Roy Fedden - Development of Sleeve Valve Engines

Development of Sleeve Valve Engines

In 1925 and 1926, Harry Ricardo wrote a series of seminal papers at the RAE claiming that the poppet valve system was already operating at its peak capability, and that any future engines would have to use sleeve valves instead. Fedden and Butler immediately turned to such a design, adapting the Mercury to become the Bristol Aquila, and the Pegasus as the Bristol Perseus. However, both of these engines quickly found themselves at the "low end" of the power spectrum as ever-larger aircraft designs demanded ever-larger engines to power them.

To solve this problem, the two designs were quickly adapted to two-row configurations, resulting in the Bristol Taurus and the superb Bristol Hercules. Not one to rest on his laurels, Fedden then started adapting the Hercules into a two-row 18-cylinder design as the Bristol Centaurus.

The Taurus was in service when World War II started in 1939, but the Hercules was still in testing. Work on the Centaurus was suspended while the final problems with Hercules production was worked out. The entire Bristol sleeve-valve range would see widespread service throughout the war on a wide variety of designs. They were so successful that the Air Ministry forced a reluctant Bristol to help with the high-power Napier Sabre project that had bogged down due to problems with their sleeves.

With Hercules production in full swing in 1941, Fedden returned to the Centaurus. Production was able to start in 1942, but at the time there were few aircraft that could be adapted to a 2,500 hp engine. Newer designs intended to mount engines of this size appeared near the end of the war, notably certain versions of the Hawker Tempest, taking over from the Sabre in that design.

For his role in creating some of the most successful aircraft engines of the era, Fedden was knighted in 1942.

The stress of wartime production needs had taken its toll on Leonard Butler, who left the company to recuperate. Although Fedden had created a long line of hugely successful engines for Bristol, he had fought constantly with management over funding priorities. Without Butler's influence it seems Fedden "had enough", and shortly after being knighted, he left Bristol to take up a variety of positions within the Government. For much of the remainder of the war, he travelled in the United States with another Bristol employee, Ian Duncan, to study their production line techniques in order to improve their own.

On his return, Duncan and Fedden set up Roy Fedden Ltd. in 1945. Their first product was a small horizontally-opposed aero engine intended to be installed within the wings of twin-engine aircraft. The Fedden O-325 saw no use. He then turned to a new turboprop design which also found little interest. Finally they decided to design their own car, powered by a three-cylinder air-cooled radial, but they found it had serious handling problems and tended to flip over when being cornered hard. This was largely due to the desire to maximise interior space coupled with the inherent difficulty of packaging a three-cylinder radial in a car chassis, which led to the engine being mounted above the rear axle, giving the car an undesirably high centre of gravity. Work started on a replacement chassis, but the rest of the company's engineers lost interest and left, and soon the company had to be dissolved.

After this, Fedden worked for a time consulting with George Dowty, but soon retired and spent his time teaching at the College of Aeronautics at Cranfield University.

Fedden was childless. He has sometimes been mistakenly described as the father of a prominent British artist called Mary Fedden. He was in fact her uncle.