diff --git a/drone_physics/body_physics.cpp b/drone_physics/body_physics.cpp
index df7d421b..d9b19f76 100644
--- a/drone_physics/body_physics.cpp
+++ b/drone_physics/body_physics.cpp
@@ -219,8 +219,8 @@ AccelerationType acceleration_in_body_frame(
     const AngularVelocityType& body_angular_velocity,
     double thrust, double mass /* 0 is not allowed */,
     double gravity, /* usually 9.8 > 0*/
-    double drag1,  /* air friction of 1-st order(-d1*v) counter to velocity */
-    double drag2 /* air friction of 2-nd order(-d2*v*v) counter to velocity */)
+    const VectorType& drag1,  /* air friction of 1-st order(-d1*v) counter to velocity */
+    const VectorType& drag2 /* air friction of 2-nd order(-d2*v*v) counter to velocity */)
 {
     assert(!is_zero(mass));
     using std::sin; using std::cos;
@@ -247,14 +247,29 @@ AccelerationType acceleration_in_body_frame(
 
      */
     /*****************************************************************/  
-    double dot_u =       - g * s_theta            - (q*w - r*v) - d1/m * u - d2/m * u * u;
-    double dot_v =       + g * c_theta * s_phi    - (r*u - p*w) - d1/m * v - d2/m * v * v;
-    double dot_w = -T/m  + g * c_theta * c_phi    - (p*v - q*u) - d1/m * w - d2/m * w * w;
+    double dot_u =       - g * s_theta            - (q*w - r*v) - d1.x/m * u - d2.x/m * u * u;
+    double dot_v =       + g * c_theta * s_phi    - (r*u - p*w) - d1.y/m * v - d2.y/m * v * v;
+    double dot_w = -T/m  + g * c_theta * c_phi    - (p*v - q*u) - d1.z/m * w - d2.z/m * w * w;
     /*****************************************************************/  
 
     return {dot_u, dot_v, dot_w};
 }
 
+AccelerationType acceleration_in_body_frame(
+    const VelocityType& body_velocity,
+    const EulerType& angle,
+    const AngularVelocityType& body_angular_velocity,
+    double thrust, double mass /* 0 is not allowed */,
+    double gravity, /* usually 9.8 > 0*/
+    double drag1,  /* air friction of 1-st order(-d1*v) counter to velocity(assumed same in 3 directions) */
+    double drag2 /* air friction of 2-nd order(-d2*v*v) counter to velocity(assumed same in 3 directions) */)
+{
+    return acceleration_in_body_frame(
+        body_velocity, angle, body_angular_velocity, thrust, mass, gravity,
+            {drag1, drag1, drag1}, {drag2, drag2, drag2});
+}
+
+
 
 /* Obsolete. for testing only. */
 AccelerationType acceleration_in_body_frame_without_Coriolis_for_testing_only(
diff --git a/drone_physics/body_physics.hpp b/drone_physics/body_physics.hpp
index dcdb2cd4..428d3078 100644
--- a/drone_physics/body_physics.hpp
+++ b/drone_physics/body_physics.hpp
@@ -125,15 +125,26 @@ AccelerationType acceleration_in_body_frame_without_Coriolis_for_testing_only(
     double thrust, double mass, /* 0 is not allowed */
     double gravity, double drag);
 
-/* The right dynamics including Coriolis's Force */
+/* The translation dynamics. drags are the same in the three directions */
 AccelerationType acceleration_in_body_frame(
     const VelocityType& body_velocity,
     const EulerType& angle,
     const AngularVelocityType& body_angular_velocity, /* for Coriolis */
     double thrust, double mass, /* 0 is not allowed */
     double gravity, /* usually 9.8 > 0*/
-    double drag1,   /* air friction of 1-st order(-d1*v) counter to velocity */
-    double drag2 = 0.0 /* air friction of 2-nd order(-d2*v*v) counter to velocity */);
+    double drag1,  /* air friction of 1-st order(-d1*v) counter to velocity(assumed same in 3 directions) */
+    double drag2 = 0 /* air friction of 2-nd order(-d2*v*v) counter to velocity(assumed same in 3 directions) */);
+
+/* The translation dynamics. drags are vectors in the three directions */
+AccelerationType acceleration_in_body_frame(
+    const VelocityType& body_velocity,
+    const EulerType& angle,
+    const AngularVelocityType& body_angular_velocity, /* for Coriolis */
+    double thrust, double mass, /* 0 is not allowed */
+    double gravity, /* usually 9.8 > 0*/
+    const VectorType& drag1,   /* air friction of 1-st order(-d1*v) counter to velocity */
+    const VectorType& drag2  /* air friction of 2-nd order(-d2*v*v) counter to velocity */);
+
 
 /* angular acceleration in body frame based on JW' = W x JW =Tb ...eq.(1.137),(2.31) */
 AngularAccelerationType angular_acceleration_in_body_frame(