I have kept the Canberra instruments as a separate section mainly because in the early days of the Canberra the Instruments were looked after by a separate RAF trade, it wasn’t until 1967/8 that the instrument trade was split up. The general instruments trade (Instrument Fitter General) was amalgamated in to the electrical trade and the Navigation instruments (Instrument fitter Navigation) became the responsibility of the Radio/Radar trades. The oxygen system became part of the airframe fitter’s empire.
A lot of questions are always asked by restorers about the position of various instruments during their restoration process. Without wishing to duck completely the answer to this question it has to be said that the only time a Canberra’s cockpit was standardised was on the day it left the assembly line. From then on it was a free for all depending on the command that it was allocated to, sometimes even the squadron. For various reasons some aircraft would be removed from service for special fits or trials giving rise to unrepresentative cockpits and instrument panels.
Unsurprisingly a lot of the surviving airframes fall in to this category. Restoring one of these does bring its own set of problems I must admit. Having served on a Sqn of PR.7s I can vouch that no two aircraft were identical 10 years on from their build date, this became just an accepted fact. So in my humble opinion there is no holy grail in cockpit restoration, my advice would have to be to research the era you are trying to portray and go for it. To make matters worse the special fits were very rarely ever fully removed and at best would have blanking plates fitted or at worst empty spaces left on the panels just to make restoration a bit more thought provoking.
These notes will attempt to describe the usage and position of the Canberra specific instruments such that you can be familiar with their operation the next time you climb in to a Canberra cockpit. Because of the variety of different marks and sub types I will continue with the theme of trying to address the basic design and not move in to the era of overloaded top consoles or the PR.9.
Going back to the original installation, the design team would have had access to the state of the art WW2 blind flying panel instruments available for the pilot. They would then have to add specific to type instruments in the space available. The navigator would have been furnished with navigation instruments taken straight from the Lancaster, including in the first instance on the B2 a full GEE installation. This didn’t allow a lot of room for the Bomb Aimer so it was a tight squeeze in the back.
Back in those hallowed days the RAF instrument trade group also looked after the Oxygen system which will be described in slightly more detail as it is one system that didn’t change an awful lot during the aircraft's life. High pressure oxygen systems were used to enable the crew to safely breathe pure oxygen in a pressurised cockpit that would be held at a pressure equivalent to 26,000ft. If the pressurisation failed the cockpit could also become a very hostile environment extremely quickly. Oxygen bottles were placed in the top hatch of the Canberra just behind the pressure bulkhead. This kept the high pressure lines to the individual regulators as short as possible. The transformation from high to low pressure was achieved by having a regulator at every crew position, this regulator could also be switched to supply oxygen on a continuous basis as opposed to a demand regime if required.
The high pressure charging point was located, just for reference purposes, in the starboard side hatch. Contents pressure gauges were located on the pilots starboard console, easily distinguishable by their broad red band showing when the contents were at a low level. Pressure breathing white line 'doll's eyes' were located on the regulators that would indicate when oxygen was demanded. The prone position regulator doll's eye was duplicated on the pilot’s front panel so that when the navigator or bomb aimer transferred from his normal seat to the prone position extension hose the pilot could monitor that he was still regularly demanding oxygen and hadn’t accidentally disconnected himself or kinked the extension hose during the transition to the nose position.
Oxygen stop valves were accessible to the crew on both port and starboard sides of the rear crew station to isolate the high pressure system should a leak occur in the cockpit. These were soft wire locked in the “On” position so that accidental operation to the “Off” position was impossible without the wire being broken. Emergency oxygen was supplied courtesy of Martin Baker should the unthinkable happen. This emergency supply was tapped in to the crew members supply by a small rubber hose fitted with a bayonet connection. On ejection the main hose would pull out of the aircrafts supply and a non return valve would close so that the emergency supply would be fed to the crew member during his safe descent.
The Blind Flying Panel shouldn’t need any real explanation, if your reading this, except to say that the gyro instruments were 115V AC electrically powered (not Vacuum). The Turn and Slip gyro was 28V powered, with an emergency supply change over switch located alongside the instrument. This emergency supply lasted for about 20 minutes.
The altimeters initially were both purely static driven devices, later on the pilot had a static-sensed, electrically driven. much more accurate device. The navigator's altimeter, well they fitted a small 115V AC vibrating collar around the basic instrument to keep it on its toes, its purpose was to stop the nav from keep tapping the altimeter to get an accurate reading.
The instruments that were used to indicate the position of trim control surfaces, flaps or Hot/Cold air selector valve all used Desynn transmitters with their respectively marked Desynn indicators. Very important of course for the tail plane indicator to work faultlessly as an incorrect take off or land position for the tail plane could have dire consequences.
The Desynn indicator system uses a variable voltage picked up by carbon brushes from two fixed resistors according to the position of a linked shaft. Not 100% reliable as the brush resistor interface was prone to wear and leave blank spots. This gave a flick of the needle which was disconcerting but sometimes had to be lived with.
