United Airline
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Does The B 744 Have The Fly By Wire Technology?

Mon Sep 15, 2003 12:19 am

Does anyone know whether or not the B 747-400 have the FLY BY WIRE TECHNOLOGY? If not, the B 747-400ER and the proposed B 747 Advanced?

Awaiting your reply. Thanks
 
Ikarus
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RE: Does The B 744 Have The Fly By Wire Technology?

Mon Sep 15, 2003 12:30 am

As far as I know the answer is No to the 744 and 744ER. Not sure what the Advanced is - is that the renamed 747-500/600 and then 747-X or whatever the A380 competitor was called?

Might be wrong though.

Regards

Ikarus

 
dw747400
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RE: Does The B 744 Have The Fly By Wire Technology?

Mon Sep 15, 2003 12:46 am

The current 747 variants do not have FBW technology, though the -400 series makes extensive use of some fairly modern avionics systems. The 747-500X and -600X were supposed to use FBW if my memory serves me, but both of them were canceled.
CFI--Certfied Freakin Idiot
 
CX Flyboy
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RE: Does The B 744 Have The Fly By Wire Technology?

Mon Sep 15, 2003 9:34 am

The current 747 development plan is for the 747EX, or 747Adv, as it seems to also be known. This is a slight stretch on the current 744 and will carry just over 400 pax in a 3 class configuration. It will have FBW technology and engines being developed for the 7E7. Cathay are looking at these but they won't be available till 2008 or later, and indeed hasn't even been formally launched yet.
 
United Airline
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What Is Fly By Wire?

Mon Sep 15, 2003 12:07 pm

Hope CX will order some.

What about the B 747-400? You sure it doesn't???

Actually WHAT does FBW mean? can anyone explain that to me?
 
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Aaron747
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RE: Does The B 744 Have The Fly By Wire Technology?

Mon Sep 15, 2003 12:13 pm

No direct links between pilot input and control surface actuation - all control inputs are fed through a computer and control surfaces are electrically signaled.
If you need someone to blame / throw a rock in the air / you'll hit someone guilty
 
Ikarus
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RE: Does The B 744 Have The Fly By Wire Technology?

Mon Sep 15, 2003 7:17 pm

Traditionally, the pilot controls are directly connected to all control surfaces, by hydraulics. FBW replaces this direct (and heavy) link with wires that merely transmit the information, not the mechanical movement, to actuators and motors at the relevant surfaces. The advantage is, the computer can be put in-the-loop. That means the computer can prevent the pilot from doing undesirable things (such as stalling, or pulling up in a stall). It also means, the computer can make the plane react to pilot inputs differently than it would if there was a direct link.

For example, if you use full deflection of some surface at high speed flight, the plane might react very violently, even tear off the surface in question, or produce structural damage. With a computer there, the deflection of the pilot control could be proportional to the rate of change of the flight path, as opposed to being proportional to the deflection. So moving the stick XX degrees to the left might produce the same result at any speed, whereas doing the same thing with a direct link would produce different results (less violent at low speeds, much more violent at high speeds). This is all theoretical - I do not know what exactly the computer does, it might well try and simulate the real thing very closely. Or it might not. One aim, apparently, is to make all planes feel the same to the pilot, so that an A320 is as sluggish as an A340 in its response, or vice versa, the 340 as lively as the 320. This reduces pilot type rating conversion times, along with similar cockpit layouts.

So, FBW allows the designer to let the plane response differently to pilot inputs than it would with direct links and hydraulics. It also allows the computer to have direct control and the final word (overruling pilot inputs) in controlling the plane.

Regards

Ikarus
 
Rick767
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RE: Does The B 744 Have The Fly By Wire Technology?

Mon Sep 15, 2003 7:44 pm

"It also allows the computer to have direct control and the final word (overruling pilot inputs) in controlling the plane."

Strictly speaking that is a function of Flight Envelope Protection, rather than Fly By Wire itself.

It only protects the aircraft from entering a very dangerous flight condition, such as a stall. The protection system therefore very rarely activates, if ever, and so the final control of the aircraft does remain with the pilot in all normal operations.
I used to love the smell of Jet-A in the morning...
 
Ikarus
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RE: Does The B 744 Have The Fly By Wire Technology?

