so in my last question, ‘trim’ popped up a lot and after reading up on it I got this: it’s used to adjust the forces on the control surfaces so that the aircraft maintains like a set input
But what I couldn’t find a simple answer on was this: how it controls/adjusts the elevator so that cruise is maintained even with the changing weight of the aircraft?
Also please, is the elevator left in the deflected position please when the plane gets the required lift to maintain cruise?
As mentioned by @Dan, trim is often achieved via a trim tab. However, there are other ways.
On big jetliners, the entire horizontal tail can rotate to trim the aircraft. The elevator (the control surface on the horizontal tail) is independently actuated as the primary pitch control system. So in this case instead of the trimming surface being on the elevator, you could say that the elevator is on the trimming surface.
The important thing about a trim system is that after you adjust it, it stays put without continued effort. This allows you to make occasional refined adjustments.
Trim appears in other similar contexts. Some light aircraft use a metal tab on the rudder or aileron as a trim surface -- you literally bend it between flights to help balance out the aircraft for hands-free flying.
Boats can use trim both in the form of flaps on the boat to adjust its pitch attitude and also on the rudder for direction.
The trim is its own control surface on the back of the elevator called a trim tab.
The simplistic explanation is that its like a little mini 'wing' attached to the elevator that, when set properly, holds the elevator in the position you want.
To be clear, what I'm saying is that the trim tab is a) A physical thing, a part of the elevator and b) Is itself subject to aerodynamic forces. It uses these aerodynamic forces to expert forces onto the elevator.
Reference your questions, trim is delicate and will absolutely need adjusting as the flight parameters change. Its not something you set once and forget about it, it needs constant changes and a change in weight would definitely alter trim
