Napier Lion

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Napier Lion at Brooklands Motor Museum

The Lion was a 12-cylinder W-block inline 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 & cars.

Early in World War I, Napier were contracted to build aero engines from other companies designs: initially a Royal Aircraft Factory model and then Sunbeams. Both proved to be rather unreliable, and in 1916 Napier decided to design their own instead. Reasoning that the key design criteria were high power, light weight, and low frontal area, the engine was laid out 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. Today these designs, of which there were only a few, are referred to as a W-block. The engine was also advanced in form, using four valve heads with twin overhead camshafts, and a single block milled from aluminum instead of the more common separate-cylinder steel construction used on almost all other designs.

The newly-renamed Lion's design was completed in 1917, and the first hand-built prototypes ran later that year. It was fitted to a de Havilland built DH.9 in early 1918, proving to have many cooling problems. In addition the milled block turned out to be difficult to build with any accuracy and they reverted to separate cylinders, although they remained aluminum. Both of these problems were worked out by the middle of the year and the engine entered production in June 1918. The first Lion I versions delivered 450 hp (335 kW) from their 24 litres. It then took the crown of the most powerful engine from the Liberty L-12, the excellent US wartime design of 400 hp (300 kW).

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

In highly-tuned racing forms the engine could reach 1,300 hp (970 kW), and it was used to break a host of world records: height, air speed, and long distance in aircraft, water speed (delivering 1,375 hp (1,025 kW) in a highly tuned Lion for 100 miles per hour (160 km/h) in 1933) and even land speed: Lions powered many of Sir Malcolm Campbell's record breakers (including over 250 mph (400 km/h) in 1932) and John Cobb's 394 MPH Mobil Railton Special in 1947 - a record that came well after the Lion had passed its prime and stood until 1960 when Mickey Thompson and Challenger 1 exceeded 400mph and returned the record to the US. The record had been held by English 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, especially designed for racing, engine from Rolls-Royce, the Rolls-Royce R.

In 1933 Hubert Scott-Paine built and raced Miss Britain III, which used a Napier Lion engine, in the United States and Venice, setting world records for a single engined boat.

During the 1930s a new generation of much larger and more powerful engines started to appear, and the Lion was clearly past its prime. Gradually, they fell further and further behind. By the time the Bristol Hercules and the Rolls-Royce Merlin arrived in the late 1930s, the Lion was too small and old-fashioned.

A marine version of the Lion, called not surprisingly the Sea Lion was used to power high speed rescue launches operated by the RAF.

Turning away from the W layout, Napier started on the design of two new engines using the even more compact H engine layout. The 16-cylinder Rapier produced 400 hp (300 kW), the 24-cylinder Dagger delivered just under to 1000 hp (750 kW). However these were both smaller than contemporary designs from other companies, and Napier had to start fresh with a new sleeve valve design, which eventually matured into the superb Sabre.

[edit] Specifications (Lion)

General characteristics

Type: 12-cylinder water-cooled W-block (3 banks of 4 cylinders) aircraft piston engine
Bore: 5.5 in (140 mm)
Stroke: 5.125 in (130 mm)
Displacement: 1,462 in³ (24 L)
Dry weight: 858 lb (390 kg)

Components

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