Berndt, Jon S
2006-03-23 21:38:10 UTC
JSBSim is more tractable than MSFS. As Jon mentioned
below, perhaps the new Markup Language would enable setting
two independent flap-like surfaces which have a virtual
deflection dependent on individual Prop Thrust.
Some time ago I mentioned there is a NASA report on
'Performance of Light Twins'. It goes into a lot of detail
on prop effects. Much more than one would want.
Ron
There are a few reports (including the one that Ron mentions) that mightbelow, perhaps the new Markup Language would enable setting
two independent flap-like surfaces which have a virtual
deflection dependent on individual Prop Thrust.
Some time ago I mentioned there is a NASA report on
'Performance of Light Twins'. It goes into a lot of detail
on prop effects. Much more than one would want.
Ron
be helpful in modeling an aircraft with JSBSim. For example:
"Longitudinal stability and control derivatives obtained from flight
data of a PA-30 aircraft"
http://ntrs.nasa.gov/index.cgi?method=display&redirect=http://hdl.handle
.net/2060/19860021264&oaiID=oai:casi.ntrs.nasa.gov:19860021264
This search will give you several applicable documents:
http://ntrs.nasa.gov/index.cgi?method=search&limit=25&offset=0&mode=simp
le&order=DESC&keywords=stability+light+twin%0D%0A
The lift coefficient delta due to propwash could be modeled. In fact -
as an aside - the effect on lift (and other coefficients) from thrust is
shown in some of the reports mentioned above. The straight lift
coefficient due to alpha is defined in the C310 <aerodynamics> section
as this:
<function name="aero/coefficient/CLalpha">
<description>Lift_due_to_alpha</description>
<product>
<property>aero/qbar-psf</property>
<property>metrics/Sw-sqft</property>
<property>aero/function/kCLge</property>
<table>
<independentVar>aero/alpha-rad</independentVar>
<tableData>
-0.3000 -1.0100
.... ....
0.3140 0.5690
0.3490 0.2880
</tableData>
</table>
</product>
</function>
The propwash gives an airflow to the wings that generates a lift force.
You can figure the velocity over the wings given the thrust produced,
roughly. You could then derive the lift over that portion of the wing,
and from that you could sort of figure out a rough contribution to lift
from thrust. Or, you could use DATCOM+ to figure that out. Or, you could
use the data provided. The point is, using the <function> definition,
you can model just about any algebraic expression with the available
properties - including tables.
Jon
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