Trimming and Control Forces

081-05-08Pablo Asensio Martínez2026-04-011 min

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.
Written and reviewed by

Pablo Asensio · 2026-04-01

Aeronautical engineer. Passed the thirteen EASA ATPL(A) theoretical knowledge exams studying from these very notes. Writes and reviews each topic against the Part-FCL Learning Objectives.

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