Aircraft Turns

Introduction:

  • By referencing the lift discussion, lift is perpendicular to the relative wind
  • When an aircraft is placed in a bank the resultant lift (the lift we talk about being perpendicular) is split between a vertical and horizontal component
  • The equal and opposite reaction to this side-ward force is centrifugal force, which is merely an apparent force as a result of inertia
  • The relationship between the aircraft's speed and bank angle determine the rate and radius of turns
  • Any time ailerons are used, adverse yaw is produced
  • Used to change the heading or direction
  • Ailerons bank the wings to determine the rate of turn
  • The elevator moves the nose of the airplane up or down to set the pitch
  • Throttle provides thrust which may be used for airspeed
  • Rudder does not turn the airplane
  • Rudder offsets any yaw effects developed by the other controls
  • Three types of turns:
    • Shallow (less than 20°)
    • Medium (20° to 45°)
    • Steep (45° or more)
  • Keep in mind turn performance principles:

Turn Aerodynamics:

  • Changing the direction of lift causes a turn
  • Lift is a resultant of the horizontal and vertical component
  • As horizontal lift increases vertical lift decreases requiring additional rudder pressure to keep the aircraft level
  • Rudder pressure counteracts adverse yaw
  • Rudder partially initiates and controls coordination
  • Airspeed bank, and radius of turn
  • Note the turn coordinator is not necessarily accurate when rolling into and out of the turn
    • Inertia will cause the ball to lag
    • Any imperfections rolling into the turn will amplify this lag

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


Instrument Flying Handbook. Figure 2-13, Forces In a Turn
Instrument Flying Handbook,
Forces In a Turn

Standard-Rate Turns:

  • Calculating Angle of Bank:

    • Standard rate turns of 3 degrees per second will require different angles of bank depending on true airspeed (faster need more, slower needs less)
    • Rule of thumb: 15% of true airspeed is about the bank angle necessary to achieve a standard rate turn

  • Entry:

    • Apply coordinated aileron and rudder pressures in the desired direction of turn
    • Use attitude indicator to establish the approximate angle of bank
    • Check the turn coordinator for coordination and rate of turn
    • Once established, the turn coordinator becomes the primary bank and the attitude now supports
    • During roll in, monitor altimeter, VSI and attitude for pitch adjustments due to loss of vertical lift
    • Airspeed becomes primary for power for constant airspeeds

  • Recovery:

    • Apply coordinated aileron and rudder opposite turn
    • Anticipate roll-out
    • Roll-out half of the bank angle before the desired heading
    • Attitude becomes primary bank while the airplane levels
    • The heading indicator becomes primary bank once established

  • Standard-Rate Turn Considerations:

    • The turn coordinator is a performance, not control instrument
      • Performance indicators display if you've achieved the desired result, but should not be referenced to control it
    • The attitude indicator is the control instrument

Magnetic Compass Turns:

  • There are a number of errors associated with using the magnetic compass to perform turns

  • If on a North heading, turning east or west, the compass indicates a lag, or shows a turn in the opposite direction initially
  • If on a South heading, turning east or west, the compass precedes the turn
  • When on an East or West heading, the compass indicates correctly in a turn in either direction
  • When on an East or West heading, accelerations result in a brief North indication
  • When on an East or West heading, decelerations result in a brief South indication
  • When on a North or South heading, no error results from diving, climbing, or changing airspeed

  • ANDS: Accelerate North, Decelerate South
  • UNOS: Undershoot North, Overshoot South

  • Magnetic Compass Turns Procedure:

    • Determine the latitude in which the aircraft is operating
      • Magnetic compass turning errors are approximately equivalent to the airplane's latitude
    • Estimate the amount of northerly turning error that corresponds to the heading to be flown
    • Enter a standard rate turn in the appropriate direction
      • When rolling out to the north, lead the roll-out by your current latitude + half the bank angle
      • When rolling out to the south, pass the roll-out by your current latitude + half the bank angle
  • An alternative, or "cheat," to determining your under or overshoot is to execute a timed turn
  • Example: The geographic coordinates of the airport are shown at the bottom-center of the approach plate, indicating a latitude of nearly 40 degrees North (rounded from 39o56'). This represents the maximum magnitude of the turning error. Therefore, the turning error ranges from zero on an easterly or westerly heading to 40 degrees on a northerly or southerly heading, resulting in an angular error of 40 degrees of latitude / 90 = 0.44 degrees of error per degree of turn. The final approach course of 054 is 36 degrees north of east, giving it a turning error of 36 * 0.44 = 15.84 degrees, which we'll just round to 16 degrees. You would then need to undershoot your turn from the course reversal to the final approach course by 16 degrees, giving you an apparent compass heading on rollout of 070

Timed Turns:

  • Through the use of the clock and the turn coordinator, changes in heading can be made in as degrees over time
  • If using standard rate turn:
    • 30° = 10 seconds
    • 45° = 15 seconds
    • 90° = 30 seconds
    • 180° = 1 minutes
    • 360° = 2 minutes

Steep Turns:

  • Any turn greater than standard-rate can be considered a steep turn
  • Enter exactly as you do a shallower turn but cross-check more rapid as the turn steepens

Climbing and Descending Turns:

  • Combine the technique used in straight climbs and descents with the various turn techniques

Level Turns:

  • Level Turns Procedure:

