General

Fuel

Oil

Type Specification: D.T.D. 109
Consumption at maximum cruise: 10 to 20 pints per hour
Main Pressures: Normal: 90 psi; Emergency minimum (5 min) = 70 psi
Auxiliary Pressures: Normal: 6 psi; Emergency minimum = 2 psi
Inlet oil temperatures: Minimum = 15°C; Maximum = 90°C; Emergency Maximum (5 min) 95°C

Ignition

Firing Order:
    1A, 3D, 2C, 6B, 3A, 5D,
    1C, 4B, 5A, 6D, 3C, 2B,
    6A, 4D, 5C, 1B, 4A, 2D,
    6C, 3B, 2A, 1D, 4C, 5B.
Magnetos: Two Rotax NG 2-1 duplex
Rotation Direction: Starboard = CCW; Port = CW (viewed from breaker end)
Speed: 1.5 x Crankshaft
Timing (fully advanced): Starboard (exhaust plugs) = 57° BTC; Port (inlet plugs) = 50° BTC
Timing (fully retarded): Starboard = 22° BTC; Port = 15° BTC
Contact breaker and spark plug gaps: See A.P.1374
Distributors: Two Rotax ND 24-4 duplex distributor heads

Carburation

Maximum Fuel Demand: 162 gph
Carburettor: S.U. type Vulture A.I.T. 42 downdraught, duplex, double entry
Feed pressure supply: 2.00 – 2.75 psi

Valves

Valve Timing: Inlets open 24° BTC; close 60° ABC; Exhausts open 60° ABC; close 20° ATC
Valve clearance (hot or cold) = 0.020"

Coolant

Type: 70% water, 30% ethylene glycol (Specification D.T.D.116A)
Outlet temperatures:
    Minimum for takeoff: 60°C; Maximum for cruising: 100°C
    Maximum for 30 min: 120°C; Maximum for climb, level flight: 120°C

Starting system: Electric turning gear. Hand turning gear for turning engine only

Airscrews:
    de Havilland variable-pitch, 35° pitch range, with constant-speed and feathering control
    Rotol variable-pitch airscrew, 35° pitch range, with constant-speed control

The Rolls-Royce Vulture II and IV engines had 24 cylinders arranged in four blocks, each having six inline cylinders; the blocks were mounted on a common crankcase at 90° angles to one other in an X-form The engine was fitted with a two-speed supercharger, a downdraught, twin-choke (twin-venturi) carburettor and an airscrew reduction gear.

The four light-allo cylindery monoblocs were mounted on the common crankcase's four faces. Separate wet steel cylinder liners were used. Liner shoulders at each end abutted the cylinder block and crankcase. Each cylinder had two inlet and two sodium cooled exhaust valves. Each cylinder block's valves were operated from a single centrally disposed camshaft through individual tappet fingers.

A balanced six-throw crankshaft was supported within the crankcase in seven lead-bronze lined bearings. The articulated H-section connecting rods were steel forgings with the master rods located in the lower starboard or D-block. The master rod carried one articulated rod and the cap carried the remaining two. A divided steel bearing shell lined with lead-bronze was captured by the master rod and cap. A floating phosphor-bronze bush was fitted in each connecting rod small end. The forged light-alloy pistons were fitted with three compression rings and two grooved scraper rings. Hardened steel floating gudgeon-pins were used.

A propeller reduction gear case was bolted to the crankcase front. A wheelcase was mounted at the crankcase rear. The wheelcase housed the drives from the crankshaft rear to the hand and electric turning gear, auxiliary gearbox drive, coolant pumps, etc. The wheelcase provided mountings for the starter motor, auxiliary gearbox tower (Vulture II), auxiliary gearbox (Vulture IV), oil pump unit, coolant pumps, and electric generator (Vulture IV).

A two-speed centrifugal supercharger was driven from the crankshaft rear end through three centrifugally-loaded clutch wheels that absorbed the high inertia loading resulting from rapid acceleration and deceleration, while torsional fluctuations were absorbed by a spring-drive shaft. The supercharger drive was transmitted through only one centrifugally-loaded clutch when in low gear, while the remaining two transmitted the drive in high gear. The clutch wheel control that determined whether the low or high gear ratio was in action, was effected by formed levers actuated by an intermediate camshaft. The camshaft itself was controlled by a servo cylinder unit operated by scavenge oil pressure. The servo cylinder incorporated a rotary valve, controlled from the cockpit, by means that either low or high gear ratio was selected.

