SITL: fixed airspeed pass-thru from simulators

libraries/SITL/SIM_Aircraft.cpp

@@ -233,7 +233,7 @@ void Aircraft::fill_fdm(struct sitl_fdm &fdm) const
     fdm.rollDeg  = degrees(r);
     fdm.pitchDeg = degrees(p);
     fdm.yawDeg   = degrees(y);
-    fdm.airspeed = velocity_ef.length();
+    fdm.airspeed = airspeed;
     fdm.magic = 0x4c56414f;
 }
 

libraries/SITL/SIM_Aircraft.h

@@ -77,6 +77,7 @@ protected:
     Vector3f position; // meters, NED from origin
     float mass; // kg
     Vector3f accel_body; // m/s/s NED, body frame
+    float airspeed; // m/s, apparent airspeed
 
     uint64_t time_now_us;
 

libraries/SITL/SIM_CRRCSim.cpp

@@ -129,6 +129,9 @@ void CRRCSim::recv_fdm(const struct sitl_input &input)
     position.y = posdelta.y;
     position.z = -pkt.altitude;
 
+    // assume zero wind for now
+    airspeed = velocity_ef.length();
+
     dcm.from_euler(pkt.roll, pkt.pitch, pkt.yaw);
 
     // auto-adjust to crrcsim frame rate

libraries/SITL/SIM_Helicopter.cpp

@@ -131,6 +131,9 @@ void Helicopter::update(const struct sitl_input &input)
     Vector3f old_position = position;
     position += velocity_ef * delta_time;
 
+    // assume zero wind for now
+    airspeed = velocity_ef.length();
+
     // constrain height to the ground
     if (on_ground(position)) {
         if (!on_ground(old_position)) {

libraries/SITL/SIM_JSBSim.cpp

@@ -405,6 +405,7 @@ void JSBSim::recv_fdm(const struct sitl_input &input)
     location.lng = degrees(fdm.longitude) * 1.0e7;
     location.alt = fdm.agl*100 + home.alt;
     dcm.from_euler(fdm.phi, fdm.theta, fdm.psi);
+    airspeed = fdm.vcas * FEET_TO_METERS;
 
     // assume 1kHz for now
     time_now_us += 1000;

libraries/SITL/SIM_Multicopter.cpp

@@ -204,6 +204,9 @@ void MultiCopter::update(const struct sitl_input &input)
     Vector3f old_position = position;
     position += velocity_ef * delta_time;
 
+    // assume zero wind for now
+    airspeed = velocity_ef.length();
+
     // constrain height to the ground
     if (on_ground(position)) {
         if (!on_ground(old_position)) {

libraries/SITL/SIM_last_letter.cpp

@@ -107,6 +107,9 @@ void last_letter::recv_fdm(const struct sitl_input &input)
     location.alt = pkt.altitude*1.0e2;
     dcm.from_euler(pkt.roll, pkt.pitch, pkt.yaw);
 
+    // assume zero wind for now
+    airspeed = velocity_ef.length();
+
     // auto-adjust to last_letter frame rate
     uint64_t deltat_us = pkt.timestamp_us - last_timestamp_us;
     time_now_us += deltat_us;