Originally posted by Evan
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Air France 447 - On topic only!
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Originally posted by guamainiac View PostSo:
An Airbus is not supposed to enter a stall.
But obviously it can.
But if it does, you can't push over and fly out of the stall.
Makes sense to me.
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Originally posted by dkmax View PostHi Guys,
I've followed this thread from the start, as fascinated as everone to try and understand how an A330 can just fall out of the sky!? The way the evidence is now pointing is quite staggering!?
I have a laymen question if I may...
With airspeed as low as 60 or even 34 knots, I just wondered if the plane had passed the point of no return? Do the control surfaces have any effect at such a low speed?
Hypothetically, if you could hoist an A330 up to 38,000ft, 0 airspeed, wings level, minimal AoA, TOGA & simply 'drop it'...
Would it fly? I guess not, but could you actually get the nose down to make it fly?
The speed at which they were actually flying was sufficient for elevator authority, as evidenced by the pitch response to control inputs throughout the sequence. Also, the recurring stall warnings were due to pitch down inputs that momentarily lowered the AoA back into a valid range (still well above stall warning threshold).
Considering the abundance of altitude, I can see no reason why pitching down during the stall, thereby reducing AoA and regaining airspeed, would not have led to recovery. But they were more intent on pitching up.
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Originally posted by DJMaxhi guys,
i've followed this thread from the start, as fascinated as everone to try and understand how an a330 can just fall out of the sky!? The way the evidence is now pointing is quite staggering!?
I have a laymen question if i may...
With airspeed as low as 60 or even 34 knots, i just wondered if the plane had passed the point of no return? Do the control surfaces have any effect at such a low speed?
Hypothetically, if you could hoist an a330 up to 38,000ft, 0 airspeed, wings level, minimal aoa, toga & simply 'drop it'...
Would it fly? I guess not, but could you actually get the nose down to make it fly?Originally posted by BoeingBobbyYes.
Are you sure, BoeingBobby, you know it is an AirBus and not a Boeing?Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.
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Originally posted by Evan View PostSince the Qantas ADIRU incident, we all know what can happen if the wrong AoA is considered valid.
Since the Colgan incident, we all know what can happen when false stall warnings occur.
I'll pretend that I have not read that.
The aircraft has no way of knowing why the speeds are indicating below 60kts
Perhaps unreliable AoA should still drive the stall warning
, but then see: COLGAN 3407.
COLGAN WHAT!!!!
I'll tell you Colgan what:
A pilot receives a stall warning and reacts by pulling up hard.
What the fuck does a false stallwarning have to do with this????
As we have discussed an nauseam, the pilots do not need AoA or stall warnings to avoid or recover from a stall. When airspeed data is unreliable and may be producing false indications below 60kts, the procedure is clearly outlined.
We don't need the stall warning active during take-off. The pilots have procedures to ensure that the flaps are at the correct setting, that they have entered the correct airplane weight in the calculation, that they are going to rotate right at Vr (and that that Vr is the correct one) and that one pilot will be closely monitoring the airpseed and pitch.
We don't need a stall warning during approach either. After all the pilots have the flaps correctly set and are flying the proper speed, and in the event that for some reason the autopilot brings the throttles to idle the pilot will detect it right away, after all one of them is flying the plane (and that basically means looking closely to the PFD where the flight mode is anounced and the airspeed and pitch displayed), and the other pilot is also monitoring the instruments, so there is no way that they'll fly dozen of seconds with the speed decaying below Vref and the pitch going abnormally up with "FLARE" shown in the flight mode announceator, especially not when there is a third required crewmwmber in the cockpit.
I have a great idea. Why don't we get rid of the stal warning alltogether? And while we are at that, we should also retire the old landing gear and take-off config warnings. There are plenty of procedures to ensure that they will not sound.
Oh, sorry. I forgot that sometimes things don't go as planned.
Finally, remember that I've said that while I don't like several Airbus features (with this stall warning inhibition being one of them), I also considered that they had nothing to do with this accident.
You have to admit, it's a difficult design decision, as each option has an inherent danger.
Meanwhile, the AF pilot's union uses this as a weak excuse to avoid the glaringly obvious reality. They seem to have no shame.
--- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
--- Defend what you say with arguments, not by imposing your credentials ---
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Originally posted by Gabriel View PostSays who?
At 60 kts there isn't going to be any useable air flow over the horizontal stab so no amount of pushover is going to have any effect. Under the circumstances as I read it the aircraft ceased to be an aircraft and became a lift (elevator for our US friends) descending at a rate of vertical knots ?If it 'ain't broken........ Don't try to mend it !
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Originally posted by brianw999 View PostSays the God of aerodynamics ? Surely a stalled wing includes the control surfaces...and it would seem that the stall in this case was down to a high angle of attack which would surely cause the tail horizontal stab to stall as well ?
At 60 kts there isn't going to be any useable air flow over the horizontal stab so no amount of pushover is going to have any effect. Under the circumstances as I read it the aircraft ceased to be an aircraft and became a lift (elevator for our US friends) descending at a rate of vertical knots ?