Carburetion was provided by a twin-choke coolant-jacketed and oil-heated carburettor that incorporated both an atmospherically-controlled mixture controls and a boost pressure controlled unit. The carburettor operated in conjunction with a progressive boost control unit.

Flight Operation

Airscrew Pitch. Vulture II and IV engines were arranged to use a variable-pitch airscrew with a constant-speed control. The cockpit governor control, in conjunction with the throttle, could be set to maintain the maximum limitations for each flight condition detailed in the Leading Particulars. This ,governor control was set to maintain the rpm for the following maximum operating conditions:

During continuous cruising (including economical cruising), the throttle and governor control were set to give optimum cruising conditions within the respective permitted ranges. Under no circumstances were the controls set to give more than 2,600 rpm.

Climbing Power and Boost

Two-Speed Supercharger Operation. During takeoff and initial climb the supercharger control was set to the low gear position and left there until an altitude of approximately 8,000 ft was reached, at which time the boost would have fallen to about +3 psi; the change to high gear was not made as soon as the boost fell below +6 psi; although the high-gear boost would have been higher for the, the engine power output would have been less. Above 8,000 ft, high gear was engaged if the climb rate was to be maintained. The limiting boost pressure of +6 psi and 2,850 rpm was not exceeded during climb in either gear.

During rich-mixture cruising and for economical weak-mixture cruising the low gear gave greater fuel economy than the high supercharger gear at all heights, and no improvement in performance was obtained by the use of the high supercharger gear below a height of approximately 7,500 ft when cruising with rich mixture, or approximately 12,000 ft when cruising at economical conditions. For emergency operation, the low gear was used up to a height of approximately 8,000 ft. Above this height the high gear gave better performance. For high speed diving the low speed gear was engaged. When coming in to land, the low speed gear was engaged to permit a rapid transition to takeoff power if necessary.

Vulture II and IV engines were normally mounted with the cylinder axes 45° to vertical with the induction manifolds in the upper and lower Vs and the exhausts discharging from each side V. Viewed from the airscrew end, the blocks were designated A, B, C and D when reading clockwise; A block was the left-upper one. A compound reduction gear enabled the airscrew shaft to be mounted coaxially with the crankshaft. A two-speed supercharger, automatic progressive boost control and an automatic carburettor with a two-position (Rich-Weak) automatic mixture control were fitted. A five-drive auxiliary gearbox, fitted separately on the Vulture II engine mounting bulkhead at the engine rear, was operated through a vertical shaft geared to the wheelcase right-hand drive, as were the electric generator, hydraulic pump, vacuum pump, R.A.E. compressor and gun-turret pump. Vulture IV engines were fitted with a three-drive auxiliary gearbox on the wheelcase underside; the electric generator was mounted on the wheelcase top.

Cylinder Blocks	Crankcase

Each cylinder block was a single aluminium casting, comprising the head and the coolant jacket. Wet steel cylinder liners were provided with shoulders that fitted against the crankcase at one end and the cylinder block at the other. A coolant joint at each liner's base was made by two rubber cellular gland rings fitting within grooves in the liner. As the coolant jackets did not make contact with the crankcase, any leakage from these joints was carried to the engine exterior. Crankcase oil leaks were also prevented by another rubber ring that was pressed by the liner flange into a chamber in the spigot bore.

