Gyrocompass
Overview
 
A gyrocompass­ is a type of non-magnetic compass
Compass
A compass is a navigational instrument that shows directions in a frame of reference that is stationary relative to the surface of the earth. The frame of reference defines the four cardinal directions – north, south, east, and west. Intermediate directions are also defined...

 which bases on a fast-spinning disc and rotation of our planet to automatically find geographical direction. Although one of important components of a gyrocompass is a gyroscope
Gyroscope
A gyroscope is a device for measuring or maintaining orientation, based on the principles of angular momentum. In essence, a mechanical gyroscope is a spinning wheel or disk whose axle is free to take any orientation...

, these are not the same devices; gyrocompass is built to use the effect of gyroscopic precession, which is a distinctive aspect of the general gyroscopic effect. Gyrocompasses are widely used for navigation
Navigation
Navigation is the process of monitoring and controlling the movement of a craft or vehicle from one place to another. It is also the term of art used for the specialized knowledge used by navigators to perform navigation tasks...

 on ship
Ship
Since the end of the age of sail a ship has been any large buoyant marine vessel. Ships are generally distinguished from boats based on size and cargo or passenger capacity. Ships are used on lakes, seas, and rivers for a variety of activities, such as the transport of people or goods, fishing,...

s, because they have two significant advantages over magnetic compasses:
  • they find true north
    True north
    True north is the direction along the earth's surface towards the geographic North Pole.True geodetic north usually differs from magnetic north , and from grid north...

     as determined by Earth's rotation, which is different from, and navigationally more useful than, magnetic north, and
  • they are unaffected by ferromagnetic materials, such as ship's steel
    Steel
    Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...

     hull
    Hull (watercraft)
    A hull is the watertight body of a ship or boat. Above the hull is the superstructure and/or deckhouse, where present. The line where the hull meets the water surface is called the waterline.The structure of the hull varies depending on the vessel type...

    , which change the magnetic field
    Magnetic field
    A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...

    .

A gyroscope
Gyroscope
A gyroscope is a device for measuring or maintaining orientation, based on the principles of angular momentum. In essence, a mechanical gyroscope is a spinning wheel or disk whose axle is free to take any orientation...

 is a spinning wheel mounted on gimbal
Gimbal
A gimbal is a pivoted support that allows the rotation of an object about a single axis. A set of two gimbals, one mounted on the other with pivot axes orthogonal, may be used to allow an object mounted on the innermost gimbal to remain immobile regardless of the motion of its support...

 so that the wheel's axis is free to orient itself in any way.
Encyclopedia
A gyrocompass­ is a type of non-magnetic compass
Compass
A compass is a navigational instrument that shows directions in a frame of reference that is stationary relative to the surface of the earth. The frame of reference defines the four cardinal directions – north, south, east, and west. Intermediate directions are also defined...

 which bases on a fast-spinning disc and rotation of our planet to automatically find geographical direction. Although one of important components of a gyrocompass is a gyroscope
Gyroscope
A gyroscope is a device for measuring or maintaining orientation, based on the principles of angular momentum. In essence, a mechanical gyroscope is a spinning wheel or disk whose axle is free to take any orientation...

, these are not the same devices; gyrocompass is built to use the effect of gyroscopic precession, which is a distinctive aspect of the general gyroscopic effect. Gyrocompasses are widely used for navigation
Navigation
Navigation is the process of monitoring and controlling the movement of a craft or vehicle from one place to another. It is also the term of art used for the specialized knowledge used by navigators to perform navigation tasks...

 on ship
Ship
Since the end of the age of sail a ship has been any large buoyant marine vessel. Ships are generally distinguished from boats based on size and cargo or passenger capacity. Ships are used on lakes, seas, and rivers for a variety of activities, such as the transport of people or goods, fishing,...

s, because they have two significant advantages over magnetic compasses:
  • they find true north
    True north
    True north is the direction along the earth's surface towards the geographic North Pole.True geodetic north usually differs from magnetic north , and from grid north...

     as determined by Earth's rotation, which is different from, and navigationally more useful than, magnetic north, and
  • they are unaffected by ferromagnetic materials, such as ship's steel
    Steel
    Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...

     hull
    Hull (watercraft)
    A hull is the watertight body of a ship or boat. Above the hull is the superstructure and/or deckhouse, where present. The line where the hull meets the water surface is called the waterline.The structure of the hull varies depending on the vessel type...

    , which change the magnetic field
    Magnetic field
    A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...

    .

