Control planes movements by "fly by wire" ?

Question

control planes movements by "fly by wire" ?

of course many have heard of fly-by-wire

making many flight corrections

to stabilize the aircraft.

but...

actually, how many movements do control planes

(rudders, ailerons, elevators, elevons

and/or flaperon) REALLY move per second ?

because i've seen a fighter jet with

missiles/bombs, when it took off,

front wheel already off the runway,

while main landing gear still at the runway,

the elevator does moves up and down a bit

(at downward position),

showing fly-by-wire at work,

and i'm sure the pilot wasn't playing

with the control stick ;)

so...

whot do you think the approximate

ACTUAL max number of movement per second

for the control planes (full FBW) ?

thanks a lot ;)

Answer 1

On fighter aircraft such as the F-16, F/A-18, F-22 etc. the flight control system typically updates the commands to the surface at about 80 to 100 times per second.

Answer 2

The impulse and feedback to/from the FCC  is non-stop, as in virtually instananeous. You can not tell it is happening. The input/output is nearly a solid line. The fluctuations that you saw in the tail of the aircraft are normal, and you really should not see much during takeoff... more during landing and then too, that is something that you take as a matter of pride as a pilot that you landed as smoothly and under control as is possible with the fewest control and throttle changes as possible.  If you see the tail flapping around all over the place, someone is scrambling to "save" a landing from being a bouncer.  Regardless...  the movement you saw, was a result of the input from the pilot, not the computer over-riding him.

Answer 3

On a fighter jet because it has such a small wing span the computer is constantly making correction to keep the aircraft stable.  If it did not have this small wing span it would not be able to achieve the tight turns that it can do.  If the series of systems  that control this failed the aircraft would instantly become uncontrollable.  On a larger plane such as the A-320 and up the movements are not as great due to a lot more stable wing.  How ever these planes do have hydrolic assist and if that is lost it would become almost impossible to move control surfaces.

Answer 4

I guess there is a bit of ambiguity here. The frantic control surface deflection mentioned here is applicable only for Relaxed Static Stability (RSS) aircraft. Not all FBW aircrafts are RSS, especially the huge ones as they dont need the maneuverability.

Having said the above, I have to shamelessly state that I dont have an answer to your question. The number of control surface deflection would be proportional to the magnitude of instability, i.e. the seperation between Aerodynamic Center and the CoG. As the aerodynamic center changes with the airspeed, the correction rate could vary.

And I am guessing that the movements you saw with the wheels down is not from the control law. It should be the pilot's doing.