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Fly-by-Wire

Posted: Fri Sep 07, 2001 5:16 am
by ejaymd11
What are the advantages of the Fly-by-Wire system, and how would it benifit an aircraft such as the MD-11.

Ejay MD-11

RE: Fly-by-Wire

Posted: Fri Sep 07, 2001 11:31 pm
by SSTjumbo
I'm not a pilot, so don't take this as 100% correct. From what I know, Fly-By-Wire controls the engines to maintain a constant speed @ cruise and whatnot. Its advantage is that the engines are more efficient in operation than if they were manually controlled. Pilots may have something totally different to say that is correct.

RE: Fly-by-Wire

Posted: Fri Sep 07, 2001 11:57 pm
by b767-400er
Actual FBW by itself reduces weight, and takes complex wires out of aircraft. FBW, coupled with Flight control computers, will have a more stablized aircraft, and envlope protection.

In relation of MD-11, I believe it will lessen the pliot's workload during approach, as Md-11s are known to be unstable, and need constant inputs to maintain course. Flight Control computer will sense the aircraft's movement, and give the correct input to maintain course.

Does the Md-11 have FBW, I know there is no FCC.

Tony,
B767-400er

RE: Fly-by-Wire

Posted: Sat Sep 08, 2001 4:37 am
by wn700driver
"What are the advantages of the Fly-by-Wire system, and how would it benifit an aircraft such as the MD-11."

None, it wouldn't.

RE: Fly-by-Wire

Posted: Sat Sep 08, 2001 4:49 am
by dc10hound
The MD11 does not have Fly By Wire.
It does have two Flight Control Computers, #1 and #2 with two channels (A and B) in each one.

RE: Fly-by-Wire

Posted: Sat Sep 08, 2001 5:03 am
by seagull
DC10,

You are mistaken. The MD-11 DOES have fly by wire, it just doesn't operate in all axis and all modes of flight. When it gets into "dual land" on an approach the MD-11 is full-up FBW, all control surface actuators are directly controlled electronically by the FCCs. In other modes there is everything from limited FBW input, to partial with the remaining controls being back-driven through the cable system, etc. Only with a major system failure that took out both FCCs would the MD-11 be truly just cable-hydraulic.

As far as handling, it is a mistake to think that you can only increase stability with FBW systems. While the MD-11 yaw dampers and LSAS are FBW controls (and the latest FCC 908 load has increased the stability and solved all of the handling issues that I am aware of), the truth is that a system such as yaw damper was around years before FBW was ever envisioned and did a fine job of increasing the stability in yaw of many aircraft. Artificial feel has been around since the late 1950s as well, so both of these things are not new and do all the job you mention.

Why FBW? Well, the main issue is saving the weight of the cable system, really. Especially with the newer aircraft having FBW capability anyway (like the MD-11), having the cables also is just more redundancy than some feel is necessary when the weight and cost is considered. However, FBW does add a flight control failure path that was not previously present.

RE: Fly-by-Wire

Posted: Sun Sep 09, 2001 9:48 pm
by Staffan
FBW is usually used for manouvering the aircraft, it has both advantages and disadvantages. The system works in the following way. There are electrical sensors in the flight yoke, the input is then passed through the wires to the hydraulic valve, that the openes giving hydraulic pressure to the hydraulic cylinder moving the control surface.

Advantages are that you don't need so much cables and hydraulic tubing in the aircraft, this saves weight. You can also change the aircraft's handling characteristics by just updating the software.

Disadvantages are that a bad powercut can make the plane unflyable (there are still many backup systems).
Also a software failure can crash the plane...

The system can give benefits such as not letting the pilot dive the plane in a to steep angle, or it kan pull up the plane if it gets below 300 feet with the gear retracted.

Staffan

RE: Fly-by-Wire

Posted: Mon Sep 10, 2001 5:29 am
by FBU 4EVER!
In addition to the weight savings,the FBW allows the plane to be designed to be neutrally stable or downright unstable.This means a CG location further aft which enhances fuel economy due to less drag.Also,the horizontal and vertical stabilizers can be smaller than they would have been on a plane with conventional controls.Saves weight and drag,too.

RE: Fly-by-Wire

Posted: Mon Sep 10, 2001 12:18 pm
by delta-flyer
you don't need so much cables and hydraulic tubing

You still have the hydraulic tubing, maybe not some of the small pilot or sensing lines, but the large supply and return lines are still there.

Where you really can get rid of the tubing is using EHA's and IAP's (ElectroHydrostatic Actuators and Integrated Actuator Packages). These are small self contained hydraulic systems, electrically driven, with integrated actuators. So instead of tubing, you need electrical cables to connect the actuators to the electrical bus.

But today's FBW a/c like the 777 and 320 use the conventional "central" hydraulic system. The next step is to introduce EHA/IAP's on the emergency system to mature the concept.

Cheers
Pete


RE: Fly-by-Wire

Posted: Mon Sep 10, 2001 4:43 pm
by SailorOrion
Delta-flyer
I think FD is going to introduce EHA/IAPs on the emergency system on the 728Jet

SailorOrion

RE: Fly-by-Wire

Posted: Mon Sep 10, 2001 8:35 pm
by dc10hound
>>DC10,

You are mistaken. The MD-11 DOES have fly by wire, it just doesn't operate in all axis and all modes of flight. When it gets into "dual land" on an approach the MD-11 is full-up FBW, all control surface actuators are directly controlled electronically by the FCCs. In other modes there is everything from limited FBW input, to partial with the remaining controls being back-driven through the cable system, etc. Only with a major system failure that took out both FCCs would the MD-11 be truly just cable-hydraulic.<<

This is a good description of Auto Flight System (AFS - Auto Pilot).

Pure fly by wire is manual flight (pilot) control inputs transmitted electrically rather than mechanically by cables.
The primary flight control systems on the MD11 are almost identical to the DC10, i.e. , all the same chains, pulleys, mixers and cables, etc. etc.

By your definition, a DC10 is FBW also (Dual Land CMD Auto Pilot, etc.)

Some electronic agumentation does occur on the MD11 though....