Instrument course notebook



Instrument course notebook


56 pages of course notes. Contains basic theory of thermometers, electricity, magnets, dynamos and batteries. Has more detailed notes on the atmosphere and gyroscopes followed by detailed description of Mk IV autopilot and all its component systems including flight controls. Includes hand-drawn colour diagrams.



IBCC Digital Archive


Alan Pinchbeck
David Bloomfield


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Cover and 32 double page notebook





Spatial Coverage


[Front cover]
1477939 LAC. BUBB
Form 714.
Rough Notebook for use in Laboratories and Workshops.
[page break]
[blank page, inside of front cover]
[page break]
[diagram of Fahrenheit and centigrade scales]
[underlined] MERCURY IN STEEL THERMOMETER [/underlined]
[hand drawn diagram of a thermometer]
[underlined] BOURDEN TUBE [/underlined]
[hand drawn diagram of a Bourden tube]
[hand drawn diagram of a bi-metal strip]
[underlined] RADIATOR THERMOMETER [/underlined]
[hand drawn diagram of a thermometer]
[underlined] Vapour Pressure Thermometer
Water B P. [/underlined]
Boiling Point at 10,000 ft is 92o C
Boiling Point at 20,000 ft is 86o C.

[page break]
[underlined] ENGINE CYLINDER THERMOMETER [/underlined]
[two hand drawn diagrams of thermo-coupling]
[underlined] MAGNETISM [/underlined]
[eight hand drawn diagrams of magnetic fields]
[page break]
[underlined] ELECTRICITY [/underlined]
Matter is made up of one or more of the 92 elements on this earth. The smallest particle of any element is an ATOM. Every atom consists of nucleus around which revolves small units of negative electricity called ELECTRONS
[two diagrams of helium and hydrogen atoms]
A [underlined] Conducter [sic] [/underlined] is a [underlined] substance [/underlined] in which there are a number of free electrons. A [underlined] Current [/underlined] of electricity is said to flow when these free electrons are made to move along the conductor by the application of a force called an ELECTROMOTIVE FORCE (E.M.F.)
E.M.F. is measured in VOLTS
An insulator contains very few free electrons and so a flow cannot be so easily set up.
Conditions for a electric current to flow are a complete circuit of conducters [sic]and E.M.F.
An E.M.F. causes a fall of pressure as potential along a conducter [sic] and between any two points in the circuit, there will be a [one indecipherable word] [underlined] potential difference [/underlined] (P.D.) which is also measured in [underlined] VOLTS. [/underlined]
page break]
[underlined] Resistance [/underlined] is the opposition to a conducter [sic] to the flow the electrons.
Resistance is measured in OHMS.
Thin wire has a greater resistance than thick wire.
Resistance of a wire is based upon material and increases with length and temperature.
The electrical energy carried by a current in a circuit is converted into [underlined] Heat [/underlined]
[underlined] Energy, Magnetic Energy [/underlined] and may be converted into [underlined] Chemical Energy. [/underlined] eg. breaking up water into hydrogen and oxygen.
The quantity of electricity is measured in [underlined] Conlombs [sic] [/underlined]
Current strength or quantity per sec is measured in [underlined] amperes [/underlined]
1 AMPERE = 1 CONLOMB [sic] per sec.
i.e. 6.23 x 1018 electrons per sec.
Work = Distance (ft) x Force (lbs)
= Volume or Quantity x Pressure
Power = Work per sec.
(1 HP = 550ft per sec)
Electrical Power = Elect [symbol] work per sec.
Electrical Power = Elect [symbol] quantity x Elect pressure per sec.
Watts = Amps x Volts.
1 KILOWATT = 1000 AMPS (1 HP = 746 watts)
100 WATTS for 10 HOURS
[page break]
[underlined] Resistances [/underlined]
[six hand drawn electrical diagrams]
The ammeter has a very low resistance and is connected in series with the circuit.
The voltmeter has a very large resistance and is connected in parallel with the conducter. [sic]
[page break]
[underlined] OHM’S LAW [/underlined]
This states that for a given conducter [sic] the current flowing is proportional to P.D applied.
