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Bristol Perseus


In late 1925 and early 1926, the RAE published a series of papers by Harry Ricardo on the sleeve valve principle. The main advantages over the traditional poppet valves was better volumetric efficiency, and the ability to operate at higher rotational speeds. This allowed a smaller engine to produce the same power as a larger one, leading to better fuel efficiency and compact design, particularly in multi-row radial engines. Roy Fedden, Bristol's primary engine designer, became interested in the concept and by 1927 he had constructed a working two-cylinder V as a testbed, with the idea of developing it into a V-12. However several problems cropped up on the design, notably that the sleeves tended to burst during the power stroke and strip their driving gears. This led to a long series of tests and materials changes and upgrades that required six years and an estimated 2 million pounds to cure; however, by 1933 the problems had been worked out, and the Perseus went on to become the first sleeve valve aero-engine in the world to be put into large quantity production.

The result was a Bristol Mercury-sized engine adapted to the sleeve valve system, the Perseus nine-cylinder, single-row, air-cooled radial, and its smaller cousin, the Bristol Aquila. The first production versions of the Perseus were rated at 580 horsepower (433 kW), the same as the same-year model Mercury, which shows that the sleeve system was being underutilised. However this was quickly uprated as improvements were introduced, and by 1936 the Perseus was delivering 810 hp (604 kW), eventually topping out at 930 hp (690 kW) in 1939, while the Perseus 100 with an increased capacity of 1,635 cu in (26.8 L) produced 1,200 hp (890 kW) at 2,700 rpm at 4,250 ft (1,296 m). This far outperformed even the most-developed versions of the Mercury.

The Perseus saw limited use in the civilian field, notably on the Short Empire flying-boats, but was more common in the then-expanding military field where it was found on the Westland Lysander, Vickers Vildebeest, Blackburn Botha, Skua and Roc bombers.

The main contribution of the Perseus is that its mechanicals were used as the basic piston and cylinder for the "twinned" versions, the tremendously successful Hercules and Centaurus. It was in these designs that the advantages of the sleeve valve were finally put to good use, and by war's end the Centaurus was one of the most powerful engines in the world.

Blackburn Botha
Blackburn Roc
Blackburn Skua
Bristol Bulldog
Bristol Type 148
Cunliffe-Owen Flying Wing
de Havilland Flamingo
de Havilland Hertfordshire
Gloster Goring
Hawker Hart
Saro A.33
Short Empire
Short Scylla
Vickers Vellox
Vickers Vildebeest Mk.IV
Westland Lysander Mk.II


Perseus XII

Type: Nine-cylinder single-row supercharged air-cooled radial engine
Bore: 5.75 in (146 mm)
Stroke: 6.5 in (165 mm)
Displacement: 1,520 in³ (24.9 L)
Length: 49 in (1,245 mm)
Diameter: 55.3 in (1,405 mm)
Dry weight: 1,025 lb (465 kg)
Valvetrain: Sleeve valve
Supercharger: Single-speed centrifugal type supercharger
Fuel system: Claudel-Hobson carburettor
Fuel type: 87 Octane petrol
Cooling system: Air-cooled
Reduction gear: 0.5:1 turning a de Havilland variable pitch propeller
Power output:
830 hp (619 kW) at 2,650 rpm for takeoff
905 hp (675 kW) at 2,750 rpm at 6,500 ft (1,980 m)
Specific power: 0.59 hp/in³ (26.75 kW/l)
Compression ratio: 6.75:1
Specific fuel consumption: 0.43 lb/(hp·h) (261 g/(kW·h))
Oil consumption: 0.28 oz/(hp·h) (11 g/(kW·h))
Power-to-weight ratio: 0.88 hp/lb (1.45 kW/kg)



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