The Mercury was developed by the Bristol Aeroplane Company in 1925 as their Bristol Jupiter was reaching the end of its lifespan. Although the Mercury initially failed to attract much interest, the Air Ministry eventually funded three prototypes and it became another winner for the designer Roy Fedden. With the widespread introduction of superchargers to the aviation industry in order to improve altitude performance, Fedden felt it was reasonable to use a small amount of boost at all times in order to improve performance of an otherwise smaller engine. Instead of designing an entirely new block, the existing Jupiter parts were re-used with the stroke reduced by one inch (25 mm). The smaller capacity engine was then boosted back to Jupiter power levels, while running at higher rpm and thus requiring a reduction gear for the propeller. The same techniques were applied to the original Jupiter-sized engine to produce the Pegasus. The Mercury's smaller size was aimed at fighter use and it powered the Gloster Gauntlet and its successor, the Gloster Gladiator. It was intended that the larger Pegasus would be for bombers but as the power ratings of both engines rose, the Mercury found itself being used in almost all roles. Perhaps its most famous use was in a twin-engine light bomber, the Bristol Blenheim. In 1938 Roy Fedden pressed the Air Ministry to import supplies of 100 octane aviation spirit (gasoline) from the USA. This new fuel would allow aero engines to run at higher compression ratios and supercharger boost pressure than the existing 87-octane fuel, thus increasing the power. The Mercury XV was one of the first British aero engines to be type-tested and cleared to use the 100-octane fuel in 1939. This engine was capable of running with a boost pressure of +9 lbs/sq.in and was first used in the Blenheim Mk IV. The Mercury was also the first British aero engine to be approved for use with variable-pitch propellers. The Bristol company and its shadow factories produced 20,700 examples of the engine. Outside the United Kingdom, Mercury was licence-built in Poland and used in their PZL P.11 fighters. It was also built by NOHAB in Sweden and used in the Swedish Gloster Gladiator fighters and in the Saab 17 dive-bomber. In Italy, it was built by Alfa Romeo as the Mercurius. In Czechoslovakia it was built by Walter Engines. In Finland, it was built by Tampella and mainly used on Bristol Blenheim bombers. Variants
- Mercury I: (1926) 808 hp, direct drive. Schneider Trophy racing engine.
- Mercury II: (1928) 420 hp, compression ratio 5.3:1.
- Mercury IIA: (1928) 440 hp
- Mercury III: (1929) 485 hp, compression ratio 4.8:1, 0.5:1 reduction gear.
- Mercury IIIA: Minor modification of Mercury III.
- Mercury IV; (1929) 485 hp, 0.656:1 reduction gear.
- Mercury IVA: (1931) 510 hp.
- Mercury IVS.2: (1932) 510 hp.
- Mercury (Short stroke): Unsuccessful experimental short stroke (5.0 in) version, 390 hp.
- Mercury V: 546 hp (became the Pegasus IS.2)
- Mercury VIS: (1933) 605 hp, see specifications section.
- Mercury VISP: (1931) 605 hp, 'P' for Persia.
- Mercury VIS.2: (1933) 605 hp.
- Mercury VIA: (1928) 575 hp (became the Pegasus IU.2)
- Mercury VIIA: 560 hp (became the Pegasus IM.2)
- Mercury VIII: (1935) 825 hp, compression ratio 6.25:1, lightened engine.
- Mercury VIIIA: Mercury VIII fitted with gun synchronisation gear for the Gloster Gladiator
- Mercury VIIIA: 535 hp, second use of VIIIA designation, (became the Pegasus IU.2P)
- Mercury IX: (1935) 825 hp, lightened engine.
- Mercury X: (1937) 820 hp.
- Mercury XI: (1937) 820 hp.
- Mercury XII: (1937) 820 hp
- Mercury XV: (1938) 825 hp, developed from Mercury VIII. Converted to run on 100 Octane fuel (previously 87 Octane).
- Mercury XVI: 830 hp.
- Mercury XX: (1940) 810 hp
- Mercury 25: (1941) 825 hp. Mercury XV with crankshaft modifications.
- Mercury 26: 825 hp. As Mercury 25 with modified carburettor.
- Mercury 30: (1941) 810 hp, Mercury XX with crankshaft modifications.
- Mercury 31: (1945) 810 hp, Mercury 30 with carburettor modifications and fixed pitch propeller for Hamilcar X.
