Bristol Perseus

The Perseus was a nine cylinder one-row radial aircraft engine produced by the Bristol Engine Company starting in 1932. It was not widely used due to the rapid introduction of much more powerful two-row engines like the Bristol Hercules, but is notable as being Bristol's first successful sleeve valve design.

In late 1925 and early 1926, the RAE published a series of papers on the sleeve valve principle. In short, the sleeve valve replaced the normal poppet valves in the engine with a rotating sleeve inside the cylinder. The sleeve rotated, and holes in the sleeve and cylinder lined up to open and close the valve. The advantages were primarily simplicity and that less energy is needed to run the system. However at higher powers and RPMs, when the engine needs to move considerably more air and so so more quickly, the sleeve design comes into its own. The sleeve is also much easier to "drive" than the poppet, there are no pushrods or rockers needed, so it is a much better design to use in "dense" two-row engines. It was this "future expansion" capability that interested Roy Fedden when he first read of the work.

By 1927 Fedden had built a working two cylinder V as a testbed, with the idea of developing it into a V-12. However several problems cropped up on the design, notably that the sleeves tended to burst during the power stroke and strip their driving gears. This led to a long series of tests and materials changes and upgrades that required six years and an estimated 2 million pounds, but by 1933 a small nine cylinder hand-built testbed called the Bristol Aquila was at production quality. It was offered for sale, but saw little use.

At the same time plans were made to adapt the Mercury-sized engine to the sleeve system, which resulted in the Perseus. The Perseus was, for all intents, a larger version of the Aquila. The first production versions were rated at 580hp, the same as the same-year model Mercury, which shows that the sleeve system was being underutilized on this design.

The Perseus saw limited use in the civilian field, notably on the Short Empire flying-boats, but was more common in the now-expanding military field where it was found on the Westland Lysander, Vickers Vildebeest, Blackburn Botha, Skua and Roc bombers.

The main contribution of the both the Aquila and Perseus is that they formed the basic piston and cylinder for the "twinned" versions, the tremendously successful Hercules and Centarus respectively. It was in these designs that the advantages of the sleeve valve were finally put to good use, and by war's end the Centarus was one of the most powerful engines in the world.

Specifications =

Layout: nine-cylinder, one-row, radial Bore/Stroke/Displacement: 5.8"/6.5"/1520 cu in (24.9l) Power: 540hp at 2400 RPM Weight: 1026 lbs (466 kg)