Mon Sep 15, 2003 7:57 pm

But without FBW, the flight Envelope Protection could not take control, right? The way I understood it is that FBW is an enabler - FBW could be a 100% replacement for hydraulics if designers wanted that, but they wanted more...

and so the final control of the aircraft does remain with the pilot in all normal operations.

True, but I always figured that the reason for keeping a human in the loop at all aren't the normal operations anyway, so having a computer that has the final word in exceptional situations is, in my personal opinion, a mistake. There've been 2 known incidents where the computer was wrong, so far. Admittedly, there've been many more incidents where humans were wrong - but as aeronautical engineer, I'd rather have 10 pilot errors than one error designed into the plane, which is why I can be rather critical towards the current applications of computer control.

Regards

Ikarus
 
Mr.BA
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RE: Does The B 744 Have The Fly By Wire Technology?

Mon Sep 15, 2003 11:10 pm

And to add to your question even the B744ERs don't have the FBW technology.
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n844aa
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RE: Does The B 744 Have The Fly By Wire Technology?

Mon Sep 15, 2003 11:48 pm

Ikarus, which crashes were caused by failure of the computers? I'm not saying I don't believe you; I'm just curious because don't recall having read about one in which a computer failure was the definitive cause.

The only possible case coming to mind is that airshow A320, and from what I understand of it, it sounded like the pilot had flown the plane too low and too slow.
New airplanes, new employees, low fares, all touchy-feely ... all of them are losers. -Gordon Bethune
 
Ikarus
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RE: Does The B 744 Have The Fly By Wire Technology?

Tue Sep 16, 2003 12:47 am

The Lufthansa crash in Warsaw - the computer did not permit thrust reversers to be used because it thought the plane had not landed yet. The plane aquaplaned down the runway with minimal breaking action, and ended up in a hill at the end of the runway.


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An Iberia hard landing (not a crash) caused because the pilot gave the command to go around in bad weather conditions but the computer refused and smashed the plane hard onto the tarmac.


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Photo © Ivan Rodriguez - IBERIAN SPOTTERS



Both accidents were analyzed and both times Airbus modified the software in the A320s as a result.

Regards

Ikarus
 
FredT
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RE: Does The B 744 Have The Fly By Wire Technology?

Tue Sep 16, 2003 1:35 am

Plenty of aircraft, FBW or not, will not allow a number of things (reverse thrust, spoilers, braking) unless they are convinced the aircraft is on the ground. If wheel spin up is one of the parameters, aquaplaning can throw a spanner in the works.

IMO there should always be a way for the pilot to tell the aircraft that "yes, we HAVE landed and you better give me thrust reverse right now". Air-ground logic input sensors do fail. If there's not, it's not an FBW problem but a design problem. If there was a means of forcing the aircraft into ground condition, it was activated, the command reached the FBW computers and was ignored, THEN I'll blame it on FBW.

I'd like to read more about the latter accident before concluding anything. Got a link?

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
Ikarus
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RE: Does The B 744 Have The Fly By Wire Technology?

Tue Sep 16, 2003 1:53 am

If you speak German and are willing to register and cough up 0.40 Euros for an article...:

http://www.spiegel.de/spiegel/0,1518,142775,00.html


Otherwise.... not sure where to find more info...

On another note - I did not state it was the FBW computer/software in particular that caused the LH accident, but a computer. I think the problem was that the wheel sensors registered a load, but not enough for the computer to accept the condition as landing. As consequence, the threshold was lowered. (Was it from 12 tons per main gear to 6 tons? Oh, dunno, I forgot the numbers...)

[Edited 2003-09-15 18:57:31]
 
777236ER
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RE: Does The B 744 Have The Fly By Wire Technology?

Tue Sep 16, 2003 2:45 am

FBW could be a 100% replacement for hydraulics if designers wanted that, but they wanted more...

Not really, hydraulic systems are still needed to actually move the control surfaces.
Your bone's got a little machine
 
Ikarus
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RE: Does The B 744 Have The Fly By Wire Technology?

Tue Sep 16, 2003 2:57 am

Well, I meant a one-to-one replacement of the control feel for the pilot... a 100% replacement in terms of the feedback the pilot receives from the controls.

Maybe I should phrase things more carefully.

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