This is maybe to some extent true if you change the angle of the THS.

But commanding ND Elevator does not change so much AoA but it changes the camber and thus the effective profile of the tail surface, thereby completely changing the lift curve.
You would need to compare the Cl of the cambered tailplane. I'm pretty sure the cambered tail will have more lift even at increased AoA.

Moreover as you already describe ND elevator would increase drag, thus increase ND forces. At these angles you can exopect the drag to be of similar magnitude if not higher that the Lift, especially for a heavily cambered profile.
what is also missing and what will also be influenced by ND elevator is the moment of the airfoil. Strong camber will add a ND moment.

Taken these aspects altogether, even if I have no specific data for the given case I would strongly tend to believe that ND elevator would have lead to Nose Down attitude change even at these AoA.

A33Zab;

Yours is a valuable contribution to this aspect of the discussion. My thanks to you for clarifying the THS system and correcting, for other readers, my mistaken impression of the THS operation. I had read the electric-motor component as "the slower" of the two driving systems, ostensibly due to the lower demands of the AFS and, in manual flight, the sidestick. I've gone back to what I have and re-read with your contribution in mind.

Chris Scott;
I've watched the A340s and A330s THS wheel on the pedestal move slowly in response to small stick movements and changes in airspeed. One can see the movement out of the corner of one's eye because of the paint but I always valued the aural confirmation of movement on those airplanes that had manual trim.

The THS response to sidestick orders is immediate, in other words. I believe then, that as the sidestick was held in the NU command position, (orders still gee-referenced but with rate/gain limits), the THS would follow through, likely at a varying rate in relation to slightly changing sidestick orders. I think once the AoA was below that which the autotrim ceases to function, it would respond to sidestick ND orders. As stated, it would certainly have responded to manual trim wheel input.

A good, (and needed) discussion on "NU" and "ND", thanks. That's exactly the way the "minus 4" symbol for the THS position on the FLT CTRL ECAM page was explained to us when learning the A320 in 1992. Minus meant "tail down, nose up", and I think made good sense once one understood.

On the "roll to the right" upon disconnection, I have to re-iterate that the fuel system for the A340 and A330 were next to flawless in maintaining cross-wing balance of fuel. And there is nothing in the BEA Note to point to cause but any fuel imbalance on this airplane is real cause for close observation. I can't see rudder trim being an issue because it is automatic as well. One doesn't "disconnect the airplane, trim, then reconnect" as one did with the DC8/B727, etc and at that point certainly, it isn't reasonable to consider that asymmetric thrust was a factor.

syseng68k
If I misnderstood what you wrote I apologize upfront, but the wing loading in a stable stall will be roughly the same as in level flight, i.e. 1g.

The main difference would be the exact point where the lift is applied. In a fully stalled wing this will move from the Quarter Chord to the middle of the chord, so the moment on the wing might change a bit but the vertical force won't change much.
In a really deep stall on the other hand it might indeed work as the force on the wing it will decrease a significant bit as the fuselage will take over some part of the lift. In the attitude of AF it might contribute ~30%, so it could work to some extent but only at a point where it might be too late.

henra:

With a little "back of the napkin" sketching, I arrive at this from your post number 120 of this thread.

With the THS not stalled, though at an angle of attack significantly displaced from the usual "nearer to horizontal" (horizontal reference being THS airfoil chord line), the effective lift force, and thus corrective pitching moment, (roughly perpendicular to longitudinal axis of the aircraft, and then acting along the fulcrum to tip the aircraft's nose back down) is reduced roughly as the sine of the angle (AoA). The larger the AoA, from a nominal airflow parallel to chord line, or AoA absolute value of zero, the greater the lost force (vector subtraction). I din't factor in camber, as I both don't know it, and expect that it would wash out. This presumes no stall. Once a THS is stalled, it's a different problem.

I sketched it out this way based on expected control forces, controllability, and control response from an input to an airfoil movement. Each knot of reduced airspeed robs the lifting force of magnitude proportional to the 1/2*k*v^2 relationships in the lift equation.

