Fly-by-Wire

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I am a pilot in the US and I am working to become an airline pilot soon. Can someone explain the advantages of fly-by-wire controls. I have talked with other pilots and in my own experience being able to feel what the airplane is doing is something no computer can reproduce. simular to driveing a car and feeling the road. so if this is the case why do both airbus and boeing make fly-by-wire the way of the future.

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Profile picture for user Deano

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The single biggest advantage of a fly-by-wire system over conventional hydraulic systems is weight, the savings are pretty high, you are right in that "seat of the pants" flying has been lost but I guess it's progress, there was alot of debate between flight crews about this but as with everything a few years down the line and nobody bats an eyelid, also another saving (evident in the Airbus) is that they could get rid of the control yoke and replace with a more convenient side-stick although Boeing opted to keep the control yoke I think after discussions with potential customers, it's all a case of good erganomics. Another thing on the Airbus in particular is the flight envelope protection system which stops the pilot trying to fly the plane outside pre-set flight envelopes, for example, the Airbus cannot exceed (or even reach if I'm not mistaken) critical alpha.

Dean

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Firstly it saves weight by removing the need for cables. Secondly it is possible to install parameters in the computer the plane may not exceed. That is for instance why in normal operations an A320 will never fly at stall speed, extreme angles of attack etc.

Profile picture for user PMN

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EDIT : Flight Test after maintainence that is :)

I did wonder what you were referring to at first!

Paul

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You don't need to flight test FBW aircraft either saving in crew, fuel, and airport costs :P

EDIT : Flight Test after maintainence that is :)

you don't have to flight test on conventional controls after maintenance either.

Profile picture for user Schorsch

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Some points are right, some not. Envelope protection would go without FBW, too. It is easier with FBW to link a computer to the controls. Everythings what goes in an Airbus would go without FBW maybe except the sidestick, because you need real force to pull.
Just because you have FBW you still have feedback "from your butt". FBW doesn't cancel the normal physics. Otherwise people would get less often sick in an Airbus aircraft than in other aircraft. But that is not the case, or if, it is related to the crappy interior of some B757 on charter duty.

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Some points are right, some not. Envelope protection would go without FBW, too.

This is true but the Envelope protection system was designed around the FBW system in the Airbus, I do not know of any hydraulic powered flight controlled aircraft in service today which has the Flight Envelope protection system as comprehensive as the Airbus unless someone can enlighten me (which, if a little misleading, was my point)

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"Envelope protection would go without FBW, too."

not strictly true, aircraft controls have been fitted with artificial 'feel' for years, this stop, or reduces the chance of you operating outside the envelope. other controls are can be stopped from working above certain speeds, or have their movement restricted at different speeds.
all this goes towards envelope protection.

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This is true but the Envelope protection system was designed around the FBW system in the Airbus, I do not know of any hydraulic powered flight controlled aircraft in service today which has the Flight Envelope protection system as comprehensive as the Airbus unless someone can enlighten me (which, if a little misleading, was my point)

Here we meet the "different approach" of Airbus towards flight controls, which was unfortunately sometimes a point of criticism of some people. The consequent drop of the Cessna-like flight controls made it possible to easily adapt envelope protection.

See it like this:
- I decide to go for FBW instead of cables and push-rods

- if I have already FBW, I can easily integrate a computer and some automatic control

- if I can modify some behaviours, I can easily restrict some areas of the envelope

- if I want to restrict some areas I can do the complete step and restrict all undesirable areas (which leads to the wrong perception of some people (even and especially B737Classic-pilots), that an Airbus is idiot-safe and "flown by the computer", what is definetly not true)

All this is in a constant loop of iterations. The encountered problems however were pretty big. New technology is a bitch, it hates you and laughs about your stupidity!

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As far as I am concerned the flight envelope protections provided in the Airbus FBW (which Boeing chose not to incorporate into the 777) are its best feature. I just pray that I never have to rely on them (but it's nice to know they are there)!

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r

if I want to restrict some areas I can do the complete step and restrict all undesirable areas (which leads to the wrong perception of some people (even and especially B737Classic-pilots), that an Airbus is idiot-safe and "flown by the computer", what is definetly not true)[/B]

It's interesting how Airbus and Boeing differ in terms of FBW design philosophy. Airbus aircraft are constantly subject to the operational restrictions of the FBW computer, and these can not be by-passed (hence a certain incident at a certain French airshow, even if the pilot was 70 feet lower than he should have been).

The FBW computer on the 777 that restricts certain manoeuvers such as extreme bank angles is designed so it can be by-passed by the pilot in an emergency. Boeing believe the pilot, not a computer, should make the ultimate decision as to what the aircraft can and can't do, and the pilot should have the knowledge to make that decision.

