Airbus FBW Sidestick
Quote from ZeeDoktor:
The A3XX sidestick (control) philosophy is not rate but attitude based, i.e. you move the sidestick to the side (and with it a caret on the PFD), and the bus will keep the attitude you demand by pointing that caret. So, for example, you move the caret in the right hand side of the PFD and the bus will maintain an attitude to follow that caret.
I'm afraid that is all incorrect!
If you move the sidestick to the side in the air, you are requesting a roll-rate proportional to the displacement. If you then centralise the stick, the bank will be maintained.
This does not apply, however, on the ground. On take-off, it is stick-to-surfaces until about one second after lift-off, when the white cross (that you call a 'caret') disappears from the PFD for the duration of the flight.
(Pitch control is a bit more complicated to explain, but intuitive.)
In the air, PIO is the result of the pilot impatiently or nervously changing the stick position before his/her previous selection (stick-position) has had the time to be effected. In that respect only, it's not so different from conventional aeroplanes. The trick is to use thumb-tip and index-fingertip for roll control; thumb-tip and middle-fingertip for pitch.
Chris
PS (by Edit)
You are right to say that, in Direct Law, it's a bit like "an airplane you learnt to fly on", i.e, roughly stick-to-surface. That does not mean "a rate-based control system", however. You are right that it feels very different from the higher laws, and is rarely practised except for short periods in the simulator.
Last edited by Chris Scott; 7th Apr 2011 at 16:59.
Reason: PS added.