Title:

Aircraft propulsion systems

Description:  This report treats the aircraft propulsion systems. It´s structured into four parts...
Author:Dieter Fröschl
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ISBN: 1405446048   ISBN: 1405446048   ISBN: 1405446048   ISBN: 1405446048 
 
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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-difference...................23%
rotation speed...........................12´000/14´000 rpm
weight......................................1000 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 6.
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.
  
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We are grateful to Dieter Fröschl for contributing this article.

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