Add open-circuit oxygen system.
Signed-off-by: Vivian Meazza <vivian.meazza@lineone.net>
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Vivian Meazza
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155
Aircraft/Generic/Oxygen/oxygen.nas
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155
Aircraft/Generic/Oxygen/oxygen.nas
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###############################################################################
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##
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## Oxygen system module for FlightGear.
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##
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## Copyright (C) 2010 Vivian Meazza (vivia.meazza(at)lineone.net)
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## This file is licensed under the GPL license v2 or later.
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##
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###############################################################################
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# Properties under /consumables/fuel/tank[n]:
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# + level_cu_ft - Current free oxygen content. Must be set by user code.
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# + capacity_cu_ft - Tank volume
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# + selected - boolean indicating tank selection.
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# + name ...........- string
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# + pressure - OUTPUT ONLY property, do not try to set
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# Properties under /controls/oxygen/
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# + altitude-norm - the selected supply altitude normalized 0 - 100% oxygen
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# + flowrate_cu_ft_ps - Max (100%) Oxygen flow rate
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# + flowrate considerations:
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# ref http://en.wikipedia.org/wiki/Human_lung
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#
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# when maximum (100%) oxygen is selected, we wish to deliver enough oxygen to fill
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# the pilot's lungs, with slight overpressure.
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#
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# let the tidal flow volume - that is the amount of gas which flows
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# into and out of the lungs on each breath = T ft^3;
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# and the number of breaths per minute at rest= N min^-1;
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# but we need to consider a pilot under stress factor = 1.5
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#
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# so flowrate (ft^3.sec^-1) = (T*1.5*N)/60
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#
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# substituting the values from the reference
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#
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# flowrate = 0.01765 * 1.5 * 20 / 60 = 0.008828
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#
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# rounding up to provide overpressure
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#
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# flowrate = 0.01 (ft^3.sec^-1)
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#========================= Initialize ===============================
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var MAXTANKS = 20;
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var INHG2PSI = 0.491154077497;
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var initialize = func {
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print( "Initializing Oxygen System ..." );
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props.globals.initNode("/systems/oxygen/serviceable", 1, "BOOL");
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props.globals.initNode("/sim/freeze/oxygen", 0, "BOOL");
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props.globals.initNode("/controls/oxygen/altitude-norm", 0.0, "DOUBLE");
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props.globals.initNode("/controls/oxygen/flowrate-cu-ft-ps", 0.01, "DOUBLE");
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for (var i = 0; i < MAXTANKS; i += 1){
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props.globals.initNode("/consumables/oxygen/tank["~ i ~ "]/capacity-cu-ft", 0.01, "DOUBLE");
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props.globals.initNode("/consumables/oxygen/tank["~ i ~ "]/level-cu-ft", 0, "DOUBLE");
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props.globals.initNode("/consumables/oxygen/tank["~ i ~ "]/selected", 0, "BOOL");
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props.globals.initNode("/consumables/oxygen/tank["~ i ~ "]/pressure-psi", 50, "DOUBLE");
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}
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oxygen();
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} #end init
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#========================= Oxygen System ============================
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var oxygen = func {
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var freeze = getprop("/sim/freeze/oxygen");
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var serviceable =getprop("/systems/oxygen/serviceable");
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if(freeze or !serviceable) { return; }
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var dt = getprop("sim/time/delta-sec");
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var oxygen_alt = getprop("controls/oxygen/altitude-norm");
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var flowrate_cu_ft_ps = getprop("controls/oxygen/flowrate-cu-ft-ps");
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var Pa = getprop("environment/pressure-inhg") * INHG2PSI;
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var flow_cu_ft = flowrate_cu_ft_ps * oxygen_alt * dt;
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var contents = 0;
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var cap = 0;
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var availableTanks = [];
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var selected = 0;
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var pressure = 2000;
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# Build a list of available tanks. An available tank is both selected, has
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# oxygen remaining.and pressure < ambient.
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var AllTanks = props.globals.getNode("consumables/oxygen").getChildren("tank");
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foreach( var t; AllTanks) {
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cap = t.getNode("capacity-cu-ft", 1).getValue();
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contents = t.getNode("level-cu-ft", 1).getValue();
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selected = t.getNode("selected", 1).getBoolValue();
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pressure = t.getNode("pressure-psi", 1).getValue();
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if(cap != nil and cap > 0.01 ) {
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# print ("Pressure ", pressure, " " , Pa);
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if(selected and pressure > Pa) {
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append(availableTanks, t);
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}
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}
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}
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# print("flow_cu_ft ", flow_cu_ft," " ,size(availableTanks));
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# Subtract flow_cu_ft from tanks, set auxilliary properties. Set out-of-gas
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# when all tanks are empty.
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var outOfGas = 0;
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if(size(availableTanks) == 0) {
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outOfGas = 1;
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} else {
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flowPerTank = flow_cu_ft / size(availableTanks);
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foreach( var t; availableTanks ) {
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cu_ft = t.getNode("level-cu-ft").getValue();
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cu_ft -= flowPerTank;
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cap = t.getNode("capacity-cu-ft", 1).getValue();
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if(cu_ft < 0) { cu_ft = 0;}
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# print ("pressure ", calcPressure(cu_ft, cap));
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t.getNode("level-cu-ft").setDoubleValue(cu_ft);
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t.getNode("pressure-psi").setDoubleValue(calcPressure(cu_ft, cap));
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}
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}
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settimer(oxygen, 0.3);
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} #end oxygen
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# We apply Boyle's Law to derive the pressure in the tank fom the capacity of the
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# tank and the contents. We ignore the effects of temperature.
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var calcPressure = func (cu_ft, cap){
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var Vc = cap;
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var Va = cu_ft;
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var Pa = 14.7;
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# print (Vc, " ", Va, " ", Pa);
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Pc = (Pa * Va)/Vc;
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return Pc;
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} #end calcPressure
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setlistener("sim/signals/fdm-initialized", initialize);
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# end
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