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AF 447 Search to resume

Old 27th Aug 2010, 00:18
  #2001 (permalink)  
 
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JD-EE
I believe somebody some time ago pointed out the part's part number was 36g? Or did I miss that getting refuted.
Arm 36g was so named due to a requirement in the regulations, and its part name is directly related to the moment it was designed to handle. HazelNuts39 found the appropriate reference, and though I haven't done a search, the original discussion on the subject is spread through pages 20 ~ 30 in this thread. I believe that OE's analysis of Arm 36g is probably correct, and tail strike protection of the rudder is probably the prime reason for its existence.

mm43
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Old 27th Aug 2010, 02:39
  #2002 (permalink)  
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mm43

Hello again. I think a discussion of Tail strike protection would be fruitful. The first consideration is to spread focal stress as the tail hits and the VS wants to keep going. With a pitch sufficient to hit tail first ~17 degrees, the Hinge axis of the rudder is roughly 34 degrees off vertical and the arm restraint would be roughly 90 degrees to the deck, so the effort seems to point to protection of the Rudder from deforming the hinge plates from a linear alignment (all seven). If the hinges deform from line, the Rudder will Bind, and not perform, an expensive fix. In this way I think the arm makes sense. OldEngineer points out the increasing danger of arm failure as the attach point decreases in size, specifically Bolt Size. The other way to express this is to say that as the attach points increase, not in mass, but in bedded area, the forces are attenuated with less structure and less risk of breakage. In arm 36g, the bolt subtracts substantial cross section from the arm, such that a failure such as we see in 447 is not surprising. Without sounding arrogant, I think rather than an arm, with its attachment vulnerability to tension, perhaps another way to address the "drop" of the Rudder relative to the VS, to protect the Rudder hinges would be to fasten plates to the spar and the Rudder Pinion, such that rather than focal (tension) strength, the area is protected by a more familiar shear solution. This would be addressed by a composite of sufficient cross section to carry the load away from the hinges, and load the Aft Spar of the VS spanwise to the Rudder Pinion(s).

It may be that the arm is after all not intended to "Balance" the shear forces of the two control surfaces under landing and tail strike events, so I have to wonder what the purpose of featuring the picture of the arm is meant to convey. At first I assumed the Picture and the numbers were included for people to make of it what they may. BEA makes no actual finding re: this arm, so does anyone have a more evolved take on the Arm issue?

Edit. Whatever people may think of my continued presence here, including those I perhaps offend regularly, my passion is genuine and my purpose is to find out the truth. I relish responses from every single person here, and could not begin to single out folks at which to direct my admiration. I am here to learn. I write no drafts, and I post without even editing for spelling and grammar. I do not even know how to drag a quote, and my prose may get brash or conceited. In person I am quite sociable, but in text, especially here, I sometimes cannot hide my feelings still. My family does much business in France, and travels regularly on Air France, a grand and enjoyable Airline to most of us, some of us like the Old Blue "Murican" legacy, no accounting for taste.

Cheers, and may the recorders be found.

bear
 
Old 27th Aug 2010, 04:22
  #2003 (permalink)  
 
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On the note on recorders, an interesting paper was published this year on Recovering Data and Voice Recorders Following At-Sea Crashes.

I can't link the paper, but i'm posting the abstract below. If anyone wants to read the whole thing, send me a PM and i'll email it to you.