What does this do to the aircraft's response ...

even with the THS not being stalled at that unusual angle of attack, it would take longer for both the elevator to influence THS, and for the lift acting on the THS to move the tail up (and thus the nose down) since the lift force isn't pushing as hard for a given flight control pitch command.

At some point at very low airspeed, depending upon CG, the airspeed ( airflow? ) may be so low that there isn't sufficient pitching moment (due to the combination of low speed influencing lift reduction, low air density, and sine of the angle vector subtraction) to move the nose at all.

Why sine of the angle?

As I sketched out the FBD on the THS, my vector component NOT adding lift increased with increased AoA, lift vector component decreasing.

Does that make sense to you?

EDITED since it was really confusing to me, and I wrote it. :p

Second EDIT: the more I think of this, the more it seems to me that an AoA indicator might be handy at high altitude. The AoA margins are reduced up there, a point which strikes home as I review HazelNuts39's graph on Mach Number and AoA and stall warning. If you lose speed at high altitude, that thin air really puts you at a disadvantage in terms of what your flight controls can do for you. :eek:

THS position-indication and "Vc Prot Law"
 

PJ2,
Thanks for reminding me that the THS display on the ECAM F/CTL page (the lower display unit, not normally displayed in the cruise), would have eventually shown either
"13° UP" or "-13° UP" for what I refer to below as "13NU". (Perhaps you can tell us which?)

As far as I know, the crew were not presented with any ECAM drills on that lower DU, despite the various failures timed at 0210 and 0211. Presumably, the CRUISE page would still have been displayed, which does not include THS? If so, the best way of reading the THS position would have been the scale on the manual pitch-trim hand-wheel, but that involves turning the head. As I think you said, there is no "whooler", or equivalent, to announce THS movement.

Quote:
The THS response to sidestick orders is immediate, in other words. I believe then, that as the sidestick was held in the NU command position, (orders still gee-referenced but with rate/gain limits), the THS would follow through, likely at a varying rate in relation to slightly changing sidestick orders. I think once the AoA was below that which the autotrim ceases to function, it would respond to sidestick ND orders.
[my highlighting]

I'm not sure you needed to include the clause highlighted, so will try to explain why.

From 02:10:51
Would the auto-trim look at AoA when and while the system considered the AoA data invalid? Was the "Vc Prot Law" or "limited-authority stability order" of Andy Tracey's paper disabled some of the time – or constantly? When the stall warning was operating, the AoA was considered valid, so the THS would stop provided the stick was neutral.
When the stall warning was not operating, the THS could auto-trim if the AoA was below the stall-warning threshold. And if the AoA data was invalidated, my understanding is that it could auto-trim regardless of how high the AoA was.
But would the back-stick not have overridden the "Vc Prot Law" anyway? If that was not the case, would the THS have ended up at 13NU?

Hope this makes some sense.

I agree with the much slowed response at the low speeds and AoA. It is quite safe to assume that any recovery at these speeds and angles would have been relatively slow.
Where I'm not so sure if I understand it correctly is the thing with the Sine.
I will give it a try based on how I understood your approach:
As long as the flow does not separate it is not the speed along the chord but the speed along the Flight Path which is relevant for the lift. Therfore the lift component which is trying to tilt the aircraft Nose Down around an unknown center of rotation will be simply a function of the square of the speed along the trajectory.
The sine will apply with regard to the center of the Earth (i.e. the external coordinate system) but not for the coordinate system of the aircraft itself. Therefore it should be irrelevant for Nose Down with regard to the aircraft coordinate system. This assumes that the sum of external forces acts at one point on the aircraft and acts in the direction of the flight path.
This is a little oversimplification because the external forces consist of gravity, momentum, aerodynamic effects and thrust of the engines. It has to be noted that the latter two do not act exactly on the same point on the aircraft therefore making my assumption not 100% correct. Therefore the aircraft coordinate system is not completely independent.

