Originally Posted by
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
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!