An aluminium joint ring was captured between the upper shoulder of each liner and the cylinder block. The resulting joints in each block and were maintained by 26 long studs that extend from the crankcase through to the block tops. The reaction of these studs was taken by the cylinder liners and ensured sound joints at either end. Ten of these long studs extended from the crankcase through the coolant jackets to the cylinder block tops. They were enclosed in Staybrite (18/8 stainless steel; 18% chromium, 8% nickel) tubes whose ends made coolant joints with the block casting; clamps at the stud upper ends distributed the pressure on each side. Four of the remaining sixteen studs were used at the block extremities two at each end; these were not enclosed in tubes as collar nuts were fitted to them. The remaining twelve studs passed from the crankcase to the cylinder head, and were being retained to the crankcase by a saddle formed at their base, through which passed short studs from the crankcase. Oil leaks were prevented where the cylinder liners spigoted into the crankcase by thin rubber rings that were captured by each flange against the crankcase. Each combustion chamber was independent and not directly bonded to its neighbor, thereby giving increased flexibility. Each rocker core formed a joint between the cylinder head and cover.

Valves

Each cylinder had two solid inlet valves and two sodium-cooled exhaust valves, all with their valve stem tips Stellite-faced. Single overhead camshafts, in conjunction with rockers, actuated the valves. Screws and locknuts on the rockers provided valve clearance adjustment. The valves were retained in their seats by two concentric coil springs, a nickel steel washer and a split collar. The spring lower ends were located in another nickel steel washer that rested on the cylinder head. A spring circlip around the valve stem retained it during spring removal. The phosphor-bronze exhaust valve guides and cast iron inlet valve guides were pressed into the cylinder head. As a further precaution against wear due to high operating temperatures, a Brightray steel (high-temperature nickel-chromium alloy) surface was applied to the exhaust valve seat and face; the valve seat inserts were of high silicon chromium steel, screwed into the block. Each block's camshaft and rocker shafts were carried in seven aluminium brackets and secured to the cylinder head by studs. Each camshaft was driven from the reduction gear at the engine front by an inclined shaft and bevel gears.

Crankshaft and Rods

The crankshaft was carried in seven flanged split main bearings located in the crankcase halves and lined with lead-bronze. Longitudinal spigots located the crankcase halves ensured the crankshaft and bearing rigidity, but also providing for the transverse firing pulse reaction. Rigidity was further ensured by diagonal bolts passing through the main bearing housings, two on each side of the transverse housing centerline. Pressurized oil was conveyed from the main oil gallery to the bearings by drilled crankcase passages to each bearing. The main hearings were supported by seven stiffening ribs in each crankcase half, and to ensure rigid main bearing shell location, the spigot length exceeded that of the opposite half-casting by 0.00015 to 0.00020". The groove width was also made 0.00025" to 0.00050" wider than the corresponding spigots in order to give assembly freedom without slackness. The lower crankcase half carried the main oil gallery pipe and the scavenge suction pipe.

Vulture II Gear Train and Timing

The inner reduction gear casing was bolted to the crankcase front face. Four inclined camshaft drives merged into the front crankcase and were fitted with bevel gears at their lower ends.

The inner spring drive shaft was of nickel steel and was serrated at the forward end. A master spline was formed so that the shaft could only he replaced in one position. The shaft central portion was waisted to give the necessary torsional flexibility and the rear end was also furnished with splines to engage the main driving gear. A master spline was also provided at the aft end. The outer drive coupling was hollow and was splined externally at both ends. It engaged the crankshaft driving bush at its forward end and the supercharger main drive gear at its aft end. The latter extended rearwards to provide the necessary length for the spring-drive shaft. Its aft end was internally serrated to engage with the spring drive shaft. Internal splines at its approximate center, engaged the drive coupling rear splines. A nut and lock washer retained a ball race located on a shoulder formed on the main drive gear aft end outer periphery An adjusting washer was fitted on the bearing inner side. At the forward end a roller bearing was fitted on the main drive gear shoulder and retained in position by the outer race. The high inertia loading, resulting from rapid supercharger impeller acceleration or deceleration, were absorbed by the friction drive, which transmitted the drive to the supercharger driving wheels.

