Chapter One Hundred and Two: The Most Reliable Plan

A turbofan engine is not particularly advanced; the real issue lies in our research approach. There are both simple and difficult types of turbofan engines, and the technological barriers are not as insurmountable as we imagine. What I am proposing today is a relatively straightforward design. By undertaking this simple design, we can gain valuable insights into the fundamentals of turbofan engines—this, I believe, will be our greatest achievement in this endeavor.

Instead of presenting my proposal immediately, Yang Hui began by discussing the difficulty and necessity of developing turbofan engines. Only by reiterating these points could he offer everyone a sense of reassurance, allowing them to listen calmly as he explained his plan.

The crowd’s response did indeed settle; they now awaited Yang Hui’s final proposal for the turbofan modification.

“We understand that the thrust increase of a turbofan engine is directly proportional to the ratio between the inner and outer bypass channels. Let’s calculate how much additional thrust this new engine needs. Assuming a maximum thrust of 7.2 tons, we must increase it by 0.4 tons. To achieve this, the bypass ratio does not need to be large—at most around 0.3 to 0.4.”

Hearing this bypass ratio of 0.3 to 0.4, the audience found it somewhat perplexing. The bypass ratio merely indicates the proportion of airflow between the inner and outer channels; a larger ratio means greater thrust augmentation. Even a small bypass ratio still qualifies as a turbofan, and the technical challenges are significant, not easily overcome.

Among so many people, only Yang Hui, Director Bai, and Xie Lianfa specialized in engines; the others only had a general understanding of the turbojet engines used at the base. While they knew the principles behind turbofans, they were truly at a loss when it came to the details. Information was not as readily available as in later years, and domestic research was obsessed with turbojets, naturally leading to limited understanding of turbofans.

Director Bai, an engine specialist, grasped Yang Hui’s reasoning. He chose not to interrupt, letting Yang Hui continue. Perhaps, by following Yang Hui’s approach, the base’s engine manufacturing could be the first to enter the turbofan era.

Though he remained silent, his actions clearly signaled support for Yang Hui. Observing that the others were watching him closely, hoping for his opinion, Director Bai simply nodded in affirmation.

With everyone once again composed, Yang Hui continued: “A small bypass ratio of 0.3 will greatly simplify research and manufacturing, and most importantly, it allows us to effectively control the fan diameter.”

What benefits come from controlling the fan diameter? They are substantial: controlling the diameter means the fan blades can be shorter, which is a great advantage. Firstly, manufacturing becomes much easier, suiting the base’s current production capabilities and increasing the yield rate, thereby lowering costs.

Are there further advantages to controlling the diameter? Yes—the engine as a whole will have a controlled diameter, which is absolutely necessary for the new aircraft. Since the aft fuselage of the new model is not planned for major modifications, the engine’s diameter cannot be increased by much.

Continuing with the benefits of a controlled fan diameter, Yang Hui elaborated on the merits of a small bypass ratio.

“By adopting a small bypass ratio, we can also preserve the high-altitude performance of the new engine to a certain extent. The reason turbofan engines underperform at high altitudes compared to turbojets is that the fan draws in less air at altitude, reducing efficiency; the larger the bypass ratio, the faster the drop in efficiency. Turbojets do not have this issue. Thus, with a smaller bypass ratio, the engine’s high-altitude flight performance will be closer to that of a turbojet.”

It is widely acknowledged that a turbofan engine with a small bypass ratio offers superior high-altitude performance compared to one with a larger ratio. For example, the F119 engine used in the later F-22 fighter employs a small bypass ratio design to accommodate high-altitude requirements, though at the cost of increased fuel consumption.

Consider the legendary Soviet MIG-31 interceptor: its engine, a turbofan, should not be able to operate at altitudes of thirty thousand meters, let alone sprint at three times the speed of sound. Yet its D30F6 turbofan engine achieves this, precisely because it is equipped with two small bypass ratio turbofans.

Thus, it becomes clear why the new aircraft must use a small bypass ratio turbofan. Ultimately, the new model evolved from the J-7, a second-generation aircraft emphasizing high-altitude, high-speed performance. The new model’s primary purpose is to train pilots for second-generation aircraft. Preserving the new trainer’s high-altitude, high-speed performance is therefore essential.

Although Yang Hui knew that third-generation fighters, which excel at low-altitude dogfighting, would soon become mainstream, training J-7 pilots was currently the priority. Otherwise, training pilots in third-generation dogfight techniques only to put them in second-generation aircraft would be disastrous. The poor low-altitude, low-speed performance of second-generation aircraft is evident—one need only recall the tragic events of the South China Sea collision and the martyr Wang Wei, who perished performing low-speed maneuvers in a second-generation fighter.

(The above merely analyzes the low-speed performance of second-generation aircraft and is in no way intended as disrespect to the heroic Wang Wei, whose memory endures forever. On that day, let us not remember only the passing of Leslie Cheung, but also honor Wang Wei’s sacrifice.)

To train second-generation fighter pilots, it is absolutely necessary to retain the new trainer’s high-altitude performance. Yang Hui went on to describe further benefits of using a turbofan.

“If we develop a small bypass ratio turbofan and use more titanium alloy components, it is entirely possible for our new aircraft to achieve a thrust-to-weight ratio of seven. Currently, increasing the turbojet’s thrust to meet the new aircraft’s requirements is most realistically accomplished with a small bypass ratio turbofan, which tests our design abilities. However, it will not overly depend on manufacturing capacity or material performance.”

His final remarks on manufacturing ability and material performance dispelled any thoughts of seeking other methods to improve engine performance. Given the current domestic situation, it is best to focus on structural design and not entertain other ideas.

Yang Hui finished saying all he needed to say, covering four areas of improvement. Though the final turbofan modification entailed significant technical risks, the rewards would be equally substantial. Once the turbofan design is mastered, the entire base could thrive—such is the magical power of an excellent engine, capable of turning decay into wonder.

Having listened to so much from this young man, it was now time to hear Director Bai’s evaluation. After all, such weighty matters are best addressed by experienced researchers—this is the disadvantage of youth: the adage “no beard, no credibility” is deeply ingrained. Yang Hui was barely over twenty; there was no changing that.

Everyone watched Director Bai, who was still pondering Yang Hui’s thrust augmentation proposal. After a long contemplation, he realized Yang Hui had finished. Without further ado, Director Bai sincerely applauded.

With Director Bai applauding, Yang Hui’s proposal was evidently feasible. The others, who had been focused on Director Bai, promptly joined in, and the small room resounded with thunderous applause.

After the applause, Director Bai spoke.

“Personally, I am quite optimistic about these improvements. Following this plan is our most reliable course of action. If we don’t, we’ll have no choice but to import foreign engines—which is absolutely unacceptable. The military would never agree to that.”

“So my opinion is to proceed with Yang Hui’s plan, modifying the Turbojet-13. This way, we not only secure domestic orders but can also profit from the engine procurement budget—after all, we now have up to six hundred million dollars available. With careful planning, we can develop the engine ourselves.”

With the initial design scheme for the new aircraft complete, preparations began for drafting the documentation—testing everyone’s “PPT” skills. In later years, the cosmic power South Korea excelled at this; their presentations were numerous and exquisite... but ultimately futile. For small nations, manufacturing military fighter jets has become nearly impossible. Even Sweden, known for its proud fighter development, has seen little progress after the Saab 39.