Chapter 888

Listening to Djokovic's question, Liu Cong's simple and honest smile became more intense: "this is just a model, the actual mass production parts are much bigger than this."

"What? Have you started mass production of the fourth generation turbofan fan fan blades? "

It's OK not to listen to this. As soon as he hears it, Djokovic's whole body is just like the encounter of some indescribable supernatural event. He can't help shivering.

Of course, it's not scared, but shocked.

However, Liu Cong asked in a strange way: "I heard that during the exercise at the eastern foot of Karakoram, your military observers had seen the latest improved version of our yun-17. The wd-60ml turbofan engine with large bypass ratio was equipped with this kind of fan blade. The diameter of this engine is 1.86M, the bypass ratio is 9, and the length of a single piece is about 0.75m Well You don't really don't know? "

When asked this question, Djokovic's face turned red. It was not only the old Russian expert, but also the executives and experts of Russian aviation industry who were present. They were all embarrassed.

They really don't know that China's Tengfei group has mass produced the fourth generation of turbofan engine fan blades. If they know this news, including Djokovic, the entire Russian aviation industry in China will never be as high as before, but will recognize and contact China, which they regard as students and descendants, with a more equal attitude Aviation industry.

As for why, it's very simple that the Russians can't make the fan blade of the fourth generation turbofan engine at all.

Looking around the world, only three companies can really master this technology, GM and Pratt & Whitney in the United States, and RORO in the United Kingdom.

In addition to the three major aviation giants, the remaining one is one that can't be touched, let alone mastered.

If not, these three giants are the only ones that can produce high thrust aeroengines with bypass ratio above 6.

To put it bluntly, it is still the three major aero engine giants who have mastered the core technology of the fan blade of the turbofan engine with large bypass ratio. Only on this basis can the outer bypass be made larger and larger, until the thrust proportion of the outer bypass is increased to about 80% of the thrust of the whole engine, thus forming the third generation of large bypass ratio and high thrust engine with high thrust, low fuel consumption, high reliability and low noise.

In contrast, the former Soviet Union and its successor, Russia, of course, also wanted to develop towards a large bypass ratio. However, until the collapse of the Soviet Union, the high thrust engine in the whole Soviet style system was only the d-18t turbofan engine on the An-124 and An-225 heavy transport aircraft.

The maximum thrust is close to 30 tons, but the bypass ratio is only 5.6. At the moment when the three major aero engine giants generally mass produce high thrust engines with bypass ratio above 9, the value of 5.6 can only be regarded as high bypass ratio, far from large bypass ratio.

As for Russia, which inherited the family business of the Soviet Union, it wanted to survive the more advanced aero-engine. The problem is that the continuous economic downturn after the disintegration completely destroyed the family base left by the Soviet Union. As a result, the fighting nation had no ambition but could not sustain it. It could only stay in the dusty design draft and the dream of those experts in the aviation industry.

The former Soviet Union, a superpower on an equal footing with the United States, and the existence of top aviation technology, did not come up with a high thrust engine with bypass ratio above 6 until the end of its life.

Did the Soviet Union not pay enough attention to it? Or are the fighting nations not working hard enough?

No, the fundamental reason is that the fan blade of turbofan engine is not too complicated.

In order to provide 80% thrust for the large bypass ratio fan in the front section of the turbofan engine, it is necessary to ensure that the speed of the fan must be large, so as to ensure that there is enough air flow through the fan to become the thrust of the engine.

The question is, how much speed does the fan need to reach in order to generate enough thrust and ensure the stable and efficient long-term smooth operation of the whole engine?

After all, the rotating shaft of the fan can not provide infinite high speed, even if the rotating shaft can, the fan blade itself can not bear such a high centrifugal force.

More importantly, due to the different travel between the tip and the root of the fan blade, the tip of the fan blade usually enters supersonic speed at high speed, while the root of the fan blade rotates in subsonic speed.

As we all know, supersonic will produce shock waves. In the category of shock waves, the nature of air resistance will change fundamentally and form a kind of shock wave resistance like water drift.

This will produce a unique phenomenon, that is, the first stage large bypass fan of large bypass ratio turbofan engine is driven by the turbine, but the thrust formed is the same as that of an asthmatic tuberculosis ghost, which is always short of breath.

Even in the extreme, the speed reaches the peak, the thrust not only can't reach the theoretical value, but also has a sharp decrease.

The reason is that the blade tip of the fan first enters the supersonic speed, forming shock wave resistance, and the air that originally came in is bounced out like water. It can only rely on the part below the middle of the blade to inhale air, so the efficiency naturally can not be improved.

Of course, this is only one of the disadvantages of the fan blade at high speed. As for reducing the service life of the blade, damaging the structural strength of the blade, and often causing damage to the blade, there are many disadvantages.There are so many bottlenecks that are difficult to overcome. The fan blades of early turbofan engines are the same as those used in Russia now. Since tip supersonic speed is so troublesome, it's better not to let the tip enter supersonic speed.

How to control it?

Of course, the blade tip travel was shortened, so turbofan engines with bypass ratio of 2 or 4 became popular in the 1960s and 1970s.

At the same time, increasing the number of blades, reducing the speed of a single blade is also an effective means to reduce the overall speed. Of course, in order to strengthen the structural strength of the blade, a convex shoulder device will be made in the middle and root of each blade.

If it is integrated in this way, it will be found that the primary fan of the whole turbofan engine is not so much a fan as a metal wall, but also a hard core wall with two rings of stiffeners.

This kind of turbofan engine not only has too much weight and the thrust to weight ratio can't be improved, but also has amazing fuel consumption. It's impossible for the efficiency of the front fan to be improved. It's all pointing to the turbine behind to provide thrust, so it's natural to become an oil tiger.

As for maintainability, not to mention whether the removal of 40 or 50 fan blades one by one will cause the maintenance personnel to collapse, it is the practice of frequently pressing the turbine to do work to provide thrust, which itself is constantly reducing the service life of various key components.

It is precisely because of the shortcomings of this kind of compromised turbofan engine that aero-engine engineers have come up with an idea, that is, whether there is a fan blade that can overcome the supersonic shock resistance, so as to make use of the supersonic speed and subsonic speed of the blade tip at the same time, so as to expand the bypass ratio of the first stage fan and increase the air runoff, so as to achieve no increase Under the premise of turbine power, the overall thrust is greatly improved.

So from the mid-1970s, the aviation experts from various aviation powers began to invest in this research. As a superpower at that time, the Soviet Union naturally followed the trend. As a result, over the past ten years, a lot of relevant theories have been put forward, but none of the finished products have been produced. The reason is that it is both simple and helpless. At that time, the Soviet Union did not have practical aviation industry design software, so it could not do complicated work The three-dimensional industrial design, naturally, can not create a modern turbine engine fan blade that can take into account both supersonic and subsonic.

Now, China's Tengfei group has applied such blades to its turbofan engine with large bypass ratio in large quantities. What does this mean?

Very simple, they have surpassed the original teacher Russia in the advanced three-dimensional industrial software!