He remained at Brazil Straker over the following years, and he was particularly influential in convincing company management to take on the repair of various aircraft engines when World War I started.
The two were inseparable for the next twenty years, and the part number of most components of Fedden's engines were prefixed "FB" to indicate the shared credit.
In September, however, a Mercury was experimentally fitted to a Bristol Scout and it dramatically improved performance, easily beating the competing Sunbeam Arab.
Convinced of the quality of the Cosmos designs, the Air Ministry "made it be known" that they would be rather happy if the company were purchased by Bristol, which eventually took place in 1920.
After Jimmy Ellor's pioneering work at the RAE on turbosuperchargers, the Jupiter was experimentally adapted with a turbo to become the first "Orion" design, although this saw little use.
Both would use a supercharger, at that time a new-fangled idea, to provide boost even at ground level and thereby deliver similar power as the Jupiter's from a much smaller engine.
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.
At the time he pitched this for very large, long-range bombers and patrol aircraft, but he stated throughout development from late 1941 that the ultimate goal was the transatlantic airline market.
Although Fedden had created a long line of hugely successful engines for Bristol, he had fought constantly with management over funding priorities.
For much of the remainder of the war, he travelled in the United States with another Bristol employee, Ian Duncan, to study US production line techniques to improve their own.
The company was provided sixty Volkswagen Type 1s by Major Ivan Hirst but was unable to sell any in the anti-German postwar climate and difficult economic conditions.
[9] The company's first product, the Fedden O-325, was a small horizontally-opposed fuel injected six cylinder sleeve valve aeroengine intended for helicopters or for submerged wing installation in aircraft.
Finally they decided to design their own car, powered by a three-cylinder air-cooled radial, but they found it had vibration and overheating problems and tended to skid badly when being cornered hard.