SITL: support a builtin tailsitter vehicle type

libraries/SITL/SIM_Aircraft.cpp

@@ -508,6 +508,19 @@ void Aircraft::update_dynamics(const Vector3f &rot_accel)
             use_smoothing = true;
             break;
         }
+        case GROUND_BEHAVIOR_TAILSITTER: {
+            // point straight up
+            float r, p, y;
+            dcm.to_euler(&r, &p, &y);
+            dcm.from_euler(0.0f, radians(90), y);
+            // no movement
+            if (accel_earth.z > -1.1*GRAVITY_MSS) {
+                velocity_ef.zero();
+            }
+            gyro.zero();
+            use_smoothing = true;
+            break;
+        }
         }
     }
 }

libraries/SITL/SIM_Aircraft.h

@@ -163,6 +163,7 @@ protected:
         GROUND_BEHAVIOR_NONE = 0,
         GROUND_BEHAVIOR_NO_MOVEMENT,
         GROUND_BEHAVIOR_FWD_ONLY,
+        GROUND_BEHAVIOR_TAILSITTER,
     } ground_behavior;
 
     bool use_smoothing;

libraries/SITL/SIM_Plane.cpp

@@ -35,6 +35,8 @@ Plane::Plane(const char *home_str, const char *frame_str) :
     thrust_scale = (mass * GRAVITY_MSS) / hover_throttle;
     frame_height = 0.1f;
 
+    ground_behavior = GROUND_BEHAVIOR_FWD_ONLY;
+    
     if (strstr(frame_str, "-heavy")) {
         mass = 8;
     }
@@ -49,8 +51,12 @@ Plane::Plane(const char *home_str, const char *frame_str) :
     if (strstr(frame_str, "-elevrev")) {
         reverse_elevator_rudder = true;
     }
+   if (strstr(frame_str, "-tailsitter")) {
+       tailsitter = true;
+       ground_behavior = GROUND_BEHAVIOR_TAILSITTER;
+       thrust_scale *= 1.5;
+   }
 
-    ground_behavior = GROUND_BEHAVIOR_FWD_ONLY;
     if (strstr(frame_str, "-ice")) {
         ice_engine = true;
     }
@@ -266,7 +272,7 @@ void Plane::calculate_forces(const struct sitl_input &input, Vector3f &rot_accel
         add_noise(fabsf(thrust) / thrust_scale);
     }
 
-    if (on_ground()) {
+    if (on_ground() && !tailsitter) {
         // add some ground friction
         Vector3f vel_body = dcm.transposed() * velocity_ef;
         accel_body.x -= vel_body.x * 0.3f;

libraries/SITL/SIM_Plane.h

@@ -97,6 +97,7 @@ protected:
     bool vtail;
     bool reverse_elevator_rudder;
     bool ice_engine;
+    bool tailsitter;
 
     ICEngine icengine{2, 14, 12, 13, 100};