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Rolls-Royce Peregrine

rr-peregrine

 

The Rolls-Royce Peregrine was a 21-litre (1,300 cu in), 885-horsepower (660 kW) liquid-cooled V-12 aero engine designed and built by Rolls-Royce in the late 1930s. First run in 1938, the Peregrine was developed during 1939 from the Kestrel. Running on 87 octane fuel, it had an international rating of 860 h.p. at 2,850 r.p.m. at 13,500 ft, and a maximum output of 885 h.p. at 3,000 r.p.m. at 15,000 ft. A number of Merlin features were incorporated and provision was made for a wide range of auxiliaries. External differences from the Kestrel included the fitting of a downdraught carburettor; this had progressive boost control, in which the "dead" range of movement of the throttle lever was eliminated.

During the 1930s the use of superchargers to increase "effective displacement" of an aircraft engine came into common use. Charging of some form was a requirement for high-altitude flight, and as the strength of the engines improved there was no reason not to use it at all times. The introduction of just such a "ground-level" supercharger to the Kestrel along with several design changes improved the power-to-weight ratio considerably, and it was generally felt that the resulting Peregrine would be the "standard" fighter engine for the impending war. Following the company convention of naming its piston aero engines after birds of prey, Rolls-Royce named the engine the Peregrine after the Peregrine Falcon (Falco peregrinus), the world's fastest and most widespread bird of prey.

Although the Peregrine appeared to be a satisfactory design, it was never allowed to mature since Rolls-Royce's priority was refining the Merlin. As a result, the Peregrine saw use in only two aircraft: the Westland Whirlwind and the Gloster F9/37.

A design feature of the Peregrine was that it was produced in both right- and left-hand tractor variants. This was done to improve aircraft handling by providing a counter-rotating propeller facility. The handing of internal parts to achieve this was a considerable complication that was later abandoned in favour of an idler gear arrangement for the Merlin propeller reduction gear.
 
Four Kestrel/Peregrine cylinder banks attached to a single crankcase and driving a single common crankshaft would produce the contemporary Rolls-Royce Vulture, a 1,700-horsepower (1,300 kW) X-24 which would be used for bombers.
 
As it transpired, aircraft designs rapidly increased in size and power requirements to the point where the Peregrine was simply too small to be useful. Although the Peregrine appeared to be a satisfactory design, it was never allowed to mature since Rolls-Royce's priority was refining and producing the Merlin. As a result the Peregrine saw use in only two aircraft: the Westland Whirlwind and the Gloster F9/37, but proved unreliable in service. With the Merlin itself soon pushing into the 1,500 horsepower (1,100 kW) range, the Peregrine and Vulture were both cancelled in 1943, and by mid-1943 the Merlin was supplemented in service by the larger Rolls-Royce Griffon.

 

RR-Peregrine-2

 

The two aircraft types that used the Peregrine, the Westland Whirlwind and the second prototype of the Gloster F9/37, were both twin-engine designs – the prototype F9/37 had used the Bristol Taurus radial engine. The Air Ministry requirement for the F9/37, a cannon-armed fighter (the Hurricane and Spitfire were armed with machine guns only at this point), was curtailed and there was no further progress with the design. The Whirlwind, despite having excellent low-altitude performance, proved uneconomical compared with single-engined fighters, and also suffered as a consequence of the Peregrine reliability problems. Low production rates of the Peregrine caused delays in delivery to squadron use. In August 1940 Ernest Hives, head of the Rolls-Royce aero engine division, wrote to Air Chief Marshal Wilfrid Freeman expressing his wish to stop work on the Peregrine, Vulture and another engine development project, the Rolls-Royce Exe to concentrate efforts on the Merlin and Griffon, but Freeman disagreed and stated that Peregrine production should continue.
 
While reliability problems were not uncommon for Rolls-Royce's new engine designs of the era, the company's testing department was told to spend all of their time on developing the more powerful Merlin to maturity. As a result of the Merlin's priority, the unreliable Peregrine was eventually abandoned with production ending in 1942. Other cannon-armed fighters, such as the Hawker Typhoon and the Bristol Beaufighter, were becoming available; and since the Whirlwind had been tightly designed around the Peregrine, changing to a different engine at this stage was not, therefore, a feasible option. Only 116 Whirlwinds and a corresponding number of Peregrines (301) were built.

 

Peregrine I
Type: 12-cylinder supercharged liquid-cooled 60-degree Vee aircraft piston engine
Bore: 5 inches (127 mm)
Stroke: 5.5 inches (140 mm)
Displacement: 1,296 in³ (21.2 L)
Length: 73.6 in (1,869 mm)
Width: 27.1 in (688 mm)
Height: 41.0 in (1,041 mm)
Dry weight: 1,140 lb (517 kg)
Valvetrain: Overhead camshaft
Supercharger: Gear-driven single-speed centrifugal type supercharger, +9 psi boost
Fuel system: Downdraught carburettor
Fuel type: Petrol
Cooling system: Liquid cooled, 70% water/30% ethylene glycol
Power output: 885 hp (660 kW) at 3,000 rpm, +9 psi boost
Specific power: 0.68 hp/in³ (31.1 kW/L)
Compression ratio: 6:1
Power-to-weight ratio: 0.77 lb/hp

 

 

 

 

 

 

 

 


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