Fly-by-Wire
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Basically it is flying using the computer and hydraulics. In the past, pilots had to use their own strenght to shift the control column to move the plane around. Now,with fly-by-wire, the hydralics do the work for pilot. Those are the basics. I'm not too sure of the details...
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Jayson,
An aircraft is piloted using the stick and pedals. Now, there has to be a mechanism that connects the stick and pedals with the control surfaces of the aircraft. For example, if the pilot pulls on the stick (to make the aircraft pitch up), you want the horizontal tail planes to change position accordingly.
There's a number of ways to accomplish this - you could use a cable/pulley system for example. If you pull on the stick, the tailplanes rotate accordingly. This works on biplanes but not on a 747 - the control surfaces are too big to move them using manual force, hence the introduction of hydraulical actuators wich do the actual hard labor. The connection between stick and actuators is still with a cable/pulley system.
In the F-16, the engineers chose to convert the mechanical force applied by the pilot on the stick into electrical signals, which could then be transmitted over electrical wires to the actuators. The main advantage of this is that this system is less vulnerable (you can easily make it redundant) and it takes less space and is easier to route through the airframe (in the traditional cable/pulley system you have steel cables under tension going from the cockpit to all control surfaces, and as you can imagine you don't want these to twist and turn too much). Also, this allowed the stick to be located off-center. Since you're using electrical wires to tranmit the control signals, they called this system "Fly-by-Wire".
One of the unexpected negative side effects of this system was that pilot's couldn't get used to the fact that the control stick didn't move (it didn't need to move - just needed to measure the direction and magnitude of the force applied by the pilot). They modified the stick so it now moves slightly.
FBW alone doesn't improve maneuverability, although the pilot has to apply almost no force at all to move the control surfaces, which makes the aircraft controlable in situations where manual control wouldn't.
The next step is quite obvious: since you have electrical signals controlling your aircraft, you can easily run these signals through a computer before you feed them to the actuators. So everything a pilot does is checked by a computer, and it will not allow control inputs that would damage the aircraft (e.g. pulling too many Gs) or exceed the aircraft's flight envelope. This frees the pilot from worrying about exceeding the aircraft's limit so he can concentrate on flying.
Even more, the F-16 is an inherently instable design - when flying it, you would need to make constant control adjustments. In the F-16, the Flight Control System computer does this for you. It's constantly moving the control surface (ever so slightly) to keep the F-16 stable.
Of course, if you have an unstable system, you need to have extremely reliable computers. That's why the F-16 has multiple computers that "vote" for the best action (control input) to take. If one computer fails or suggests a wrong solution, it is out-voted by the other computers.
This is just a rough outline but I hope this helps
stefaan
An aircraft is piloted using the stick and pedals. Now, there has to be a mechanism that connects the stick and pedals with the control surfaces of the aircraft. For example, if the pilot pulls on the stick (to make the aircraft pitch up), you want the horizontal tail planes to change position accordingly.
There's a number of ways to accomplish this - you could use a cable/pulley system for example. If you pull on the stick, the tailplanes rotate accordingly. This works on biplanes but not on a 747 - the control surfaces are too big to move them using manual force, hence the introduction of hydraulical actuators wich do the actual hard labor. The connection between stick and actuators is still with a cable/pulley system.
In the F-16, the engineers chose to convert the mechanical force applied by the pilot on the stick into electrical signals, which could then be transmitted over electrical wires to the actuators. The main advantage of this is that this system is less vulnerable (you can easily make it redundant) and it takes less space and is easier to route through the airframe (in the traditional cable/pulley system you have steel cables under tension going from the cockpit to all control surfaces, and as you can imagine you don't want these to twist and turn too much). Also, this allowed the stick to be located off-center. Since you're using electrical wires to tranmit the control signals, they called this system "Fly-by-Wire".
One of the unexpected negative side effects of this system was that pilot's couldn't get used to the fact that the control stick didn't move (it didn't need to move - just needed to measure the direction and magnitude of the force applied by the pilot). They modified the stick so it now moves slightly.
