A320 G-load sidestick

[basics]

In conventional airplane when we move the control column to and fro, elevator moves accordingly and aircraft would pitch up or down at a rate commensurate with the force we apply on the control column.
What goes on exactly in normal law on A320? what do we mean by 'G-load maneuver is ordered'? what is the value of the G-load we are demanding? and how would it affect if we push or pull the sidestick hard or softly?

thanks in advance

[Dream Land]

I am not the one to give you a highly technical answer, but some of the benefits would include that, different size aircraft will handle almost the same, so transitionining is simplified, also, in theory, your aircraft responds similarly whether or not you are clean or fully configured.

You don't feel the feedback associated with a particular aircraft design because it keeps any feedback hidden. To me there's no great satisfaction to hand fly the Airbus, but over all I would never want to go back to a conventional aircraft.

Cheers D.L.

[Gary Lager]

When you push or pull the sidestick, the aircraft will respond by loading on unloading the aircraft accordingly. Full backstick should equate to the max normal g-load permitted i.e. 2.5g, with the commanded load proportional with sidestick deflection. This relationship falls down near the bottom edge of the envelope as low protection takes precedence over pitch demand. Pushing/pulling the stick hard does nothing except change the rate at which the commanded g is applied - the eventual pitch load will still be proportional to the final deflection.

[Microburst2002]

what a coincidence, i have just written this in another thread:

Boeings, fbw or not, behave conventionally in the sense that they are speed stable (they tend to maintain the angle of attack due to their static longitudinal stability even when stick free). To manoeuvre a boeing you need to exert forces in the stick, which produce g forces prpportional to the stick forces, thus changing path. This is achieved by making the elevators deflection directly related to stick deflection. Stick Force is what matters, however. You need to feel the force, even if the flight control system is hydraulically powered. The flight control system gives feedback to the pilot by means of stick forces. When you trim the stick force, the airplane will tend to maintain the angle of attack, at the expense of flight path which means you will slightly oscillate in altitude and pitch maintaining the trim speed and only need few and small inputs to maintain flight path.

Airbus fbws behave differently. They are path stable, which means that they tend to keep the trayectory even at the expense of speed and angle of attack, as if they had a different form of longitudinal stability. the airplane will oscillate in speed and even pitch maintaining flight path. In the bus, we achieve the g forces for manoeuvring by deflecting the stick. g force is proportional to stick deflection, not to stick force. The feedbackis not given to the pilot, but to computers. You can't really speak of stick-free in an A320. they are never stickfree. Stick free means "tend to maintain trayectory". Thereore forces in the stick are not necessary. Trim is not necessary at all. There is a THS, and there is "autotrim", but in fact the A320 is a trimless airplane. In the THS jam or dual hydraulic blue remaining ALTN LAW keeps autotrim with elevators alone.

All airplanes are manoeuvred in by inducing g forces. You want the nose up, you pull the stick. You want the nose down: you push the stick. When you achieve the desired flight path we want the airplane to be stable and tend to maintain it. You will only need a few smalls input to maintain the flight path precisely. Forces in boeings, deflections in airbuses.

In the fbws we don't have to trim. That is all the difference. No resemblance to a CWS nor an autopilot.

When pilots say that to "really fly" the A320 you have to disconnect computers to bring the DIRECT LAW... I feel sick because I know they don't know very much about flight controls and flight at all... No airplane could be certified that had a fbw direct law system with no stick forces.


A boeing (beoing is shorter than conventional airplane) is flown by exerting forces to change flight path, then trimming the stick forces when stablished on the desired flight path and speed. An airbus is flown by deflecting the sidestick to change flight path, then release it when stablished on the desired flight path and speed.

Inputs-target achieved-trim
Inputs-target achieved-stick release

I don't know if there could be a fbw flight control system with spring loaded sidesticks where the normal law was based in a parameter different than g force, such as rate of pitch change or something. I think the system in airbus fbws is very clever. Of course it has pros and cons. Among the cons, the lack of "direct to the pilot's brain feedback" from the sidestick. There is no aerodynamic feel of the airplane, but it gives the pilot great control.