Pitch Trim Principles

An airplane will seek the indicated airspeed for which it is trimmed. We might call this the principle of trim, and it is the basis for pitch stability and airplane control. If you understand this basis, you can predict an airplanes response to just about any change in power, control input, autopilot command and even wind shear.

Tom Turner

Tuesday, March 15, 2016 at 12:00 AM ET

Verified

The tailBeaconX weighs just 90 grams, about that of a medium-size tomato. uAvionix

Key Takeaways:

The "principle of trim" dictates that an airplane will seek the indicated airspeed for which it is trimmed, forming the fundamental basis for pitch stability and control.
Trim settings are dynamic and require continuous adjustment across all flight phases (takeoff, climb, cruise, descent, approach) in response to changes in power and aircraft configuration.
Inadequate pilot understanding and response to trim, particularly in critical scenarios like go-arounds, is a leading cause of fatal accidents due to the potential for rapid, uncommanded pitch-up and subsequent stalls if not aggressively counteracted.

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An airplane will seek the indicated airspeed for which it is trimmed. We might call this “the principle of trim,” and it is the basis for pitch stability and airplane control. If you understand this basis, you can predict an airplane’s response to just about any change in power, control input, autopilot command and even wind shear.

We all should know by now to adjust attitude with the pitch control, then trim off the pressure so the elevator stays where you want. But according to the NTSB, the most common fatal crash scenario directly results from inadequate pilot knowledge of and response (or lack of response) to the principle of trim. What is this principle of trim? How can we use this understanding to anticipate airplane control requirements, and to avoid the most frequent cause of fatal accidents?