Recently, Mxsmanic posted:
writes:
Trimming doesn't change the ability of the horizontal stabilizer to
correct for CG location, etc. It merely adds in an initial deflection
of the elevator so as to make the effort needed by the pilot to move
it is small. Imagine having to hold a constant twenty pounds of
elevator on a cross country 
.
But doesn't trim in most aircraft involve moving the elevator with a
trim tab?
On many aircraft, the trim tab moves independently of the elevator, and on
others the elevator is adjusted.
That is, if the elevator is moved up by the trim, then
there's that much less travel remaining in the elevator in that
direction. So if you have quite a bit of trim, your safety margin for
additional elevator movement is reduced. Right?
Trimming the elevator reduces the amount of effort required by the pilot
to hold altitude. If one is carrying a lot of "up" trim, for example, then
the aircraft is likely to be near critical AOA. The last thing you'd need
is have a lot more "up" elevator movement available.
In an aircraft in which the entire stabilizer moves for trim, I
suppose you could set any amount of trim and still have full travel in
both directions (doesn't the 737 work this way?).
The overall range of a stabilizer's movement is usually the same
regardelss of trim settings. IOW, you don't usually get more "up" than
full "up".
Neil