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AF 447 Search to resume

Old 4th Apr 2011, 22:09
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Originally Posted by PJ2
This is the left main gear and inboard section of the [left] wing; the structure to the far right is the pylon mount for the left engine.
PJ2,
I know how familiar you are with the airplane and have never been near it myself. My comment was based on the lower wing skin visible just to the right of the upper end of the MLG leg, that is in the way of retracting the gear towards the right. If you are right, then it must be a wheel well door, since the gear retracts towards the fuselage. If that is a door, then it being in closed position would be counter to the theory that the gear was released from the uplock due to impact forces. Are you sure the structure to the far right is not a flap track (*)?

regards,
HN39

PS: (*)BEA Interim Report #2 has photographs of flap track 3 on pp.20-21

Last edited by HazelNuts39; 4th Apr 2011 at 22:46. Reason: text improvement and PS
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Old 4th Apr 2011, 22:09
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Attitude at Impact




From a previous post.
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Old 4th Apr 2011, 22:56
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Tyres

"Question regarding the tyres in the photos. I am surprised they are not crushed / squashed by the pressure at that depth."

Rapid water ingress. All air squeezed out.
But rubber itself is compressible.

So the tyres should look much smaller then normal, which I think they do.
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Old 4th Apr 2011, 23:00
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ZeeDoktor
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mm43, are you suggesting some kind of deep stall? I doubt an intact and in-CG air frame would maintain your depicted attitude and velocity vectors.
 
Old 4th Apr 2011, 23:05
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mm43, are you suggesting some kind of deep stall? I doubt an intact and in-CG air frame would maintain your depicted attitude and velocity vectors.
Why so?

deep stall or spin, vectors look about right?
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Old 4th Apr 2011, 23:17
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HN39,

You think you are looking forwards at the R/H MLG; whereas PJ2 sees himself looking aft at the L/H MLG.

However, the MLG is normally mounted on the rear spar, at the intersection point of a diagonal bracing spar, sometimes referred to as the "Bermuda triangle", so I agree with you that the top-right item is unlikely to be part of an engine pylon.

Chris
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Old 4th Apr 2011, 23:27
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ZeeDoktor

I will need to go back and dig out the post which had the Attitude at Impact images included. I believe I was referring at the time to a form of Deep Stall where the aircraft was slowly spinning within the vortex it created. This possibly as a result of an non-recovered stall. The BEA in Interim Report No.1 made mention that the tail was rotating to port at impact.
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Old 4th Apr 2011, 23:33
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It would seem that based on the vectors, and if the A/C was within CG limits, positive pressure at elevator wing surface will induce pitch down moment, thus not maintaining positive pitch angle. There is no elevator shadowing from main wing components (which is the definition of a deep stall, really). Could a transport category aircraft be certified if a deep stall condition can be produced simply by stalling in a double flameout / power idle? I don't think so.

EDIT: Unless spinning of course, you are correct. It took an incredibly unfortunate conspiracy of fluid dynamics to get them into this state!
 
Old 4th Apr 2011, 23:39
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August 2006, the TU 154M near Donetsk, stall at 39,000 feet, [presumably flat] spin, fell 14,000 feet per minute max. Impacted 3 NM from the onset of the upset.
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Old 4th Apr 2011, 23:46
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Lots of use of the term "deep stall" here recently but don't you, almost by definition, need a T-tail for that?
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Old 4th Apr 2011, 23:46
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Yes HN39,

As I tried to explain, I'm with you on this one, for what it's worth. The engine and pylon are mounted on the front spar, so do not feature among the parts in question. We are looking forward at the R/H MLG.
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Old 4th Apr 2011, 23:50
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HN39, Chris, I agree with you, thanks - sharper eyes than mine. The other gear (partially buried truck) would be the left, then.
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Old 4th Apr 2011, 23:52
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@wiggy: Yes, for a classical deep stall. But if combined with a spin, you can produce a similar effect (a vortex) with non T-tail a/c. At which point, deep stall simply means a stall which you cannot terminate unless positive power input is available to re-attach air flow across control surfaces.
 
