Aviation Notes – Jim's

January 16, 2008

2A- Flight Instrument Systems

Filed under: — jcramer @ 11:39 pm

Gyroscopic Instruments

  • Preflight testing of gyro instruments:
    • Attitude Indicator -max 5º of bank during taxi turns
    • Heading Indicator – aligned with compass
  • Gyro procession most pronounced when rolling out of 180º turn, on attitude indicator.
  • Turn coordinator show a ‘standard rate’ turn of 3º per second or 360º in 2 minutes (and it also displays rate of roll; indirectly it displays the bank attitude).
  • Inclinometer measures the balance between centrifugal force (CF) and horizontal component of lift (HCL).  “Step on the ball”

Turn Coordinator

  • During taxi turns, turn coordinator should show a turn in the correct direction, while the ball should go the opposite way.
  • Compass:Compass Roll
    • Magnetic dip causes the most significant compass errors.
    • No compensation needed when turning to East or West headings.
    • When turning from a North heading, the compass will initially indicate a turn int he opposite direction.
    • Roll out early when turning to North headings.
    • When turning from a South heading, the compass will turn properly, but will lead the turn.
    • Turn past South headings when turning toward them.
  • Pitot Static Instruments:
    • Air speed indicator, altitude indicator, and vertical air speed indicator.
    • Va is not marked on the air speed indicator.
    • If pitot and drain hole are blocked and static is open, air speed indicator becomes an altitude indicator.
    • Use of alternate static source will cause:
      • Altimeter to read higher
      • Air speed indicator to read faster
      • VSI to read a climb
  • Altimeter indicates a higher altitude when turned to a higher setting, and a lower altitude when turned to a lower setting.
  • “When flying from a high to a lowtemperature, or hot to cold, look out below.”  The altimeter measures the number of air molecules between the plane and the ground.  When air is colder, the air is more dense and the altimeter indicates a lower altitude.
  • When using flight levels, such as FL210, you are referring to pressure altitudes.  Above 18,000′, altimeters are set at 29.92.
  • Setting your altimeter to 29.92 will give you pressure altitude.
  • Altimeter: Altimeter
    • Thin red with triangle tip is 10,000′ increments.
    • Short, thick hand shows 1,000′ increments.
    • Long, thing hand shows 100; increments.
    • NOTE: This altimeter shows just over 12,000′.
  • During a skidding turn to the right, the centrifugal force is greater than the horizontal lift and the load factor is increased.

Skidding Turn-A

Skidding Turn-B

  • In a coordinated turn, the turning force and the centrifugal forces are exactly balanced and the ball is centered.

Coordinated Turn

  • In a slipping turn there is not enough centrifugal force to balance the turning force.

Slipping Turn-A

Slipping Turn-B

  • The mini plane on the attitude indicator will show a turn int he opposite direction when rolling out from a 180º skidding turn to straight-and-level coordinated flight.
  • A mach meter presents the ratio of the plane TAS to the speed of sound.
  • Pre-take off check of heading indicator: after 5 minutes, set the indicator to the magnetic heading of the plane and check for proper alignment after taxi turns.
  • One characteristic that a properly functioning gyro depends upon for operation is the resistance to deflection of the spinning wheel or disc.
  • Use the local altimeter setting to better vertically separate from other aircraft.
  • At constant power and indicated altitude, an ↑ in temperature will increase both TAS and true altitude.  You get higher TAS in warmer, thinner air because of less parasitic drag.
  • The displacement of a turn coordinator during a constant turn will increase as angle of bank increases.  The turn coordinator indicates the rate of turn, which ↑’s with bank and ↓’s with higher speed.
  • Pressure altitude is the altitude read on your altimeter when the instrument is adjusted to indicate height above the standard datum plane.

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