[table showing Volts, Current and V/I]
Thus we show V/I is constant. If the above figures are for copper then for a similar gauge iron wire V/I = 14 . Thus V/I for Iron is 7 times as great as for copper. These ratios express the resistance of the conducter [sic] in ohms.
Therefore ohm’s law can be written
V/I = R. I = V/R V = I x R
[page break]
[underlined] Costings of Work Done by Electricity [/underlined]
The rate at which work is done by electricity is measured in [underlined] Watts [/underlined] the cost is measured in kilowatt hrs = 1000 watts for 1 hr = A Board of Trade Unit = 1 B.O.T.O [sic] = [underlined] 1 UNIT [/underlined]
Find the cost of supply a 500 watt fire. 100 watt lamp. 100w Radio for 5 hrs a day - 7 day week @ 1D per unit 2/-1/2
How many 60w on 5 amp @ 240 volts.
60 = 5 x 240
60 = 1200
[page break]
[underlined] MAGNETIC OF CURRENT [/underlined]
[a page of hand drawn magnetic diagrams]
[page break]
Current in the coil makes on face N the other south. Coil moves to bring it’s north opposite south of permenant [sic] magnet and south opposite north. It turns against the hairsprings so that the pointer measures strength of current
[hand drawn diagram of an electric motor]
[underlined] ELECTRO MAGNETIC INDUCTION [/underlined]
[hand drawn diagram of an electro magnet]
When a magnet is plunged into a coil current flows in one direction. When magnet is removed current is reversed. There is only an induced current when lines of force are being cut. The size of the [inserted] induced [/inserted] E.M.F is proportional to the rate at which lines of force are cut.
[underlined] Lenz’s Law. [/underlined] The direction of an induced
[page break]
E.M.F. is such as to oppose the motion producing it.
[underlined] The Simple Dynamo [/underlined]
[hand drawn diagram of a simple dynamo]
Rotating coil in a magnetic field is the easiest way of continuously cutting lines of force and hence of producing a continuous induced E.M.F.
The size of the E.M.F. depends upon 1.) Speed of rotation 2.) Strength of the magnetic field 3.) The number of turns on the coil.
[underlined] D. C. Dynamo [/underlined]
[hand drawn diagram of a brush and commutator]
A commutator is joined to each end of the coil - note that the gap between the two halves is opposite the brushes when the coils vertical. As the induced E.M.F changes its direction the brushes make contact with the reverse ends of the coil. The current therefore always flows out at one brush and always flows in at the other, although it continues to alternate in the coil itself.
[underlined] Modifications to the Simple Dynamo [/underlined]
1) A soft iron armature is used to increase the effect of the magnetic field the iron is laminated in order to reduce eddy.
[page break]
[underlined] PRIMARY CELLS [/underlined]
1.) [underlined] SIMPLE CELL [/underlined]
[hand drawn diagram of a simple cell]
Bubbles will eventually form (HYDROGEN) on Copper plate and so stop current.
2.) [underlined] LACLANCHÉ [sic] CELL [/underlined]
[hand drawn diagram of a Leclanché cell]
3.) [underlined] DRY CELL [/underlined]
[hand drawn diagram of a dry cell]
[underlined] SECONDARY CELL [/underlined]
[hand drawn diagram of a secondary cell]
[underlined] On Charging [/underlined] - By passing an electric current through + plate it becomes lead peroxide, - plate is reduced to spongy lead.
[underlined] On Discharge [/underlined] - Both plates tend to become lead sulphate (white.)
[page break]
[five hand drawn diagrams of electrical circuits]
6 Compare Current passed by
a) Two 3 [ohm symbol] in series
b) Two 3 [ohm symbol] in parallel
at a pressure of 24V.
[hand drawn diagram of an electrical circuit]
[page break]
2). Many turns of wire on H shaped armature
3). Turns are distributed round the core
[hand drawn graph showing electrical output of coils]
The curve is made smoother by circular pole pieces.
The curve is made smoother by diagonal slotting.
Electric magnets used instead of permanant [sic] magnetics.
More than one pair of poles.
[underlined] 2. Phase A.C. [/underlined]
[hand drawn diagrams of electric generation]
[page break]
Suppose two separate but similar A.C. supplies to be plotted on the same graph. It is unlikely to have the maximal of the would occur at the same time. The result shown in the graph could be obtained by having two coils mounted on the same axis at right angles to one another and rotating in the same field. The ends of the coils would be lead to separate slip rings. The result would be two phase A.C. Alternatively the coils could be stationary and the field magnets made to rotate (The Rotor). Advantage equals small currents for field excitation can be fed through brushes and slit [sic] rings while large currents and voltages from the armature are led away through stationary leads.
