SITL: added a MotorBoat class

a sailboat with zero sail area

libraries/SITL/SIM_MotorBoat.h

@@ -0,0 +1,41 @@
+/*
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+/*
+  MotorBoat simulator class
+*/
+
+#pragma once
+
+#include "SIM_Sailboat.h"
+
+namespace SITL {
+
+/*
+  a MotorBoat simulator. We re-use SailBoat but force motor_connected and sail_area to 0
+ */
+class MotorBoat : public Sailboat {
+public:
+    MotorBoat(const char *frame_str) : Sailboat(frame_str) {
+        motor_connected = true;
+        sail_area = 0.0;
+    }
+
+    /* static object creator */
+    static Aircraft *create(const char *frame_str) {
+        return new MotorBoat(frame_str);
+    }
+};
+
+} // namespace SITL

libraries/SITL/SIM_Sailboat.cpp

@@ -41,7 +41,8 @@ namespace SITL {
 Sailboat::Sailboat(const char *frame_str) :
     Aircraft(frame_str),
     steering_angle_max(35),
-    turning_circle(1.8)
+    turning_circle(1.8),
+    sail_area(1.0)
 {
     motor_connected = (strcmp(frame_str, "sailboat-motor") == 0);
 }
@@ -68,8 +69,8 @@ void Sailboat::calc_lift_and_drag(float wind_speed, float angle_of_attack_deg, f
     }
 
     // apply scaling by wind speed
-    lift *= wind_speed;
-    drag *= wind_speed;
+    lift *= wind_speed * sail_area;
+    drag *= wind_speed * sail_area;
 }
 
 // return turning circle (diameter) in meters for steering angle proportion in the range -1 to +1

libraries/SITL/SIM_Sailboat.h

@@ -38,6 +38,11 @@ public:
     }
 
     bool on_ground() const override {return true;};
+
+protected:
+    bool motor_connected;       // true if this frame has a motor
+    float sail_area; // 1.0 for normal area
+
 private:
 
     // calculate the lift and drag as values from 0 to 1 given an apparent wind speed in m/s and angle-of-attack in degrees
@@ -69,7 +74,6 @@ private:
     Vector3f wave_gyro;         // rad/s
     float wave_heave;           // m/s/s
     float wave_phase;           // rads
-    bool motor_connected;       // true if this frame has a motor
 };
 
 } // namespace SITL