AirSpeed: added parameter ARSPD_USE

setting ARSPD_ENABLE to 1 and ARSPD_USE to 0 allows the airspeed
sensor to be initialised and logged without it being used for flight
control. This is very useful when initially testing an airspeed sensor
in a new plane. It also makes it possible to enable/disable the use of
the airspeed sensor during a flight at any time.

ArduPlane/ArduPlane.pde

@@ -999,7 +999,7 @@ static void update_current_flight_mode(void)
 					nav_roll = 0;
 				}
 
-				if (g.airspeed_enabled == true)
+				if (g.airspeed_enabled == true && g.airspeed_use == true)
                                 {
 					calc_nav_pitch();
 					if (nav_pitch < (long)takeoff_pitch) nav_pitch = (long)takeoff_pitch;
@@ -1017,7 +1017,7 @@ static void update_current_flight_mode(void)
 			case MAV_CMD_NAV_LAND:
 				calc_nav_roll();
 
-				if (g.airspeed_enabled == true){
+				if (g.airspeed_enabled == true && g.airspeed_use == true) {
 					calc_nav_pitch();
 					calc_throttle();
 				}else{

ArduPlane/Attitude.pde

@@ -11,7 +11,7 @@ static void stabilize()
 	float ch4_inf = 1.0;
 	float speed_scaler;
 
-	if (g.airspeed_enabled == true){
+	if (g.airspeed_enabled == true && g.airspeed_use == true){
 		if(airspeed > 0)
 			speed_scaler = (STANDARD_SPEED * 100) / airspeed;
 		else
@@ -130,7 +130,7 @@ static void crash_checker()
 
 static void calc_throttle()
 {
-  if (g.airspeed_enabled == false) {
+  if (g.airspeed_enabled == false || g.airspeed_use == false) {
 	int throttle_target = g.throttle_cruise + throttle_nudge;
 
     // TODO: think up an elegant way to bump throttle when
@@ -188,7 +188,7 @@ static void calc_nav_pitch()
 {
 	// Calculate the Pitch of the plane
 	// --------------------------------
-	if (g.airspeed_enabled == true) {
+	if (g.airspeed_enabled == true && g.airspeed_use == true) {
 		nav_pitch = -g.pidNavPitchAirspeed.get_pid(airspeed_error, dTnav);
 	} else {
 		nav_pitch = g.pidNavPitchAltitude.get_pid(altitude_error, dTnav);
@@ -349,7 +349,7 @@ static void set_servos(void)
 			if (
 					(control_mode == CIRCLE || control_mode >= FLY_BY_WIRE_B) &&
 					(abs(home.alt - current_loc.alt) < 1000) &&
-					((g.airspeed_enabled ? airspeed : g_gps->ground_speed) < 500 ) &&
+					(((g.airspeed_enabled && g.airspeed_use) ? airspeed : g_gps->ground_speed) < 500 ) &&
 					!(control_mode==AUTO && takeoff_complete == false)
 				) {
 				g.channel_throttle.servo_out = 0;
@@ -386,7 +386,7 @@ static void set_servos(void)
             // FIXME: use target_airspeed in both FBW_B and g.airspeed_enabled cases - Doug?
 			if (control_mode == FLY_BY_WIRE_B) {
 				flapSpeedSource = ((float)target_airspeed)/100;
-			} else if (g.airspeed_enabled == true) {
+			} else if (g.airspeed_enabled == true && g.airspeed_use == true) {
 				flapSpeedSource = g.airspeed_cruise/100;
 			} else {
 				flapSpeedSource = g.throttle_cruise;

ArduPlane/Parameters.h

@@ -85,6 +85,7 @@ public:
 		k_param_sonar_enabled,
 		k_param_airspeed_enabled,
         k_param_ahrs,  // AHRS group
+		k_param_airspeed_use,
 
         //
         // 150: Navigation parameters
@@ -319,6 +320,7 @@ public:
     AP_Int8		inverted_flight_ch; // 0=disabled, 1-8 is channel for inverted flight trigger
     AP_Int8		sonar_enabled;
     AP_Int8		airspeed_enabled;
+    AP_Int8		airspeed_use;
     AP_Int8		flap_1_percent;
     AP_Int8		flap_1_speed;
     AP_Int8		flap_2_percent;
@@ -436,6 +438,7 @@ public:
         inverted_flight_ch      (0),
         sonar_enabled			(SONAR_ENABLED),
         airspeed_enabled		(AIRSPEED_SENSOR),
+        airspeed_use			(1),
 
         // PID controller    initial P        initial I        initial D        initial imax
         //-----------------------------------------------------------------------------------

ArduPlane/Parameters.pde

@@ -270,6 +270,13 @@ static const AP_Param::Info var_info[] PROGMEM = {
 	// @User: Standard
 	GSCALAR(airspeed_enabled,       "ARSPD_ENABLE"),
 
+    // @Param: ARSPD_USE
+	// @DisplayName: Use Airspeed if enabled
+	// @Description: Setting this to Enabled(1) will enable use of the Airspeed sensor for flight control when ARSPD_ENABLE is also true. This is separate from ARSPD_ENABLE to allow for the airspeed value to be logged without it being used for flight control
+	// @Values: 0:Disabled,1:Enabled
+	// @User: Advanced
+	GSCALAR(airspeed_use,       	"ARSPD_USE"),
+
 	GGROUP(channel_roll,            "RC1_", RC_Channel),
 	GGROUP(channel_pitch,           "RC2_", RC_Channel),
 	GGROUP(channel_throttle,        "RC3_", RC_Channel),

ArduPlane/radio.pde

@@ -85,7 +85,7 @@ static void read_radio()
 	g.channel_throttle.servo_out = g.channel_throttle.control_in;
 
 	if (g.channel_throttle.servo_out > 50) {
-		if(g.airspeed_enabled == true) {
+		if(g.airspeed_enabled == true && g.airspeed_use == true) {
 			airspeed_nudge = (g.flybywire_airspeed_max * 100 - g.airspeed_cruise) * ((g.channel_throttle.norm_input()-0.5) / 0.5);
         } else {
 			throttle_nudge = (g.throttle_max - g.throttle_cruise) * ((g.channel_throttle.norm_input()-0.5) / 0.5);