Was a bit lengthy and probably even more difficult to understand what I mean but I hope I understood your description correctly if not you can ignore my comment.

Hi Chris - I'm struggling a little to understand what you mean. I'm not referencing anything too complicated, just the statement regarding the Abnormal Law, below.

Now I know the BEA has stated that the airplane never reverted to "Abnormal Law" as a result of the high AoA but they dont' explain why and that is really confusing. Another piece missing, which will show up sooner or later.

Here's my reference - not sure it answers your question:



- in pitch: - Nz law, (with recovered autotrim).

"In haste", as you say Chris!...gotta do some work. Hor's de combat so to speak, over the next while.

henra, 122

Not at all and thanks for the patience. Shows just how much I (don't)
know about aerodynamics.

Ok, if lift doesn't change significantly until beyond stall, but
the position does, other methods could be used, such as >1 pressure
transducers at critical points on the surface. If these were summed
differentially. the position of lift could be calculated, thus approach to
stall.

Going back to the strain gauge solution, assume that the lift position
produces a variable twisting moment to the wing ?. If so, this could
be measured to determine lift position.

Probably completely off the wall and i'm sure there's no shortage of
ideas, but it is Friday :)...

Quote from Lonewolf_50:
The recorded cockpit briefing about temperature not developing as planned/forecasts may be of no moment ... or maybe a clue pointing to TAT readings sensing beginning to degrade as Airspeed sensing began to go wrong?

I'm inclined to think the former. Looking again at that Jetstar A330-200 incident FDR-trace that mm43 kindly provided us last night (GMT), the TAT down-spike when Mach and CAS collapse is quite small (~5C), whereas the coincident up-spike of SAT is large (nearly 25C), in order nearly to meet the TAT – as you would expect at Mach 0.2.
When looking at the possibility of step-climbs, we look at the decreasing weight and the SAT (and its deviation from ISA), not TAT. Some large jets are limited mainly by buffet margins, others by thrust (the classic examples being respectively the VC10 and B707-320). With its high-bypass turbofans the A330-200 is thrust-limited, so the higher the temperature, the later the step-climb. The crew would have been comparing the SAT readings with the forecast OATs on their computer flight-plan: hence the remark.

Considering your second option, on the other hand: if the CAS/Mach readings had already started insidiously under-reading, causing an over-reading SAT, the A/C would have been actually speeding-up without their knowledge. Not sure if it's possible to prove or disprove that possibility. GS doesn't help because we don't know the wind-component.

Abnormal Law.
 

PJ2:
I didn't go into 'Abnormal Law" as stated by BEA and 'confirmed' by this data:
http://www.pprune.org/tech-log/45283...ml#post6499464 for whole post.

@PJ2:

Quote:

---

would this be a correct understanding of what you meant?

---

and

@Chris:
Exact! Thx to you both for making this clear and with apologies, english is not the native language.

A33Zab;
Did you actually mean:-

Actual AOA could be indeed 40° while not triggering ABNORMAL ATTITUDE LAW due to a median CAS value < 60 kts (resulting in a AOAi of 0°) as already mentioned in the BEA ‘leak’.

Abnormal Law.
 

@mm43:

Yes, indeed in this context from the BEA May, 27 update:

Zoom climb
 

Nobody knows what is going to happen when an a/c enters a thunderstorm. No one.

If a strong enough updraft occurs it could push the plane up at 7000 fpm at the same time sending the nose down thus possibly causing nose up trim.

In addition no one knows for sure what the airplane will do when it is in a deep stall.

One thing i know, it is difficult to fly an out of control plane with trim alone.

uncommanded climb
 

GarageYears

"your are implying the climb was NOT of the pilots command? I can see nothing to support that assertion. "

Theres nothing to support it either.

Quote:
Hi Chris - I'm struggling a little to understand what you mean. I'm not referencing anything too complicated, just the statement regarding the Abnormal Law, below. Now I know the BEA has stated that the airplane never reverted to "Abnormal Law" as a result of the high AoA but they dont' explain why and that is really confusing.