Both approaches are correct, it's just interesting.

Paul

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Well, depends what controls are disturbed, and to what degree they are disturbed.

again, not necessary.....i've worked on aircraft where the whole operating systems are removed and overhauled, the control surface itself has been removed and repaired as required.
everything is refitted, rigged ,inspected, and functioned... but no airtest. the aircraft has left, and gone straight to another airport, and then a transatlantic flight....but no airtest.

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the single biggest advantage of a FBW system is the ability to design an aircraft that is very efficient, but no human could fly free-hand.

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the single biggest advantage of a FBW system is the ability to design an aircraft that is very efficient, but no human could fly free-hand.

I can understand this in the F-22 which is the case but airliners are more stable than an F-22 so is this the biggest advantage to commercial airlinesrs i'm not so sure.

Thank you all for all your feedback I have learned alot.

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I can understand this in the F-22 which is the case but airliners are more stable than an F-22 so is this the biggest advantage to commercial airlinesrs i'm not so sure.

Thank you all for all your feedback I have learned alot.

Yes it is used on the A330 and A340 as we employ active c of g control. Boeing just use the tail fuel tank as a means of getting more fuel on board whereas widebodied Airbus types shift fuel forward and backward during a flight to place the c of g as close to the center of pressure as possible. This has the effect of making the aircraft less stable (which the fbw deals with) but it removes any vertical force required from the tailplane and therefore its associated drag. We achieve a fuel burn reduction of approximately 3.5% as a result. This saving is worth millions.

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you learn something new everyday and sometimes twice a day. thanks wysiwyg

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r

It's interesting how Airbus and Boeing differ in terms of FBW design philosophy. Airbus aircraft are constantly subject to the operational restrictions of the FBW computer, and these can not be by-passed (hence a certain incident at a certain French airshow, even if the pilot was 70 feet lower than he should have been).

The FBW computer on the 777 that restricts certain manoeuvers such as extreme bank angles is designed so it can be by-passed by the pilot in an emergency. Boeing believe the pilot, not a computer, should make the ultimate decision as to what the aircraft can and can't do, and the pilot should have the knowledge to make that decision.

Both approaches are correct, it's just interesting.

Paul

Which is only partly correct. The accidient you are talking of is the crash in Strasbourg. The pilot used the system faulty. It remaines the best forest landing ever.
But to the topic: Airbus envelope-protection cvan easily by-passed. If even I know it every pilot will know it. The bottom line of the whole system is the direct law, which has no envelope protection. This law cannot be set but at least you can switch of some computers and force the system to divert to this law.
However, if you look closely at some accidents you will find some which would have been prevented with envelope protection. The future will see aircraft which are even tighter protected by the computer in order to save weight by reducing safety margins (without reducing the safety itself).

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Which is only partly correct. The accidient you are talking of is the crash in Strasbourg. The pilot used the system faulty. It remaines the best forest landing ever.

It's never been proved the systems of the A320 that crashed at Habsheim were faulty. The aircraft should have performed the fly-past at 100 feet, not the 30 feet it was actually at, and so the computer did exactly what it was programmed to do..Land the plane. Pilot error was officially blamed.

Watching the video of the accident it's amazing only 3 out of 136 people on board lost their lives.

Paul

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It's never been proved the systems of the A320 that crashed at Habsheim was faulty. The aircraft should have performed the fly-past at 100 feet, not the 30 feet it was actually at, and so the computer did exactly what it was programmed to do..Land the plane. Pilot error was officially blamed.

Watching the video of the accident it's amazing only 3 out of 136 people on board lost their lives.

Paul

The pilot got too low and the computer switched to a different mode. The pilot was definetly responsible, on the other hand I would not say he behaved irresponsible. He just didn't know the system enough and wanted to perform a nice display. He actually unveiled the biggest issue on FBW computer aided and envelope protected aircraft: the pilot has to know, understand and use the offered systems right. Things that wiork in the heads of engineers and in the hands of test pilots don't necessarily work in real life.

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Has anyone yet mentioned that FBW systems offer a potentially greater degree of flight safety by allowing multiple, redundant control systems to co-exist ?

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Has anyone yet mentioned that FBW systems offer a potentially greater degree of flight safety by allowing multiple, redundant control systems to co-exist ?

No, that wasn't mentioned. The limiting factor of controls is often the availibility of hydraulic power. In some terms FBW has a disadvantage because it needs electricity while other flight controls directly pull on the actuator, therefore no need for electricity. Anyways, if hydraulic power is available so is electricity.

For military aircraft this may be of use because I have alternative ways. both convetional controls and FBW have already proven their reliability. The next step would be to take away the rudder panels from the pilot or to reduce his authority on it to a absolute minimum (yaw damper rules and pilot nmay give advice).