82 Questions
What is the primary function of a gimbal in a gyroscope?
To allow freedom of movement about one or more perpendicular axes
How many degrees of freedom does a gyroscope typically have?
Three
What is the axis of veer in a gyroscope?
The vertical axis perpendicular to both the spin and tilt axes
What is the primary component of a gyroscope that spins rapidly?
The rotor
What is the purpose of the inner gimbal in a gyroscope?
To pivot the frame itself
What is the limitation of a gyroscope?
It cannot detect movement about its plane of spin
What is the primary function of a gimbal in a gyroscope?
To maintain the rotor's original attitude and direction of spin axis
How many gimbals are required to provide freedom in both axes of tilt and veer?
Two
What is the property of a gyroscope that resists any force tending to change the plane of rotation of its rotor?
Gyroscopic rigidity
What are the three factors that affect the rate of precession in a gyroscope?
Force, moment of inertia, and angular velocity
What happens when the spin axis of the rotor becomes aligned with the axis of the outer gimbal?
Gimbal lock occurs
What is the purpose of mechanical stops in a gimbal system?
To prevent gimbal lock
What is the result of gimbal lock?
The outer gimbal rotates 180 degrees
What is the direction of the angular change in direction of the plane of rotation under the influence of an applied force?
At a point 90 degrees away from the applied force
What is the relationship between the moment of inertia and the rate of precession?
The greater the moment of inertia, the smaller the rate of precession
What is the name of the axis about which a torque is applied in a gyroscope?
Input axis
What is a major problem with air-driven gyro instruments?
Dirt and dust
What is the rotational speed of the high-speed rotors in electrically-driven gyro instruments?
21 000 rpm
What is the primary advantage of electrically-driven gyro instruments over air-driven gyro instruments?
Less maintenance effort
What is the purpose of the squirrel cage induction motor in an electrically-driven gyro instrument?
To rotate the rotor
What is the typical rotational speed of a DC electric gyro instrument?
4200 rpm
What is the primary advantage of AC electric gyro instruments over DC electric gyro instruments?
Higher rotational speed
What is the purpose of the torque motors in an electrically-driven gyro instrument?
To maintain the erection of the gyro
What is the effect of a failure in the power supply of an electrically-driven gyro instrument?
A flag marked 'off' is displayed
What is the primary disadvantage of DC electric gyro instruments?
Lower rotational speed
What is the typical power supply voltage for an AC electric gyro instrument?
115-V, 400-Hz, three-phase AC
What is the primary function of an artificial horizon in an aircraft?
To provide pilots with an indication of an aircraft's pitch and roll attitude
What is the reason for waiting 30 minutes before removing a gyro from an aircraft?
To allow the rotor to cease spinning to prevent damage
How does an electrically driven gyro slow down after power is removed?
Through the use of electrical or dynamic braking
What is the purpose of the pendulous vane assembly in a fixed sky plate artificial horizon?
To precess the gyro to maintain a vertical spin axis
What is the limitation of an electrically driven gyro?
All of the above
How does the artificial horizon provide a display of pitch and roll?
Through the deflection of the gimbals from the stable reference
What is the function of the erection system in an artificial horizon?
To align the gyro with respect to gravity
What is the purpose of the roll angle pointer in a fixed sky plate artificial horizon?
To measure the roll of the aircraft
What is the advantage of an electrically driven gyro over an air-driven gyro?
It can slow down quickly after power is removed
What is the purpose of the miniature aircraft in the fixed sky plate artificial horizon?
To provide a reference for the pitch and roll attitude of the aircraft
How does a displacement gyro measure displacement?
By utilizing the gyro's property of rigidity in space
What is the main difference between a displacement gyro and a rate gyro?
Rate gyros use rigidity in space to measure displacement
How does a rate gyro determine the rate of movement?
By subjecting the gyro to precessive forces against spring pressure
What establishes the pitch and roll attitude reference in aircraft gyroscopes?
Gyroscopes having spin axes arranged vertically
How is aircraft transport rate drift corrected?
By referencing gyro to the center of the Earth
What is the purpose of a gyro erection system?
To maintain gimbals aligned with gravity
How are forces created to precess the gyro from its normal position in an aircraft?
By changing gimbal balance
What are normal erection rates for gyro systems?
1 - 5 degrees a minute
Why did older designs of attitude gyros require manually operated caging devices?
To hold gimbals in place during rotor start
When do directional gyros need to be reset to the magnetic heading?
