Trimming the Aircraft

Introduction:

  • Trimming is one of the most basic skills a pilot must possess
  • Trimming the aircraft allows for the relief of control pressures to stabilize the aircraft
  • It generally does not come easy to most pilots and therefore requires attention and practice

WARNING:
All procedures are GENERALIZED.
Fly the maneuver in accordance with the Pilot Operating Handbook (POH)
and/or current Standard Operating Procedures (SOPs)


Trim Basics:

  • 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
  • This is done either by trim tabs (small movable surfaces on the control surface) or by moving the neutral position of the entire control surface all together
    • Trim tabs are likely to be on the aileron, elevator and rudder
  • Trimming is accomplished by deflecting the tab in the direction opposite to that in which the primary control surface must be held
  • 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
  • Because the trim tabs use airflow to function, trim is a function of speed. Any change in speed results in the need to re-trim the aircraft
  • 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
  • In the pattern, if you have trimmed appropriately, you shouldn't have to use back stick at all, which should also prevent you from exceeding approach speed/on-speed
  • Pitch-Power-Configuration-Trim
  • You are working to trim for an airspeed!
  • If you are changing your airspeed in any way then your trim will be off

Trimming Procedure:

  1. Set and steady your airspeed (can be in a climb, descent, or level)
    • When you change pitch, power, or configuration, wait at least five seconds before you touch the elevator trim
  2. Set the initial trim position by reducing the pressure on the controls
    • If the nose feels heavy, trim nose up
    • If the nose feels light, trim nose down
  3. Take your hands off of the controls
    • If the nose stays level, your trim has been set
    • If the nose wants to go up, you didn't set enough down trim
    • If the nose wants to go down, you didn't set enough up trim
  4. Set the attitude, then trim off the pressure with the appropriate correction
  5. Repeat steps 3 - 4 until the aircraft maintains the desired attitude

Trimming by Control Surface:

  • Rudder trim is the most common on general aviation
    • The rudder is trimmed right for power increases and slower airspeeds
    • Trim the rudder left for power reductions and higher airspeeds
  • Elevator trim:
    • Trim the elevator up for power reductions and slower airspeeds
    • Trim the elevator down for power additions and higher airspeeds
  • 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

Common Errors:

  • Over controlling
  • Trimming when the aircraft's airspeed is changing

Airman Certification Standards:

Airman Certification Standards:

Conclusion:

  • Consider practicing maneuvers on a flight simulator to introduce yourself to maneuvers or knock off rust
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References: