|Type||Piston V-12 aero engine|
|Major applications||Westland Whirlwind|
|Developed from||Rolls-Royce Kestrel|
|Developed into||Rolls-Royce Vulture|
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 the British manufacturer Rolls-Royce in the late 1930s. It was essentially the ultimate development of the company's Kestrel engine, which had seen widespread use in military aircraft of the pre-war period.
Due to the wartime priority of Rolls-Royce Merlin development and production, the Peregrine saw limited use and was cancelled with only 300 engines being built.
Design and development
During the 1930s the use of superchargers to increase "effective displacement" of an aircraft engine came into common use. Charging[nb 1] 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 Kestrel used supercharging for boost from the start, but by the 1930s it had reached the limits of what its frame could handle in terms of power output. However, there was room to improve the strength of the engine, which would allow it to run at even higher boost levels with only modest increases in weight. This improved the power-to-weight ratio considerably, and it was generally felt that the resulting design would be the "standard" fighter engine for the impending war.
Following the company convention of naming its piston aero engines after birds of prey,[nb 2] Rolls-Royce named the engine the Peregrine after the peregrine falcon (Falco peregrinus), the world's fastest and most widespread bird of prey.
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. This was a common feature of German designs, but relatively rare on UK engines. 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 F.9/37. The Vulture was fitted to the Hawker Tornado and Avro Manchester, but proved unreliable in service. With the Merlin itself soon pushing into the 1,500 horsepower (1,100 kW) range, the Peregrine was cancelled in 1943.
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's reliability problems. Low production rates of the Peregrine caused delays in delivery for 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 as the Whirlwind had been tightly designed around the Peregrine, changing to a different engine at this stage was not a feasible option. Only 116 Whirlwinds and a corresponding number of Peregrines (301) were built.
Specifications (Peregrine I)
Data from Lumsden 
- 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
- Related development
- Related lists
- Compressing the induction air to increase mass flow-rate and hence oxygen available for combustion.
- The naming tradition was started by managing director, Claude Johnson, in 1915 with the Eagle, Hawk and Falcon engines.
- Gunston 2004, p. 63.
- "The World's Fastest Animal Takes New York". Smithsonian. Retrieved 2010-11-08.
- Rubbra 1990, p. 53.
- Rubbra 1990, p. 136.
- Lumsden 2003, p. 200.
- Rubbra 1990, p. 118.
- Bowyer 1984, p. 154.
- Pugh 2000, p. 263.
- Lumsden 2003, p. 183.
- Lumsden 2003, p. 198.
- Bowyer, Michael J.F. Interceptor Fighters for the Royal Air Force, 1935-45. Wellingborough, Northamptonshire, UK: Patrick Stephens Ltd., 1984. ISBN 0-85059-726-9.
- Gunston, Bill. Development of Piston Aero Engines. Cambridge, England. Patrick Stephens Limited, 2006. ISBN 0-7509-4478-1
- Lumsden, Alec. British Piston Engines and their Aircraft. Marlborough, Wiltshire: Airlife Publishing, 2003. ISBN 1-85310-294-6.
- Pugh, Peter. The Magic of a Name - The Rolls-Royce Story - The First 40 Years. Cambridge, England. Icon Books Ltd, 2000. ISBN 1-84046-151-9
- Rubbra, A.A. Rolls-Royce Piston Aero Engines - a designer remembers: Historical Series no 16 :Rolls Royce Heritage Trust, 1990. ISBN 1-872922-00-7