Actually, the amount of stick you need to generate that rate of climb isn't a lot: as a rule of thumb for my TCAS responses (passed on down by an old hand) I use: 1° of pitch change results in about your Mach number in Rate of Climb: If you're doing .8 and you pull 1° of pitch, your ROC will be around 800ft/min. I haven't actually used 10° on a TCAS RA :eek:, but lesser changes indicate those numbers are pretty close. It's not difficult (and certainly not severe) to pull 10°: there's your 8000ft/min climb rate... for a short time at least.

a lot of the discussions on the airbus fbw and just what is HAL capable of have questioned whether airbus actually do stall testing to garner data, does this post from way back throw any light on that

page 111 post2216

Quote:
Originally Posted by AM
The Concorde prototypes had a crew escape hatch
I'm not sure what your point is, but all the Airbus prototypes I've been on have had crew escape hatches. They would be used in case something went very badly during any of the many stall tests that were done

Quoting Capn Bloggs
You're measuring the stick movement by the effect of pitch on the plane - rather than the position of the control surface.

Having never flown anything heavy, my assumption is that to reach an 800FPM climb (FACs not-withstanding), you would pull back on the stick far enough so that your target ROC was reached in perhaps 5 or 10 seconds. Then you would relax the stick a bit to hold that ROC.

However, if the control surface (the elevator) jammed in place you would find yourself at 800FPM in say 7 seconds, 1600FPM in 15 seconds, 2400FPM in 24 seconds, and only a your airspeed would keep you from completing an inside loop.

If that rate of climb isn't enough to build up to what was seen in RADAR, then perhaps the pilot was merely trying to maintain altitude in a sudden down-draft. He may have been very aggressive in trying to restore altitude and attempted to cause that 1 degree pitch up in much less than 7 seconds.

The point is that a control surface movement applied for 5 seconds can be very normal - but when jammed in place for tens of seconds can be very severe.

Also, there is no deicing provided on the tail of the A320.

CG
 

On a swept wing, CG will always move back with fuel consumption if you deplete inside tanks first, which is preferential for wing loading

( assuming no other tanks, only wing tank )

The Stabilizer is for stability (hence the name), but it does not necessarily have to "push down the tail" for that. Only the momentum arms around the center of gravity, the wing area and the lift over AoA curve slope define whether an aircraft is stable or not, this does not determine the direction of the stabilizer force. To word it very simplistic, an aircraft is stable if the wing loading of the forward wing is greater (taking into account the sign) than that of the aft wing. If the wing loading of the aft wing is negative, this is the trivial case. But it might be also slightly positive (the stabilizer lifts the tail) while still maintaining stability. All modern gliders produce lift on the tail for speeds lower than best glide. However, to compensate for the pitching moment of a cambered airfoil on the main wing, the stabilizer always has to move the nose up (i.e. a Canard has to produce lift, a conventional tail has to push the tail down)
The highest stabilizer downforce required for modern transport aircraft is to compensate the extreme pitching moment of the main wing with full flaps. In cruise, modern aircraft do not produce significant downforce, some even produce slight lift. However, due to complexity trim tanks do disappear again, and we are now moving a bit away again from the idea of the stabilizer producing lift, as the drag penalty of the stabilizer downforce is neglectable in transonic cruise.

Thank you Volume for reinforcing that very point; the THS of a modern airliner has a negative camber, a point that I believe has been lost in the preceding discussion.

If that is the case it seems somewhat dilatory to not provide the aircraft stall and post stall behavior information to the simulator designers. The sim behavior would be then be correct; and we are repeatedly told that it is not as there is 'no data' to base the behavior on.

post 3061 - RetiredF4
What good would that do ? If "the system" wants 1g, if you trim the THS nose down, won't it just keep feeding in up elevator to counter you, until it is finally full up ? By that stage you will have far more THS nose down trim than is healthy. Might you then be in a worse place than from whence you came ?

No. When you apply full forward stick you get full elevator travel, at least until the lower G limit of -1 is reached. If you manually move the trim wheel, automatic stabiliser trimming stops for a period of time. Hence, a little nose down stab trim can be a bad thing if the pilot then subconciously is relying on the FBW to complete the THS nose down travel.

In the very high AOA cases they claim there is no valid data set upon which to build a sim model. Yet Airbus used a sim to model the AF447 flight. From that experience they changed the stall recovery to include the selection of flaps one below FL210, the goal being to extend slats, thereby decreasing the net angle of attack. They also noted an improved stall recovery with manual stab trim, exactly as in almost every modern transport jet.

We used to go decades without hearing of a stall accident. Now it seems to be weeks. What gives?

