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 naturally seeks the indicated airspeed it is trimmed for, forming the foundation of pitch stability and overall control.
Pilots must constantly adjust trim across all flight phases to counteract pitch changes caused by power adjustments or configuration changes (e.g., flaps, landing gear), as these alter airflow over trim tabs.
Failure to correctly manage trim, particularly during critical maneuvers like a go-around where trim is set for slow approach speeds, can lead to dangerous nose-up pitch and stalls, identified as the most common fatal accident scenario.

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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?