Napier Rapier

Rapier
Preserved Napier Rapier at the Shuttleworth Collection
Type	Piston aero engine
Manufacturer	Napier & Son
First run	1929
Major applications	Fairey Seafox Short S.20

The Napier Rapier was a British 16-cylinder H pattern air-cooled aero engine designed by Frank Halford and built by Napier & Son shortly before WWII.

Design and development

The Rapier was the first of Napier's H cylinder engines. The rationale for the H is fairly straightforward. Rather than having an engine with fewer large cylinders, why not more small cylinders? It was believed that an H pattern engine would provide substantially more power and higher RPM's for the same frontal area as a large liquid-cooled V engine. Maximum RPM in a dive was 4,800.

The H-block has a compact layout, as it essentially consists of two vertically opposed inline engines lying one beside another driving side by side crankshafts. Another advantage is that since the cylinders are opposed, the motion in one is balanced by the opposite motion in the one on the opposite side, leading to very smooth running. The Rapier suffered many of the same problems as the later Dagger and Sabre engines. The Fairey Seafox and Short S.20 were both powered by the Napier Rapier.

Applications

List from Lumsden. ^[1]

• Airspeed Courier (1 built)
• Blackburn H.S.T.10 (1 built)
• Bristol Bulldog
• de Havilland DH.77 (1 built)
• Fairey Seafox (66 built)
• Saro Cloud (1 built)
• Short S.20 (1 built)

Engines on display

• A preserved Rapier engine is on static display at the Shuttleworth Collection, Bedfordshire, England.^[2]

Specifications (Rapier V)

Data from Lumsden.^[3]

General characteristics

• Type: 16-cylinder air-cooled H engine
• Bore: 3.5 in (88.9 mm)
• Stroke: 3.5 in (88.9 mm)
• Displacement: 538.78 cu in (8.55 litres)
• Length: 57.37 in (1,457 mm)
• Width: 23.37 in (594 mm)
• Height: 36 in (914 mm)
• Dry weight: 720 lb (327 kg)

Components

• Valvetrain: 1 inlet and 1 exhaust valve per cylinder.
• Supercharger: Fully supercharged
• Fuel system: 1 Claudel carburettor
• Fuel type: 87 octane
• Cooling system: Air-cooled

Performance

• Power output: 340bhp at 4,000 RPM at 13,000 ft
• Compression ratio: 6.00:1
• Power-to-weight ratio: 0.47 hp/lb

See also

Related development

• Napier Dagger
• Napier Sabre
  

Comparable engines

• Fairey Prince (H-16)
  

Related lists

• List of aircraft engines
  

References

Notes

1. ^ Lumsden 2003, pp. 172-173.
2. ^ Ogilvy 1989, ch.4.
3. ^ Lumsden 2003, p.173.

Bibliography

• Gunston, Bill (1986). World Encyclopedia of Aero Engines. Wellingborough: Patrick Stephens. pp. 121. 
• Lumsden, Alec. British Piston Engines and their Aircraft. Marlborough, Wiltshire: Airlife Publishing, 2003. ISBN 1-85310-294-6.
• Ogilvy, David. Shuttleworth - The Historic Aeroplanes. Shrewsbury, England: Airlife Publishing Ltd., 1989 ISBN 1-85310-106-0

External links

• British aero-engine data table - Oldengine.org
• Napier Rapier article from Flightglobal archive - 1935