# Trimming and Control Forces

> Purpose of trimming and methods to reduce pilot workload.

- **Subject:** 081 — Principles of Flight
- **Section:** 081-05 — Control
- **Topic code:** 081-05-08
- **Last reviewed:** 2026-04-01
- **Author:** Pablo Asensio Martínez
- **HTML version:** https://pilotsyllabus.com/en/principles-of-flight/control/trimming/

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## Trim Tab
A small surface on the trailing edge of a primary control.
*   **Operation**: Deflects in the **opposite** direction to the control surface.
*   **Effect**: Creates a small aerodynamic force that pushes the main control surface into the desired position, holding it there without pilot effort.
*   **Fixed Trim Tab**: Adjustable only on the ground.
*   **Controllable Trim Tab**: Adjustable by pilot wheel/switch.

## Other Tabs
*   **Balance Tab**: Coupled to move opposite to the main surface automatically. Reduces stick force (Makes control lighter).
*   **Anti-Balance Tab**: Coupled to move in the **same** direction. Increases stick force (Makes control heavier). Used on "all-moving" tailplanes (stabilators) to prevent over-controlling.
*   **Servo Tab**: The pilot controls the TAB, and the tab flies the CONTROL SURFACE. Used on large manual aircraft (e.g., DC-9 rudder) to overcome heavy loads.

## Mass Balance
Weights added ahead of the hinge line (often inside the nose of the control surface).
*   **Purpose**: To bring the Center of Gravity (CG) of the control surface onto or ahead of the Hinge Line.
*   **Prevents Flutter**: High-speed vibration caused by aerodynamic/inertial interaction.

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Free study notes from pilotsyllabus.com. Not a substitute for training at an approved ATO.