pitot.cxx

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/*
 * SPDX-FileName: pitot.cxx
 * SPDX-FileComment: the pitot air system
 * SPDX-FileCopyrightText: Written by David Megginson, started 2002.
 * SPDX-FileContributor: modified by Eric van den Berg, 01 Nov 2013
 * SPDX-License-Identifier: 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>
#include <Main/util.hxx>
 
#include "pitot.hxx"
 
 
PitotSystem::PitotSystem ( SGPropertyNode *node )
    :
    _name(node->getStringValue("name", "pitot")),
    _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.
{
}
 
PitotSystem::~PitotSystem ()
{
}
 
void
PitotSystem::init ()
{
    std::string branch;
    branch = "/systems/" + _name;
 
    SGPropertyNode *node = fgGetNode(branch.c_str(), _num, true );
    _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);
    if ( _stall_factor < 0 ) { // |stall angle| > 90°
                _stall_factor = cos(60 * SGD_DEGREES_TO_RADIANS);
        }
}
 
void
PitotSystem::bind ()
{
}
 
void
PitotSystem::unbind ()
{
}
 
void
PitotSystem::update (double dt)
{
    if (_serviceable_node->getBoolValue()) {
        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);
    }
}
 
 
// Register the subsystem.
#if 0
SGSubsystemMgr::Registrant<PitotSystem> registrantPitotSystem(
    SGSubsystemMgr::POST_FDM,
    {{"static", SGSubsystemMgr::Dependency::SOFT},
     {"vacuum", SGSubsystemMgr::Dependency::SOFT}});
#endif
 
// end of pitot.cxx