Abstract – The international aviation safety community has
concluded that existing methods of blackbox localization and
recovery are not effective in deep ocean situations, and
occasionally not effective even in relatively shallow water when
the acoustic pinger is buried or covered in debris. The majority
of these pingers are provided by two companies, Teledyne
Benthos and Dukane, according to pre-determined form and
function, and these devices are essentially “built to spec.” The
purpose of this paper is to identify the shortcomings in the
existing, decades-old functionality and to recommend the
introduction of acoustic modem technology to provide orders of
magnitude improvement in blackbox localization and data
recovery.
Fundamental ocean physics clearly indicates that the
following conceptual changes should be considered:
1. The current pinger technology operates at nearly 40 kHz
frequency. Simply reducing the frequency to perhaps 12
kHz will substantially increase range in seawater and
even improve performance when the device is covered in
sand or debris.
2. The devices use very short sinusoidal tones (usually
called tonals) as their signals. Ocean propagation often
is highly selective in frequency due to the constructive
and destructive alignment of propagation paths – some
frequencies are supported, others are canceled.
Furthermore, it is difficult to transmit sufficient energy
into the water with these signals.Tonals are very poor
candidates for robust, reliable ocean signaling.
In addition to fundamental issues, the current system
operates by a water-activated commencement of repetitive
transmissions (pings) of these short tonals the moment the device
enters the water – even though no listening devices are present.
This is a waste of energy.
In this paper, we provide a brief overview of acoustic
propagation from the perspective of its differences with more
commonly understood radio frequency (RF) propagation. We
follow that with our suggestions for substantial changes in
operational concept, specifically arguing for wider bandwidth
waveforms with more sophisticated receiver processing.
However, given the effort to utilize more complex systems, we
recommend they be further adapted to support underwater
acoustic communications (acomms). This will provide blackbox
and crash recovery far more effectively than is now possible, and
can support data recovery when the devices themselves cannot be
recovered. In particular, acomms modems can be used in support
of long-range, accurate position estimation by either manned or
unmanned platforms. Our proposed system will be somewhat
larger than the present system, but it will significantly enhance
the ability to find a submerged black box.
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Old 27th Aug 2010, 04:50
  #2004 (permalink)  
 
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HN39
Were these the statements from the interim QF72 report that gave a minus 4 degree alpha protect control authority?
Flight envelope mechanisms
• First upset was close to worst possible
scenario:
– 4 degrees alpha prot, 6 degrees anti pitch-up
• AOA processing algorithm using just two
sensors only on A330 and A340
– different algorithms used on other Airbus
aircraft
If Alpha protect authority is limited, the authority may vary based on CAS.
At lower speeds, more authority would be needed. If the aircraft was actually slower than the flight control system recognized, then it might be possible to have inadequate Alpha protect authority=prompt stall entry on a Vmo/Mmo protect pitchup.
I haven't had much luck finding more information on any Alpha protect authority design logic. I might also be mis-interpreting the meaning of the QF-72 report.
However, that was a very astute call of yours pointing to an authority limitation.
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Old 27th Aug 2010, 05:39
  #2005 (permalink)  
 
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"arm 36g" again!

Originally written by HN39 in Post #481:-

The FAR Part 25 regulations specify an ultimate load corresponding to 24*1.5=36 g. The rudder and supporting hinge brackets must be able to support an inertia ultimate load acting parallel to the hinge line of 24*1.5=36 times the weight of the rudder. Since Arm 36g is at an angle of 38 degrees to the rudder hinge line, 120 000 N in the direction of that arm corresponds to 94 561 N along the rudder hingeline, and hence to a rudder mass of 268 kg.
As described above, the true relationship between "Arm 36g" and the rudder hingeline is revealed, and my translation was deservedly "trashed".

mm43

Last edited by mm43; 27th Aug 2010 at 06:16.
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Old 27th Aug 2010, 06:12
  #2006 (permalink)  
 
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Location of AF447?

I am only 3 pages behind so sorry for the thread drift (It has been a busy week). Thanks for the feedback on my previous post. I have updated the FODDA drift graphs to include some of the suggestions. There are now 4 Nm (30 sec @ 480 knots) circles from the LKP. The max and min body drift area is shown about the nominal centreline. The SAR slick bifurcated angles have been projected back 20 Nm but located from what I believe is the most likely location of impact with the water. The blue line to the west is the ‘incoming’ angle of the lighter right side of the slick (54 deg off horizontal). The dark left side of the slick is made up of 3 sections basically a near vertical (85 deg) top and bottom section with the centre third at 65 deg. I have shown both these angles. The 85 deg line coincides closely with the body drift centreline. The 65 deg line is way out to the east. This may imply the most likely location is a bit further to the left than calculated by FODDA. I still have to look at the probability of other locations.
Regards
FF


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Old 27th Aug 2010, 10:32
  #2007 (permalink)  
 
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If the fin had parted at altitude, its assumed aspect after "stabilizing" would be LE down, trailing the Rudder.
Bearfoil,
have you ever seen a video of a wing coming down after separation ?
In all cases I have seen the wing was tumbling down in a flat attitude.
Never I have seen a wing coming down LE first.
That's due to the Lift being created by the LE.
Center of Lift on a Wing is roughly Quarter Chord. CG is roughly MId- Chord. So it is longitudinally highly instable.
That's why in a flying wing plane you have specific S- shaped chords and the CG far in front of the Quarter Chord line.
Try flying with a wing only where the CG is mid Chord: Good Luck !!

