Plane: It is possible to disarm with left rudder.

Using is_flying() avoid accidentally disarming while flying.

ArduPlane/Plane.h

@@ -786,7 +786,7 @@ private:
     void set_control_channels(void);
     void init_rc_in();
     void init_rc_out();
-    void rudder_arm_check();
+    void rudder_arm_disarm_check();
     void read_radio();
     void control_failsafe(uint16_t pwm);
     void trim_control_surfaces();

ArduPlane/radio.cpp

@@ -76,8 +76,8 @@ void Plane::init_rc_out()
     }
 }
 
-// check for pilot input on rudder stick for arming
-void Plane::rudder_arm_check() 
+// check for pilot input on rudder stick for arming/disarming
+void Plane::rudder_arm_disarm_check()
 {
     //TODO: ensure rudder arming disallowed during radio calibration
 
@@ -85,45 +85,60 @@ void Plane::rudder_arm_check()
     
     static uint32_t rudder_arm_timer;
 
-    if (arming.is_armed()) {
-        //already armed, no need to run remainder of this function
-        rudder_arm_timer = 0;
-        return;
-    } 
-
     if (! arming.rudder_arming_enabled()) {
-        //parameter disallows rudder arming
+        //parameter disallows rudder arming/disabling
         return;
     }
 
-    //if throttle is not down, then pilot cannot rudder arm
+    //if throttle is not down, then pilot cannot rudder arm/disarm
     if (channel_throttle->control_in > 0) {
         rudder_arm_timer = 0;
         return;
     }
 
-    //if not in a 'manual' mode then disallow rudder arming
+    //if not in a 'manual' mode then disallow rudder arming/disarming
     if (auto_throttle_mode ) {
         rudder_arm_timer = 0;
         return;      
     }
 
-    // full right rudder starts arming counter
-    if (channel_rudder->control_in > 4000) {
-        uint32_t now = millis();
-
-        if (rudder_arm_timer == 0 || 
-            now - rudder_arm_timer < 3000) {
-
-            if (rudder_arm_timer == 0) rudder_arm_timer = now;
-        } else {
-            //time to arm!
-            arm_motors(AP_Arming::RUDDER);
-        }
-    } else { 
-        // not at full right rudder
-        rudder_arm_timer = 0;
-    }
+	if (!arming.is_armed()) {
+		// when not armed, full right rudder starts arming counter
+		if (channel_rudder->control_in > 4000) {
+			uint32_t now = millis();
+
+			if (rudder_arm_timer == 0 ||
+				now - rudder_arm_timer < 3000) {
+
+				if (rudder_arm_timer == 0) rudder_arm_timer = now;
+			} else {
+				//time to arm!
+				arm_motors(AP_Arming::RUDDER);
+				rudder_arm_timer = 0;
+			}
+		} else {
+			// not at full right rudder
+			rudder_arm_timer = 0;
+		}
+	} else if (!is_flying()) {
+		// when armed and not flying, full left rudder starts disarming counter
+		if (channel_rudder->control_in < -4000) {
+			uint32_t now = millis();
+
+			if (rudder_arm_timer == 0 ||
+				now - rudder_arm_timer < 3000) {
+
+				if (rudder_arm_timer == 0) rudder_arm_timer = now;
+			} else {
+				//time to disarm!
+				disarm_motors();
+				rudder_arm_timer = 0;
+			}
+		} else {
+			// not at full left rudder
+			rudder_arm_timer = 0;
+		}
+	}
 }
 
 void Plane::read_radio()
@@ -177,7 +192,7 @@ void Plane::read_radio()
         throttle_nudge = 0;
     }
 
-    rudder_arm_check();
+    rudder_arm_disarm_check();
 
     if (g.rudder_only != 0) {
         // in rudder only mode we discard rudder input and get target