I build this model to simulate a real jet engine, even though is electric. Is very basic so everybody can build it.

The way I designed and built my jet engine model is not the best way to do it. I can imagine a million ways to build a better model, more realistic, more reliable and even easier to build. But for now this is what I got.

Main parts:

DC motor strong enough of at least 12 volts
DC power supply of at least 12 volts (depending on the DC motor you have).
Rheostat, the same sold to dim light-bulbs.
Gearbox with flywheel, found in many car toys. Is better if the housing of the gearbox is made of metal because plastic could melt at such high speeds.
Some kind of metal sheet you can cut to made the fan blades.
Ammeter or voltmeter gauge.
A potentiometer of around 50K.
Electromagnet coil from a solenoid or whatever source.
4 diodes.
2 or 4 permanent magnets.
Cartonboard to help make the exterior of the jet engine.
Body filler for cars, to make the exterior.
Hard wire to help support everything. I generally use the ones that are on those cheap clothes hangers made of wire. They are strong enough, but flexible enough to shape it the way you want.
Glue. I prefer hot glue for most parts, but practically any glue will work.
White, silver and black paint.

Step 1: Attach DC Motor With Gearbox Flywheel

The basics of my jet engine model is very simple. Attach the DC motor to the gearbox. The idea is that the motor moves the part of the gearbox that was attach to the wheels of the car toy. Put a plastic lever to hit the small gear of the flywheel so it can make noise. Some gearbox already have it installed, some don't.

Step 2: Put Magnets and Coil for Gauge

Now put 2 or 4 permanent magnets on the main shaft in a way that the coil can be close to them when they rotate. Put them in - + - + polarity pattern. The idea is that the magnets will pass close to the coil and generate a small amount of current that we are going to use to move the gauge. But to make this work you need to put 4 diodes in bridge configuration to convert the AC current that we are generating to DC. Google "diode bridge" to get more info about it. Also you need to put a potentiometer in between the coil and the gauge to calibrate the gauge to the right sensitivity.

Step 3: Rheostat for Speed Control

We need to control the motor speed. For this put the rheostat between the power that come from the wall and the power supply. If you don't know how, you can google how to connect rheostats to light bulbs. Instead of the light bulb we are putting the power supply. Don't try this if you are not sure. This is high current we are dealing with. And using the wrong power supply could damage it. The simpler power supply, the better. An alternative is find a DC rheostat so we can control the voltage after the power supply. I could not find any in my area, so that is why I use the ones for light bulbs. But if you can find one that can handle the DC motor, will work the same way. The idea is just control how much current goes to the motor in a gradual way, so that would be our throttle.

Step 4: Fan

For the fan, you are free to do it the way you want. I cut each blade from a thin metal sheet, and glue them. You can make them from carton board and paint it. Or you can even 3d print the fan, if you have access to an 3D printer. There are great 3D models of jet fans on www.thingiverse.com

Step 5: Housing

You can make the housing with cartonboard and later add the body filler to the exterior to make the shape. You are going to need to sand a lot so is hard work and messy. Ones is smooth and the correct shape, paint it with glossy white paint. The inside of the engine should be paint it black. The front of the engine generally has a silver edge that you can optionally paint.

Step 6: Starter Mechanism

The starter and the fuel control knobs are mechanically connected. The starter has a switch that connects the motor to the power supply. That switch can also be activated by the fuel control lever when is in run position. Make the starter spring loaded so wants to return to norm position, and only locks on start position if the fuel control lever is in cutoff position. The idea is so the starter stays in start position until you move the fuel lever to run position, and now the fuel control lever will keep the switch on. Also, the fuel lever is part of the base of the rheostat. The rheostat should be installed in a way that can rotate, not only the knob part that is suppose to rotate, but also the entire rheostat base. That base is what the fuel control moves to increase speed when is in run position. Is complicated to explain so you should watch the part 3 video to better understand it.

In the future I am going to build a much better jet engine model and I am going to record a video on how to build it. I plan to 3D print the main parts, have reverse, be controlled by arduino, have a LCD display to show a bunch of gauges (like a real one), go from idle to stop much slower like a real engine, be more detailed, etc. Until then, I hope my instructions are helpful so you can build one.