Revert "Fix steam locomotive adhesion bug"

This reverts commit 1fb1ba8.

Author: peternewell

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

@@ -5196,9 +5196,20 @@ protected override void UpdateTractiveForce(float elapsedClockSeconds, float t,
                     float reciprocatingInertiaAngleFactor = 0;
                     float connectRodInertiaAngleFactor = 0;
 
-                    // Calculate the "angle variation factors" for the Inertia                        
-                    reciprocatingInertiaAngleFactor = (cos + ((CrankRadiusFt / ConnectRodLengthFt) * (float)Math.Cos(2 * crankAngleRad)));
-                    connectRodInertiaAngleFactor = (cos + ((CrankRadiusFt * RodCoGFt) / (ConnectRodLengthFt * ConnectRodLengthFt)) * (float)Math.Cos(2 * crankAngleRad));
+                    // Calculate the "angle variation factors" for the Inertia
+                    // Account for the position of the crosshead position. In other words it depends upon whether the Rods and Reciporating gear is above or below the axle.
+                    if (crankAngleRad > 0 && crankAngleRad < Math.PI)
+                    {
+                        // forward stroke
+                        reciprocatingInertiaAngleFactor = (cos + ((CrankRadiusFt / ConnectRodLengthFt) * (float)Math.Cos(2 * crankAngleRad)));
+                        connectRodInertiaAngleFactor = (cos + ((CrankRadiusFt * RodCoGFt) / (ConnectRodLengthFt * ConnectRodLengthFt)) * (float)Math.Cos(2 * crankAngleRad));
+                    }
+                    else
+                    {   
+                        // reverse stroke
+                        reciprocatingInertiaAngleFactor = (cos - ((CrankRadiusFt / ConnectRodLengthFt) * (float)Math.Cos(2 * crankAngleRad)));
+                        connectRodInertiaAngleFactor = (cos - ((CrankRadiusFt * RodCoGFt) / (ConnectRodLengthFt * ConnectRodLengthFt)) * (float)Math.Cos(2 * crankAngleRad));
+                    }
 
                     // Calculate the speed factor to allow for variation in speed
                     // Adjust the above factor to allow for the speed of rotation on the parts - based upon Eq 8 (pg 21)