4. AIS (Gyroscopic Instruments) in aeronatical.pdf

AIS (Gyroscopic Instruments)

1. AIRCRAFT INSTRUMENT SYSTEM
(AIS)
1

2. Gyroscopic Instruments
•Three of the six Basic instruments utilise a gyroscopic type
of sensing element
•These three instruments are
–Gyro horizon
–Direction/Heading indicator
–Turn and bank indicator
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Gyroscopic
Instrument

3. Gyroscope
Gyroscope
•Essential element for 3 of the basic six instruments as
mentioned earlier as well as remote control systems, auto
piloting and weapon systems
Gyroscope --- Greek words ‘Gyros’ (rotation) and ‘skopos’ (to
observe).
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Gyroscopic
Instrument

4. Gyroscope
Gyroscope
•Why are gyroscopic instruments essential in aircraft
navigation?
•Gyroscopic instruments are of great importance in aircraft
navigation because of its ability to
–Maintain a constant spatial reference and thereby
–Provide indication of aircraft’s attitude with respect to the
earth
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Gyroscopic
Instrument

5. Construction of Gyroscope
Gyroscope Construction
•Gyroscope used in the aircraft instruments comprises of
–Rotor or wheel which spins at high speed
–Rotation is about an axis passing through its centre of mass
•Spin axis
–Rotor is mounted in
concentrically pivoted rings
called gimbals
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Gyroscopic
Instrument

6. Construction of Gyroscope
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Gyroscopic
Instrument
Gyroscope Construction
•The symmetrical rotor spinning rapidly about its axis and free to
rotate about one or more perpendicular axes.
•Freedom of movement about one axis is usually achieved by
mounting the rotor in gimbal, and complete freedom can be
achieved by using two gimbals.

7. Degree of Freedom
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Gyroscopic
Instrument
Gyroscope (Degree of Freedom)
Mounting of the rotor is such that it has
three degrees of freedom
•About an axis perpendicular
through its centre (XX
’
)
✓Spinning freedom
•About a horizontal axis at right
angles to the spin axis (YY
’
)
✓Tilting freedom
•About a vertical axis perpendicular
to both the other axes (ZZ
’
)
✓Veering freedom

8. Degree of Freedom
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Gyroscopic
Instrument
Gyroscope (Degree of Freedom)
•Three degrees of freedom are
obtained by mounting the rotor in
two concentrically pivoted rings
✓Inner and outer rings
•The whole assembly is known as the
gimbal system of a free or space
gyroscope
•In normal operating position, all the
axes are mutually at right angles to
each other and the axes intersect at
centre of gravity of the rotor

9. Gyroscopic Properties
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Gyroscopic
Instrument
Properties of Gyroscope
The system will not exhibit any gyroscopic properties unless the
rotor is spinning
However, when a rotor is rotating at high speed it exhibits two
basic properties
✓Rigidity
✓Precession
Both the properties depend upon the principle of conservation
of angular momentum

10. Gyroscopic Properties
Fundamental Definitions
a. Momentum. Mass x Velocity (m x v)
b. Angular Velocity. Instantaneous linear velocity at the periphery of a circle
divided by the radius of the circle and is normally measured in radians per
second. ω=v/r.
c. AngularMomentum. The angular momentum is the product of the
instantaneous linear momentum (mv) and the radius of rotation. Angular
momentum L = mv x r = mωr
2.

angular momentum is related to angular velocity by L =Iω
d. Moment of Inertia. The moment of inertia of a body is the summation of mr
2.
for
every particle of mass "m". Thus angular momentum of any body can be
expressed as IW.
e. Radius of Gyration. The radius of gyration of a body is that distance from the
axis of rotation at which all the mass of that body can be considered to
act.
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Gyroscopic
Instrument

11. Gyroscopic Properties
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Gyroscopic
Instrument
Rigidity
•Spinning rotor of the gyro has rotational velocity, which results in
angular velocity at any point on the rotor
•Further, since the rotor has mass, the angular velocity produces
angular momentum
•As per Newton’s first law of motion (?)
✓Any moving body tends to continue its motion in a straight line
•In case of a spinning gyroscope there is a moment of inertia about
the spin axis which tends to maintain the plane of rotation of the
gyro
•Consequently, the spin axis of the gyro will hold on to the fixed
direction until acted upon by any external force
This property is known as Rigidity/Rigidity in Space

12. Laws of Gyro Dynamics
Rigidity
•Therefore, Rigidity in Space means that the
rotor of a free gyro always points in the
same direction no matter which way the
base/frame of the gyro is positioned.
•Gyroscopic rigidity depends upon several
design factors: Weight for a given size,
Angular velocity, Bearing friction
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Gyroscopic
Instrument
The First Law of Gyro Dynamics
If a rotating body is so mounted as to be completely free to move
about any axis through the center of mass, then its spin axis remains
fixed in inertial space however much the frame may be displaced.

