From 05fa7130fc328cca43272b65de7ae508339d53e6 Mon Sep 17 00:00:00 2001
From: janodesbois <jean.pellotier@wanadoo.fr>
Date: Thu, 31 Oct 2013 20:28:12 +0100
Subject: [PATCH] pitot tube using velocities/mach as mach norm, not the u
 componant

---
 src/Systems/pitot.cxx | 9 +++++++--
 src/Systems/pitot.hxx | 2 ++
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/src/Systems/pitot.cxx b/src/Systems/pitot.cxx
index 4f18431cd..8fdbdd19e 100644
--- a/src/Systems/pitot.cxx
+++ b/src/Systems/pitot.cxx
@@ -37,6 +37,8 @@ PitotSystem::init ()
     _serviceable_node = node->getChild("serviceable", 0, true);
     _pressure_node = fgGetNode("/environment/pressure-inhg", true);
     _mach_node = fgGetNode("/velocities/mach", true);
+    _alpha_deg_node = fgGetNode("/orientation/alpha-deg", true);
+    _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);
 }
@@ -57,14 +59,17 @@ PitotSystem::update (double dt)
     if (_serviceable_node->getBoolValue()) {
         double p = _pressure_node->getDoubleValue();
         double mach = _mach_node->getDoubleValue();
-        mach = std::max( mach , 0.0 );
+        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)     
         }
-        _measured_total_pressure_node->setDoubleValue(p_t_meas);
+        _measured_total_pressure_node->setDoubleValue(mach);
     }
 }
 
diff --git a/src/Systems/pitot.hxx b/src/Systems/pitot.hxx
index 7f1e48787..cad000f22 100644
--- a/src/Systems/pitot.hxx
+++ b/src/Systems/pitot.hxx
@@ -60,6 +60,8 @@ private:
     SGPropertyNode_ptr _mach_node;
     SGPropertyNode_ptr _total_pressure_node;
     SGPropertyNode_ptr _measured_total_pressure_node;
+    SGPropertyNode_ptr _alpha_deg_node;
+    SGPropertyNode_ptr _beta_deg_node;
 };
 
 #endif // __SYSTEMS_PITOT_HXX