Operation

A gyroscope
Gyroscope
A gyroscope is a device for measuring or maintaining orientation, based on the principles of angular momentum. In essence, a mechanical gyroscope is a spinning wheel or disk whose axle is free to take any orientation...

 is a spinning wheel mounted on gimbal
Gimbal
A gimbal is a pivoted support that allows the rotation of an object about a single axis. A set of two gimbals, one mounted on the other with pivot axes orthogonal, may be used to allow an object mounted on the innermost gimbal to remain immobile regardless of the motion of its support...

 so that the wheel's axis is free to orient itself in any way. When it is spun up to speed with its axis pointing in some direction, due to the law of conservation of angular momentum
Angular momentum
In physics, angular momentum, moment of momentum, or rotational momentum is a conserved vector quantity that can be used to describe the overall state of a physical system...

, such a wheel will normally maintain its original orientation to a fixed point in outer space
Outer space
Outer space is the void that exists between celestial bodies, including the Earth. It is not completely empty, but consists of a hard vacuum containing a low density of particles: predominantly a plasma of hydrogen and helium, as well as electromagnetic radiation, magnetic fields, and neutrinos....

 (not to a fixed point on Earth). Since our planet rotates, it appears to a stationary observer on Earth that a gyroscope's axis is completing a full rotation once every 24 hours.Although the effect is not visible in a specific case when the gyroscope's axis is precisely parallel to the Earth's rotational axis. Such a rotating gyroscope is used for navigation in some cases, for example on aircraft, where it is known as heading indicator
Heading indicator
The heading indicator is a flight instrument used in an aircraft to inform the pilot of the aircraft's heading. It is sometimes referred to by its older names, the directional gyro or DG, and also direction indicator or DI.- Use :The primary means of establishing the heading in most small...

, but cannot ordinarily be used for long-term marine navigation. The crucial additional ingredient needed to turn such gyroscope into a gyrocompass, so it would automatically position to true north, is some mechanism that results in an application of torque
Torque
Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....

 whenever the compass's axis is not pointing north.

One method uses friction
Friction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of friction:...

 to apply the needed torque: the gyroscope in a gyrocompass is not completely free to reorient itself; if for instance a device connected to the axis is immersed in a viscous fluid, then that fluid will resist reorientation of the axis. This friction force caused by the fluid results in a torque
Torque
Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....

 acting on the axis, causing the axis to turn in a direction orthogonal to the torque (that is, to precess) along a line of longitude. Once the axis points toward the celestial pole, it will appear to be stationary and won't experience any more frictional forces. This is because true north is the only direction for which the gyroscope can remain on the surface of the earth and not be required to change. This axis orientation is considered to be a point of minimum potential energy
Potential energy
In physics, potential energy is the energy stored in a body or in a system due to its position in a force field or due to its configuration. The SI unit of measure for energy and work is the Joule...

.

Another, more practical, method is to use weights to force the axis of the compass to remain horizontal (perpendicular to the direction of the center of the Earth), but otherwise allow it to rotate freely within horizontal plane. In this case, gravity will apply a torque forcing the compass's axis toward true north. Because the weights will confine the compass's axis to be horizontal with respect to the Earth's surface, the axis can never align with the Earth's axis (except on the Equator) and must realign itself as the Earth rotates. But with respect to the Earth's surface, the compass will appear to be stationary and pointing along the Earth's surface toward the true North Pole.

Since the gyrocompass's north-seeking function depends on the rotation around the axis of the Earth that causes torque-induced gyroscopic precession, it will not orient itself correctly to true north if it is moved very fast in an east to west direction, thus negating the Earth's rotation. However, aircraft commonly use heading indicators or directional gyros
Heading indicator
The heading indicator is a flight instrument used in an aircraft to inform the pilot of the aircraft's heading. It is sometimes referred to by its older names, the directional gyro or DG, and also direction indicator or DI.- Use :The primary means of establishing the heading in most small...

, which are not gyrocompasses and do not position themselves to north via precession, but are periodically aligned manually to magnetic north."

History

The first, not yet practical, form of gyrocompass was patented in 1885 by Marinus Gerardus van den Bos. Usable gyrocompass was invented in 1906 in Germany by Hermann Anschütz-Kaempfe
Hermann Anschütz-Kaempfe
Hermann Franz Joseph Hubertus Maria Anschütz-Kaempfe was a German scientist and inventor. In his quest to navigate to the North Pole by submarine, he became interested in the concept of the gyrocompass. In 1905 he founded, with Friedrich Treitschke the first firm to manufacture gyroscopic...

, and after successful tests in 1908 became widely used in German Imperial Navy.

In United States, Elmer Ambrose Sperry
Elmer Ambrose Sperry
Elmer Ambrose Sperry was a prolific inventor and entrepreneur, most famous as co-inventor, with Herman Anschütz-Kaempfe of the gyrocompass.Sperry was born at Cincinnatus, New York, United States of America...

 produced a workable gyrocompass system (1908: patent #1,242,065), and founded the Sperry Gyroscope Company
Sperry Corporation
Sperry Corporation was a major American equipment and electronics company whose existence spanned more than seven decades of the twentieth century...

