ArduPlane: Add Q_Option for tilt yaw control in transition

ArduPlane/quadplane.cpp

@@ -280,6 +280,7 @@ const AP_Param::GroupInfo QuadPlane::var_info[] = {
     // @Bitmask: 20: Force RTL mode-forces RTL mode on rc failsafe in VTOL modes overriding bit 5(USE_QRTL)
     // @Bitmask: 21: Tilt rotor-tilt motors up when disarmed in FW modes (except manual) to prevent ground strikes.
     // @Bitmask: 22: Scale FF by the ratio of VTOL/plane angle P gains in VTOL modes rather than reducing VTOL angle P based on airspeed.
+    // @Bitmask: 23: Force yaw control in transition for tiltrotors
     AP_GROUPINFO("OPTIONS", 58, QuadPlane, options, 0),
 
     AP_SUBGROUPEXTENSION("",59, QuadPlane, var_info2),
@@ -1680,7 +1681,7 @@ void SLT_Transition::update()
         }
         quadplane.hold_hover(climb_rate_cms);
 
-        if (!quadplane.tiltrotor.is_vectored()) {
+        if (!quadplane.tiltrotor.is_vectored() && !quadplane.option_is_set(QuadPlane::OPTION::FORCE_TRANSITION_TILT_YAW)) {
             // set desired yaw to current yaw in both desired angle
             // and rate request. This reduces wing twist in transition
             // due to multicopter yaw demands. This is disabled when

ArduPlane/quadplane.h

@@ -618,6 +618,7 @@ class QuadPlane
         FS_RTL=(1<<20),
         DISARMED_TILT_UP=(1<<21),
         SCALE_FF_ANGLE_P=(1<<22),
+        FORCE_TRANSITION_TILT_YAW=(1<<23),
     };
     bool option_is_set(OPTION option) const {
         return (options.get() & int32_t(option)) != 0;