Andy: unfortunately, none of your suggestions helped (details below).
How are you modelling washout in YASim? From the violent roll that
comes with every stall, it looks like all of the wing is stalling
simultaneously, so the plane loses roll control from the ailerons at
the same time as it loses lift from the wings.
As you know (but others might not), real wings on GA aircraft are
twisted so that the incidence angle at the wing root is higher than
the incidence angle at the wing tips -- that way, the wing root always
has a higher AOA and will stall first, dropping the nose while the
wing tips (and ailerons) are still effective. Because of the washout,
a typical gentle stall in a Skyhawk or Cherokee (for example) has no
noticeable roll component, even if there is a sharp nose drop.
Perhaps there's a problem with the washout code in YASim right now.
[specific comments follow]
Andy Ross writes:
> Try modifying the "flap" setting on the hstab (the effectiveness of
> the stabilizor flaps) until full elevator is just barely enough to
> acheive stall AoA. You are helped in this because (I think) the
> "approach" configuration in the file actually represents a stall. The
> solver prints out the elevator required to trim for approach in the
> solution report, make this as close to 1.0 as you can.
>
> This might be enough to fix your problem -- you could still get a
> viscious asymettric stall with violent control input, but gentle
> motion of the yoke wouldn't be able to pull the nose high enough.
Unfortunately, it seems to make no difference. I modified the value
of hstab/flap0/@lift until I got the following in the solution:
YASim solution results:
Iterations: 1181
Drag Coefficient: 22.8378
Lift Ratio: 101.002
Cruise AoA: -0.842131
Tail Incidence: 0.597357
Approach Elevator: -0.994847
CG: -2.337, 0.000, -0.132
A gentle, power-off stall still results in a violent roll.
> The problem with the stalls themselves should be fixeable with the
> stall subtag on the wing. There is a "width" parameter that controls
> the sharpness of the lift curve peak. It's roughly twice the radius
> of curvature of the top of the peak, in degrees (not exactly, because
> I'm using a cubic interpolant, but close enough). It's currently set
> to six, which I would think would be pretty gentle. But you could try
> a higher value and see what you get. Is it possible I have a unit bug
> in there?
> Another tunable you could play with is the "peak" number. This
> controls how high the "normal" lift peak is in relation to the more
> fundamental one at 45� generated by the underlying surface model.
> Setting this value higher results in a sharper lift drop past the
> stall. Lower values produce more gentle curves. I have *no* idea
> what the right value for this is; I haven't seen any data on wing lift
> though the full 360� of AoA. :)
I changed wing/stall/@width to 12 and wing/stall/@peak to 1.1, and saw
no significant difference in the stall behaviour -- a gentle,
power-off stall still results in a violent roll.
All the best,
David
--
David Megginson, [EMAIL PROTECTED], http://www.megginson.com/
_______________________________________________
Flightgear-devel mailing list
[EMAIL PROTECTED]
http://mail.flightgear.org/mailman/listinfo/flightgear-devel
