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Pilot's Handbook of Aeronautical Knowledge
Flight Instruments
Gyroscopic Flight Instruments

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Pilot's Handbook of Aeronautical Knowledge



Table of Contents

Chapter 1, Introduction To Flying
Chapter 2, Aircraft Structure
Chapter 3, Principles of Flight
Chapter 4, Aerodynamics of Flight
Chapter 5, Flight Controls
Chapter 6, Aircraft Systems
Chapter 7, Flight Instruments
Chapter 8, Flight Manuals and Other Documents
Chapter 9, Weight and Balance
Chapter 10, Aircraft Performance
Chapter 11, Weather Theory
Chapter 12, Aviation Weather Services
Chapter 13, Airport Operation
Chapter 14, Airspace
Chapter 15, Navigation
Chapter 16, Aeromedical Factors
Chapter 17, Aeronautical Decision Making




The turn coordinator can be used to establish and maintain
a standard-rate turn by aligning the wing of the miniature
aircraft with the turn index. Figure 7-22 shows a picture of a
turn coordinator. There are two marks on each side (left and
right) of the face of the instrument. The first mark is used to
reference a wings level zero rate of turn. The second mark
on the left and right side of the instrument serve to indicate
a standard rate of turn. A standard-rate turn is defined as a
turn rate of 3° per second. The turn coordinator indicates only
the rate and direction of turn; it does not display a specific
angle of bank.

If inadequate right rudder is applied in a right turn, a slip results. Too much right rudder causes the aircraft to skid through the turn. Centering the ball results in a coordinated turn.
Figure 7-22. If inadequate right rudder is applied in a right turn, a
slip results. Too much right rudder causes the aircraft to skid through
the turn. Centering the ball results in a coordinated turn.

The inclinometer is used to depict aircraft yaw, which is
the side-to-side movement of the aircraft's nose. During
coordinated, straight-and-level flight, the force of gravity
causes the ball to rest in the lowest part of the tube, centered
between the reference lines. Coordinated flight is maintained
by keeping the ball centered. If the ball is not centered, it can
be centered by using the rudder.

To center the ball, apply rudder pressure on the side to which
the ball is deflected Use the simple rule, "step on the ball," to
remember which rudder pedal to press. If aileron and rudder
are coordinated during a turn, the ball remains centered in the
tube. If aerodynamic forces are unbalanced, the ball moves
away from the center of the tube. As shown in Figure 7-22, in
a slip, the rate of turn is too slow for the angle of bank, and
the ball moves to the inside of the turn. In a skid, the rate of
turn is too great for the angle of bank, and the ball moves
to the outside of the turn. To correct for these conditions,
and improve the quality of the turn, remember to "step on
the ball." Varying the angle of bank can also help restore
coordinated flight from a slip or skid. To correct for a slip,
decrease bank and/or increase the rate of turn. To correct for
a skid, increase the bank and/or decrease the rate of turn.

Yaw String
One additional tool which can be added to the aircraft is a
yaw string. A yaw string is simply a string or piece of yarn
attached to the center of the wind screen. When in coordinated
flight, the string trails straight back over the top of the wind
screen. When the aircraft is either slipping or skidding,
the yaw string moves to the right or left depending on the
direction of slip or skid.

Instrument Check
During the preflight, check to see that the inclinometer is
full of fluid and has no air bubbles. The ball should also be
resting at its lowest point. When taxiing, the turn coordinator
should indicate a turn in the correct direction while the ball
moves opposite the direction of the turn.

Attitude Indicator
The attitude indicator, with its miniature aircraft and horizon
bar, displays a picture of the attitude of the aircraft. The
relationship of the miniature aircraft to the horizon bar is
the same as the relationship of the real aircraft to the actual
horizon. The instrument gives an instantaneous indication of
even the smallest changes in attitude.

The gyro in the attitude indicator is mounted in a horizontal
plane and depends upon rigidity in space for its operation.
The horizon bar represents the true horizon. This bar is
.xed to the gyro and remains in a horizontal plane as the
aircraft is pitched or banked about its lateral or longitudinal
axis, indicating the attitude of the aircraft relative to the true
horizon. [Figure 7-23]

The gyro spins in the horizontal plane and resists deflection of
the rotational path. Since the gyro relies on rigidity in space,
the aircraft actually rotates around the spinning gyro.
An adjustment knob is provided with which the pilot may
move the miniature aircraft up or down to align the miniature
aircraft with the horizon bar to suit the pilot's line of vision.
Normally, the miniature aircraft is adjusted so that the wings
overlap the horizon bar when the aircraft is in straight and level
cruising flight.