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 constantly seeks the indicated airspeed for which it is trimmed, forming the foundation of pitch stability and control, and allowing pilots to predict its response to various inputs.
Trim settings are dynamic and must be actively managed across all flight phases—takeoff, climb, cruise, and descent—to maintain desired airspeeds, reduce pilot workload, and ensure smooth transitions.
Improper trim management, especially during critical phases like a go-around, is a leading cause of fatal accidents; the high nose-up trim typically set for final approach can cause a dangerous pitch-up upon power application, requiring forceful forward pressure to avoid a stall.

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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?