AF330

Good evening,

*The normal law protects the aircraft throughout the flight envelope, as follows :
‐ load factor limitation
‐ pitch attitude protection
‐ high-angle-of-attack (AOA) protection
‐ high-speed protection.

The side-stick commands a g load request.

*LOAD FACTOR LIMITATION
The load factor is automatically limited to:
+2.5 g to -1 g for clean configuration.
+2 g to 0 for other configurations.

PITCH ATTITUDE PROTECTION
Pitch attitude is limited to :
‐ 30 ° nose up in conf 0 to 3 (progressively reduced to 25 ° at low speed).
‐ 25 ° nose up in conf FULL (progressively reduced to 20 ° at low speed).
‐ 15 ° nose down (indicated by green symbols “=” on the PFD’s pitch scale).
The flight director bars disappear from the PFD when the pitch attitude exceeds 25 ° up or 13 ° down. They return to the display when the pitch angle returns to the region between 22 ° up and 10 ° down.

Ok so we are in configuration 0.
I pull the side-stick FULL AFT. I am basically demanding 2.5g
So the plane will reach 2.5g but I know that trim stops at 1.3g

Now comes Pitch Angle Protection. Can anyone explain what happens next to our G load? How does the plane react? What about trim?*

Let's say that High AoA protections are not available for the moment....

Thanks a lot,
A.Roy

80ktsClamp

It will stop pitching at 30 degrees nose up.

You'll end up in low speed protection after the speed decays which will command a nose down since the plane does not have enough thrust to sustain long periods of time at 30 degrees nose up.

I'm not going to assume that low AOA isn't available since that's not logical.

Turbo and Ozone

I don't know where you got the part about no trim past 1.3g. It is true that the trim is inhibited past 33 deg bank in normal law, and that probably equates to 1.3g, but that doesn't mean that it will cut out at 1.3g every time. I believe the auto trim is restricted by bank, not g. Let me know if you find something that says otherwise. Additionally, the trim will NOT work in direct law, and in Alpha Prot the trim is inhibited, but only in the nose up direction.

As for the aircraft response, you are right, it will stop at 30 deg nose up per the pitch protection. As it approaches 30NU, the elevator will unload the airplane to 1 g (and the THS will, in turn, trim to streamline the elevator).

As the speed decays, the limit will gradually reduce from 30 to 25, again by using the elevator first and then using the THS to streamline it.

As the airspeed decays further, you would normally reach high AOA, but in this case, it is inop, which means you are in alternate law or worse, so High AOA protection is replaced by "low speed stability." At low speed stability you will get the "speed speed" warning a few knots above stall, and the aircraft will try to nose over further to avoid it. If you continue to pull aft on the stick, you can override it and induce a stall. Note that you will not get alpha floor because you are in less than normal law.

-------
And now that I read what I just wrote, I would also say that the airplane will not stop at 30NU in the first place, because you were probably in alternate law the whole time (because you said High AOA protection was not active) so it will just go up to 45-85 degrees nose up, probably, depending on what kind of speed you had going into this thing, and give you a spectacular stall.

UAL T38 Phlyer

...Because the questions posted here smell very suspiciously like a non-pilot trying to get information for a lawsuit.....

Post cautiously.

AF330

Good evening,

Yes - I am a school student.

By the way, a pilot told me that trim is not available over 1.3G and below 0.3G, confirmed by F-COM.

Well, let me recap for vertical side-stick movents - please correct me If I am wrong.

When we pull the stick, we basically tell the computer how fast we want to increase/decrease pitch, also called G Load.
If my pitch angle is NOT increasing/decreasing, then I am at 1g. To maintain any G above/under 1g, the plane will have to keep increasing/decreasing pitch.
So stick is saying (e.g) it want's 2.5g. That is equal to the fastest pitch-up demand. So lower the G, lower the speed at which pitch will increase.

In the Airbus FBW system, you have pitch angle protection = 30° Configuration Clean.
So at a certain point, you will not be able to increase G, as the pitch angle will no more increase. It means that you will be at 1g.*

Now you also have pitch trim - it maintains the current aircraft's pitch at 1G.
It doesn't work over 1.3G and under 0.5G. But even if you release the stick, with a G > 1.3G, the aircraft will maintain the current pitch angle because it would have gone back to 1G (Aircraft is no more pitching).

AoA has the priority. The plane can hit Aprot at a low pitch angle.

Am I right?

Thanks a lot,
AF330

ShyGuy

Like that guy/journalist outing pilots with flight deck photos in flight, this guy is probably gonna end up with some "Airbus pilots don't even know their own systems" article......

AF330

? I am NOT an Airbus pilot.

Turbo and Ozone

Hey thanks for that info about the trim/G limits. My company books doesn't have that, but there it is in the airbus books, go figure.

As for your conclusions, do not confuse rate of pitch change with g load. It is possible at high speeds to have a high g with a slow rate of change in pitch. That said, your basic understanding is correct, if you pull back farther, the airplane will pitch faster (for a given airspeed).

Secondly, we do not attain 1 g simply because we reach 30 degrees, as you seem to have written. 30 degrees is a computer limit imposed by spoiler elevator computer (SEC) 2 in normal law. In an aircraft with conventional flight controls, you could maintain 2.5g well past 30 degrees, increasing it or decreasing it as desired. If you never decrease it, you will do a loop if you have enough thrust. However, most aircraft do not have enough thrust to do a loop at only 2.5g. My other airplane, the T-6 Texan II, requires 3-4g at 230-250 knots. Keep in mind that in order to maintain 1 g (also known as positive g) while inverted, you must actually "pull" (accelerate) the airplane by using continued back pressure through the back side of the loop. If you do not, you will feel weightless (0 g) in the transition to free-fall until aerodynamics prevail again.

The second to last paragraph is approximately correct, although the SEC does not think in terms of G, only in terms of streamlining the elevator. Confining the conversation to the 30 deg up scenario, we can roll with your 1 g assumption for now.

The last thing you said is important. Yes, you can get into Alpha Prot with a low pitch. You can also stall the airplane with a low pitch. These are both based on AOA only. There is only 1 way to stall an airplane, which is exceeding the critical angle of attack. This actually has very little (nothing) to do with pitch. There is also only 1 way to get to alpha Prot, which is increasing AOA to the margin prior to stall that the Flight Augmentation Computer (FAC) calculates as an appropriate safety margin based on configuration, speed, and weight.

A crystal clear understanding of the difference between pitch and AOA helps us to make sense of all this.

Good luck!

Turbo and Ozone

That was a very long answer to a complicated question, but in a nutshell, you will get 2.5 g up until you get to the 30 degree pitch protection. Pitch protection will override the g-command (side stick demand). Also believe I misspoke slightly about rate of change vs g-load. In normal law, the airbus will ALWAYS pitch faster (due to increased g-demand) with a greater side stick deflection, *regardless of airspeed*, until another protection (in this case g-protection) intervenes. This is a function of the ELAC2 computer, and is not the conventional aerodynamics I explained in paragraph 2 of my previous post.