[underlined] 3. Phase A.C. [/underlined]
See next page.
[page break]
[underlined] Mark IV ENGINE SPEED INDICATOR [/underlined]
Consists of 1 3 phase A. C. Generator 2 Indicator (A.C. Induction Motor Type)
[underlined] 3. Phase A. C.Generator [/underlined]
Consists of 4 pole permenant [sic] magnet which rotates between 3 Stator Coils. 3 seperate [sic] A. Cs will be produced within the coils differing in phase by a 120o hence 3 phase A. C.
It can be seen by fig 2. that the total algebraic sum of the 3. E.M.Fs is zero.
Also it is seen that since the 3 coils of the indicator have equal resistances (i.e. it is a balanced lode) then no wires are necessary to take current back to generator.
[hand drawn diagram of a 3 phase generator]
[hand drawn graph showing 3 phase output, fig 2 mentioned above]
[page break]
[underlined] INDICATOR [/underlined]
[hand draw diagram of an A.C. induction motor]
4 Pole permenant [sic] magnet surrounded by copper sleeve rotates against tension of hairspring carrying the R.P.M pointer.
[page break]
[underlined] The Atmosphere
Composition [/underlined] An ocean of air round the earth. Air is a mixture of 79% Nitrogen 20% Oxygen 04% Carbon di-oxide water vapour and dust.
[underlined] Air Pressure [/underlined] At S.L. 1 cu. ft of air weighs .08lb. Air pressure is the [underlined] total [/underlined] weight of a column of air to the top of the atmosphere. It can be measured by the mercury Barometer ([one indecipherable word] type very accurate) aneroid Barometer (without liquid therefore portable).
[underlined] The Altimeter [/underlined] the Altimeter is fitted in all aircraft and it measures the height of the aircraft above sea level. [underlined] It is an aneroid Barometer [/underlined] with the scale calibrated in feet. This is possible because air pressure [underlined] falls with height [/underlined] 1 in of mercury per 1000 ft or 1 [indecipherable character] millibar 30 ft. The air tight case is connected with the static tube. [deleted] Atmen [/deleted] At mean S.L. air pressure is 14 lbs per [square symbol] “ or 30” of mercury or 1013.2 millibars.
[underlined] Calibration [/underlined] since the pressure at a height is affected by the temperature of the an altimeter has to be calibrated by assuming certain atmospheric temperatures etc.
A formula connecting height with
[page break]
pressure can be worked out knowing 1 M.S.L. pressure 2 M.S.L. temperature. 3 Temperature at a given height.
[hand drawn table of temperature and pressure]
[page break]
[underlined] Conversion HG - MB [/underlined]
[hand drawn graph of Inches of Mercury and Millibars]
[page break]
[underlined] BOOST GAUGE [/underlined]
1/2 LB [square symbol] “ = 1” H.G. (APPROX)
HENCE 1” HG ABOVE 30” DEDUCT 1/2 LB [square symbol] “
1” HG BELOW 30” ADD 1/2 LB [square symbol] “
[page break]
[underlined] The Gyroscope [/underlined]
[two hand drawn diagrams of a gyroscope]
[underlined] Properties of Gyroscope [/underlined]
1 The rotor tends to maintain its plane of spin in space.
2 A force tending to twist the outer ring (torque) causes precession of the inner ring. Torque on inner presses outer ring.
[underlined] Sperry’s rule of precession [/underlined]
Replace the torque by push on rim of the rotor. A point 90o in direct of spin will by [sic] in direction of precession.
[underlined] Earth Gyro.[/underlined]
If the inner ring is purposely unbalanced by a weight it can be made to precess the outer ring round in step with earths rotation.
[underlined] Connection between Size of Torque & Speed of Precession [/underlined]
The size of torque required :- Increases with 1 rate of precession
[page break]
2 Speed of Rotor 3 Weight of Rotor, 4 Diameter of Rotor.
Simple fractions - Cent - Fahren - inches to miles - Ohm’s law - amps, watts, volts.
