Glad to tell you that I finally make the metal turbofan engine kits now after a month since I have made the 3d-printed version. I become more familiar with this engine after the first trial. However, I find I suffer from new problems.
Why is it hard to make turbofan engine kits?
1. design problem
10 years ago, to be frank, I found I knew nothing about the aircraft engine even though I was one of the domestic professional auto mechanic experts. It's totally different things to know how the car engine works than to know how the aircraft engine works， even though they share similar basic principles. Not to say understand the working principle of turbofan engine kits. Car engines use internal combustion to generate rotational motion, while jet engines rely on jet propulsion to produce thrust. Car engines are designed for efficiency and torque, while jet engines prioritize high power output and stability at high speeds and altitudes.
At that time, I never had a chance to see the real aircraft engine in my daily life, just like everyone else. So most of us only can feel the limited charm of it from a few copies of military airplane magazines or televisions. And there are limited technical materials you can find from the current markets, the diagram in particular. At the time when our team began manufacturing the car engine kits, we had never dared dream of designing a turbofan engine kit one day. Because most of us even didn't know how to see and understand the internal design diagrams of aircraft engines at that time.
I think this is a common phenomenon in some cases. That's why only a few aircraft engine kits exist in the current market. And I'm sad to find other existing ones even have errors in design.
Luckily, a few years before, a professor from Beijing aviation university sought cooperation with my team when he came across the design of my inline four-engine kits on the internet. He taught me a lot about technical aviation knowledge. To better understand how the aircraft engine works, I even became one of his apprentices in his lab for a year. It was at that time that I had a chance to assemble a real aircraft engine together and disassemble it with his students. Day by day, I become more and more familiar with aircraft engines.
2. building difficulty
as i said the last time, it consists of more than 1000pcs screws to connect, which means repeated steps and high patience are required. Of course, I will consider using the anti-loosening screws so that the engine can be tightened well and it's not easy to lose among the different parts of the engine. However, I came across a new problem when I built the 2nd sample. A screw just slips into the hole of the internal aircraft engine when I tighten it. And I find it hard to take it out. The problem is that, if I want to find out this screw, I need to dismantle and re-build the whole turbofan engine kit, as all the parts are connected together with one middle axle. No wonder why it takes such a long time, more than a year, to repair a real aircraft engine for aviation technicians. So I recommend that transparent tape should be put to cover the hole during the building process to avoid this problem. And I'm also thinking of making a transparent cover rather than a hollow hole. so the users don't have to suffer from it.
Tolerances are specified for various aspects of engine components, including dimensions, clearances, fits, and surface finishes. For example, tolerance levels may be defined for bore diameter, piston ring gap, valve clearances, bearing fits, and many other critical dimensions and parameters.
We have discovered that when applying jet paint to the body of our turbofan engine, even the original had a very minimal error, only around 0.01mm. However, during the final processing of the products, there was an error accumulation of approximately 2mm in the outer contour. It increases the difficulty of succeeding in manufacturing these turbofan engines.
Additionally, I would like to apologize for not being able to accurately replicate the correct number of compressor stages in this scale model engine. Typically, a turbofan aero-engine consists of 11 stages of low-pressure compression. The compression ratio is approximately 1.2 raised to the power of 11. A higher compression ratio results in a larger and more compressed gas volume, ultimately generating stronger thrust from the engine.
During the production process, we encountered limitations in length and space. As a result, we had to modify the number of compression stages by reducing it by 4. Therefore, in the middle section of the engine, you will only see 4 low-pressure compression blades.
4. color problem
Since the anodized color treatment cannot be performed on this sample, the paint tray can only be adjusted manually to adjust the desired color. I have painted this engine several times and was surprised to find that it's hard to make the same color as shown on my computer. So you can see it's greener on the 2nd sample I have. I'm keen on looking for dark green and as close as black color. black green? Maybe. I have communicated with several model engineers. They told me if it can work if it's under professional industrial production.
5. oil pipe system
The oil pipe system typically consists of a network of pipes, tubes, and fittings that connect the oil reservoir or sump to the various engine components. The pipes are made of materials that can withstand the high temperatures and pressures encountered within the engine. I 3d printed a totally metal oil pipe for it. I was surprised to find out that if the hole is not matched with it, I needed to re-make it again and again. I changed almost 5 black oil pipes.
The previous motor is 100 rpm, and under the clamping resistance, it is less than 60 rpm. The speed is too slow. it means it cannot restore. So I replace the motor with a speed of about 400 rpm, the torque will be larger, and the speed will increase and the taste will be restored. Happiely, after a month of search, i finnaly find the right motor in righ size, which meets my needs.
2. external different color
you might be curious about the different colors in the external turbofan engine kits. It's because of the different materials used in the aircraft engine in reality.
Aero engines are designed with different materials in different sections based on their temperature and strength requirements. The displayed colors of these sections can vary due to the materials' reactions to high temperatures. The bottom section uses cast iron and nickel alloy for high-temperature tolerance, the middle section uses stainless steel and titanium alloy for heat resistance, and the front section uses composite materials like carbon fiber for lighter weight.
Regarding lubricating oil treatment, aero-engines do require lubrication to minimize friction and wear between various moving parts. Lubricating oil is used to ensure smooth operation and increase the engine's lifespan. However, this lubrication is primarily internal and not visible externally. Therefore, when observing a real engine, you would typically see the original color of the materials used rather than any oil treatment.
Of course, I use one material for this motor instead of nickel alloy, because of the cost problem, or I will really go bankrupt. Ha ha. I choose to paint different colors here to restore the feature of the real engine.
4. Building time
It took me about 3.5 hours to assemble it as I get more familiar with it the 2nd time. I think it will take 24hrs for average people to build a turbofan engine that works. I also spent more than ten hours debugging.
5. position of the air vent
The position of the air vent of the nacelle has been prepared here. In order to maintain the taste of the original engine and restore the details as much as possible, the size has basically been confirmed. If there is a chance later, the nacelle can be directly linked to the turbofan engine.
As long as you gently push the switch valve, you can hear different sounds from the engine. This is mainly to simulate the different sounds of the engine at different idle speeds. In addition, I made a manual switch on the inside, if it is suitable when your engine is out of power, you can turn it on manually.
7. the bracket
as you can see, 4 wheels are added to the bottom bracket. I use the non-slippery wheels so that it will be not easy to run and fall apart. So it can stand safely on your desk in your office.
8. U-shape design
In the beginning, when I finally finish assembled the turbofan engine kits, all I want is to display them in my office room. However, a little kid in the neighborhood came and play in my office. he wanted to take it from the high desk into the floor to look what it is. Luckily, I saw this scene and save this sample's life, otherwise, it will be dropped into the floor. so I gave up using the U-shaped groove design. The tightened screws are added to the side of the engine. In the previous U-shaped slot design, the user can easily pick up the engine. But now, it cannot be taken off easily for safety. Of course, you can also loosen it if you want.
please note that the blades must be installed in the right direction otherwise you need to take it apart and re-build it again. It happened to me several times in the past.
Mr Qi Zhong