Sync'ed with JSBSim v1.1.10

- Fixed an error which prevented the equatorial and polar radii from <planet> to be propagated to the initial conditions.
- The planet radii in <planet> can now be specified by the tags <equatorial_radius> and <polar_radius> which are more self explanatory than <semimajor_axis> and <semiminor_axis> (which are still valid).
- Improved the error messages returned by FGTable: the file name and line number where the error occurred are now printed.
- Check the number of <input> tags for flight controls such as <pure_gain> (GitHub issue #497). This avoids a crash when some or all <input> elements are missing.
- JSBSim now accepts 2 sign conventions for the cross product inertia (xy, xz, yz) in <mass_balance> (GitHub Pull Request #502). The sign convention is specified by the parameter negated_crossproduct_inertia which defaults to true for backward compatibility.
- Turbine engines can now windmill even before they start (GitHub issue #494 and Pull Request #509).
- Fixed a sign error in the computation of aero/h_b-mac-ft (GitHub Pull Request #508 )
- Fixed a bug where FGTable instances were not untied from the property manager during their destruction. This could lead to segmentation faults when the property manager was later destroyed.
- Exceptions raised by FGTable are now instances of the TableException class.

src/FDM/JSBSim/FGFDMExec.cpp

@@ -731,6 +731,7 @@ bool FGFDMExec::LoadModel(const string& model, bool addModelToPath)
       }
       // Reload the planet constants and re-initialize the models.
       LoadPlanetConstants();
+      IC->InitializeIC();
       InitializeModels();
     }
 

src/FDM/JSBSim/initialization/FGInitialCondition.h

@@ -682,6 +682,9 @@ public:
       @return Trim type, if any requested (version 1). */
   int TrimRequested(void) const { return trimRequested; }
 
+  /** Initialize the initial conditions to default values */
+  void InitializeIC(void);
+
   void bind(FGPropertyManager* pm);
 
 private:
@@ -710,7 +713,6 @@ private:
   bool Load_v1(Element* document);
   bool Load_v2(Element* document);
 
-  void InitializeIC(void);
   void SetEulerAngleRadIC(int idx, double angle);
   void SetBodyVelFpsIC(int idx, double vel);
   void SetNEDVelFpsIC(int idx, double vel);

src/FDM/JSBSim/math/FGTable.cpp

@@ -36,6 +36,8 @@ JSB  1/9/00          Created
 INCLUDES
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
 
+#include <assert.h>
+
 #include "FGTable.h"
 #include "input_output/FGXMLElement.h"
 
@@ -107,9 +109,23 @@ FGTable::FGTable(const FGTable& t) : PropertyManager(t.PropertyManager)
 
 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 
+unsigned int FindNumColumns(const string& test_line)
+{
+  // determine number of data columns in table (first column is row lookup - don't count)
+  size_t position=0;
+  unsigned int nCols=0;
+  while ((position = test_line.find_first_not_of(" \t", position)) != string::npos) {
+    nCols++;
+    position = test_line.find_first_of(" \t", position);
+  }
+  return nCols;
+}
+
+//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
 FGTable::FGTable(FGPropertyManager* propMan, Element* el,
-                 const std::string& prefix)
+                 const std::string& Prefix)
-  : PropertyManager(propMan), Prefix(prefix)
+  : PropertyManager(propMan)
 {
   unsigned int i;
 
@@ -142,7 +158,7 @@ FGTable::FGTable(FGPropertyManager* propMan, Element* el,
     std::cerr << el->ReadFrom()
               <<"  An unknown table type attribute is listed: " << call_type
               << endl;
-    throw("Execution cannot continue.");
+    throw TableException("Unknown table type.");
   }
 
   // Determine and store the lookup properties for this table unless this table
@@ -157,10 +173,11 @@ FGTable::FGTable(FGPropertyManager* propMan, Element* el,
     // The 'internal' attribute of the table element cannot be specified
     // at the same time that independentVars are specified.
     if (internal) {
-      cerr << endl << fgred << "  This table specifies both 'internal' call type" << endl;
+      cerr  << el->ReadFrom()
-      cerr << "  and specific lookup properties via the 'independentVar' element." << endl;
+            << fgred << "  This table specifies both 'internal' call type" << endl
-      cerr << "  These are mutually exclusive specifications. The 'internal'" << endl;
+            << "  and specific lookup properties via the 'independentVar' element." << endl
-      cerr << "  attribute will be ignored." << fgdef << endl << endl;
+            << "  These are mutually exclusive specifications. The 'internal'" << endl
+            << "  attribute will be ignored." << fgdef << endl << endl;
       internal = false;
     }
 