Struggling? That makes two of us! Sorry it didn't make sense. By the way, I had not considered the possibility of Abnormal Attitude Law. Perhaps I should.

If the initial drop of IAS on ASI 1 and ASI 3 was sufficient to trigger Abnormal Attitude Law, what would have happened when the ASI 1 recovered to 215kt at FL375? The IAS/Mach, AoA, Pitch, and Roll no longer justified it. In these circumstances, you note:
After aircraft recovery, and until the aircraft is on the ground, the available laws are:
- in roll: - yaw alternate law, (in this case Alternate Law 2)
- in pitch: - Nz law, (with recovered autotrim).

So autotrim would have been recovered? In which case, it would have resumed trimming: partly, perhaps, to neutralise the increasing up-elevator that had been selected by the system – to maintain the G demanded by the sidestick as the airspeed fell – while the THS had been frozen. It would certainly have needed to trim nose-up for the continuing decay of actual CAS as the aircraft approached FL380.

It is unclear precisely when the AoA reached +30, but at that point the THS would presumably be disabled again. My assumption is that the 1 minute taken for the THS to move from 3NU to 13NU would have been completed before that point.

In the post you are discussing, I proposed that the PF's "nose-up inputs" may have overridden any stall protection in Pitch-Alternate Law. If Abnormal Attitude Law had been triggered, it seems from Andy Tracey's paper that stall protection is not provided.

Reading the above, it all sounds exceedingly speculative in the absence of data. I only post it to show that, after some thought, I share your present confusion.

PS
Thanks, A33Zab, I had no knowledge of the BEA's "Leak". Whoops... :{

A33Zab;

Thanks for your note re Abnormal Law...yes, I knew from the BEA 'leak' that the aircraft had not entered "Abnormal Law". In my note to Chris I was describing how the autotrim function would return once the aircraft was within the AoA limits for it's operation. Why it didn't go into Abnormal Law as a result of the high AoA does make sense to me, thanks.

To be sure, in all cases of all Laws, the THS is trimmable through the mechanical system unless jammed.

Please don't worry about your English...you're doing just fine.

Turn rate during rapid descent
 

Forgive please, if this is already addressed...

During the descent - in a nearly level attitude - the aircraft turned either 90 to the right, or 270 to the left. Now then -

If the crew actually felt they were overspeed, and noted the fact they were changing direction, did they not feel the centrifugal force that would be created by that change in velocity vector?

With benefit of hindsight, this would seem to be a crude but effective means of differentiating between overspeed vs underspeed, when Pitot instruments are unreliable. Turning at anything approaching a standard rate, at or above cruise Mach, would glue one to his seat. :8

Hi,
A very humbly question: is the speed from Pitots corrected with AoA data?

If not, or if a 61° AoA is not take in compute (as "invalid"), the IAS from Pitots has to be: cos61 x square root (107² +107²) = 0.48 x 151 = 72kts IMHO (61°, 107kts refering to post#100, first figure).

As syseng68k suggests, probably that simple strain gauge tranducers would do the job (on the mechanical link between the actuator and the control surface, and even on the control surface itself). All the strain signals (along with IMU signals, GPS signals, AoA signals, airspeed signals,...) could feed in real time an aerodymical model of the A/C (control surface+airframe) to derive these aerodynamical authorities and much more: in particular, it could also help to cross-check the integrity of all the incoming signals (navigation and attitude, AoA and airspeeds,...) in a more efficient/flexible way than it is currently done, and generate a reliable stall warning.

To further illustrate that good reminder from Chris Scott, here are two views from the left hand side of the THS :

http://i25.servimg.com/u/f25/11/75/17/84/af447_19.png

http://i25.servimg.com/u/f25/11/75/17/84/af447_20.png

Good eyes are needed, but a scale is visible just forward of the THS.
Both THS are at the GND SET position, which is also 4 deg UP, or minus 4. That’s the position where the THS is automatically reset after every landing.
The 0 (zero) position is also visible, with 2 units above and 14 below.