Vulture II Accessories

The auxiliary gearbox drive was transmitted from the right layshaft though a spur gear with an integral bevel gear at its rear that engaged two further bevel gears, both of which were internally serrated. On the Vulture II engine, the upper bevel gear engaged the vertical shaft that drove the five-drive auxiliary gearbox main shaft through a further bevel pinion. On the Vulture IV engine, the upper bevel gear and its vertical shaft drove the electric generator that was mounted directly to the wheelcase top facing. The lower bevel gear drove the fuel pump and the three-drive auxiliary gearbox mounted directly on the lower wheelcase facing. The spur and integral bevel gears were serrated to a layshaft that carried the drive rearwards to a spur gear that engaged with the coolant pump drive. The spur and bevel gear was secured to the screwed layshaft at the forward end by a nut and key washer. A roller bearing was interposed between the bush on which the gear bore and the washers. At the rear, the spur and bevel gear shaft abutted against an adjusting washer and had a ball bearing mounted on its aft side.

Coolant was distributed by two centrifugal pumps mounted at the engine rear. The port pump was driven indirectly from the crankshaft through the port layshaft, which engaged a spur gear with a shaft extending aft to finally engage the pump drive. The starboard pump was driven by a similar spur gear arrangement. Each coolant pump circulated coolant through the upper and lower blocks on the side where the pump was mounted. Each pump had an inlet from the radiator and two outlets to the blocks. The block coolant outlets merged and led from each upper block into a the header tank. Air vents for use when filling and drain plugs were also provided.

Fuel Pump

The gear-type fuel pump was driven from the starboard layshaft through a bevel gear, lower auxiliary drive and a skew gear. Inlet and outlet pipes connected it to the aircraft fuel system and engine fuel system. A disc and relief valve fitted in the pump casing rear end returned surplus delivery-side fuel to the inlet side through a pump casing passage. Oil delivered through a pipe and union lubricated the drive shaft and bearing at the front end; these formed a part of the main pressure system with one end being attached to the pump casing. Passages in the casing conveyed oil to the drive shaft forward end. The pump gears, gear bushes and drive shaft bushes at the casing rear end were fuel lubricated. The pump support bracket was drilled to communicate with the fuel inlet and small radial drillings in the support bracket enable fuel to reach the pump driven gear bush. A drilled passage in the pump casing communicated with the support bracket drilling, and fuel for lubrication purposes was delivered to the rear driving shaft bush. A common drain passage for both oil and fuel was provided between the oil passage and fuel lubricant passage in the pump casing. A fuel pressure reducing valve was mounted near the carburettor on the left side; this valve maintained a constant fuel pressure of approximately 2 psi under the conditions encountered during flight when starvation might occur. Flexible piping from the fuel pump supplied the reducing valve, which delivered direct to the carburettors on the left side. An air balance pipe connected one side of the valve control diaphragm with carburettor air intake pressure, which was also connected to the float chamber, thereby placing the three in equilibrium.

Two-Speed Supercharger

Supercharger Casing

The high speed centrifugal supercharger used with Vulture II and IV engines incorporated a two-speed gear that provided a moderate gear ratio (5.464:1) for takeoff and low altitude flying, and a higher gear ratio (7.286:1) for high altitude flying. These two ratios gave calculated impellor speeds of 15,572 and 20,765 rpm at normal engine speed (2,850 rpm). Layshaft spindles disposed in planetary form around the spring drive and supercharger impellor drive with centrifugally-loaded clutches in their driving gears comprised the driving assembly. The impellor was coaxial with the crankshaft and enclosed by the supercharger casings. The supercharger casing inner half was bolted to the wheelcase and also supported the drive's forward ball-bearing. The casing outer half supported the intake elbow and driving spindle at the rear end. The inner and outer supercharger casings were aluminium alloy castings. The inner casing housed the diffuser vane ring, rotor and rotor guide vanes. The diffuser vane ring was machined from an aluminium alloy casting and had tangentially-disposed diffuser vanes. The ring was supported in the inner casing by square-section studs that fitted into square apertures in the ring; nuts, lock washers, etc., on the outer casing exterior retained them in position; the vane ring studs also helped secure the outer casing. The impellor comprised the rotor and guide vanes, with the two blade sets mounted in a continuous manner. The rotor was machined from an aluminium alloy forging and the guide vanes from a nickel steel forging. Both parts were internally serrated and engaged the serrated rotor shaft at the rear end. A square-sectioned rib on the impellor front face rotated in a concentric groove formed on front half casing rear face. A similar rib on the guide rear face spigoted into the intake elbow front face. At the casing rear end the intake spigoted into the casing and the two parts formed a housing for the drive rear end. A drilled passage, suitably plugged, at the base of the front casing connected with an annular space in the volute casing front from which oil from the spindle forward bearing drained. This passage was connected by another passage with the drain at the casing bottom. The drain was also connected by a vertically-drilled passage, with another passage that registered with a drilling in the intake elbow, which drained oil from the rear bearing.

