"The thrust is not enough, our requirement is that it must reach 12 tons, and the thrust-to-weight ratio should ideally reach 6.5, which is the most basic requirement, so I think this time we need to make another big change to the engine, even the core engine. ”

In the early years, he was responsible for the localization of the Spey 202 engine, although it was not completed in the end, but Chief Engineer Wu was quite clear about this engine, and its core engine design scheme seemed to be a little old in the eighties.

Directly put forward the request: "Spey's core machine is not bad, but we have higher requirements this time, so we should also make some corresponding improvements, first of all, the temperature of the high-temperature turbine, if it can be increased, it is best to mention some up, this is what a high-thrust military turbofan should look like." ”

Spey's high-temperature turbine technology was at its peak in the late sixties, and the total pre-turbine temperature of 1,168 degrees Celsius was already obvious compared to the data of the eighties when the aero engines were often above 1,300 degrees Celsius.

As the chief engineer, he knows very well that as long as the total turbine temperature of the engine can be raised to the current international mainstream level, the thrust should reach 12 tons, so he will directly put forward the corresponding requirements.

As the head of the Rolls-Rodiscopy project department, the Dam team has calculated various improvement options for the engine, and it may be a good idea to increase the total turbine temperature.

"This idea is definitely fine, but I don't think there is a need to make too radical improvements, based on cost control considerations, just increase the temperature to about 1250 degrees Celsius, once it exceeds 1300, it is not necessary. ”

After all, it is based on the improved design of Spey's core machine, only according to the high-pressure compressor originally designed by Spey, the high-temperature turbine it can match also has a certain range of requirements, even if it can exceed this range of data, it may not be able to continue to increase thrust in the future.

This is confidential data that only Spey developers can know, and for various reasons, it is difficult for him to say it, and it is not a big problem to directly use the cost issue as an excuse.

"If you decide to push the total temperature of the high-temperature turbine to 1250 degrees Celsius, then it perfectly matches the air flow rate of the core engine of the TF-41, which is enough as a core engine of the third generation of high-thrust turbofans. ”

The air flow rate of the core engine during the Spey 202 period was 57kg/s, and when it was later improved to TF-41, the high-pressure compressor of the core machine was also optimized, and the original 12-stage high-pressure compressor was successfully changed to 11-stage by using a more efficient compressor blade shape, achieving the purpose of weight reduction.

The core engine of TF-41 is actually better than Spey 202, after the successful realization of the compressor weight reduction design, under the same force, there is also the possibility of increasing the speed of the core machine, and once the speed is increased, the air flow will naturally increase, which is the same as the reason that the air volume of the electric fan will change at different speeds.

They are all technical people, and after learning that the Republic is going to ask for a high-thrust military turbofan engine, Dam can almost guess the required and predetermined target data.

It is also very gorgeous to give data: "The air flow of the core engine of the TF-41 is 66kg per second, the flow data of the core engine of the F-100 is 61kg, and the F-110 engine being developed by General Motors should be about 68kg according to our budget, so the 66kg air flow of our core machine can already meet the needs." ”

In terms of air flow data alone, Wang Zhengguo still recognizes that the original TF-41 was developed and positioned as an attack aircraft and multi-purpose aircraft, which is roughly no different from the prototype F-101 of the F-110, and the data of the two will definitely be similar.

Overall, the changes to the core machine are really small, and there is basically no need for too much surgery, and the risk control is already quite good, which is worth recognizing.

But to say how satisfactory the improvement of this core machine is, it is not necessarily, at least in terms of weight, it has not been reduced, and it is still at the level of the original TF-41.

As the technical director of the project that has been decided, Chief Engineer Wu of course has to ask the question: "Weight loss! A very important problem we are facing now is weight reduction, otherwise it will be impossible to improve the thrust-to-weight ratio data, is there any way in this regard?"

If you want to reduce the weight of the TF-41, this is really not an easy task, as the chief engineer of the Spey project department of Rolls-Royce, Dam is also very troubled by this request, this is for the TF-41, God!

Regardless of Spey or TF-41, these two are the highest level in the field of aero engine technology in Europe and the United States in the sixties and seventies, it can be said that it was developed at any cost, the cost of TF-41 alone is as high as 2.4 million US dollars, and the RM-8 in the same period only needs 1 million US dollars, how to open the gap between the two?

To give an example: more than 80% of TF-41 compressor blades are made of titanium alloy, while RM-8 only accounts for 40%, which not only widens the cost, but also means that TF-41 uses a large number of titanium alloy blades, resulting in a difficult start if you want to reduce the weight of the engine.

The most common way to reduce the weight of the mature original engine model is to switch to a lighter material, so the question is, is there any material that can be more suitable for engine blades than titanium alloy in the eighties?

Obviously, at this time, the TF-41 has no point in reducing the weight of the engine material, at most it is to do some quiet repair work, and do some material replacement in other corners, but the effect is really not much, and the cost will rise and fly, which is definitely not suitable.

Fortunately, Rolls-Royce is a century-old store after all, even if the Spey project department has declined, but the technical background is still not bad, and soon came up with another plan.

"If you really want to achieve weight reduction, what we can do now is only to do things in low-pressure compressors and fans, which is relatively easier, TF-41 fans, low-pressure compressors add up to a total of five levels, the design has fallen behind, the current mainstream military turbofan engine low-pressure section is 3 levels, so this aspect has to be ruthless!"

Even if you are preparing to make a big change, it is more convenient to operate on a low-pressure compressor, with less work and more controllable risks, which is the best way you can think of at the moment.

"We've done calculations that we can cut the low-pressure fan by one step without compromising the efficiency of the engine, using a more advanced wide-chord fan blade technology, which can reduce some of the weight and shorten the engine length. ”

It is necessary to choose a better fan blade type, so as to reduce the first-level fan, Wang Zhengguo remembers that after the Republic of the upper plane completed the localization of Spey 202, the follow-up modification plan is to cut off the first-level fan, which is absolutely fine.

The turbofan engine in the 60s can be forgiven for choosing a five-stage low-voltage fan, but now it is the 80s, and it must no longer be taken out to deceive, and re-optimization and improvement is the inevitable result, which is the same as Wang Zhengguo and Chief Engineer Wu predicted.

But cutting off the first-stage low-voltage fan can completely solve the problem?

This seems to be a little too easy to think, you need to know that the low-voltage fan that was cut off is made of titanium alloy blades, and the weight is not very obvious, and the weight loss effect brought by it is impossible to cure the disease.

"With the above improvement scheme, the thrust of the new engine should be able to reach the standard of just 12 tons, and the thrust-to-weight ratio will roughly exceed 6, if you can be satisfied with this data, the design can be finalized in three years at most, and the technical risk will not be too large, and the cost will not be much. ”