Thermojet

A thermojet is a rudimentary type of jet engine. At its heart is an ordinary piston engine, but instead of this driving a propellor, it drives a compressor. The compressed air is channelled into a combustion chamber, where fuel is injected and ignited. The high temperatures generated by the combustion cause the gasses in the chamber to expand. These gasses escape at high pressure from the exhaust of the engine, creating a reactive force that drives the engine.

These engines are reasonably inefficient because of the comparatively poor power-to-weight ratios of piston engines when compared to gas turbines. In fact, when such engines have been constructed, the aircraft designers would have achieved better results had they simply mounted a propellor on the engine instead. Nevertheless, the concept actually works and has been demonstrated in a number of different aircraft.

Thermojet research was abandoned at the end of World War II as the turbojet was demonstrably a far more practical solution to jet power.

• The first application of the thermojet principle was by Henri Coanda in his Coanda-1910 aeroplane (1910).

• It was next explored by Secondo Campini in the early 1930s, although it was not until 1940 that an aircraft (the Campini Caproni CC.2) would fly powered by his engine.

• NACA engineer Eastman Jacobs was actively pursuing thermojet research in the early 1940s for a project that came to be known as Jake's jeep but which was never completed as turbojet technology overtook it.

• Japanese engineers developed the Tsu-11 engine to power Ohka kamikaze aircraft as an alternative to the rocket engines that these aircraft were then using.

• The Soviet Mikoyan-Gurevich I-250 (N) designed in 1944 used a piston engine to drive both a propeller at the nose of the plane, and a compressor leading to a jet exhaust at the tail.