| BMW 803 | |
|---|---|
 BMW 803 on display at theDeutsches Museum | |
| Type | Radial engine |
| National origin | Germany |
| Manufacturer | BMW |
| Developed from | BMW 801 |
TheBMW 803 was a German aircraft engine, an attempt byBMW to build ahigh-outputaircraft engine by coupling twoBMW 801 engines back-to-back, driving contra-rotating propellers. The result was a 28-cylinder, four-rowradial engine, each comprising a multiple-bank in-line engine with two cylinders in each bank, which, due to cooling concerns, were liquid cooled.
One problem with scaling up any piston engine design is that eventually a point is reached where the crankshaft becomes a major engineering challenge. This was a problem that affected almost all engines of the 2,500 hp (1,900 kW) class, including BMW's own 18-cylinderBMW 802 project. For the 803 the engineers decided to avoid this problem by simply not using a common crankshaft, and driving a set of independent contra-rotating propellers. The front engine drove the front propeller directly, while the rear engine drove five smaller auxiliary shafts that passed between the cylinders of the front engine before being geared back together to drive the rear propeller. This layout resulted in a large gearbox on the front of the engine, and the front engine needing an extended shaft to clear the gearbox.
Two additional auxiliary shafts transmitted the power from the front engine to the rear in order to drive thesupercharger and accessories of the front engine. This meant that both engines could be operated independently of one another.
The 803 had two valves per cylinder andoverhead camshafts. Displacing 83.6 litres, and using the same 156 mm bore and identical stroke measurements as each cylinder of the 801 used,[1] the four-row 803 engine weighed 2,950 kg (6,490 lb) dry, and 4,130 kg (9,086 lb) fully loaded.[2]
For all this weight it delivered 3,900 PS (3,847 hp; 2,868 kW). Although this made it the most powerful German engine design, itspower-to-weight ratio was only about 0.98 kW/kg (0.60 hp/lb), comparing rather poorly with other large designs like theJunkers Jumo 222 at 1.7 kW/kg, the primary powerplant design for the advancedBomber B design competition, which was designed to use only two engines of over 1,500 kW (2,000 hp) output.Specific power of the complex BMW 803 was likewise poor, at about 34.4 kW/L, compared to the 222's 40 kW/L, as wasspecific fuel consumption, at 380 g/kWh (0.63 lb/hp·h), comparable to late generationturboprops.
As with most coupled engines, like the earlierDaimler-Benz DB 606 andDB 610, the 803 was not a success on the test-bed, and did not enter production. About twelve prototypes were built.[1]
The engine was intended to be used only on the largest of designs, notably theFocke-Wulf Fw 238, theFocke-Wulf Ta 400 six-enginedAmerikabomber design competition competitor, and other largebombers. The big, 6-BMW 801-engined Ta 400 was proposed in 1942 as an upgraded version of the never-producedFocke-Wulf Fw 300, and was meant to compete directly against theMesserschmitt Me 264,Junkers Ju 390, and by the timeframe of February 1943;[3] what became Heinkel'sAmerikabomber contract design, theHeinkel He 277 — itself meant to be powered by only a quartet of 1,470 kW (1,973 hp) output BMW 801E radials from the start[4] — for the May 1942-approvedAmerika Bomber contract, for a trans-Atlantic range strategic bomber designed to attack New York City from European bases. The projected range was enough for the round trip from France to New York, but it was of course never realized. The Focke-Wulf firm even intended to use the BMW 803 powerplant for single-seatfighter design, and it also appeared on severalBlohm & Voss designs as well. None of these designs was particularly inspiring, and as the engine never matured the project was cancelled.
A single example remains in theDeutsches Museum Flugwerft Schleissheim.
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