Specifications:
| Bore: | ||
| Stroke: | ||
| Capacity: | ||
| Gear Ratio | ||
| Diameter | ||
| Weight (bare/dry) | ||
| Octane No. | ||
| Power: Take-Off | 725 hp @ 2,650 rpm
100 Octane: |
|
| Power: Maximum | 840 hp @ 2,750 rpm @ 14,000 ft (4,270m)
100 Octane: |
@ 2,500 ft (760m) |
| Power: Normal Climb | @ 13,000 ft (3,965m) |
@ 2,500 ft (760m) |
| Power: Maximum Economical Cruise | @ 16,000 ft (4,880m) |
@ 9,250 ft (2,820m) |
Design/Structure:
Cylinders - Open-ended barrel machined from an alloy steel forging. Bores surface-hardened. Forged aluminium-alloy heads shrunk and locked into position.
Pistons - Full-skirted type. Machined inside and outside from aluminum-alloy forgings. One sindle and one double scrapper ring and two gas rings. Robust fully-floating, case-hardened gudgeon pins.
Connecting rods - "I" section, machined from steel alloy stampings.
Crankshaft - Two-piece, machined from alloy steel stampings. Front half incorporates a large diameter crank-pin, is surface hardened all over. Seperate tail-shaft for auxiliary drives. Carried on two main roller-bearings, with a deep-groove journal-bearing at the reduction end and steadying bearing in rear.
Crankcase - Machined from aluminum-alloy forgings, split on centre-line of cylinders and held with nine through-bolts.
Valve Gear - Two inlet and two sodium-cooled stellited exhaust valves and stellited seats per cylinder. Clearances bewteen rockers and valves automatically compensated for expansion. A two-row cam runs concentric with the crankshaft in front of the crank at one eigth engine speed in an anti-crank direction. It operates the tappets through rollers on floating bronze bushes, and thence by push-rods enclosed in oval tubes.
Carburation - Claudell-Hobson carburetter, with delayed action acceleration pump, variable datum automatic boost and mixture control with slow-running runout. controlable hot and cold air-intakes. Hot oil circulated around the chokes.
Supercharger - High-speed centrifugal type. Driven off the crankshaft through spring-drive and automatic centrifugal clutches. Aluminum-alloy supercharger casing with integral diffuser vanes. Aluminum-alloy volute casing. Whole unit mounted behind the rear wall of the crankcase on nine crankcase bolts.
Ignition - Dual ignition by two B.T.H. or Rotex magnetos transversely mounted on rear cover and driven by bevel gearing from crankshaft. Variable-timing device interconnected with carburetter to give best setting for various throttle openings. Completely screened ignition system.
Lubrication - Dry sump, with pressure feed. Duplex gear pump incorporating pressure and scavenge units in one assembly. Seperate feed and scavenge filters. Special device provides high initial oil pressure for rapid opening to full power.
Airscrew Drive - Self-centralising bevel-epicyclic gear. All bearings pressure-lubricated. Airscrew shafts suitable for either fixed or controllable-pitch hubs. Oil-transfer housing and internal oil-seal provided for Hamilton pitch-controll mechanism.
Accessory Drives - Provision for single or dual feed pump, high and low pressure air-compressors, shaft-driven electric generator, hydraulic pump, vacuum pump.
Starter System - Combined electric and hand turning gear.
Exhaust System And Cowling - Complete standardised units, combining ring-type exhaust manifold and long or short-chord cowlings are available. Long chord cowlings embody controllable gills.
Applications:
|
– Airspeed Cambridge – Blackburn Skua – Boulton Paul P.108 – Bristol Blenheim – Bristol Bolingbroke – Bristol Bulldog – Bristol Bullpup – Bristol Type 101 – Bristol Type 118 – Bristol Type 133 – Bristol Type 142 – Bristol Type 146 – Bristol Type 148 – Breda Ba.27 |
– Fairey Flycatcher – Fokker D XXI – Fokker G.1 – GA Hamilcar X – Gloster Gamecock – Gloster Gladiator – Gloster Gauntlet – Gloster Gnatsnapper – Gloster Goring – Hawker Audax – Hawker F.20/27 – Hawker Fury – Hawker Hart – Hawker Hind |
– Hawker Hoopoe – IMAM Ro.30 – Koolhoven F.K.52 – Miles Martinet – Miles Master – PZL P.11 – Saab 17 – Supermarine Sea Otter – Valmet Vihuri – Vickers Jockey – Westland Interceptor – Westland Lysander |
Wikipedia
Gunston, Bill (2006). World Encyclopedia of Aero Engines: From the Pioneers to the Present Day (5th ed.). Stroud, UK: Sutton. ISBN 0-7509-4479-X.