A ball-bearing on the rotor pinion rear side carried the rotor shaft and was retained in a housing by a circular nut threaded onto the casing boss. An oil slinger fitted behind the ball bearing lubricated it. The rotor shaft rear end was enclosed by phosphor-bronze floating bushes. The outer flanged bush was fixed in the casing and enclosed the outer bush floating bush; the inner bush carried the rotor shaft. An oil pipe connected to the intake casing base lubricated the bushes through a drilled passage in the casings. The rotor shaft was threaded to accepts a washer, nut and a lock washer that retained the guide vane bush immediately forward of the flanged bush.

An oil relief valve and union were fitted at the supercharger base. Scavenge oil from the engine sump passed through the union and upwards via an external pipe to circulate through the throttle valves to prevent icing. The oil then drained from the carburettor left side down another external pipe to the outlet on the relief valve casing. The relief valve was normally closed except when pressure in the oil delivery pipe exceeded a predetermined value; the valve then opened, bypassing oil to the casing outlet side.

The friction drive, two-speed operating mechanism, the spring drive shaft, impellor inertia and friction drive, served to damp out torsional oscillations of the shaft that drove the various auxiliaries, including the supercharger itself. The drive for each gear was transmitted through multi-plate friction clutches whose driving torques were predetermined by the centrifugal action of weights that allowed a safe torque margin under normal conditions, and also permitted momentary slip if the engine speed suddenly changed.

Each gear clutch was disengaged though a ball thrust bearing whose inner race engaged levers integral with the centrifugal weights and so opposed their action on the clutch pressure plates. There were six weights mounted on each of the three planet clutch casings. Ball thrust outer race rotation was prevented by stop pegs attached to the selector sleeve; the selector fork had a slot that engaged the pegs, allowing relative axial, but not rotational, outer race housing movement. Three fixed planet gears connected the main gearshaft, which was driven from the crankshaft, to two gears on the impellor spindle, which was mounted coaxially with the crankshaft. The lower gear ratio was obtained through the upper gearshaft, which meshed with the aft impellor shaft gear; the higher gear ratio was obtained through the two gearshafts positioned below, and meshing with, the forward smaller impeller shaft gear. A two-way valve controlled by the pilot directed scavenge oil under pressure to each side of a relay piston and cylinder mounted at the supercharger base. The piston moved cams that simultaneously engaged one gear and disengaged the other.

Fuel priming and the volute drain system was accomplished via an external piping system, which injected atomized fuel into the induction manifolds. At the front and rear ends of each upper side induction manifold a priming jet and a hole connected with the volute drain discharged into the induction system. The four fittings were interconnected by piping and by transverse holes in the central manifold, and were supplied by two main flexible pipes, one of which led from the left side to the priming pump connection, and the other, on the right side, which was coupled with the supercharger volute base, at which point a venturi was fitted. Two additional priming jets, one at each supercharger delivery elbow, were connected by flexible hoses and a small filter to the priming point. During cold conditions or long idling periods, when liquid fuel may have collected in the supercharger volute, the pressure difference between the induction pipes and atmosphere caused flow through the venturi at the supercharger volute base. Liquid fuel draining to the venturi fitting was drawn upwards into the air stream and redistributed to the four priming jets into the induction system.

Exhaust Manifold

The Vulture II exhaust was designed to accommodate installations where rearward exhaust gas discharge interfered with aircraft structures such as wings, etc. Hence, exhaust gases were discharged near the engine front. An air-cooled manifold for each cylinder block collected exhaust gasses; its forward end was swept outwards and rearwards and terminated in a nozzle pointing aft, through which the gases were discharged. The manifold, including the swept portion, were jacketed with air being introduced at the jacket front and discharged at the nozzle and also at the manifold rear. As a hot spot could have been formed on the curve inside, a pipe that passed through the curve was provided and through this pipe a stream of air flowed when the aircraft was in flight.