13. Gyroscopic Properties
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Gyroscopic
Instrument
RIGIDITY IN SPACE

14. Gyroscopic Properties
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Gyroscopic
Instrument
Rigidity
•Since rigidity is product of angular velocity & mass
✓Rigidity of a gyroscope may be increased by increasing either its
angular velocity or mass or both
•How can we increase the angular velocity?
✓Increasing the speed of rotation of the rotor
✓Decreasing the diameter of the rotor
➢Rotor diameter is constraint vis-à-vis the instrument
✓Hence, gyro rotor is made to rotate at a high speed
•Similarly, mass of the rotor is constraint by its size limitations
✓But angular momentum could be improved if the mass is
concentrated at the rim (outer side) of the rotor

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Gyroscopic
Instrument
Precession
Precession is the second important
characteristic of gyroscopes. By applying a
force to the horizontal axis of the gyro, a unique
phenomenon occurs. The applied force is
resisted. Instead of responding to the force by
moving about the horizontal axis, the gyro
moves in response about its vertical axis. Stated
another way, an applied force to the axis of
the spinning gyro does not cause the axis to
tilt. Rather, the gyro responds as though the
force was applied 90° around in the direction
of rotation of the gyro rotor. The gyro rotates
rather than tilts.
Gyroscopic Properties

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Gyroscopic
Instrument
Precession
•Therefore, Precession is defined as the
angular change in direction of the spin
axis when acted upon by an external
force
When an external force is applied about
an axis perpendicular to the axis of spin,
the rotor will move about a third axis
perpendicular to those spin and torque.
The Second Law of Gyro-dynamics
Gyroscopic Properties

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GYROSCOPIC PRECESSION
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Gyroscopic
Instrument

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Gyroscopic
Instrument
Precession
•The rate at which a gyro precesses is dependent upon
✓The magnitude of the applied force
➢Greater the applied force greater will be the rate of
precession
✓Rigidity of the rotor
➢Greater the rigidity of the rotor the slower will be the rate
of precession for a given applied force
•A gyro will continue to precess so long as the applied force is
maintained until the plane of rotation becomes coincident with
that of the force
Gyroscopic Properties

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Gyroscopic
Instrument
Free Gyro
•All gyroscopes must have freedom for the rotor to rotate
and to precess
✓Gyroscopes cannot precess about the axis of rotation
✓But precession may take place about either of the two
axes at right angles to the plane of rotation
•A gyroscope which has freedom to precess about both
these axes is known as free gyro and is said to have two
degrees of freedom of precession
Types of Gyroscope

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Gyroscopic
Instrument
Free Gyro
Such a gyroscope is as shown
•Number of degrees of freedom of
precession is same as the number of
gimbals
•Rotor is mounted in the inner gimbal
which as a whole is mounted on the
outer gimbal
•Thus
✓Rotor spins about XX axis
✓Inner gimbal has freedom of
movement about YY axis and
✓Outer gimbal has freedom of
movement about ZZ axis
Types of Gyroscope

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Gyroscopic
Instrument
Free Gyro
If the frame of the free gyro is fixed to
the instrument panel of an aircraft,
what would have happened?
The aircraft could have pitched, rolled
or even inverted but the spin axis of the
gyroscope would remain aligned with
the same fixed point in space
Types of Gyroscope

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Gyroscopic
Instrument
Tied Gyro
Aircraft instruments that employ gyros provide a
fixed reference, about which the movement is
indicated to the pilot.
•Directional gyro provides the pilot with aircraft
heading information and so its reference axis is
the vertical axis (Yaw axis of aircraft)
✓The gyro rotor should be sensitive to
movement about this axis and no other
axis
•Attitude indicator provides the pilot with
aircraft attitude information with reference to
the pitch and roll axes of the aircraft
✓Thus the gyro rotor should be sensitive to
movement about these axes
Types of Gyroscope

