BMW 802

From Wikipedia, the free encyclopedia
Jump to: navigation, search
BMW 802
Type Radial engine
Manufacturer BMW
First run 1943

The BMW 802 was a large air-cooled radial aircraft engine, built using two rows of 9 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.[1]

Design and development[edit]

Soon after the 801 entered testing, BMW engineers turned to building much larger versions. One idea was to "simply" bolt two 801's back to back. Although seemingly simple, the resulting BMW 803 was in fact fantastically complicated, even giving up on air cooling to be liquid-cooled instead. Another idea was to simply 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 and just 3.3 cubic inches larger than the British Bristol Centaurus.

One problem with the 801 was its poor altitude performance, due almost entirely to the simple single-stage two-speed mechanical 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[2] three-speed supercharger. The lowest-speed setting would not "rob" as much power at low altitudes, allowing the engine to produce 2,600 PS (1,912 kW) for takeoff, and still produce 1,600 PS (1,176 kW) at 12,000 m (39,000 ft). This was a dramatic improvement on the 801A's 1,600 PS (1,176 kW) for takeoff and 1,380 PS (1,015 kW) maximum at 15,100 ft (4,600 m), especially notable considering the engine was less than 30% larger in displacement. In addition, airflow through the engine had been carefully managed to enable the straightest possible path into and out of the engine. [3] A 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.[4] The combination of the fan and ejector thrust from the exhaust balanced the total internal engine drag.[5] The engine weighed 3,380 lb (1,530 kg).[6] It was projected it could produce 3,000 hp (2,200 kW; 3,000 PS).[7]

Development was still underway in late 1943 when BMW decided the project simply wasn't worthwhile. With their BMW 003 axial-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 simply weren't worth building. Postwar, the British scientific mission's leader, Sir Roy Fedden, called it "interesting and innovative" [8] and considered it "one of the most interesting piston engines seen in Germany". [9]

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 (2,059 kW), (some report 2,900 PS (2,133 kW)) 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.

Specifications (BMW 802)[edit]

General characteristics

  • Type: 18-cylinder supercharged two-row radial engine
  • Bore: 156 mm (6.142 in)
  • Stroke: 156 mm (6.142 in)
  • Displacement: 53.671 L (3,275.2 in³)

Components

Performance

  • Power output:
  • 1,912 kW (2,563 hp) for takeoff
  • 1,176 kW (1,575 hp) at 12,000 m (39,000 ft)
  • Specific power: 35.6 kW/L (0.78 hp/in³)
  • Compression ratio: 6.5:1

See also[edit]

Comparable engines
Related lists

References[edit]

Notes[edit]

  1. ^ Gunston 1989, p.27.
  2. ^ Christopher, p.81
  3. ^ Christopher, pp.81-2
  4. ^ Christopher, p.82
  5. ^ Christopher, p.82
  6. ^ Christopher, p.81
  7. ^ Christopher, p.81
  8. ^ quoted in Christopher, p.81
  9. ^ Christopher, p.82

Bibliography[edit]

  • Gunston, Bill. World Encyclopaedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9
  • Jane's Fighting Aircraft of World War II. London. Studio Editions Ltd, 1989. ISBN 0-517-67964-7

External links[edit]