[JSBSim] An improvement and 2 bug fixes

- Electric engines RPM is now exported in UDP sockets.
- The sign of the XZ inertia has been fixed in the property inertia/ixz-slug_ft2 (was just an output error, the correct XZ inertia was used internally). Thanks to Nikolai Verner Christensen for reporting the bug.
- The parameter <ignitionn2> was wrongly affected to N1. Bug reported by Nikolai Verner Christensen and fixed by Jonathan Redpath. Thanks to them.

src/FDM/JSBSim/input_output/FGOutputFG.cpp

@@ -47,6 +47,7 @@ INCLUDES
 #include "models/FGPropulsion.h"
 #include "models/FGFCS.h"
 #include "models/propulsion/FGPiston.h"
+#include "models/propulsion/FGElectric.h"
 #include "models/propulsion/FGTank.h"
 
 #if defined(WIN32) && !defined(__CYGWIN__)
@@ -216,32 +217,37 @@ void FGOutputFG::SocketDataFill(FGNetFDM* net)
   net->num_engines = min(FGNetFDM::FG_MAX_ENGINES,Propulsion->GetNumEngines()); // Number of valid engines
 
   for (i=0; i<net->num_engines; i++) {
-    if (Propulsion->GetEngine(i)->GetRunning())
+    FGEngine* engine = Propulsion->GetEngine(i);
+    if (engine->GetRunning())
       net->eng_state[i] = 2;       // Engine state running
-    else if (Propulsion->GetEngine(i)->GetCranking())
+    else if (engine->GetCranking())
       net->eng_state[i] = 1;       // Engine state cranking
     else
       net->eng_state[i] = 0;       // Engine state off
 
-    switch (Propulsion->GetEngine(i)->GetType()) {
+    switch (engine->GetType()) {
     case (FGEngine::etRocket):
       break;
     case (FGEngine::etPiston):
-      net->rpm[i]       = (float)(((FGPiston *)Propulsion->GetEngine(i))->getRPM());
-      net->fuel_flow[i] = (float)(((FGPiston *)Propulsion->GetEngine(i))->getFuelFlow_gph());
+      {
+        FGPiston* piston_engine = static_cast<FGPiston*>(engine);
+        net->rpm[i]       = (float)(piston_engine->getRPM());
+        net->fuel_flow[i] = (float)(piston_engine->getFuelFlow_gph());
         net->fuel_px[i]   = 0; // Fuel pressure, psi  (N/A in current model)
-      net->egt[i]       = (float)(((FGPiston *)Propulsion->GetEngine(i))->GetEGT());
-      net->cht[i]       = (float)(((FGPiston *)Propulsion->GetEngine(i))->getCylinderHeadTemp_degF());
-      net->mp_osi[i]    = (float)(((FGPiston *)Propulsion->GetEngine(i))->getManifoldPressure_inHg());
-      net->oil_temp[i]  = (float)(((FGPiston *)Propulsion->GetEngine(i))->getOilTemp_degF());
-      net->oil_px[i]    = (float)(((FGPiston *)Propulsion->GetEngine(i))->getOilPressure_psi());
+        net->egt[i]       = (float)(piston_engine->GetEGT());
+        net->cht[i]       = (float)(piston_engine->getCylinderHeadTemp_degF());
+        net->mp_osi[i]    = (float)(piston_engine->getManifoldPressure_inHg());
+        net->oil_temp[i]  = (float)(piston_engine->getOilTemp_degF());
+        net->oil_px[i]    = (float)(piston_engine->getOilPressure_psi());
         net->tit[i]       = 0; // Turbine Inlet Temperature  (N/A for piston)
+      }
       break;
     case (FGEngine::etTurbine):
       break;
     case (FGEngine::etTurboprop):
       break;
     case (FGEngine::etElectric):
+      net->rpm[i] = static_cast<float>(static_cast<FGElectric*>(engine)->getRPM());
       break;
     case (FGEngine::etUnknown):
       break;

src/FDM/JSBSim/models/FGMassBalance.h

@@ -126,6 +126,8 @@ public:
   double GetMass(void) const {return Mass;}
   double GetWeight(void) const {return Weight;}
   double GetEmptyWeight(void) const {return EmptyWeight;}
+  /** Returns the coordinates of the center of gravity expressed in the
+      structural frame. */
   const FGColumnVector3& GetXYZcg(void) const {return vXYZcg;}
   double GetXYZcg(int axis) const  {return vXYZcg(axis);}
   const FGColumnVector3& GetDeltaXYZcg(void) const {return vDeltaXYZcg;}
@@ -172,7 +174,9 @@ public:
   double GetTotalPointMassWeight(void) const;
 
   const FGColumnVector3& GetPointMassMoment(void);
+  /// Returns the inertia matrix expressed in the body frame.
   const FGMatrix33& GetJ(void) const {return mJ;}
+  /// Returns the inverse of the inertia matrix expressed in the body frame.
   const FGMatrix33& GetJinv(void) const {return mJinv;}
   void SetAircraftBaseInertias(const FGMatrix33& BaseJ) {baseJ = BaseJ;}
   void GetMassPropertiesReport(int i);
@@ -209,7 +213,7 @@ private:
   double GetIyy(void) const { return mJ(2,2); }
   double GetIzz(void) const { return mJ(3,3); }
   double GetIxy(void) const { return -mJ(1,2); }
-  double GetIxz(void) const { return -mJ(1,3); }
+  double GetIxz(void) const { return mJ(1,3); }
   double GetIyz(void) const { return -mJ(2,3); }
 
   /** The PointMass structure encapsulates a point mass object, moments of inertia

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

@@ -459,7 +459,7 @@ bool FGTurbine::Load(FGFDMExec* exec, Element *el)
   if (el->FindElement("ignitionn1"))
     IgnitionN1 = el->FindElementValueAsNumber("ignitionn1");
   if (el->FindElement("ignitionn2"))
-    IgnitionN1 = el->FindElementValueAsNumber("ignitionn2");
+    IgnitionN2 = el->FindElementValueAsNumber("ignitionn2");
   if (el->FindElement("idlen1"))
     IdleN1 = el->FindElementValueAsNumber("idlen1");
   if (el->FindElement("idlen2"))