Rolls-Royce Merlin XX

Rolls-Royce Merlin XX. The Merlin XX was a pivotal development of the iconic Rolls-Royce Merlin engine, introduced in 1940 to deliver significantly improved performance at higher altitudes. It incorporated a new two-speed, two-stage supercharger, a critical advancement that allowed Royal Air Force fighters and bombers to maintain power in the thin air of combat altitudes. This engine became a cornerstone of British air power during the middle years of the Second World War, powering legendary aircraft in crucial theatres like the Battle of Britain and the Combined Bomber Offensive.

Design and development

The design and development of the Merlin XX was driven by the urgent need to counter the performance of German fighters like the Messerschmitt Bf 109 at altitudes above 20,000 feet. Engineers at Rolls-Royce Limited, led by figures like Ernest Hives, focused on supercharger improvement, adopting a two-speed, two-stage design. This system used an improved SU Carburettor and an additional supercharger impeller, with an intercooler to manage the increased charge air temperature. The development program, which involved intensive testing at the Royal Aircraft Establishment at Farnborough Airfield, was accelerated by the pressures of the war, leading to its rapid entry into service. Key production was also undertaken by the Ford Motor Company at its Manchester plant under the Shadow Factory scheme to meet massive demand.

Operational history

The Merlin XX entered operational history in late 1940, initially equipping the Hawker Hurricane Mk.II and later the Supermarine Spitfire Mk.III and Mk.VI. Its enhanced high-altitude performance was immediately valuable, allowing RAF Fighter Command to more effectively challenge the Luftwaffe during the later stages of the Battle of Britain and the subsequent Circus offensive over occupied Europe. The engine's reliability and power made it the preferred choice for the Avro Lancaster Mk.I bomber, forming the backbone of RAF Bomber Command's heavy bomber force during the strategic bombing campaign against Nazi Germany. It also powered maritime patrol aircraft like the Avro Shackleton in the post-war period, seeing service into the 1950s.

Variants

Several key variants of the Merlin XX were produced to suit different airframes and roles. The Merlin 20 series formed the core, with the Merlin XX itself being the standard model. The Merlin 21 and Merlin 22 featured minor differences in ancillary drives and mounting points for specific aircraft like the Supermarine Spitfire Mk.V. The Merlin 23 and Merlin 24 were optimized for lower-altitude performance, often used in aircraft like the Hawker Sea Hurricane. The Merlin 25 introduced a cropped impeller for better medium-altitude power, notably used in later marks of the Avro Lancaster. These developments directly influenced the design of the American-built Packard V-1650, which powered the North American P-51 Mustang.

Specifications (Merlin XX)

* **Type:** 12-cylinder, liquid-cooled, supercharged V12 engine * **Bore:** 5.4 inches (137 mm) * **Stroke:** 6.0 inches (152 mm) * **Displacement:** 1,649 cubic inches (27.0 L) * **Length:** 88.7 inches (2.25 m) * **Width:** 30.8 inches (0.78 m) * **Height:** 40.0 inches (1.02 m) * **Dry weight:** 1,640 lb (744 kg) * **Supercharger:** Two-speed, two-stage centrifugal * **Fuel system:** SU Carburettor with automatic mixture control * **Cooling system:** Liquid-cooled, with ethylene glycol * **Power output:** 1,280 hp (954 kW) at 3,000 rpm at 6,250 ft (1,905 m) with +9 lbs boost * **Specific power:** 0.78 hp/cu in (35.3 kW/L) * **Compression ratio:** 6.0:1

Applications

The Merlin XX was installed in a wide range of iconic British military aircraft. Its primary fighter applications included the Hawker Hurricane Mk.II, the Supermarine Spitfire Mk.III, and the high-altitude Supermarine Spitfire Mk.VI. It was the definitive engine for the Avro Lancaster Mk.I and early Avro Lincoln bombers, which carried out devastating raids on targets like Hamburg and Berlin. Other notable applications were the Fairey Barracuda torpedo bomber, the Westland Whirlwind heavy fighter, and the Canadian Car and Foundry Hawker Hurricane variants built for the Royal Canadian Air Force. Post-war, it was used in the Avro Shackleton MR.1 maritime patrol aircraft.

Category:Aircraft piston engines Category:Rolls-Royce aircraft engines Category:World War II aircraft engines of the United Kingdom