Update the suction model as per Alex Perry's recommendations.

[flightgear.git] / src / Systems / vacuum.cxx

diff --git a/src/Systems/vacuum.cxx b/src/Systems/vacuum.cxx
index 19bde57773912bd073779970f47bd67dc4650bc6..5244a4e7b3ad9128afff5416db7151eef66f4793 100644 (file)
--- a/src/Systems/vacuum.cxx
+++ b/src/Systems/vacuum.cxx
@@ -7,8 +7,9 @@
 #include <Main/fg_props.hxx>
 
 
-VacuumSystem::VacuumSystem ()
+VacuumSystem::VacuumSystem( int i )
 {
+    num = i;
 }
 
 VacuumSystem::~VacuumSystem ()
@@ -16,14 +17,15 @@ VacuumSystem::~VacuumSystem ()
 }
 
 void
-VacuumSystem::init ()
+VacuumSystem::init()
 {
-                                // TODO: allow index of pump and engine
-                                // to be configured.
-    _serviceable_node = fgGetNode("/systems/vacuum[0]/serviceable", true);
+                                // TODO: allow index of engine to be
+                                // configured.
+    SGPropertyNode *node = fgGetNode("/systems/vacuum", num, true );
+    _serviceable_node = node->getChild("serviceable", 0, true);
     _rpm_node = fgGetNode("/engines/engine[0]/rpm", true);
     _pressure_node = fgGetNode("/environment/pressure-inhg", true);
-    _suction_node = fgGetNode("/systems/vacuum[0]/suction-inhg", true);
+    _suction_node = node->getChild("suction-inhg", 0, true);
 }
 
 void
@@ -48,9 +50,14 @@ VacuumSystem::update (double dt)
     } else {
         double rpm = _rpm_node->getDoubleValue();
         double pressure = _pressure_node->getDoubleValue();
-        suction = pressure * rpm / (rpm + 10000.0);
-        if (suction > 5.0)
-            suction = 5.0;
+        // This magic formula yields about 4 inhg at 700 rpm
+        suction = pressure * rpm / (rpm + 4875.0);
+
+        // simple regulator model that clamps smoothly to about 5 inhg
+        // over a normal rpm range
+        double max = 5.39 - 1.0 / ( rpm * 0.00111 );
+        if ( suction < 0.0 ) suction = 0.0;
+        if ( suction > max ) suction = max;
     }
     _suction_node->setDoubleValue(suction);
 }