Airbus Sidestick Logic/Command
 

Fellow Engineers...the pilots dont really know the answer so I thought I will try it here and put it amongst us intellects :} Im sure you all could come up with some good answers...please see below, original is in the Tech Log forum...

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Hey Everyone!

Before im referred to the search function, Ive already done my research but I have a follow up question below:

Call me a bit sad, but I was pondering this last night in bed http://images.ibsrv.net/ibsrv/res/sr...ilies/nerd.gif. In regards to the Airbus Family sidesticks, I understand the logic as the following (correct where necessary):

Lets first consider 2 seperate logics, Logic 1, where we do not consider the Takeover buttons ("TOB", excuse my improvised acronym) and Logic 2, where the TOB has been used.

Logic 1

• PIC is assigned to whichever pilot inputs a command from their sidestick first.
  • i.e. P1 moves his stick, he is PIC while he makes a commanded input, he reurns his stick to the centre position, to which P2 then provides an input and subsequently becomes PIC and so on....
• If there is an input from both sticks, (who inputs first is PIC) the command from each are algebraically summed, but the total command is limited to the maximum command of 1 stick.
  • i.e. P1 moved 75% displacement port (currently PIC), P2 then moves 60% displacement Port, System only registers 25% displacement of the 60% from P2?
  • P1 moves 25% displacement port (currently PIC), P2 then moves 25% starboard, total command = 0% displacement?
  • Is the command from the sticks an attitude or a rate??

Logic 2

• If P1 is PIC, and P2 wants some action, he hits the TOB and becomes PIC while the TOB is in detent.
• If the P2 TOB is held for 30-40s, the logic becomes latched with P2 as PIC until either takeover buttons are pressed again.
  • if given the above, P1 then presses the TOB for 2s, for that duration P1 becomes PIC, but after the 2s detent it reverts the system back to original Logic 1??
  • if given the above, P2 (PIC) presses the TOB for 2s, for that 2s P2 still remains as PIC for the 2s, but after it reverts the system back to Logic 1??

PLEASE correct any of the above...my main question is below:

If P1 is PIC (under Logic 1), he has a heart attack/gets shot and slumps on his stick...consequently a 100% displacement left is input to the system....P2 thinks "oh crap" grabs his stick, moves 100% right displacement, then hits the TOB, there is an instantaneous input from extreme left to extreme right. How does the system cope with this instant "jump" as im pretty sure its not acceptable to the system. Is the command rate limited? if so, how? is the mm displacement rate limited to the FCC or is the FCC output rate limited?

Please dont debate the probability/relevance/ins & outs of the above scenario, im more interested in what the system would do!! Sorry if I have over-thought such a small detail, BUT im an Engineer by trade http://images.ibsrv.net/ibsrv/res/sr...s/badteeth.gif its in my nature! :P

Thankyou for reading the above. I would be really grateful to relevant contributions! Thanks for your expertise http://images.ibsrv.net/ibsrv/res/sr...lies/smile.gif

You are right with your synopsis of sidestick priorities and logic.

However all inputs are fed into the FBW computers (ELAC & SEC) They operate within the parameters of a virtual flight envelope. So regardless of sidestick input, the aircraft will only manoeuvre within those parameters.

Only if the ELACs and SECs are switched off, then you enter what is called direct law and the control surfaces follow sidestick input.

ELACs and/or SECs is one way but not the "only" way. :=

Is the command from the sticks an attitude or a rate??

The sidesticks on airbus a/c are rate controllers rather than pure pitch/roll input devices. The greater the input, the faster rate of change of movement.