As the CG was pretty much forward for the AF447 takeoff, at 23%, the THS had probably been set initially at a position around 6 deg UP.


DozyWannabe, if tomorrow I don’t make it, I want my wife, children, best friends, to have a look TOO at MY data when my authorities will set their dirty move.

PS : Thanks for your friendly pm - I will answer or comment when time permits.


EDIT : Much better view on the scale on this image proposed by aguadalte
Punta Cana, Dominican Republic: Orbest Airbus A330-200 CS-TRA - detail of horizontal stabilizer - Punta Cana International Airport - PUJ / MDPC - photo by M.Torres - Travel-Images.com

http://i25.servimg.com/u/f25/11/75/17/84/af447_13.jpg

Promotion recommendation
 

I move that jpete, Probationary PPRuNer, be promoted immediately to Newby 1st class, with Elephant stamp and Star. Seconders? Ah. I see Thread Boss has already done that in effect.

Thank you jpete, for a wonderful tool. I hadn’t grasped the full power of Googles’ ‘site:’ prefix, and was only using it simplisticly to search my counties’ sites.
____

Thanks also all you others, who responded to my ISUS search query (ICUS sic). I drove the first steam age A320s for a bare 100 hrs or so, and I see the pneumatics are as always. However, I was mostly interested to discover the degree of autonomy that the new digital S/B 'A/H' has.

I twice suffered loss of all driven flight instruments, (not on the 'bus!) once a total shut-down for 8-10 mins, and the other more insidiously with both the ADI & HSI freezing in place with no warnings at all, both in dark-night. I therefore used to be somewhat paranoid about finding out how long each type that I flew could last on battery power, after loss of all electrics (had once), and would develop an Apollo 13 like power-down procedure, until all that was left was the 3A (IIRC) S/B AH, a torch, and the SB pneumatic gauges, radio sched call each 30 mins, from the one (motorbike rated) 20 A.H. NiCad battery in the belly, just in case I lost all elects again. With 3 hours max to the nearest available, highly desirable. I also frequently practiced hand flying on cruise to 'freshen up,’ and was always very manually current.

This preamble is to say that, given the 'bus’s zero stick-feedback, zero throttle-feedback, and non-amplified vertical attitude tape response (as, say, the Concord had in cruise), the thought of hand flying the A320 on cruise was a bridge too far for me. To return to the thread: Even given that hand-flying is actually only providing joystick like CWS inputs in Airbus's FBW logic, and far too coarse for the delicate inputs needed at high altitude, I cannot see how any line pilot, and possible even any test-rated pilot could hand fly this extreme initial jet upset, the cause of which remains a mystery I understand.

My interest in the ISIS was actually related to the soundness of the attitude display, whether it’s attitude reference is integrally sourced as the original A320s were, or whether the ISIS is dependent on external reference in any way. The manufacturers specifications make no mention of this. If the ISIS *is totally independent in attitude, it does seem odd that there appears to have been no flight guidance reference made to it, at least discussed. In such an upset, I would have been glued to it, regardless of all other indications.

But then, who can discuss realistically the forces in the interior of a Cb, except those who have done so and survived, usually with hairy stories?

In regard to PJ2’s comment: “..never saw the "slight increase"!” (a pitch-up) PJ2, it certainly existed in the climb. In every previous type I flew when possible I used to hand-fly to TOC. Constant refresh of cp movement/mach tuck, etc. That went out on the 320, with the pitch up. It was approx 0.2 deg/sec, which required approx 10 g nose down force applied to the top curve of the side stick to neutralize. (A gentle little-finger pressure.) Somewhere on file I have copies of the two (typewritten) letters I wrote to Airbus directly, requesting an explanation for the apparent external force being applied in CWS, which could compound a situation if a pilot chose to rely on CWS in some situation. Seems it may have been the 1g at increasing altitude effect. I never did heard back from Airbus.

