BMW 801
The BMW 801 was a powerful German air-cooled 14-cylinder-radial aircraft engine built by BMW and used in a number of German Luftwaffe aircraft of World War II. Production versions of the twin-row engine generated between 1,560 and 2,000 PS. It was the most produced radial engine of Germany in World War II with more than 61,000 built.
The 801 was originally intended to replace existing radial types in German transport and utility aircraft. At the time, it was widely agreed among European designers that an inline engine was a requirement for high performance designs due to its smaller frontal area and resulting lower drag. Kurt Tank successfully fitted a BMW 801 to a new fighter design he was working on, and as a result the 801 became best known as the power plant for the famous Focke-Wulf Fw 190. The BMW 801 radial also pioneered the use of what would today be designated an engine control unit: its Kommandogerät engine management system took over the operation of several aviation engine management control parameters of the era, allowing proper operation of the engine with just one throttle lever.
Design and development
Precursor design
In the 1930s, BMW took out a license to build the Pratt & Whitney Hornet engines. By the mid-30s they had introduced an improved version, the BMW 132. The BMW 132 was widely used, most notably on the Junkers Ju 52, which it powered for much of that design's lifetime.In 1935 the RLM funded prototypes of two much larger radial designs, one from Bramo, the Bramo 329, and another from BMW, the BMW 139. BMW's design used many components from the BMW 132 to create a two-row engine with 14 cylinders, supplying 1,550 PS. After BMW bought Bramo in 1939 both projects were merged into the BMW 801, learning from the problems encountered in both projects.
The BMW 139 was originally intended to be used in roles similar to those of the other German radials, namely bombers and transport aircraft, but midway through the program the Focke-Wulf firm's chief designer, Kurt Tank suggested it for use in the Focke-Wulf Fw 190 fighter project. Radial engines were rare in European designs as they were considered to have too large a frontal area for good streamlining and would not be suitable for high speed aircraft. They were most popular on naval aircraft, where their easier maintenance and improved reliability were highly valued. Efforts to improve these designs led to new cowling designs that reduced the concerns about drag. Tank felt that attention to detail could result in a streamlined radial that would not suffer undue drag, and would be competitive with inlines.
The main concern was providing cooling air over the cylinder heads, which generally required a very large opening at the front of the aircraft. Tank's solution for the BMW 139 was to use an engine-driven fan behind an oversized, flow-through hollow prop-spinner open at the extreme front, blowing air past the engine cylinders, with some of it being drawn through S-shaped ducts over a radiator for oil cooling. However this system proved almost impossible to operate properly with the BMW 139; early prototypes of the Fw 190 demonstrated terrible cooling problems. Although the problems appeared to be fixable, since the engine was already fairly dated in terms of design, in 1938 BMW proposed an entirely new engine designed specifically for fan-cooling that could be brought to production quickly.
801 emerges
The new design was given the name BMW 801 after BMW was given a new block of "109-800" engine numbers by the RLM to use after their merger with Bramo. The 801 retained the 139's older-style single-valve intake and exhaust, while most in-line engines of the era had moved to either three or four valves per cylinder, or in British use for their own radials, sleeve valves. Several minor advances were worked into the design, including the use of sodium-cooled valves and a direct fuel injection system, manufactured by Friedrich Deckel AG of Munich.The supercharger was rather basic in the early models, using a single-stage two-speed design directly geared to the engine which led to rather limited altitude performance, in keeping with its intended medium-altitude usage. One key advancement for the 801 was the Kommandogerät, a mechanical-hydraulic unit that automatically adjusted engine fuel flow, propeller pitch, supercharger setting, mixture and ignition timing in response to a single throttle lever, dramatically simplifying engine control. The Kommandogerät could be considered to be a precursor to the engine control units used for many vehicles' internal combustion engines of the late 20th and early 21st centuries.
There was a considerable amount of wind tunnel work done on the engine and BMW-designed forward cowling at the Luftfahrtforschungsanstalt facility in Völkenrode, leading to the conclusion it was possible to reduce drag equivalent to. It also maximized the use of positive air pressure to aid cooling of cylinders, heads, and other internal parts.
