Merge pull request #453 from Sharpe49/power-supply-fix-tractive-force-eb

Fix tractive force not equal to zero during emergency braking
https://bugs.launchpad.net/or/+bug/1940163

Author: cjakeman

Source/Orts.Simulation/Simulation/RollingStocks/MSTSDieselLocomotive.cs

@@ -551,7 +551,7 @@ protected override void UpdateTractiveForce(float elapsedClockSeconds, float t,
             // Advanced configuration (TF table) - use a user defined tractive force table
             // With Simple adhesion apart from correction for rail adhesion, there is no further variation to the motive force. 
             // With Advanced adhesion the raw motive force is fed into the advanced (axle) adhesion model, and is corrected for wheel slip and rail adhesion
-            if (LocomotivePowerSupply.MainPowerSupplyOn)
+            if (LocomotivePowerSupply.MainPowerSupplyOn && Direction != Direction.N)
             {
                 // Appartent throttle setting is a reverse lookup of the throttletab vs rpm, hence motive force increase will be related to increase in rpm. The minimum of the two values
                 // is checked to enable fast reduction in tractive force when decreasing the throttle. Typically it will take longer for the prime mover to decrease rpm then drop motive force.
@@ -648,6 +648,10 @@ protected override void UpdateTractiveForce(float elapsedClockSeconds, float t,
                     DieselEngines.HandleEvent(PowerSupplyEvent.StopEngine);
                 }
             }
+            else
+            {
+                TractiveForceN = 0f;
+            }
 
             if (MaxForceN > 0 && MaxContinuousForceN > 0 && PowerReduction < 1)
             {