diff --git a/libraries/AP_InertialSensor/AP_InertialSensor.cpp b/libraries/AP_InertialSensor/AP_InertialSensor.cpp
index cb691f5f89..f03bcd3fa3 100644
--- a/libraries/AP_InertialSensor/AP_InertialSensor.cpp
+++ b/libraries/AP_InertialSensor/AP_InertialSensor.cpp
@@ -1301,6 +1301,51 @@ check_sample:
     _have_sample = true;
 }
 
+
+/*
+  get delta angles
+ */
+bool AP_InertialSensor::get_delta_angle(uint8_t i, Vector3f &delta_angle) const 
+{
+    if (_delta_angle_valid[i]) {
+        delta_angle = _delta_angle[i];
+        return true;
+    } else if (get_gyro_health(i)) {
+        // provide delta angle from raw gyro, so we use the same code
+        // at higher level
+        delta_angle = get_gyro(i) * get_delta_time();
+        return true;
+    }
+    return false;
+}
+
+/*
+  get delta velocity if available
+*/
+bool AP_InertialSensor::get_delta_velocity(uint8_t i, Vector3f &delta_velocity) const
+{
+    if (_delta_velocity_valid[i]) {
+        delta_velocity = _delta_velocity[i];
+        return true;
+    } else if (get_accel_health(i)) {
+        delta_velocity = get_accel(i) * get_delta_time();
+        return true;
+    }
+    return false;
+}
+
+/*
+  return delta_time for the delta_velocity
+ */
+float AP_InertialSensor::get_delta_velocity_dt(uint8_t i) const
+{
+    if (_delta_velocity_valid[i]) {
+        return _delta_velocity_dt[i];
+    }
+    return get_delta_time();
+}
+
+
 /*
   support for setting accel and gyro vectors, for use by HIL
  */
diff --git a/libraries/AP_InertialSensor/AP_InertialSensor.h b/libraries/AP_InertialSensor/AP_InertialSensor.h
index 1f3c7fee1d..cd6ce813d7 100644
--- a/libraries/AP_InertialSensor/AP_InertialSensor.h
+++ b/libraries/AP_InertialSensor/AP_InertialSensor.h
@@ -118,23 +118,14 @@ public:
     const Vector3f &get_gyro_offsets(void) const { return get_gyro_offsets(_primary_gyro); }
 
     //get delta angle if available
-    bool get_delta_angle(uint8_t i, Vector3f &delta_angle) const {
-        if(_delta_angle_valid[i]) delta_angle = _delta_angle[i];
-        return _delta_angle_valid[i];
-    }
-
+    bool get_delta_angle(uint8_t i, Vector3f &delta_angle) const;
     bool get_delta_angle(Vector3f &delta_angle) const { return get_delta_angle(_primary_gyro, delta_angle); }
 
     //get delta velocity if available
-    bool get_delta_velocity(uint8_t i, Vector3f &delta_velocity) const {
-        if(_delta_velocity_valid[i]) delta_velocity = _delta_velocity[i];
-        return _delta_velocity_valid[i];
-    }
+    bool get_delta_velocity(uint8_t i, Vector3f &delta_velocity) const;
     bool get_delta_velocity(Vector3f &delta_velocity) const { return get_delta_velocity(_primary_accel, delta_velocity); }
 
-    float get_delta_velocity_dt(uint8_t i) const {
-        return _delta_velocity_dt[i];
-    }
+    float get_delta_velocity_dt(uint8_t i) const;
     float get_delta_velocity_dt() const { return get_delta_velocity_dt(_primary_accel); }
 
     /// Fetch the current accelerometer values