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Ricardo, Sir Harry Ralph (1885–1974), mechanical engineer, was born on 26 January 1885 at 13 Bedford Square, London, the eldest of three children and only son of Halsey Ralph Ricardo (1854–1928), architect, a descendant of the brother of David Ricardo, economist, and his wife, Catherine Jane, daughter of , civil engineer. He was educated at Rugby School (1898–1903) and Trinity College, Cambridge (1903–7). From the age of ten he was using tools and building engines, and in his first two terms at Cambridge he built a single-cylinder motorcycle engine; riding a machine fitted with this engine he covered 40 miles on a quart of petrol, winning a fuel economy race and bringing himself to the notice of Bertram Hopkinson, professor of mechanism and applied mechanics. Hopkinson persuaded Ricardo to spend his four years at Cambridge helping him with research on the factors limiting the performance of the petrol engine, even though this meant reading for an ordinary rather than an honours degree. While at Cambridge, Ricardo also designed a two-stroke cycle engine to study the flow of air and gas through the cylinder. A 15 hp version of this engine, named the Dolphin, was produced for fishing boats and motor cars by a company started by a cousin.

Ricardo obtained his ordinary degree in 1906 and spent a further year researching at Cambridge. In 1907 he joined his grandfather's firm, Rendel and Robertson (later Rendel, Palmer, and Tritton), first as an inspector of machinery, then as head of a department for designing the specialized mechanical equipment needed for large civil engineering projects. At the outbreak of war he was classified in a reserved occupation but military work was slow in coming, although he designed aero-engines made in 1915 by Brotherhood and Beardmore.

Ricardo's big opportunity came in 1916 with the development of the tank and his appointment as consulting engineer to the mechanical warfare department. He was asked first to explore the willingness of some manufacturers to make a new and more powerful engine and, when they agreed, to undertake its design. The successful design and production of the 150 hp engine and two larger engines giving 225 hp and 300 hp and incorporating features for improving combustion turned Ricardo into a professional and gave him the confidence to start his own company. By April 1917 one hundred of his engines were being produced per week, and the two larger engines were developed. In 1918 he became consulting engineer in aero-engines to the Air Ministry.

In July 1917, after the death of his grandfather, Ricardo launched his own company with the help of a three-year contract from the Asiatic Petroleum Company for research on fuels and detonation. Apart from this research Ricardo & Co. undertook the design of any form of internal combustion or related engine and also offered consulting services. A laboratory designed by his father was built at Shoreham by Sea, Sussex, in 1919 and, except during 1940–5 when it moved to Oxford for security reasons, the company remained at Shoreham. Ricardo communicated his results on the effect of fuel properties to Sir Robert Waley Cohen of the Shell group, whose company sponsored the extensive research on fuels and detonation at Shoreham (1918–21). During this contract Ricardo and his team, which consisted of H. T. Tizard, D. R. Pye, and Oliver Thorneycroft, developed the single-cylinder variable compression engine and the concept of the toluene (later octane) number for rating fuels. In 1922 and 1923 Ricardo's The Internal Combustion Engine (2 vols.) was published. In later editions the title was The High-Speed Internal Combustion Engine.

Ricardo's lifelong contributions to the development of the internal combustion petrol and diesel engine were based on skilful research and outstanding design. His diffident and polite manner concealed great determination and tenacity in the pursuit of technical achievement. Many notable designs were produced over the years including a side-valve engine (which gave as good performance as the more expensive overhead-valve design), two-stroke and four-stroke cycle diesel engines for automotive and aircraft usage, and sleeve-valve designs for advanced aircraft engines. Most of the world's engine manufacturers used Ricardo's designs at some stage of their history and, after a successful patent case in 1932, paid royalties or consulting fees to the company. In 1939–46 Ricardo was very active in government research and particularly on the sleeve-valve aero-engine. He was a member of the war cabinet engineering advisory committee (1941–5). He also undertook the design of a governor and fuel control for the first Whittle jet engine. Ricardo published extensively in professional journals and long after his retirement in 1964 kept in touch with engineers, young and old, in the company.

In 1929 Ricardo was elected FRS. He was president of the Institution of Mechanical Engineers, 1944–5, and was knighted in 1948. He received honorary degrees from Birmingham (1943), Turin Polytechnic (1960), and Sussex (1970), and an honorary fellowship of Trinity College, Cambridge (1967). He was an honorary member of the British, Dutch, and American mechanical engineering institutions, Manchester College of Technology (1935), and the Deutsche Akademie der Luftfahrtvorschung (1938). He was awarded the Rumford medal of the Royal Society (1944), the Clayton and James Watt (1953) medals of the Institution of Mechanical Engineers, the Lancaster and Crompton medals of the Institution of Automobile Engineers, and medals from the Royal Aeronautical Society, the Institute of Fuel, the Society of Automotive Engineers, USA, and others.

Ricardo married in 1911 Beatrice Bertha (d. 1975), daughter of Charles Bowdich Hale, their family doctor; she was an art student at the Slade School. They had three daughters. They lived for most of their happy family life near Shoreham, where his hobby was boating, and after 1945 at Woodside, Graffham, in Sussex, where in his ninetieth year Ricardo broke his leg in a fall. He died six weeks later, on 18 May 1974, at King Edward VII Hospital, Midhurst, Sussex.

William Hawthorne, rev.


H. Ricardo, Memories and machines, the pattern of my life (1968) · W. Hawthorne, Memoirs FRS, 22 (1976), 359–80 · personal knowledge (1986) · The Times (20 May 1974), 16 g · The Times (22 May 1974), 22g


CAC Cam., papers · IWM, technological papers |  IWM, corresp. with Sir Henry Tizard


W. Stoneman, two photographs, 1931–43 · photograph, repro. in Hawthorne, Memoirs FRS

Wealth at death  

£168,256: probate, 20 Aug 1974, CGPLA Eng. & Wales