Airbus Flight Controls Question:

[CVividasku]

Originally Posted by Sim25

That's not correct. Roll law is a roll angle target law. Pilot's order is integrated... If disturbance causes the plane to leave the target it will go back, without pilot intervention.

No it's that.
The roll law is a roll rate law.
As per FCOM DSC-27-20-10-30 :
The roll rate requested by the pilot during flight is proportional to the sidestick deflection, with a maximum rate of 15 °/s when the sidestick is at the stop.

[Sim25]

Originally Posted by Check Airman

So you’re saying if in a 5 degree bank, a gust pushes you to 15 degrees, the FBW will return you to 5 degrees?

I don't see why under normal conditions it shouldn't.

[Sim25]

Originally Posted by CVividasku

No it's that.
The roll law is a roll rate law.
As per FCOM DSC-27-20-10-30 :
The roll rate requested by the pilot during flight is proportional to the sidestick deflection, with a maximum rate of 15 °/s when the sidestick is at the stop.

This isn't opposed to what I was saying
Again the pilots input is integrated so the aircraft behaves the way it's described...

[Sim25]

See https://arc.aiaa.org/doi/10.2514/6.1989-3594 for reference...

[CVividasku]

Originally Posted by Sim25

See https://arc.aiaa.org/doi/10.2514/6.1989-3594 for reference...

I'd like to see where exactly they say that.
If the pilot is asking for 0 roll rate, the target is zero roll rate. Not a constant bank angle.

At least, what I'm saying is consistent with the in-flight behavior of the plane. You still have to counter the gusts. Less than a conventional aircraft, but you still have to counter them.

[Sim25]

Originally Posted by CVividasku

I'd like to see where exactly they say that.
If the pilot is asking for 0 roll rate, the target is zero roll rate. Not a constant bank angle.

Ok last take on this: I cite (out of the paper I referenced): "The objectives are thus: To have an absolutely neutral spiral mode for a bank attitude lower than 33° ie: with the sidestick in neutral position, the lateral attitude will be frozen in spite of any lateral gusts." later it is discribed that "On the other hand, as far as gusts are concerned, the aircraft will respond with modes p1 and p2. If the aircraft is subjected to lateral gusts, as the stick remains in the zero position, the PHI_C target is therefore unchanged and the control loop will counter the gust to bring the aircraft back to its initial lateral attitude."

Of course you have to make inputs in gusty conditions, you want the aircraft to stay on the dsired path (especially while maintaining the center line of the runway when landing). The loop isn't closed in this respect. If you enagage a nav lateral ap mode, it would, but not while hand flying.

Hope this clarifies it

[CVividasku]

That's interesting. However I'm really not sure it would pass the test of reality. I'm really not sure the wings would stay level in gusty conditions. People fight with the stick in order to keep the wings level, not because they notice their flight path going sideways.

It's very surprising. We can't know for sure except if we're in the design office. I'll try to ask some friends in Toulouse.

[Sim25]

Who do you think wrote this paper? Give the headline a try.

[CVividasku]

I'm going to bet it's the guy whose name is written on top of it, who did a PhD in fly by wire for helicopters.
I'd love to read it, however I'm not gonna pay 25 bucks for this paper.

I'd be amazed if it was really unnecessary to use the sidestick to maintain a zero bank angle in gusty conditions.
Did you ever try that yourself in flight ?

[AerocatS2A]

Originally Posted by Uplinker

I manage flying without thinking about any computer equations.

I know the FBW, (and auto-thrust* and GS Mini), are there. I know what they do and how they help me, and I know how to operate the side-stick without creating PIOs. Then I just fly the 'plane by feel, observation and experience, and it all works very well.


*older A330 auto-thrust can be 'lazy' near the ground in certain conditions but you simply deal with it.

That’s great. Other pilots like to know what’s going on under the hood. It doesn’t mean they don’t do exactly what you do operationally, ie fly the plane, they just have an interest in how it works as well.

[Uplinker]

Fair comment. Don't get me wrong; so do I, but not down to such detail as in post #19 etc. On short finals on a gusty day; that is probably over-thinking it, somewhat !

(A lot of pilots do not understand GS Mini, but I made sure I do, and how it helps us, but I don't need to know any equations to understand it, just what it does. )

The OP asks:

.......So your on final, Normal Law, AP off. Wing tips in a gust. Does the FBW flight control system stop the gust induced bank(because you didn't command it)? And does it actually attempt to return to its previous bank? Now you don't wait for all of this. You correct with sidestick. Are you augmenting the flight controls? Or does the plane sense your input and completely give you back full control? In other words...the plane with full sidestick is a 15 degree/sec roll rate. You correct with half sidestick, so what would be the roll rate command if the system is also responding to a gust?

I read that as not asking for a realy deep explanation of the computer programming; but more about how the FBW reacts and the relative authority of the FBW and the side-stick, and whether the side-stick inputs cancel the FBW inputs.

From memory, so please correct me; the FBW can command 25° roll rate, the side-stick 15°.

It's a fantastic system though; I absolutely love it