Examination of German Gyro-Sextant
S KS - 3D.
S U M M A R Y.
The gyro sextant described is a modification of the standard German (Plath) Bubble sextant, in which a gravity controlled gyro has replaced the bubble. There is nothing novel in the sextant construction or in the averaging mechanism, but it has been fully described in this report for record purposes. The gyro is stable and induced precession dies away rapidly.
The sextant is heavy and somewhat awkward to use and its accuracy under stable conditions is not as good as that of a bubble sextant.
The dimensions of the Gyro sextant are as follows: -
Length 14 inches.
Width 6 inches.
Height 10 inches.
Weight 6 Ibs. 12 ozs.
Gyro-Operation and accuracy.
The purpose of the gyro is to provide a stable artificial horizon for the sextant,as it only stabilises a beam of light, and has no mechanical output, it is possible to reduce it to a simple bottom-heavy rotor, running on a point in a bearing cup. The rotor is air-driven, and is run up to about 1200 r.p.m., either with a pump (hand or foot) or with compressed air. Observations are taken on the sextant while the gyro is running down, probably over the speed range 800 - 300 r.p.m. This allows about 12 mins. (See graph, page 5). The appended translation of the working instructions gives a good idea of the method of operation.

The gyro sextant in the form described is not considered satisfactory. Extreme care in handling is necessary and since the gyro line of sight is maintained in the horizontal by the resultant direction of gravity it is improbable that accurate results will be obtained on a rolling ship. The bubble sextant is more convenient and gives results of equal or better accuracy. Either type of Sextant should be capable of giving a fix at sea, under calm conditions, within one to three miles, and provided a large number of observations are made similar accuracy may be obtainable in a moderate sea.




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