|Type||Piston X-24 aero-engine|
|First run||September 1936|
|Major applications||Fairey Battle|
|Developed into||Rolls-Royce Pennine|
The Rolls-Royce Exe, or Boreas, was a 24-cylinder air-cooled X block sleeve valve aircraft engine intended primarily for the new Fairey Fleet Air Arm aircraft, particularly the Fairey Barracuda. The Exe was relatively powerful for its era, producing about 1,100 hp (820 kW). This is notable given the relatively small 22 litres (4.8 imp gal; 5.8 US gal) displacement, the Merlin requiring 27 litres for approximately the same power level. The X-24 layout made this quite a compact engine.
The Exe was under development in 1939, having been started in the 1930s, along with the Peregrine and Vulture. Work on the Exe was suspended in August 1939, and stopped about August 1940. Ernest Hives, head of the Rolls-Royce aero engine division, wanted to stop work on the Exe, Peregrine, and Vulture to concentrate on the Merlin and Griffon engines. An enlarged version, the Rolls-Royce Pennine, was built later in the war, but cancelled as jet engines became the company's focus.
Originally intended for the Supermarine Type 322 and Fairey Barracuda the Exe was only test flown in a Fairey Battle, the first flight taking place on 30 November 1938. This aircraft continued in use for some time as a communications aircraft where the Exe was noted to be quite reliable in service.
- Type: 24-cylinder supercharged air-cooled 90-degree X layout aircraft piston engine
- Bore: 4.225 in (107.3 mm)
- Stroke: 4.0 in (100 mm)
- Displacement: 1,348 in3 (22.09 L)
- Dry weight: 1,530 lb (690 kg)
- Valvetrain: Sleeve valve
- Supercharger: Gear-driven centrifugal type supercharger, single stage
- Fuel type: Petrol
- Cooling system: Pressure air-cooled
- Reduction gear: 0.358:1, left hand tractor
- Power output: 1,150 hp (860 kW) at 4,200 rpm, +4.5 psi boost at sea level
- Compression ratio: 8:1
- Power-to-weight ratio: 0.75 hp/lb (1.23 kW/kg)
- This name was dropped due to conflict with the Bristol Aeroplane Company's series of Greek mythology named engines, Lumsden 2003, p.201.
- Lloyd 1978, p4-5.
- Pugh 2000, p.263-265.
- Rubbra 1990, p.148.
- Gunston 1989, p. 142.
- Lumsden 2003, p.201.
- Gunston, Bill. World Encyclopaedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9
- Lloyd, Ian Rolls-Royce: The Merlin at War (1978, Macmillan London) ISBN 0-333-24016-2
- 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 (2000, Icon Books Cambridge) 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