Rudder only aircraft (RUDDER_ONLY)

Description

This parameter configures ArduPlane for "2-Channel" aircraft (Throttle + Rudder/Elevator) that lack ailerons, such as polyhedral gliders or vintage designs. When enabled, the autopilot's roll control logic drives the rudder servo instead of aileron servos to turn the aircraft.

The Mathematics

The roll controller output (PID) is re-routed:
$$ \text{Rudder Output} = \text{Yaw Control} + \text{Roll Control} \times \text{KFF\_RDDRMIX} $$

The Engineer's View

Defined in ArduPlane/Parameters.cpp.

• Setup: The transmitter's Aileron stick should be mapped to the RCMAP_YAW channel. The Rudder servo connects to the Yaw output.
• Constraint: Ground steering logic is disabled or altered in this mode.
• Damping: Requires YAW2SRV_DAMP tuning to prevent oscillation.

Tuning & Behavior

• Default Value: 0 (Disabled)
• 1: Enable Rudder Only mode.
• Note: You must ensure KFF_RDDRMIX is set (typically 1.0) for the roll controller to have authority over the rudder.