ABC Dragonfly – Wikipedia

L’ ABC Dragonfly It was a radial aeronautical engine with a 9 -cylinder air -cooled 9 -cylinder developed by the British company ABC Motors Ltd. In the late ten years of the twentieth century, during the final stages of the First World War.

Designed by Granville Bradshaw as an alternative to the now obsolete rotary engines, although started to production it was a driving unit burdened by numerous design problems that revealed unresolved, afflicted by rapid overheating and strong vibrations that will determine the abandonment of the project, ^[3] However, it was used in numerous prototypes between the end of the conflict and the early 1920s.

After in 1917 the tests carried out on the experimental 7 -cylinder ABC Wasp air -cooled ABC was very promising, Granville Bradshaw, the designer and owner of the ABC Motors, decided to start the development of an enlarged version capable of delivering a higher power, 9 Dragonfly cylinders. ^[first]

The new engine, designed to be simple and easy to build, was expected to be able to deliver a power equal to 340 HP (254 kW) for a weight of 600 LB (273 kg). He also proposed the technological peculiarity experienced on the Wasp, the copper plating of the cylinder lamellar parcels, an expedient that according to what Bradshaw declared it was so efficient in dispersing the heat that by pouring the water this would not be able to boil. ^[4]

Based on promised performance, Sir William Weir, at the time responsible for aeronautical supplies, decided to sign a substantial supply order for Dragonfly, ^[first] With 11 500 units ordered to 13 suppliers since June 1918. ^[4] It was expected that in 1919 most of the models supplied to the Royal Air Force were equipped with a Dragonfly, and there were many plane models designed around the large 9 -cylinder, including Sopwith Dragon, a snipe development already in service, Nieuport Nighthawk and Siddeley Siskin. However, the order was never escaped and the production stood on 1 147 units built, of which in the early 2000s there were still about ten those mounted on aircraft still in flight conditions. ^[3]

The engine is shortly described by the aviation historian Bill Gunston in his book Plane Speaking , in the chapter entitled Cancel the Others… . In the text Gunston says that Bradshaw had shown that he was better as a seller than as a designer, showing himself evasive when he was asked to talk about the initial tests which were substantially revealed of the serious problems congenital to his excessively acclaimed engine.

Already heavier than 30 kg than the project specifications, the Dragonfly was suffering from a serious tendency to overheating. Gunston indicated it as the worst air -cooled aeronautical engine never made. The copper plating of the cooling fins proved useless; At operating speed the heads tended to reach temperatures so high as to make them shine with opaque red, and in extreme cases they caused damage due to heat and even carbonization of the propeller. The developed power descended well below estimates, even when the engine was employed at 15% more than the project specifications (managing to express only 315 HP), while fuel consumption was greater than expected. To try to remedy the problem, the redesign of the cylinders took a moderate success in improving the cooling of the engine, however it was realized that the vibrations transmitted by the Dragonfly already from the early stages of development derived from the torsional resonance frequency of its engine tree , a condition still scarcely known at the time of its development. ^[first] These problems have proven to be unsolvable, with a consequent extremely low operational life (approximately from 30 to 35 hours per engine), so any further attempt to develop the Dragonfly was finally abandoned.

Gunston’s observations suggest that its development was also promoted in relation to the end of the conflict, as the only other aeronautical engine still in production at the time of the signing of the Armistice of Compiègne, on 11 November 1918, was the V12 Rolls -Royce Eagle cooled liquid; Orders for all the other engines of the period were canceled in favor of Dragonfly.

Dragonfly I

Version produced in 1918, power paid 320 HP (239 kW).

Dragonfly IA

Variant deeply revised, with new pistons, new cylinders heads and new lubrication system; Power paid 360 HP (268 kW).

• ( IN ) C.G. Grey (ed.), Jane’s Fighting Aircraft of World War I , London, Studio, 1990, ISBN 1-85170-347-0.
• ( IN ) Bill Gunston, World Encyclopedia of Aero Engines , London, Guild Publishing, 1986.
• ( IN ) Alec Lumsden, British Piston Engines and their Aircraft , Marlborough, Wiltshire, Airlife Publishing, 2003, ISBN 1-85310-294-6.

Publications