At frequent intervals during flight
What is the purpose of the roll attitude pointer on the flight director instrument?
To command the pilot to fly the aircraft symbol towards it
How many command bars are there on the flight director instrument?
One for pitch and one for roll
What is the purpose of the glideslope pointer located on the flight director instrument?
To capture the runway glideslope beam
Why are the command bars on the flight director instrument called 'command bars'?
Because they command the pilot to fly the aircraft symbol towards them
What signals supply the commands to the command bars on the flight director instrument?
Reference signals from navigation aid receivers
What is the limitation minimized or eliminated with respect to gimbal lock on the attitude sphere?
Roll limitation
What is the purpose of caging gyros during aerobatic manoeuvres?
To avoid damage to the instruments
How do attitude gyro instruments reset or erect the gyro?
By restoring gimbal alignment
What is the maximum limit of pitch attitude from level flight for modern attitude gyro instruments?
85 degrees nose up or nose down
What is used to eliminate apparent drift and transport rate in the gyro erection system?
Vacuum air
What happens if the inner gimbal in the air-driven gyroscope is not maintained perpendicular to the outer gimbal?
Precession occurs
In the early aircraft vacuum gyro system using venturis, what is an issue related to the speed of generating suction?
No suction until reaching a reasonable airspeed
What provides the precessing force to re-erect the gyro to the local vertical in the flapper door erection system?
Opening of door 'A'
What maintains the spin of the rotor at approximately 15,000 rpm in the air-driven gyroscope?
Impinging air from the jets
What is a disadvantage of using vacuum in gyroscope systems at high altitudes?
Decreased vacuum due to lower atmospheric pressure
Why are filters considered very important in air-driven gyro systems?
To avoid contamination shortening serviceable life
What is the term used to describe the uninterrupted, uninhibited motion of a gyroscope's rotor around three perpendicular axes?
Toppling
Which type of gyroscope has the complete freedom to move about three axes acting at right angles to each other?
Space Gyro
What is the term for the observed effect of a gyro's apparent rotation or drift while it's actually staying fixed in space?
Earth rate
What will happen if a perfectly balanced and frictionless space gyro is left alone to spin with no external forces acting on it?
It will appear to rotate or drift away
What does transport wander refer to in gyroscope terminology?
Observed tilting of the gyro's spin axis
What term is used to describe the combination of Earth rate and transport wander in gyroscopic behavior?
Apparent drift
What needs to be controlled in a gyroscope to convert it into an Earth gyro for practical usability in aircraft instruments?
Drift and transport wander
When a space gyroscope is referenced to any parameter other than Earth, it is known as what type of gyro?
Tied gyro
Which type of gyros determine the pitch, roll, and directional attitudes of an aircraft?
Displacement gyros
What is the term for the apparent shifting or rotating of a gyroscope while the Earth rotates beneath it?
Apparent drift
In the older design of the artificial horizon, how is pitch and roll attitude displayed?
Using a stabilised spherical element with blue and black/brown halves
What determines the climb and descent attitude in the artificial horizon display?
The colour of the upper and lower halves
How does the artificial horizon indicate bank angle?
Using a pointer and scale
Why is pitch restricted to 85° in the artificial horizon display?
To avoid gimbal lock
What is the main purpose of an Attitude Director Indicator (ADI)?
To provide aircraft attitude and steering information
Why were certain flight and navigation instruments integrated to form an Attitude Director Indicator (ADI)?
To compound indications and ease pilot mental processing
What is the view represented by an Attitude Director Indicator (ADI)?
From behind the aircraft looking forward
What is the main advantage of an Attitude Director Indicator (ADI) in aircraft instrumentation?
Combines related instruments to simplify pilot information
What distinguishes an Attitude Director Indicator (ADI) from an Attitude Reference Indicator (ARI)?
Slightly different displays but same operation
Why is an Attitude Director Indicator (ADI) also named as an Attitude Reference Indicator (ARI)?
Due to the similar operation and functions
Study Notes
Artificial Horizon and Gyroscopes
- The artificial horizon (AH) provides pilots with an indication of an aircraft's pitch and roll attitude.
- The gyro spin axis is maintained in a vertical position or horizontal plane of rotation relative to the Earth.
- The gyro is an Earth-referenced gyro, maintained by an erection system to re-align the gyro with respect to gravity in case of drift or errors.
Gyroscope Fundamentals
- A gyroscope consists of a symmetric rotor spinning rapidly about its spin axis.
