From 863423054e9feaf919e4b5bcc63964937424bf4b Mon Sep 17 00:00:00 2001
From: curt <curt>
Date: Wed, 22 Mar 2000 21:59:59 +0000
Subject: [PATCH] Updates to vacuum system model from Alex Perry.
---
src/Cockpit/steam.cxx | 67 ++++++++++++++++++++++++++++++++++---------
src/Cockpit/steam.hxx | 6 +++-
2 files changed, 58 insertions(+), 15 deletions(-)
diff --git a/src/Cockpit/steam.cxx b/src/Cockpit/steam.cxx
index 0d8ca2547..860e8e900 100644
--- a/src/Cockpit/steam.cxx
+++ b/src/Cockpit/steam.cxx
@@ -57,6 +57,9 @@ double FGSteam::the_VSI_case = 29.92;
double FGSteam::the_VSI_fps = 0.0;
double FGSteam::get_VSI_fps() { _CatchUp(); return the_VSI_fps; }
+double FGSteam::the_VACUUM_inhg = 0.0;
+double FGSteam::get_VACUUM_inhg() { _CatchUp(); return the_VACUUM_inhg; }
+
double FGSteam::get_MH_deg () { return FGBFI::getHeading (); }
double FGSteam::get_DG_deg () { return FGBFI::getHeading (); }
@@ -94,14 +97,15 @@ void FGSteam::set_lowpass ( double *outthe, double inthe, double tc )
(*outthe) = (*outthe) * ( 1.0 - tc )
+ inthe * tc;
} else
- if ( tc > 5 )
+ if ( tc > 5.0 )
{ /* Huge time step; assume filter has settled */
(*outthe) = inthe;
} else
{ /* Moderate time step; non linear response */
- tc = exp ( -tc );
- (*outthe) = (*outthe) * ( 1.0 - tc )
- + inthe * tc;
+ double keep = exp ( -tc );
+ printf ( "ARP: Keep is %f\n", keep );
+ (*outthe) = (*outthe) * keep
+ + inthe * ( 1.0 - keep );
}
}
@@ -116,16 +120,26 @@ void FGSteam::_CatchUp()
{ if ( _UpdatesPending != 0 )
{ double dt = _UpdatesPending * 1.0 / current_options.get_model_hz();
int i,j;
- double d;
+ double d, the_ENGINE_rpm;
/*
- Someone has called our update function and we haven't
- incorporated this into our instrument modelling yet
+ Someone has called our update function and
+ it turns out that we are running somewhat behind.
+ Here, we recalculate everything for a 'dt' second step.
*/
/**************************
- This is just temporary
+ This is not actually correct, but provides a
+ scaling capability for the vacuum pump later on.
+ When we have a real engine model, we can ask it.
*/
- the_ALT_ft = FGBFI::getAltitude();
+ the_ENGINE_rpm = FGBFI::getThrottle() * 26.0;
+
+ /**************************
+ This is just temporary, until the static source works,
+ so we just filter the actual value by one second to
+ account for the line impedance of the plumbing.
+ */
+ set_lowpass ( & the_ALT_ft, FGBFI::getAltitude(), dt );
/**************************
First, we need to know what the static line is reporting,
@@ -133,11 +147,11 @@ void FGSteam::_CatchUp()
*/
the_STATIC_inhg = 29.92;
i = (int) the_ALT_ft;
- while ( i > 18000 )
- { the_STATIC_inhg /= 2;
- i -= 18000;
+ while ( i > 9000 )
+ { the_STATIC_inhg *= 0.707;
+ i -= 9000;
}
- the_STATIC_inhg /= ( 1.0 + i / 18000.0 );
+ the_STATIC_inhg *= ( 1.0 - 0.293 * i / 9000.0 );
/*
NO alternate static source error (student feature),
@@ -152,9 +166,34 @@ void FGSteam::_CatchUp()
NO capability for a fixed non-zero reading when level.
NO capability to have a scaling error of maybe a factor of two.
*/
- set_lowpass ( & the_VSI_case, the_STATIC_inhg, dt/9.0 );
the_VSI_fps = ( the_VSI_case - the_STATIC_inhg )
* 7000.0; /* manual scaling factor */
+ set_lowpass ( & the_VSI_case, the_STATIC_inhg, dt/9.0 );
+
+ /**************************
+ The engine driven vacuum pump is directly attached
+ to the engine shaft, so each engine rotation pumps
+ a fixed volume. The amount of air in that volume
+ is determined by the vacuum line's internal pressure.
+ The instruments are essentially leaking air like
+ a fixed source impedance from atmospheric pressure.
+ The regulator provides a digital limit setting,
+ which is open circuit unless the pressure drop is big.
+ Thus, we can compute the vacuum line pressure directly.
+ We assume that there is negligible reservoir space.
+ NO failure of the pump supported (yet)
+ */
+ the_VACUUM_inhg = the_STATIC_inhg *
+ the_ENGINE_rpm / ( the_ENGINE_rpm + 10000.0 );
+ if ( the_VACUUM_inhg > 5.0 )
+ the_VACUUM_inhg = 5.0;
+
+/*
+> I was merely going to do the engine rpm driven vacuum pump for both
+> the AI and DG, have the gyros spin down down in power off descents,
+> have it tumble when you exceed the usual pitch or bank limits,
+> put in those insidious turning errors ... for now anyway.
+*/
/**************************
Finished updates, now clear the timer
diff --git a/src/Cockpit/steam.hxx b/src/Cockpit/steam.hxx
index adc222875..2254dc7fc 100644
--- a/src/Cockpit/steam.hxx
+++ b/src/Cockpit/steam.hxx
@@ -67,8 +67,12 @@ public:
static double get_TC_radps ();
static double get_VSI_fps ();
+ // Engine Gauges
+ static double get_VACUUM_inhg ();
+
private:
- static double the_ALT_ft, the_STATIC_inhg;
+ static double the_ALT_ft;
+ static double the_STATIC_inhg, the_VACUUM_inhg;
static double the_VSI_fps, the_VSI_case;
static int _UpdatesPending;