Electricity - accumulator - dynamos. Electric Motors. AC - DC. Generators. - Atmosphere. [two indecipherable words]
[page break]
[underlined] Installation of Follow Up Cable [/underlined] (Cont)
the loop in the end of the spring slips over the pin projecting from the mounting unit.
The servo-motor piston must be placed in an extreme position so that the cable may be attached to the short end. Attach the cable to the piston by a shackle, the pin of which must locate in the slot of a Clevis plate underneath the servo-motors. Pass the cable around free pulleys where necessary and lead it to the rear of the mounting unit. Before attaching cable to the pulley rotate it round until it is fully wound and release 1/4 of a turn. Pass the cable once round the pulley and through the hole provided and mark where it passes through the hole. (Disconnect the pulley and cable and then solder the nipple on the end of the cable). Apply opposite extreme [one indecipherable word] holding tension on pulley, now pull slack cable through the pulley and tie knot where marked. Tin the cable before
[page break]
cutting off the waste correct installation may be checked by the direction of movement of the follow up pulleys or the follow up indices.
1 Elevator [underlined] down. [/underlined] [symbol] index moves up: [symbol] pulley moves anti - clockwise
2 Right aileron [underlined] up. [/underlined] - [symbol] index moves right. [symbol] pulley moves anti - clockwise.
3 Right rudder. [symbol] index moves left. [symbol] pulley moves anti - clockwise. The servo - motor piston must be central before this check is carried out.
[page break]
[hand drawn diagram of a automatic control pipe lay-out]
[page break]
[underlined] Mk IV Auto Pilot - George
Compressor [/underlined] This is the eccentric type of rotary compressor, having the two compression chambers set at 180o apart. Each chamber contains a light alloy rotor with 10 steel blades. Free to slide in slots. The blades are thrown out by centrifugal force into contact with the linings of the compressor. This is drawn in as the space between the rotor and the casing increases and when the space is decreasing, is compressed and forced out at high pressure. Oil is admitted to the chamber through two jets size 42 thousandth front and 63,000th rear and is required to seal the compartment for air tightness and to lubricate. There are three unions, air inlet, oil inlet, and delivery from which air at 60lbs per [square symbol] “ is emitted. Filters are fitted in the inlet union oil and air. Before fitting new compressor check the following. 1 Correct type 2 Removal of inhibitor [deleted] gun [/deleted] [inserted] oil [/inserted] by washing out with anti - freezing oil 3 Check gland asbestos yarn gasket etc 4 Check copper washers for correct size and
[page break]
[two hand drawn diagrams one of an Oil Reservoir and Separator and one of an Automatic valve]
[underlined] Oil Reservoir & Seperator [sic] [/underlined]
The lower part of this is for the oil, the upper part being the seperator, [sic] air & oil from the compressor impinge on the wall of the reservoir the oil falling to the bottom to be re-used, and the air going up through the union to the next
[page break]
component, the chemical Air Dryer. From the lower part, oil is fed through a filter to the oil cooler which has a finned radiator. The oil then passes to the Automatic Valve which can be situated between the reservoir and the cooler or between the cooler and compressor. If the reservoir is fitted lower than the compressor the valve ensures an oil supply to the compressor on starting. If the compressor is lower than the reservoir the valve prevents the former from being flooded with oil when it is not in use. It is fitted in the lowest part of the oil system. Oil changed on each minor. Automatic Valve and Oil Cooler flushed with 50 - 50 anti - freeze and petrol and system re - pressured [inserted] [underlined] NB [/inserted] [/underlined] There are fibre washers on Oil Reservoir. Oil level [inserted] to be [/inserted] maintained. Arrow of Auto - valve points in direction of Compressor.
[page break]
[five hand drawn diagrams showing Chemical air Dryer, Automatic Test Cock and Main Control Cock]
[page break]
[underlined] Chemical Air Dryer [/underlined] (To prevent freezing up)
The Chemical Air Dryer consists of an inner and outer container, the former being filled as follows, 1 gauze disc, 2 silica Gel, (To within approx 1/2” from the top) 3 gauze filter, 4 Half inch cotton wool and then the perforated lid. Recharging must be done immediately prior to flight. 1 Wash container with hot water and allow to dry before using. 2 Silica Gel must be returned to stores in tins provided when u/s. Silica gel is u/s when colour changes from white to brown.