@@ -182,7 +199,7 @@ FGTable::FGTable(FGPropertyManager* propMan, Element* el,
       } else if (lookup_axis == string("table")) {
         lookupProperty[eTable] = node;
       } else if (!lookup_axis.empty()) {
-        throw("Lookup table axis specification not understood: " + lookup_axis);
+        throw TableException("Lookup table axis specification not understood: " + lookup_axis);
       } else { // assumed single dimension table; row lookup
         lookupProperty[eRow] = node;
       }
@@ -202,7 +219,8 @@ FGTable::FGTable(FGPropertyManager* propMan, Element* el,
       if (FindNumColumns(test_line) == 2) dimension = 1;    // 1D table
       else if (FindNumColumns(test_line) > 2) dimension = 2; // 2D table
       else {
-        cerr << "Invalid number of columns in table" << endl;
+        std::cerr << tableData->ReadFrom()
+                  << "Invalid number of columns in table" << endl;
       }
     }
 
@@ -211,7 +229,10 @@ FGTable::FGTable(FGPropertyManager* propMan, Element* el,
     if (brkpt_string.empty()) {
      // no independentVars found, and table is not marked as internal, nor is it
      // a 3D table
-      throw("No independent variable found for table.");
+      std::cerr << el->ReadFrom()
+                << "No independentVars found, and table is not marked as internal,"
+                << " nor is it a 3D table." << endl;
+      throw TableException("No independent variable found for table.");
     }
   }
   // end lookup property code
@@ -243,9 +264,15 @@ FGTable::FGTable(FGPropertyManager* propMan, Element* el,
 
     if (nRows >= 2) {
       nCols = FindNumColumns(tableData->GetDataLine(0));
-      if (nCols < 2) throw(string("Not enough columns in table data."));
+      if (nCols < 2) {
+        std::cerr << tableData->ReadFrom()
+                  << "Not enough columns in table data" << endl;
+        throw TableException("Not enough columns in table data.");
+      }
     } else {
-      throw(string("Not enough rows in the table data."));
+      std::cerr << tableData->ReadFrom()
+                << "Not enough rows in table data" << endl;
+      throw TableException("Not enough rows in the table data.");
     }
 
