Solve for the elevator control input during approach. It turns out that

the downforce from the tail due to elevator trim is a significant contribution
to total lift.

diff --git a/src/FDM/YASim/Airplane.cpp b/src/FDM/YASim/Airplane.cpp
index d92d4f9623d5a6bd9a9c527b1beeee42bc2d0899..be30389c1a8580a36d676008eccf5d6dbb005b86 100644 (file)
--- a/src/FDM/YASim/Airplane.cpp
+++ b/src/FDM/YASim/Airplane.cpp
@@ -1,3 +1,5 @@
+#include <stdio.h>
+
 #include "Atmosphere.hpp"
 #include "ControlMap.hpp"
 #include "Gear.hpp"
@@ -10,6 +12,10 @@
 #include "Airplane.hpp"
 namespace yasim {
 
+// gadgets
+inline float norm(float f) { return f<1 ? 1/f : f; }
+inline float abs(float f) { return f<0 ? -f : f; }
+
 Airplane::Airplane()
 {
     _emptyWeight = 0;
@@ -146,6 +152,13 @@ void Airplane::setCruise(float speed, float altitude)
     _tailIncidence = 0;
 }
 
+void Airplane::setElevatorControl(int control)
+{
+    _approachElevator.control = control;
+    _approachElevator.val = 0;
+    _approachControls.add(&_approachElevator);
+}
+
 void Airplane::addApproachControl(int control, float val)
 {
     Control* c = new Control();
@@ -804,6 +817,9 @@ void Airplane::solve()
        // Run an approach iteration, and do likewise
        runApproach();
 
+       _model.getBody()->getAngularAccel(tmp);
+       float apitch0 = tmp[1];
+
        _model.getBody()->getAccel(tmp);
        float alift = _approachWeight * tmp[2];
 
@@ -840,7 +856,23 @@ void Airplane::solve()
             return;
         }
 
-       // And apply:
+        // And the elevator control in the approach.  This works just
+        // like the tail incidence computation (it's solving for the
+        // same thing -- pitching moment -- by diddling a different
+        // variable).
+        const float ELEVDIDDLE = 0.0001f;
+        _approachElevator.val += ELEVDIDDLE;
+        runApproach();
+        _approachElevator.val -= ELEVDIDDLE;
+
+       _model.getBody()->getAngularAccel(tmp);
+       float apitch1 = tmp[1];
+        float elevDelta = -apitch0 * (ELEVDIDDLE/(apitch1-apitch0));
+
+        // Now apply the values we just computed.  Note that the
+        // "minor" variables are deferred until we get the lift/drag
+        // numbers in the right ballpark.
+
        applyDragFactor(dragFactor);
        applyLiftRatio(liftFactor);
 
@@ -851,15 +883,27 @@ void Airplane::solve()
            continue;
        }
 
-       // OK, now we can adjust the minor variables
+       // OK, now we can adjust the minor variables:
        _cruiseAoA += 0.5f*aoaDelta;
        _tailIncidence += 0.5f*tailDelta;
+        _approachElevator.val += 0.5f*elevDelta;
        
        _cruiseAoA = clamp(_cruiseAoA, -0.174f, 0.174f);
        _tailIncidence = clamp(_tailIncidence, -0.174f, 0.174f);
+        _approachElevator.val = clamp(_approachElevator.val, -1.f, 1.f);
+
+        fprintf(stderr, "p0 %6f p1 %6f e %5f d %5f\n",
+                apitch0, apitch1, _approachElevator.val, elevDelta); // DEBUG
+
+        fprintf(stderr, "l %5f d %5f aoa %5f inc %5f ele %5f\n",
+                _liftRatio, _dragFactor, _cruiseAoA, _tailIncidence,
+                _approachElevator.val);
 
