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AF330

Fly-by-wire airbus

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Hi, this is not related to sim but just for general knowledge!

I am learning and I have some doubts about the FBW system, Airbus, thanks to help! ;)

 

Wikipedia: " *Fly-by-wire* (FBW) is a system that replaces the conventional manual flight controls

of an aircraft with an electronic

interface. The movements of flight controls are converted to electronic signals transmitted by wires (hence the fly-by-wire term), and flight control computers determine how to move theactuators

at each control surface to provide the ordered response. The fly-by-wire system also allows automatic signals sent by the aircraft's computers to perform functions without the pilot's input, as in systems that automatically help stabilize the aircraft "

 

1) So the signals of the various movements of the flight controls are sent to "computers". Is it sent to the DMC computers?

 

2) How does A/P comunicate with the plane? Does the A/P also send his data somewhere?

 

3) If we would lose FADEC, we have to gravity feed, right?

 

Wikipedia: The Airbus A320 and its fly-by-wire brethren are protected from dangerous situations such as low-speed stall overstressing by flight envelope protection

 

4) Do the AoA senqors send their data to the flight envelope protection?

 

5) Are their very sharp bank angle sensors? If yes, where does it send it's data? If no, how does the plane calculate it?

 

6) There is a mechanical back-up for pitch trim in alternate and direct law, what is that mechanical back-up?

 

7) If anyone could add something or precise something, it would be really helpful for me!

 

Thanks a lot!

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Thanks Graham,

But these guys on airliners know what are the different fly by wire systems and the answers of my questions! I first have to learn the link between AoA and the flight envelope protection....

 

But when I will understand what is FBW for airbus, I will go to your link for sure ;)

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Your post was very useful, but quite lost.... as you said.

 

http://bits.me.berkeley.edu/me39c/Spring97/Projects/b777/p1.jpg

Here is the FBW for a 777, is it the same for Airbus?

 

If yes, here are the answers of my question for me! Thanks to help!

 

1) Yes, the data management computer (DMC) are the primary flight computers. The movement of the flight controls are sent there.

 

2) The autopilot sends what we enter to the primary flight computers  then to the actuator control electronics then wherever you tell him (ailerons, tail...) by wires.

 

3) Yes we would use gravity feed.

 

4) I don't know what the flight envelope protection is!

 

5) No idea!

 

6) Nothing, just hydraulics.

 

Thanks to help or confirm!

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I could very well be wrong, but I believe the flight envelope is a set of limits (pitch, yaw, roll), where the Airbus aircraft will not intervene to limit unsafe and/or excessive maneuvering of the plane. Outside of the 'envelope', the aircraft will intervene to bring itself back into the envelope. If I am incorrect, please correct me and give me a virtual dope slap.

 

Graham

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I was reading F-COM, flight controls and here is what I have learnt:

1) The movements of the stick are connected to the are connected by wires to the F/CTL computer, then there are the hydraulics motors and the hydraulic pressure goes to the requested surface. The surface then gives back a feed back to the F/CTL.Why do we need hydraulic pressure for the sticks when you are flying manually?

 

2) The side-sticks are connected to the ELAC (Ailerons) and the elevators, and the spoilers (SEC) while landing.The speed brakes are also connected to the SEC computers.

 

3) The SEC computers receives data from the A/P, the side-sticks and the pedals and uses the ADIRU, Radio Altimeter (QNH), SFCC, LGCIU, FMGS and ACCELERO to calculate the exact pressure required, communicated by the A/P or the stick while flying manually. The 2 ELAC computers receives data from the A/P and the side-sticks and uses ADIRU, LGCIU, QNH, ACCELERO to calculate the requested hydraulic pressure on the elevators and the ailerons. The roll orders are also sent to the SEC Computers from the ELAC *"AND THE FAC"* computers. But why is it required? The FAC computers uses FMGS data and ADIRU to calculate the hydraulic pressure required for the rudder.

 

4) The pedals are mechanically connected to the rudder. But they still send their data to the ELAC computers, why is it needed? To help to calculate the hydraulic pressure of the ailerons? But we don't use ailerons and rudder at the same time! Or is it for the elevators (for take-off) as they are also connected to the ELAC system?

It's all for now, thanks to explain and clear my doubts!

 

Kind regards,

AF330

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Why do we need hydraulic pressure for the sticks when you are flying manually?

 

That is a bit of a strange question..Hydraulic pressure is not for the sidesticks, it is for the actuation of the control surfaces. No hydraulic pressure and the aircraft is a flying dart.

 

 

 

 

The roll orders are also sent to the SEC Computers from the ELAC *"AND THE FAC"* computers. But why is it required?