     Type = tt2D;
@@ -296,14 +323,14 @@ FGTable::FGTable(FGPropertyManager* propMan, Element* el,
   if (dimension > 2) {
     for (b=2; b<=nTables; ++b) {
       if (Data[b][1] <= Data[b-1][1]) {
-        stringstream errormsg;
+        std::cerr << el->ReadFrom()
-        errormsg << fgred << highint << endl
+                  << fgred << highint 
-             << "  FGTable: breakpoint lookup is not monotonically increasing" << endl
+                  << "  FGTable: breakpoint lookup is not monotonically increasing" << endl
-             << "  in breakpoint " << b;
+                  << "  in breakpoint " << b;
-        if (nameel != 0) errormsg << " of table in " << nameel->GetAttributeValue("name");
+        if (nameel != 0) std::cerr << " of table in " << nameel->GetAttributeValue("name");
-        errormsg << ":" << reset << endl
+        std::cerr << ":" << reset << endl
-                 << "  " << Data[b][1] << "<=" << Data[b-1][1] << endl;
+                  << "  " << Data[b][1] << "<=" << Data[b-1][1] << endl;
-        throw(errormsg.str());
+        throw TableException("Breakpoint lookup is not monotonically increasing");
       }
     }
   }
@@ -312,14 +339,14 @@ FGTable::FGTable(FGPropertyManager* propMan, Element* el,
   if (dimension > 1) {
     for (c=2; c<=nCols; ++c) {
       if (Data[0][c] <= Data[0][c-1]) {
-        stringstream errormsg;
+        std::cerr << el->ReadFrom()
-        errormsg << fgred << highint << endl
+                  << fgred << highint 
-             << "  FGTable: column lookup is not monotonically increasing" << endl
+                  << "  FGTable: column lookup is not monotonically increasing" << endl
-             << "  in column " << c;
+                  << "  in column " << c;
-        if (nameel != 0) errormsg << " of table in " << nameel->GetAttributeValue("name");
+        if (nameel != 0) std::cerr << " of table in " << nameel->GetAttributeValue("name");
-        errormsg << ":" << reset << endl
+        std::cerr << ":" << reset << endl
-                 << "  " << Data[0][c] << "<=" << Data[0][c-1] << endl;
+                  << "  " << Data[0][c] << "<=" << Data[0][c-1] << endl;
-        throw(errormsg.str());
+        throw TableException("FGTable: column lookup is not monotonically increasing");
       }
     }
   }
@@ -328,19 +355,19 @@ FGTable::FGTable(FGPropertyManager* propMan, Element* el,
   if (dimension < 3) { // in 3D tables, check only rows of subtables
     for (r=2; r<=nRows; ++r) {
       if (Data[r][0]<=Data[r-1][0]) {
-        stringstream errormsg;
+        std::cerr << el->ReadFrom()
-        errormsg << fgred << highint << endl
+                  << fgred << highint 
-             << "  FGTable: row lookup is not monotonically increasing" << endl
+                  << "  FGTable: row lookup is not monotonically increasing" << endl
-             << "  in row " << r;
+                  << "  in row " << r;
-        if (nameel != 0) errormsg << " of table in " << nameel->GetAttributeValue("name");
+        if (nameel != 0) std::cerr << " of table in " << nameel->GetAttributeValue("name");
-        errormsg << ":" << reset << endl
+        std::cerr << ":" << reset << endl
-                 << "  " << Data[r][0] << "<=" << Data[r-1][0] << endl;
+                  << "  " << Data[r][0] << "<=" << Data[r-1][0] << endl;
-        throw(errormsg.str());
+        throw TableException("FGTable: row lookup is not monotonically increasing");
       }
     }
   }
 
-  bind(el);
+  bind(el, Prefix);
 
   if (debug_lvl & 1) Print();
 }
@@ -363,6 +390,13 @@ double** FGTable::Allocate(void)
 
 FGTable::~FGTable()
 {
+  // Untie the bound property so that it makes no further reference to this
+  // instance of FGTable after the destruction is completed.
+  if (!Name.empty() && !internal) {
+    string tmp = mkPropertyName(nullptr, "");
+    PropertyManager->Untie(tmp);
+  }
+
   if (nTables > 0) {
     for (unsigned int i=0; i<nTables; i++) delete Tables[i];
     Tables.clear();
@@ -375,20 +409,6 @@ FGTable::~FGTable()
 
 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 
-unsigned int FGTable::FindNumColumns(const string& test_line)
-{
-  // determine number of data columns in table (first column is row lookup - don't count)
-  size_t position=0;
-  unsigned int nCols=0;
-  while ((position = test_line.find_first_not_of(" \t", position)) != string::npos) {
-    nCols++;
-    position = test_line.find_first_of(" \t", position);
-  }
-  return nCols;
-}
-
-//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-
 double FGTable::GetValue(void) const
 {
   double temp = 0;
@@ -396,13 +416,19 @@ double FGTable::GetValue(void) const
 
   switch (Type) {
   case tt1D:
+    assert(lookupProperty[eRow]);
     temp = lookupProperty[eRow]->getDoubleValue();
     temp2 = GetValue(temp);
     return temp2;
   case tt2D:
+    assert(lookupProperty[eRow]);
+    assert(lookupProperty[eColumn]);
     return GetValue(lookupProperty[eRow]->getDoubleValue(),
                     lookupProperty[eColumn]->getDoubleValue());
   case tt3D:
+    assert(lookupProperty[eRow]);
+    assert(lookupProperty[eColumn]);
+    assert(lookupProperty[eTable]);
     return GetValue(lookupProperty[eRow]->getDoubleValue(),
                     lookupProperty[eColumn]->getDoubleValue(),
                     lookupProperty[eTable]->getDoubleValue());
@@ -432,7 +458,7 @@ double FGTable::GetValue(double key) const
   }
 
