1949 issue. France In France, the works of René Leduc were notable. Leduc's Model, the Leduc 0.10 was one of the first ramjet-powered aircraft to fly, in 1949. The Nord 1500 Griffon reached in 1958. Engine cycle Air as it passes through a ramjet duct changes state (eg changes in temperature, pressure, volume) as it is compressed, heated and expanded in a thermodynamic cycle known as the Brayton cycle. This cycle also applies to the gas turbine engine. For a fixed amount of air its change in state is represented with pairs of quantities on diagrams, usually temperature~entropy or pressure~volume. The cycle is named after George Brayton, the American engineer who developed it, although it was originally proposed and patented by Englishman John Barber in 1791. It is also sometimes known as the Joule cycle. Design The first part of a ramjet is its diffuser (compressor) in which the forward motion of the ramjet is used to raise the pressure of its working fluid (air) as required for the combustion of fuel. It is then passed through a nozzle to accelerate it to supersonic speeds. This acceleration gives the ramjet forward thrust. A ramjet is much less complex than a turbojet in so far as it comprises an air intake, a combustor, and a nozzle but no turbomachinery. Normally, the only moving parts are those in the fuel pump, which sends the fuel to the spray nozzles in the combustor (liquid-fuel ramjet). Solid-fuel ramjets are simpler with no need for a fuel system. By way of comparison, a turbojet uses a compressor driven by a turbine. This type of engine produces thrust when stationary because the high velocity air required to produce compressed air (i.e. ram air in a ramjet) is produced by the compressor itself (fast spinning rotor blades). Construction Diffusers The diffuser is that part of the ramjet which converts the high velocity of the air approaching the intake into high (static) pressure required for combustion. High combustion pressures minimize wasted thermal energy which appears in the exhaust gases (by reducing entropy rise during heat addition). Subsonic and low-supersonic ramjets use a pitot-type entrance for the inlet to capture air. This is followed by a widening internal passage (subsonic diffuser) to achieve a lower subsonic velocity which is required at the combustor. At low supersonic speeds a normal (plane) shock wave forms in front of the inlet. For