So once the Wing would start falling LE first and would build sufficient Airspeed the LE would rise, thereby flattening the attitude, likely starting a rotation.
And that's exactly the behaviour you see in VidCaps where a plane lost its Wing. There was an ugly video on ysoutube of a P-68 shedding its Wing during aerobatics.

The forward/bottom corner would enter the water first, explaining the lack of further LE damage upward as the fin tapers in chord and width.
Esactly that would NOT happen !
see my explanation above.
It would hit randomly, possibly rotating but generally flat.

And that is what makes the upward bending of the lower ribs in the VS perfectly fit to the assumption of BEA that it got lost upon impact in a downward direction and not so much to a loss at altitude which would probably be more sideward than anything else.
Having said that I wouldn'i rule it out completely but I strongly tend to agree with BEA on this particular aspect.

Last edited by henra; 27th Aug 2010 at 10:34. Reason: spelling corrected
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Old 27th Aug 2010, 11:05
  #2008 (permalink)  
 
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FluidFow,

Interesting analysis !
If I continue my rough calculations and pursue my theory of high altitude stall and how it came to it, I arrive at a distance travelled by the aircraft of ~25-30nm.

1 Minute decelleration from 270kts IAS (~480 kts) to 220kts (~400kts).
Average speed: ~440kts
=> Distance travelled ~ 7.33nm.
Stall
4 Minutes decelleration from 400kts to 100kts
Average speed: ~250kts
=> Distance travelled ~16.7nm
Assuming not a linear but a more progressive deceleration (due to drag increasing progressively with increasing AoA especially after the stall).
I would rather expect the distance travelled to be closer to 30nm.

If we now assume a radius of turn of 3nm and a circle of 240°
we would have a distance travelled while circling of ~12.5nm

That would leave us 12-18nm and would bring us pretty close to the slick. Maybe 2-3nm beyond.
So I would venture to expect the crash area to be closer to the slick than in your grafic if we would pursue the logic of the above scenario.

All pure speculation though.
But the scenario can still be made consistent.
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Old 27th Aug 2010, 13:40
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FluidFlow,

You analysis which has the likely impact to the right of the track is smack dab in the middle of the area searched extensively by the Brazilian Air Force in the several days immediately following the crash. Putting aside whether bodies were floating on the surface at that point, the other large pieces of the plane were surely there to be seen. And were not.
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Old 27th Aug 2010, 15:20
  #2010 (permalink)  
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I think you are quite wrong. The Vertical Stabilizer is NOT a wing, it is a FIN. It has ALL LIFT designed out of it. It is symmetrical in chord, and falls ballistically. The concentration of mass is low and Frontal, so the expected aspect is as I describe, it FALLS bottom down. There may be excursions in spiral, but these are slight, and eventually degrade into "0" as the Rudder Centers. The Rudder has no desire to remain deflected in ballistic trajectory, there is no impetus to sustain it. BEA is wrong if they project a conclusion based on the Fin acting as a wing.

Of course the flying wing is unstable, it has camber, and is not aerodynamically docile, as the Fin is designed to be. Come to think of it, the upward bending lower ribs solidify the opinion of entry into the water exactly as I have said, forward lower corner down, at not insignificant velocity. I think BEA have no opinion on the lower LE damage, as I do. If the VS popped out after impact, it had lost almost all of its energy, but almost certainly too much of it to end up as the significant damage expressed in the LE. It is a stretch to believe that the Fin "Rolled" over the Dorsal Fin, causing the damage to LE.