   // the key is somewhere in the middle, search for the right breakpoint
-  // The search is particularly efficient if 
+  // The search is particularly efficient if
   // the correct breakpoint has not changed since last frame or
   // has only changed very little
 
@@ -508,7 +534,7 @@ double FGTable::GetValue(double rowKey, double colKey, double tableKey) const
   }
 
   // the key is somewhere in the middle, search for the right breakpoint
-  // The search is particularly efficient if 
+  // The search is particularly efficient if
   // the correct breakpoint has not changed since last frame or
   // has only changed very little
 
@@ -625,28 +651,33 @@ void FGTable::Print(void)
 
 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 
-void FGTable::bind(Element* el)
+string FGTable::mkPropertyName(Element* el, const std::string& Prefix)
+{
+  if (!Prefix.empty()) {
+    if (is_number(Prefix)) {
+      if (Name.find("#") != string::npos) { // if "#" is found
+        Name = replace(Name, "#", Prefix);
+      } else {
+        cerr << el->ReadFrom()
+              << "Malformed table name with number: " << Prefix
+              << " and property name: " << Name
+              << " but no \"#\" sign for substitution." << endl;
+      }
+    } else {
+      Name = Prefix + "/" + Name;
+    }
+  }
+
+  return PropertyManager->mkPropertyName(Name, false);
+}
+
+//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+void FGTable::bind(Element* el, const string& Prefix)
 {
   typedef double (FGTable::*PMF)(void) const;
   if ( !Name.empty() && !internal) {
-    string tmp;
+    string tmp = mkPropertyName(el, Prefix);
-    if (Prefix.empty())
-      tmp  = PropertyManager->mkPropertyName(Name, false); // Allow upper
-    else {
-      if (is_number(Prefix)) {
-        if (Name.find("#") != string::npos) { // if "#" is found
-          Name = replace(Name,"#",Prefix);
-          tmp  = PropertyManager->mkPropertyName(Name, false); // Allow upper
-        } else {
-          cerr << el->ReadFrom()
-               << "Malformed table name with number: " << Prefix
-               << " and property name: " << Name
-               << " but no \"#\" sign for substitution." << endl;
-        }
-      } else {
-        tmp  = PropertyManager->mkPropertyName(Prefix + "/" + Name, false);
-      }
-    }
 
     if (PropertyManager->HasNode(tmp)) {
       FGPropertyNode* _property = PropertyManager->GetNode(tmp);

src/FDM/JSBSim/math/FGTable.h

@@ -226,6 +226,19 @@ combustion_efficiency = Lookup_Combustion_Efficiency->GetValue(equivalence_ratio
 @author Jon S. Berndt
 */
 
+/** Exception convenience class.
+  */
+
+/*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+DECLARATION: TableException
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
+
+class TableException : public std::runtime_error
+{
+public:
+  TableException(const std::string& msg) : std::runtime_error{msg} { }
+};
+
 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 CLASS DECLARATION
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
@@ -302,11 +315,10 @@ private:
   mutable int lastRowIndex, lastColumnIndex, lastTableIndex;
   double** Allocate(void);
   FGPropertyManager* const PropertyManager;
-  std::string Prefix;
   std::string Name;
-  void bind(Element*);
+  void bind(Element* el, const std::string& Prefix);
 
-  unsigned int FindNumColumns(const std::string&);
+  std::string mkPropertyName(Element* el, const std::string& Prefix);
   void Debug(int from);
 };
 }

src/FDM/JSBSim/models/FGAuxiliary.cpp

@@ -223,7 +223,7 @@ bool FGAuxiliary::Run(bool Holding)
   hoverbcg = in.DistanceAGL / in.Wingspan;
 
