|Manufacturer||Napier & Son|
|Major applications||Martin-Baker M.B.1 (one aircraft only)
Percival Mew Gull
The Napier Javelin was a British six-cylinder inline air-cooled engine designed by Frank Halford and built by Napier & Son. First flown in March 1934 in the prototype of the Percival Mew Gull racing aircraft, the engine was also used in the Spartan Arrow biplane and the Percival Gull.
- Initial version producing 150 hp.
- A longer stroke and increased capacity version of 160 hp.
- A Mark III with a starter motor, generator and other improvements for the Martin Baker MB.1.
Specifications (Javelin I)
Data from 
- Type: 6-cylinder inverted inline air-cooled engine.
- Bore: 4.5 in (114.3 mm)
- Stroke: 5.25 in (133.35 mm)
- Displacement: 501 cu in (8.21 L)
- Length: 58.5 in (1486 mm)
- Width: 26 in (660.4 mm)
- Height: 31.5 in (800 mm)
- Dry weight: 410 lb (186 kg)
- Valvetrain: Overhead cam poppet-valves
- Fuel system: Twin updraught carburettors
- Fuel type: Petrol
- Cooling system: Air-cooled
- Reduction gear: Direct drive, left hand tractor
- Power output: 150 hp (112 kW) at 2,000 rpm
- Compression ratio: 5.3:1
- Power-to-weight ratio: 0.365 hp/lb
- Comparable engines
- Related lists
- Lumsden 2003, p.173.
- Lumsden 2003, p.174.
- Lumsden, Alec. British Piston Engines and their Aircraft. Marlborough, Wiltshire: Airlife Publishing, 2003. ISBN 1-85310-294-6.