Include axle friction in total friction

This over-estimates a bit the friction force (this has happened for a while), as Davis A and B already include rolling friction

Author: cesarBLG

Source/Orts.Simulation/Simulation/RollingStocks/MSTSLocomotive.cs

@@ -3186,6 +3186,8 @@ protected virtual void UpdateAxles(float elapsedClockSeconds)
 
             foreach (var axle in LocomotiveAxles)
             {
+                /*axle.FrictionN = DavisAN * axle.WheelWeightKg / MassKG;
+                axle.DampingNs = DavisBNSpM * axle.WheelWeightKg / MassKG;*/
                 axle.BrakeRetardForceN = BrakeRetardForceN * axle.BrakeForceFraction;
                 axle.TrainSpeedMpS = SpeedMpS;                //Set the train speed of the axle mod
                 axle.WheelRadiusM = DriverWheelRadiusM;
@@ -3203,6 +3205,7 @@ protected virtual void UpdateAxles(float elapsedClockSeconds)
             else TractionForceN = Math.Abs(TractiveForceN);
             MotiveForceN = LocomotiveAxles.AxleMotiveForceN;
             BrakeForceN = LocomotiveAxles.AxleBrakeForceN;
+            RollingFrictionForceN = LocomotiveAxles.AxleFrictionForceN;
 
             if (elapsedClockSeconds > 0)
             {

Source/Orts.Simulation/Simulation/RollingStocks/MSTSSteamLocomotive.cs

@@ -6684,7 +6684,17 @@ private float NormalisedCrankAngle(int enginenumber, int cylinderNumber, float c
 
 
         protected override void UpdateAxles(float elapsedClockSeconds)
-        { 
+        {
+            foreach (var axle in LocomotiveAxles)
+            {
+                /*axle.FrictionN = DavisAN * axle.WheelWeightKg / MassKG;
+                axle.DampingNs = DavisBNSpM * axle.WheelWeightKg / MassKG;*/
+                axle.BrakeRetardForceN = BrakeRetardForceN * axle.BrakeForceFraction;
+                axle.TrainSpeedMpS = SpeedMpS;                //Set the train speed of the axle mod
+                axle.WheelDistanceGaugeM = TrackGaugeM;
+                axle.CurrentCurveRadiusM = CurrentCurveRadiusM;
+                axle.BogieRigidWheelBaseM = RigidWheelBaseM;
+            }
             foreach (var engine in SteamEngines)
             {
                 var axle = engine.AttachedAxle;
@@ -6741,20 +6751,13 @@ protected override void UpdateAxles(float elapsedClockSeconds)
                     axle.FrictionN = N.FromLbf(3.8f * Me.ToIn(engine.CylindersDiameterM) * Me.ToIn(engine.CylindersDiameterM) * Me.ToIn(engine.CylindersStrokeM) / (Me.ToIn(axle.WheelRadiusM * 2.0f)));
                 }
             }
-            foreach (var axle in LocomotiveAxles)
-            {
-                axle.BrakeRetardForceN = BrakeRetardForceN * axle.BrakeForceFraction;
-                axle.TrainSpeedMpS = SpeedMpS;                //Set the train speed of the axle mod
-                axle.WheelDistanceGaugeM = TrackGaugeM;
-                axle.CurrentCurveRadiusM = CurrentCurveRadiusM;
-                axle.BogieRigidWheelBaseM = RigidWheelBaseM;
-            }
 
             LocomotiveAxles.Update(elapsedClockSeconds);
 
             TractiveForceN = LocomotiveAxles.DriveForceN;
             MotiveForceN = LocomotiveAxles.AxleMotiveForceN;
             BrakeForceN = LocomotiveAxles.AxleBrakeForceN;
+            RollingFrictionForceN = LocomotiveAxles.AxleFrictionForceN;
 
             if (LocoNumDrvAxles <= 0)
             {

Source/Orts.Simulation/Simulation/RollingStocks/MSTSWagon.cs

@@ -2370,6 +2370,14 @@ private void UpdateTrainBaseResistance()
             {
                 UpdateTrainBaseResistance_ORTS();
             }
+
+            // TODO: the Davis A and B parameters already include rolling friction. Thus, there is an over-estimation
+            // of the rolling friction forces, due to a small amount of friction being inserted to the axle module.
+            // This needs to be fixed by inserting the Davis A and B parameters to the axle, to the 'friction' and
+            // 'damping' axle parameters respectively, and their calculation must be removed from UpdateTrainBaseResistance_ methods
+            // This means that low/high speed friction has to be calculated and passed to the axle module elsewhere
+            // Davis C is related to air speed and must be calculated here and not inside the axle module
+            FrictionForceN += RollingFrictionForceN;
         }
 
         /// <summary>

Source/Orts.Simulation/Simulation/RollingStocks/TrainCar.cs

@@ -571,14 +571,15 @@ public Direction Direction
 
         // TrainCar.Update() must set these variables
         /// <summary>
-        /// Force transmitted to rail, excluding brake force
+        /// Force transmitted to rail, excluding brake and friction force
         /// Adhesion-corrected tractive force
         /// </summary>
         public float MotiveForceN;
         /// <summary>
         /// Tractive force generated by the engine(s)
         /// </summary>
         public float TractiveForceN = 0f;
+        public float RollingFrictionForceN;
         // Gravity forces have negative values on rising grade. 
         // This means they have the same sense as the motive forces and will push the train downhill.
         public float GravityForceN;  // Newtons  - signed relative to direction of car.