   FGColumnVector3 vMac = in.Tb2l * in.RPBody;
-  hoverbmac = (in.DistanceAGL + vMac(3)) / in.Wingspan;
+  hoverbmac = (in.DistanceAGL - vMac(3)) / in.Wingspan;
 
   return false;
 }

src/FDM/JSBSim/models/FGInertial.cpp

@@ -94,8 +94,12 @@ bool FGInertial::Load(Element* el)
 
   if (el->FindElement("semimajor_axis"))
     a = el->FindElementValueAsNumberConvertTo("semimajor_axis", "FT");
+  else if (el->FindElement("equatorial_radius"))
+    a = el->FindElementValueAsNumberConvertTo("equatorial_radius", "FT");
   if (el->FindElement("semiminor_axis"))
     b = el->FindElementValueAsNumberConvertTo("semiminor_axis", "FT");
+  else if (el->FindElement("polar_radius"))
+    b = el->FindElementValueAsNumberConvertTo("polar_radius", "FT");
   if (el->FindElement("rotation_rate")) {
     double RotationRate = el->FindElementValueAsNumberConvertTo("rotation_rate", "RAD/SEC");
     vOmegaPlanet = {0., 0., RotationRate};
@@ -229,7 +233,7 @@ void FGInertial::SetGravityType(int gt)
   // Messages to warn the user about possible inconsistencies.
   switch (gt)
   {
-  case eGravType::gtStandard: 
+  case eGravType::gtStandard:
     if (a != b)
       cout << "Warning: Standard gravity model has been set for a non-spherical planet" << endl;
     break;

src/FDM/JSBSim/models/FGMassBalance.cpp

@@ -117,9 +117,14 @@ static FGMatrix33 ReadInertiaMatrix(Element* document)
 
   // Transform the inertia products from the structural frame to the body frame
   // and create the inertia matrix.
-  return FGMatrix33( bixx, -bixy,  bixz,
+  if (document->GetAttributeValue("negated_crossproduct_inertia") == string("false")) 
-                    -bixy,  biyy, -biyz,
+    return FGMatrix33( bixx,  bixy, -bixz,
-                     bixz, -biyz,  bizz );
+                       bixy,  biyy,  biyz,
+                      -bixz,  biyz,  bizz );
+  else
+    return FGMatrix33( bixx, -bixy,  bixz,
+                      -bixy,  biyy, -biyz,
+                       bixz, -biyz,  bizz );
 }
 
 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

src/FDM/JSBSim/models/FGMassBalance.h

@@ -65,12 +65,22 @@ CLASS DOCUMENTATION
 
     The inertia tensor must be specified in the structural frame (x axis
     positive aft, y axis positive out of the right wing and z axis upward). The
-    sign of the inertia cross products are not modified by JSBSim so in most
+    sign of the inertia cross products are optional by JSBSim.
-    cases, negative values should be provided for <ixy>, <ixz> and <iyz>.
+    if negated_crossproduct_inertia == "true", then define:
-
+        ixy = -integral( x * y * dm ),
+        ixz = -integral( x * z * dm ),
+        iyz = -integral( y * z * dm ).
+    else if negated_crossproduct_inertia == "false", then define:
+        ixy =  integral( x * y * dm ),
+        ixz =  integral( x * z * dm ),
+        iyz =  integral( y * z * dm ).
+    default is negated_crossproduct_inertia = "true".
+    We strongly recommend defining negated_crossproduct_inertia = "false", 
+    which is consistent with the specifications in the field of flight dynamics. 
+    
     <h3>Configuration File Format for \<mass_balance> Section:</h3>
 @code{.xml}
-    <mass_balance>
+    <mass_balance negated_crossproduct_inertia="true|false">
         <ixx unit="{SLUG*FT2 | KG*M2}"> {number} </ixx>
         <iyy unit="{SLUG*FT2 | KG*M2}"> {number} </iyy>
         <izz unit="{SLUG*FT2 | KG*M2}"> {number} </izz>
@@ -98,6 +108,11 @@ CLASS DOCUMENTATION
         ... other point masses ...]
     </mass_balance>
 @endcode
+    
+    @see Stevens and Lewis, "Flight Control & Simulation"
+    @see Bernard Etkin, " Dynamics Of Atmosferic Flight"
+    @see https://en.wikipedia.org/wiki/Moment_of_inertia#Inertia_tensor
+    @see https://www.mathworks.com/help/physmod/sm/ug/specify-custom-inertia.html
   */
 
 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

src/FDM/JSBSim/models/flight_control/FGActuator.cpp

@@ -67,6 +67,8 @@ FGActuator::FGActuator(FGFCS* fcs, Element* element)
   initialized = 0;
   saturated = false;
 
