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The Gyroscopic Instruments

The gyroscopic instrument family is so named because the instruments are powered by gyroscopes. Gyroscopes are very similar to the spinning tops you played with as a child. The high rate of rotation of the spinning mass causes it to resist changes in axis of motion. A gyroscope is placed inside each of the instruments, and the airplane literally moves around the spinning gyro while the gyro remains stationary. This allows the airplane to be bumped, change bank or pitch, or go through turbulence without upsetting the correct information displayed on these instruments.

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climbing turn to the right

The attitude indicator is the most important member of the gyroscopic instrument family. It displays the attitude of the aircraft in relation to the earth’s horizon, thus showing bank and pitch information. It is sometimes called an artificial horizon. During your first few hours of flight training you will learn to use the nose of the aircraft and its relationship to the horizon to correctly enter and stay in turns, keep the aircraft straight and level, and makes climbs and descents. During most flight you will use these outside references, rather than internal instruments, to correctly fly the aircraft. You will, however, learn to use the attitude indicator and other instruments, to verify the precision of your flying. And when you lose outside visual references due to clouds or reduced visibility, you will learn to fly the airplane correctly with reference to internal instruments.

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The heading indicator is the chief direction instrument for the aircraft. It is sometimes called the directional gyro, or DG. Due to the many errors in the aircraft magnetic compass, the heading indicator’s use of a gyroscope allows it to maintain directional accuracy over time.

Gyroscopes also have one major drawback: they exhibit a physical principle called precession. It is impossible to completely maintain a gyroscope in a frictionless environment. Whenever an airplane changes pitch or direction, friction acts on the gyro by applying a force approximately 90 degrees ahead of the direction of rotation. These forces are small, but still lead to minor erroneous indications that increase over time.

Due to precession, it is important to recheck the heading indicator against the magnetic compass every 15 minutes or so. This should be rechecked only in straight and level flight.

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The turn and bank indicator is the third member of the gyroscope family. It utilizes a gyroscope to indicate rate of turn and can also be used as a secondary instrument to indicate bank. A turn and slip indicator uses a needle to indicate full rate or half rate turns, while the turn and bank or turn coordinator utilizes a miniature airplane to indicate this information.

Placing the needle or miniature airplane on the left or right marking will indicate a standard rate turn. A standard rate turn is defined as a two-minute turn 360-degree turn. In other words, for every minute, the aircraft will turn through 180 degrees, or half of a complete circle. A half standard rate turn only turns through 180 degrees in two minutes.

Why is the rate of turn information important? During your later instrument rating training, air traffic control you expect you to complete most of your turning maneuvers at standard rate.

The inclinometer is a non-gyroscopic indicator usually contained in the turn coordinator or turn and slip indicator. The inclinometer is simply a ball contained in colorless fluid similar to the leveling tools utilized by carpenters. It allows you to make sure that the airplane’s vertical axis is correctly aligned with the other axes of the aircraft. If the rudder is not applied correctly in turns or other flight, the airplane can skid or slip, placing the vertical axis out of alignment. By using the rudders to center the ball on the inclinometer, coordinated flight is assured. The inclinometer will help you gain a correct feel for the airplane as you are learning to make smooth, coordinated maneuvers.