What It Looks Like

You've probably heard an instructor say, "Trim's your friend." It's a catchy way to remind you to adjust the trim to relieve control forces. When your airplane is properly trimmed, it will maintain the desired airspeed and attitude with minimal control inputs from you, the pilot.

But what if there is no way to adjust trim in flight? For example, most airplanes have a tab, or small control surface, on the trailing edge of the elevator or stabilator that can be adjusted from the cockpit for nose-up, takeoff, and nose-down trim. Many powerful singles (200 hp and up) also have adjustable yaw (rudder) trim to counter the effects of torque and P-factor on takeoff and climb. However, few two- or four-place single-engine airplanes with fixed-pitch propellers have yaw trim that can be adjusted from the cockpit. In place of an adjustable trim tab on the rudder, you'll likely find a fixed trim tab.

A fixed tab can be adjusted, but you have to do it by physically bending the tab to the right or left. Obviously, this has to be done on the ground.

It's a trial-and-error process. Suppose you are in straight-and-level cruise at a steady airspeed and you've adjusted the pitch trim to maintain that airspeed and attitude. If you have to maintain some pressure on one of the rudder pedals to keep the wings level and the ball centered in the inclinometer, it's a good bet that the airplane's rudder is out of trim.

How do you adjust the fixed tab to trim the airplane? Bend it opposite the correction. For example, if the ball is right of center and you have to push on the right rudder pedal to center the ball ("step on the ball"), you would bend the tab to the left to correct the out-of-trim condition. That displaces the rudder to the right in flight; it trims the rudder.

The trick is to bend the tab just the right amount. That's where the trial and error comes into play. Also, you have to decide what phase of flight you are trimming the tab for-takeoff and climb or cruise. It may not be appropriate to adjust the fixed yaw trim tab on a primary trainer for cross-country cruise flight because it spends most of its time in touch and goes and maneuvering. On the other hand, a four-place single flown primarily on trips should probably not be trimmed for the takeoff and climb phases. Decide what the primary use of the airplane is, and adjust the trim accordingly over several flights.

Always consult your instructor or the fixed-base operator's mechanic before adjusting a fixed trim tab on a rental airplane. There may be a good reason why it should not be changed from its present position. Even if the tab does need to be adjusted, chances are that the airplane's owner won't want you to take this task upon yourself.