The back part of the airplane, which most people call the tail is also known
as the empennage. This includes the
vertical stabilizer (sometimes called the fin), the rudder,
the horizontal stabilizer, the elevator and the pointy bit at the
back of the fusilage.
In this picture I want to point out the ground-adjustable rudder trim,
that little triangular tab sticking off the lower trailing edge of the rudder.
It is thin metal and can be curved to one side or the other by bending it
with your fingers. Resist the temptation to straighten it out during the preflight
inspection. It has likely already been bent into a position that helps to
keep your airplane flying straight. How does it work? Imagine that you are
trying to to fly in a straight line but constantly need to apply right rudder
to prevent yaw. Over the life of your airplane, it has developeed a little
asymetry that makes this necessary. So after you land, you bend the
trudder trim tab slightly to the left. On the next flight, airflow over that
tab deflects the rudder slightly to the right, and you no longer have to
hold that right rudder. Of course the associated drag is still there.
You can just barely distinguish the elevator trim tab in this picture.
If you look just aft of the tip of the arrow indicating the elevator, you
can see a dark line that runs horizontally across the elevator. That
is the hinge that attaches the trim tab to the elevator. While you are flying,
you set an attitude using the elevator. Instead of having to physically hold
the elevator in the position you want, you reach over to the trim wheel and
turn it. Turning the trim wheel deflects the trim tab, and when it is
correctly set, air flow over the elevator trim tab pushes the elevator into
exactly the position that you wanted it held. If you apply nose-up trim, the
trim tab moves down, to hold the elevator up. If you apply nose-down trim,
the trim tab moves up to hold the elevator down.
The elevator horn stabilizes your elevator in two ways. One,
it projects up or down into the airstream, making it easier to move the elevator
against the force of air, and two, it is weighted, helping to prevent flutter
of the elevator. You can find similar weights in the ailerons, for the same
The red airplane shown here also has
ground-adjustable aileron trim. I haven't seen it on many airplanes, but in
the picture you can see the tab extending from the trailing edge of the aileron.
If the pilot felt a constant need for right aileron (needing to turn the
yoke to the right), he could bend this tab up slightly before his next flight.
That would deflect this left aileron down, and the right aileron up, correcting
Almost all airplanes have some kind of elevator trim, even if it is just a
friction lock for the elevator control. Larger airplanes have rudder and aileron
trim that is adjustable in flight. Trims may be mechanically, hydraulically
or electrically operated.
This page written 11 November 2003 by Robyn Stewart.
Copyright 2003 Flying Start
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