// pitot.cxx - the pitot air system.
// Written by David Megginson, started 2002.
//
+// 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
+# include <config.h>
+#endif
+
#include <simgear/constants.h>
#include <Main/fg_props.hxx>
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.
{
}
SGPropertyNode *node = fgGetNode(branch.c_str(), _num, true );
_serviceable_node = node->getChild("serviceable", 0, true);
_pressure_node = fgGetNode("/environment/pressure-inhg", true);
- _density_node = fgGetNode("/environment/density-slugft3", true);
- _velocity_node = fgGetNode("/velocities/airspeed-kt", true);
- _slip_angle = fgGetNode("/orientation/side-slip-rad", 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);
+ if ( _stall_factor < 0 ) { // |stall angle| > 90°
+ _stall_factor = cos(60 * SGD_DEGREES_TO_RADIANS);
+ }
}
void
{
}
-#ifndef INHGTOPSF
-# define INHGTOPSF (2116.217/29.9212)
-#endif
-
-#ifndef PSFTOINHG
-# define PSFTOINHG (1/INHGTOPSF)
-#endif
-
-
void
PitotSystem::update (double dt)
{
if (_serviceable_node->getBoolValue()) {
- // The pitot tube sees the forward
- // velocity in the body axis.
- double p = _pressure_node->getDoubleValue() * INHGTOPSF;
- double r = _density_node->getDoubleValue();
- double v = _velocity_node->getDoubleValue() * SG_KT_TO_FPS;
- v *= cos(_slip_angle->getDoubleValue());
- if (v < 0.0)
- v = 0.0;
- double q = 0.5 * r * v * v; // dynamic
- _total_pressure_node->setDoubleValue((p + q) * PSFTOINHG);
+ double p = _pressure_node->getDoubleValue();
+ 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;
+ 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);
}
}