Flight Control Systems


Cessna-172N Aileron System
Figure 1: Cessna-172N Aileron System


  • Deflection of trailing edge control surfaces, such as the aileron, alters both lift and drag
  • With aileron deflection, there is asymmetrical lift (rolling moment) about the longitudinal axis and drag (adverse yaw)
  • Different types:
    • Cessna 172: Freez type
  • Ailerons cut into the airflow under the wing when raised
  • Used in part to turn the aircraft left and right
  • The yoke manipulates the airfoil through a system of cables and pulleys
  • Always act in an opposing manor
    • Yoke "turns" left: left aileron rises creating downward lift, as the right lowers creating upward lift
    • Yoke "turns" right: right aileron rises creating downward lift, as the left lowers creating upward lift
  • Remember the thumb trick to tell which aileron is up
    • Place your hands on the yoke with your thumbs facing straight up, if you turn left your thumbs are then pointing left, and you will notice the left aileron up, and vice versa if right
  • Aileron trim, if equipped, helps relieve pressure on the yoke on the aileron for rolling

Cessna-172N Rudder System
Figure 2: Cessna-172N Rudder System


  • Rudders create a yawing moment which manipulates the aircraft about the vertical axis
  • This manipulation is commonly referred to a "yaw"
  • The rudder manipulates the airfoil through a system of cables and pulleys
  • In practice, both aileron and rudder control input are used together to turn an aircraft, the ailerons imparting roll
    • This relationship is critical in maintaining coordination or creating a slip
    • Improperly ruddered turns at low speed can precipitate a spin
  • Movement:
    • "Step" on the right rudder pedal: rudder moves right creating a yaw to the right
    • "Step" on the left rudder pedal: rudder moves left creating a yaw to the left

Cessna-172N Elevator System
Figure 3: Cessna-172N Elevator System


  • Creates a pitching moment
  • Manipulate the lateral axis
  • Elevators are attached to the trailing edge of the horizontal stabilizer
  • A stabilator is a combination of both the horizontal stabilizer and the elevator (the entire surface moves)
  • Used to pitch the aircraft up and down by creating a load on the tail
  • The yoke manipulates the airfoil through a system of cables and pulleys
  • Movement:
    • Yoke "pulls" back: elevator raises creating downward lift, raising the nose
    • Yoke "pushes" forward: elevator lowers creating upward lift, lowering the nose

Cessna-172N Elevator Trim System
Figure 4: Cessna-172N Elevator Trim System

Trim Tabs:

  • Trim controls a neutral point, like balancing the aircraft on a pin with unsymmetrical weights

  • Trim tab:
    • Helps relieve pressure on the yoke on the elevator for pitching
    • Controlled through a system of cables and pulleys
    • Anti-servo: moves with control surface
    • Servo: moves opposite the control surface
    • Typically located on the right side of the elevator
      • Trim tab adjusted up: trim tab lowers creating positive lift, lowering the nose
        • This movement is very slight
      • Trim tab adjusted down: trim tab raises creating positive lift, raising the nose
        • This movement is very slight
  • To learn more about how to use the trim tab in flight see the trimming the aircraft


  • Flight Control Failure:
    • Of the two cables that connect any control surface (one for each direction), it is unlikely either, but especially both will fail
    • In the event of such a failure remember the trim is a separate cable and still has functionality
    • Through the combination of trim and one cable, you can conduct an emergency, no flap landing
    • Please read Look, Ma, no elevator! by Barry Schiff for more information

AirGizmos Gust Lock
Figure 5: Gust Locks


  • Some aircraft may have gust locks which must be removed prior to manipulating the controls or risk damage [Figure 5]