DONE 3D Airplane Systems - Gyroscopic Flight Instruments

Question 0

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1. Which instruments contain gyroscopes? (FAA-H-8083-25)

Answer 0

The most common instruments containing gyroscopes are the turn coordinator, heading indicator, and attitude indicator.

Question 1

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2. What are the two fundamental properties of a gyroscope? (FAA-H-8083-25)

Answer 1

Rigidity in space—A gyroscope remains in a fixed position in the plane in which it is spinning.
Precession—The tilting or turning of a gyro in response to a deflective force. The reaction to this force does not occur at the point where it was applied; it occurs at a point 90° later in the direction of rotation. The rate at which the gyro precesses is inversely proportional to the speed of the rotor and proportional to the deflective force.

Question 2

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3. What are the various sources that may be used to power the gyroscopic instruments in an airplane? (FAA-H-8083-25)

Answer 2

In some airplanes, all the gyros are vacuum, pressure, or electrically operated; in others, vacuum or pressure systems provide the power for the heading and attitude indicators, while the electrical system provides the power for the turn coordinator. Most airplanes have at least two sources of power to ensure at least one source of bank information if one power source fails.

Question 3

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4. How does the vacuum system operate? (FAA-H-8083-25)

Answer 3

Air is drawn into the vacuum system by the engine-driven vacuum pump. It first goes through a filter, which prevents foreign matter from entering the vacuum or pressure system. The air then moves through the attitude and heading indicators, where it causes the gyros to spin. A relief valve prevents the vacuum pressure, or suction, from exceeding prescribed limits. After that, the air is expelled overboard or used in other systems, such as for inflating pneumatic deicing boots.

Question 4

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5. How does the attitude indicator work? (FAA-H-8083-25)

Answer 4

The attitude indicator’s gyro is mounted on a horizontal plane (a bar representing true horizon) and depends upon rigidity in space for its operation. The fixed gyro remains in a horizontal plane as the airplane is pitched or banked about its axis, indicating the attitude of the airplane relative to the true horizon.

Question 5

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6. Discuss the limits of an attitude indicator. (FAA-H-8083-25)

Answer 5

Pitch and bank limits depend upon the make and model of the instrument. Limits in the banking plane are usually from 100°–110°, pitch limits are usually from 60°–70°. If either limit is exceeded, the instrument will tumble or spill giving incorrect indications until reset. Some modern attitude indicators will not tumble.

Question 6

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7. The attitude indicator is subject to what errors? (FAA-H-8083-15)

Answer 6

Attitude indicators are free from most errors, but depending on the speed with which the erection system functions, there may be a slight nose-up indication during a rapid acceleration and a nose-down indication during a rapid deceleration. There is also a possibility of a small bank angle and pitch error after a 180° turn. These inherent errors are small and correct themselves within a minute or so after returning to straight-and-level flight.

Question 7

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8. How does the heading indicator operate? (FAA-H-8083-25)

Answer 7

It uses the principle of rigidity in space; the rotor turns in a vertical plane, and the compass card is fixed to the rotor. Since the rotor remains rigid in space, the points on the card hold the same position in space relative to the vertical plane. As the instrument case and the airplane revolve around the vertical axis, the card shows clear, accurate heading information.

Question 8

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9. What are the limitations of the heading indicator? (FAA-H-8083-25)

Answer 8

Pitch and bank limits vary with design and make of instrument. On some light airplanes, the limits are about 55° of pitch and 55° of bank. When either is exceeded, the instrument “tumbles” or “spills” giving incorrect indications until reset with the caging knob. Some modern instruments are designed in such a manner that they will not tumble.

Question 9

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10. What error is the heading indicator subject to? (FAA-H-8083-25, FAA-P-8740-16)

Answer 9

Because of precession, caused chiefly by friction, the heading indicator will creep or drift from a heading to which it is set. Among other factors, the amount of drift depends upon the condition of the instrument. The heading indicator may indicate as much as 15 degrees of error per every hour of operation.

Question 10

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11. How does the turn coordinator operate? (FAA-H-8083-25)

Answer 10

The turn part of the instrument uses precession to indicate direction and approximate rate of turn. A gyro reacts by trying to move in reaction to the force applied thus moving the needle or miniature aircraft in proportion to the rate of turn. The slip/skid indicator is a liquid-filled tube with a ball that reacts to centrifugal force and gravity.

Question 11

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12. What information does the turn coordinator provide? (FAA-H-8083-25)

Answer 11

It shows the yaw and roll of the aircraft around the vertical and longitudinal axes. The miniature airplane indicates direction of the turn as well as rate of turn. When aligned with the turn index, it represents a standard rate of turn of 3° per second. The inclinometer of the turn coordinator indicates the coordination of aileron and rudder. The ball indicates whether the airplane is in coordinated flight or is in a slip or skid.

Question 12

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13. What will the turn indicator indicate when the aircraft is in a skidding or a slipping turn? (FAA-H-8083-25)

Answer 12

Skid—The ball in the tube will be to the outside of the turn; too much rate of turn for the amount of bank.
Slip—The ball in the tube will be on the inside of the turn; not enough rate of turn for the amount of bank.