Corrections of Uwe Borchert

Function

The gas turbine should develop a very high thrust featuring a low weight. In addition, it should be very reliable and not especially demanding in terms of fuel quality.

How it works

On the left the air is sucked in and strongly compressed by several accordingly formed compressor wheels. In the middle fuel is continuously injected. The corresponding pressure drives the turbine wheels, arranged on the same shaft as the compressor wheels and provides for a suitable advance while leaving the nozzle.

Below in the picture the fuel injection pump is visible for adding the kerosene. Kerosene (airplane petrol) makes do because of its continuous combustion only with a relatively low octane rating, resembling more the diesel oil. On top the starter is visible partly, starting the whole process via a double bevel wheel drive.

The advantages of a gas turbine are founded in the combination of machine efficiency and high energy density. A shaft power turbine with Free power turbine, e.g., the model Rolls Royce 250C40B, features with a continuous performance of 450 kW a mass of only 280 kg (incl. gearbox with outlet rev of 6000, 1/min). The continuous performance efficiency amounts to just 24%. Modern Otto engines approach this value, diesel engines with their more favourable performance efficiency of more than 40% (however, only in one operating point!), do not. Although there are some small airplanes operating with diesel engines.

In addition, you should consider that the abovementioned turbine can deliver an even 75 kW higher performance for approx. five minutes. If you leave out the gearbox with its big gear reductions, an unbeatable combination of efficiency and weight to power ratio arises for the aviation. At the moment the gas turbine cannot substitute for the vehicle drive and the internal combustion engine not for the airplane drive. 06/08