Andy Ross writes:
> And it *was* trimming for zero /controls/elevator{-trim}. That's the
> whole point: It's not a bug in the solver. The pitching moment* at
> the specified cruise conditions is very near zero; that's what the
> solver does. The problem is that a real aircraft under those
> conditions *doesn't* have its trim wheel set to zero. So the "feel"
> to someone comparing the aircraft's trim behavior to a real one is as
> if the trim is more nose down than it should be.
j3cub.xml originally had the following entry for cruise:
<cruise speed="64" alt="0">
<control-setting axis="/controls/throttle[0]" value="0.75"/>
<control-setting axis="/controls/mixture[0]" value="0.75"/>
</cruise>
>From what I understand, with elevator trim and elevator set to zero,
the plane should be trimmed for 64 kcas (74 mph). However, if I zero
the elevator and elevator trim, the nose drops and eventually settles
around 110-120 mph. What accounts for the difference?
You can test this by commenting out my elevator axis line in
the cruise element in the latest j3cub.xml, then starting
fgfs --altitude=3000 --vc=64 --aircraft=j3cub
> Your Cherokee, for example, probably wants to fly at something like
> 80 knots with the trim wheel centered (I'm guessing). An
> equivalent YASim model would likely have a cruise configuration of
> 110 knots, would set the trim to that speed, and would therefore
> "feel" nose heavy despite the aerodynamic behavior being identical.
> The fix is to examine the trim wheel in cruise and set that value
> as a control input to the cruise configuration.
That's very helpful -- thanks. Note that the small planes I've flown
tend to use a bit of forward (nose-down) trim in cruise, not nose-up.
All the best,
David
--
David Megginson, [EMAIL PROTECTED], http://www.megginson.com/
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