[underlined] Test Cock. [underlined]
This is a three - way cock having two positions. In the test position air is supplied to the units from an outside source. In the flying position, air from the a/c compressor passes straight through the cock to the main control cock. 1 On a Mk IV ensure that cock is lock [sic] in flying position on D. I and between flight inspections. 2 Mk IV A Check that locking tab is in position on
[page break]
D. I and between flight Inspection. If it is necessary to strip the cock ensure when replacing together that plunger is put in the correct way - blanked - off end to the top of Test Cock.
[underlined] Main Control Cock [/underlined]
This has three positions, 1 [underlined] Out [/underlined] :- the jets and centraliser are connected to atmosphere by annular groove air passes back to regenerated system through a choke which is fitted to maintain a pressure so that; a There is always an adequate supply of oil to the compressor b So that [one indecipherable word] seperation [sic] is ensured.
2 [underlined] Spin [/underlined] :- air is fed to the jets, relay valve, torque valve and steering control. The centraliser pipe-line is still exhausted to atmosphere.
3 [underlined] In [/underlined] :- air is fed to the above components and the centralisers, to de-centralise the gymbal system and feed the main valve
1 With datums coincident on the
[page break]
inner and outer barrels M.C.C is then in the out position.
2 The handle can be fitted in any six positions
3 Name plate fitted with the “Out” in line with the handle when datums are coincident.
4 Ensure distance pieces fitted between name plate and outer casing
[hand drawn diagram of an Air Intake Throttle]
[page break]
[underlined] Air Intake Throttle
Purpose [/underlined] To maintain and regulate a pressure not exceeding 60lbs [square symbol] “ in the system, and to act as a non-return valve to prevent air from Compressor (Oil Reservoir & C.A.D) carrying oil along regenerative pipe lines.
[underlined] Description [/underlined]
Has three connections, to Compressor, Regen & Supply systems. Consists of a sylphon bellow the outside of which is sealed off. Inside is a powerful spring which normally holds them open, a piston runs down the centre and when engine is not running, a small return spring pressing against a collar on the piston holds the piston on the seating and gives a non - return action. When engine is started the piston is drawn of its seating as the Compressor commences to draw air in.
The lower connection (supply) feeds the air round the bellows. As pressure increases in the system this pressure will increase and the bellows
[page break]
will be contracted against tension of spring the piston will then be forced up off its seating and air supply to Compressor will be cut off.
An inlet or breather at top of A.I.T. allows an additional supply of air to be sucked in when starting - up it also acts as a compensator for slight leaks. An arrow indicates direction of flow to Compressor.
Is situated on teed piece between A I Cock and Main Control Cock.
[underlined] Steering Control [/underlined]
Is used by Bomb aimer or Pilot can do a course change. Filter in inlet (centre connection) gauze and cotton, through which air passes into the two compartments beneath the knife edge valves which are held in position by a spring. Air leaves the compartment by the two outside unions at base and on to course change valve via turn regulator.
When steering control is operated, the pulley rotates the rotor arm which forces
[page break]
[underlined] STEERING CONTROL [/underlined]
[hand drawn diagram of steering control system]
[page break]
one of the leak valves resting on the springs in the compartment. This valve depresses the knife edge valve and so prevents air from entering. At the same time air escapes through the leak valve and so pressure in compartment will fall. This will effect the the [sic] pressure on that side of the course change valve, and as the pressure on oposite [sic] still remains at 60lbs [square symbol] “ the valve will move and through links and levers will apply torque to the inner ring of gyro which will precess outer ring. As rudder control valve is connected to outer ring there will be a movement of the rudder via the servo.
The filter is cleaned on every Major inspection.
[underlined] Steering lever [/underlined] To enable pilot to change course of a/c - is connected to steering control by a bowden cable.
