Alvis Leonides Major

Leonides Major
Type	Radial engine
National origin	United Kingdom
Manufacturer	Alvis
Major applications	Westland Whirlwind
Developed from	Alvis Leonides

Last updated July 10, 2025

The Alvis Leonides Major is a British air-cooled 14-cylinder radial aero engine developed by Alvis from the earlier nine-cylinder Leonides.^[1]

Design and development

In 1951 Alvis started development of a 14-cylinder, two row radial of 1,118 cu in (18.3 L) displacement, based on the Leonides. Certification covered the Mk. 702/1 for aeroplanes at 875 hp (652 kW) and the 751/1 for helicopters at 850 hp (630 kW). The only numerous model of the Major was the Mk. 755/1, a medium supercharged, de-rated, obliquely mounted direct-drive and fan cooled engine fitted to the Westland Whirlwind Mks. 5, 6, 7 and 8.^[2]

Variants

Data from:British Piston Engines and their Aircraft.^[3]

Leonides Major 702/1: 850–875 hp (634–652 kW) for aeroplanes, also known as A.LE.M.1-1 in Air Ministry
Leonides Major 751/1: 850 hp (630 kW) for helicopters, also known as A.LE.M.1-2
Leonides Major 755/1: 780 hp (580 kW) for helicopters in a 35° canted mounting, also known as A.LE.M.1-6 and as Mk.155 in civil aircraft
Leonides Major 755/2: 780 hp (580 kW) for helicopters in a vertical mounting, also known as A.LE.M.1-6 and as Mk.160 in civil aircraft

Applications

Bristol Type 173 Mk3 – 2x 755/1 (Mk.155) 780 hp (580 kW); 2x 755/2 (Mk.160) 780 hp (580 kW)
Handley Page HPR.5 Herald – four 850 hp (630 kW) 702/1
Westland Whirlwind 1x 755/1 (Mk.155) or 1x 755/2 (Mk.160) 780 hp (580 kW)

Specifications (Leonides Major 702/1)

Data fromJane's All the World's Aircraft 1956-57.^[4]

General characteristics

Type: 14-cylinder twin-row air-cooled radial piston engine, geared down and supercharged
Bore: 4.80 in (122 mm)
Stroke: 4.41 in (112 mm)
Displacement: 1,118 cu in (18.32 L)
Length: 70.9 in (180 cm)
Diameter: 38.9 in (99 cm)
Dry weight: 1,200 lb (540 kg) (dry)

Components

Valvetrain: 2 sodium cooled valves per cylinder, driven by 2 cam discs
Supercharger: Single speed single stage driven at 6.5:1
Fuel system: Fuel injection, low pressure via Hobson or SU pump
Fuel type: 100/130 octane
Oil system: Dry sump, pressure and scavenge pumps
Cooling system: Air-cooled
Reduction gear: Farman type epicyclic, ratio 0.533:1
2 spark plugs per cylinder, twin BTH C.14.C/1 magnetos

Performance

Power output: (international rating) 860 hp (642 kW) at 1,500 ft (457 m)
Compression ratio: 6.8:1
Fuel consumption: 60 imp gal (72 US gal; 270 L) per hour (at maximum continuous power)
Oil consumption: 6-12 pint/h (3.4-6.8 L/h)

References

↑ Gunston, Bill (1989). World encyclopaedia of aero engines (Fully rev. 2nd ed.). Wellingborough: P. Stephens. p. 13. ISBN 1-85260-163-9.
↑ Lumsden 2003, pp.60-61.
↑ Lumsden, Alec (2003). British Piston Engines and their Aircraft. Marlborough, Wiltshire: Airlife Publishing. pp. 60–61. ISBN 978-1-85310-294-3.
↑ Bridgman, Leonard, ed. (1956). Jane's all the World's Aircraft 1956–57. London: Jane's all the World's Aircraft Publishing Co. Ltd. pp. 417–419.

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[Gunston-1] Gunston, Bill (1989). World encyclopaedia of aero engines (Fully rev. 2nd ed.). Wellingborough: P. Stephens. p. 13. ISBN 1-85260-163-9.

[2] Lumsden 2003, pp.60-61.

[Lumsden-3] Lumsden, Alec (2003). British Piston Engines and their Aircraft. Marlborough, Wiltshire: Airlife Publishing. pp. 60–61. ISBN 978-1-85310-294-3.

[JAWA56-57-4] Bridgman, Leonard, ed. (1956). Jane's all the World's Aircraft 1956–57. London: Jane's all the World's Aircraft Publishing Co. Ltd. pp. 417–419.

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