-        if(dragFactor < 1.00001 && liftFactor < 1.00001 &&
-           aoaDelta < .000017   && tailDelta < .000017)
+        if(norm(dragFactor) < 1.00001 &&
+           norm(liftFactor) < 1.00001 &&
+           abs(aoaDelta) < .000017 &&
+           abs(tailDelta) < .000017 &&
+           abs(elevDelta) < 0.00001)
         {
             break;
         }

diff --git a/src/FDM/YASim/Airplane.hpp b/src/FDM/YASim/Airplane.hpp
index 9a38700a029387fc1db9dfbf66ee41d21ad18e38..f44d496fc7e629e50fb5e9b336652f80f63194c1 100644 (file)
--- a/src/FDM/YASim/Airplane.hpp
+++ b/src/FDM/YASim/Airplane.hpp
@@ -46,6 +46,7 @@ public:
     void setApproach(float speed, float altitude, float aoa); 
     void setCruise(float speed, float altitude);
 
+    void setElevatorControl(int control);
     void addApproachControl(int control, float val);
     void addCruiseControl(int control, float val);
 
@@ -67,6 +68,7 @@ public:
     float getLiftRatio();
     float getCruiseAoA();
     float getTailIncidence();
+    float getApproachElevator() { return _approachElevator.val; }
     char* getFailureMsg();
 
 private:
@@ -135,6 +137,7 @@ private:
     float _liftRatio;
     float _cruiseAoA;
     float _tailIncidence;
+    Control _approachElevator;
     char* _failureMsg;
 };
 

diff --git a/src/FDM/YASim/FGFDM.cpp b/src/FDM/YASim/FGFDM.cpp
index dc34a075955c8f25abf1f7d37ee0a7c406c6c583..edd2cc231609f13d638106c7befd9b923a098131 100644 (file)
--- a/src/FDM/YASim/FGFDM.cpp
+++ b/src/FDM/YASim/FGFDM.cpp
@@ -36,6 +36,11 @@ static const float CIN2CM = 1.6387064e-5;
 FGFDM::FGFDM()
 {
     _nextEngine = 0;
+
+    // Map /controls/elevator to the approach elevator control.  This
+    // should probably be settable, but there are very few aircraft
+    // who trim their approaches using things other than elevator.
+    _airplane.setElevatorControl(parseAxis("/controls/elevator"));
 }
 
 FGFDM::~FGFDM()

diff --git a/src/FDM/YASim/YASim.cxx b/src/FDM/YASim/YASim.cxx
index aa3ed775ca82b00be640b257b0d1c102afe0683b..7b33a8fd5d37f4fb7c8ae60e6c4a20c3acf0ab40 100644 (file)
--- a/src/FDM/YASim/YASim.cxx
+++ b/src/FDM/YASim/YASim.cxx
@@ -74,11 +74,13 @@ void YASim::report()
     float drag = 1000 * a->getDragCoefficient();
 
     SG_LOG(SG_FLIGHT,SG_INFO,"YASim solution results:");
-    SG_LOG(SG_FLIGHT,SG_INFO,"      Iterations: "<<a->getSolutionIterations());
-    SG_LOG(SG_FLIGHT,SG_INFO,"Drag Coefficient: "<< drag);
-    SG_LOG(SG_FLIGHT,SG_INFO,"      Lift Ratio: "<<a->getLiftRatio());
-    SG_LOG(SG_FLIGHT,SG_INFO,"      Cruise AoA: "<< aoa);
-    SG_LOG(SG_FLIGHT,SG_INFO,"  Tail Incidence: "<< tail);
+    SG_LOG(SG_FLIGHT,SG_INFO,"       Iterations: "<<a->getSolutionIterations());
+    SG_LOG(SG_FLIGHT,SG_INFO," Drag Coefficient: "<< drag);
+    SG_LOG(SG_FLIGHT,SG_INFO,"       Lift Ratio: "<<a->getLiftRatio());
+    SG_LOG(SG_FLIGHT,SG_INFO,"       Cruise AoA: "<< aoa);
+    SG_LOG(SG_FLIGHT,SG_INFO,"   Tail Incidence: "<< tail);
+    SG_LOG(SG_FLIGHT,SG_INFO,"Approach Elevator: "<<a->getApproachElevator());
+    
 
     float cg[3];
     char buf[256];