|Séguine brothers "Gnome" rotary aircraft engine|
The French Séguine brothers were the first to create a successful rotary engine and manufacture it. By 1909 it was the engine of choice for a number of early aircraft, because it had much lower weight per horsepower.
A gasoline engine needs a flywheel to smooth the power delivered by the pulses of the cylinders firing, but a flywheel is dead weight. Earlier aircraft engines were liquid cooled that also added the weight of the liquid coolant, pump, and radiator.
The rotary engine is attached to the propeller and the crankshaft is secured to the airframe, so the cylinders rotate (see video), and that rotation does the work of a flywheel, so no need for the weight of a flywheel. Being air cooled there are no coolant, pump, or radiator (does that remind you of old VW Beetle ads?).
As long as it runs, the engine's rotation keeps air moving over the cylinders to cool the engine. However, that rotation also creates torque that made an aircraft difficult to control, because of the heavy whirling engine. Too sudden acceleration on take off, for example, flipped aircraft — often fatally.
The Séguine's Gnome engine drew a mix of fuel and oil through the hollow crankshaft into the crankcase then into the bottom of the cylinders and through a valve in the piston into the firing area of the cylinder. The valve was designed so that it was simple and light weight.
French and British rotary engines were superior to German ones, so when allied fighters crashed behind enemy lines, the Germans tried to salvage their rotary engines to put in German fighters.
To make rotaries more powerful resulted in even more torque and greater difficulty controlling an aircraft. Increasing speed of aircraft made the radial air cooled engine practical, in which the cylinders and crankcase are secured to the airframe and the propeller to the crankshaft.
An animation shows a Gnome engine at work and has additional information about it, and why it gave way to the radial air cooled engine.
Copyright © 2004 John F. Yeaman