Carburetion

Figs. 22a and 22b. Carburettor

A down-draught S.U. carburettor (Figs. 22a and 22b) was fitted to the Vulture II and IV engines. It featured dual chokes (venturis), dual float chambers, a single accelerator pump, aneroid-operated mixture controls (one for altitude and the one for boost pressure), and twin diffusers. Fuel was supplied to each float chamber, from the reducing valve through the connection marked (1), a common pipe communicating with both float chambers. Needle valves (5) coupled to the floats (2) regulated fuel flow. An air balance passage (4) connected the float chambers to the air intake and prevented differences between these two localities from upsetting the mixture ratio. The horse-shoe shaped floats fitted around the diffuser housings and main jet tapered needles. The diffuser was a hollow flanged tube, countersunk into the casting and retained by a flanged bush, which also formed a bearing surface for the tapered needles. It was bored the same diameter for approximately 3/4 of its length, decreasing in diameter at the lower end to fit closely with the main jet needle that passed through it. At the upper end, diametrically-opposite holes registered with the annular passage communicating with the pressure balance chamber. Near the diffuser center a series of holes were submerged under the normal fuel level. At the lower end, radially-drilled holes passed fuel from the main jet well into the space between the diffuser and diffuser cover.

The slow-running jet, located on the diffuser housing side, comprised a tube with a flanged head that rested on the casing; slightly below the head the tube was threaded to screw into the casting. Between the thread and flanged head, two holes were drilled in the tube so they registered with a counterbored hole in the casting and formed an annular space around the hole. The slow-running jet was located in the slow-running tube middle, with the tube bottom communicating with an inclined passage in the diffuser well. The slow-running jet was connected with the three progressive delivery orifices, fitted in the choke tube housing, by a passage drilled in the choke housing whose upper end communicated with the annular space around the jet. A barrel type cutoff valve , fitted in the slow-running passage, was positively operated by the cockpit throttle lever and cut the fuel supply to the slow-running jets. This valve provided a positive means for stopping the engine and prevented continued afterfiring when the ignition switches were cut.

Mixture control for both altitude and boost pressure operating conditions involved two aneroid capsules fitted to the carburettor. The expansion and contraction of these capsules governed the position of tapered needles in their respective diffuser wells and thus regulated fuel flow to suit prevailing conditions. The right capsule was enclosed in a housing through which intake or pressure balance air entered along passage; an air pressure decrease due to altitude caused the capsule to expand due to an internal spring. This expansion pressed the tapered needle further into the main jet orifice and reduced fuel flow to the diffuser to suit the reduced air volume passing through the carburettor. Immediately below the capsule, a tapered spring with an adjusting screw through its center was secured at its base by a locknut. This screw adjusted the relative capsule and tapered needle position, with the coil spring retaining it in position. At the capsule upper end a stud was screwed into a tapered hole in the capsule end plate; the stud formed a connecting rod whose upper end contacted an actuating arm. A secondary arm was also fitted as a safety device against the possibility that the capsule was punctured or rendered inoperative, in which case the capsule expanded, causing the tapered needle to assume the maximum weak position, which was harmful to the engine in most operating conditions. A collet fitted on this connecting rod engaged the secondary rod and returned the jet to its maximum rich position.

The left capsule was similar in construction and operation to the altitude capsule, but regulated the mixture based on boost pressure. Its construction included a two-position Rich-Weak control operated by the pilot through a suitable linkage. The control comprising a cam and lever, illustrates the automatic weak position. Automatic rich was enabled by rotating the cam until the arm engaged the capsule connecting rod and raised the tapered needle from the jet. If the cam were moved to automatic-weak for economical cruising, the throttle could not be opened to give boost pressures between +2.25 and +3.75 psi unless the mixture control was also moved to the automatic rich position, but at greater boost pressures the aneroid contracted and lifted the jet needle sufficiently to restore the mixture strength independently of the mixture control arm.

