pitot system stalls at high angles, using /system/pitot[x]/stall-deg

diff --git a/src/Systems/pitot.cxx b/src/Systems/pitot.cxx
index 7658f41a0989fbeda47aa6480f1bdbe0dfdecb58..cf3eb2590a03af3ac93ce0125af390f58c71ae4b 100644 (file)
--- a/src/Systems/pitot.cxx
+++ b/src/Systems/pitot.cxx
@@ -1,7 +1,7 @@
 // pitot.cxx - the pitot air system.
 // Written by David Megginson, started 2002.
 //
-// Last modified by Eric van den Berg, 24 Nov 2012
+// Last modified by Eric van den Berg, 01 Nov 2013
 // This file is in the Public Domain and comes with no warranty.
 
 #ifdef HAVE_CONFIG_H
@@ -19,7 +19,9 @@
 PitotSystem::PitotSystem ( SGPropertyNode *node )
     :
     _name(node->getStringValue("name", "pitot")),
-    _num(node->getIntValue("number", 0))
+    _num(node->getIntValue("number", 0)),
+    _stall_factor(cos(node->getDoubleValue("stall-deg", 60.0) * SGD_DEGREES_TO_RADIANS ))
+                       // this is the projection factor for the stall angle.
 {
 }
 
@@ -41,6 +43,9 @@ PitotSystem::init ()
     _beta_deg_node = fgGetNode("/orientation/side-slip-deg", true);
     _total_pressure_node = node->getChild("total-pressure-inhg", 0, true);
     _measured_total_pressure_node = node->getChild("measured-total-pressure-inhg", 0, true);
+    if ( _stall_factor < 0 ) { // |stall angle| > 90°
+               _stall_factor = cos(60 * SGD_DEGREES_TO_RADIANS);
+       }
 }
 
 void
@@ -61,14 +66,21 @@ PitotSystem::update (double dt)
         double mach = _mach_node->getDoubleValue();
         double alpha = _alpha_deg_node->getDoubleValue() * SGD_DEGREES_TO_RADIANS;
         double beta = _beta_deg_node->getDoubleValue() * SGD_DEGREES_TO_RADIANS;
-        mach = mach * fabs(cos(alpha)) * cos(beta);
-        mach = std::max( mach , 0.0 ); // we want a mach=0 if the airflow comes from behind
-        double p_t = p * pow(1 + 0.2 * mach*mach, 3.5 );    // true total pressure around aircraft
-        _total_pressure_node->setDoubleValue(p_t);
-        double p_t_meas = p_t;
-        if (mach > 1) {    
-          p_t_meas = p * pow( 1.2 * mach*mach, 3.5 ) * pow( 2.8/2.4*mach*mach - 0.4 / 2.4 , -2.5 );    // measured total pressure by pitot tube (Rayleigh formula, at Mach>1, normal shockwave in front of pitot tube)     
+           double x_proj_factor = cos(alpha) * fabs(cos(beta));  // the factor to project the total speed vector on the longitudinal body axis
+
+        double p_t = p;                                                                                // pitot tube stalled: total pressure = static pressure
+        double p_t_meas = p;
+
+        if ( x_proj_factor > _stall_factor ) {                         // NOTE: alpha: -180 - 180, beta: -90 - 90, pitot probe is stalled at more than 60 deg
+            p_t = p * pow(1 + 0.2 * mach*mach*x_proj_factor*x_proj_factor, 3.5 );              // total pressure in the pitot tube if not stalled
+            p_t_meas = p_t;
+
+            if (mach > 1) {
+                p_t_meas = p * pow( 1.2 * mach*mach, 3.5 ) * pow( 2.8/2.4*mach*mach - 0.4 / 2.4 , -2.5 );    // measured total pressure by pitot tube (Rayleigh formula, at Mach>1, normal shockwave in front of pitot tube)
+            }
         }
+
+        _total_pressure_node->setDoubleValue(p_t);
         _measured_total_pressure_node->setDoubleValue(p_t_meas);
     }
 }

diff --git a/src/Systems/pitot.hxx b/src/Systems/pitot.hxx
index cad000f2233b9a5f3fc62a14b896ac1a9804e56b..f694439d906eb70425df762d4e941d1ce6ac90d1 100644 (file)
--- a/src/Systems/pitot.hxx
+++ b/src/Systems/pitot.hxx
@@ -1,7 +1,7 @@
 // pitot.hxx - the pitot air system.
 // Written by David Megginson, started 2002.
 //
-// Last modified by Eric van den Berg, 24 Nov 2012
+// Last modified by Eric van den Berg, 01 Nov 2013
 // This file is in the Public Domain and comes with no warranty.
 
 
@@ -55,6 +55,7 @@ private:
 
     std::string _name;
     int _num;
+    double _stall_factor;
     SGPropertyNode_ptr _serviceable_node;
     SGPropertyNode_ptr _pressure_node;
     SGPropertyNode_ptr _mach_node;