Trimming The Aircraft

• Trim refers to employing adjustable aerodynamic devices on the aircraft to adjust forces so the pilot does not have to manually hold pressure on the controls
• Depending on the airplane, trim may use a tab, an adjustable stabilizer, a spring or bungee system, or another approved mechanism.
  • Pitch trim is common; rudder or aileron trim may or may not be installed. Verify the actual system in the POH or AFM.
• A conventional trim tab generally moves opposite the associated primary surface, but servo tabs, anti-servo tabs, stabilizer trim, and spring systems operate differently.
• The force of the airflow striking the tab causes the main control surface to be deflected to a position that corrects the unbalanced condition of the aircraft
• Airspeed changes alter aerodynamic control forces and commonly require retrimming; the amount and direction depend on aircraft design, power, configuration, and loading.
• An aircraft properly trimmed in pitch seeks to return to the original speed before the change due to its stability.
• Trimming is a constant task as soon as you change any power setting, airspeed, altitude, or configuration
• Proper trimming decreases pilot workload allowing for attention to be diverted elsewhere, especially important for instrument flying
• Proper trim reduces steady force in the pattern, but the pilot must continue using the primary controls to maintain the desired attitude, airspeed, and flight path.
• Use the sequence control, power, configuration, then trim: establish the desired condition first and trim off the remaining sustained pressure.

1. Set and steady your airspeed (can be in a climb, descent, or level)
   • After changing pitch, power, or configuration, maintain the desired condition with the primary controls and allow the response to develop as appropriate before trimming off sustained pressure; there is no universal five-second rule.
2. Set trim by gradually reducing the sustained control force while continuing to maintain the desired flight path with the primary controls.
   • If the nose feels heavy, trim nose-up.
   • If the nose feels light, trim nose-down.
3. Reduce pressure on the controls, possibly by momentarily releasing the control yoke.
   • If the nose remains level, the trim is properly set.
   • If the nose rises, add nose-down trim;
   • if it falls, add nose-up trim.
4. Set the attitude, then trim off the pressure with the appropriate correction
   • Small applications of trim make large changes in the pitch attitude.
     • Be patient and make multiple changes to trim, if necessary.
5. Repeat steps 3 - 4 until the aircraft maintains the desired attitude
   • Once the aircraft is in trim, relax on the control yoke as much as practicable.
     • When pressure is held on the yoke, unconscious pressures are applied to the elevator and ailerons, which displaces the aircraft from its desired flightpath.
     • Proper trim should leave little sustained control force, but it is not an altitude-hold system and does not relieve the pilot of continuous monitoring and control.

• Installed trim systems vary by airplane.
  • When rudder trim is installed, set it to relieve the sustained rudder force required for coordinated flight; direction and amount are aircraft- and condition-specific.
• Elevator trim:
  • Use the primary pitch control to establish the desired attitude and airspeed, then apply the installed pitch-trim system in the direction that relieves the sustained force.
• Aileron:
  • Used as required to level an aircraft
• Trim Tabs:
  • A servo trim tab moves opposite of the surface it is trimming
  • An anti-servo trim tab moves with the surface it is trimming

General Common Errors

• Overcontrolling with large or rapid trim adjustments.
  • Make small trim changes to relieve the pressure you are already holding.
    • Observe the response before adding more trim so the airplane does not begin an unwanted pitch or bank change.
• Using trim to fly the airplane instead of first establishing the desired attitude with the primary controls.
  • Establish and hold the flight condition with the primary controls before trimming.
    • Use trim to remove sustained pressure, not to command the maneuver.
• Making repeated trim adjustments before attitude and airspeed stabilize.
  • Stabilize the desired attitude and airspeed before trimming off the remaining pressure.
    • Avoid chasing an airspeed trend with repeated trim inputs.
• Neglecting trim after a sustained change in power, airspeed, or configuration.
  • Reassess control pressure after the new flight condition is established.
    • Relieve sustained forces while maintaining the desired flightpath.
• Using an unfamiliar trim control in the wrong direction or without understanding its effect.
  • Identify each installed trim control and its direction of operation before flight.
    • Follow the aircraft procedure for the available trim axes and verify the response to a small input.
• Carrying an unrecognized out-of-trim condition through an automation change.
  • Anticipate control forces when changing automation or taking manual control.
    • Hold the required attitude with the flight controls and follow the aircraft procedure to restore appropriate trim.

Instrument Flight Common Errors

• Chasing vertical-speed indications with trim.
  • Use the instrument cross-check to establish a measured attitude correction first.
    • Allow the performance indications to respond, then trim only the sustained pressure needed for the stabilized condition.
• Allowing the instrument scan to deteriorate while adjusting trim.
  • Continue checking attitude, altitude, heading, and airspeed while trimming.
    • Slow the task down if trim adjustments begin to distract from aircraft control.

• Airman Certification Standards.