FBW alone doesn't improve maneuverability, although the pilot has to apply almost no force at all to move the control surfaces, which makes the aircraft controlable in situations where manual control wouldn't.
The next step is quite obvious: since you have electrical signals controlling your aircraft, you can easily run these signals through a computer before you feed them to the actuators. So everything a pilot does is checked by a computer, and it will not allow control inputs that would damage the aircraft (e.g. pulling too many Gs) or exceed the aircraft's flight envelope. This frees the pilot from worrying about exceeding the aircraft's limit so he can concentrate on flying.
Even more, the F-16 is an inherently instable design - when flying it, you would need to make constant control adjustments. In the F-16, the Flight Control System computer does this for you. It's constantly moving the control surface (ever so slightly) to keep the F-16 stable.
Of course, if you have an unstable system, you need to have extremely reliable computers. That's why the F-16 has multiple computers that "vote" for the best action (control input) to take. If one computer fails or suggests a wrong solution, it is out-voted by the other computers.
This is just a rough outline but I hope this helps
stefaan
Stefaan Vanhastel
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Hello everyone!
I decided to use this good old thread to ask one thing about FBW system's control surfaces. I have read that F-16's horizontal stabilizers are moving during the taxing due to bumps on the taxiways. Actually this can be seen very clearly from various video clips.
But do these control surfaces moves in flight too? Of course if there is turbulence etc. the system tries to keep the plane stable by moving ailerons. FBW does thousands corrections every second but are these corrections so small that you can't actually see anything special to happen? I presume that these things are quite relevant to all FBW fighter jets.
Thanks for your time and answers!
I decided to use this good old thread to ask one thing about FBW system's control surfaces. I have read that F-16's horizontal stabilizers are moving during the taxing due to bumps on the taxiways. Actually this can be seen very clearly from various video clips.
But do these control surfaces moves in flight too? Of course if there is turbulence etc. the system tries to keep the plane stable by moving ailerons. FBW does thousands corrections every second but are these corrections so small that you can't actually see anything special to happen? I presume that these things are quite relevant to all FBW fighter jets.
Thanks for your time and answers!
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Copy and paste, from other threads on similar subjects.
Depending on the angle of attack and a speed and the wing formation (and a lot of other variables) sometimes when used in conjunction/symmetrically ailerons act like flaps under some conditions and can act like elevators and other conditions. It is a way of mixing control surfaces to get more controlability and maneuverability out of an aircraft.
I have some of my model airplanes set up so the ailerons are flaperons I also have the flaps set so they can be positive or negative (so they work like elevons). As a result when I get into a flat spin I can adjust the controls to the point that I can climb while in a flat spin. I don't think I was a first person to do this.
Another benefit of having the controls blended this way is if a control surface fails, the other control surfaces can compensate for the problem, often without much noticeable change in controllability. I think there was an F-16 or F-18 that had a control failure or malfunction and one of the control surfaces went to the full stop, the chase pilot noted the condition and may have even filmed it, however the computer system works so well and the controls were so redundant that the pilot allegedly didn't even notice that there was a problem with control ability. I would suspect that a master caution, and some sort of warning would have displayed, but other than that apparently the plane flew normally for normal flight. The plane was able to land safely, even with a jammed control surface.
I suspect
the F-22's flight control computer automatically figures out how to blend the control surfaces to get the best controlability and maneuverability out of aircraft. 
hehe
It's too bad that Alaskan airline that crashed because the elevator trim screw stripped due to lack of lubrication didn't have redundant independently controlled control surfaces, controlled from a computer with the ability to compensate for failures.
On a side note: This is from an old post I made, when people were debating about the buzz phrase “flyby light”.
Depending on the angle of attack and a speed and the wing formation (and a lot of other variables) sometimes when used in conjunction/symmetrically ailerons act like flaps under some conditions and can act like elevators and other conditions. It is a way of mixing control surfaces to get more controlability and maneuverability out of an aircraft.
I have some of my model airplanes set up so the ailerons are flaperons I also have the flaps set so they can be positive or negative (so they work like elevons). As a result when I get into a flat spin I can adjust the controls to the point that I can climb while in a flat spin. I don't think I was a first person to do this.
