A320 Low speed stability

[zonnair]

While reading about the low speed stability, the following question arose, as nothing is explicitly said about it.

During Low speed stability (replaces AoA protection when in alternate law)a gentle nose down signal is intoduced between 5 to 10 knots above stall speed to keep the speed from falling below these values. Can the pilot override this, or not?

Thanks in advance,

[ceststupid]

I reckon, the nose down and throttle up would happen...so would return back to nose up after a short period :)

[Clandestino]

The A320 pilot can can override either low or high speed stability with moderate stick inputs. At least that's how it works on A320 sim, I've never flown real 320 in altn law.

[zonnair]

Thanks my man. So the bus can get into a stall in alternate law? No need for direct law.

[Clandestino]

If you keep pulling, yes.

[zonnair]

Gracias otra vez!!!:ok:

[Clandestino]

Niets te danken.

[ceststupid]

Would the A320 Increase the throttles also if you continued pulling back near the stall?

[Clandestino]

It wouldn't in alternate and direct laws. Automatic setting of TOGA thrust, known as alpha floor is available only in normal law, when alpha protection prevents the pilot from stalling the aeroplane and alpha prot can't be overriden by the stick input anyway.

[ceststupid]

Thanks, I understand now :) I'm not an A320 pilot, just a PPL but I am very interested in learning about these things :)

[h3dxb]

Gentlemen,
Can someone me explain how to get in the so called >alternate< or >direct< law in air ??

Please read once more yr manual before telling somebody such a thing.
There is no direct law in air. How do U want to get in ? Only when U loose all Prims and Secs, but than U have only mechanical inputs.

Of course can the pilot be so unlucky to get in a situation, where normal law in pitch control failed , but than alpha 1 Prot takes over, when this fails , Vc Prot comes, this is overideable in lowspeed only.

But for this we have the high paid chimps :ok:

Logic for the elec control is PRIM1>2>3>SEC1>2
Normal>alternate>protection and direct on GRD

Now calculate the possibility and praise Airbus :D

Sorry but direct law in air is a misunderstanding of the philosophy

rgds

[Dani]

Are you really talking about Airbus?

Everytime you are in alternate and lower the gear you are in direct mode. So it's pretty important to know what to do in direct law.

Or do you lower the gear on ground only?

dani

[Clandestino]

Can someone me explain how to get in the so called >alternate< or >direct< law in air ??

They're not "so called", this is official Airbus terminology. FCOM 1.27.30 has it very neatly explained.

So, has the Airbus really changed FBW arhitecture on latest A320s from FAC/ELAC/SEC to PRIM/SEC, or what we have here is the charge of the MSFS brigade?

[h3dxb]

DEAR ALL

pls check once more yr manuals, for a so called direct law U need
-triple ir fault
-triple prim fail
-two elev fault
-both eng out

in all other failure/law configs U have still protections, in alternate mode the AOA protection is still there. RYFM :ok:

Ground mode or direct law for pitch control is till 8 sec after liftoff, from 100 ft down to ground U swap into flare mode, touchdown + 2 sec direct law.
So U R really unhappy when U get >>>direct law<<< in flight !!!

rgds

[Dream Land]

Please read once more yr manual before telling somebody such a thing.
There is no direct law in airYou must specify between the A320 and A330, the A320 can degrade to Direct Law while in flight.

[Clandestino]

A330 and 340 can too. FCOM 1.27.30 FLIGHT CONTROLS - RECONFIGURATION CONTROL LAWS refers, no matter whether it's 320, 330 or 340 manual. Getting into direct law while airborne on TA Airbi is very unlikely yet it's possible.

What's the name of the thread, anyway?

[ALK A343]

All Fly by wire Airbus airplanes can end up in direct law in flight. On the A320 series it is a bit more common though than on the A330/340 as the architecture of the flight control computers is less sophisticated. On the A320 if you loose both flight augmentation computers (FAC) in flight you revert back into alternate law and upon landing gear extension into direct law. On the A330/340 a simple dual radio altimeter fault will have you ending up in direct law upon landing gear extension when the autopilot is switched OFF, we practice this exercise in the simulator. Low speed and high speed stability on all fly by wire Airbus can be overridden by the pilot and since alpha floor is not available in alternate and direct law the aircraft will stall.

[Dream Land]

Thanks for correcting me. :\

[DesiPilot]

Not to forget if you have duar RA fault, when you extend the gear, the aircraft will go from Normal law to Direct law.

[shortfuel]

h3dxb, have you read the title of this thread?

We're talking A320 here, not A330! So no PRIM, no SEC's (and I mean Secondary Flight Control Computer not Spoilers Elevator Computer)...on A320.

It's quite feasible to end in Direct law on A320, and far more unprobable on A330 I admit.
If a failure leads you to fly in alternate law, you WILL end in Direct Law once the gear is down, why? Because there is no Flare law in ALTN law, the only way to flare the aircraft is to put it in Direct law...it has been designed like that.