 

 

The pedals are mechanically connected to the rudder. But they still send their data to the ELAC computers, why is it needed? To help to calculate the hydraulic pressure of the ailerons? But we don't use ailerons and rudder at the same time! Or is it for the elevators (for take-off) as they are also connected to the ELAC system?

 

Again you are showing a lack of understanding when it comes to the basics of flying.   Aileron & Rudder can be used at the same time - For example,they are used for coordinated turn's through the yaw damper & during crosswind landings. 

 

 

The  3 SEC's provide roll control using the spoilers. The ELAC's 1 or 2 will always process any orders first before sending them to the SEC's  

 

 

Back to your question  - Think of the ELAC's as the primary computers.  All your inputs will go through ELAC 1 while ELAC 2 stays in a backup mode.   

 

If you move the rudder pedals a signal is sent to ELAC 1.  The ELAC calculates yaw damping, rudder trim & turn coordination orders and sends it to the FAC computers.  The FAC computers control the yaw damper servos and rudder trim. 

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Thanks

 

1) The sidestick is connected with the ELAC and the SEC computers. So where does it go next? Direcetely to the surface?

 

2) Am I right on the other things?

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Guys very easy.

 

Fly by wire means that all the actuators are controlled by electric cables (ARINC BUS). This is like a net cable able to communicate 2 ways in blocks of data. You send command and unit responds with its movement etc.

 

The Airbus uses 7 computers to fly. 2 ELAC, 3 SEC and 2 FAC. These together with the 2 FMGC the autopilot is controlled.

 

The stabilizer is the only flight surface that uses a wire to control it. Controlled by the wheels in the cockpit you can move the stabilizer, but again you need hydraulic pressure to move it. Can not be done just by the cable.

 

FADEC if it dies the engine will also stop. That is why there is 2 channels inside to make sure that one is always running. Modern engines can not run if the FADEC system is not working.

 

The flight envelope is controlled by a simple rule. The airplane is making movements of MAX 1G and this is controlled by all the computers together. Also all the computers are talking together at all time via the ARINC buses. ELAC are the main computers together with the FAC's.

 

To go much deeper than this FCOM is next :-)

And remember that the computers inside a Airbus are really old and very slow. Not a new INTEL chip but old save and not to warm cpu.

 

Jesper

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So the side-sticks don't use hydraulics for the ailerons. They can use it for spoilers. So they by-pass the hydraulic system for the ailerons, right? They just give the signal to the ELAC computer that they have been turned, right?

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Just leave my previous post, it is completely wrong.

So the elevators uses wires but what for ailerons, rudder and spoilers?

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^_^ I know the bus is a bit confusing.

 

The stick the pilot uses to fly the bus is just a joystick. All input are electrical and goes to the computers. To give the pilot the feeling that he is flying a plane the stick are "tricked" with some springs to give it some feel like flying the older planes. This is some different springs that makes the movement of the stick a little harder.

 

All the surfaces are controlled by hydraulic pressure. Even the stabilizer, but this is the only one where you can move it with a cable. Again the cable is just giving input to the hydraulic valve to move it in either direction. Auto pilot is moving the stabilizer with electric signals which also at the same time moves the stabilizer wheel in the cockpit. This is the only leftover of the old systems.

 

Rest of the bus is just actuators that get's electrical signals to move. 

 

What is so great with this new "fly by wire" Is that you can remove all the problems of stability etc. During the test flights and re-program the computers to fix it.

 

If you imagine the A318 and A319. Here you have some great wings and a lot of lift. A small fuselage and a big tail. All this together gives drag and makes the plane a bit unstable.

Here they just fix the problems with the computers and voila the plane can fly stable at all time.

 

The story never ends haha. So reading the FCOM etc. Explains a little more about all the systems but Airbus never tell the hole story :wacko:.

 

Jesper 

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Thanks a lot, but could you just explain the elevators thing? It goes to the ELAC computers but then? The only difference is that it is then connected by a cable and not a wire, or is there something else?

 

Thanks

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Well what exactly goes on is a airbus secret haha.

 

But as mentioned above the ELAC are master computers. Them and the 3 SEC are controlling the elevators only sending ARINC signals to the actuators on the elevator, 2 on each side.

When one elevator is used the other one function as a damper. Damper means to make the movements calm and can be used when there is turbulence.

 

So the elevators are hydraulic operated with a ARINC signal to command them. All the actuators only have electric plugs and hydraulic lines, that is it. No cables.

 

Jesper 

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Thanks, so what is the difference with the ailerons or the spoilers? Is it a difference signal?

Or is it the same concept?

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It is all same concept. The computers decide what to use and when.

 

This is all programmed into the flight envelope. Like low speed you need more spoiler together with the ailerons and higher speed less or none.

All is controlled by ARINC signals to the actuators.

 

Jesper

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