Elevator trim on big 'uns

[ColdWaterSurf]

Not sure if this is the appropriate forum or not.. apologies if not.

Flying the Microsoft Flight Sim 737 level on autopilot I've noticed that the elevator trim is constantly adjustung itself, and that off autopilot the aircraft is impossible to trim correctly, even if turbulence, wind etc are set to zero.

Is this the case on real big jets? And if so, why?

[HPSOV]

When the autopilot in engaged it is always trimming the aircraft. Not constantly back and forward if thats what flightsim is doing, real aircraft will make lots of tiny changes. When in manual flight you do have to constantly trim during and speed/configuration changes. But if you are flying straight and level you should be able to trim it out and not have to touch it again.

[quid]

Seeing as how it's a Flight Sim question, I don't know how technical you want to get. But, most (all?) modern day jet aircaft trim the stabilizer, not the elevator. The yoke will move the elevator with control inputs, but the stabilizer will trim out the forces.

[QAVION]

"Flying the Microsoft Flight Sim 737 level on autopilot I've noticed that the elevator trim is constantly adjusting itself,.."

The trim scale is normally a fixed decal on top of the moving part of the yoke. Whenever the yoke moves, the trim pointer on the fixed part of the yoke appears to move (not sure if this is applicable in MSFS). If the autopilot is correcting its heading due to both airplane(imbalance) and external influences(wind, etc), then the yoke will be moving(giving the appearance that the trim is moving).

The electric pilot-operated manual trim is superimposed on this autopilot movement. If manual electric trim is set up properly, it may help to stop constant corrections by the autopilot.

Rgds.
Q.

[scroggs]

So, Qavion, tell me again just exactly how the elevator trim is shown on the yoke? And how it affects the aircraft's heading? RTFQ, methinks. Or learn the difference between elevators and ailerons!