The accelerator pump, located in the casting between the float chambers, connected the chokes via a drilled passage. Fuel flowed from the float chamber to the pump barrel upper end through a hole drilled in the casting that registered with a hole drilled in the pump barrel liner; a second smaller hole also communicated with a hole in the float chamber casing; this hole relieved the displaced air as the piston ascended. The aluminum piston was bored through its center to accept a bolt that was threaded at its lower end and with an eyelet on its upper end over which a forked joint was located. Between the bolt's threaded portion and the piston, a flanged bush was fitted and a check valve was freely mounted on the bush. Bleed holes drilled in the piston allowed fuel to pass from the barrel upper part to the lower part. In the delivery passage between the pump jets in the chokes and the pump, a second check valve prevented fuel from returning to the piston barrel as the piston rose. The delivery passages to the chokes were horizontal slots milled in the casting.

Fig 23. Automatic Boost Control

The Vulture II and IV automatic boost control differential (Fig. 23-11) was embodied with the relay unit and the emergency cut-out valve was omitted. In addition, a three-cam arrangement operated in conjunction with the aneroid control spring tappet. The variable datum control comprised a device that provided an overriding control over the cockpit throttle lever, eliminating the need to constantly observe, and compensate for, boost gauge changes. The variable datum control compensated for lost motion between the cockpit throttle control and throttle opening. With the three-cam arrangement on the Vulture II, throttle movement turned three cams mounted on a single shaft with each cam consecutively engaging a separate arm on a rocker that was in contact with the aneroid control spring. Independent adjustment provided for each of the three conditions is described below.

The three-cam arrangement allowed a dwell at economical cruising boost, maximum cruising boost and climbing or takeoff boost. The arms on the rocker were normally set to give minimum dwell, but the dwell period could be adjusted over a limited range. The control linkage also maintained lower boost pressures up to full altitude without progressively opening the throttle with altitude.

Figure 23 shows that the aneroid chamber (16) and metal bellows (3) received boost pressure in chamber (2), which exerted a pressure inside the bellows by passage (15). A spring (17) opposed bellows collapse and caused the bellows, at the required boost pressure, to assume a position so that ports (8) and (9) were closed. Lever 19, attached to the cockpit throttle lever, moved cam (18), determining the aneroid unit position by rocker (24). Spring (22) maintained the cams and rocker arms in contact. A piston valve (4) was coupled to the aneroid and controlled the admission of boost pressure by passage (7), and suction pressure by passage (6) to relay cylinder opposite ends through ports (8) and (9). The relay cylinder piston (10) was connected to one differential sun wheel (11), the planet cage of which was coupled to the cockpit lever (1). The other sun wheel was coupled to the throttle (12). The atmosphere change-over valve (13) was coupled to the hand lever (1).

Automatic Boost Control Operation: The first few engine revolutions, when the throttle slightly opened, produced a pressure reduction in aneroid chamber (2). As valve (4) was in the downward position, this reduced pressure was admitted by passage (6) and port (9) at the left cylinder end. Atmospheric pressure was admitted to the other cylinder end through the valve (13) and port (8). The throttle then could be slightly opened be means of the cockpit throttle lever before movement of the piston (10) took place. At that point the change-over valve (13) was about to cause boost pressure via passage (7) to be substituted for atmospheric pressure for relay operation purposes. When the cockpit throttle lever was set to give a required boost as, for example, when cruising, the piston valve would take up a position when ports (8) and (9) were closed. If the boost did not at first balance the spring pressure, then ports (8) and (9) opened, admitting suction and boost pressure to each side of the relay piston, causing it to move in a direction that would close or open the throttle valves through differential (11). This continued until the boost changed and balanced spring (17), restoring the piston valve to a position that closed ports (8) and (9). Altitude or air intake pressure changes had similar effects – altering the boost for a given throttle valve opening, causing piston valve out-of-balance and then a corresponding throttle valve correction by piston (10).

When the rated altitude was reached, the relay piston was at the cylinder forward end and the throttles were wide open. Annular groove (23) communicated with the supercharger suction side and returned to the system boost pressure which might otherwise leak past the shaft when the piston rear side was subjected to pressure. Boost pressure reset was effected be the adjusting screen (24). Screw (26) determined the fully open throttle position and was to be adjusted with the throttles in this position.

