Trim functionality in Microsoft Flight Simulator X, Lockheed Martin Prepar3D and Laminar Research X-Plane

  1. Trim on a real Airplane
  2. Trimming in MSFX and Prepar3D
  3. Adjusting an X-Plane plane for realistic trim using PlaneMaker and choosing the right CLS2Sim settings
  4. Trimming in CLS2Sim

Trim on a real Airplane

In a real airplane letting go of the yoke doesn't mean the plane will fly at a constant pitch attitude. The ideal position of the yoke for the plane to hold attitude is influenced by many things such as speed and center of gravity. To relieve the pilot of the need to constantly push (or pull) on the flight yoke, a trim tab is placed on the trailing edge of the elevator in order to help keep the elevator at a given position. The trim tab is much smaller than the elevator, but since it is placed at the trailing edge of the elevator it has more leverage and can therefore keep the elevator in a given position. The procedure for trimming is holding the yoke in the ideal position by hand and using the trim wheel to cancel out all forces until the yoke remains in the same position when released. With the airplane trimmed properly, the pilot can essentially now fly "hands-off".

Trimming in MSFX and Prepar3D

Let's look at the FSX and Prepar3D trim systems. The key thing to understand is that the FSX and Prepar3D trim systems are designed for mechanical joysticks (non force feedback). With a mechanical joystick the only place of no resistance is at the physical center of the joystick motion and it can't be changed, therefore the procedure of trimming as described in the above section can not be applied. To counter this, Flight Simulator X and Prepar3D do not change yoke forces, but instead the elevator position when trimming. Now, the yoke remains in center position, while the simulation adds a artificial offset to the yoke input.

-> In MSFX, to achieve realistic trim, read the "Software Trim" section below.

Adjusting an X-Plane plane for realistic trim using PlaneMaker and choosing the right CLS2Sim settings

Configuring x-plane to work with force feedback yoke.

Many X-Plane airplanes are not set up to work with a force-feedback yoke. You will need to update an existing airplane in Plane Maker if it is configured for use with a spring-based yoke.

Why a different setup?

With a spring-based simulator yoke, the position of the yoke bears no relationship to the position of the elevator itself, nor to the attitude of the aircraft. Notice that when you're trimming your simulator for a pitch-up attitude while yoke stays in place, the airplane pitches up. This indicates that the trim wheel changes the position of the elevator control surface. This is done so that if you release the yoke, it will settle in the neutral position that corresponds to that trim, same as in a real aircraft.

How exactly the trim affects elevator position is specific to an airplane.


In the Trim tab, set the the following checkboxes:

In the Autopilot tab, set the following checkboxes:

Now if you change the trim while holding the yoke in one place, the elevator controls will not move and the airplane pitch will not change. However, forces on the yoke will change. Trim your simulator the same way as you would trim real airplane: set the pitch, hold it, adjust the trim until you release the pressure from the yoke.

Trimming in CLS2Sim

The force feedback systems of Brunner Elektronik AG all have the ability to change their neutral position, allowing the simulation of real-life trim. Unfortunately Flight Simulator X and Prepar3D have not accounted for this possibility in their implementation. Furthermore, the influence of trimming is not proportional to the attitude of the aircraft, preventing CLS2Sim from cancelling out unrealistic trim effects.
CLS2Sim provides two modes of operation for trim namely Software and Hardware. Software trim is used by default. To Use hardware trim, check the checkbox "Use hardware trim" in the trim tab.

Software Trim

Software trim reads the trim position from the simulation and button presses mapped to "Trim - ..." actions will be transmitted to the simulation. In MSFX, to achieve realistic trim behaviour, you need to edit the "aircraft.cfg" file of the plane you will be flying. Search for the setting "elevator_trim_limit" and set it to "0.1". Be careful not to enter any spaces, so that the line will read exactly "elevator_trim_limit=0.1". Open CLS2Sim, go to the setup tab and gradually increase the trim "Movement %" setting until the yoke movement is satisfactory.

Trim compensation

When using software trim, trim compensation can be activated. This somewhat migitates the elevator momevent effect when trimming the elevator without moving the yoke.
The optimal solution is editing the plane, so that trimming will not have any effect on the elevator.

Hardware Trim

CLS2Sim decouples the trim functionality from the simulation. Consequently the simulation has no knowledge of the current trim setting of the yoke and most commercial trim controls will not work out of the box. To help circumvent this limitation, the remote control interface of CLS2Sim provides read and write access to the hardware trim data, allowing third-party software to interact with it.

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