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AF 447 Search to resume

Old 27th Aug 2010, 03:50
  #2001 (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, 04:39
  #2002 (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 05:16.
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Old 27th Aug 2010, 05:12
  #2003 (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, 09:32
  #2004 (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 09:34. Reason: spelling corrected
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Old 27th Aug 2010, 10:05
  #2005 (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, 12:40
  #2006 (permalink)  
 
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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, 14:20
  #2007 (permalink)  
bearfoil
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henra

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 15:16.
 
Old 27th Aug 2010, 15:03
  #2008 (permalink)  
 
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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, 15:53
  #2009 (permalink)  
 
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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, 16:02
  #2010 (permalink)  
 
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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 17:05. Reason: Edit Block added
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Old 27th Aug 2010, 16:04
  #2011 (permalink)  
 
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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, 17:04
  #2012 (permalink)  
 
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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, 17:38
  #2013 (permalink)  
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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, 18:05
  #2014 (permalink)  
 
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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, 18:20
  #2015 (permalink)  
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I'll go with that, save some time.

bear
 
Old 27th Aug 2010, 18:20
  #2016 (permalink)  
 
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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, 18:41
  #2017 (permalink)  
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henra

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 19:04.
 
Old 27th Aug 2010, 19:18
  #2018 (permalink)  
 
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GreatBear

In Post #1673 I included a screen shot taken in the Recife RCC showing that the FAB were searching from the LKP.

SaturnV

I have overlaid the FAB's Position of Corpos graphic information on the equivalent data published by the BEA. The reference points were the background Google Earth bathymetry. This leads me to reiterate that the data published by the FAB's media arm bore little or no relationship to the truth.



The FIR boundary (red), the Último Reporte position (red) and TASIL position (black) from the FAB's graphic have also been included.


mm43
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Old 27th Aug 2010, 19:41
  #2019 (permalink)  
 
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Bearfoil:
The "Airfoil" shape hasn't anything to do with The VS' purpose.

Without an airfoil shape the VS wouldn't create lift and therefore couldn't provide vectored force (work) upon the airframe, no?
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Old 27th Aug 2010, 19:53
  #2020 (permalink)  
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Machaca

The VS exists to prevent the a/c from getting out of shape, period. A Rudder isn't a necessity, as you know, which means the VS needn't be so equipped, and the shape in cross section does not create an airfoil. Technically, and I insist on it, an airfoil has an asymmetric cross section, not a symmetrical one. An a/c can fly with large razor blades for wings, airfoil isn't at all necessary. Examples abound, but I've started a discussion in Tech Log, rather than here, hope to see you,

bearfoil, friend of airfoilmod
 

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