In the meantime I go back to exploring the implications of RetiredF4's eye opening post (his~her reference to Ostawiri & Naik’s post stall study of the NACA 44x airfoil lift curves specifically) which has chilling implications which I find quite disturbing.

In memory.

First of all: Thanks a lot for the interesting reference.

However there is one thing where I have to admit I disagree a little bit with your conclusion.
The drag along the flightpath would apply a Nose down moment on the Aircraft of (Rho/2 Cd A V^2 * sin (Alpha)* distance from center of rotation (sin Alpha ~0,87 @60°) while lift would act with the cosine, being 0,5 @60°.
Overall moment at 60° would be 0,5 * 1,0 + 0,87 *1,6 = 1,885 times the constant rest.
at 46;5° it would be 0,72 * 1,2 + 0,69 *1,2 = 1,698 times the rest.

Therefore the increase in drag would have more impact than the reduction in Lift in the given example.
The overall ND moment would increase in your given example.
As I already mentioned: at these AoA Drag acting on the tail is a good thing. It supports Nose down moment.

Re @ Henra
 

Re Henra

Lets face the fact, that finally it´is the sum of all moments, which lead to the desired outcome. Wether the CD produces some ND input and CL produces some NU input or vice versa, the effectiveness of it depends on the sum of the individual forces. And as stated before, the CD and CL change of the wing has its share in the equation as well.

If we agree, that it never was the designed specification of this THS to get the AC out of a 60° AOA but to keep the aircraft in balance under the normal flight conditions by creating less or more ANU forces (curvature to produce downward lift on the THS), then the regime we are talking about here is as distant as the moon from the sun.

To get the desired AND vector, the THS airfoil has to produce lift opposite to its original design ( like if the main wing would have to produce not upward lift, but downward lift like during extreme pushover). I´m not saying that that is not possible, there are airfoils with symetrical curvature working as well by just changing the AOA of the airfoil (like the F-104 Starfighter main wing), but those designs are specifically crafted for that aircraft and its desired performance, and despite that, it had been highly succeptable to stalls and creating high amount of drag once outside desired flight envelope. I´ve lost lots of friends in accidents with this otherwise wonderful aircraft.

Another point i´m still curious, but have no expierience in it, so just correct me. I get the impression, that some posters simplify the function between lift and drag to the region of the pre stall flight envelope, and thus setting a constant between drag and lift, meaning where there is drag on an airfoil, there also has to be equivalent lift. 35 years ago i learnt in my academics classes, that if the airfoil produces lift, it also causes drag called induced drag (but not vice versa) up to max CL is reached (nearly linear function of drag and lift), but after that point drag continuous to increase while lift decreases. In our post stall discussion there are no formulas available to compute lift from drag, because there is no constant behaviour anymore outside the wind tunnel.

It is also way off reality to disregard the huge amount of drag produced by that stalled airfoil in the context of recovery efforts. To get any usefull output of the ND movement, we have to get the wind flowing over the lifting devices by increasing speed (which is the ultimate reason to decrease the AOA). When we increase the drag and thus reduce the forward velocity vector even more, we increase the descent rate by a comparable amount, thus increasing the total AOA again.

So it is no sense in discussing single points of some more or some less lift if it is not changing the overall problem to get the aircraft out of the extreme AOA condition within the available altitude.

One thing i´m sure : The simple stick forward and wait, like some are saying here, would only have worked up to a defined value of AOA and speed, and i see that value of AOA well below 45°. The discussion what the crew did do wrong in recovering the aircraft once established in the descent (estimnated FL 300 downward ) is IMHO useless, because there was no "conventional method" available which would have brought AF447 out of this position.

The problem lies in the beginning with the extreme climb rate, the chance to recover the following upset ended somewhere between FL 370 and FL 300.

