Auto-coordination helps users with no hardware rudder pedals fly airplanes when rudder input is required for coordinated turns, to help with asymmetric thrust conditions and to help with crosswind take-offs and landings.
Which aircraft get auto-coordination
Auto coordination is applied only to aircraft, not rotorcraft. For successful operation of a helicopter it is absolutely necessary to have means of operating the anti-torque pedals, through pedals or a twisting joystick.
When is auto-coordination active?
Auto-coordination is active whenever no joystick axis is configured for the “Yaw” input. If actual pedals or a joystick with twist-grip is connected and the axis assigned, auto-coordination will never be applied.
If a plane is equipped with a Yaw Damper and it is turned on by the pilot, has power and is not failed, auto-coordination is not applied, regardless of joystick configuration. The yaw damper is relied upon for coordinated turns and auto-coordination does not interfere with it. Note that that requires the yaw damper to be configured. In testing, we found a number of published aircraft that had yaw damper switches in the cockpit but no configured yaw damper, so the switch would not do anything. In that case (the yaw damper constants being all zero), the yaw damper switch position is ignored as it is a dummy. Please consult the article on autopilot constants to learn how to configure the yaw damper if your airplane needs one.
Auto-coordination for X-Plane 11 aircraft
X-Plane 11 aircraft loaded in X-Plane 12 get the exact same rudder assist as in X-Plane 11. A proverse rudder input of 20% of the aileron input is applied when the user deflects the aileron. No assistance is provided for crosswind or asymmetric thrust.
Auto-coordination for X-Plane 12 aircraft
Aircraft authored with Plane Maker 12 allow configuration of the auto-coordination controller. The auto-coordination controller is a PID controller that seeks to keep beta (sideslip angle) at 0 degrees. That means, it applies rudder to keep the fuselage aligned with the airflow, and in doing so, it works against adverse yaw and helps with coordinated turns. Keeping the slip angle at 0 however also helps cancel P-factor and spiraling slipstream, so you will notice that the auto-coordination applies right rudder in high-power, high-AoA situations in single-engine propeller aircraft, where right rudder is needed to keep the airplane coordinated in climb, which a simple aileron coupling could not achieve. Note that this also works in single-engine flight of a multi-engine aircraft: With a failed engine in a twin, the auto-coordination will step onto the live engine in an effort to compensate for asymmetric thrust. Note that it tries to achieve zero side slip, not zero ball, i.e. it tries to center a yaw string, not the inclinometer. With OEI it will naturally “split the ball” and require a slight bank into the good engine to fly straight.
The controller is a PID controller that gets the beta angle in degrees as input and acts directly on the rudder, like the pilot would with rudder pedals. The controller gains can be tuned in flight in the Developer->Show Autopilot Constants window, in the “yaw” tab. Note that X-Plane does not save those values permanently, so once a good tuning is established, the values must be saved to the aircraft file in Plane Maker.
The beta angle input into the controller changes smoothly from slip angle to crab angle as the aircraft climbs or descends 5 meters from the surface. This is what allows crosswind takeoffs and landings even with no hardware to perform realistic cross-controlling. In a crosswind landing, the controller will try to eliminate crab angle as the aircraft is flared over the runway. This needs to be anticipated by the pilot who needs to apply slight opposite aileron as the auto-coordination kicks out the crab before touchdown.