Linear Actuator Trim Tab

Well it all depends on what kind of a linear actuator you have and the associated driver electronics you have. If your linear actuator is driven by a stepping motor, then you may not need any feed back system to tell the driver the error between where you wish to be and where you actually are. If instead you have a DC motor then you will likely need to have some feedback system in a control loop. Don't forget to test the dynamic components of your system so that your feedback system does not cause the system to oscillate or self destruct in a runaway oscillation. Remember that when you calculate the Laplace transform of your system that you must always keep the poles in the left half plane for stability. You could of course instead do this completely digitally with a Z transform instead. In this case the poles must remain inside the unit circle for a stable system.

Regardless of the control system you use, you should include some limit switches that activate at the limit of travel to stop your actuator from trying to move beyond its limit. You may even want to include some collision switches to the system that will turn OFF the driver when things go out of control.

If none of my suggestions make any sense, or they don't dust off some cobwebs from some old (motion) control theory, hire an engineer or get ready to duck.

"Switch" = rotary potentiometer.
Actuator is equipped with linear potentiometer.
The potentiometers are connected in a Wheatstone bridge circuit with a balance relay that energizes extend/retract solenoids that drive the actuator until the potentiometers match.

That's one possibility among others, such as pneumatic pressure vs. a spring.

To be certain of the intent of your question:

We are discussing the remote adjustment of flight control surface trim tabs.

There is a system in the plane today, and you wish to convert it to something else.

You are correct. At this time, there is nothing installed right now. The one company that I have seen build these trim servos are Ray Allen Company (RAC) servos. The servo I would use is the T3-12A (12-14vDC, 150ma no load current, 40lbs of force). One of my associates used limit switches connected to a dial to control the position of the trim tab. It acts like a rocker switch, but it's a dial. I want to be able to mimic a wire trim system where the dial is rotated to add/decrease trim. If the operator wants to adjust the trim, they just move the dial again, but the dial is not moved to a center position to stop the trim motor.

One approach that I was described to me is using an analog DC motor controller, DC linear actuator with feedback and a potentiometer. These would be the same parts used in robotics.

Check out Firgelli. I use their L12 actuator with integrated controller. Add a pot and you're in business.