Robert Graham

 Aircraft engines are propulsion systems for aircrafts.  Early Jet Engines: ◦ John Stringfellow: Steam Engine ◦ Wright Brothers Commission Charlie Taylor for Inline Aeroengine (12-horsepower) ◦ Roll-Royce Conway (World's first production turbofan) enters service ◦ Hyper-X (first scramjet to maintain altitude)

 Before 1945, piston engines were widely used. After this time, jet engines (which were gas turbine engines) came to the forefront, for their speed increases. After 1950, jet engines with good fuel economy were introduced, and jet airlines (gas turbine powered) began carrying passengers in 1958.

 In jet engines today, energy is added to the gas stream in the combustor, where air is mixed with fuel and ignited. Combustion increases the temperature, velocity, and volume of gas flow. This is directed through a nozzle over the turbine's blades, spinning the turbine and powering the compressor.

 Civil & Military Jets ◦ Civil turbofans today have a low exhaust speed (low specific thrust - net thrust divided by airflow) to keep jet noise to a minimum and to improve fuel efficiency. ◦ Military turbofans, however, have a relatively high specific thrust, to maximize the thrust for a given frontal area, jet noise being of less concern in military uses relative to civil uses.  Rocket engines ◦ Used for high altitude flights because they give very high thrust and their lack of reliance on atmospheric oxygen allows them to operate at arbitrary altitudes. This is used for launching satellites, space exploration and manned access, and permitted landing on the moon in 1969.

 Fuel Costs ◦ In 2007, the cost of jet fuel, while highly variable from one airline to another, averaged 26.5% of total operating costs, making it the single largest operating expense for most airlines. Thus, fuel is a high consumption is a high motivation in engine use.  Fuel Consumption ◦ Propellant consumption in jet engines is measured by Specific Fuel Consumption, Specific impulse or Effective exhaust velocity. They all measure the same thing, specific impulse and effective exhaust velocity are strictly proportional, whereas specific fuel consumption is inversely proportional to the others.

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