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Radial Engine



BMW nine-cylinder radial engine for Junkers Ju 52
Displacement27.700 cm³
Bore * stroke155,5 * 162 mm
Compression6,0 - 6,5 : 1
Performance507 kW (690 PS) at 2100 1/min
Weight430 - 530 kg

Air-cooled radial engines in aircrafts

The radial engine has had a large and decisive impact on the history of the piston-stroke engine in airplanes. The engine is most often air-cooled, except for a few that were liquid-cooled or even diesel - pre combustion chamber engines. The radial engine features a compact construction method with a lot of cylinders, all of them receiving an equal share of the cooling airflow. In between there is still space for a second, staggered arranged row, very favourably also for the mass offset. Tests have been done with radial engines with up to four cylinder rows.

In rotary engines the crankshaft remains stationary.

In picture 4 the crankshaft is fixed, the whole crankcase and the cylinders rotate (with the propeller). It is a problematic construction because the air-fuel mixture has a long and difficult way from the crankshaft regin to the clinder head, only being acceptable in the first aeroplane engines with low power. For such an engine in a motorcycle look here.

Piston pressure via head and side connecting rods on one crankpin

All pistons/cylinders are arranged in one level. In order to connect them with one single crankpin, a master connecting rod is necessary, holding together all the other rods. Picture 2 displays the master connecting rod on top to the right. It is clearly more massive than the others. The crankshaft, displayed in picture 3 and divided for assembly purposes, has an offset per cylinder row. The cylinder number is odd because of the universal firing order of four-stroke engines.

Starting is possible without electric motor or starter

Self starting was tried out for the radial engine, because it offers the best preconditions of all multi-cylinder engines. There is always at least one cylinder which could start the engine by ignition of its aerial fuel mixture. At the moment these tests are taken up again, indeed, with electronic influence - with petrol direct injection.

BMW builds radial engines in license

The engine shown on top is a BMW-132 engine in license of Pratt and Whitney. It is produced since 1928 and developed further later on. For example, they increase the surface of cooling fins and adapt the engine from inches to metrical measures and increase the power output. Some engine types feature direct fuel injection to make it less prone to movements around the longitudinal axis or transverse axis. A 132 engine powers the first traffic airplane across the Atlantic.

Are radial engines suitable for vehicles?

There have been few attempts in history to insert radial engines in vehicles, although its advantages are not effective. One Beetle prototype developed by professor Porsche in 1936 featured a flat, air-cooled radial engine. 01/08




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