Most of today's large passenger aircraft are powered by jet engines. Yes there are many prop aircraft as well, as we have shown, but long haul and larger aircraft rely on the extra power of a jet engine. When you look at the inside of a jet engine (or at least that part of it that is seen when you take away the cowling, the cover that you see when you board an aircraft) it looks terribly complicated with hundreds of tubes, pipes, wires and goodness knows what else. But in reality the principle behind a jet engine is amazingly simple.

A jet engine has four stages. Air is sucked in at the front, compressed to a high pressure (which raises its temperature), has fuel sprayed on it, is ignited by an electrical spark, and the resulting explosion forces hot exhaust gases out of the back of the engine, thrusting the plane forward. Very simply put the four stages are: suck, squeeze, bang, blow !

The first part, at the front of the engine and a part that is clearly visible when you look at the front of a jet engine, is the fan. Made of titanium the blades are aligned at exactly the right angle to suck air in at the correct speed. Part of the incoming air is also directed round the core of the jet engine, to help cool it down as the inside temperatures are high.

The compressor is made up of a series of fans that squeeze the incoming air into ever smaller chambers, increasing its pressure by up to 12 times. The final chamber into which this highly compressed air is forced is the combustion chamber. Around the combustion chamber are a series of nozzles that spray a fine mist of jet fuel onto this compressed air, which is then ignited by a spark from an electrical source, just as in a car. The air and fuel catch fire (ignite) producing high temperature burning gases. The temperature of these gases is around 2700°C, so the inside of this combustion chamber needs to be made of ceramic material. When gas is heated it expands and needs to escape. This it does through the nozzle at the rear of the jet and it is this escaping, high temperature, high-speed exhaust gas that drives the plane forward. The gases also drive the compressor and intake fans once the jet is operating. The speed of the engine is varied by the pilot controlling the flow of fuel, just as you use an accelerator in a car.

The history of jet engines goes back a very long way, much further than you might think. In the 1st century AD the Phoenicians had realised that steam could be used through nozzles to turn a sphere, though they found no satisfactory use for this. In the 13th century the Chinese invented fireworks and the rocket principle, which is basically the same as a modern jet engine. Progress then stalled for several centuries but the idea of a jet engine (a gas turbine by another name) never quite went away. In 1791 a patent was granted to an Englishman, John Barber, for a gas turbine. Work continued thereafter but it was the 20th century that saw the breakthrough.

The Wright brothers were the first to fly in a fuel-powered aircraft (1903) but it was the gradual approach of war and an increase in military planning that set minds thinking in the mid 1930s. In 1937 Sir Frank Whittle, another Englishman, designed the first jet engine though at the same time, and unaware of each other's existence, Hans von Ohain was progressing well in Germany on a similar project. He linked up with Ernst Heinkel and the world's first jet airplane, the Heinkel He 178, took to the air in August 1939, just weeks before the outbreak of war. Since then the technology has been refined and developed to the point where we now have jet engines that can power planes such as the A380. Today's jet engines are immensely powerful and very reliable. For an extended and very detailed feature on the development and operation of the jet engine we can recommend the Wikipedia page on – http://en.wikipedia.org/wiki/Jet_engine

Modern jets are also becoming more efficient in fuel consumption despite their growing size, a factor that, with the price of fuel, is of vital importance to the airlines as between 30% and 50% of the airlines' operating costs are fuel. About 7% of the world's oil consumption is accounted for by airlines, yet the average fuel consumption for the new generation of aircraft (A380 and B787) is claimed at 3 litres per 100 passenger kms (78 passenger miles per gallon) which is better than a family car. Yet these figures can be misleading as the Airbus estimates assume the plane is totally full (with either 555 passengers or 835) and that the car has just the driver in it.

For an Airbus A320 (100 passengers) the plane uses about 665 gallons per hour. On a flight from, say, London to Madrid (two hours) this would equate to about 1330 gallons, plus extra for taxiing, take-off and taxiing after touchdown, so assume 1500 gallons. That works out at 15 gallons per passenger. A normal car with driver and passenger driving between London and Madrid (1000 miles) with a good fuel consumption of 33 mpg, would also use about 15 gallons per passenger, though this excludes any fuel used by Eurotunnel shuttle or ferry between Dover and Calais. If you add two more passengers to the car the fuel consumption drops to 7.5 gallons per person, half that of the plane, though that does not factor in the stops for food, rest, probably at least one overnight stop and the comfort, or lack of it, of four people in a family car. But you wouldn't have to put up with airport hassles ! It's an interesting debate. Certainly, on transoceanic routes planes are the only viable option but for shorter haul routes high speed trains should, with environmental concerns in mind as well as comfort, take over – as they have in France with the TGV and other countries with high speed railways. Britain has none as yet.