Rolls-Royce Merlin

Workers assembling cylinder blocks on the Hillington Merlin production line in 1942

Workers assembling cylinder blocks on the Hillington Merlin production line in 1942

Line with Rolls-Royce Merlin is a family of aircraft engines, developed during the 1930s by the British firm Rolls Royce to fill a gap in its range between Rolls-Royce Kestrel 22-liter engine and the famous Rolls-Royce R 36 liters equipped the seaplane competition Supermarine firm. Thanks to their high power density, they were considered some of the best engines of the Second World War. They were produced in 168,040 copies, 55,873 by Packard in the United States. The name of this engine is not the magician of King Arthur, but the name of Merlin in English.


The development was started as a private initiative on own funds Henry Royce in 1932 as the PV-12 (PV private venture). In October 1933, the Air Ministry agreed to fund the development and gives the name of the Merlin engine. A first version appeared in July 1934, the Merlin A, capable of delivering 790 horsepower at 2700 rpm. But the engine suffers from many problems, mainly in the gears of the gear and shirts and cooling by evaporation. The following Merlin B has four valves per cylinder, making an angle of 45 ° as in automobile engines of the brand. Tried in February 1935, this engine delivers a power of 950 horses. Merlin C sees the manufacture changed by the casting of the housing into three parts and the two cylinder blocks, the valves are always 45 °.

The E version (which derives from C) is reliable enough to pass the test of fifty hours, providing 955 horsepower with peaks 1045. F is when preparation is proposed Merlin G, which has parallel vertical valves to the cylinders. The engine turns better and pass the test one month before the model F. Series production is started, the F becomes Merlin Merlin I, but production is quickly stopped after 172 copies, model G (Merlin II) is produced in large quantities. The engine is tested for the first time in flight in 1935 on a Hawker Hart.

The coolant used is ethylene glycol produced by the company Prestone in the United States. Following the request of the Air Ministry in 1936 to provide modern fighters for the RAF, the only two aircraft in the study can satisfy the demands are the Hawker Hurricane and Supermarine Spitfire. Both using the Merlin, this engine is essential to the British war effort.

The first series of engines with a questionable reliability, while Rolls-Royce launches a superb program of quality control that would make the reputation of its engines. Some engines were collected at the outlet of the assembly and are twirled on a bench at full power until the fault. They were then removed to find the piece that sold the piece was then reworked to be made stronger. After two years of this procedure, Merlins became extremely reliable engines can run for eight hours at full speed without any problem.

Description and characteristics of Merlin 61

Merlin is a V-12 for gasoline whose two banks of cylinders are at 60 °, while the ignition is in the sequence: 1A, 6B, 4A, 3B, 2A, 5B, 6A, 1B, 3A, 4B, 5A , 2B (the cylinder 1A is the farthest to the right from the driver).

Each cylinder has two intake valves and two exhaust, they are cooled to sodium, and actuated by a camshaft head. The power of the motor is achieved by a carburetor with automatic control of wealth. Air is supplied by a compressor in two stages at two speeds, the air stream being cooled between the two stages by a heat exchanger. The coolant is a mixture of 70% water and 30% ethylene glycol pressurized. Lubrication is provided by an oil circuit having a pump pressure and two drain pumps.

dry weight: 745 kgcourse: mmalésage 152.4: 137.2 mmcylindrée 27 litrestaux compression: 6:1 specific power: 43,3 kW litrerapport power / weight: 1,57 kW kgpuissance: 1565 hp (1170 kW) at 3000 rpm at 3740 meters .1 390 hp (1035 kW) at 3000 rpm at 7170 meters altitude.


The increase in engine power made in two ways, using fuel octane increasingly high and perfecting the compressor. These changes made it possible to increase the intake pressure in the cylinders and therefore the final engine power without increasing displacement. This possibility exists because, among other things, the powerful American oil industry, capable of providing the quantity expensive new fuel instead the Germans who do not have this possibility, were forced to increase the size of their engines that therefore showed less interesting in terms of power / ground.

The first major change appears with the X Merlin who uses a two-speed compressor, whose license was acquired from Farman in 1935, this innovation reduces the power consumption of the mechanical compressor at low altitude, when n ‘ no need to charge, for against the length of the motor increases. In 1939, the decision to focus on fuel octane 100 is taken, the pressure previously limited to 3 kg/cm2 intake is increased to 6.

