TradHeli: COLYAW not applied when the motor is not running

libraries/AP_Motors/AP_MotorsHeli.cpp

@@ -578,7 +578,9 @@ void AP_MotorsHeli::move_swash(int16_t roll_out, int16_t pitch_out, int16_t coll
         coll_out_scaled = _collective_out * _collective_scalar + _collective_min - 1000;
 	
         // rudder feed forward based on collective
-        if (_tail_type != AP_MOTORS_HELI_TAILTYPE_SERVO_EXTGYRO) {
+        // the feed-forward is not required when the motor is shut down and not creating torque
+        // also not required if we are using external gyro
+        if (motor_runup_complete() && _tail_type != AP_MOTORS_HELI_TAILTYPE_SERVO_EXTGYRO) {
             yaw_offset = _collective_yaw_effect * abs(coll_out_scaled - _collective_mid_pwm);
         }
     }