Rotary engine: What are its advantages?

Rotary engine
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Today's article will focus on a rotary engine with reciprocating piston movement and a rotating crankcase. Since we are talking about a rotary engine with reciprocating piston movement, we will not discuss the Wankel engine, even though it belongs to the group of rotary engines, because its rotary piston revolves around an eccentric shaft.

We will, therefore, be interested in a completely different type of engine, which is a rotary engine, the pistons of which perform a reciprocating movement and whose crankcase rotates (rotates) together with the entire engine.


What is a rotary engine?

A rotary engine is a type of radial engine, usually designed with an odd number of cylinders, whose crankshaft is rigidly attached to the structure of an aircraft, car, or motorcycle, and its crankcase, together with the cylinders, rotates (revolves) around it.

In the past, a rotary engine of this type was mainly used to drive airplanes, but it has also found its application in motorcycles and cars.

The history of the rotary engine in a nutshell

The first rotary engine with reciprocating motion of the piston and rotating casing was introduced in 1889 in Paris. Its inventor was Félix Millet, who patented this engine in 1888.

The rotary engine was mainly used in airplanes during the First World War, but also in the years just before the start of the war. This type of engine met all the criteria required of the engine in those days. It was powerful, relatively reliable, and had a lower weight compared to other types of engines because it did not need a flywheel, thanks to its smoother operation.

In addition to their advantages, rotary engines also had disadvantages. The main one was too high fuel consumption, partly because the engine was running at full throttle but also because of poor valve timing. However, by the time the war ended, the rotary engine had become obsolete and slowly fell out of use as radial engines replaced it.

Deployment of rotary engines

As mentioned, rotary engines were mainly used in airplanes, but several cars and motorcycles were equipped with rotary engines. Among the first motorcycles powered by a rotary engine, we can include the Millet motorcycle from 1892, which won many races.

Another motorcycle with a rotary engine was the Charles Redrup motorcycle, which was equipped with a three-cylinder rotary engine with a volume of 303 cm3.

Cars with rotary engines were produced by the American companies Adams-Farwell, Bailey, Balzer, and Intrepid. For example, the Adams-Farwell car company was producing cars with 3-cylinder rotary engines in 1898, and shortly after that, they switched to 5-cylinder rotary engines.

Rotary engine and its construction

The rotary engine predominantly uses the four-stroke cycle and has the cylinders arranged around the crankshaft like the radial engine. However, instead of a fixed cylinder block and a rotating shaft, a rotary engine is equipped with a stationary (fixed) crankshaft around which the entire cylinder block rotates. This engine's crankshaft is attached to the structure of the aircraft, motorcycle, or car.

There are many other similarities between the rotary and radial engines. Like the radial engine, the rotary engine is often equipped with an odd number of cylinders to ignite and ensure smooth engine operation. Rotary engines with an even number of cylinders were usually two-in-line. If it is a single-row rotary engine, it is also a flat engine.

Most rotary engines have cylinders arranged around a single crankshaft like a radial engine. There were also rotary boxer engines or even single-cylinder rotors.

Rotary engine and its advantages

The biggest advantage of a rotary engine is the fact that the entire engine rotates and behaves like a flywheel, thanks to which the engine runs smoother and also has less vibration.

Vibration is a serious problem in all aircraft engines. It is also undesirable in automobile engines, as it is necessary to equip the engine with a heavy flywheel to reduce it.

Other advantages of the rotary engine include excellent air cooling even at low speeds or during idling.

Rotary engine and its disadvantages

The biggest disadvantage of rotary engines is manifested when increasing power. As power increases, so does the engine's weight and, thus, the gyroscopic moment, which tries to turn the entire aircraft (or another machine) in the direction of rotation of the engine.

This problem can be partially solved with airplanes by ensuring the opposite rotation of the airplane's propeller.

Other disadvantages of rotary engines include their high fuel consumption compared to different types of engines. This fact contributed significantly to the demise of rotary engines and their replacement by other, more economical engines.

Other rotary engines

In addition to the configuration of cylinders moving around a fixed crankshaft, there are several other designs of rotary engines. Among the most famous is the Wankel engine, which has a stationary (fixed) eccentric shaft around which a rotary piston rotates.