Roy Fedden

Sir Roy Fedden
Born	Alfred Hubert Roy Fedden (1885-06-06) 6 June 1885 Bristol region, England
Died	21 November 1973(1973-11-21) (aged 88)
Occupation(s)	Engineer, aircraft engine designer
Years active	Early 1900s–1940s
Known for	Bristol Engine Company's piston aircraft engines, including Bristol Jupiter, Mercury, Pegasus, Perseus, Taurus, Hercules, Centaurus
Notable work	Development of sleeve valve engines for aircraft

Sir Alfred Hubert Roy Fedden MBE, FRAeS (6 June 1885 – 21 November 1973) was a distinguished engineer responsible for the majority of the Bristol Engine Company's acclaimed piston aircraft engine designs.

Early life

Born in the Bristol region to a well-to-do and prominent family, Fedden was the younger brother of artist Romilly Fedden. His family was notable locally for being the first to own an automobile, a circumstance that parallels the early experiences of fellow engine innovator Harry Ricardo. This exposure likely played a significant role in shaping his career path. Fedden attended Clifton College, where he was more recognized for his athletic abilities than academic achievements. Upon completing his schooling, he chose not to join the military and instead committed to pursuing an apprenticeship in engineering.

Apprenticeship

Completing his apprenticeship in 1906, Fedden quickly moved to design an entire automobile. He successfully persuaded the local company Brazil Straker to employ him, leading to the production of the well-received Shamrock model. Over subsequent years at Brazil Straker, Fedden was instrumental in encouraging company leadership to undertake the maintenance of various aircraft engines at the outbreak of World War I. This initiative expanded the firm's operations to include manufacturing Rolls-Royce Hawk and Falcon engines, as well as significant components for the renowned Rolls-Royce Eagle. Although Henry Royce extended an offer for a senior role within his organization, Fedden opted to remain with Brazil Straker.

In 1915, alongside his draughtsman Leonard Butler—who would become his close collaborator for two decades—Fedden began designing his own aero engines. Reflecting their partnership, most component part numbers bore the prefix "FB." During World War I, they developed two engines: the 14-cylinder Mercury radial engine, distinguished by its helically arranged cylinders rather than conventional dual rows, and the larger, traditional single-row nine-cylinder Jupiter engine producing approximately 400 horsepower (kW).

Cosmos Engineering and the Jupiter

File:Bristol Jupiter.jpg

The Bristol Jupiter, developed by Roy Fedden

During this era, the aviation division of Brazil Straker was acquired by Cosmos Engineering, where development of the engine designs continued. Both models were prepared for trials in 1918, but initial interest was minimal. However, in September, a Mercury engine was experimentally installed in a Bristol Scout, significantly enhancing its performance and easily surpassing the rival Sunbeam Arab. Subsequently, Bristol tested the Jupiter in their new Badger aircraft, which also outperformed the competing ABC Dragonfly engine. Although production for both engines was slated to begin immediately, the conclusion of the war days later led to the cancellation of the contract.

Following the war's end, Cosmos lacked production-ready designs and experienced a rapid decline in repair work, leading to insolvency. Confident in Cosmos' engine designs, the Air Ministry discreetly encouraged Bristol to acquire the company, which occurred in 1920. Sir George White later recalled that Bristol obtained the Mercury design along with seven engines and all Cosmos assets, including Fedden and his design team, for merely £15,000. Most accounts indicate this acquisition happened primarily due to Air Ministry persuasion, understandable given the fragile economic climate of the time.

Bristol soon identified a use for the larger engine design, initiating production at their new facility in Filton under the name Bristol Jupiter. The Jupiter achieved commercial success globally and elevated Fedden to one of Europe's highest-paid engineers. Building on Jimmy Ellor's pioneering work on turbosuperchargers at the RAE, an experimental turbocharged version of the Jupiter was developed as the first "Orion" model, although it saw limited application.

By the late 1920s, as the Jupiter became outdated, Fedden and Butler began developing two new engines. Both incorporated a supercharger, then an innovative technology, enabling consistent power output even at ground level from smaller engines comparable in power to the original Jupiter. Reusing a previous name, one design evolved into the Bristol Mercury, while a more powerful engine matching the Jupiter’s original size became known as the Bristol Pegasus.

Development of sleeve valve engines

In 1925 and 1926, Harry Ricardo published influential papers at the RAE arguing that conventional poppet valve systems had reached their performance limits and that future engines would need to adopt sleeve valve technology. Promptly responding to these findings, Fedden and Butler modified the Mercury into the Bristol Aquila and transformed the Pegasus into the Bristol Perseus. However, as aircraft grew larger and demanded more power, these engines quickly became underpowered.