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Gyroscopic
Instrument
Tied Gyro
•Turn indicator provides the pilot with
information to indicate rate of turn
✓Thus the gyro rotor should be sensitive to
movement about the vertical axis
A gyroscope is not sensitive to movement about its
spin axis, so its rotor must be maintained at right
angle to the required axis for maximum sensitivity
In case we require the spin axis of the gyroscope to
be tied to a particular direction, such a gyroscope is
called a tied gyroscope
Types of Gyroscope

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Gyroscopic
Instrument
Tied Gyro
•Movement about normal/vertical axis would
indicate change in heading
•Thus we require a directional gyro to be sensitive
about this axis
•Since we know that gyro is not sensitive about the
spin axis it is clear that a gyro with vertical spin
axis would not be suitable
•Thus we need a gyro which has horizontal spin
axis
Types of Gyroscope
Directional Gyro
Spin axis horizontal
(Yaw ), DG, HI

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Gyroscopic
Instrument
Tied Gyro
•Attitude indicator is required to indicate aircraft
altitude with reference to the aircraft pitch and
roll axes
•Thus we require a directional gyro to be sensitive
about these axes
•Since we know that gyro is not sensitive about the
spin axis it is clear that a gyro with longitudinal
and lateral spin axis would not be suitable
•Thus we need a gyro which has vertical spin axis
Types of Gyroscope
Vertical Gyro
Spin axis vertical
(Pitching and Rolling), AH

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Rate Gyro
•It has modified single degree of
freedom; can only measure rate of
change of angle with time (rather than
indicating direction).
•It uses precession property.
•Used in Turn Indicator. Output is in
Degree/sec.
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Gyroscopic
Instrument
Types of Gyroscope

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Gyroscopic
Instrument
In a Gyroscope, spin axis remains aligned to some point in
space to indicate any angular movement. However, any
deviation of a horizontally aligned spin axis from its point of
reference is known as gyro drift or gyro wander
Gyro drift or wander can be of two types
✓Real drift/wander
✓Apparent drift/wander
Gyroscope Drift

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Gyroscopic
Instrument
Real Drift
Real drift arises due to constructional abnormalities which
leads to physical deviations e.g. it could be due to
•Manufacturing defect or natural wear and tear
•Bearing friction which is always there present in the spin
axis
✓If the friction is symmetrical, it would slow down the
rotor
✓If asymmetrical, it causes the gyro to precess
•Such errors cannot be predicted and hence no
corrections can be applied
Gyroscope Drift

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Gyroscopic
Instrument
Apparent Drift
Apparent drift is due to the earth’s rotation which is also
called “Earth Rate”
≈15° per hour
In this case, the gyro spin axis does not physically
wander away from its pre-set direction
✓But to an observer it appears to have changed its
direction
✓This is because the gyro maintains its direction with
respect to a fixed point in space, whereas the
observer rotates with the earth
✓Thus with passage of time, the gyro appears to
have changed directions with reference to earth
datum
Gyroscope Drift
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Gyroscopic
Instrument
Apparent Drift
Lets assume horizontal spin axis of a gyro is
positioned at North Pole:
•An observer initially at position A observes
the gyro spin axis to be directly in line with
him
•Six hours later, the Earth having rotated
90°, the observer now views the gyro from
position B
•The observer does not however
appreciate his own motion, and the gyro
spin axis appears to have moved
clockwise in the horizontal plane through
90°
Gyroscope Drift
A
B

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Gyroscopic
Instrument
Apparent Drift
•Twelve hours later, the gyro spin axis
appears to have moved through 180°, the
observer now views the gyro from position
C.
•After 24 hours, the observer is back in the
original position, the gyro spin axis appears
as it was when first aligned.
•This apparent motion in the horizontal
plane is known as gyro drift or earth rate
Gyroscope Drift
A
B

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Gyroscopic
Instrument
Apparent Drift
Now if the same gyro is taken to the equator and aligned with
true north it would not suffer at all from apparent drift due to earth
rotation
•Because the earth reference point and space reference point
are in alignment and remain so
•Thus we can see that the rate of apparent drift due to earth
rotation varies with latitude
✓It is maximum at the poles and
✓Nil at the equator
If a horizontal spin axis gyro is at the Poles
•It drifts through 360° in 24 hours (maximum drift)
Thus, Earth rate or Drift at any intermediate latitude will be
15.04° ˣ sin (Latitude°) per hour
Gyroscope Drift
B
❑Earth rate (-)ve in
Northern hemisphere
❑Earth rate (+)ve in
Southern hemisphere