+  CheckInputNodes(1, 1, element);
+
   if ( element->FindElement("deadband_width") ) {
     deadband_width = element->FindElementValueAsNumber("deadband_width");
   }
@@ -74,7 +76,7 @@ FGActuator::FGActuator(FGFCS* fcs, Element* element)
     hysteresis_width = element->FindElementValueAsNumber("hysteresis_width");
   }
 
-  // There can be a single rate limit specified, or increasing and 
+  // There can be a single rate limit specified, or increasing and
   // decreasing rate limits specified, and rate limits can be numeric, or
   // a property.
   Element* ratelim_el = element->FindElement("rate_limit");
@@ -133,7 +135,7 @@ void FGActuator::ResetPastStates(void)
   FGFCSComponent::ResetPastStates();
 
   PreviousOutput = PreviousHystOutput = PreviousRateLimOutput
-    = PreviousLagInput = PreviousLagOutput = Output = 0.0; 
+    = PreviousLagInput = PreviousLagOutput = Output = 0.0;
 }
 
 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@@ -166,7 +168,7 @@ bool FGActuator::Run(void )
   }
 
   PreviousOutput = Output; // previous value needed for "stuck" malfunction
-  
+
   initialized = 1;
 
   Clip();
@@ -223,7 +225,7 @@ void FGActuator::Hysteresis(void)
   // "Output" is - for the purposes of this Hysteresis method - really the input
   // to the method.
   double input = Output;
-  
+
   if ( initialized ) {
     if (input > PreviousHystOutput)
       Output = max(PreviousHystOutput, input-0.5*hysteresis_width);

src/FDM/JSBSim/models/flight_control/FGDeadBand.cpp

@@ -56,6 +56,8 @@ FGDeadBand::FGDeadBand(FGFCS* fcs, Element* element)
   Width = nullptr;
   gain = 1.0;
 
+  CheckInputNodes(1, 1, element);
+
   Element* width_element = element->FindElement("width");
   if (width_element)
     Width = new FGParameterValue(width_element, PropertyManager);

src/FDM/JSBSim/models/flight_control/FGFCSComponent.cpp

@@ -116,7 +116,7 @@ FGFCSComponent::FGFCSComponent(FGFCS* _fcs, Element* element) : fcs(_fcs)
                                             PropertyManager ));
     init_element = element->FindNextElement("init");
   }
-  
+
   Element *input_element = element->FindElement("input");
   while (input_element) {
     InputNodes.push_back(new FGPropertyValue(input_element->GetDataLine(),
@@ -212,6 +212,30 @@ void FGFCSComponent::ResetPastStates(void)
 
 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 
+void FGFCSComponent::CheckInputNodes(size_t MinNodes, size_t MaxNodes, Element* el)
+{
+  size_t num = InputNodes.size();
+
+  if (num < MinNodes) {
+    cerr << el->ReadFrom()
+         << "    Not enough <input> nodes are provided" << endl
+         << "    Expecting " << MinNodes << " while " << num
+         << " are provided." << endl;
+    throw("Some inputs are missing.");
+  }
+
+  if (num > MaxNodes) {
+    cerr << el->ReadFrom()
+         << "    Too many <input> nodes are provided" << endl
+         << "    Expecting " << MaxNodes << " while " << num
+         << " are provided." << endl
+         << "    The last " << num-MaxNodes << " input nodes will be ignored."
+         << endl;
+  }
+}
+
+//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
 void FGFCSComponent::SetOutput(void)
 {
   for (auto node: OutputNodes)
@@ -329,7 +353,7 @@ void FGFCSComponent::Debug(int from)
       if (clip) {
         cout << "      Minimum limit: " << ClipMin->GetName() << endl;
         cout << "      Maximum limit: " << ClipMax->GetName() << endl;
-      }  
+      }
       if (delay > 0) cout <<"      Frame delay: " << delay
                                    << " frames (" << delay*dt << " sec)" << endl;
     }

src/FDM/JSBSim/models/flight_control/FGFCSComponent.h

@@ -117,6 +117,7 @@ protected:
 
   void Delay(void);
   void Clip(void);
+  void CheckInputNodes(size_t MinNodes, size_t MaxNodes, Element* el);
   virtual void bind(Element* el);
   virtual void Debug(int from);
 };

src/FDM/JSBSim/models/flight_control/FGFilter.cpp

@@ -52,6 +52,9 @@ FGFilter::FGFilter(FGFCS* fcs, Element* element)
   : FGFCSComponent(fcs, element), DynamicFilter(false), Initialize(true)
 {
   C[1] = C[2] = C[3] = C[4] = C[5] = C[6] = nullptr;
+
+  CheckInputNodes(1, 1, element);
+
   for (int i=1; i<7; i++)
     ReadFilterCoefficients(element, i);
 