To address this challenge, both designs were adapted into two-row configurations, resulting in the creation of the Bristol Taurus and the highly regarded Bristol Hercules. Continuing innovation led Fedden to develop an 18-cylinder two-row adaptation of the Hercules called the Bristol Centaurus.

When World War II commenced in 1939, Taurus engines were operational while Hercules units remained under testing. Centaurus development was paused until Hercules production issues were resolved. Throughout the conflict, Bristol’s sleeve-valve engines were extensively deployed across numerous aircraft models. Their success was such that the Air Ministry compelled a reluctant Bristol to assist with resolving difficulties on the high-powered Napier Sabre, which faced its own sleeve valve challenges.

With Hercules manufacturing fully underway by 1941, Fedden resumed work on Centaurus production starting in 1942. At that time, few aircraft could accommodate an engine delivering 2,500 hp. Newer designs capable of housing such power emerged late in the war—most notably certain variants of the Hawker Tempest, which eventually replaced Sabre-powered versions.

Even as Centaurus production began, Fedden contemplated developing an even larger engine intended for very large long-range bombers and patrol planes. From late 1941 onward he emphasized that his ultimate objective was to serve transatlantic commercial aviation. This ambition led to conceptualizing an enlarged Centaurus variant called Orion with roughly 4,000 hp output. They also explored a four-row 28-cylinder configuration but conducted minimal development on that front.

In recognition of his significant contributions to advancing aircraft engine technology during this period, Fedden was honored with a knighthood in 1942.

Later war and after

The demands of wartime manufacturing significantly impacted Leonard Butler, prompting him to step away from the company to recover. Despite Fedden’s development of a series of highly successful engines for Bristol, he frequently clashed with management over budget allocations. With Butler no longer present to mediate, Fedden appeared to reach his limit; shortly after receiving a knighthood, he departed from Bristol to accept various governmental roles. Throughout much of the war's remaining period, he traveled across the United States alongside fellow Bristol employee Ian Duncan, studying American production line methods with the aim of enhancing their own manufacturing processes.

In 1945, Fedden led a Ministry of Aircraft Production (MAP) delegation tasked with investigating German aviation technology and research. This assignment, referred to as the "Fedden Mission", included visits to the V-2 manufacturing site and labor camps located in Nordhausen. He authored multiple articles analyzing German engine engineering and production techniques, ultimately determining that while German engines were inferior to British designs in supercharger technology and power density, their fuel injection systems and single-lever controls were notably advanced.

Upon returning to Britain, Fedden and Duncan founded Roy Fedden Ltd. in 1945. The company received sixty Volkswagen Type 1 vehicles from Major Ivan Hirst, but due to the postwar anti-German sentiment and challenging economic conditions, none were sold. The firm’s initial product was the Fedden O-325, a compact horizontally opposed six-cylinder fuel-injected sleeve valve aeroengine designed for helicopter applications or installation within aircraft wings. This engine outperformed any flat-four or flat-six American counterparts and was even considered for the U.S. Ercoupe aircraft. However, development ceased when "Roy Fedden Limited" entered liquidation in June 1947. Subsequently, Fedden pursued a new 1,350 hp (1,010 kW; 1,370 PS) turboprop project named the Cotswold, intended for wing-mounted use in either tractor or pusher configurations. Bill Gunston documented three distinct tractor-style nacelle layouts for this design, but it never advanced beyond planning stages. Later efforts focused on creating their own automobile powered by a three-cylinder air-cooled radial engine; however, this vehicle suffered from vibration issues, overheating, and poor handling during sharp turns. Although work began on an improved chassis, waning interest among engineers led to staff departures and ultimately the company's closure.

Following these ventures, Fedden briefly consulted for George Dowty before retiring to concentrate on teaching at the College of Aeronautics at Cranfield University.

Fedden had no children. He is sometimes incorrectly identified as the father of renowned British artist Mary Fedden, who was in fact his niece.

Bibliography

• Gunston, Bill. By Jupiter! London, The Royal Aeronautical Society, 1978. ISBN 0-903409-07-0
• Gunston, Bill. World Encyclopedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9
• Lumsden, Alec. British Piston Engines and their Aircraft. Marlborough, Wiltshire: Airlife Publishing, 2003. ISBN 1-85310-294-6.

External links

• Roy Fedden at Rolls-Royce.com

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• Fedden Power Units