On Friday 25 February 2011 08:13:57 Geoff McLane wrote:
> Hi Ron,
>
> Many thanks for taking the time to explain. I 'think'
> I understand a little more ;=))
>
> As you state, using sine(alpha) continues to allow
> up and down moments as you flex say the elevator with
> a tail wind, but prevents the very 'unrealistic'
> aircraft 'tumbling' I have seen...
>
> Regards,
> Geoff.
The function we just played with has nothing to do with elevator deflection.
If you want to effect that you need to look at this function:
<function name="aero/coefficient/Cmde">
<description>Pitch_moment_due_to_elevator_deflection</description>
<product>
<property>aero/qbar-psf</property>
<property>metrics/Sw-sqft</property>
<property>metrics/cbarw-ft</property>
<property>fcs/elevator-pos-rad</property>
<value>-1.1220</value>
</product>
</function>
Add the cosine of alpha to the product list:
<function name="aero/coefficient/Cmde">
<description>Pitch_moment_due_to_elevator_deflection</description>
<product>
<property>aero/qbar-psf</property>
<property>metrics/Sw-sqft</property>
<property>metrics/cbarw-ft</property>
<cos>
<property>aero/alpha-rad</property>
</cos>
<property>fcs/elevator-pos-rad</property>
<value>-1.1220</value>
</product>
</function>
This will reduce elevator effectiveness to zero as alpha climbs through +/-90
degrees and reverse the elevator sense for alphas above that range. I
believe this is a plausible aerodynamic effect as, above 90 degrees, the
elevator becomes a leading edge device. Again, this is a gross
simplification and not aerodynamic "truth." It ignores entirely the effect of
downwash on the elevator, among other things.
Ron
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