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Gyroscopic
Instrument
•Diagram shows a gyro at the equator, with its spin
axis horizontal to the observer, when viewed at
point A
•After six hours, the Earth having rotated through
90°, the observer at point B will view the gyro as a
vertical axis gyro
•After another six hours, the spin axis again appears
horizontal
•This apparent change of the spin axis in its vertical
plane is known as gyro topple
At equator, gyro topple is 360° in 24 hours. Thus,
Apparent Topple at any intermediate latitude will
be
15.04° ˣ cos (Latitude°) per hour
Gyroscope Topple
A
B
Equator

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Gyroscopic
Instrument
Depending on whether a gyro has a vertical or horizontal spin axis, the
rotation of the earth has a different effect
•Horizontal axis gyro
At poles : max drift & no topple
At equator : no drift & max topple
•Vertical axis gyro
At poles : no drift & no topple
At equator : no drift & max topple
Math:
If a horizontal spin axis gyro is set with its axis aligned in an east/west
direction at latitude 45°N. What would be the attitude of its spin axis
after 3 hours?
Gyroscope Drift &
Topple

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Gyroscopic
Instrument
•This is an additional form of apparent topple/drift, which primarily occurs when
the gyro is placed on a platform, such as aeroplane, and is transported in
easterly/westerly direction at latitudes other than the equator. (i.e. location of
gyro moves but the spin axis remains fixed).
•To an observer on the aircraft, the spin axis of a horizontally aligned gyro would
appear to drift even though no change of latitude has occurred.
➢Transport drift occurs at the same time as Earth rate
➢In the northern hemisphere, the effect of the earths rotation will increase the
transport drift in the easterly direction as the aircraft and the earth are
moving in the same direction. While, earth rotation will reduce the rate of
transport drift in the westerly direction as earth and the aircraft are moving
in the opposite direction.
➢Transport drift in the easterly direction in northern hemisphere is (-)ve
➢Transport drift in the westerly direction in northern hemisphere is (+)ve
➢The opposite rules will apply for southern hemisphere
Transport Drift

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Gyroscopic
Instrument
•Transport Drift = (u/60) × tan(latitude°) per hour
Where,
u = component of groundspeed in east/west direction along equator
Transport Topple = Rate of change of longitude° per hour ×cos latitude° per hour
Math:
A directional gyro is set to read 270
o
. The aircraft flies for 80 minutes along a
track of 270
o
true along the parallel of 20
o
north at a groundspeed 540 knots.
What is the gyro reading at the end of the flight if there is no change in the
aircrafts true track?
Now calculate the gyro reading if the aircraft flew along 090
o
true?
Transport Drift

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Gyroscopic
Instrument
•This happens when gimbal orientation is such
that spin axis becomes coincident with any of
the axis of freedom
•Gimbal lockis the loss of one degree of freedom
•In a three-dimensional, three-gimbalmechanism
that occurs when the axes of two of the
threegimbalsare driven into a parallel
configuration
•This locks the system into rotation in a
degenerate two-dimensional space
Gimbal Lock

38. Artificial Horizon/
Attitude Indicator
❑Gives the pilot pitch and roll information.
❑Operates with a gyroscope rotating in the horizontal plane (i.e.
vertical spin axis) having freedom of movement in all the three
axes. The gyro spin axis is maintained vertical with reference to
the center of the earth. Thus, It mimics the actual horizon
through its rigidity in space.
❑As the aircraft pitches and rolls in relation to the actual horizon,
the gyro gimbals allow the aircraft and instrument housing to
pitch and roll around the gyro rotor that remains parallel to the
ground.
❑A miniature horizontal representation of the airplane is fixed to
the instrument housing. A painted semi sphere simulating the
horizon, the sky and the ground is attached to the gyro gimbals.
The sky and ground meet at what is called the horizon bar. The
relationship between the horizon bar and the miniature airplane
are the same as those of the aircraft and the actual horizon.
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Gyroscopic
Instrument

39. Artificial Horizon/
Attitude Indicator
❑Graduated scale indicates the
degrees of pitch and roll.
❑The instrument is either air or
electrically driven. Electric power is
supplied to the gyro from the
aircraft Instrument Inverter.
❑The rotor spins at high speed e.g.
22,400 R.P.M approximately about
vertical axis.
❑High altitudes ac avoids a vacuum
power for gyro because pump
efficiency is limited in the thin, cold
air.
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Gyroscopic
Instrument

