Internal combustion engines had been in development throughout the 19th Century and became more widely available after Karl Benz utilized them for the first automobile, which he patented in 1886. The Wright Brothers decided to power their airplane with a 12 hp, 4-cylinder water-cooled gasoline engine that would rotate two 8 ft propellers mounted to the wings. Although the machine was greatly underpowered, it was able to become airborne for 12 seconds and cover a distance of 120 ft. Subsequent flights were longer and soon larger, more powerful engines were combined with new airframes to achieve sustained, powered flight. A technological revolution had begun.

The rapid evolution of aircraft design following the Wright Brothers’ historic flight drove the development of more and more powerful internal combustion engines which were constructed in various configurations. In-line engines had a series of cylinders arranged in a row which would fire in alternating succession to turn a crankshaft. The  cylinders could be aligned either above the crankshaft or below it (which provided better visibility for the pilot). In-line engines allowed for greater streamlining of the fuselage and offered a higher weight-to-horsepower ratio than other types. V-type engines placed the cylinders in two in-line banks set 30°- 60° apart. Radial engines arranged 3 to 9 cylinders (always an odd number) in a circle around the crankshaft. Additional rings of cylinders could be added for more power. Radial engines had very high power-to-weight ratios and proved to be very rugged and reliable. They were used extensively in military aircraft during WWII. However, they also produced considerable drag and made streamlining difficult. Opposed or O-Type engines (see example in photo above) are the most common type found in smaller aircraft today. They consist of two banks of cylinders aligned opposite each other in a horizontal plane with the crankshaft in the middle. General aviation has favored this type of engine because of their high power-to-weight ratio, comparatively low vibration, and low profile when installed on the wings of twin-engine aircraft.