Hazelnuts
RetiredF4;
I simply read the traces. After Clandestino in post #393 (p.20) I'm not so sure about Nz law maintaining flightpath / '1g' in turbulence.
I do the same, but then lets see what Clandestino wrote:
............Sidestick neutral iz not 1G it is 0G.
There is one word missing at the end, it is 0 g
change. As the basic and overall topic of Nz-Law is to maintain a flightpath ( = flightpath stable = 1 g flight ) the sidestick in neutral commands no deviation from this 1 g flight, which means no loadfactor
change at high speed or no pitch rate
change in low speed.
Sidestick command does not order G in absolute terms. It adds G demand to already measured, therefore if hit by updraft giving you 1.3G, pull on the stick that would give you 1.1 absolute from straight and level will now result in 1.4 pitch up. Push giving 0.9 would now be 1.2.
He is wrong there. What he might be is referring to s the fact, that a dampening input is added to the normal LAw command.
LTTM- TURBULENCE DAMPING FUNCTION (bolding by me)
General:
The purpose of the Turbulence Damping Function implemented in the Electrical
Flight Control System is to damp the structural modes induced by atmospheric
turbulence.
Architecture
The Turbulence Damping Function consists of two lanes:
Longitudinal lane. The longitudinal Turbulence Damping command is computed by the FCPC1 (FCPC2 as a redundancy) as a function of the Nz accelerometer information. It is added to the normal law command and transmitted to the associated elevator servo-controls.
Rear lateral lane
The rear lateral Turbulence Damping command is computed by the FCPC1
(FCPC3 as a redundancy) as a function of the informationof a specific Ny
accelerometer located at the rear bulkhead level. It is added to the normal law command and transmitted to the associated yaw damper.
To sum it up, if the SS is in neutral (= 1 g flight) and turbulence is disturbing the flightpath away from this one g flight, an opposing command is added to the existing 1 g flight command or like Clandestino likes to put it to the 0 g- change command).
If not hands off, but with a SS command of 1.2 g an updraft and thus increase of commanded g change by .4 g (which would give us 1.6 g) would stimulate the system to counter this increase by adding up to the commanded 1.2 g, thus maintaining the ordered 1.2 g of the SS as close as possible.
Any deviation from the flightpath (1 g with hands off, ordered g change with SS or AP inputs) will be opposed by the dampers by an respective counter action command within the capabilities of the system.
Letīs face the fact, anything else would be not helpful at all.
That the SS command adds to the already existing g, thus the SS command not giving a specific amount of flightpath change (load factor change at high speed, pitch rate change at low speed) is against any basic principle the C* law is funded on. But anybody feel free to point me to some reference here. Imho such an aircraft would not be controllable.
In the discussion there were also comments concerning load factor demand in high speed and pitch rate in low speed. Some here seem to believe, that in low speed the aircraft keeps the last pitch, if the stick is in neutral.
The aircraft will maintain a given flightpath, if we intend to change that flightpath with a SS input the gain will be load factor change at high speed and pitch rate change in low speed, but it still will maintain flightpath and not pitch in low speed with SS neutral (assumed that no protections are involved).
Again feel free to correct my research here.
When discussing the crew actions, their motivation of those actions and the resulting aircraft behaviour, which again constitutes an feedback channel to the crew, it is of immense importance to know how the systems work.
franzl