This model has a nice fit, but its hard to build, as to get everything moving is difficult. Worst than that, its really hard to find it, which is a shame, as it is one of the most educational and astonishing models ever. This is the last generation, the early one had an electric motor to make it work by itself.
The most interesting part is that it has most of the componenets of the real one, and its really interesting. On the front, its the "simplest"part, a planetary gear reduction.
The propeller is of constant speed, variable pitch, and also works, you can rotate the hub and see the inclination changing.
Then it has a shaft, connecting to the "engine itself. Its on the rest that the fuel is converted into movement. Right after the shaft, we have the inlet guide vanes.
Inside this lies the first part: the compressor.
In here there are a few set of turbines, the ones that spin, paired with static ones.
Both are needed, in order to compress the air, and as we can see, its size also gets smaller, in order to get really big compression rates.
We may say that there are 3 stages: the first 2 blades have a low compression rate, followed by a medium compression and a high compression. In here the air already heats up due to the compression.
After that, the air is diverted to the combustion chamber.
If there is a flaw in the model, its in the combustion chamber... the original has a lot of holes, so that it has air flowing inside and on the outside. The combustion temperature, which occurs inside it, is very high, and needs the air around to cool it and keep it from melting. More than that, I believe that all the combustion chambers are interconnected.
The nozzle sprays the fuel, and a spark ignites it, and produces an increase of air volume, due to the heating and the combustion.
All of that air is "harvested"on the end, the hot stage. In here, its speed is decreased thru a series of blades, but it also transforms that speed into movement on the shaft that connects gear reduction, compressor blades and collector blades.
This is what trully has to handle temperature, as it is directly on the end of the heated gas.
If it was a turbojet, there was no front shaft, and the push would come simply from the exhaustion of the hot gas. This air exits at very high speeds, around Mach 2, which would be good for a plane which would need to travel at that speed, but for slower speeds, its not effective.
A turboprop/turboshaft doesnt rely on the exit air speed, but on harvesting that speed into a shaft that can be geared and used to move a propeller, generator, etc.
A turbofan is used in a similar way, with the difference that there is no extra shaft, but an extra set of big blades that are powered by the exit air.
This allows big power output, with a simpler mechanics, which allows higher reliability. One of the biggest evolution was instead of using only one shaft for everything, using 2 or 3, so that each can have its speed tuned, as each stage of the compressor requires its own speed.
One characteristic is that these engines usually dont have a starter... They are started with an air compressor! the air compressor forces air inside the medium compressor chamber, which makes the shaft start turning.
When it reaches the right speed, fuel is injected and ignited, and then it can go by itself. This is the reason why it is required specialized equipment to start a jet engine. On the other hand, these tunnels aren't only used to start up, but also to bleed some compressed air and power directly the hydraulic system. This is one of the reasons why some power controls are lost when all the engines shut off.
So, this is a marvelous model, which is to be assembled by grown ups only. it has very small parts, but its one of the most interesting "things" there is. I hope revell makes it again!
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