Swing-piston engine

In these examples the "piston" is typically not cylindrical as in a modern internal combustion design, and is generally rectangular in cross-section as seen from the top, rotating in a flat disk "cylinder".

Notable among them was John Ericsson's design of 1843, which powered the USS Princeton, the United States' first screw-powered steamship.

Charles Parsons examined the concept and appears to have produced two swing-piston engine designs before moving on to the steam turbine.

[2] It is unclear whether or not any internal combustion swing-piston engine has ever reached production, but the closest attempt appears to be the German World War II-era design by Otto Lutz [de].

Each "cylinder" from Lutz's design was 0.70 m in diameter and only about 30 cm in depth, providing 445 hp from 140 kg, an excellent power-to-weight ratio compared even to jet engines of the era.

The swing-piston gas generator was located in the middle of a long nacelle, with a five-stage axial compressor in front and a three-stage turbine behind.

The compressor was used both to act as a supercharger for the piston engine, as well as provide cold air to cool the turbine.

The actual power to the propeller, combining both the pistons and the turbines, was 4,930 hp at 10,000 m altitude, far greater than any German wartime project.

Lutz's design was intended to power very long-range bombers and patrol aircraft, where fuel economy was more important than simplicity and performance.

[8][9] In 2009, Russian billionaire industrialist Mikhail Prokhorov announced his plans to enter an automotive business with a series of a lightweight hybrid vehicles using this design as their prime mover.

[10] Another recent introduction aimed at the hybrid market is the "Hüttlin Kugelmotor", which combines the swing-piston concept with a modified swashplate to produce a spherical design that directly powers an internal electrical generator.