The Bell 407 Trim and Force Trim works nicely but the controls need to be setup properly. Here is my experience in getting it to work.
If you are not sure what Force Trim is, you are welcome to discuss.
Arm Force Trim
On the 407 there is a toggle switch on the overhead panel for Force Trim and it must be switched on.
Assign a button to the Set Rotor Longitudinal Trim (“Force Trim”) as well as the other 4 Trim assignments as shown in the picture below.
The key is to assign the cyclic to “Set Cyclic Longitudinal Axis” and “Cyclic Lateral Axis”. By default, it is set to Aileron and Elevator which a helicopter flight control system does not have. The elevator and aileron axis do work on MSFS helicopters, but that is the reason Force trim does not work. The Elevator position is not fed into the Cyclic control system. Also, do set the Rotor Lateral and Longitudinal Trim settings as well.
Operation in Flight
Then in flight, if you hold that button in you set your pitch attitude with the cyclic. Whatever pitch attitude you obtained when releasing the button, the pitch will be trimmed for that attitude.
In RL the force of the stick is actually released and you move the stick to the new central position, but I think here it is more like the attitude is trimmed and then when you move the joystick back to the central position, the helicopter is actually trimmed for the attitude where you released the button.
How do you know Force trim is working and how to test it?
What I did was trim the cyclic full aft or forward so that you have to deflect your joystick fully to maintain your attitude. When you click the “Force Trim” button (“Set Rotor Longitudinal Trim” joystick assignment) you can then move the joystick into a new position and when you release the button, that attitude is the new trimmed value.
I did the same but with Elevator and Aileron assigned and it did NOT work anymore.