Parts of the Aircraft

Empennage

The back part of the airplane, which most people call the tail is also known as the empennage.C150 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 reason.

trailing edge of C150 wingThe 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 the problem.

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 Initiatives

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Cessna 150 head on

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