    • Perform clearing turns
    • Pick a reference point or heading
      • The farther the better to prevent movement
      • Be sure to be sitting "normal" when picking a point
      • This point should not move in your "picture"
    • Slowly turn toward desired point or heading
      • To establish the desired angle of bank, the pilot should use outside visual reference points as well as the attitude indicator
      • The horizon should "cut" the cowling in a specific place when in the level turn, this can be referenced by rivets or where the horizon crosses the instrument panel
      • The cowling gives some indication as well as the attitude indicator of bank angle, the turn coordinator does not
      • Avoid overbanking
      • Set the pitch to minimize descent
      • Set the pitch to minimize descent
      • Apply rudder as necessary to remain coordinated
      • Scan instruments
    • Roll out turn on point or heading
      • Level out by the coordinated use of the ailerons and rudder applied in the opposite direction of the turn
      • Roll out half your bank angle ahead of the desired heading
      • Example: 30° means roll out should begin 15° ahead of the desired heading
    • Complete cruise checklist
    PITCH BANK POWER
    Primary Altimeter Turn Coordinator Airspeed Indicator
    Supporting Attitude / VSI Attitude MP and/or RPM

Change of Airspeed in Turns:

  • The angle of bank necessary for a given rate of turn is proportional to the true airspeed
  • Changes in airspeed mean the angle of bank must be varied to maintain constant rate of turn
  • Airspeed decreases, angle of bank decreases and pitch increases
  • Airspeed increases, angle of bank increase and pitch decrease
  • Altimeter is primary for pitch
  • Turn coordinator is primary for bank
  • Manifold pressure and tachometer is primary for power
  • Two methods to practice:
    • Airspeed is changed after the turn is established
    • The airspeed change is initiated simultaneously with the turn entry

Control-Performance Method:

  • Control instruments are the instruments that control an action while performance instruments measure what you've done
  • For turns, the control instrument is the Attitude Indicator while the performance instrument is the Turn Indicator
  • Start by turning to the desired bank angle with the attitude indicator, the control instrument
  • Next, reference the performance instrument to determine if the desired performance has been achieved
  • If not, return to the control instrument to make adjustments
    • If less than standard rate, increase bank angle
    • If more than standard rate, decrease bank angle
  • Return to the performance instrument after each refinement
  • Flying solely by the performance instrument will cause the pilot to chase the performance, lagging indicators

Common Errors:

  • Failure to adequately clear the area, as appropriate
  • Attempting to execute the turn solely by instrument reference
  • Attempting to sit up straight, in relation to the ground, during a turn, rather than riding with the airplane
  • Insufficient feel for the airplane as evident by the inability to detect slip/skids without reference to flight instruments
  • Attempting to maintain a constant bank angle by referencing the cant of the airplane's nose
  • Fixating on the nose reference while excluding wingtip reference
  • Ground Shyness: making "flat turns" (skidding) while operating at low altitudes in a conscious or sub-conscious effort to avoid banking close to the ground
  • Holding rudder in the turn
  • Gaining proficiency in turns in only one direction (usually left)
  • Failure to coordinate the use of throttle with other controls
  • Altitude gain/loss during the turn
  • Pitch:
    • Preoccupation with bank control during turn entry and recovery
      • If bank control pressure and rate of bank change are consistent, a sense of the time required for an attitude change will be developed
    • Failure to understand or remember the need for changing the pitch attitude as the vertical lift component changes, resulting in consistent loss of altitude during entries
    • Changing the pitch attitude before it is necessary
    • Over-controlling the pitch changes
    • Failure to properly adjust the pitch attitude as the vertical lift component increases during the roll-out, resulting in consistent gain in altitude on recovery to headings
    • Failure to turn during turn entry and following turn recovery
    • Failure to maintain straight-and-level cross-check after roll-out
    • Erratic rates of bank change on entry and recovery, resulting from failure to cross-check the pitch instruments with a consistent technique appropriate to the changes in lift
  • Bank:
    • Over-controlling, resulting in overbanking upon turn entry, overshooting and undershooting headings, as well as aggravated pitch, airspeed, and trim errors
    • Fixation on a single bank instrument
    • Failure to check for precession of the horizon bar following recovery from a turn
      • If the heading indicator shows a change in heading when the attitude indicator shows level flight, the airplane is turning
      • If the ball is centered, the attitude gyro has precessed; if the ball is not centered, the airplane may be in a slipping or skidding turn
    • Failure to use the proper degree of bank for the amount of heading change desired
    • Failure to remember the heading to which the aircraft is being turned
    • Turning in the wrong direction due to misreading or misinterpreting the heading indicator or to confusion regarding the location of points on the compass
  • Power:
    • Failure to cross-check the airspeed indicator as pitch changes are made
    • Erratic use of power control due to either improper throttle friction, inaccurate settings, changing the airspeed, abrupt over-controlled pitch and bank changes, or failure to recheck the airspeed to note the effect of a power adjustment
    • Poor coordination of throttle control with pitch and bank changes
  • Trim:
    • Failure to recognize the need for a trim change
    • Failure to understand the relationship between trim and attitude/power changes
    • Chasing the vertical speed needle
  • Compass Turns:
    • Faulty understanding or computation of lead and lag
    • Fixation on the compass during the roll-out
  • Standard-Rate Turns:
    • Controlling angle of bank with turn coordinator

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: