[JSBSim] Add Windmilling flag

The flag allows to disable the windmilling of Turbine engines.

src/FDM/JSBSim/input_output/FGXMLElement.cpp

@@ -424,6 +424,28 @@ double Element::FindElementValueAsNumber(const string& el)
 
 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 
+bool Element::FindElementValueAsBoolean(const string& el)
+{
+  Element* element = FindElement(el);
+  if (element) {
+    // check value as an ordinary number
+    double value = element->GetDataAsNumber();
+
+    // now check how it should return data
+    if (value == 0) {
+      return false;
+    } else {
+      return true;
+    }
+  } else {
+    cerr << ReadFrom() << "Attempting to get non-existent element " << el << " ;returning false"
+         << endl;
+    return false;
+  }
+}
+
+//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
 string Element::FindElementValue(const string& el)
 {
   Element* element = FindElement(el);

src/FDM/JSBSim/input_output/FGXMLElement.h

@@ -273,6 +273,16 @@ public:
               data is missing. */
   double FindElementValueAsNumber(const std::string& el="");
 
+  /** Searches for the named element and returns the data belonging to it as a bool.
+      This function allows the data belonging to a named element to be returned
+      as a bool. If no element is found, false is returned. If no
+      argument is supplied, the data for the first element is returned.
+      @param el the name of the element being searched for (the empty string by
+      default)
+      @return the data value for the named element as a bool, or false if the
+              data is missing. Zero will be false, while any other number will be true. */
+  bool FindElementValueAsBoolean(const std::string& el="");
+  
   /** Searches for the named element and converts and returns the data belonging to it.
       This function allows the data belonging to a named element to be returned
       as a double. If no element is found, HUGE_VAL is returned. If no

src/FDM/JSBSim/models/propulsion/FGTurbine.cpp

@@ -75,6 +75,7 @@ FGTurbine::FGTurbine(FGFDMExec* exec, Element *el, int engine_number, struct Inp
   InjectionTime = 30.0;
   InjectionTimer = InjWaterNorm = 0.0;
   EPR = 1.0;
+  disableWindmill = false;
 
   Load(exec, el);
   Debug(0);
@@ -187,8 +188,14 @@ double FGTurbine::Off(void)
 {
   Running = false;
   FuelFlow_pph = Seek(&FuelFlow_pph, 0, 1000.0, 10000.0);
-  N1 = Seek(&N1, in.qbar/10.0, N1/2.0, N1/N1_spindown);
-  N2 = Seek(&N2, in.qbar/15.0, N2/2.0, N2/N2_spindown);
+  // some engines have inlets that close when they are off. So, if a flag is true disable windmilling
+  if (disableWindmill == false) {
+    N1 = Seek(&N1, in.qbar/10.0, N1/2.0, N1/N1_spindown);
+    N2 = Seek(&N2, in.qbar/15.0, N2/2.0, N2/N2_spindown);
+  } else {
+    N1 = Seek(&N1, 0, N1/2.0, N1/N1_spindown);
+    N2 = Seek(&N2, 0, N2/2.0, N2/N2_spindown);
+  }
   EGT_degC = Seek(&EGT_degC, in.TAT_c, 11.7, 7.3);
   OilTemp_degK = Seek(&OilTemp_degK, in.TAT_c + 273.0, 0.2, 0.2);
   OilPressure_psi = N2 * 0.62;
@@ -263,7 +270,7 @@ double FGTurbine::Run()
     InjectionTimer += in.TotalDeltaT;
     if (InjectionTimer < InjectionTime) {
        thrust = thrust * InjectionLookup->GetValue();
-       InjWaterNorm = 1.0 - (InjectionTimer/InjectionTime);	
+       InjWaterNorm = 1.0 - (InjectionTimer/InjectionTime); 
     } else {
        Injection = false;
        InjWaterNorm = 0.0;
@@ -487,7 +494,8 @@ bool FGTurbine::Load(FGFDMExec* exec, Element *el)
     InjN1increment = el->FindElementValueAsNumber("injection-N1-inc");
   if (el->FindElement("injection-N2-inc"))
     InjN2increment = el->FindElementValueAsNumber("injection-N2-inc");
-
+  if (el->FindElement("disable-windmill"))
+    disableWindmill = el->FindElementValueAsBoolean("disable-windmill");
   string property_prefix = CreateIndexedPropertyName("propulsion/engine", EngineNumber);
 
   IdleThrustLookup = GetPreFunction(property_prefix+"/IdleThrust");

src/FDM/JSBSim/models/propulsion/FGTurbine.h

@@ -105,6 +105,7 @@ CLASS DOCUMENTATION
   <augmethod> {0 | 1 | 2} </augmethod>
   <injected> {0 | 1} </injected>
   <injection-time> {number} </injection-time>
+  <disable-windmill> {0 | 1}</disable-windmill>
  </turbine_engine>
 @endcode
 
@@ -142,6 +143,7 @@ CLASS DOCUMENTATION
   injection-time - Time, in seconds, of water injection duration 
   InjN1increment - % increase in N1 when injection is taking place
   InjN2increment - % increase in N2 when injection is taking place
+  disable-windmill - flag that disables engine windmilling when off if true
 </pre>
 
 <h3>NOTES:</h3>  
@@ -276,6 +278,7 @@ private:
   bool Augmentation;
   bool Reversed;
   bool Cutoff;
+  bool disableWindmill;    ///< flag to disable windmilling of engine in Off phase
   int Injected;            ///< = 1 if water injection installed
   int Ignition;
   int Augmented;           ///< = 1 if augmentation installed