Europa Aviation Ltd wrote
>We agree that the sense of the trim operation should be as you describe.
>
>To state the operation formally:-
>
>To trim the aircraft nose up (tab moves down), press the bottom of the
>rocker switch, and the indicator moves up.
"Indicator up" = "nose-up trim": that all sounded very sensible until I
started to think about my own experience of trimmers.
The Cessnas I usually fly have a wheel mounted more-or-less on the vertical
panel for trim. To trim the aircraft nose up, you move the visible
periphery of the wheel down (equivalent to pushing the bottom half inwards)
and the trim tab moves down, giving increased nose-up trim. All in
agreement so far. However, my memory, from 3 days ago when I last flew one,
is that after the above operation, the indicator will have moved _down_, ie
it follows, somewhat more slowly, the sense of movement of the trim wheel
itself.
I guess it stems from the type of installation mentioned by Graham where
the wheel is mounted in a horizontal panel with the top half available for
manipulation. The indicator would then show which end was being made
artificially "heavy". I agree that it makes less sense when you mount the
wheel on a vertical panel, so that "indicator down" means "up trim", "nose
up" or "tail heavy". However, in 16 years of flying Cessnas I have never
noticed that it doesn't make sense until this very moment! On the other
hand, if the arrangement described by Roger were mounted in the horizontal
plane, the indications would be surely be misleading to most pilots.
I guess I could live with an _indicator_ which moved in the opposite to the
sense I expected, as long as the _switch_ itself worked as described. Is
there any standard for pitch trim indicators? Shouldn't we conform to it if
there is one? Some ergonomic decisions can have life-&-death implications
(like the old one of: is it the aeroplane or the horizon line that moves in
your artificial horizon?) but although this probably doesn't come into that
category, it would be nice to get it right (however you define that!).
Sorry if this has muddied the waters further - maybe some input is needed
---From people who fly aircraft with other types of pitch trim indication (and
actuation).
cheers
Rowland
... that's Rowland with a 'w' ...
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