AC_AttitudeControl: added an option for pitch weathervaning

when nose-in or tail-in, if the aircraft has significant pitch
asymmetry in hover then we would spin around in no wind if we use
pitch as an input

this makes pitch input for nose-in and tail-in optional and off by
default to preserve existing behaviour

libraries/AC_AttitudeControl/AC_WeatherVane.cpp

@@ -87,6 +87,13 @@ const AP_Param::GroupInfo AC_WeatherVane::var_info[] = {
     // @User: Standard
     AP_GROUPINFO("LAND", 8, AC_WeatherVane, _landing_direction, -1),
 
+    // @Param: OPTIONS
+    // @DisplayName: Weathervaning options
+    // @Description: Options impacting weathervaning behaviour
+    // @Bitmask: 0:Use pitch when nose or tail-in for faster weathervaning
+    // @User: Standard
+    AP_GROUPINFO("OPTIONS", 9, AC_WeatherVane, _options, 0),
+    
     AP_GROUPEND
 };
 
@@ -97,7 +104,7 @@ AC_WeatherVane::AC_WeatherVane(void)
     AP_Param::setup_object_defaults(this, var_info);
 }
 
-bool AC_WeatherVane::get_yaw_out(float &yaw_output, const int16_t pilot_yaw, const float hgt, const float roll_cdeg, const float pitch_cdeg, const bool is_takeoff, const bool is_landing)
+bool AC_WeatherVane::get_yaw_out(float &yaw_output, const int16_t pilot_yaw, const float hgt, const float roll_cdeg, float pitch_cdeg, const bool is_takeoff, const bool is_landing)
 {
     Direction dir = (Direction)_direction.get();
     if ((dir == Direction::OFF) || !allowed || (pilot_yaw != 0) || !is_positive(_gain)) {
@@ -159,13 +166,17 @@ bool AC_WeatherVane::get_yaw_out(float &yaw_output, const int16_t pilot_yaw, con
     const float deadzone_cdeg = _min_dz_ang_deg*100.0;
     float output = 0.0;
     const char* dir_string = "";
+
+    // should we enable pitch input for nose-in and tail-in?
+    const bool pitch_enable = (uint8_t(_options.get()) & uint8_t(Options::PITCH_ENABLE)) != 0;
+
     switch (dir) {
         case Direction::OFF:
             reset();
             return false;
 
         case Direction::NOSE_IN:
-            if (is_positive(pitch_cdeg)) {
+            if (pitch_enable && is_positive(pitch_cdeg)) {
                 output = fabsf(roll_cdeg) + pitch_cdeg;
             } else {
                 output = MAX(fabsf(roll_cdeg) - deadzone_cdeg, 0.0);
@@ -193,7 +204,7 @@ bool AC_WeatherVane::get_yaw_out(float &yaw_output, const int16_t pilot_yaw, con
             break;
 
         case Direction::TAIL_IN:
-            if (is_negative(pitch_cdeg)) {
+            if (pitch_enable && is_negative(pitch_cdeg)) {
                 output = fabsf(roll_cdeg) - pitch_cdeg;
             } else {
                 output = MAX(fabsf(roll_cdeg) - deadzone_cdeg, 0.0);

libraries/AC_AttitudeControl/AC_WeatherVane.h

@@ -10,7 +10,7 @@ class AC_WeatherVane {
         CLASS_NO_COPY(AC_WeatherVane);
 
         // Calculate and return the yaw output to weathervane the vehicle
-        bool get_yaw_out(float &yaw_output, const int16_t pilot_yaw, const float hgt, const float roll_cdeg, const float pitch_cdeg, const bool is_takeoff, const bool is_landing);
+        bool get_yaw_out(float &yaw_output, const int16_t pilot_yaw, const float hgt, const float roll_cdeg, float pitch_cdeg, const bool is_takeoff, const bool is_landing);
 
         // Function to reset all flags and set values. Invoked whenever the weather vaning process is interrupted
         void reset(void);
@@ -31,6 +31,10 @@ class AC_WeatherVane {
             TAIL_IN = 4, // backwards, for tailsitters, makes it easier to descend
         };
 
+        enum class Options {
+            PITCH_ENABLE = (1<<0),
+        };
+    
         // Paramaters
         AP_Int8 _direction;
         AP_Float _gain;
@@ -40,6 +44,7 @@ class AC_WeatherVane {
         AP_Float _max_vel_z;
         AP_Int8 _landing_direction;
         AP_Int8 _takeoff_direction;
+        AP_Int16 _options;
 
         float last_output;
         bool active_msg_sent;