The Mk4 Ground Position Indicator was an instrument that gave a fair indication of your ground position. Receiving its data from the Green Satin radar and the G4 compass it was a mechanical computer marvel.
The Air Position Indicator was the same as was used in the Lancaster having been developed in the war. It consisted of an Air Mileage unit fitted in the port wheel well that sent its data to a motor which, via a flexible drive, drove an indicator placed directly in front of the navigator. Once again accuracy was not up to GPS standards.
Also in front of the Navigator in the early Canberra’s would have been the master compass indicator this instrument was easily readable down to a single degree. The compass detector was fitted on the starboard wing tip and the amplifier was fitted in the cockpit starboard side close to the floor. Although the amplifier contained valves it very rarely gave any trouble unless someone spilt fluid in to the ventilation holes. As mentioned earlier, over time other instruments were fitted, some aircraft having Decca Navigator fitted, the first of the really accurate Nav aids that became available. An important instrument for the navigator was the Automatic Direction Finder fitted as part of the Marconi sub-miniature Radio Compass.
VX185 (the prototype Mk5) did have Loran fitted to do an Atlantic trip, but as far as I know this was the only aircraft to ever have this fitted Zero reader and Tacan made life a little easier on both the pilot and the Nav allowing them to get on with the business of the day rather than just wondering where they were. Radio Altimeters of various marks were fitted on certain marks and the altimeter was always fitted on the pilot's panel. But this digresses slightly from the original intention of these Notes.
Returning to the pilot's station the infamous E2 compass sits in the direct vision of the pilot. Needing very careful adjustment during compass swings with a brass key and easily upset by any outside influences it was, as one nav told me, there more as a moral booster than a useful instrument.
Later on and directly in the pilot’s line of sight the resetable G-meter was fitted to give an instant reading of the amount of G he was pulling. A prolonged effort was made to keep the G to a minimum at all costs on the Canberra when it became apparent that the aircraft was going to have to serve much longer than anyone ever anticipated. A lot of knowledge on this subject was gained when using the Low Altitude Bombing System (LABS) showing just how quickly the fatigue life of an aircraft could be used up in a very short period of time. A permanent record of the G pulled of course was kept on the Penny and Giles fatigue meter fitted at the Datum point inside the bomb bay (occasionally in the port wheel bay (B(I)8s)). Read every after flight by the instrument tradesman and then recorded in the F700. Any heavy G usage led to an immediate but unwanted phone call to the squadron commander.
Fuel level gauges were fitted on the engine instrument panel, quite accurate and an extremely reliable system which consisted of capacitor columns and capacitor belts inside the tanks (not the tip tanks). If used, the tip tanks were always full and would start to feed to the rear tank immediately on start up. The varying fuel levels in the tanks altered the capacitance of the units which was in turn fed by coax to several bomb bay mounted Smiths 28V fuel gauge amplifiers. This change in capacitance was converted inside the amplifiers to vary the readings of the fuel gauges.
Very easy to talk about but just ask a Canberra airframe fitter about the problems of getting the capacitance belts to fit inside a replacement tank. Then cover your ears.
Oil pressure indicators unusually used a 28V AC supply which was transformed down from the main instrument inverter to feed an engine mounted transducer (a device which converts liquid or mechanical pressure to a changing electrical output) that was fed to the indicators. A useful feature of this system was that if the power failed to the instrument it would show off scale high or low (depending on type) as opposed to a real time engine oil pressure failure which would indicate a stubborn zero. A clever differentiation on a critical instrument.
Engine RPM indicators used a tried and tested 3 phase AC tachometer bolted directly to the side of the engine to feed the indicators, these required no external power to work correctly and gave very accurate and reliable readings. These remained unchanged throughout the Canberra’s service life.
Hydraulic pressure gauges that indicated main system and brake pressure were normal Bowden tube instruments fed via small hydraulic relay isolation valves that would limit the fluid loss if either a gauge or its associate piping sprang a leak.
Other instruments that were fitted according to need would have included a prone position bomb sight (with an early mechanical computer fitted on the port side prone position) for the bomber versions, a photo sight in the PR versions and of course the 'brought along' sextant if northerly latitudes were on the agenda.
Last but not least of course there was the Sangamo Western DC voltmeter on the main control panel, if this started to show anything other than a stable 28Volts then you knew you were in trouble. English Electric saw fit to have an AC voltmeter on the pilot’s panel on early aircraft but this was removed as it really served no useful purpose because if the AC supply went out of tolerance a top hatch mounted torque meter switch that continually monitored the AC supply would automatically bring on line the standby inverter.
That concludes the instrument section of the Canberra systems not by any means a complete coverage of all the variations that existed but I hope it has given the flavour of the early Canberra instrument fits.