There is a change coming to the JSBSim modeled atmosphere. A new standard atmosphere class is being completed that models the U.S. Standard Atmosphere (1972) all the way up to 1000 km. FlightGear interacts with the FDM atmosphere in a predictable way, since the user may want to set conditions. Currently, this is the code that permits the controlling application (FlightGear) to control the atmosphere:
If the property /environment/params/control-fdm-atmosphere is set to true,
then the JSBSim atmosphere model is set to UseExternal and the Temp, Press,
and Density are set:
Atmosphere->UseExternal();
Atmosphere->UseExternal();
Atmosphere->SetExTemperature(
Atmosphere->SetExPressure(pressure->getDoubleValue()*70.726566);
Atmosphere->SetExDensity(density->getDoubleValue());
Otherwise, UseInternal is set.
Atmosphere->UseInternal();
Each pass through the copyToJSBSim function is called, these parameters are
set:
Atmosphere->SetExTemperature(
Atmosphere->SetExPressure(pressure->getDoubleValue()*70.726566);
Atmosphere->SetExDensity(density->getDoubleValue());
These have no effect if UseInternal is set.
That was the old way. None of these API methods are present in the new
model. The new way isn't here yet, but will be after the upcoming release of
FlightGear. As reported on the JSBSim developer mailing list,
I have submitted new updates to Codestriker for the new standard atmosphere
model if anyone wants to have another look at how it is shaping up:
https://sourceforge.net/apps/codestriker/jsbsim/codestriker.pl?action=list_t
opics&sstate=0
The documentation is shaping up at the same time here:
http://jsbsim.sourceforge.net/JSBSim/classJSBSim_1_1FGStandardAtmosphere.htm
l
In the new version of the standard atmosphere model, external applications
such as FlightGear will be able to control the atmosphere by setting sea
level conditions, or at-altitude conditions using any of these API calls
(see the documentation at the second link, above, for more information on
these):
void SetSLTemperature
<http://jsbsim.sourceforge.net/JSBSim/classJSBSim_1_1FGStandardAtmosphere.ht
ml> (double t, eTemperature
<http://jsbsim.sourceforge.net/JSBSim/classJSBSim_1_1FGStandardAtmosphere.ht
ml> unit=eFahrenheit);
void SetTemperature
<http://jsbsim.sourceforge.net/JSBSim/classJSBSim_1_1FGStandardAtmosphere.ht
ml> (double t, double h, eTemperature
<http://jsbsim.sourceforge.net/JSBSim/classJSBSim_1_1FGStandardAtmosphere.ht
ml> unit=eFahrenheit) {};
void SetTemperatureBias
<http://jsbsim.sourceforge.net/JSBSim/classJSBSim_1_1FGStandardAtmosphere.ht
ml> (double t, eTemperature
<http://jsbsim.sourceforge.net/JSBSim/classJSBSim_1_1FGStandardAtmosphere.ht
ml> unit=eFahrenheit);
void SetSLTemperatureGradedDelta
<http://jsbsim.sourceforge.net/JSBSim/classJSBSim_1_1FGStandardAtmosphere.ht
ml> (double t, eTemperature
<http://jsbsim.sourceforge.net/JSBSim/classJSBSim_1_1FGStandardAtmosphere.ht
ml> unit=eFahrenheit);
void SetTemperatureGradedDelta
<http://jsbsim.sourceforge.net/JSBSim/classJSBSim_1_1FGStandardAtmosphere.ht
ml> (double t, double h, eTemperature
<http://jsbsim.sourceforge.net/JSBSim/classJSBSim_1_1FGStandardAtmosphere.ht
ml> unit=eFahrenheit);
void SetSeaLevelPressure
<http://jsbsim.sourceforge.net/JSBSim/classJSBSim_1_1FGStandardAtmosphere.ht
ml> (double pressure, ePressure
<http://jsbsim.sourceforge.net/JSBSim/classJSBSim_1_1FGStandardAtmosphere.ht
ml> unit=ePSF);
Several units are available for the setters - both metric and English. The
density is calculated from the temperature and pressure, so it is not
specified. The point of this is that the temperature - and the temperature
profile - are controllable by the calling application. The sea level
pressure can be set by the calling application. I will be adding the ability
to set the pressure at a particular altitude/elevation, but that's not ready
yet. These two items should allow a great deal of control over the
atmosphere, with the atmosphere remaining internally consistent.
The winds modeling have been moved to another class, FGWinds. Additional
wind effects are hoped to be modeled, such as downbursts, 1 minus cosine
gusts, etc.
Additionally, I am considering the modeling of temperature and pressure
"turbulence", as well - slight fluctuations of those parameters based on
temporal and spatial conditions.
Comments?
Jon
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