BFF CL Software - Short User Guide


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Appendix G. Failure Mode Loading.

Tab 10 in the Configuration Manager to make the Failure Mode settings.

A single byte FSUIPC offset is used to indicate a failure mode is active (eg hydraulic systems failure). When failure is indicated by the offset the CL software adds additional loading to the affected control axes. The failure loading is ramped up over a specified transition time.

The additional load components that are available are Spring Stiffness (cf Lift Gain), Damping and Mass. Reference should be made to the values for these terms used in the normal flight loading settings for each axis (Tabs 1, 2 & 3) when setting the additional values for failure loading.


Implementing effective failure mode loading which is significantly heavier than normal flight loading requires that the mechanical transmissions are designed with sufficient loading capacity from the outset.

Therefore the failure load requirements and their effect on transmission ratios need to be considered at the project design stage.

If the system loading capacity is designed to cover only normal flight loading then it can be very easy to set additional failure mode loading which will quickly drive the motors to full output. This can potentially damage the drive cards if failure conditions and loading is held for extended periods.

If your system does not have the load capacity for additional failure loading then it is recommend that only additional Damping is added in the case of failures. This can be used to generate a sluggish/heavy feel to the controls in the event of system failures without substantially increasing the sustained loading magnitudes.

Configuration Settings:

  1. In Configuration Manager (V1.10 or later) go to Tab 10 and set Item 1 (Enable Failure Loading) = 1.
  2. Item 2 (Failure Indicator Offset) is the single byte FSUIPC offset read to determine system failure status. The byte is bit significant -

    b0 = All axes failed (= 1)
    b1 = Elevator axis failed
    b2 = Aileron axis failed
    b3 = Rudder axis failed

    This offset should be written by the flight sim software or 3rd party application as required for the failure modes required.
  3. Items 3 to 11 allow additional Spring Stiffness (Lift Gain), Damping and Mass settings to be made for each axis. In the event of a failure being indicated on an axis the CL software will ramp up these additional loading components.

    Note: An individual component will only be active if it is active in the normal flight loading settings for that axis. For example if Mass effects are disabled for normal flight then they will also be disabled for failure loading regardless of the setting made here.
  4. Item 12 (Load Transition Rate) sets the transition period over which the additional loading is ramped up. It also applied when the failure offset is cleared and the failure loading ramps down.
  5. Remember to SAVE your configuration settings.

The settings can be tested using the Fail_Load buttons in the Show_Elev, Show Ail and Show_Rud windows. Click the button to toggle the failure mode loading on and off.

WARNING: Take care with the levels of additional failure loading that is set. If the mechnical transmissions in the controls are not designed to deliver the higher levels of failure loading then it can be very easy to induce full scale output in the motors, which if held for extended periods may cause heating damage to the cards.



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