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Dragonfly
	ABC Dragonfly at the Science Museum (London)
Type	Radial aero engine
National origin	England
Manufacturer	ABC Motors Limited
Designed by	Granville Bradshaw
First run	1920
Number built	1,147

The ABC Dragonfly was a British radial engine developed towards the end of First World War. It was expected to deliver excellent performance for the time and was ordered in very large numbers. It proved, however, to be extremely unreliable and was abandoned when its faults were unable to be corrected.^[1]

[edit] Design and develoment

ABC Motors was founded in 1911 by Granville Bradshaw, who was also the company's chief designer. In 1917, after initial promising tests of the ABC Wasp air-cooled radial, Bradshaw produced a design for a larger and more powerful engine, the nine-cylinder Dragonfly.^[2] The engine was simple and easy to produce, and was predicted to give 340 hp (254 kW) for a weight of 600 lb (273 kg).^[2] One distinctive feature was the use of copper-plated cooling fins, which were claimed by Bradshaw to be so effective that water would not boil on the surface of the radiators.^[3]

On the basis of the promised performance, Sir William Weir, the Director of Aeronautical Supplies, made the decision to place large orders for the Dragonfly,^[2] with 11,500 engines having been ordered from 13 suppliers by June 1918.^[3] It was planned that a large proportion of RAF aircraft would be powered by the Dragonfly in 1919. Types designed to be powered by the Dragonfly included the Sopwith Dragon (a derivative of the existing Snipe), the Nieuport Nighthawk, and the Siddeley Siskin. Of this order 1,147 engines were built but only nine or ten actually flew.^[4]

Testing showed severe problems with the much vaunted engine. It was subject to extreme overheating, the copper-plated cooling fins proving useless; showed much poorer fuel consumption than expected; and suffered severe vibration, running at the resonance frequency of the crankshaft.^[2] These problems proved unsolvable, and the Dragonfly was eventually abandoned.

[edit] Variants

Dragonfly I: 1918, 320 hp (239 kW)
Dragonfly IA: 360 hp (268 kW), revised pistons and cylinder heads, revised oil system.

[edit] Applications

[edit] Specifications (Dragonfly IA)

Data from Jane's Fighting Aircraft of World War I ^[5]

General characteristics

Type: 9-cylinder air-cooled radial engine
Bore: 5½ in (139.7 mm)
Stroke: 6½ in, (165.1 mm)
Displacement: 1,389.86 in³ (22.78 L)^[2]
Dry weight: 600 lb (273 kg)

Components

Valvetrain: 3 overhead valves, 2 inlet and 1 outlet per cylinder
Fuel system: Twin carburettors
Oil system: 2 oil pumps
Cooling system: Air-cooled

Performance

Power output: 340 hp (254 kW) at 1,650 rpm
Specific power: 0.24 hp/in³ (11 kW/L)
Specific fuel consumption: 0.56 pints per bhp/hour(0.32 L/kW)
Oil consumption: 7 pints per hour (3.3 L/hr)
Power-to-weight ratio: 0.56 hp/lb (0.93 kW/kg)

[edit] References

[edit] Notes

^ Lumsden 2003, p.52.
^ ^a ^b ^c ^d ^e Gunston 1986, p.8.
^ ^a ^b Bruce 1974, p.292
^ Lumsden 2003, p.53.
^ Grey 1990, p.256

[edit] Bibliography

Bruce, J.M. "Sopwith Snipe...:...the RAF's First Fighter. (Part 2). " Air Enthusiast International Volume 6 Number 6, June 1974. Bromley, UK: Fine Scroll.
Grey, C.G. (ed.). Jane's Fighting Aircraft of World War I. London, Studio, 1990. ISBN 1 85170 347 0.
Gunston, Bill. World Encyclopedia of Aero Engines. London: Guild Publishing, 1986.
Lumsden, Alec. British Piston Engines and their Aircraft. Marlborough, Wiltshire: Airlife Publishing, 2003. ISBN 1-85310-294-6.

[edit] External links

Wikimedia Commons has media related to: ABC aircraft engines

[0] Lumsden 2003, p.52.

[gunstonworld_enginep8-1] Gunston 1986, p.8.

[brucep292-2] Bruce 1974, p.292

[3] Lumsden 2003, p.53.

[JanesairWW1p256-4] Grey 1990, p.256

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