Fixes to the trim on ground feature.

* Skip the gears when located over water. They will be skipped by the ground reactions anyway making the trim irrelevant.
* Ignore the ground bumpiness during the trim. The trim algorithm seems not to
be robust enough to handle that. This does not make much difference to the
converged solution anyway since the bumpiness is generally low.
* Fixed the WOW status for contacts over water (was 'false' is now 'true').
* All the gear/contact data are now properly reset when WOW==false. The reset
code is now common to all the case where WOW is false.

src/FDM/JSBSim/initialization/FGTrim.cpp

@@ -402,8 +402,11 @@ void FGTrim::trimOnGround(void)
     FGColumnVector3 normal, vDummy;
     FGLocation lDummy;
     double height = gearLoc.GetContactPoint(lDummy, normal, vDummy, vDummy);
-    c.normal = Tec2b * normal;
 
+    if (gear->IsBogey() && !GroundReactions->GetSolid())
+      continue;
+
+    c.normal = Tec2b * normal;
     contacts.push_back(c);
 
     if (height < hmin) {

src/FDM/JSBSim/models/FGLGear.cpp

@@ -298,6 +298,7 @@ const FGColumnVector3& FGLGear::GetBodyForces(FGSurface *surface)
 
     // Does this surface contact point interact with another surface?
     if (surface) {
+      if (!fdmex->GetTrimStatus())
         height -= (*surface).GetBumpHeight();
       staticFFactor = (*surface).GetStaticFFactor();
       rollingFFactor = (*surface).GetRollingFFactor();
@@ -305,8 +306,11 @@ const FGColumnVector3& FGLGear::GetBodyForces(FGSurface *surface)
       isSolid =  (*surface).GetSolid();
     }
 
+    FGColumnVector3 vWhlDisplVec;
+    double LGearProj = 1.0;
+
     if (height < 0.0) {
-      WOW = isSolid;
+      WOW = true;
       vGroundNormal = in.Tec2b * normal;
 
       // The height returned by GetGroundCallback() is the AGL and is expressed
@@ -314,8 +318,7 @@ const FGColumnVector3& FGLGear::GetBodyForces(FGSurface *surface)
       // this height in actual compression of the strut (BOGEY) or in the normal
       // direction to the ground (STRUCTURE)
       double normalZ = (in.Tec2l*normal)(eZ);
-      double LGearProj = -(mTGear.Transposed() * vGroundNormal)(eZ);
-      FGColumnVector3 vWhlDisplVec;
+      LGearProj = -(mTGear.Transposed() * vGroundNormal)(eZ);
 
       // The following equations use the vector to the tire contact patch
       // including the strut compression.
@@ -326,8 +329,7 @@ const FGColumnVector3& FGLGear::GetBodyForces(FGSurface *surface)
           vWhlDisplVec = mTGear * FGColumnVector3(0., 0., -compressLength);
         } else {
           // Gears don't (or hardly) compress in liquids
-          compressLength = 0.0;
-          vWhlDisplVec = 0.0 * vGroundNormal;
+          WOW = false;
         }
         break;
       case ctSTRUCTURE:
@@ -335,19 +337,16 @@ const FGColumnVector3& FGLGear::GetBodyForces(FGSurface *surface)
         vWhlDisplVec = compressLength * vGroundNormal;
         break;
       }
+    }
+    else
+      WOW = false;
 
+    if (WOW) {
       FGColumnVector3 vWhlContactVec = vWhlBodyVec + vWhlDisplVec;
       vActingXYZn = vXYZn + Tb2s * vWhlDisplVec;
       FGColumnVector3 vBodyWhlVel = in.PQR * vWhlContactVec;
       vBodyWhlVel += in.UVW - in.Tec2b * terrainVel;
-
-      if (isSolid) {
       vWhlVelVec = mTGear.Transposed() * vBodyWhlVel;
-      } else {
-        // wheels don't spin up in liquids: let wheel spin down slowly
-        vWhlVelVec(eX) -= 13.0 * in.TotalDeltaT;
-        if (vWhlVelVec(eX) < 0.0) vWhlVelVec(eX) = 0.0;
-      }
 
       InitializeReporting();
       ComputeSteeringAngle();
@@ -375,14 +374,12 @@ const FGColumnVector3& FGLGear::GetBodyForces(FGSurface *surface)
       // Prepare the Jacobians and the Lagrange multipliers for later friction
       // forces calculations.
       ComputeJacobian(vWhlContactVec);
-
     } else { // Gear is NOT compressed
-
-      WOW = false;
       compressLength = 0.0;
       compressSpeed = 0.0;
       WheelSlip = 0.0;
       StrutForce = 0.0;
+      vWhlDisplVec.InitMatrix();
 
       LMultiplier[ftRoll].value = 0.0;
       LMultiplier[ftSide].value = 0.0;
@@ -397,11 +394,6 @@ const FGColumnVector3& FGLGear::GetBodyForces(FGSurface *surface)
 
       ResetReporting();
     }
-
-  } else if (gearPos < 0.01) { // Gear UP
-
-    WOW = false;
-    vWhlVelVec.InitMatrix();
   }
 
   if (!fdmex->GetTrimStatus()) {

src/FDM/JSBSim/models/FGSurface.cpp

@@ -79,6 +79,9 @@ void FGSurface::resetValues(void)
   maximumForce = DBL_MAX;
   bumpiness = 0.0;
   isSolid = true;
+  pos[0] = 0.0;
+  pos[1] = 0.0;
+  pos[2] = 0.0;
 }
 
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