Why do aircraft pitch trim move after takeoff and after landing?

Question

Why do aircraft pitch trim move after takeoff and after landing?

Answer 1

The pitch trim is "set" for takeoff to start with -

The setting is adequate for initial climb, so no pressures are held in the controls -

When the airplane accelerates to enroute climb, the trim is set for higher speed -

That is - set for the nose to be lower -



For approach and landing, the trim is set to have no control forces during landing -

That equates to have the trim force pulling nose up - to fly slow -

As soon as the airplane touches down the trim is reset to zero or required position -

Answer 2

An aircraft's pitch trim doesn't move after takeoff and after landing by itself as your question implies, the pilot changes the elevator trim to take out control back pressure to keep from getting tired. In small aircraft, the pilot's muscles work against the elevator's forces to set the attitude he wants. The trim relieves him of this work as the trim actuator counterbalances the elevators forces. After landing, the plane is not flying anymore, and no re-trimming is necessary. The elevator trim indicator has a takeoff position, again, because the plane isn't flying before takeoff, the trim should be put in this position to anticipate its need when the plane takes off. The pilot re-trims the plane as needed during climb and leveling off at the cruise altitude. There are also roll and yaw trim in more complex aircraft.

Answer 3

Trim is used to hold the aircraft in the desired attitude.



The airplane is a bit like a see-saw, pivoting around its Centre of Gravity. As the angle at which the wing meets the air changes, the point at which lift operates (the Centre of Lift) moves back and forward across the wing and thus closer to or further from, the Centre of Gravity. That makes the airplane want to pitch up and down.



That is resisted by the tailplane and you can adjust the tailplane to both make the nose move up and down, or, when you want to fly in a certain attitude, hold the airplane in that attitude, without you having to hold the controls.



It is just a matter of balancing the see-saw.

Answer 4

The landing gear and flaps are retracted after takeoff and that affects trim. After landing it doesn't matter.

Answer 5

the trim is adjusted before take off to a standard setting..then after take off and when stopping climbing the pitch control is used more.

Answer 6

Because the aircraft attitude in the air is different than when setting on the ground.