But again, the related topic is on A320, not A330/340.

Edit: this msg is redondant with ALK's...saw it after.

[zonnair]

That's it!!

Flare mode only effects the pitch control. When L/G down (in alternate law), this will revert to direct stick-to-elevator relationship (DIRECT MODE)

However. there is an exception, when in alternate law due to the abnormal attitude laws. In this case there is no reversion to direct law at landing gear extension, as everything is working properly.

[PantLoad]

Can the A-320 series Airbus be stalled in flight in normal law? If so, under
what conditions/circumstances?

The answer can be found in the FCOM.....


Fly safe,


PantLoad

[shortfuel]

Out of memory (so no precise ref.):

In "appropriate" conditions (i.e. high angle of attack, severe loss of energy...) + :
- normal law + autothrust inop
- ...EPR Control Mode Fault (IAE engines)
- One Engine Inoperative with S>0

Basically all conditions in normal law leading to a loss of Alpha Floor function or part of it (thrust part for instance here).

However. there is an exception, when in alternate law due to the abnormal attitude laws. In this case there is no reversion to direct law at landing gear extension, as everything is working properly.
Any reference for that? ;)

[Nick 1]

Why you want to stall an Airbus 320 ???

Nick 1

[bucket_and_spade]

Do you Airbus jockeys find it difficult to keep aware of how the aircraft will try and perform in certain abnormal situations i.e. when the control laws change and in different phases of flight? As a non-Airbus pilot I get the impression that it would be very easy to lose track of exactly what the aircraft capabilities/protections/responses/etc. will be with degraded control logic.

Genuine question.

B&S

[zonnair]

Even the intellegency of such a wonderful European creation, sometimes causes questions. My dear B&S. Don't worry to much about it.


Quote:
However. there is an exception, when in alternate law due to the abnormal attitude laws. In this case there is no reversion to direct law at landing gear extension, as everything is working properly.
Any reference for that? http://static.pprune.org/images/smilies/wink2.gif


FCOM 1.27.30 Abnormal attitude laws


Out of memory (so no precise ref.):

In "appropriate" conditions (i.e. high angle of attack, severe loss of energy...) + :
- normal law + autothrust inop
- ...EPR Control Mode Fault (IAE engines)
- One Engine Inoperative with S>0

Basically all conditions in normal law leading to a loss of Aplha Floor function or part of it (thrust part for instance here).


You are still having your AoA protection, meaning you won't exceed alpha max, even with sidestick fully aft.

[PantLoad]

Shortfuel is correct....

Good job!

Fly safe,


PantLoad

[Dani]

B&S, you don't really "feel" the transition from one law to another, except the direct of course, where it is a little instable and small correction on the stick cause stronger inputs, some sort of a sporty aerobatic plane in level flight.

You only know that you changed laws by looking at the warnings and cautions you get on the ECAMs. Most of the time you come out of the sim and the instructor says "that was now alternate" and you say, uh, that's why. But you don't have a big red lamp on your dashboard where it says "ludicrous law now".

So everything is pretty much straight forward and doesn't need any special intellectual or haptic challenges. One point on the "Golden rules of Airbus flying" says "an Airbus behaves like any other aircraft", and so it is.

Dani

[shortfuel]

Thanks for the ref. Zonnair, never spotted that one! Never wanna get close to it.

So you think, this A/C cannot stall in quoted conditions just thanks to the remaining AoA prot.

If you get the chance, in a sim, on a final:
CONF Full, Gear down, Fail the A/THR and request significant negative W/S, see what happens...:rolleyes:

[Clandestino]

What happens is pilot hits toga, follows SRS even if it requires full back stick and survives the sim scenario. Emphasis being on "pilot".

Dear certain PPRuNers, you are mixing up alpha floor and alpha prot. Despite both having "alpha" in their names, they're quite different animals. Alpha prot is function of FBW that limits AoA, alpha floor is automatic setting of TOGA thrust regardless of power levers position. As long as normal law is alive and kicking, alpha prot is available, but alpha floor can be deactivated through autothrust deactivation (this is not mere disconnection). The horror scenario described in the previous post may end up in aeroplane hitting the ground (or trees) at very high angle of attack and engines at idle, but it can not end up in stall. And I don't merely think that fully operational A320 can't stall due to alpha prot - that it can't is a fact and not an opinion.

[zonnair]

At alpha max (AoA protection) you will go down, if no additional power is added. But going down does not mean stall. Alpha floor has indeed nothing to do with this. It is just another feature that prevent the a/c from stalling, but only when A/THR is operational.

Conclusion indeed is: In normal law you will have AoA protection that will prevent the a/c from excessive AoA (stalling). This does not mean it prevent it from descending or from being slammed into the ground due to WS, or whatever senario you would like to create. For that you still need pilots input.