Fly by wire aircraft
 

Hello again everybody, I am curently studying aerospace engineering at college, I have 2 fly by wire questions that although are general aircraft questions, I think particular relate to the A320. I was hoping an experianced A320 engineer could give me some guidance;

Q1) In a full time fly by wire equipped aircraft, pitch and roll servo jack position is achieved utilising:-

a) Linear variable differential transducers, thus ensuring full interchangeable components
b) Rotary variable differential transducers for roll and linear variable transducers for pitch
c) Rotary variable differential transducers for pitch and linear variable transducers for roll

Q2) In a full time fly by wire aircraft, Autopilot signals from the flight management guidance computer are :-

a) Used to control the flight control surfaces via the autopilot electrical actuator
b) Integrated into the electrical flight control system via the two electrical flight control computers
c) Fed directly to each flight control surface servojack not being utilised by the electrical flight control computers

Thankyou for your help.

Q1 will depend entirely upon the design examples you've been given, any of those answers are possible.

Q2 should be (b) since the Autopilot is providing control systems for the main AFCS negative feedback loops.


Which college is teaching and examining aircraft design via multiple choice? I can't say I'm awfully impressed (with the teaching approach, not you - nothing wrong with asking questions if you don't know the answer).

G

Hello Ben,

If you want my opinion, I think Q1 would probably be A.

For a linear actuator (jack), an LVDT would be the obvious choice for position monitoring, probably mounted internally. As far as I know, there are no rotary vane actuators on the A320.

These LVDTs may be interchangeable - this depends entirely on the design of the jacks

I'll ask a man who does know these things for certain, and get back to you.

If question 'a' is specific to A320 then the answer is C - feedback position is signalled for the Elevators (pitch) by RVDT and on the Ailerons (Roll) by LVDT. But still think its a bad question.

As for Q2 - As Ghengis has stated - answer B - however Airbus does not have FCC's (a Mr Boeing invention) they have ELAC's (Elevator Aileron Computers) SEC's (Spoiler Elevator Computers) and FAC's (Flight Augmentation Computers)

Hope this helps

Just to further clarify,

Jet you are correct in that there are no FCC's on an A320. But the same role is performed by the FMGC's, which as well as being a flight management computer provide guidance comands which are fed to the relevant sub systems within the EFCS.

It's just a different name for a box which does the same thing. Although it is combined with the FMC on the 'bus.

Terminology

Any FBW system will have an inceptor (control) which provides a control signal into the AFCS (Automatic flight control system) which is a negative feeback loop (more likely a complex multiple loop with rate integration incorporated) into which is also fed rate / position sensor information from control position / aircraft position / rate of change data. The output is a function of the input control signal and the feedback data, and designed to keep the aircraft at whatever condition is required by the main input signal (specific heading, airspeed, attitude, etc.).

This is universal. However, in what order the black boxes are arranged to achieve this, and exactly what sensors or inceptors are used will vary a lot. This is where the difference in company terminology comes in.

G