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Need to interject something- we are acting like you can always push over and fly out of a stall. (Boeing Bobby talking about dropping a plane from a baloon, Brian talking about the "God of aerodynamics").
There are some aircraft and some situations where you may be unable to push over and fly out of a stall:
-Certain T-tailed aircraft in deep-stall situations where the tail is "trapped" in foul air.
-Certain aircraft where the CG is way aft.
-Sad situations where the horizontal control surfaces are gone.
-Certain aircraft and flight modes where you will stall the tail as well as the wing (again, this requires a CG different from the "classic" airplane)
Of course, all that being said, a statement that is much more reliable is that you can "always*" push over and avoid a stall. (One really nice thing about stall warnings is that they start before you stall).
(*ok, I should say almost always...because there's almost always a few exceptions).Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.
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Originally posted by Gabriel View PostWHAT!?!?!?!
I'll pretend that I have not read that.
So yes, perhaps the AoA should always remain valid when in flight mode. I really don't see what difference it would make either way. But the engineers might have considered something we have not considered.
I think the Airbus engineers simply designed the system to rule out data inputs when the data is coming from an out-of-range sensor. I think they did this mainly to prevent nuisance stall warnings on the ground, and possibly to cover any unforeseen opportunities for system misbehaviors in the air. As for UAS, I think they considered the UAS indications and the calvary charge warning to be sufficient to get the pilots back on the instruments. I think Airbus has concluded that without RELIABLE air data, the aircraft is in a degraded (but still flyable) state, protections are no longer reliable, and this is when pilots MUST be skilled and competent. This situation is as follows:
- airspeed in unreliable,
- stall protections are lost,
- stall warnings are unreliable OR lost,
- you're in manual flight now boys,
- you damn well better set your pitch and airspeed,
- and it damn well better be from the memory procedure and the QRH.
That is the point I am making there. In these conditions, you can't rely on stall warnings. In fact, in the case of AF447, relying on the stall warning may have contributed to their tendency to keep pulling up once in the fully developed stall. The report points this out.
Originally posted by Gabriel View PostCome on Evan, I expect better than that from you.
Originally posted by Gabriel View PostWhat the fuck does a false stallwarning have to do with this????
Originally posted by Gabriel View PostI agree, finally on one.
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Originally posted by brianw999 View PostSays the God of aerodynamics ? Surely a stalled wing includes the control surfaces...and it would seem that the stall in this case was down to a high angle of attack which would surely cause the tail horizontal stab to stall as well ?
At 60 kts there isn't going to be any useable air flow over the horizontal stab so no amount of pushover is going to have any effect. Under the circumstances as I read it the aircraft ceased to be an aircraft and became a lift (elevator for our US friends) descending at a rate of vertical knots ?
1st, surely a stalled wing does not necessarily need to have it's control surfaces (ailerons) stalled, and even less the stabilizer / elevator need to be stalled. In fact, in your typical stall scenario (where the pilot recovers from it before it reaches a ridicously high AoA) not all the sections of the wing are stalled (although the wing as a whole is) and the stabilizer / elevator is not even close to stall.
2nd, Guamaniac, to whom I was responding, didn't mention a thing about 60 kts.
3rd, AF was never ever at 60 kts, probably it never reached as slow as twice that much either.
4rth, even if the stabilizer elevator was stalled, (which could have been the case here), the stall isn't the end of lift (and for our British friends I don't mean "elevator" here), and the lift is not the only aerodynamic force that can lower the nose, especially at very high angles of attack. A few weeks ago I made an effort to explain this and even made a graphical explanation that included two airplanes at a very high AoA (one with the stabilizer in a nose-up posotion and another in a nose-down position) together with a real lift and drag plot vs AoA for very high AoAs and the graphical calculation of the aerodynamic forces and pitching moments made by the stabilizer clearly showing that it CAN lower the nose even if stalled. Preparing this explanation was a lot of work and a time that I took from smething else that I could have done with it, so I'd appreciat if you give it a look. http://forums.jetphotos.net/showthre...rag#post581968
5th, Don't ask me for a proof, but I bet that if you hang an A330 (or just about any airplane) steadily in an horizontal attitude and just cut the string, the plane will aim it's nose down despite an initial AoA of 90 degrees both in the wing and the tail. The reason for me to think this is that the center of pressure (both in the wing and in the tail) moves back from 25% of the chord at AoAs below stall to 50% of the chord at 90° of AoA.
6th, Factually in the AF accident, in the brief moments when the pilots did push down, the airplane reduced its AoA, even when the airplane was already awfully stalled with AoAs well beyond 45°. Unfortunately the pilots were not consistent with these push down attempts and in fact pulled up most of the time.
7th. I am the God of arodynamics and I have never said such a thing
--- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
--- Defend what you say with arguments, not by imposing your credentials ---
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Gabriel...has anyone made light of the fact that apparently, the vertical stabilizer/rudder survived the flight?
Heck, maybe that explains the abscence of ITS?Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.
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