criticizing the "Lateral rods".

HazelNuts39 I don't know the A400m, but notice a shift in thinking relative to the VS. There are 4 pair of Brackets, eight clevis pins. Take note of the "Eyes" at the bracket tops. Pair 1 and Pair 4 have much thicker eyes than the two center hold downs/brackets. .....447 impact: I think I see the exchange of energy now as a continuum, though certainly happening at rapid speed. I also think that the Horizontal velocity was kept alive until the nose dropped beneath the waves, making the Horizontal component more energetic than if a nose sub is not taken into account.

Crew Rest
I have looked at great length at the crew rest capsule. From a theory of tail, midsection, nose entry, I think I can hazard an opinion of what happened in the hold. The capsule appears to have an envelope of laminated skins of Aluminum. My guess would be two laminae, with a powerful adhesive joint to make a strong ratio of strength to weight. (The adhesive has the characteristic color of a phenolic resin, but that remains open.) The damage to this skin is more involved than simply being crushed between the Belly and the Cabin floor as the Fuselage flattened on to the surface of the Ocean. The Rest, if enclosed at impact, we may have three separate compression/decompression cycles. first, the Hold flattens out, reducing the volume of its structure, and pressurizes the rest capsule to some value higher than ambient Hold in Fall. The capsule may have held for a short time (even if not "pressurized").

As the Cabin floor comes crashing down on the hold and its contents, the capsule is overpressured, and expands (perhaps even explosively). The damage to the skin of the capsule is certainly rip/tear, but the damage also shows, via the delamination of the skin, that there was an explosion of some great force. Not at all a chemical or other type of explosion, but similar to a scuba tank or pressure cooker failure. Very energetic.

henra If horizontal speed was maintained, perhaps in a skimming reaction, the nose dropping into the water would create a substantially larger acceleration to the VS than previously entertained? Perhaps approaching the 66g?

bear

Last edited by bearfoil; 6th Sep 2010 at 01:09.
 
Old 6th Sep 2010, 04:20
  #2119 (permalink)  
 
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Bearfoil wrote:-

mm43 I believe the a/c was in Aternate Law almost immediately, and #II at that. RTLU is auto at reversion, and will not release more sweep until Flaps/slats aiui. It also is not possible to reacquire Normal Law until landing and re program.
Yes, I fully understand the RTLU lock at Normal to Alternate Law and the slats extension to clear the RTLU locked position.

What I am seeking is clarification that RTLU WRN message will be generated at Law change. It seems like more information overload (e.g. Wind Shear Fault WRN at FL350!) and in that respect I suspect that a rudder pedal depressed and held created the reason for it.
A complete failure of all tail components is entertained at impact.
I agree with that.
If sufficiently left un snubbed by hydraulics, Rudder flutter could happen at almost any speed above the Stall. The definition of flutter would be strained at lower speeds, consider for now that the Rudder "vibrated" rapidly from max. aero pressure then back again.
That part I do not agree with. Let me put it this way.
  1. I don't believe the rudder was damaged at altitude.
  2. Damage occurred during the impact phase.
  3. The horizontal velocity component was relatively low.
  4. Departure of the V/S and Rudder was due to a complex combination of forces -
  • Aerodynamic to terra oceania.
  • Reactive buoyancy moments.
For instance the rudder's bottom damage is possibly a combination of the tail-cone/APU exhaust pipe being deflected into it and the rudder slamming hard-over to port as the hydraulics let go. There is absolutely (IMO) no signs of trailing edge "flutter" damage to be seen.

Initial bottom up compression through the aft frames compounded by the V/S downward thrust weakened the No.2/3 clevis mounts sufficiently for them to be torn out as the V/S rotated forward. Likewise, the No.1 mounts suffered a similar fate, but the lug mounts were ripped from the V/S as it rotated forward and to port. This indicates to me that longitudinal continuity still existed between the empennage and the fuselage forward of the aft pressure bulhead (frame 80) as this detachment took place.

No high speed impact damage with water is evident to the V/S composites as was noted on the Outer Spoiler.

NOTE: (IMO) I'm not so sure the horizontal impact velocity was even 100 knots. Recovered items, e.g. galley, toilets etc.. don't indicate that sort of speed. This was no "skipping stone" impact. The aircraft dug a watery hole and rapidly came to a complete stop, though then subject to the reciprocal buoyancy moments that completed the cycle of damage.

mm43

Last edited by mm43; 6th Sep 2010 at 10:59.
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Old 6th Sep 2010, 07:31
  #2120 (permalink)  
 
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''High vertical speed''

Hello!

Would be possible from the structural analyze of recovered parts to have a fair estimation of energy/speed (particularly vertical speed) at impact - a generally accepted value or a range , and then to make scenarios regarding pre-impact evolution of aircraft?
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