In the early days of aviation, rotary aircraft engines were used extensively, especially during WWI. These powerplants were particularly unique in that their lack of conventional reciprocating elements provided smooth operation. You may ask yourself: “How does a rotary engine work without moving parts?” To answer this, we will outline how rotary engines produce power and how they differ from other engine types.
Unlike other engines, the crankshaft remains stationary while the cylinder heads and crankcase rotate around it. Essentially, the crankcase acts as a big flywheel to enhance smoothness between firing strokes. Without an actual flywheel, rotary engines were comparatively lighter than conventional engine types. In terms of configuration, the crankshaft is mounted to the aircraft’s frame, while a propeller is affixed to the crankcase.
As the crankcase spins, it generates its own flow of cooling air, thereby keeping the engine cool. Meanwhile, the air-fuel mixture is sent to the heads via a copper pipe coming from the crankcase, and then, it is distributed through the hollow crankshaft before it enters the crankcase. Due to the simplicity of its operation, rotary engines were prized by fighter pilots on both sides of WWI.
One of the only major issues pilots encountered with rotary engines was the unusually high rate of fuel consumption. This was attributed to the engine’s inclination to being operated at wide open throttle most of the time and a less than optimal valve timing. However, perhaps the biggest problem was the inertia that the rotating engine generated. Eventually, pilots realized that left turns were difficult because of the spinning inertia produced by such engines.
Toward the end of the 1920s, rotary engines no longer found use in aircraft as the new and improved radial design engines had replaced it due to its better power and fuel economy. Such benefits meant that pilots could remain over as target or engaged in battle for longer periods of time with the same fuel load. Due to this, the British relied on rotary engines longer than other countries.
Like other engine types, early rotary engines were available in a few variations. For instance, some rotaries were of the Monosoupape type, meaning that there was a single valve per cylinder for both intake and exhaust. At the time, most rotary engines had separate intake valves. Another peculiarity was that the engine had no rotating camshafts, as previously mentioned. Instead, a stationary annular ring took the place of camshaft lobes. Rollers on the ends of the pushrods followed the contour of this single cam ring.
Rotary engines also had different methods of controlling engine speed and power. For example, some took advantage of a hit-and-miss switch that fired cylinders every second or during every third power stroke, whereas others interrupted ignition through the use of a “blip” switch or interrupted fuel flow. Regardless of the operational method they employed, rotary engines served as reliable options for many years.
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