The next phase is the work of Stanley Hooker, which greatly improves the efficiency of the compressor, thanks to aerodynamic work on the internal air flow to it. The carburetor is moved to avoid further increasing the length of the group. These changes give rise to Merlin XX which is more powerful in altitude, it indeed provides 1,175 horsepower at over 6000 meters against 1 060-4 500 meters to the Merlin II. Certain engine variants, however, are optimized for low altitude, with propeller blades compressor shortened. One of these new Merlins is the Merlin 45 fitted to the Spitfire MkV. Hooker also decides to move to two-stage compressor: for bombers, he set up a compressor Rolls-Royce Vulture upstream of the normal compressor Merlin 46, giving birth to Merlin 60. However, the rise in temperature and pressure of the mixture now needs to cool before you do go into the cylinder, where it could detonate prematurely. The new engine can deliver its full power to nearly 10,000 feet.

Different versions, this engine will be equipped with a large number of aircraft of all types, from the heavy bomber fighter Supermarine Spitfire, Hawker Hurricane, Boulton Paul Defiant, Avro Lancaster, de Havilland Mosquito, Handley Page Halifax, Fairey Fulmar, Armstrong Whitworth Whitley, Curtiss P-40, P-51 Mustang

Advantages and disadvantage of feeding carburetor

Maintaining a feed carburetor has been often criticized for a lack Merlin, it can cause the engine to stall during a sudden maneuver negative G, as when pushing on the joystick the plane . Drivers Messerschmitt Bf 109 and used it often has the advantage that gave them direct injection to sow a Supermarine Spitfire on their heels. However, the use of a carburetor was not without advantage, far from it: The power system is much easier to effect and maintain, and more reliable, because of the absence of pumps necessary injection system that requires much more filtered fuel. In addition, a small carburetor modification, conceived in March 1941 by Miss Tilly Shilling in Farnborough, greatly remedied the problem with the introduction of a breakthrough in the membrane tanks, which finally allowed the negative G maneuvers over short periods . In 1943, the arrival of American Bendix-Stromberg anti-G, which were mounted on the Merlin 66, finally solved the problem.

American Production

During the Battle of Britain in 1940, the British government decided to provide licensed motor plans to the Americans in the event of defeat. The company Packard Motor Company gave its agreement in September to start production engine for both the British and the Americans, adapting the techniques of mass production of American industry. The first two examples were presented August 2, 1941 in Detroit factory and mass production began in 1942.

Use in armored

During the Second World War, the Merlin was adapted in some British tanks under the name of “Meteor”, particularly in Cromwell and Comet tanks and at the end of the war, in the Centurion tank. Subsequently, it also equipped the Conqueror and the South African Olifant tank.

Automotive use

In the 1960s, John Dodd, Kent, England, got the engine in the vehicle design called The Beast (the Beast). Devoid of compressor, providing 850 horsepower (some believe it was a Rolls Royce Meteor) and resulted in a TH-400 automatic transmission from General Motors on a fiberglass frame. Listed in the Guinness Book of Records, The Beast is considered the world’s most powerful road car.


Production of Rolls Royce

Merlin In July 1934, 790 hp at 2500 rev / min and 4000 m.

Merlin B February 1935 4 valves per cylinder, the intake valves on a ramp to 45 ° relative to the cylinder head, 950 hp at 3700 meters.

Merlin C cylinder block cast separately, the team Supermarine Type 300.

Merlin D

Merlin E Enhanced version C.

Merlin Merlin I or F 172 copies, the intake valves on a ramp to 45 ° relative to the cylinder heads.

Merlin Merlin II or G 1030 hp at 3000 rev / min and 5500 m.

Merlin III

Merlin X compressor at two speeds.

Merlin XII using a mixture of ethylene glycol and water under pressure for cooling the used Spitfire Mk II.

Merlin XX use fuel octane index 100 instead of 87, 1300 c.

Merlin 45-stage compressor and speed, mans Spitfire Mk V.

Merlin 46

Merlin 47 Team Spitfire HF VI

Merlin 60 two-stage compressor, the team Spitfire Mk IX.

Merlin cylinder block 61 into two parts.

Merlin 63 Team Spitfire Mk VIII.

Merlin 65

Merlin yoke casting 66 separately and screwed onto the housing.

Merlin 67

Merlin 76

Merlin 85

Merlin 100

Merlin 130

Merlin 140

266 Merlin team the Spitfire Mk XVI.

Meteor version intended to equip armored compressor removed and any use of light alloy.

Production Packard

V-1650-1 used on the P-40F

V 1650-3

V-1650-7 used on the P-51 Mustang

V 1650-9


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