Aircraft propulsion systems

Aircraft propulsion systems

This report treats the aircraft propulsion systems. It's structured into

four parts.

1st part: the turbojet engine

2nd part: the turbofan engine

3rd part: the turboprop engine

4th part: the ramjet engine

1st part: the turbojet engine:

The first turbojet engine was flown in Germany in 1939. It was tested on a

Heinkel He 178.

The engines which now are in use, are in a great deal more complicated and

are producing more thrust.

A cutaway view of a three shaft turbojet engine with afterburner, as used

at the supersonic fighter PANAVIA TORNADO, the Turbo Union RB 199-34R is

shown here.

The technical data from the RB199-34R are:

max. thrust with afterburner..71 kN

pressure-difference23%

rotation speed12`000/14`000 rpm

weight1000 kg

70 kg air per second are going the following way through the engine:

At first the air is sucked through low-press-compressor. In this case it

has three stages. (A stage consists of a single row of rotating and fixed

compressor blades.) The LP-compressor is working with low rotation speed.

Then the air is passing the three stage MP-compressor. After it the air has

only 87% of its intake volume.

While the air is going through the HP-compressor with six stages, it's

compressed to 77% of its original volume.

After the HP-compressor the air is passing the fuel injector and the flame

holder where the mixture explodes.

The last part of the RB199-34R is the afterburner, where some extra fuel

can be injected for more thrust.

The hot air exhausts finally through the convertible expansion nozzle.

The turbojet engine is used in supersonic fighter aircraft. For example the

F-15 'EAGLE', MiG-29 'FULCRUM' and SR-71 'BLACKBIRD'

2nd part: the turbofan engine:

A typical turbofan is the Rolls Royce Trent 800 which you can see here.

The only difference between the turbojet and the turbofan is a big 'fan'

which is placed in front of the LP-compressor. The fan (half

compressor-half propeller) pushes about 50% of the intaken air around the

engine for producing extra thrust. The remainder of the air goes the way

through the conventional engine. So the turbofan is a compromise between

the turbojet and the propeller engine.

This engine is used in most of the civil transport aircraft, because it's

very quiet and efficient.

3rd part: the turboprop engine:

The turboprop engine is principally a smaller turbojet engine-only the

turbine part is bigger.

Normally there are added two to four stages which are powering the

propeller.

The propeller is connected over a reduction gear and an extended shaft with

the faster rotating turbines. Some extra power is given by the exhausting

gases.

The turboprop power plant is used for subsonic speeds up to 600 km/h. It is

more efficient than a turbofan, but only up to speeds from 500 km/h.

The fastest turboprop-powered aeroplane is the Russian Tupolew TU-95 'BEAR'

4th part: the ramjet engine:

The ramjet power plant is the simplest engine, but it has one big

disadvantage: it produces no usable thrust at low subsonic speeds. That

means for landing, starting and taxiing a ramjet powered aeroplane needs

some extra thrust from another engine.

The reason why it produces no thrust at low speeds is that there are no

compressor stages inside the engine.

At high speed the air is compressed while it's passing the diffuser. Then

it goes through the fuel injector and the flame holder were the mixture

explodes. It exhausts through the variable expansion nozzle.

The most efficient speed of the ramjet power plant is from Mach 3 to Mach

A Ramjet powered typical aircraft is the North American X-15.

At last a comparison of the four engines:

* TURBOPROP: most efficiency up to 600 km/h

* TURBOFAN: most efficiency up to 900 km/h

* TURBOJET: most efficiency from 800 km/h to Mach 3

* RAMJET: most efficiency from Mach 3 to Mach 6

I hope you've enjoyed my report.

Thank you for paying attention.

(c) by Froschl Dieter