The BMW 802 was a large air-cooled radialaircraft engine, built using two rows of nine cylinders to produce what was essentially an 18-cylinder version of the 14-cylinder BMW 801. Although promising at first, development dragged on and the project was eventually cancelled to concentrate on jet engines instead.
Design and development
Soon after the 801 entered testing, BMW engineers turned to building much larger versions. One idea was to bolt two 801's back to back. Although seemingly a simple concept, the resulting, 83.5 litre displacement BMW 803 was in fact fantastically complicated, while being of the same cylinder layout as the largest-ever aircraft piston engine ever used by the Americans at any time, the 71.5 litre displacement Pratt & WhitneyWasp Major, the BMW 803 gave up on air cooling to be liquid-cooled instead. Another idea was to add more cylinders to the 801 design, and since radials need to have an odd number of cylinders per row, the next "size up" was a two-row 9-cylinder design, the 802, which emerged having an almost identical displacement to the American 18-cylinder Wright R-3350 Duplex Cyclone two-row air-cooled radial aviation engine - itself first run inMay 1937, over two years before the outbreak of war in Europe - and just larger than the British Bristol Centaurus. One problem with the 801 was its poor altitude performance, due almost entirely to the single-stage two-speed, mechanically-driven supercharger it used. Since the 802 was not a necessity given the success and emerging flexibility of the 801's basic design, the engineers decided to take the time needed to address this problem by including an improved two-stage three-speed supercharger. The lowest-speed setting would not "rob" as much power at low altitudes, allowing the engine to produce 2,600 PS for takeoff, and still produce 1,600 PS at. This was a dramatic improvement on the 801A's 1,600 PS for takeoff and 1,380 PS maximum at, especially notable considering the engine was less than 30% larger in displacement. In addition, airflow through the engine had been carefully managed by the BMW aviation powerplant engineering team — via a forward cowl that seemed to owe much to the BMW-engineered, integral forward cowl design used for the 801 and its own forward cowl-contained oil cooling system — to enable the straightest possible path into and out of the engine. A twelve-blade fan and stator compressed incoming air, then fed into the supercharger; remaining air was channeled in three paths: through the intercooler and the front and rear cylinder baffles; all three streams rejoined behind the rearmost row of cylinders into the exhaust. The combination of the fan and ejector thrust from the exhaust balanced the total internal engine drag. The engine weighed, the same weight as the complex twinned Daimler-Benz DB 601s that comprised the troubled "DB 606" power systems, best known for powering the Heinkel He 177Aheavy bomber, each of which generated some 2,700 PS at sea level for takeoff — the American Wright Duplex-Cyclone, however, only weighed 1,212 kg for nearly the same displacement and engine configuration as the 802. The 802 was eventually projected to be capable of producing, a power level that the Duplex-Cyclone would equal and surpass in the post-war years, up to some 2,610 kW through a trio of power-recovery turbines per engine in their exhaust systems in later subtypes, mechanically connected to the Duplex-Cyclone's crankshaft. Development was still underway in late 1943 when BMW decided the project wasn't worthwhile. With their BMW 003axial-flow turbojet engine finally maturing and considerably larger models of turbojet and even turboprop powerplants entering the prototype phase from both BMW and their competitors, it appeared that large piston engines weren't worth building. Postwar, the British scientific mission's leader, Sir Roy Fedden, called it "interesting and innovative" and considered it "one of the most interesting piston engines seen in Germany". A further improvement led to P.8011, which replaced the supercharger with two smaller turbochargers, driving contra-rotating propellers. This raised the takeoff power to about 2,800 PS, and dramatically improved altitude performance. As with most German turbocharger projects, the lack of quality high-temperature alloys meant the project was never able to enter production.
