A motorjet is a rudimentary type of jet engine
Jet engine
A jet engine is a reaction engine that discharges a fast moving jet to generate thrust by jet propulsion and in accordance with Newton's laws of motion. This broad definition of jet engines includes turbojets, turbofans, rockets, ramjets, pulse jets...

 which is sometimes referred to as thermojet, a term now commonly used to describe a particular and completely unrelated pulsejet design.


At the heart the motorjet is an ordinary piston engine (hence, the term motor), but instead of (or sometimes, as well as) driving a propeller
Propeller (aircraft)
Aircraft propellers or airscrews convert rotary motion from piston engines or turboprops to provide propulsive force. They may be fixed or variable pitch. Early aircraft propellers were carved by hand from solid or laminated wood with later propellers being constructed from metal...

, it drives a compressor
Gas compressor
A gas compressor is a mechanical device that increases the pressure of a gas by reducing its volume.Compressors are similar to pumps: both increase the pressure on a fluid and both can transport the fluid through a pipe. As gases are compressible, the compressor also reduces the volume of a gas...

. The compressed air is channeled into a combustion chamber
Combustion chamber
A combustion chamber is the part of an engine in which fuel is burned.-Internal combustion engine:The hot gases produced by the combustion occupy a far greater volume than the original fuel, thus creating an increase in pressure within the limited volume of the chamber...

, where fuel
Fuel is any material that stores energy that can later be extracted to perform mechanical work in a controlled manner. Most fuels used by humans undergo combustion, a redox reaction in which a combustible substance releases energy after it ignites and reacts with the oxygen in the air...

 is injected and ignited. The high temperatures generated by the combustion cause the gases in the chamber to expand and escape at high pressure from the exhaust
Exhaust gas
Exhaust gas or flue gas is emitted as a result of the combustion of fuels such as natural gas, gasoline/petrol, diesel fuel, fuel oil or coal. According to the type of engine, it is discharged into the atmosphere through an exhaust pipe, flue gas stack or propelling nozzle.It often disperses...

, creating a thermal reactive force that provides useful thrust.

Motorjet engines provide greater thrust than a propeller alone mounted on a piston engine; this has been successfully demonstrated in a number of different aircraft.


  • In 1908 French
    The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

     inventor René Lorin
    René Lorin
    René Lorin , a graduate of the Ecole Centrale Paris, invented the ramjet. In 1908 he patented a subsonic ramjet design.Lorin published the principles of a ramjet in articles in the journal L'Aérophile from 1908 to 1913, expressing the idea that the exhaust from internal combustion engines could be...

     proposed using a piston engine to compress air that would then be mixed with fuel and burned to produce pulses of hot gas that would be expelled through a nozzle to generate a propelling force.
  • In 1917, O. Morize of Chateaudun, France, proposed the Morize ejector scheme in which a reciprocating engine drove a compressor supplying air to a liquid fueled combustion chamber which discharged into a convergent-divergent tube and ultimately out into the atmosphere.
  • The term "motor jet" was established in a patent filed in Britain by J.H. Harris of Esher, U.K., in 1917.
  • It was next explored by Secondo Campini
    Secondo Campini
    Secondo Campini was an Italian engineer and one of the pioneers of the jet engine.Campini was born at Bologna, Emilia-Romagna. In 1931 he wrote a proposal for the Italian Air Ministry on the value of jet propulsion and in 1932 demonstrated a jet-powered boat in Venice...

     in the early 1930s, although it was not until 1940 that an aircraft, the Caproni Campini N.1 (sometimes referred to as C.C.2), would fly powered by his engine. Campini established the misnomer thermojet at this time to describe his motorjet.
  • NACA
    National Advisory Committee for Aeronautics
    The National Advisory Committee for Aeronautics was a U.S. federal agency founded on March 3, 1915 to undertake, promote, and institutionalize aeronautical research. On October 1, 1958 the agency was dissolved, and its assets and personnel transferred to the newly created National Aeronautics and...

     engineer Eastman Jacobs
    Eastman Jacobs
    Eastman Nixon Jacobs was a leading aerodynamicist who worked for NACA's Langley Research Center from the 1920s to the 1940s. He was responsible for advancing many fields in aerodynamics, dealing particularly with wind tunnels, airfoils, turbulence, boundary layers, and Schlieren...

     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
    The Tsu-11 was a primitive, motorjet-style jet engine produced in small numbers in Japan in the closing stages of World War II. It was principally designed to propel the Japanese Ohka flying bomb, a kamikaze weapon....

     motorjet engine to power Ohka
    The Yokosuka MXY-7 Ohka was a purpose-built, rocket powered human-guided anti-shipping kamikaze attack plane employed by Japan towards the end of World War II...

     aircraft as an alternative to the solid-fuel rocket engines that these aircraft were then using.
  • The Soviet
    Soviet Union
    The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....

     Mikoyan-Gurevich I-250 (N)
    Mikoyan-Gurevich I-250 (N)
    The Mikoyan-Gurevich I-250 was a Soviet fighter aircraft developed as part of a crash program in 1944 to develop a high-performance fighter to counter German turbojet-powered aircraft such as the Messerschmitt Me-262...

     designed in 1944 used a piston engine to drive both a propeller at the nose of the plane, and a motorjet compressor leading to a jet exhaust at the tail. Between 10 and 50 I-250 (a.k.a. MiG-13) aircraft were produced, serviced, and flown by the Soviet Navy through 1950.
  • Canadian inventor Mark Nye (Nye Thermodynamics Corporation) built a successful thermojet based on a single stage axial fan of his own design driven by a V6 automobile engine in 2002. The jet pipe consisted of three 45 gallon drums welded together with a cable operated variable area nozzle and a fabricated flame holder. This gasoline fueled, 85 lbf (0.378098837275 kN) thrust design was as used to power his three wheeled dragster to victory on Discovery’s JunkYard Wars in Los Angeles
    Los Ángeles
    Los Ángeles is the capital of the province of Biobío, in the commune of the same name, in Region VIII , in the center-south of Chile. It is located between the Laja and Biobío rivers. The population is 123,445 inhabitants...

     in August 2002.

Motorjet research was nearly abandoned at the end of World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

 as the turbojet was a more practical solution to jet power as it used the jet exhaust to drive a gas turbine
Gas turbine
A gas turbine, also called a combustion turbine, is a type of internal combustion engine. It has an upstream rotating compressor coupled to a downstream turbine, and a combustion chamber in-between....

, providing the power to drive the compressor without the additional weight of a piston engine that generated no thrust. One of the primary advantages of the motorjet layout was that the reciprocating engine provided power for the compressor and no turbine power section was needed. However, the metallurgy and understanding of the design of turbines had advanced to the point after WWII where it was feasible to create a turbine to operate reliably in the high velocity hot gas environment downstream of the combustor and the motorjet idea lost focus.

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