Pitching moment at large AoA
 

@RetiredF4 and Henra;

Perhaps you should have another look at Figure 6 in the document linked by
zumBeispiel six weeks ago. Admittedly that is not an A330, but what makes it different?

First you have to reduce AoA to unstall the wing, then you need to increase speed to not stall again.

indeed there is no way to calculate Lift from drag as Lift is not a function of drag.
What we have are merely datapoints from experiments on given airfoils.

That is everything we have. That said I hope I wasn't unclear when referring to drag acting as lift. That does not mean a mixing of Cl and Cd. They are orthogonal to each other. The trick is the coordinate system. When the aircraft has a high AoA there is an angle between both Cl an Cd and the Airframe itself as Cl and Cd are measured along the stream of air, i.e.the flight path. Wwhereas the moment and its related arm act on the airframe which is angled against these forces.
Lets assume the plane is falling at 90°. In that case it would only be the drag component of the Tail that would lead to ND forces. The Cl compnent would work orthoginally to the flight path, i.e. forward, which would be Nulll in that case.
I hope it gets clearer now what I want to explain.

Wing Aero
 

In all these pages, I have seen no mention of the basic airfoil of the A330. It's probably some version of supercritical, correct? What is its stall behavior?

RetiredF4
I don't think this is correct. Sustained full forward sidestick is effectively a demand for minus 1g. If the initial elevator movement did not achieve this the THS would immediately move in a nose-down trim sense to assist - if necessary as far as the stop. The difficulty lies in recognising the requirement for the forward sidestick.

Hi Tyro,

"The maximum elevator deflection is 30° nose up, and 17° nose down. The maximum THS deflection is 13.5° nose up, and 4° nose down."

I agree with RetiredF4. If the side stick had been held fully forward, the stab trim could have changed the THS's angle of attack by about 17.5 degs. Unfortunately, all that would have achieved would have been to INCREASE its angle of attack. The Stab is permanently stalled in their situation.

Greybeard;

On these airplanes the airfoil section (thickness, camber and 'incidence') varies considerably from wing root to tip. The stall behaviour is not simply a function of the airfoils, but involves all of the wing and even all of the airplane including the fuselage.

As others have mentioned, what matters is the NET pitching moment. If there is enough pitching moment nose down, rotation nose down will occur.
There is Lift and Drag after stall. Lift does not suddenly dissapear post stall but follows a variable path toward zero lift at ~ 90 degrees angle of attack (and becomes 100% drag there)
The path depends on:

Angle of attack-The Primary variable
Aspect Ratio,
Airfoil thickness ratio,
Reynolds Number that the wing is operating at.

Take some time to understand the following document regarding post stall aerodynamics.
http://home.comcast.net/~shademaker/...tStall44XX.pdf

Promotion reccomendation: K.I.S.S. "tool" for finding stuff in past threads*
 

Hi,

(*) jpete 1st post

Perfect! And with the Simple Characteristics defended by Kelly Johnson, Einstein, St. Exupéry, Occam, Leonardo Da Vinci and (some) other designers / engineers.


Machaca told me (and he was right) to look all posts before the ones i made and was making on a/c recorders. And now i will be able to post, checking not only here (AF447) but in many other PPRuNe threads.

Albert Einstein's: "everything should be made as simple as possible, but no simpler."

Leonardo Da Vinci's: "Simplicity is the ultimate sophistication."

Antoine de Saint Exupéry's: "It seems that perfection is reached not when there is nothing left to add, but when there is nothing left to take away."

Harry Hawker's: "Simplify, and add lightness."

William of Ockham: "the simplest explanation is most likely the correct one."

Bertrand Russell: Whenever possible, substitute constructions out of known entities for inferences to unknown entities."

K.I.S.S. The acronym was first coined by Kelly Johnson, lead engineer at the Lockheed Skunk Works (creators of the Lockheed U-2 and SR-71 Blackbird spy planes, among many others).

When possible we must avoid K.I.C.S. designs. There are (many) examples...