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Gyroscopic
Instrument
Artificial Horizon/
Attitude Indicator

41. Artificial Horizon/
Attitude Indicator
➢Inner Gimbal (IG) of the gyro is
pivoted to an outer gimbal (OG)
➢Pivot axis is parallel to the aircraft
lateral axis
➢OG is in turn pivoted to the instrument
casing
➢Pivot axis is parallel to the aircraft
longitudinal axis
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Gyroscopic
Instrument

42. Artificial Horizon/
Attitude Indicator
Since instrument casing is attached to
the airframe
➢Any change in aircraft attitude
must take place about the
vertically referenced gyro
➢Thus if the pitch attitude
changes, the IG will pitch
up/down relative to the gyro spin
axis
➢Also, if the roll attitude changes,
the OG will roll left or right relative
to the gyro spin axis
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Gyroscopic
Instrument

43. Artificial Horizon/
Attitude Indicator
➢Attached to the OG is the sky, ground
and horizon simulating plate which is
viewed through the face of the
instrument
➢A spindle (bar) is pivoted to the OG
which is parallel to the horizon
➢Horizon bar is driven by a spindle
attached to the IG
➢Printed on or attached to the glass
cover of the instrument is the
miniature aircraft symbol
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Gyroscopic
Instrument

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Gyroscopic
Instrument
Artificial Horizon/
Attitude Indicator

45. Artificial Horizon/
Attitude Indicator
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Gyroscopic
Instrument

46. Artificial Horizon/
Attitude Indicator
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Gyroscopic
Instrument

47. Artificial Horizon/
Attitude Indicator
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Gyroscopic
Instrument
•BANKING SCALE: Only Banking, No Turning Indication

48. Artificial Horizon/
Attitude Indicator
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Gyroscopic
Instrument
•PITCHING SCALE: Only Pitch, No climb/ descent Indication

49. Artificial Horizon/
Attitude Indicator
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Gyroscopic
Instrument

50. Artificial Horizon/
Attitude Indicator
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Gyroscopic
Instrument

51. Artificial Horizon/
Attitude Indicator
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Gyroscopic
Instrument

52. Artificial Horizon/
Attitude Indicator
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Gyroscopic
Instrument

53. Turn-and-Slip Indicator
Turn-and-Slip Indicator
❑The turn and slip indicator consists of two
independent mechanisms contained in the
same case → Turn Indicator & Inclinometer
❑Purpose of TURN AND SLIP Indicator is to
➢Measure and display the aircraft rate of turn
➢Indicate whether the aircraft is correctly banked
for a co-ordinated turn with no slip and skid
❑The pilot uses them together when making
banked turns.
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Gyroscopic
Instrument

54. ❑The turn-and-slip indicator is actually two separate devices in a same housing: a turn
indicator pointer and slip indicator ball. The turn pointer is operated by a gyro.
❑The ball is a steel ball, in a glass tube filled with fluid. It moves in response to gravity and
centrifugal force experienced in a turn.
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Gyroscopic
InstrumentTurn-and-Slip Indicator

55. Turn-and-Slip Indicator
Turn-and-Slip Indicator
❑The turn indicator works on the principle of rate
gyro
❑The rate gyro is a horizontal spin axis gyro which
is sensitive to movement about the aircraft yaw
axis
❑The slip indicator or inclinometer works on
Centrifugal & Centripetal force to indicate the
slipping (due to steep bank) and skidding
(during under bank) of the aircraft if any.
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Gyroscopic
Instrument

56. ➢Turn indicators indicate the rate at which the aircraft is turning (Whether the aircraft is turning and How
fast the heading is changing).
➢Three degrees of turn per second cause an aircraft to turn 360° in 2 minutes. This is considered a
standard turn.
➢Faster aircraft tend to turn more slowly (may have 4-min turns i.e. 1.5 ° per second ).
➢Instrument is reqr to mark whether it is a 2-or 4-minute turn indicator.
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Gyroscopic
InstrumentTurn-and-Slip Indicator
1 Sec = 3°
60 Sec = 1 Min = 180 °
i.e. 360 ° covers in 2 Min

