Hi Jos & Graham, My theory about the tailplane was based on the principle of a
FULLY aerodynamically balanced "all moving" tailplane, this being the perfect
situation for efficiency. (Jos - MY interpretation of "aerodynamically balanced"
being specifically related to an "all moving" tailplane that is not deflected
at all from it's current position by it's relative airflow, including any
changes
to that airflow, ie the center or point of the lifting force (downforce)
generated by the tailplane acts through the pivot (torque tube))
However, IF Graham's info about the C of L being deliberately designed to be NOT
quite acting through the pivot (due to this short period oscillation - whatever
that is!) is true, and I am very pleased and interested to bow to his most
extensive experience of the Europa development and learn about this, then this
means that the Europa tailplane is not quite perfectly aerodynamically balanced.
Thus, unless the Angle of Attack of the tailplane is at any time zero (most
unlikely) then a small tab deflection in the relevant direction would be
required
to counter the rotating force created on the tailplane by the airflow.
(I would class this as another "unwanted" rotational force as in my previous
text under variances!). This rotating force - and the corresponding amount of
tab deflection required to offset it to maintain trimmed flight would vary
slightly
depending on the relative airflow to the tailplane and the corresponding
amount of lift (downforce) being generated. This aerodynamic imbalance of
the tailplane must I feel only be slight - the whole downforce generated by the
tail is fairly small and is needed just to balance the wing's own imbalance
of forces.
(Question - WHY then are some people's tabs completely flush in steady trimmed
flight.....?!)
This aside though, I still fully stand by my comments of how the tailplane,
especially
the tabs work in principle. The tabs, when trimmed by the pilot correctly,
hold the tailplane in the desired position as set by the elevator control.
The tabs would ideally be flush (fully aerodynamically balanced tailplane)
but will have a permanent, slightly variable deflection if Graham's info on the
tailplane not being fully aerodynamically balanced is true (as I'm sure it
is..!)
Jos - of course the trim control is necessary - vital in fact to keep the
elevator
control where the pilot wants it and to provide "feel" or "weight" (the
anti-trim
part as you call it) to the stick to stop the pilot "breaking things"
as you most eloquently put it! But I think that without trim tabs fitted the
elevator control would be VERY LIGHT to move (not heavy) throughout the entire
range, dangerously so without extreme care. A perfectly aerodynamically
balanced
(all moving!) tailplane without trim tabs fitted would be completely without
weight or feel at all throughout the entire elevator range (most undesirable).
The trim tabs we have are very powerful being so far from the torque tube
and if set even slightly out of the correct trimmed position would make the
stick very heavy to hold in position. This of course is not force generated by
the tailplane itself, rather the (rotating) force being applied to the tailplane
by the incorrectly set trim (tabs).
Best Regards, Jon
(Sorry about the length again!)
--------
G-TERN
Classic Mono
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=298854#298854
|