B737 Feel And Centering Unit

[wof]

I am getting confused about the "centering" part in the feel and centering unit. What does actually "centering" means? my second question is, in the 737-800 the Ailerons have feel and centering unit, so does the Elevators (but why the elevators have ELEVATOR FEEL COMPUTER also when there's a feel and centering unit?)

[IFixPlanes]

To make it short:
"Centering" means getting the controls back to the center = 0.

The elevator feel computer only adjust the column force in relation to the airspeed.

[wof]

thanks for the response IFixPlanes

""Centering" means getting the controls back to the center = 0."

1) when does the "centering the controls back (to zero)" occours?

"The elevator feel computer only adjust the column force in relation to the airspeed."

2) then what is the purpose of the feel and centering unit in both Ailerons and Elevators?

also what is the difference between the Elevator feel system and Speed Trim system? I've been reading the FCOM and got confused about both.

[IFixPlanes]

Originally Posted by wof

... 1) when does the "centering the controls back (to zero)" occours?...

Hydraulic power on and hands away from the controls.

Originally Posted by wof

... 2) then what is the purpose of the feel and centering unit in both Ailerons and Elevators?

More deflection → more force

[wof]

so the airspeed does not affect the force on the control wheel. only on the control column due to the Elevator Feel System. thanks that really helps!

but I am still confused about the difference between the Elevator feel system and Speed Trim system. they both add force on the control column whenever I deviate from the trimmed speed. so what is difference?

[BOAC]

so the airspeed does not affect the force on the control wheel.

- that's it (I think.....). 3000psi of hydraulic pressure moves the elevator and ailerons, not you, so you would not otherwise "feel" a thing!

Elevator feel system and Speed Trim system.

- quite separate. Speed trim only operates at certain limited times, and trims the TAILPLANE to make the control force effectively 'heavier' so as to return the a/c to the trimmed speed. Elevator feel makes the ELEVATOR feel heavier with speed, not the tailplane.

Puzzled by your reference to control 'wheel'? 'Feel' is present in the aileron AND elevator system. As far as I know the aileron 'feel' is purely spring.

[wof]

"quite separate. Speed trim only operates at certain limited times, and trims the TAILPLANE to make the control force effectively 'heavier' so as to return the a/c to the trimmed speed. Elevator feel makes the ELEVATOR feel heavier with speed, not the tailplane."

but in both cases there's a force on the control column which require retrimming, correct?

[BOAC]

Not really - the speed trim is designed to return you to the trimmed speed at which point there will be no need for trim. You will probably not notice it.

Elevator feel is there to let you 'know' that the loads are higher due to speed. If you are holding a force on the elevator without trimming (unlikely?) then yes, I suppose you would need more trim at higher speed. A bit academic, really.