Napier Lion

Lion
Napier Lion II at Canada Aviation Museum
Type	Piston aero-engine
Manufacturer	Napier & Son
First run	1917
Major applications	Handley Page Hyderabad Vickers Vernon

The Napier Lion was a 12-cylinder broad arrow configuration aircraft engine built by Napier & Son starting in 1917, and ending in the 1930s. A number of advanced features made it the most powerful engine of its day, and kept it in production long after contemporary designs had stopped production. It is particularly well known for its use on a number of racing designs, in aircraft, boats, and cars.

Design and development

Early in the First World War Napier were contracted to build aero engines to designs from other companies: initially a Royal Aircraft Factory model and then Sunbeams. Both engines proved to be unreliable, and in 1916 Napier decided to design their own. Reasoning that the key design criteria were high power, light weight, and low frontal area, Napier's engineers laid out the engine with its 12 cylinders in what they called a "broad arrow"—three banks of four cylinders sharing a common crankcase. This suggested the design's first name, the Triple-Four. The configuration is also known as a W engine.^[1] The engine was also advanced in form, the heads using four valves per cylinder with twin overhead camshafts on each bank of cylinders and a single block being milled from aluminium instead of the more common separate-cylinder steel construction used on almost all other designs.

Cutaway view showing the double overhead camshaft arrangement

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Under A. J. Rowledge, the design of the engine, which had been renamed Lion, was completed in 1917, and the first hand-built prototypes ran later that year. It was fitted to an DH.9 in early 1918, and many cooling problems were observed during testing. In addition, the milled block was difficult to build with the required accuracy and the design reverted to separate cylinders, although they remained aluminium. Both problems were solved by the middle of the year and the engine entered production in June 1918. The first Lion I versions delivered 450 horsepower (340 kW) from their 24 litres. This output made the Lion the most powerful Allied aircraft engine, which had previously been the Liberty L-12, which produced 400 horsepower (300 kW).

As the most powerful engine available (particularly after a turbocharger became an option in 1922), the Lion went on to commercial success. Through the years between the wars the Lion was ubiquitous, and Napier manufactured little else. They stopped making cars in 1925, and little thought was given to replacing their world-famous product. Between the wars the Lion engine powered over 160 different types of aircraft.

The Napier Lion installed in the Napier-Railton car.

In highly tuned racing versions the engine could reach 1,300 hp (970 kW), and it was used to break many world records: height, air speed, and distance in aircraft, boats, delivering 1,375 hp (1,025 kW) in a highly tuned Lion for a water speed record of 100 mph (160 km/h) in 1933. In land speed records, Lion engines powered many of Sir Malcolm Campbell's record breakers including a record of over 250 mph (400 km/h) in 1932 and John Cobb's 394 mph (634 km/h) Railton Mobil Special in 1947—a record that came well after the Lion had passed its prime and stood until the 1960s. The record had been held by British drivers for 32 years. Lions powered successful entrants in the most prestigious event in air racing, the Schneider Cup, in 1922 and 1927, but were then dropped by Supermarine in favour of a new engine, the Rolls-Royce R, which had been designed specially for racing.

During the 1930s a new generation of much larger and more powerful engines started to appear, and the Lion became uncompetitive. By the time the Bristol Hercules and the Rolls-Royce Merlin arrived in the late 1930s, the Lion was obsolete.

The Sea Lion, a marine version of the Lion, was used to power high speed air-sea rescue launches operated by the RAF. The Lion aero engine was also adapted to power propeller-driven motor sleighs, which were used for high-speed transport and SAR duties on sea ice by the Finnish Air Force and Navy.

Turning away from the broad arrow layout, Napier designed new engines using the more compact H engine layout. The 16-cylinder Rapier produced 400 hp (300 kW), the 24-cylinder Dagger delivered just under 1,000 hp (750 kW). These were both smaller than contemporary designs from other companies, so Napier started afresh with a new sleeve valve design, which evolved into the Sabre.

Variants

Applications

Aircraft

Napier Lion at Brooklands Motor Museum

Other applications

• British Power Boat Company Type Two 63 ft HSL
• British Power Boat Company 60 ft 4 in^[4]

Engines on display

Preserved Napier Lion engines are on static display at the following museums:

• Brooklands Museum
• Canada Aviation Museum
• Imperial War Museum Duxford
• National Maritime Museum^[5]
• Solent Sky

Specifications (Lion II)

Data from Lumsden^[6]

General characteristics

• Type: 12-cylinder water-cooled W-block (3 banks of 4 cylinders) aircraft piston engine
• Bore: 5.5 in (139.7 mm)
• Stroke: 5.125 in (130.17 mm)
• Displacement: 1,461.6 in³ (23.9 L)
• Length: 57.5 in (1460 mm)
• Width: 42.0 in (1067 mm)
• Height: 43.5 in (1105 mm)
• Dry weight: 960 lb (435 kg)

Components

• Valvetrain: Two intake and two exhaust valves per cylinder actuated via double overhead camshafts per cylinder block.
• Cooling system: Water-cooled

Performance

• Power output: 480 hp (358 kW) at 2,200 rpm at 5,000 ft
• Specific power: 0.32 hp/in³ (15.0 kW/L)
• Compression ratio: 5.8:1
• Power-to-weight ratio: 0.5 hp/lb (0.82 kW/kg)

See also

• Napier-Bentley
• Vehicles powered by Napier Lion engines

Comparable engines

• Farman 12We
• Hispano-Suiza 18R
• Lorraine 12E Courlis

Related lists

• List of aircraft engines

References

Notes

Bibliography

External links

Wikimedia Commons has media related to Napier Lion.

• "The Napier Lion Aeromotor" (PDF). Flight XI (13): 397–402. March 27, 1919. No. 535. Retrieved January 12, 2011.  Contemporary technical description of the Lion with photographs and drawings.