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Distance Reading (DR) Compass, Mk 1

Technical Information

Catalogue No: C1495
Category: Navigation/Inertial
Object Type: Indicator/Instrument
Object Name: Distance Reading (DR) Compass, Mk 1
Part No: 6A/741
Serial No: 2333/42
Manufacturer: Unknown
Year of Manufacture: 1942
Dimensions: Width (mm): 240
Height (mm): 400
Depth (mm): 240
Weight (g): 5,960
Location: Rack RAA10 [Main Store]

A.C.O./ R / 44
DR Compass Mk. 1
Master Unit
Serial No. 2333/42


The Distant Reading Compass was standard equipment in most multi-engined aircraft in the RAF throughout World War II until it was replaced by the Sperry ‘Gyrosyn’ compass. It consists of a master unit containing both the gyro and magnetic elements normally stowed in a part of the aircraft away from large masses of magnetic material which would distort the Earth’s magnetic field. This master unit feeds, through an electrical transmission system, repeater compass cards on the pilot’s and navigator’s panels and wherever heading indications are required. The complete compass system operates from the aircraft 24 V DC supply. The pilot or navigator has control switches for starting and stopping the master unit and a variation setting corrector control to adjust the repeaters to read true instead of magnetic heading. A complete system comprises a master unit, variation setting corrector, a control switch box and a number of repeaters. The master unit holds the magnetic element, the gyroscope, the monitoring and follow-up mechanism and the transmitter for operating the repeaters. The complete assembly is suspended in gimbals.
The system uses an electric magnetic inductor element fixed to the aircraft in azimuth which detects the direction of the Earth’s magnetic field relative to the aircraft and transmits this information electrically to the gyro element.
The D.R. Compass was developed by the Automatic Telephone and Electric Company (in 1961 merged with Ericsson Telecommunications and Plessey to form Plessey Telecommunications) and the Royal Aircraft Establishment from a model originally produced by the Air Ministry and S.G. Brown Ltd in 1934.
Some 30,000 of these instruments were made at the A.T.& E. Strowger Works in Liverpool during the WWII years.
This unit was donated to the RAA by John Jenkinson whose Father acquired it from the Oxford University Physics Laboratory.

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