@@ -88,11 +91,11 @@ void FGFilter::ResetPastStates(void)
 
 void FGFilter::ReadFilterCoefficients(Element* element, int index)
 {
-  // index is known to be 1-7. 
+  // index is known to be 1-7.
   // A stringstream would be overkill, but also trying to avoid sprintf
   string coefficient = "c0";
   coefficient[1] += index;
-  
+
   if ( element->FindElement(coefficient) ) {
     C[index] = new FGParameterValue(element->FindElement(coefficient),
                                     PropertyManager);
@@ -151,9 +154,9 @@ bool FGFilter::Run(void)
   } else {
 
     Input = InputNodes[0]->getDoubleValue();
-    
+
     if (DynamicFilter) CalculateDynamicFilters();
-    
+
     switch (FilterType) {
       case eLag:
         Output = (Input + PreviousInput1) * ca + PreviousOutput1 * cb;

src/FDM/JSBSim/models/flight_control/FGGain.cpp

@@ -57,6 +57,8 @@ FGGain::FGGain(FGFCS* fcs, Element* element) : FGFCSComponent(fcs, element)
   InMax =  1.0;
   OutMin = OutMax = 0.0;
 
+  CheckInputNodes(1, 1, element);
+
   if (Type == "PURE_GAIN") {
     if ( !element->FindElement("gain") ) {
       cerr << element->ReadFrom()

src/FDM/JSBSim/models/flight_control/FGKinemat.cpp

@@ -56,6 +56,8 @@ FGKinemat::FGKinemat(FGFCS* fcs, Element* element)
   double tmpDetent;
   double tmpTime;
 
+  CheckInputNodes(1, 1, element);
+
   Detents.clear();
   TransitionTimes.clear();
 

src/FDM/JSBSim/models/flight_control/FGLinearActuator.cpp

@@ -51,6 +51,8 @@ CLASS IMPLEMENTATION
 FGLinearActuator::FGLinearActuator(FGFCS* fcs, Element* element)
   : FGFCSComponent(fcs, element)
 {
+  CheckInputNodes(1, 1, element);
+
   ptrSet = nullptr;
   if (element->FindElement("set")) {
     string property_string = element->FindElementValue("set");

src/FDM/JSBSim/models/flight_control/FGPID.cpp

@@ -57,6 +57,8 @@ FGPID::FGPID(FGFCS* fcs, Element* element) : FGFCSComponent(fcs, element)
   IsStandard = false;
   IntType = eNone;       // No integrator initially defined.
 
+  CheckInputNodes(1, 1, element);
+
   string pid_type = element->GetAttributeValue("type");
 
   if (pid_type == "standard") IsStandard = true;
@@ -190,7 +192,7 @@ bool FGPID::Run(void )
   }
 
   if (test < 0.0) I_out_total = 0.0;  // Reset integrator to 0.0
-  
+
   I_out_total += Ki->GetValue() * dt * I_out_delta;
 
   if (IsStandard)

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

@@ -190,8 +190,9 @@ double FGTurbine::Off(void)
   FuelFlow_pph = Seek(&FuelFlow_pph, 0, 1000.0, 10000.0);
   // 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);
+    // Need a small non-zero increment for acceleration otherwise acceleration will be 0 if N1 = 0
-    N2 = Seek(&N2, in.qbar/15.0, N2/2.0, N2/N2_spindown);
+    N1 = Seek(&N1, in.qbar/10.0, N1/2.0 + 0.1, N1/N1_spindown);
+    N2 = Seek(&N2, in.qbar/15.0, N2/2.0 + 0.1, N2/N2_spindown);
   } else {
     N1 = Seek(&N1, 0, N1/2.0, N1/N1_spindown);
     N2 = Seek(&N2, 0, N2/2.0, N2/N2_spindown);