I'm out on a limb I know, I've gotten a little too explicit and may be extrapolating too heavily, but my picture of the VS portion seems clearer and more in line with Occam than BEA.

have an excellent day,

bear

edit SaturnV Some help please. If the Brazilians were searching FluidFlow's impact point in the days after the crash, why would they be expected to see anything? Drift?

Last edited by bearfoil; 27th Aug 2010 at 16:16.
 
Old 27th Aug 2010, 16:03
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SaturnV,

Maybe the Brazilian AF searched there on June 1 and 2, maybe not. Your post (#1666) contains illustrations showing significant aerial unsearched area southeast of the "Ultimo Reporte." The Brazilian Ultimo Reporte was based on a 02:14 estimated position. The BEA's LKP at 02:10 is, itself, southwest of the Ultimo Reporte...

GB
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Old 27th Aug 2010, 16:53
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GB,

don't forget that oceanic currents in that area can be very strong, including large eddies. The currents can go in completely different directions and speeds at specific depths. Debris, depending on its weight and size would be sinking at different rates with currents at various depths affecting it very differently. Needless to say, the deeper the water, more chances of things getting "strewn around" .
The debris field on the bottom of the sea therefore cannot always be an indicator of the sequence of events...

From Deep Submergence Vehicles experience, you can end up with a rover 20-40km away where you dropped it off, and this is with their thrusters at full speed trying to compensate!
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Old 27th Aug 2010, 17:02
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The Vertical Stabilizer is NOT a wing, it is a FIN. It has ALL LIFT designed out of it. It is symmetrical in chord
Bearfoil,
Yes if there is no Angle of Attack, it has no Lift.
BUT:
As soon as it gets minimal AoA it will start producing lift and pitching moment. Into the direction where it started building AoA.
The Flow around the round LE will start creating Lift due to Bernoulli Effect.
Take a good book on aerodynamics and you will see what I mean.
Look at aerobatics aircraft. They have fully symmetrical wings as well. And yet they fly. And they fly in the same way any other aircraft flies.
just with a little more AoA.
Or more technically:
If you look at a wing Polar of a symmetrical Profile (NACA Report 460, e.g. 0006 or 0009) you will see that the moment coefficient around the the Quarter Chord Line is constant (Null) for quite a large range of Alpha. That means the aerodynamic center is the Quarter Chord Line.
If your Cg is behind that point you get a positive moment coefficient i.e. the Wing will increasingly pitch into the direction where it started to pitch to, i.e. it is highly unstable.
Remember: Also a symmetrical Profile is a Wing !!!
It does just not produce lift at Alpha = 0.

and falls ballistically
No in all likelyhood it won't !
(See explanation above)

Edit:
It won't fall bottom first either, as the drag in that direction is much higher than LE first (High Cd of the lower side of the fin).
Only if the lower part would be very much heavier than the upper part, it could fall with the lower side first.
But I'm not aware of any reason why with an Airbus fin this should be the case.
So in a first move it would probably pitch in a dircetion where the drag is less, which would be LE in front and then the instability will take over.
Which likely will cause rotation around roughly the half chord axis
/Edit

Edit2:
The Fin is basically a Wing.
It becomes a fin by being placed so far aft behind CG and aerodnamic center of the plane itself.
/Edit2

Last edited by henra; 27th Aug 2010 at 18:05. Reason: Edit Block added
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Old 27th Aug 2010, 17:04
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the two bears:

current vectors over a five day period centered on June 2


current vectors over five day period centered on June 7


cumulative search grids through June 5 (circle excluded)


locations of recovered bodies between June 6 and 16


Yes, there is a small area to the SE of the last known position that was not covered by the search grids from June 1 through 5.
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Old 27th Aug 2010, 18:04
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AF447 Search: Unified Approach

Not for the "why," but for the "where," I'm wondering if an effort has been launched (or should be launched) to unify the many lines of thought and theories expressed during the last year here and by BEA (including the Drift Group's findings) using some sort of Bayesian probability logic applied to the grand picture... an approach that might integrate not just the drift calcs and thier probabilities, but the ACARS clues and aircraft flight behaviors as well. Assigning all known and speculated possibilities (including wacko ideas) weighted probabilities. and then doing the esoteric calculations (way beyond my own skillset), would it be possible to zero in on a high-probability search area for a Phase 4 reflecting what is known today?

