Manufacturing The Merlins
Initially, all Merlins were manufactured by Rolls-Royce; however, as World War II got into full stride, it was very apparent that even with rapid expansion Rolls-Royce's manufacturing capability would be incapable of keeping up with demand.
To meet this challenge, Ford Motor Company in England was approached to build Merlins under license, and, rather surprisingly, Ford built Merlins to closer tolerances than Rolls-Royce did! The reasoning for this apparent anomaly was the fact that Ford was geared to produce inexpensive cars at a high volume, and therefore all parts needed to be interchangeable, whereas Rolls-Royce relied on highly skilled craftsmen to hand fit all assemblies. Obviously, this approach would not work in the crisis environment of World War II. Ground was broken for a new plant in Trafford Park, a suburb of Manchester located in the grim industrial northwest of England, and by 1941 the new facility was turning out complete Merlins. All Ford-built engines were single-stage, two-speed, 20-series engines mainly for bombers. Between June 1941 and March 1946, a remarkable 30,400 Merlins were produced at Trafford Park.
At the same time negotiations were taking place for Ford production in England, similar negotiations took place in Detroit with Henry Ford. These negotiations fell through, but the Ford company got their hands on all the engineering drawings for the Merlin. It is interesting to note that when Henry Ford rejected the request to build the Merlin, he set out to build his own aircraft V-12 engine. Although the Merlin cylinder dimensions and configuration were used, automotive practice replaced aircraft design practice in several key areas. Side-by-side connecting rods replaced the blade-fork rods, and a cast crankshaft was used. After spending $2 million and a year, Ford (Detroit) gave up on this design. Never one to pass up a business opportunity, Henry Ford found out that the Army was looking for a 450-hp engine for its new tanks. Ford (Detroit) kept the 60° cylinder bank angle and made a V-8 engine out of the V-12 aircraft engine by removing the middle four cylinders and reworking it for natural aspiration. Ford (Detroit) manufactured 25,741 of these tank V-8 engines, the majority of which ended up in Shermans. A final, 750-hp tank engine that reverted to the V-12 configuration was manufactured.
In 1938 and 1939 negotiations were initiated with Ford of France for Merlin production. The plan was for Ford to manufacture Merlins in partnership with Matra. Negotiations were still ongoing when the situation in France deteriorated, and it obviously became futile to continue. The French Merlins were intended for French Air Force aircraft.
Packard built Merlins
Packard Car Company , also located in Detroit, was approached. This time things fared a lot better than they had with Ford. Packard turned out to be a good choice due to their high standard of workmanship and experience with building aircraft V-12 engines in the 1920s and 1930s.
Work started in 1940, and Packard test-ran their first engine in 1941. However, many major obstacles needed to be overcome to reach this milestone, such as redrawing all the British blueprints in order to convert them from first-angle projection to the third-angle projection used in the United States and to include manufacturing specifications in American terminology.
Several significant improvements were incorporated in the Packard engines , such as the replacement of the g-sensitive SU (Skinner's Union, Carburetor Division of Morris Group) carburetor by the far superior Bendix injection carburetor. Because of the tremendous production pressures Rolls-Royce was under, particularly in 1940 and 1941, it had been unable to introduce a two-piece cylinder bank into production; thus, Packard was first to manufacture the two-piece cylinder head and bank assemblies .
U.S.-manufactured magnetos were used; the AC Delco units were similar in design to and interchangeable with their British BTH counterparts.
Perhaps the most significant change made by Packard was the redesign of the supercharger drive for the two-stage engines. Rather than use the Farman drive used by Rolls-Royce, Packard preferred an epicyclic drive patented by Wright Aeronautical. The Wright Aeronautical blower drive was used only on the two-stage engines; the single-stage engines followed and were interchangeable with the Rolls-Royce design.
Crankshaft bearing material also changed; Rolls-Royce used a lead bronze with a lead-indium flash, whereas Packard used silver with a lead-indium flash. This was a common design practice in the United States, particularly for manufacturers of large radials.
Engines supplied by Packard to North American Aviation and Curtiss featured SAE No. 50 propeller shaft splines, and engines supplied to Canada for Mosquito, Lancaster, and Hurricane production used the standard British propeller shaft spline, the SBAC (Society of British Aircraft Constructors).
Packards delivered to or procured by the U.S. Army were designated V-1650 , using the standard Army nomenclature where the "V" signified the configuration of the cylinders and the "1650" denoted the displacement in cubic inches rounded out.
The dash number designated the development stage. A V-1650-1 was equivalent to a Merlin 28 or 29 with single-stage, two-speed supercharger.
The V-1650-3, -7, -9, -22, -23, and -24 were two-stage, two-speed engines. Merlin-224 and Merlin-225 single-stage, single-speed engines were equivalent to Rolls-Royce Merlin 24s and 25s that were being supplied to Canadian airframe manufacturers.
The Merlin-266 was equivalent to the Rolls-Royce Merlin 66 for Spitfire production.
Continental tools up for Merlin production
Continental Motors built a new manufacturing facility in Muskegon, Michigan, in 1942 initially to build Pratt & Whitney R- 1340s for North American T-6 advanced trainers. When this contract was complete, Continental tooled up for Merlin production using some of Packard's subcontractors for major castings such as head, cylinder bank, and crankcase. Interestingly, one of the primary suppliers of castings was the Maytag Washing Machine Company. Maytag qualified for this work due to their broad experience with large intricate aluminum castings, which were used extensively in prewar washing machines. This explains the nickname the P-51 received during World War II of "Maytag Messerschmitt"! Continental's production amounted to nearly 1,000 engines.
Merlin engine -- Exhaust systems
Exhaust systems were continually under development to optimize the various requirements. For the night bombing offensive over Germany, flame damping was of paramount importance. German night fighters were always on the lookout for the giveaway blue flame issuing from the glowing red-hot exhaust stacks.
The Handley Page Halifax, a four-engine bomber, used a manifold system with a single "fishtail" outlet on each side of the engine for flame quenching. The Avro Lancaster, another four-engine bomber, retained individual ejector stacks with a shroud covering the individual jet stacks.
Considerable development also took place for fighter exhaust systems where the prime requirement was to take advantage of the exhaust energy to propel the aircraft to a higher speed. Rolls-Royce had performed early investigations and determined that simple ejector stacks were preferable to the weight and complexity of turbo-supercharging; consequently, the Merlin was never developed with a turbo.
Early designs consisted of siamesed ejector manifolds with three outlets per cylinder bank; this later gave way to various designs based on individual stacks. The resulting thrust horsepower could be considerable; in a well-designed installation over 200-thrust horsepower could be recovered at 24,000 ft and 400 mph. The higher the altitude and the higher the speed, the greater the effect.