On the day Yang Hui met with Rouse, Yang Hui took Rouse and his party to see the core machine entity transported from 624, the metal color after high temperature roasting is impossible to fake, along with the core machine there is also the resume of this core machine in the 624 Institute, which lists in detail the data that this core machine is used for those tests, how long the test time, and how long is the service life left in the end.

What I see now is the information that Southwest Science and Industry can disclose to MTU, and MTU finally has a deeper understanding of the technical capabilities of Southwest Science and Industry, and it can be regarded as putting down the worries in my heart.

Since Southwest Science and Industry has taken MTU to see this key core equipment, at the invitation of Rouse, Southwest Science and Industry naturally wants to take a look at the part of MTU, the power giant of the Federal Republic of Germany, which is responsible for research and development.

Unlike the core machine of Southwest Science and Industry, which is an integral equipment, these cold-end components developed by MTU need to be assembled with the core machine to become a complete engine before the overall effect can be seen.

"Yang, what you see now is the MTU company in the past three years to develop a variety of supporting parts, in the design technology of large-diameter low-voltage fans, we cooperate with the world-famous Siemens gas turbine branch, Siemens has the experience of designing and manufacturing high-power gas turbines, and they also have some unique experience in designing this kind of fan.

With that, Rouse brought Yang Hui to the assembled fan, although the box was large, it still couldn't hide the dazzling light of the fan blades.

Reach out. Pick up the loose blades placed in the fan, and carefully observe the differences in the blades. In the end, Yang Hui was a little puzzled when he came to a conclusion.

"The blade is supposed to be made of titanium, but it looks like it's a solid design. Is there a bit of a disconnect between this design and the hollow design that is now the mainstream of the world? ”

Yang Hui's question is very level, in the international advanced large bypass ratio turbofan jet aero engine manufacturing, most of the fan blades are using more advanced hollow blades, or exploring composite blades, the benefits of this design are very many.

On the one hand, it can effectively reduce the weight of the engine and increase the thrust-to-weight ratio a little, although the fan blades are made of titanium alloy, but even if the blades are made of hollow, they will not save much weight in the end. But the good thing is that talk is better than nothing.

However, the financial pressure brought by the manufacturing and maintenance costs of this hollow blade is actually much higher than the small weight reduction advantage brought by the use of this hollow blade.

The reason why the fans of engines with large bypass ratio turbofans really used this hollow design in the manufacture have to be mentioned again when Rolls-Royce developed the RB211 engine.

Among the many advanced technologies used in Rolls-Royce's classic is not only the three-rotor design, which is still drooling two thousand years later, but also the powerful practitioner of the large ducted fan design.

The reason for using this advanced large bypass ratio fan design is that under the thrust requirement of up to 20 tons, the engine is required to be larger, and the engine is bigger at the same time, the fan naturally needs to be bigger.

That's good. At that time, there was a big obstacle that plagued Rolls-Royce, and this technical problem was no less than the cutting-edge technology of the three-rotor, and one of the technical problems that dragged Rolls-Royce down was this large-diameter fan manufacturing technology.

Why is there such a difficulty? No matter how large the fan blades were, they were only two meters in diameter, and it was a piece of cake to deal with this problem with the British machining and manufacturing technology at the time.

That's what the words say. But when the fan blades were made of traditional solid titanium, unfortunately I could only say one thing: I'm sorry, this thing can't be used.

Why was it originally used in the first generation of turbofan engines? Can't you use it on a second-generation turbofan engine?

The reason for this is that the gap between the bypass ratio between the first generation and the second generation of civilian turbofan engines is too large, and the bypass ratio of the first generation turbofan engine is actually very small. How small is it?

The bypass ratio of the first generation of civil turbofan engines is generally around 1, and the bypass ratio of Spey 512 in the civil turbofan engines of this period is only 0.7. Therefore, without much surgery, the afterburner is directly installed, and people can use it as the engine of the fighter, which is the well-known Spey 202 engine (turbofan 9).

During this period, there was a more powerful but inconspicuous civilian turbofan engine for military use, which was the power RM8 engine of the Swede's Saab 37 Thunder fighter, which was improved from the famous Pratt & Whitney JT8D civilian turbofan engine.

The same design without a fan, directly installed afterburner, after doing this, this engine has a bypass ratio of 1.05, but it can also be used in Sweden's Saab 37 fighter, so as to create this turbofan engine with an afterburner thrust of 12.7 tons.

To cite these somewhat off-topic examples, there is only one point to mention, that is, the bypass ratio of the early first-generation turbofan engines was generally relatively small, and the bypass ratio was not even much larger than that of military turbofan engines.

In this case, the design of the fan naturally does not need to have a large diameter, and the fan blade diameter of the turbofan engine in this era is relatively small.

Although the small-diameter fan has to bear centrifugal force during operation, because the tip of the blade is relatively close to the center of the disc, the diameter of the fan does not need to exceed 1.5 meters, even if the weight of the blade itself after rotation plus centrifugal force, the mechanical strength of the blade can also withstand the load added to it.

However, when it came to the second generation of civilian turbofan engines, everything was different, and at this time, the large bypass ratio of the engine was required, and the aircraft of this period were all going bigger, and the engines were naturally concentrated in the development of 20-ton big guys.

On the one hand, in order to save fuel consumption, on the other hand, and for greater thrust, this led to Rolls-Royce desperately choosing a larger bypass ratio design fan design, the bypass ratio is indeed increased, and the bypass ratio design of 5 is directly achieved.

The large bypass ratio design can definitely increase the air intake of the fan, because the most suitable way to increase the air intake of the fan is naturally to increase the fan diameter, which is why the aircraft engine that people see when they take civil aircraft is so short and thick.

RB211 as the pioneer of the 20-ton turbofan engine with a large bypass ratio, the fan diameter has inevitably increased to 2 meters, and it is not possible to use solid fan blades at this time.

The weight of the blades of the solid fan blades plus the centrifugal force will exceed the mechanical strength limit of the titanium alloy blades, if you insist on using the solid blades, it will cause the fan to break due to the strong centrifugal force during operation, which will be a major engine design accident.

In this case, Rolls-Royce had to choose to make the leaves into a hollow honeycomb structure and then add a thin layer of skin. This structure greatly reduces the weight of the blades, but the main reason for reducing the weight of the blades is not to improve the thrust-to-weight ratio of the engine, but to reduce the centrifugal force acting on the blades when the fan is running.

Of course, after using this hollow design, Rolls-Royce has made some improvements to the shape of the blades of the fan, which has many advantages such as increased resistance to foreign impacts, increased surge margin, and reduced number of blades.

All in all, in short, the hollow fan blades that were popular in the 80s were because the diameter of the fan was too large, if the diameter of the fan was not too large, it would be a complete waste to adopt this design, and now this 7.5-ton large duct is necessary to reach two meters in diameter than the fan diameter of the turbofan?

It is completely impossible, even with a fan diameter of two meters, it is impossible for a small regional airliner to use such a large diameter engine with a wings at a safe height above the ground.

This leads to Rouse's last fluttering conclusion, and although it is a partner, Rouse will still only say the conclusion, and the deeper reasons why it is done above will not be said. On the one hand, it is not necessary, and on the other hand, it is in the need for secrecy.

"The diameter of the seven-ton turbofan engine is only more than 1.5 meters at most, not to mention ourselves, even as our opponent RB715 engine fan diameter is 1.45 meters, and the fan diameter of this order of magnitude is just enough to solidify the fan blades without breaking." (To be continued.) )