David Megginson wrote:
> That was not happening, however; instead, with 0 elevator and 0
> elevator trim, all aircraft would continue pitching downwards and
> accelerating past Vne. Setting the elevator property solved the
> problem. I don't know why it wasn't trimming for 0
> elevator/elevator trim.
You misunderstand what I wrote. Your solution is correct, but you
should be using /controls/elevator-trim instead of /controls/elevator.
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.
* That doesn't mean you can't get the aircraft past the speed with
"hands off" by inducing a phygoid oscillation. But the trim speed
is guaranteed to be correct. The aircraft won't nose down and
diverge.
Take off in an aircraft, set the elevator trim to zero (or to whatever
value appears in the configuration file) and duplicate the cruise
conditions. The required elevator will be zero. It may "feel" nose
heavy, but it's not. You're just expecting a different initial trim
condition than you're getting.
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.
Andy
--
Andrew J. Ross Beyond the Ordinary Plausibility Productions
Sole Proprietor Beneath the Infinite Hillsboro, OR
Experience... the Plausible?
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