Another benefit of having the controls blended this way is if a control surface fails, the other control surfaces can compensate for the problem, often without much noticeable change in controllability. I think there was an F-16 or F-18 that had a control failure or malfunction and one of the control surfaces went to the full stop, the chase pilot noted the condition and may have even filmed it, however the computer system works so well and the controls were so redundant that the pilot allegedly didn't even notice that there was a problem with control ability. I would suspect that a master caution, and some sort of warning would have displayed, but other than that apparently the plane flew normally for normal flight. The plane was able to land safely, even with a jammed control surface.
I suspect
the F-22's flight control computer automatically figures out how to blend the control surfaces to get the best controlability and maneuverability out of aircraft. hehe
It's too bad that Alaskan airline that crashed because the elevator trim screw stripped due to lack of lubrication didn't have redundant independently controlled control surfaces, controlled from a computer with the ability to compensate for failures.
On a side note: This is from an old post I made, when people were debating about the buzz phrase “flyby light”.
Many here have given many good reasons. Let me add some or at least try to make things a little clearer, but I’m liable to confuse some of you even more. :lol
Redundancy with good programming and enough working input sensors, and different controls surfaces can fill in for others if a single (or more in some cases) fails. Example if one elevator jams it won’t jam the other in an isolated system. Or Example if you lose elevators the computer can use flaps or and vectored thrust to control the aircraft.
Enhanced flight characteristics. Example: While braking the control surfaces can cross control, then net effect is increased braking. (for those that don’t understand sample: flaps down, down elevator can cancel out each others response but the extra drag from doing so will act as a brake) Example: If you have elevators that operate independently if you cross control them with the ailerons the net effect will be braking. Example: Rolling with the ailerons can be enhance by having elevators that act independently of each other but complement the ailerons.
If you still don’t understand what I am talking about, watch a modern aircraft land on a carrier. In the old days, each elevator acted as one, the ailerons always acted diametrically opposed. With computer assisted flight controls it’s not necessary to do that anymore, so each flight control can act independently. You can have a single control input get mixed into several controls. So you can have redundancy, and enhanced flight performance.If your ailerons can act independently, then they can be used as flaps.
Fly by wire and fly by light is essentially the same thing, the only difference in flyby light is the electrical signal is converted to light then back to be transferred over fiber optics. Fly by light is not faster. Light travels the same speed as electricity. In the world of data you can fit more bandwidth on fiber optic systems so in that way it could in theory be faster if the bandwidth was the limiting factor. The bandwidth needed for flight controls is very low so data backup is not very likely. Fly by wire systems are a little slower as they have another stage of conversion as they are an electrical signal before and after they are light. The key advantage to fly by light over of fly by wire systems can be more jam/ECM EMP resistant if built right. Long sensitive wires of fly by wire systems can act like antennas to pull stray signals, ECM, EMP and can more easily be jammed or damaged, so sometimes in a hostile environment fly by light is better.
If your going to send data a long distance or at high bandwidth then optical would be more efficient but I would hardly call from one end of a plane to another long distance :rollin Flight controls really shouldn’t use up much bandwidth either. Since the distance across an aircraft is so short no repeaters will be needed :lol
Computer assisted flight controls generally make an aircraft easier to fly; I also agree with those that say computer assisted aircraft have a lot less of a feel to them. In non computer assisted aircraft, you are more likely to notice a response in an aircraft is changing before things are terminal. With older aircraft you could often tell if they were icing up, or the fuel or hydraulic fluid was running out ect.
If Alaska Airlines Flight 261 had redundancies in the elevator control, the aircraft would have made it to the mainland and probably would have been able to land safely. If there was redundancies and it had a flyby wire system that was semi smart in compensating for failures, the plane could probably landed safely without even noticing much of a problem.
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Thanks for the "older" answer which explained my question quite well. Anyway as I thought this subject is quite complicated because there is no single answer. And of course I meant that do these control surfaces move when the plane is just flying in a straight line but you probably got that already.
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Salute!
To Viper dude.........