. The unit was adopted by the U.S. Navy (1911), and played a major role in World War I. The Navy also began using Sperry's "Metal Mike": the first gyroscope-guided autopilot steering system. In the following decades, these and other Sperry devices were adopted by steamships such as the RMS Queen Mary
RMS Queen Mary
RMS Queen Mary is a retired ocean liner that sailed primarily in the North Atlantic Ocean from 1936 to 1967 for the Cunard Line...

, airplanes, and the warships of World War II. After his death in 1930, the Navy named the USS Sperry after him.
Before the success of gyrocompass, several attempts had been made in Europe to use gyroscope instead. By 1880, William Thomson (lord Kelvin) tried to propose a gyrostat (tope) to the British Navy. In 1889, Arthur Krebs
Arthur Krebs
Arthur Constantin Krebs was a French officer and pioneer in automotive engineering....

 adapted an electric motor to the Dumoulin-Froment marine gyroscope, for the French Navy. Giving the Gymnote submarine the ability to keep a straight line under water during several hours, it allowed her to force a naval block in 1890.

Errors

A gyrocompass is subject to certain errors. These include steaming error, where rapid changes in course, speed and latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...

 cause deviation
Deviation
Deviation may refer to:* Deviation , the difference between the value of an observation and the mean of the population in mathematics and statistics** Standard deviation, which is based on the square of the difference...

 before the gyro can adjust itself. On most modern ships the GPS or other navigational aids feed data to the gyrocompass allowing a small computer to apply a correction. Alternatively a design based on an orthogonal triad of fibre optic or ring laser gyroscope
Ring laser gyroscope
A ring laser gyroscope consists of a ring laser having two counter-propagating modes over the same path in order to detect rotation. It operates on the principle of the Sagnac effect which shifts the nulls of the internal standing wave pattern in response to angular rotation...

s will eliminate these errors, as they depend upon no mechanical parts, instead using the principles of optical path difference
Optical path length
In optics, optical path length or optical distance is the product of the geometric length of the path light follows through the system, and the index of refraction of the medium through which it propagates. A difference in optical path length between two paths is often called the optical path...

 to determine rate of rotation.

See also

  • Acronyms and abbreviations in avionics
    Acronyms and abbreviations in avionics
    -A:*ACARS: Aircraft Communications Addressing and Reporting System.*ACAS: Airborne Collision Avoidance System.*ACP: Audio Control Panel.*ACS: Audio Control System.*ADAHRS: Air Data and Attitude Heading Reference System.*ADC: Air Data Computer....

  • Heading indicator
    Heading indicator
    The heading indicator is a flight instrument used in an aircraft to inform the pilot of the aircraft's heading. It is sometimes referred to by its older names, the directional gyro or DG, and also direction indicator or DI.- Use :The primary means of establishing the heading in most small...

    , also known and direction indicators, are lightweight gyroscopes employed on aircraft (not to be mistaken with gyrocompasses)
  • Fluxgate compass
    Fluxgate compass
    The basic fluxgate compass is a simple electromagnetic device that employs two or more small coils of wire around a core of highly permeable magnetic material, to directly sense the direction of the horizontal component of the earth's magnetic field...

  • Fibre optic gyrocompass
    Fibre optic gyrocompass
    A fibre optic gyrocompass is a compass and instrument of navigation. It is often part of a ships set of compasses, which also include a conventional gyrocompass and a magnetic compass....

  • Inertial navigation system
    Inertial navigation system
    An inertial navigation system is a navigation aid that uses a computer, motion sensors and rotation sensors to continuously calculate via dead reckoning the position, orientation, and velocity of a moving object without the need for external references...

    ; a more complex system that also incorporates accelerometers
  • Schuler tuning
    Schuler tuning
    Schuler tuning is a modification to the electronic control system used in inertial navigation systems that accounts for the curvature of the Earth. An inertial navigation system, used in submarines, ships, aircraft, and other vehicles to keep track of position, determines directions with respect...


External links

  • Elmer A. Sperry case file at the Franklin Institute
    Franklin Institute
    The Franklin Institute is a museum in Philadelphia, Pennsylvania, and one of the oldest centers of science education and development in the United States, dating to 1824. The Institute also houses the Benjamin Franklin National Memorial.-History:On February 5, 1824, Samuel Vaughn Merrick and...

    contains records concerning his 1914 Franklin Award for the gyroscopic compass
  • "A Job Thought Impossible", the story of Chrysler Corporation's mass-production of previously hand-made gyrocompasses for World War II naval requirements.
  • Errors of the Gyrocompass
  • Using the Gyrocompass
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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