# Gyrocompass

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Gyro compass from the company Anschütz; cut

The gyro compass is a compass that is oriented parallel to the earth's axis of rotation and thus shows the north-south direction. Due to its horizontal suspension, it is not a free, but a tied top . As such, it looks like a meridian , but needs two to four hours for alignment (settling time). Since a course and speed-dependent travel error must be taken into account in the course display, gyrocompasses are mainly used on slow-moving ships . They work independently of the earth's magnetic field and therefore do not show the magnetic, but the true (astronomical) north direction.

The course gyro, which is often used in small aircraft, is a free gyro , but it is often confused with the gyro compass. Modern inertial or inertial navigation systems also work with free gyroscopes . However, in addition to the direction, they also provide an exact position determination by integrating the accelerations of the aircraft in three dimensions.

## Working principle

Fig. 1: Structure of a gyro compass, schematic

The gyrocompass consists of a rapidly rotating gyro , usually in a cardanic suspension . In addition, it is arranged in such a way that a torque acts on it as long as its direction of rotation does not point north. If the direction of rotation points to the north and thus the axis of rotation in the direction of rotation of the earth, the torque (the cross product of the radius perpendicular to the direction of rotation and the force due to the acceleration in the direction of the earth's rotation) becomes zero. In the experiment set-up shown next to it, it is suspended as a pendulum. It can only orient itself freely parallel to the earth's surface.

Fig. 2: Functional principle of a gyro compass

The schematic drawing in Fig. 2 shows, viewed from the South Pole, a gyro compass moving along the equator. At first its axis of rotation sn is parallel to the earth's surface. According to the conservation of angular momentum , the axis maintains its direction even when moving to the second position shown. Due to the special suspension, the gyro can only align itself force-free in two planes. Gravity acts on the third direction. It tries to tilt the axis along the arrows marked D. The torque it generates tilts the axis of rotation out of the plane of the drawing and causes the top to precess . By damping the rotary motion around point A , the top comes to rest when the acting force disappears. This is the case when the gyro axis points in the north-south direction ("meridian-seeking gyro").

Movements of the top along a meridian cause magnetic declines. Then the top no longer points exactly north, but in the direction that results from the sum of the latitude (cos φ) dependent speed on the earth's surface and that with which the top is moved. A speed along the meridian of 20 km / h causes the distraction of only 0.5 °, known in navigation as a driving error. At 150 km / h it increases to 5 °. If the top moves along a meridian at the equator's speed of rotation of 1600 km / h, it is 45 °.

The gyrocompass fails near the poles because the earth's axis of rotation points almost vertically out of the surface and the torque projected onto the horizontal plane becomes very small. These problems led to the development of three-gyro compasses .

A gyro compass is sensitive to acceleration (e.g. when a ship starts moving or changes course). The resulting display errors can largely be eliminated by the so-called Schuler vote (for details see Schuler period ). The investigations go back to Maximilian Schuler . Other settings are useful for rapidly changing accelerations, such as those that occur when a ship is pitching or rolling.

A modern gyro compass achieves a dynamic alignment accuracy of less than 0.5 °, better than an optical fiber gyro .

## history

Léon Foucault experimented in 1851 with a gyroscope developed by Johann Gottlieb Friedrich von Bohnenberger in 1810 and rediscovered by Alfons Renz in 2004 and discovered his tendency to align itself parallel to the earth's axis when the axis was forced into the horizontal. In this connection he spoke of a meridian top. Around 1900 August Föppl and others were looking for technical solutions for a rapidly rotating top.

In 1876 William Thomson received a patent for a compass. His student John Perry received a US patent for a gyrocompass in 1919.

In 1904 Hermann Anschütz-Kaempfe received a patent for the technical principle of a gyro compass. Anschütz-Kaempfe was studying medicine and art history at that time. His acquaintance with the Austrian polar explorer Julius von Payer gave him the idea of crossing under the North Pole with a submarine . Anschütz-Kaempfe tried hard to find solutions for the technical requirements of such a trip. Conventional magnetic compasses cannot be used in a submarine because the iron cover shields the earth's magnetic field. He carried out his first tests with prototypes of the new compass on March 11, 1904 on the steamer Schleswig in the Baltic Sea . Since 1908 the gyro compass was used by the German Navy.

At the same time, various other inventors came up with the idea of ​​using a gyroscope in a compass. So let Elmer Ambrose Sperry in 1908 patented a gyrocompass. When Sperry wanted to sell gyrocompass systems to the Imperial Navy in 1914 , a patent dispute broke out between Anschütz-Kaempfe and Sperry before the Imperial Patent Office in Berlin, to which Albert Einstein was consulted as an expert in 1914. He initially spoke out against Anschütz fights. His reason: the patent specification only refers to the Foucault pendulum, but not to the “meridian top”. In Einstein's opinion, Anschütz-Kaempfe had dealt too little with Foucault's investigations into the gyroscope for him to be the inventor.

After Einstein got to know the patent applicant Anschütz-Kaempfe and his way of working, he changed his mind. A personal friendship developed between the two. In another patent procedure in which Anschütz-Kaempfe approached Kreiselbau GmbH because of the invention of the artificial horizon for aircraft, Einstein asked the court in 1918 to dismiss him as an expert. From then on Einstein exchanged ideas about the gyro compass with Anschütz-Kaempfe, which led to a number of decisive improvements and which resulted in the spherical compass , a completely sealed gyro system that is protected against manipulation and largely insensitive to interference. In 1922, Anschütz-Kaempfe was awarded a patent for this, which also mentions Einstein's part in the invention.

The company of the same name founded by Anschütz existed until 1994 before it was taken over by the American company Raytheon . However, it still operates as Raytheon Anschütz GmbH.

Commons : Gyroscopic Compasses  - collection of images, videos and audio files

## Footnotes

1. ^ Heinrich Meldau: The Anschütz gyro compass, self-steering and course writer. Arthur Geist Verlag, Bremen 1935.
2. See Jörg F. Wagner; Helmut Sorg; Alfons Renz: The machine of Bohnenberger . In: GeoBit 10 (2005), 4 GIS, pp. 19–24: Jörg F. Wagner; Helmut Sorg; Alfons Renz: The machine of Bohnenberger . In: European journal of navigation. The leading journal for systems, services and applications, Vol. 3 (2005), 4, pp. 69-77; Alfons Renz: Bohnenberger's gyroscope. A typical Tübingen invention . In: Tübinger Blätter 93 (2007), pp. 27–34.
3. ^ Jobst Broelmann : The emergence of the gyro compass as a navigation aid for military and civil use. In: Roland G. Foerster & Heinrich Walle (eds.): Military and technology. Interrelationships with the State, Society and Industry in the 19th and 20th Centuries. Mittler, Herford 1992, ISBN 3-8132-0368-9 , p. 221.
4. Dieter Lohmeier & Bernhardt Schell (ed.): Einstein, Anschütz and the Kiel gyrocompass. The correspondence between Albert Einstein and Hermann Anschütz-Kaempfe and other documents. Revised 2nd edition. Raytheon Marine, Kiel 2005, ISBN 3-00-016598-3 .
5. Patent DE394667 : gyroscope for measuring purposes. Registered on February 18, 1922 , published on May 8, 1924 , applicant: Anschütz & Co. GmbH.
6. Bernd Sorge: Einstein, Anschütz and the Kiel gyrocompass. In: Brandenburg surveying. Issue 2/2007, pp. 114–116 ( PDF; 72 kB ).