GB
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Old 27th Aug 2010, 18:38
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henra

Excellent! Thank you, you are of course correct. I too am correct in saying that a slab of granite counter top will fly! It will, as will a brick, a cricket bat, etc.

We are in test territory, as I say, I am extrapolating, and this is a learning challenge for me. I promise not to throw the book at you, especially the equations of the Swiss Plumber. The Fin is meant to split the airstream equally, and the Captain who does that most often will please his FAs in the back as they roll their trolleys. If he goofs, he adds Rudder, which truly turns the Fin into a wing, by adding Camber.

I again disagree with your Lift thesis however. The Wing is designed to be UNstable in flight, the required correction being accomplished by the moment arm of the tail feathers. In balancing the a/c, Lift is corralled into work.

The Fin, if lost at altitude and in the condition we see in the photographs, Has monstrous drag at the bottom, with partial hoops and loose skin. The LE has second most, and the rest of the assembly for purposes of discussion has nil. Weight is at the bottom, of course, again with the LE coming in second. Sweep and Taper exaggerate the very limited overall effect on aerodynamics, especially as ALL instability disappears with loss of altitude and a gain of airstream BOXING.

The effect of the airstream at stable vertical trajectory acts to sustain the least "offensive" (to the air), ASPECT.

I do modelling as a hobby, now I'm retired, and have a hot wire and extra Foam in the shop. Shall I construct an honest model and drop it from the second story of the asylum? Wager?

all the best henra, bear
 
Old 27th Aug 2010, 19:05
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why bother ?

Re VS condition, isn't there info or video from the NY wake accident which would show what happens ?
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Old 27th Aug 2010, 19:20
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I'll go with that, save some time.

bear
 
Old 27th Aug 2010, 19:20
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Bearfoil,

The Fin is meant to split the airstream equally,... he adds Rudder, which truly turns the Fin into a wing, by adding Camber.
Adding Rudder will turn the Wing into a High Lift Wing (It's like setting Flaps).
But even without application of rudder in still air the plane would return into straight flight albeit slower and with some oscillations.

The LE has second most, and the rest of the assembly for purposes of discussion has nil.
Actually the drag coefficient of the fin from LE side is the lowest of the hole thing. That's the main reason why an airfoil profile is used for the fin.
It has the lowest Cd of all shapes.

Shall I construct an honest model and drop it from the second story of the asylum? Wager?
Good idea !!!
Make it from solid foam, round of the LE nicely with sanding paper and grind down the TE, so it's pointy.
Dropping from 2nd Floor upwards should give a good idea about behaviour.

I venture to guess it will tumble aound all axis and fall relatively slowly.
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Old 27th Aug 2010, 19:41
  #2020 (permalink)  
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You are getting dangerously close to an onslaught of Bernoulli banter. As a pilot, I am familiar with aerodynamics, so I will question your framing VS/Rudder as a High Lift Wing. I am on strong ground here, and must insist you be more specific. The Lift isn't Lift, strictly speaking, but can be characterised as such, for ease of understanding by those unfamiliar. If you shoot back with a defense of terms ("Lift"), I will be forced to get into why Bernoulli is for basic understanding, but is difficult to release, even for professionals, who do not pursue more complete study.

The model, if necessary, must have a fully articulating Trailing edge, ("Flap") since of course RTLU was inop, (or was it, actually?).

Hint: If you count molecules, by sheer number the work is on the high pressure side of the "Panel". Hint #2: A ruddered VS is a High "Descent" wing, and that's why using Bernoulli confuses even pilots.

I'll just keep going while you write. The "Airfoil" shape hasn't anything to do with The VS' purpose. It is an artifact of an engineering consideration having to do with strength v. drag/weight. A perfect VS has NO dimension relative to airflow, obviously. It would resemble a perfectly flat sheet of infinitely strong material with a similar panel hinged at the TE.

over to you,
small bear

Last edited by bearfoil; 27th Aug 2010 at 20:04.
 

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