Airline Expansion and Innovation(1927 - 1941)

Engine Technology: Water-Cooled Engines

Most airplanes in the 1920s used engines cooled by water. While powerful for their size, water-cooled engines were heavy and unreliable. They required large radiators, which created aerodynamic drag, as well as heavy and complex pumps and plumbing systems, which often leaked. Still, they were more powerful than the bulky air-cooled engines of the time and were widely used on all types of aircraft.

Liberty V-12
Smithsonian Institution, National Air and Space Museum

Liberty V-12

Designed for light bombers in World War I, the Liberty V-12 was widely used during the 1920s. Liberty engines powered the Post Office's de Havilland DH-4s and most mail planes used by early airlines.

Although powerful, the water-cooled Liberty was not as efficient or reliable as the new generation of air-cooled engines introduced by the Wright and Pratt & Whitney companies in the late 1920s.

Type:                    Water-cooled, V-type, inline
Cylinders:           12
Displacement:   27 L (1,649 cu in)
Power:                 400 hp at 1,800 rpm
Weight:                384 kg (844 lb)
Manufacturer:     Lincoln Motor Co., Detroit, Mich., 1918


de Havilland DH-4
Smithsonian Institution, National Air and Space Museum

De Havilland DH-4

By 1921 modified de Havilland DH-4 light bombers were being used as mail planes. They soon become the symbol of the U.S. Air Mail Service. The first DH-4 built in the United States hangs in the Museum's Looking at Earth gallery.