Sunbeam Arab Explained

The Sunbeam Arab was a British First World War-era aero engine.

Design and development

By 1916 the demand for aero-engines was placing huge demands on manufacturing. To help ease the pressure, the War Office standardised on engines of about 2000NaN0; one of these was a V-8 water-cooled engine from Sunbeam known as the Arab. Using cast aluminium alloy cylinder blocks and heads with die-cast aluminium alloy pistons, the Arab had a bore of 120mm and stroke of 130mm for a capacity of 11.762L, developing 208- at 2,000 rpm.

First bench-run in 1916, the Arab was obviously inspired by the Hispano-Suiza V-8 engines but with very little in common when examined in detail. After submission to the Internal Combustion Engine Committee of the Advisory Committee on Aeronautics Sunbeam received an order for 1,000 in March 1917. The order formed part of the strategy of Sir William Weir to bypass the skilled engineering workforce needed to build Rolls-Royce Eagle and Falcon engines, through the use of cast aluminium cylinder blocks that minimised the need for machining.[1] However, the Arab was ordered before flight testing, and when the engine went into the air, chronic vibration problems emerged which were never cured. The initial order was increased to 2,000 in June 1917 as well as another 2,160 to be built by Austin Motors (1,000), Lanchester Motor Company (300), Napier & Son (300), and Willys Overland (560) in the United States of America.[2] Despite this massive manufacturing effort, the Arab proved largely useless, and nearly half of the production run of the Bristol Fighter, Britain’s best two-seat fighter of the First World War, went into storage because plans to power the aircraft with the Arab were abandoned due to the engine’s failings.[3]

Service use of the Arab was limited because of poor reliability and persistent vibration problems, causing some 2,350 orders to be cancelled and remaining orders 'settled', compensating manufacturers for costs incurred.[4]

Developed from the Arab were the inverted V-8 Sunbeam Bedouin, straight-six Sunbeam Dyak, W-12 Sunbeam Kaffir, and 20-cylinder radial Sunbeam Malay.[5]

Variants

Arab
  • The production engine loosely based on the Hispano-Suiza 8 V-8 engines.
    Bedouin
  • In common with many other contemporary engine manufacturers, the Arab was redesigned to run inverted and given the name Sunbeam Bedouin. Intended to provide better forward visibility for single-engined aircraft, there is no evidence that the Bedouoin was fitted to an aircraft or flew.
    Kaffir
  • A W-12 broad-arrow engine using blocks, heads and valve-gear from the Arab, giving 3000NaN0. Bore remained the same at 1202NaN2, but with a stroke of 1352NaN2.
    Dyak
  • A straight-six extrapolation of the Arab retaining the 1202NaN2 stroke and 1302NaN2 bore of the Arab, but with only two valves per cylinder as opposed to the three valves on the Arab.[6]
    Pathan
  • Coatalen expressed his interest in diesel engines by designing a diesel derivative of the Dyak with the same attributes, developing 1000NaN0 at 1,500 rpm. Only prototypes of the Pathan were built.
    Malay
  • The Sunbeam Malay was a 20-cylinder radial aircraft engine of 29.40NaN0 capacity manufactured by Sunbeam using five four-cylinder blocks from the Arab arranged around a central crankshaft. The Malay retained the 1202NaN2 × 1302NaN2 bore and stroke of the Arab, as well as the three valves per cylinder and overhead camshafts. Nominally rated at 5000NaN0, the Malay was not put into production.[7]

    Applications

    Data from Brew.

    References

    Bibliography

    External links

    Notes and References

    1. Ewer, 2023 p.10
    2. Brew 1998
    3. Ewer, 2023 p.10
    4. Brew 1998
    5. Brew 1998
    6. Brew 1998
    7. Brew 1998

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