Further tuning of derailment capability.

Source/Documentation/Manual/physics.rst

@@ -4499,7 +4499,7 @@ Open Rails calculates when it is likely that a train derailment has occurred. Th
 when the train is in a curve. Light (empty wagons) can sometimes derail due to 'string lining' where the train forces attempt to pull the train 
 in a straight line, rather then following the curve.
 
-OR calculates the Nadal Critera for each wagon, and then calculates the actual L/V ratio based upon the wagon weight and the relevant 
+OR calculates the Nadal Criteria for each wagon, and then calculates the actual L/V ratio based upon the wagon weight and the relevant 
 "in train" forces. Open Rails uses some calculated default parameters for the various parameters required to determine the actual L/V
 ratio, however more accurate results will be obtained if actual parameters are entered into the ENG or WAG file. The derailment calculations 
 use information relating to the wagon dimensions, weight and wheel profile information.

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

@@ -1197,7 +1197,7 @@ public virtual void UpdateTunnelForce()
         /// these factors is not practical so only some of the key factors are considered. For eaxmple, wheel wear may determine whether a particular car will derial or not. So the same 
         /// type of car can either derail or not under similar circumstances.
         /// 
-        /// Hence these calculations provide a "generic" approach to determining whether a car will derial or not.
+        /// Hence these calculations provide a "generic" approach to determining whether a car will derail or not.
         /// 
         /// Buff Coupler angle calculated from this publication: In-Train Force Limit Study by National Research Council Canada
         /// 
@@ -1578,16 +1578,18 @@ public void UpdateTrainDerailmentRisk(float elapsedClockSeconds)
                     DerailmentCoefficient = TotalWagonLateralDerailForceN / TotalWagonVerticalDerailForceN;
 
                     // use the dynamic multiplication coefficient to calculate final derailment coefficient, the above method calculated using quasi-static factors.
-                    // The quasi-static do not include allowance for wheel unloading due to static carbody pitch. Hence the following factors have been used to adjust to dynamic effects.
-                    // They have been adjusted slightly based upon derailment accident reports. Original figures quoted were 2 x for standard curves, and 3.1 x for turnouts. 
-                    if (IsOverJunction())
+                    // The differences between quasi-static and dynamic limits are due to effects of creepage, curve, conicity, wheel unloading ratio, track geometry, 
+                    // car configurations and the share of wheel load changes which are not taken into account in the static analysis etc. 
+                    // Hence the following factors have been used to adjust to dynamic effects.
+                    // Original figures quoted - Static Draft = 0.389, Static Buff = 0.389, Dynamic Draft = 0.29, Dynamic Buff = 0.22. 
+                    // Hence use the following multiplication factors, Buff = 1.77, Draft = 1.34.
+                    if (CouplerForceU > 0 && CouplerSlackM < 0)
                     {
-                        DerailmentCoefficient *= 2.17f;
+                        DerailmentCoefficient *= 1.77f; // coupler in buff condition
                     }
                     else
                     {
-                       // DerailmentCoefficient *= 1.4f;
-                        DerailmentCoefficient *= 2.0f;
+                        DerailmentCoefficient *= 1.34f;
                     }
 
                     var wagonAdhesion = Train.WagonCoefficientFriction;