> From: syd adams [mailto:adams....@gmail.com] > > Does jsbsim ? I've just begun to look into it , so I don't really know > jsbsim's capabilities.
It's not automatic - not a natural effect calculated by JSBSim code itself.
Like many things in JSBSim, the facilities are present to let the aircraft
flight model developer add these kinds of things. The contributions from the
tail, (such as moment due to elevator, lift due to elevator) are functions
of alpha and qbar. Both alpha and qbar are affected by propwash, since
propwash speeds up the airflow immediately behind it if it is producing
thrust. When defining lift or moment contributions from the elevator, the
alpha and qbar that are parts of that definition can be modified by a
function that includes the effects of propwash. So, it's very configurable.
You could even include the effects of beta (sideslip) so the effects are
blended out if beta is too high.
Here's an example from Hal's P-51D Mustang. This is from an old version, so
it may have changed by now, but it illustrates the approach. In the
<aerodynamics> section of the config file - but outside of any <axis>
element - is this definition of qbar due to propwash:
[Note: <v> is shorthand for "value", and <p> is shorthand for "property".]
<function name="aero/thrust-qbar_psf">
<product>
<v> 0.5 </v>
<p> atmosphere/rho-slugs_ft3 </p>
<pow>
<sum>
<p> velocities/u-aero-fps </p>
<product>
<p> propulsion/engine/prop-induced-velocity_fps </p>
<v> 2.0 </v>
</product>
</sum>
<v> 2.0 </v>
</pow>
</product>
</function>
Later, within the pitch axis definition, is this definition:
<function name="aero/coefficient/Cmde">
<description>Pitch_moment_due_to_elevator</description>
<product>
<property>aero/thrust-qbar_psf</property>
<property>metrics/Sw-sqft</property>
<property>metrics/cbarw-ft</property>
<property>fcs/elevator-pos-rad</property>
<table>
<independentVar>velocities/mach</independentVar>
<tableData>
0.0000 -0.80000
2.0000 -0.200
</tableData>
</table>
</product>
</function>
[Note that while this function definition is named "aero/coefficient/Cmde"
it is not really a coefficient, but an actual moment in units of foot
pounds. The "coefficient" part of the name is a holdout from years past.]
In the second code snippet you can see the "aero/thrust-qbar_psf property
used.
I hope this helps a bit.
Jon
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