Old 4th Apr 2011, 23:57
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One way to get there, fast

Lose control into a spiral dive due to a loss of instruments, go near sonic in the descent, come out of the overcast and be able to see the water and even the horizon what with lightning and/or the moon, roll to wings level, and pull really, really hard. If the flight control system will let you apply full-up elevator regardless of the angle of attack or g, the outcome could be that you hit the water wings level, nose up, and at a relatively low forward speed but with an unsurvivable rate of sink.
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Old 4th Apr 2011, 23:58
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ZeeDoktor

OK, , that makes sense, though wouldn't a spin by itself produce the postulated impact geometry (i.e is an aircraft rotating in a deep stall simply spinning in the classic sense of the "spinning" word) ?
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Old 5th Apr 2011, 00:09
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Originally Posted by wiggy
Lots of use of the term "deep stall" here recently
It depends how you define "deep stall". For some it just means an AoA substantially greater than that at which the stall first manifests itself. The T-tail problem is the airplane being "locked-in" in that condition.

Originally Posted by ZeeDoktor
Could a transport category aircraft be certified if a deep stall condition can be produced simply by stalling
As far as I am aware, no one on this thread really knows how the airplane was certificated in this respect. Some contributors, for example PBL, on the basis of a literal interpretation of the relevant regulations, have suggested that an investigation of its stalling characteristics beyond "alpha max" was not required, by virtue of the AoA protections incorporated in its flight control system in "normal law".

That said I should emphasize that without further evidence, all talk about stall, deep stall, superstall, flat spin, etc. in relation to AF447 is just speculation and, IMHO, not the most likely scenario of what happened.

regards,
HN39

Last edited by HazelNuts39; 5th Apr 2011 at 01:05. Reason: text in italics added
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Old 5th Apr 2011, 00:48
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Tailspin turtle, only two problems with that scenario. One, there was no lightning with this particular complex; none detected by satellite, nor by ground stations. Apparently lightning is infrequent in the ITCZ. Two, the moon was behind them.



A LH 744 on the same track saw no lightning, but did have St. Elmo's fire.

Also,






Source:
http://cloudsat.cira.colostate.edu/d...04_E00_1AA.htm

click on segment 31 for the radar profiles of the mesoscale convective complex.
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Old 5th Apr 2011, 00:58
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I like this quote from D.P. Davies regarding "superstalls".
There is no point in discussing the irrecoverable case any further, except perhaps to say that those aeroplanes which have been lost in such manoeuvres finally reached the ground substantially level laterally, having defied all efforts to roll or spin them out of the stabilized condition; only slightly nose down in pitch, with little or no forward speed; at an extremely high incidence; rotating only very slowly in yaw; with (in one case) all the engines flamed out because of being exposed to such massive angles of incidence; and finally with an enormous vertical velocity.

The quote seems very relevant to AF447.

HN39 quote:
As far as I am aware, no one on this thread really knows how the airplane was certificated in this respect. Some contributors, for example PBL, on the basis of a literal interpretation of the relevant regulations, have suggested that an investigation of its stalling characteristics beyond "alpha max" was not required, by virtue of the AoA protections incorporated in its flight control system in "normal law".
In the vicinity of alpha max I would expect predictable stall behavior.
Well beyond alpha max, I would expect stall characteristics approaching those of a swept wing flat plate airfoil-in other words, terrible.
That work-of-art Airbus airfoil, optimized for cruise, was probably never even tested well past alpha max. I expect that the Airbus AOA protection system was considered to be better than a stick pusher and thus sufficient to prevent flight outside the design flight envelope.
Somehow, AF447 exceeded its design envelope, and that is the question which the information from the black boxes needs to answer.
It may well be more complex than pitot icing. Let us hope that the information is still available.

Last edited by Machinbird; 5th Apr 2011 at 01:27.
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Old 5th Apr 2011, 01:11
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Machinbird;

Terminology surrounding a deep stall can be confusing, but D.P. Davies' quote puts it all into context. Once you get there, there is probably no way out (without a tail 'chute).
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Old 5th Apr 2011, 01:29
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ZeeDoctor,

Keep in mind that your basic swept wing tends to tip-stall first. This causes a shift in center-of-lift forward and my understanding is that therefore swept wings are inheritantly more succeptable to deep-stalls than straight-wings. I don't know what kind of protections modern transport category aircraft have to prevent this but any computerized protections for AF447 were believed to be unavailable.
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