Figs. 28 and 29. Auxiliary Gearbox Drive

The five-drive auxiliary gearbox used with the Vulture II was separately mounted on the airframe firewall at the engine rear. It drove the generator, compressor, gun-turret pump, undercarriage hydraulic pump and vacuum pump. A gear type oil pump was fitted for general lubrication of its bushes and gears. A second eccentric plunger oil pump supplied oil to the vacuum pump. The gearbox drive was taken from the engine right side upwards through a vertical shaft to a universal driving shaft and subsequently to the gearbox. An alternative three-drive auxiliary gearbox arrangement was used with the Vulture IV engine. The drive passed downwards through a vertical drive shaft and through the universal shaft to a gearbox; the former arrangement was more suited to bombers while the latter was more suited to fighters.

The auxiliary gearbox was driven from the right supercharger layshaft through a spur gear with a bevel gear integral at its rear end. This engaged two further bevel gears; the upper one was internally serrated and engaged the vertical shaft in the auxiliary gearbox tower. The vertical shaft was serrated at its upper end and engaged a bevel pinion, which in turn engaged the coupling shaft bevel gear that was connected to the forward universal joint.

Figure 28 shows that the housing (1) mounted on the gearbox tower was an aluminum alloy casting that enclosed the bevel shaft (2) with its integral bevel gear, a ball bearing (3), roller bearing (4), circular nut (5), circlip (6) and a lock washer (7). The ball bearing (3) was fitted on the shaft lower end, and the roller bearing (4) on the upper end. An adjusting washer (8) was fitted between the ball bearing and the pinion; the complete assembly was retained by the circular nut that screwed into the casing. The bevel gear (9) that engaged the pinion was fitted in a separate bearing housing (10). This housing had a sleeve (11) at its center that enclosed the ball bearing (12), and on the ball bearing inner side a spacer washer (13) and internal circlip (l4) were also fitted. The front driving shaft passed through this ball bearing and had a bevel gear (9), lock washer (17) and circular nut (16) secured it to the splined shaft end. The shaft front end was carried in a bush (18) fitted in a boss in the aluminum casting. A Gits Brothers Manufacturing Company oil seal (19) was fitted at the ball bearing rear; beyond this point the shaft diameter increased to form a serrated coupling. The intermediate driving shaft (20) was spherical at the and teeth formed on the sphere engaged the front driving shaft serrations. An aluminum bush (21) was fitted in the front shaft and radiused to accept the intermediate driving shaft sphere. A circular gland nut (22) with a radiused retaining piece, felt washer and adjusting spacer in its inner circumference, screwed on the front driving shaft end to form a spherical coupling that united the front shaft and intermediate shaft. This was internally serrated and had a nut washer and packing to form a lubricant seal at the rear end. The serrations on the intermediate shaft engaged the longer rear drive shaft (23), which extended to the rear coupling. The rear coupling was similar to the front coupling, with a radiused retaining piece, felt washer and adjusting spacer secured by a circular gland nut. Riveted locking clips secured both circular gland nuts. The, coupling shaft cover was split and at both ends rubber rings were fitted to provide a flexible mounting between the engine and gearbox. The cover was secured by Jubilee clips. This arrangement enabled quick auxiliary gearbox removal.

In operation, the square shaft (4) rotated the rotor (5), which pressed against the eccentric cover inside face (10). As the plunger (8) was located by the sliding block (9) inside the rotor (5), it oscillated and rotated so that oil was drawn in through the inlet port (11) and delivered under pressure through an outlet in the fixed bush (6) to a drilled passage in the casing. Vertical and horizontal passages were used to convey the oil to a facing that registered with a similar facing on the front casing. A vertical drilling in the front casing connected its upper end with a horizontal drilling through which oil was delivered to the vacuum pump. Two relief valves and one check valve were incorporated in the pump casing. The upper left relief valve controlled the oscillating pump pressure and the lower left relief valve controlled the gear pump pressure. The check valve prevented oil from draining back from the oil passages supplied by the oscillating pump.