1、BRITISH STANDARD BS G118:1949 Specification for Aircraft magnetic compass direct-reading NOTEThe Institution desires to call attention to the fact that this standard is intended to include the technical provisions necessary for the supply of the material herein referred to, but does not purport to c
2、omprise all the necessary provisions of a contract.BSG118:1949 This BritishStandard, having been approved by the Aircraft Industry Standards Committee and endorsed by the Chairman ofthe Engineering Divisional Council, was published under theauthority of the General Council of the Institution on 25Au
3、gust1949 BSI02-2000 ISBN 0 580 34527 0 A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Su
4、mmary of pages This document comprises a front cover, an inside front cover, pagesi andii, pages1 and2 and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Amendments i
5、ssued since publication Amd. No. Date CommentsBSG118:1949 BSI 02-2000 i Contents Page 1 Definitions 1 2 General construction 1 3 Detailed construction 1 4 Accuracy 2 5 Corrector 2ii blankBSG118:1949 BSI 02-2000 1 Preferred types and sizes. Pilots compass. 1)1 Definitions For the purpose of this Brit
6、ishStandard the following definitions shall apply: 1.1 magnetic compass a direct-reading instrument for use on aircraft to indicate the direction of the aircraft relative to the earths magnetic field 1.2 friction error the angular distance between the two setting positions when the magnet system is
7、deflected through a specified angle and released first on one side and then on the other side of the meridian 2 General construction The construction of the instrument shall be mechanically sound, suitable for its purpose, and in accordance with the requirements laid down in BS G100, 2)“General requ
8、irements for indicating instruments and electrical apparatus for aircraft.” 3 Detailed construction a) The detailed construction of the instrument shall be in accordance with relevant requirements laid down in BS G100. b) The compass liquid shall be clear and free from bubbles, sediment and discolor
9、ation, and shall contain no materials likely to cause discoloration of the bowl or compass system. It shall not freeze above50 C. Where a bubble trap is provided, bubbles shall not be formed in such a way as to interfere with the performance of the compass. c) The compass bowl shall be provided with
10、 means of preventing leakage of the fluid or formation of bubbles, over a range of temperature from40 to+70 C. d) The compass liquid shall be de-aerated during the filling process, and the compass shall be capable of being used at reduced pressures corresponding to heights up to35,000ft. without der
11、angement or formation of bubbles in the liquid. e) All materials, except the magnets and correcting devices, used in the construction of the compass shall be non-magnetic. f) Any paint or materials used inside the compass bowl shall not themselves discolour or deteriorate under the prolonged action
12、of the compass liquid at any temperature within the range quoted in Clause3 c) and when subjected to the action of strong sunlight, nor shall they cause discoloration of the liquid. g) The pilots compass (platform-mounted type) shall be provided with a rotatable grid ring, and with a system of grid
13、wires and filament wires suitable for parallel steering. The grid ring shall be provided with a suitable locking device. The grid ring shall be graduated from0 to360 with the four cardinal points marked with letters. A lubber line shall be attached to the bowl so that the course can be read from the
14、 grid ring. h) The pilots compass (roof-mounted type) shall be similar to the platform-mounted type, but shall be adapted for mounting in the inverted position and provided with a mirror for taking readings from the pilots position beneath the compass. i) The pilots compass (dashboard-mounted type)
15、shall be provided with a graduated compass card, from which the compass readings are read directly against a fixed lubber line. j) The observers compass shall be provided with a compass card graduated from0 to360 , and a prism or other means for viewing, simultaneously, the compass card and a distan
16、t object. The compass may be a hand-held type, or a fixed type in which the prism or viewing system can be rotated in azimuth with respect to the card and shall be capable of adjustment for distant objects at different elevations. k) The types of compass which are designed for fixing to the aircraft
17、 (i.e.excluding hand-held type) shall contain an anti-vibration mounting to enable the compass to meet the requirements of BS G100. Dashboard mounted BritishStandard aircraft instrument case. Type1. Preferred units of graduation Degrees,0360 . 1) No standard case is applicable to compasses of other
18、types. 2) In course of preparation.BSG118:1949 2 BSI 02-2000 4 Accuracy a) Directional error. The directional error of the compass on any heading shall not exceed 1 , with the exception of dashboard-mounted types in which the error shall not exceed 2 . b) Balance. The magnet system shall be balanced
19、 so that in England the plane of the card or magnet system shall be between the horizontal and an angle of2 North low. A change of vertical force of1C.G.S. unit acting on the compass shall not change the plane by more than3 . c) Angle of heel or tilt. When the compass is tilted from the horizontal,
20、through an angle of18 (or15 in the case of a hand-held type) the magnet system shall remain free to rotate on its pivot. d) Friction error. The magnet system shall be deflected10 and then released first on one side of the meridian and then on the other. The friction error shall not exceed2 at a norm
21、al testing temperature. During this test the compass shall be kept free from vibration. e) Performance. In addition to the information called for in BS G100, the manufacturer shall also provide the following information: i) The magnetic moment of the magnet system (in C.G.S. units). ii) The time of
22、swing as defined by the following test at normal testing temperature: The magnet system shall be deflected90 from the meridian and kept there for an interval of30seconds in order to allow the compass liquid to settle. The time shall be measured for the system when released to return to5 , i.e.,throu
23、gh an angle of85 . iii) The overswing at normal temperature when the magnet system is released from rest at90 deflection. iv) The swirl error, as determined by the following test: The compass shall be mounted in its normal horizontal position with the magnet system lying in the meridian. After allow
24、ing the magnet system to settle, the compass shall be rotated at a uniform rate through360 in30seconds. The deflection of the magnet system shall then be measured and the time taken for the magnet system to return to within2 of the meridian. v) The temperature of the compass and the value of the hor
25、izontal component of the earths magnetic field during each test, for temperatures of the compass of approximately20 C.,15 C. and50 C. NOTEThe temperature quoted shall be the temperature of the compass liquid itself and not merely the ambient temperature at which the test is carried out, which may be
26、 different from that of the liquid. The values differ greatly for different types of compass and hence it is not possible to specify any standard values. 5 Corrector Means shall be provided, capable of being used integral with the compass, or as a separate unit, for correcting the deviations of the
27、compass.blankBS G118:1949 BSI 389 Chiswick High Road London W4 4AL BSIBritishStandardsInstitution BSI is the independent national body responsible for preparing BritishStandards. It presents the UK view on standards in Europe and at the international level. It is incorporated by Royal Charter. Revis
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