Napier Javelin

In 1927 Montague Napier reached an agreement with  Major Frank B. Halford to act as a consultant designer for D Napier & Son.  Napier was determined to enter into the the market for air-cooled engines and Halford was a natural choice.  Both Montague Napier and Halford believed that this was the way ahead due to the lightweight nature of the engine and having push rod operated overhead valves.  Napier’s remit to Halford was for an air-cooled engine between 6.6 litres and 11.8 litres.

The Napier Javelin was the first engine Halford designed for the Company.  This was similar to the ‘Cirrus Hermes’ and the ‘De Havilland Gypsy’, having an inverted six cylinder 8.2 litre giving 170bhp at 2,100rpm.  The E97 Javelin I was introduced in 1932 but later redesigned with a longer stroke and capacity as the Javelin III

Napier Javelin E97 Engine

Cylinders. 6    In-line

Bore & Stroke.  4.1/2″ x 5.1/4″

Power Output Range   170 SHP @ 2,100 rpm

Spartan Arrow 160 h.p. E97 Javelin - Civil Tourer Trainer G-ABST

The Napier Javelin engine was first flown in March 1934 in a prototype Percival Mew Gull.  The engine was only marginally successful powering a number of Percival light aircraft such as the Gull IV and a racing Mew Gull.  It was also installed in the Sparten Arrow, Martin Baker MB1 and the Commonwealth Wackett twin engine aircraft.  Regrettably during the 1930’s this engine had earned a reputation for cutting out on takeoff, a problem that always remain unsolved.

Napier Javelin in Percival Gull port
Napier Javelin in Percival Gull port

There are no known surviving Napier Javelin engines.

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