Preserving Warbird artifact at a time.
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Gyrosyn Compass Master Indicator CL2 Sperry RAF Avro Shackleton, English Electric Canberra


Gyrosyn Compass Master Indicator CL2 Sperry RAF Avro Shackleton, English Electric Canberra

This is a Gyrosyn Compass Master Indicator Type C.L.2, made by Sperry, as used in large aircraft in both British military and civil service during the 1950's in Reconnaissance/Bomber aircraft such as the Avro Shackleton and English Electric Canberra, see description below. See photos of its placement at the navigators station in the Avro Shackleton and Canberra. It was also placed in passenger aircraft of the BOAC, according to archival documents, but I've not located any specific photo references.  
Measures 5.75in diameter and ~10in deep, and rather heavy. It is in terrific condition given its age.  The dial markings are clear and the glass and case are intact. The center knob "Autopilot" rotates and centers on a detent, but its function must require the correct electrical input.  The Variation Setting knob rotates the card within the small window north of center. There is a thin sliding ring around the dial to which a small triangular pointer is attached, and opposite of the pointer is a small handle for manually rotating the ring to set the pointer on the desired heading.  

From FLIGHT Magazine April 1954 PPs 390-391
Gyro Magnetic Compass. The G.4.F (fighters) and G.4.B (bombers) will already be familiar to most Service pilots. The instrument supplies on a vertical face a constant indication of actual magnetic heading. No longer need heading information be obtained from the constantly swinging liquid compass and fed into a constantly drifting gyro D.I. This compass is both magnetic and gyro-stabilized. In all reasonable aircraft attitudes it indicates actual heading. There is no noticeable swing or waver, and the face itself is large enough to permit accurate course-holding to within extremely small limits. It functions, moreover in the "natural" sense; that is in a left turn the lubber line moves to the left round the dial, and vice versa.  Being partially a gyro instrument it has, of course, limits (at plus or minus 85 deg in pitch or roll). It may subsequently take a long time to re-align if left by itself—several hours for 180 deg. But this is immediately noticeable, and resetting is simplicity itself. The pilot merely presses the clearly marked button and turns it until the dot and cross in the annunciator window (two o'clock in the dial rim) alternate steadily. If for some reason the magnetic detector unit fails, the compass can be employed as a plain gyro D.I. Sperry produce three versions of the instrument, the C.L.I (and C.L.1A), the C.L.2 and the C.L.3. These correspond respectively to the Services' G.4.F, G.4.B, and G.4.F.T. The C.L.I is a straightforward gyro-magnetic compass using magnets for deviation correction of the detector unit (usually located in the tail or wingtip), an amplifier and the indicator. The C.L.I A is similar, but utilizes an electro-magnetic compensation system, so that this can be carried out from the cockpit. The C.L.2, intended primarily for large aircraft, is the instrument specified for the B.O.A.C. panel. It has a detector unit, an amplifier and a master indicator located at the navigator's position, with a control panel. One or two gyro units almost identical in appearance with the C.L.I are fitted in the pilots' panels. If required, local magnetic variation can be set in at the master indicator so that all indications will be in relation to true north. The C.L.3 is a combination of the C.L.I and 2; it is intended for aircraft in which a navigator is not carried, but where variation control and azimuth monitoring of Air Position Indicator or radio compass are required. The compass dial in this case is identical with that of the C.L.I. It can be said that a compass of the G.4.F type is now regarded as vi for jet aircraft where accurate and constant directional information must be provided, even during violent and prolonged manoeuvring at high speed.

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