[underlined] Steering Control [/underlined] - Test before installation by applying pressure of 60 lbs and attaching U tube of wow water to outlet - allowance of 1/2” on each side
[page break]
[underlined] AILERON CENTRALISER [/underlined]
[hand drawn diagram of an Aileron Centraliser]
[page break]
[underlined] Servo Motors
Follow Up [one indecipherable word] Guide [/underlined]
[hand drawn diagram of a disc with numbers on and a corresponding chart of numbers and letters]
[underlined] Clutches
D I [/underlined] 1 Take clutch lever out and test a/c controls by moving pulley in all all [sic] directions (reason to prove a/c controls are OK.) Put clutch lever in move each a/c at control singly should hear clutch slip in. Test a/c controls with clutch in. [underlined] Leave clutch in [/underlined]
There is an overide [sic] on the servo. Movement of a/c controls with clutches in is not so great as when clutches are out.
[underlined] Stripping of Servo Motor Clutches [/underlined]
1 Remove 2 BA nuts and locking tap from top of operating spindle
[page break]
2 Remove split pins and take out clutch locking assembly pins, remove clutch claw arm.
3 Remove spring tension assembly with box spanner.
4 Remove clutch plate from splined shaft with special tool (Extractor)
5 Remove follow - up pulley and dowel plate by means of two 4 BA screws taking care not to damage flange underneath.
6 Remove stop plate assembly.
[hand draw diagram of a R. E. Centraliser assembly]
[underlined] R. E. CENTRALISER [/underlined]
[page break]
[two hand drawn diagrams of Clutch Cable Layouts]
[underlined] CLUTCH CABLE LAYOUT [/underlined]
[page break]
[hand drawn diagram of a Rudder and Elevator Unit]
[underlined] RUDDER AND ELEVATOR UNIT [/underlined]
[page break]
[underlined] RUDDER & ELEVATOR UNIT [/underlined]
[hand drawn diagram]
[underlined] The Gyroscope [/underlined] is pivotted [sic] 15o off the vertical and also off centre. [underlined] The Azimuth Balance [inserted] Adjustment weight [/inserted] [/underlined] is attached to the inner ring and controls the amount of precession on the outer ring. [underlined] The Out of Balance weight [/underlined] precesses the inner ring to [inserted] conform to [/inserted] the earth’s curvature. [underlined] The Azimuth Balance [/underlined] helps to precess outer ring to the earths rotation. [underlined] Watts weight [/underlined] 1. Counteract the effect of centrifugal force on out of balance mass when [inserted] flying straight [/inserted] 3 To give extra stabilisation.
[underlined] Cross Balance Weight [/underlined] is to steadily
[page break]
balance outer ring. [underlined] Top and Bottom balance weight [/underlined] is to steadily balance inner ring
[hand drawn diagram of component layout]
[page break]
[underlined] PRECESSING VALVE AND TORQUE MOTOR [/underlined]
[hand drawn diagram of a Precessing Valve and Torque Motor]
[page break]
[hand drawn diagram of a Relay Valve]
[underlined] RELAY VALVE [/underlined]
[page break]
[hand drawn diagram of Elevator Movement Mechanism]
Aileron Plate [/underlined]
Force of Gravity Control Weight counteracts the forces in either direction of fore and aft of the a/c.
[page break]
[underlined FILTERS
Rudder and Elevator Plate. Subsidiary Main [/underlined]
Rudder Main Valve. 3
Elevator and Elevator Valve 3
Relay Valve 1
Course Change Gear 2
Spinning Jet 1
Centraliser 2
Servo motor pipes 2
[underlined] Components [/underlined]
Anti Intake Throttle 1
Compressor (Air & Oil inlets.) 2
Oil Reservoir Outlet 1
Chemical Air Dryer 1
Steering Control 1
[page break]
[underlined] CABLE LAYOUT MK IV [/underlined]
[hand drawn diagram of a cable layout]
[page break]
6. Look for cable fraying or cracking and test spring tension of Spring Tensioner.
[page break]
[underlined] BREEZE WIRING CONDUIT [/underlined]
[hand drawn diagram of components]
[page break]
[underlined] Fault Finding [/underlined]
1 Indic reads above zero when empty.
2 Pointer does not move off vertical when switched on or tank being filled.
3 Pointer comes 180o in advance when switched on and rotates correctly.
4 Pointer gives a fixed reading when tanks are known to be empty.
Bent plunger.
Broken supply lead.
Brush not contacting resistance.
Bad contact at indicator.
Crossed supply leads.
Locating [inserted] pin [/inserted] dislodged from brush.



George Bubb, “Instrument course notebook,” IBCC Digital Archive, accessed August 25, 2019,

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