801A and 801B
The first BMW 801As ran in April 1939, only six months after starting work on the design, with production commencing in 1940. The 801B was to be identical to the 801A except for the gearbox, which reversed the direction of the propeller rotation to counterclockwise as seen from behind the engine. The A and B models were intended to be used in pairs on twin-engine designs, cancelling out net torque and making the plane easier to handle. There is no evidence the 801B ever left the prototype stage. The BMW 801A/B engines delivered 1,560 PS for takeoff. Major applications of the 801A/L engines include multiple variants of the Junkers Ju 88 and Dornier Do 217.801C and 801L
The BMW 801C was developed for use in single- or multi-engined fighters and included a new hydraulic prop control and various changes intended to improve cooling, including cooling "gills" on the cowling behind the engine in place of the original slots. The 801C was almost exclusively used in early variants of the Focke-Wulf Fw 190A. The BMW 801L was an A model with the hydraulic prop control mechanism introduced with the 801C engine. The C and L models delivered the same power as the original A model.801D-2 and 801G-2
The 801C was replaced with the BMW 801 D-2 series engines in early 1942, which ran on C2/C3 100 octane fuel instead of the A/B/C/L's B4 87 octane, boosting takeoff power to 1,700 PS. The BMW 801G-2 and H-2 models were D-2 engines modified for use in bomber roles with lower gear ratios for driving larger propellers, clockwise and counterclockwise respectively. As with the 801B engine design, however, the 801H-2 engine did not leave the prototype stage.The newer, 100 octane D-2 series and its derivatives had higher gear ratios, and higher compression ratios, than the earlier, 87 octane versions. The compression ratio of the 100 octane series was raised to 7.2 from the 6.5 of the 87 octane versions. This was possible because of the better fuel and the better shape of the combustion chamber.
The D-2 models were tested with a system for injecting a 50–50 water-methanol mixture known as MW50 into the supercharger primarily for its anti-detonation effect, allowing the use of increased boost pressures. Secondary effects were cooling of the engine and charge cooling. Some performance was gained, but at the cost of engine service life. This was replaced by a system that injected fuel instead of MW50, known as C3-injection, and this was used until 1944. The serious fuel shortage in 1944 forced installation of MW50 instead of C3-injection. With MW50 boosting turned on, takeoff power increased to 2,000 PS, the C3-injection was initially only permitted for low altitude use and increased take-off power to 1,870 PS. Later C3-injection systems were permitted for low-to-medium altitude use and raised take-off power to more than 1,900 PS.
Supercharger development
With the engine being used in higher-altitude fighter roles, a number of attempts were made to address the limited performance of the original supercharger. The BMW 801E was a modification of the D-2 using different gear ratios, of 6:1 at low speed and 8.3:1 at high speed, that tuned the supercharger for higher altitudes. Although takeoff power was unaffected, cruise power increased over 100 hp and "high power" modes for climb at nearly 1,500 to 1,650 PS; and combat were likewise improved by up to 150 hp. The E model was also used as the basis for the BMW 801R, which included a much more complex and powerful two-stage four-speed supercharger, as well as die cast hydronalium cylinder heads, strengthened crankshaft and pistons, and chromed cylinders and exhaust valves; it was anticipated this version would produce over, or over with MW 50 methanol-water injection.The 801E not only had higher gear ratios, but also had better supercharger internal aerodynamics. In 5-minute overboost, the 801E could provide 2,300 PS on the test stand in 1942.
The 801R, with its 2-stage, 4-speed supercharger, had a critical altitude of 11,000 meters. Above that altitude, the R could use additional boost by nitrous-oxide injection. The R was also bi-fuel. At its critical altitude, the R could deliver 1,400 PS.
In spite of these improvements, the E model was not widely used. Instead, continued improvements to the basic E model led to the BMW 801F, which dramatically improved performance across the board, with takeoff power increasing to 2,400 hp, making the 801 the only German aviation engine of an existing type that had a producible subtype that could exceed 1,500 kW from a proven military aircraft powerplant. It was planned to use the F on all late-model Fw 190s, but the war ended before production started.
The 801F's supercharger had higher critical altitude, than the earlier D-2 series. The improved gear ratios increased the engine's critical altitude to between 7,000 and 8,000 meters. The 801F also had a stronger crankshaft and a fuel-injector pump of higher capacity. The version also had larger intake- and exhaust-valves, with increased valve-overlap. The engine, in the TF powerplant form also had better internal and external aerodynamics. The supercharger intake was relocated to the wing-root of the Fw 190, to improve supercharging. On the test bench, the 801F could deliver 2,600 PS in 1945.
The 801F was 25 centimeters longer, than the earlier 801 versions. The reason for this was to keep the balance of gravity of the Ta 152 aircraft.
In 1944, the strongest production version of the 801, the 801S went into production. It had the same gear ratios, as the 801E, and it's supercharger used swirl-throttling. It used the parts of the earlier D-2, and in some parts, the above mentioned more advanced versions. The S also had an improved and simplified master controller and different magneto timing. The 801S also had altered valve-timing. In special-emergency mode, it could deliver 2,200 PS at sea-level.