57. Rate of Turn Scale
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Gyroscopic
InstrumentTurn-and-Slip Indicator

58. Rate of Turn Scale
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Gyroscopic
InstrumentTurn-and-Slip Indicator

59. Rate of Turn Scale
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Gyroscopic
InstrumentTurn-and-Slip Indicator

60. Rate of Turn Scale
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Gyroscopic
InstrumentTurn-and-Slip Indicator

61. INCLINOMETER. Allows to measure the quality of the turn
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Gyroscopic
InstrumentTurn-and-Slip Indicator

62. ❑Slip Indicator/ Inclinometer.
▪The ball responds only to gravity during coordinated straight-and-level flight. Thus, it
rests in the lowest part of the curved glass between the reference wires.
▪When a turn is initiated and the aircraft is banked, both the centrifugal and
centripetal forces of the turn act upon the ball.
▪lf the turn is coordinated, the ball remains in place.
▪Should a skidding turn exist, the centrifugal force exceeds the centripetal force on
the ball and it moves in the direction of the outside of the turn.
▪During a slipping turn, there is more bank than needed, and centripetal force is
greater than the centrifugal force acting on the ball. The ball moves in the curved
glass toward the inside of the turn.


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Turn-and-Slip Indicator
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Gyroscopic
Instrument

63. 63
Turn-and-Slip Indicator
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Gyroscopic
Instrument

64. Left Turn
Ball Right = Skid (Centrifugal force more, less banking)
Centre = Co-Ordinated Turn (Good combination of bank
and turn)
Ball Left = Slip [Banking is more, Centripetal Force is more
than Centrifugal Force]

Right Turn
Ball Right = Slip [Banking is more, Centripetal Force is
more than Centrifugal Force]
Centre = Co-Ordinated Turn (Good combination of bank
and turn)
Ball Left = Skid (Centrifugal force more, less banking)
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Turn-and-Slip Indicator
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Gyroscopic
Instrument

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Gyroscopic
InstrumentTurn-and-Slip Indicator
•INCLINOMETER.

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Gyroscopic
InstrumentTurn-and-Slip Indicator
CO-ORDINATED TURN SKID TURN
SLIP TURN

67. Operating Principle
❑Uses the Principle of Gyroscopic principle of precision to measure the rate
of turn
❑Uses a Horizontal rate gyro which is restricted to one of its axis
❑Plane of rotation is perpendicular to the horizon
❑Spin axis is parallel to the horizon
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Turn-and-Slip Indicator
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Gyroscopic
Instrument

68. Operating Principle
•Rotor is either electrically driven or is air driven
•Both types of drives are structured to produce
a low speed of 4500 rpm
•Spring is placed between the gimbal and the
instrument case
•A pointer is attached to the gimbal which
indicates the rate of turn over a scale
•A damping device is generally used to ensure
smooth changes in the rate of turn
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Turn-and-Slip Indicator
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Gyroscopic
Instrument

69. Operating Principle
❑The restricted gyro in the instrument is not free to rotate in one of its axis
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Turn-and-Slip Indicator
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Gyroscopic
Instrument

70. Operating Principle
•When the aircraft yaws about the vertical axis
–Applies a force to the gyro rotor at the front in line with the spin axis
–Thus the gyro will precess this force with 90º in the direction of rotation. As
the gyro precesses, the rotor and the gimbal ring tilts until the precessing
force matches the tension of the spring.
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Turn-and-Slip Indicator
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Gyroscopic
Instrument

71. Operating Principle. Consider the aircraft has turned left (i.e yaw)
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Turn-and-Slip Indicator
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Gyroscopic
Instrument

72. Operating Principle
•When the precessing and the spring force balances, precession ceases,
and the gyro remains inclined for the duration of the turn
–Giving an indication of the actual rate of turn shown by the pointer’s
position on the scale
•When the aircraft stops turning, the gyro returns to its original horizontal
position under the action of the spring
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Turn-and-Slip Indicator
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Gyroscopic
Instrument

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Turn-and-Slip Indicator
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Gyroscopic
Instrument

74. Errors in Turn-and-Slip Indicator
•Erroneous indications are caused if the rotor speed fluctuates too far from
its normal
•If the rotor speed falls below the design rpm, both the gyro rigidity and
precession forces vary
•Hence, the precession force is unable to match the spring tension to the
calibrated scale
–The turn indicator will therefore under read
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Turn-and-Slip Indicator
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Gyroscopic
Instrument