Flight Instruments

Question 1

Which instruments have gyroscopes?

Answer 1

• Attitude Indicator
• Heading Indicator
• Turn Coordinator

Question 2

How are the gyroscopic flight instruments (AI, DG, TC) powered?

Answer 2

• AI & DG are powered by the vacuum system
• TC is powered by electricity

Question 3

Describe how the attitude indicator instrument works in regards to the gyro, and how it’s mounted?

Answer 3

• Vacuum system forces air into the flight instrument
• Uses rigidity in space principle
• Gyro spins on a vertical axis and attached to gimbals that allows the airplane to roll and pitch, giving accurate level flight information on the instrument

Question 4

What gyroscopic principle does the attitude indicator & heading indicator use?

Answer 4

Rigidity in space

Question 5

What gyroscopic principle does the turn coordinator use?

Answer 5

Gyroscopic precession

Question 6

What is gyroscopic precession?

Answer 6

The force applied to a gyro is felt 90° in the direction of which the gyro is spinning

Question 7

How does the gyro spin in the heading indicator?

Answer 7

• On its vertical axis (i.e. spins from top to bottom

Question 8

Is the heading indicator north seeking?

Answer 8

• No, so you have to match the heading to the magnetic compass
• Once set, the DG is preferred to use because of the lack of magnetic error the compass has (i.e. ANDS, UNOS, etc.)

Question 9

How are the gimbals mounted on to the gyro on the attitude indicator?

Answer 9

• There’s a pitch & roll gimbal
• This allows the airplane to pitch & roll as the gyro maintains rigid in space

Question 10

What instrument uses pendulous vanes?

Answer 10

• The attitude indicator

Question 11

Describe how the pendulous vanes work:

Answer 11

• Gyro is mounted inside of a rotor case where air bleeds out evenly through ports when the gyro is upright
• The exhaust ports (4 in total) are offset to each other attached by arm linkages
  • As the gyro tilts, more of one port is blocked by the linkage arm, creating a blocked airway and air it still being vented through the opposing air vent creates a force (gyroscopic precession)
  • Due to precession, the force is applied 90° in the direction of the rotation of the gyro forcing it back into its level position and even exhausting air flow is equalized again

Question 12

During taxi, what is the preflight for the turn coordinator?

Answer 12

• The plane should indicate a turn in the correct direction, and the ball in the inclinometer should move in the opposite direction

Question 13

What are some errors that can happen with the attitude indicator?

Answer 13

• Slight nose up or nose down indication with the acceleration or deceleration
• Small bank indication after conducting an 180° turn

Question 14

What is a indicated in the inclinometer:

during a slip?

during a skid?

Answer 14

Skid
- Ball falls to the inside of a turn
- The rate of turn is too much

Skid
- The ball is on the outside of turn
- The bank angle is too shallow

Question 15

How does the turn coordinator gyro function?

Answer 15

• The gyro is mounted canted to allow the instrument to indicate the roll of the a/c
• Uses gyroscopic precession to indicate the rate of turn

Question 16

How is the static port connected to the VSI?

Answer 16

• The diaphragm (aneroid wafer) is connected directly to the static port
• The case is connected to the static port via a calibrated leak

Question 17

Explain how the VSI works:

Answer 17

1. As a/c changes altitude, the aneroid wafer pressure changes immediately due to it being connected directly to the static port
2. The pressure in the case, since it’s calibrated differently is briefly delayed, until the a/c levels, and the pressure equalizes again

Question 18

What information does the VSI display?

Answer 18

• Trend: Shows whether you’re in a climb or descent trend
• Rate: Shows FPM on climb/descent

Question 19

What indications will show on your flight instruments when using the alternate static port?

Answer 19

Due to the venturi effect of airflow around the fuselage, the air pressure outside the flight deck is higher than the pressure inside. This causes the following errors on the pitot static system:

1. Altimeter: Indicates higher than actual alt.
2. ASI: Will indicate faster than actual
3. VSI will show a momentary climb, then read normally