On 04/12/2010 06:14 PM, Fred Klein wrote:
> I've always understood that the elevator or an all-flying tail
> (horizontal tail plane) has a "job"...namely, to exert a force, either
> up or down, in order to balance the lift of the wing and stabilize the
> flight path of a normally configured aircraft (i.e., not a canard type).
> To do this "job" requires "work"; the tail plane is never neutral.
I understood the tail plane of the Europa is aerodynamically neutral
indeed, and the sole function of the trim tabs is to give the pilot
tactile feedback and to push the tailplane in such a position that the
trim tab neutralizes itself again.
Without the trim tabs, the tail plane would be happy to remain in any
position where you set it, including in positions that pull excessive
G's. It is the trim tab that spoiles this neutrality and always tries to
work out a tail plane position where it can line up again with the tail
plane. So, the trim tab will always remain in the same relative position
of the tail plane regardless trim setting, but it is the whole
combination of tail plane and trim tab that change incidence as a whole
relatively to the main wings.
You might want to execute the following experiment:
Put a spring clamb on the trim tab and overlap it with the tail plane.
It should try to keep the tail plane and trim tab lined up.
Now carefully exercise the trim button and see what happens: It is not
the trim tab that moves, but the whole tailplane/trim tab combination!
This is what happens in flight as well. The clamb is no longer there,
but instead a flow of air over and under the trim tab, and as soon as
the trim tab tries to move outside the airflow, it will be pused back to
the tail plane, just as if there is a spring clamb on them.
This is true as long as you don't push or pull on the stick. As soon as
you do that, you will push or pull the trim tab out of its center, and
it becomes subject to a disbalance in air flow. It is the air pushing
against the trim tab what gives you the feeling of resistance when you
push or pull on the stick... As soon as you release the force, it will
rotate again to the same relative position.
Frans
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