Tutorials : How Trims Work

Mike Shellim 13 Mar 2003

updated 12 May 2008

This section describes 

Background: how trims work

The trim position of any control is determined by (a) the position of the trim lever and (b) by an offset which is programmable by the user. Both parameters are displayed in the Control Adjustments screen.

The actual trim is the sum of the two values:


In the example above, the actual trim is -10 + 0 = -10. 


The OFFSET parameter is programmable and flight mode dependent.

Re-centring the Trim Lever

As part of the test flying procedure, you will normally alter the position of the flight trims. After flight testing, it's normally a good idea to recentre the trim lever, but obviously you don't want to lose the trim positions on the model.

Remember that when you centre the trim lever, the value of LEVER will become zero. In order to maintain the trim position, you must adjust OFFSET to compensate. In the example above, if you centre the trim lever, OFFSET must be changed to -10. 

The adjustment of OFFSET can be done manually through the previous screen. Alternatively you can use the TRIM-CENT menu:

The TRIM-CENT menu shows the applied trim value (the sum of LEVER and OFFSET) for each control TA, TB, TC, TD. To centre a trim lever,

  1. Select the flight mode using your flight-mode switch (only necessary if you have set different flightmodes).
  2. Enter the TRIM-CENT menu
  3. Select the control you wish to centre
  4. Press the key again. A confirmatory beep sounds, and OFFSET is adjusted so that the trim lever can be moved to centre.

You can now centre the trim lever. 

Note that if you have mulitple flight modes, the procedure is quite complicated. For each flight mode, you have to move the trim to where it was during flight tests, and then repeat the steps above. There is some scope for error here, and personally I favour setting the value of OFFSET manually via the CENTRE menu.


With thanks to Peter Bailey.