The F-16's flaperons and horizontal tail surfaces move all the time. They move when taxiing and they move constantly when just flying st and level.
The control surfaces in the Viper are all independent. The move wherever they have to to achieve the pilot commanded attitude. Gear down is different, as AoA and pitch rate are blended into the control laws to make the jet feel like a "normal" jet. But it's still a basic gee-command/attitude command system.
Go look at my LEF failure pic (interview section). The things( flaperons and horizontal tails) were all over the place to keep me going with the pointy end ahead.
And for a final comment: The Viper IS NOT UNSTABLE! It has "relaxed" static stability. Average pilots would not be able to fly real smooth. A few would be able to fly the thing about exerting superior aviator skills and "touch". The FBW and FLCS computers smooth things out and dampen pitch rates and such so one does not get into PIO situations. The FBW is separate from the "stability" aspect. Airbus crowd-killers have FBW, but they are stable with respect to C.G. and such. The Viper is less "stable", but the FBW and FLCS control laws make the thing fly and feel like a "normal" jet.
gotta digest my turkey and such...........
Salute from the USA!
To Viper dude.........
The F-16's flaperons and horizontal tail surfaces move all the time. They move when taxiing and they move constantly when just flying st and level.
The control surfaces in the Viper are all independent. The move wherever they have to to achieve the pilot commanded attitude. Gear down is different, as AoA and pitch rate are blended into the control laws to make the jet feel like a "normal" jet. But it's still a basic gee-command/attitude command system.
Go look at my LEF failure pic (interview section). The things( flaperons and horizontal tails) were all over the place to keep me going with the pointy end ahead.
And for a final comment: The Viper IS NOT UNSTABLE! It has "relaxed" static stability. Average pilots would not be able to fly real smooth. A few would be able to fly the thing about exerting superior aviator skills and "touch". The FBW and FLCS computers smooth things out and dampen pitch rates and such so one does not get into PIO situations. The FBW is separate from the "stability" aspect. Airbus crowd-killers have FBW, but they are stable with respect to C.G. and such. The Viper is less "stable", but the FBW and FLCS control laws make the thing fly and feel like a "normal" jet.
gotta digest my turkey and such...........
Salute from the USA!
Gums
Viper pilot '79
"God in your guts, good men at your back, wings that stay on - and Tally Ho!"
Viper pilot '79
"God in your guts, good men at your back, wings that stay on - and Tally Ho!"
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My eyes have seen the glory of the Lord and the esthetics of the Flightline
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Just for fun sometimes we used to grip the sidestick very tightly while hydraulic power was applied...you can actually see the flight control surfaces move in response to the pulse in your hand. True!
Best Regards,
Best Regards,
Joe Sambor
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Joe you are so right. When doing a engine rune and not touching the stick, the stabs would move when you pushed the throttle up to try and maintain 1 "G"
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Thanks Gums for the very detailed answer. I could presume that these flaperon and horizontal tail surface movements are quite small and quick. Even so small that it may be impossible to tell which one is moving and when. It really requires a lot of calculating to keep the plane flying.
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Sorry to bother You guys again but can any one of you tell or estimate how large these control surface movements really are? I mean is it able see or notice when the plane is flying level? Of course I forgot to ask this last time but what can you do. 
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The side stick controller feedback on the F-16 is very good, (I don’t fly em) but trying to make huge surface deflections on the ground (bleeds) is very difficult (the jet is not going to Screw You) Very well designed. When the stick is between your legs (other fighters) you can pump the surfaces with full deflection in all directions with little or no effort.
You definitely can tell when pilots do the trim check during launch, and if they are using the buttons on the stick or the wheels on the panel.
"Make no Mistake" (Yes I'm Pro Bush) The F-16 is the Backbone of the fighter world only replacing the F-4.
You definitely can tell when pilots do the trim check during launch, and if they are using the buttons on the stick or the wheels on the panel.
"Make no Mistake" (Yes I'm Pro Bush) The F-16 is the Backbone of the fighter world only replacing the F-4.
My eyes have seen the glory of the Lord and the esthetics of the Flightline
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