Post 3069 - Leightman 957

http://www.mediafire.com/view/sdwzcc...ll-nasa-03.jpg
http://www.mediafire.com/view/2sa52g...l/Capture5.PNG
http://www.mediafire.com/view/2t762l...28129_full.jpg
http://www.mediafire.com/view/idkla5...26847_full.jpg
http://www.mediafire.com/view/d62mdh...26845_full.jpg
http://www.mediafire.com/view/fq4874...ain_H-1242.pdf

Deep Stall
 

When the AF accident took place I went to the sim to reproduce the accident.

35000 ft ,ALTN LAW , pitch up , gained altitude , until stall.Once the airplane was completed stalled , with R/D nearly 10000ft/min , started recovering.

As per manual. Nothing . Tried a few times with and without power but with sidestick ALWAYS full forward. Result: crash.

There is only wat to get out of the stall.Keep the sidestick full forward and imediatelly manually pitch down the trim wheel.Very fast. And then you recover at about 20,25 thousand feet.

Furthermore:

Airbus blames it is impossible to stall the airplane in NORMAL LAW. IT isn`t. It is possible and it already happen without consequences.

Did you throttle back, or bank the a/c 90 degs, or lower the gear etc., to try and get the nose down? If so and were unable to recover as you have written, the a/c should not have been certified in it's present state, IMHO.

Was the appropriate high altitude stall data programmed into the simulator?

Are you for real? 40° AOA, full power, 10° nose up descending at 10,000ft/min all the while banking/turning and you think the FBW will be trying to give you 1g? In any case, a full nose down stab+full nose up elevator is bound to be better than the other combination when you're trying to get out of a stall if the silly FBW is opposing your full nose-down stick input...

I don`t know if the sim really reproduces the airplane bahaviour. But it is supposed to do it.
Despite I think test pilots never took the airplane to such conditions in order to see it.

Thanks for your input. I don't think they did either.

The system wants, what is demanded by the SS position. Therfore the positioning of the SS to nose down is the first priority. If that works, than fine, but if it does not work fast enough, than the trim most probably is already all the way up.

If we look back to the documented stall accidents we know, that most crews were reluctant to do that in an appropriate way. The ND input was not present at all, was not far enough nose down, not long enough down or accompanied by noseup inputs averaging in an overall nose up input. This inapropriate SS handling may command a loadfactor value greater than the one present while descending in a stalled attitude. The consequence is that the flight computers may drive the elevators and in turn the THS trim to full nose up position.

As long as the elevators are nose up from neutral, the trim will not move afaik despite the SS nose down position. As the certification requirement is -1 and +2.5g, I assume that a full nose down SS input would not deliver more than 0 G (i could not find a reference with the applicable loadfactor demands in relation to the SS position). A controlled manual trim input would assist the SS input and not counter it.

In A320 series the THS trim might have stopped depending on the law reconfiguration, and it might only be available in mechanical mode.

But is there time for error and try?
As I said before, follow the procedure, which says under step 2.b
" Nose down pitch trim .......as needed.

RetiredF4;I concur. Experiments with the A330 sim, (understand the arguments re sim "duplication of stall" and "no-data", etc.), demonstrated that the THS followed SS position; full-ND SS brought a -13° THS setting (the result of an extended NU SS), to approximately -2°, recovering the stall in about 45" with a height loss of about 15,000ft. Manual rotation of the trim wheel forward could only help.

IIRC from the Perpignan accident report, the THS stops trimming with a stall warning. I would have to consult the report again to see if a comment or recommendation regarding the use of manually setting the THS would have provided conditions for recovery - they didn't have much altitude to start with...

Yep, I agree. You would ideally like to dial in a 300 knot trim setting, and only if you absolutely needed it to break a stall would you go to a lower trim setting. But them you better have PNF primed to dial it back pronto as soon as the airspeed begins to accelerate past 200 knots.

Probably better to rock the aircraft out of the stall than to dial in those last few nose down units. More than likely, it would be a quicker and more positive recovery.

8501
 

Flaps extension below 20000 or speed brake is the only way to recover
Tested in the sim .. No other inputs will change the turbulent flow .. Perhaps trimming the THS but at 15000 fpm highly unlikely given the severity of emergency and unreliable speed compunded by adr aural warninge and messages . Switching off adr"s and extending the flaps below 20000 and speed brakes , trying to fly pitch n power or BUSS is the only way to recover

Being in a stalled aircraft in turbulence is no fun ,Being in a stalled iced laden aircraft in turbulence in IMC is time to get the QRH prayer mats out.
If you are brave/dumb enough to go into a 50,000 foot CB you will probably be iced up as well and the aircraft deep stall recovery techniques practiced in the sim may not work .
It may need a combination of tail plane ice stall recovery techniques combined with gentle yaw and roll induced by gentle application of rudder to get the gravity working in the right direction to give you relative airflow without overloading the wing or control surfaces.
Keep in mind that any aircraft when it is iced up can be a wobbly thing to control ,and you may encounter some un-commanded pitch ,roll and yaw changes to the attitude that can be confusing .