- The spin axis is free to rotate about one or more perpendicular axes, providing three degrees of freedom.
- The gyro has three axes of freedom: spinning, tilting, and veering.
Axes of Freedom
- Spinning freedom is about an axis perpendicular to the spin axis.
- Tilting freedom is about a horizontal axis at right angles to the spin axis.
- Veering freedom is about a vertical axis perpendicular to both the spin and tilt axes.
Gyroscopic Properties
- Gyroscopic rigidity or inertia is the property of resisting any force that tends to change the plane of rotation of the rotor.
- Gyroscopic precession is the angular change in direction of the plane of rotation under the influence of an applied force.
- The rate of precession depends on the strength and direction of the applied force, the moment of inertia of the rotor, and the angular velocity of the rotor.
Gimbal Lock
- Gimbal lock occurs when the spin axis of the rotor becomes aligned with the axis of the outer gimbal.
- This condition is normally prevented by limiting the movement of the inner gimbal with mechanical stops.
- If the inner gimbal reaches these stops, the forces acting on the gimbal system cause the outer gimbal to rotate 180 degrees, a process called "toppling."
Electrically-Driven Gyroscopes
- Electrically-driven gyros are designed for operation on electrical power derived from the aircraft power supplies.
- They have higher speed, lower current consumption, and less noise compared to air-driven gyros.
- AC electrically powered gyros can run much faster than air-driven gyros, providing a more rigid gyroscopic reference.
AC and DC Gyro Systems
- AC gyro systems have higher speed, giving greater inertia and rigidity, but are more complex and have higher cost.
- DC gyro systems are simpler, lighter, and lower-cost, but have a lower maximum rotor speed and higher current consumption.
Gyro Limitations
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A particular limitation of all gyros is that the gyro should never be removed from the aircraft until at least 30 minutes has passed from the time the power source was disconnected.
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Electrically driven gyros may incorporate a form of electrical or dynamic braking to slow the gyro rotor quickly once power is removed.### Gyroscopes
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A displacement gyro measures displacement around it by using the property of rigidity in space.
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A rate gyro determines rate of movement by being subjected to precessive forces against spring pressure.
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The higher the rate of movement, the greater the inertial force applied to the gyro, resulting in precession.
Gyroscope Applications in Aircraft
- Aircraft gyroscopes establish two essential reference datums: • A reference against which pitch and roll attitude changes can be detected. • A directional reference against which changes about the vertical axis can be detected.
- These references are established by gyroscopes with spin axes arranged vertically and horizontally, respectively.
Gyro Indicators
- Gyroscopes use the fundamental property of rigidity to establish a stabilized reference unaffected by movement of the supporting body.
- Precession is used to control the effects of apparent and real drift, maintaining a stabilized reference datum.
Correction of Drift
- Several factors can control drift for horizontal-axis gyroscopes: • Applying fixed torques that unbalance the gyroscope and cause it to precess at a rate equal and opposite to the Earth rate. • Applying a torque that has a similar effect to that stated above, but which can be varied according to the latitude. • Referencing the gyro to the center of the Earth.
Transport Wander and Drift
- Apparent drift is composed of Earth rate and transport wander.
- Earth rate is the effect where the gyro appears to precess at 15° per hour due to the Earth's rotation.
- Transport wander occurs when a gyroscope is transported from one point on the planet to another, appearing to tilt.
Gyro Erection Systems
- A gyro erection system maintains the gyro rotor and gimbals aligned at right angles to each other.
- The system depends on the particular design of gyro: • Directional gyro: rotor spin axis aligned horizontally to detect movement of the aircraft in azimuth. • Attitude gyro: rotor spin axis aligned vertically to detect aircraft movement in pitch and roll relative to the Earth's horizon.
Caging and Erection
- Older designs of attitude gyros required manual caging devices to hold the gimbals in place during rotor start and before take-off.
- Modern attitude gyro instruments have complete freedom in the roll axis and do not require manual caging.
Vacuum Gyro System
- Air-driven gyro rotors can run on a very low positive pressure or a very low vacuum.
- A vacuum can be supplied from a venturi mounted in the airstream or an engine-driven pump.
- The vacuum is used to spin the gyro rotor and for the gyro erection system to reference the gyro to the Earth.
Learn about the basic components and functionality of gyroscopes, including the spin axis, gimbals, and freedom of movement. Understand how gyroscopes work as mechanical devices and their applications.
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