FAA Flight Instructor Airplane (FIA)Aerodynamics and Principles of FlightEasy
A student pilot asks a CFI about the primary aerodynamic function of a trim tab mounted on the trailing edge of the elevator. Which statement best describes it?
- AIt serves as the primary control surface for pitch changes during normal maneuvering
- BIt acts as a spoiler on the elevator, reducing tail-down force during cruise flight
- CIt creates an aerodynamic force that holds the main control surface in a desired position without requiring continuous pilot pressure
- DIt increases the effective camber of the wing to generate additional lift at low airspeeds
Show answer & explanationAnswer & explanation
Correct answer: C. It creates an aerodynamic force that holds the main control surface in a desired position without requiring continuous pilot pressure
A trim tab is a small auxiliary control surface that, when deflected, creates an aerodynamic force that holds the primary control surface (such as the elevator) in the desired position, relieving the pilot of the need to hold continuous control pressure.
Why the other options are wrong
- A. Wrong — the elevator itself, not the trim tab, is the primary pitch control surface
- B. Wrong — trim tabs are not spoilers and do not function that way
- D. Wrong — trim tabs act on control surfaces, not the wing's camber
Trim Tab
A small movable surface on a control surface's trailing edge that aerodynamically holds the control surface in a set position, relieving pilot control pressure.
- Deflects opposite the desired control surface movement to hold position
- Reduces pilot workload without acting as primary flight control
- Other tab types include servo, balance, and anti-servo tabs
Memory trick: A trim tab is a tiny helper holding the big surface steady so your arm can rest