Hi Machinbird,

Thanks for the link - but I think you mean "Lift does not suddenly dissapear post stall but follows a variable path toward zero lift at ~ 90 degrees angle of attack."

Previous posters have suggested that if the stab angle of attack is about 45 degs (around the second lower peak of CL), then changing the angle would merely reduces the lift on the tail (hence aircraft nose would rise).

Re LI9nk
 

Machinebird, the link is known and my statement concerning the effectiveness of the THS for ND is based on it. .

See my post No. 35 and PickyPerkins post No. 100 in this thread.

Another thought to relation of THS and wing:
In the post-stall the main wing produce some ANU lift, the tail produces some AND lift. Due to the more sophisticated design of the wing it could be possible that the wing produces more ANU lift than the THS could counter with AND lift. Remember, in normal operation the THS only produces ANU lift, therfore the camber is on the downside of the THS.

And lets look at the drag, which is working as a turning force around the lateral axis: The drag of the forward part of the fuselage and of the forward parts of the wings woking ANU night well be greater than the AND force by the fuselage aft of the wings and the THS.

Entire plane aero
 

Hi,

Quote:

---

even all of the airplane including the fuselage

---

The "rectangular belly" is perhaps an "important part" of this?

Fully agreed. That is the real unknown when it comes to the net effect at 60°.
It might indeed be the case that the forward fuselage creates equal or higher lift than the tail, although at least for the A330-200 with the relatively short forward fuselage I doubt it.
edit:
Where I do not fully agree is the hypothesis taht the main wing will create a net NU moment. In non stalled condition the Center of lift is close to the quarter chord line. At fully stalled condition the Center of lift will move to the mid chord line. (It is only in a transient phase when the tips start to stall and the root is not yet stalled where you might encounter a NU effect. But at 50°+ AoA that is defintiely not the case any more)
/edit

This assumption is to some extent supported by the cm curve in the link as it suggests a net reduciton of cm with increasing AoA, i.e. a ND tendency.

If this was the case with AF447 we will probably never know as it appears that the Pilots unfortunately never really tried it.

hmm, somehow I'm completely at a loss how you know that for sure !?

Would you mind sharing your source ?

Hi henra

post 147 first line is copied from FCOM.

The elevator was effective in the correct sense as reported by BEA. It wasn't used enough to recover.

Hi CONF,

If the information is accurate, I wouldn't call it a "dirty move". It may not be pleasant to hear, but according to what the minister has been told, the pilots were supposedly trained to handle pitot icing/blockage incidents, mode reversion and all that comes inbetween in this incident.

Note that he's not saying the aircraft is blameless - he can't because the information is out that the pitots were probably the initiating factor. The BEA were the ones who released that information publicly when their initial interim report was released a couple of years back - if they really wanted to "stitch up" the pilots then they would never have released that information.

As I said earlier - the BEA can be said to have handled a single AF/Airbus incident "badly", though personally speaking I wouldn't have wanted any part in that political minefield. That incident was 23 years ago and they're still dealing with the damage that did their reputation today. It would be utter madness for them to try to do so again, so I say again, give them a chance.

Pilot error?
 

DozyWannabee

“I ask again - why is it you're asking this of the BEA and no other accident investigation bureau/institution? Is one incident forever going to preclude acceptance of any finding of theirs that includes "pilot error" as a factor?

Also, you're a pilot, I'm an engineer - but I wouldn't trust myself to derive a correct conclusion from the raw data. What makes you so sure you could? “

Just for the record, the mission of EVERY investigating body, is to gather the facts and make a determination of Probable Cause and to recommend a fix, but NOT to affix blame, fault, or liability, which is left to legal venues.

As a pilot all I want is all the given facts and then I can make my own conclusion regarding what to do about it. In this case avoid thunderstorms at all costs. Period.

It is way too early to start figuring out how to recover from an out of control deep stall, when in fact they won’t even allow pilots to practise “hand flying” in the simulator at altitude, let alone in the airplane.

No one knows what the plane is going to do.