ABC Dragonfly

The ABC Dragonfly was a British radial engine developed towards the end of the 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 when its faults were unable to be corrected, was abandoned, never powering a production aircraft.

History

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 9-cylinder Dragonfly. 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). One distinctive feature was the use of copper-plated cooling fins, which were claimed by Bradshaw to be so effective water would not boil on the surface of the radiators. Bruce 1974, p.292]

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, with 11,500 engines having been ordered from 13 suppliers by June 1918. 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.

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

pecifications

Data from Jane's Fighting Aircraft of World War I Grey 1990, p.256] pistonspecs

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) Gunston 1986, p.8.]
length=
diameter=
width=
height=
weight=600 lb (273 kg) (specified)
valvetrain=3 overhead valves, 2 inlet and 1 outlet "per" cylinder
supercharger=
turbocharger=
fuelsystem=twin carburetters
fueltype=
oilsystem=2 oil pumps
coolingsystem=Air cooled
power=340 hp (254 kW) (specified) (320hp@1650rpm (bmep=110.5psi))
specpower=0.24 hp/in³ (11 kW/L)
compression=
fuelcon=
specfuelcon=0.084 US Gallon per BHP hour (0.32 L/kW, 0.56 pints per BHP hour)
oilcon=8.4 US Gallon per hour (4.0 L/hr, 7 pints per hour)
power/weight=0.56 hp/lb (930 W/kg)

References

Notes

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.
* Gray, 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.