Chapter 153: The Gear Transmission Scheme

Yang Hui conveyed the base's proposal to Shi Ping, who did his best to pass along the intent. Whether a collaboration could actually materialize, however, was not something Shi Ping could decide on his own.

After Shi Ping relayed the message, a definitive response from Hongdu arrived shortly thereafter. Hongdu indicated that they were open to cooperation on the new primary trainer aircraft and were also willing to discuss the Yangtze 750 motorcycle engine.

Yang Hui had anticipated this. As long as the senior management at Hongdu were not out of their minds, there was no reason to refuse cooperation on the trainer aircraft. As for the motorcycle engine, there was even less to debate; by 1983, Hongdu was not the only factory producing the Yangtze 750—there were several across the Republic.

More importantly, at this time, the capital of Guizhou Province, where Base 0011 was located, had begun to introduce the technology for the 750, and Yang Hui remembered from his previous life that Base 0011 had indeed gone on to produce this model.

As the factory that had pioneered the production of the 750, Hongdu knew the Ministry of Industry was eyeing the technology. Rather than waiting for an administrative order to forcibly seize it, it was better to offer it now to earn some goodwill, and perhaps even make a little profit.

Once Shi Ping had finalized the collaboration on the new primary trainer with the base, he prepared to depart and return to Hongdu to continue the aircraft's design. In Yang Hui’s previous life, the design of the Hongdu K-8 had only accelerated after negotiations with Pakistan in 1986. Now, however, it was only 1983, advancing the timeline by three years.

Furthermore, at Yang Hui's suggestion, not only had the technology for the future K-8 been identified early, but Yang Hui had also proposed the engine that would eventually power it.

"Team Leader Shi, I hope you will carefully consider these suggestions. The TFE731 engine has excellent performance, with a thrust range between 1.5 and 2 tons and very low fuel consumption."

Yang Hui did not know why he was so fixated on the TFE731, repeating his recommendation several times. Shi Ping, however, took note of it and decided to factor this engine into the design of the new trainer.

Yang Hui’s obsession with this engine had its reasons. Developed by the American company Garrett, it was designed to meet the needs of 1970s and 80s business jets. It was quiet, highly efficient, and exceptionally reliable in terms of performance and safety. Most importantly, it featured a high bypass ratio and, crucially, a geared turbofan design, which was the aspect that most attracted Yang Hui.

What exactly was a geared transmission? This required a look at the history of aero-engine development.

From the earliest centrifugal engines, the industry evolved toward axial-flow engines. An axial-flow engine relies on a long shaft connecting the high-temperature power turbine at one end to the compressor at the other, forming a single-spool rotor. Early turbojet engines were single-spool. Later, to improve performance, engineers discovered that if the compressor could operate differentially—allowing different stages to rotate at varying speeds to adapt to different working environments—the engine would perform better.

This led to the dual-spool engine, and eventually the more formidable and complex triple-spool engine. With more rotors, different compressor stages could operate at different speeds. However, multi-spool engines had a major drawback: one shaft had to be nested inside another. This not only created significant manufacturing difficulties but also resulted in poor transmission efficiency.

Then came another solution: geared transmission. By using planetary gears, only one shaft was needed. Through planetary gear reduction, each compressor stage could operate at its optimal speed. Moreover, the gear ratio could be adjusted based on different requirements—this was the brilliance of geared engines.

While geared transmission was impressive, it had lost out to the multi-spool design in the early days due to a fatal flaw: the ultra-high rotational speeds of aero-engines meant that the small planetary gears had to rotate at equally high speeds. How could one solve the heat generation under such conditions and ensure the gears operated safely and durably?

Despite these inherent challenges, the immense efficiency of geared transmission remained highly coveted. Coming from the future, Yang Hui knew full well the potential of this technology.

How did geared transmission make a comeback in the 21st century? Data alone was not enough; an example was needed. By the future era, geared transmission was not yet widely used, but it was employed in the new generation of commercial engines by the American company Pratt & Whitney, and it received an unprecedented market response. Before this engine even entered mass production, Pratt & Whitney had already begun developing a series of derivatives: the "PurePower" engine family.

This series was named one of the 50 greatest inventions of 2011 and described as "the most significant development in the aviation industry in 2011." The new PurePower engines set a new industry standard for environmental protection and noise reduction, cutting noise by 50 percent compared to similar engines—a remarkable achievement for 21st-century passenger aircraft. Beyond noise reduction, they also significantly improved fuel efficiency and emissions by double-digit percentages.

While these impressive figures were due in part to Pratt & Whitney’s years of experience, the greatest credit went to the geared transmission technology. Otherwise, why would engines from industry giants like Rolls-Royce, GE, and CFM not be as advanced?

For the Republic’s aero-engine industry to stage a comeback, it had to bet on geared transmission, which was currently being overlooked. Only by working together could they succeed. Following the international giants while playing with traditional engine structures would only ever leave them eating dust.

Now that there was an opportunity to engage with an engine that already utilized geared transmission, Yang Hui had to take it seriously. At this time, Garrett was not yet a super-giant like Pratt & Whitney, GE, or Rolls-Royce, making cooperation more likely. Although Garrett was an American company, one could leverage the currently favorable relations between the Republic and the United States.

In the 1980s, the U.S. was quite open to the Republic. While they remained tight-fisted regarding high-thrust engines, refusing even to export finished products, they had relaxed restrictions significantly on medium-thrust engines. One need only look at the "Super-7" project in his previous life to see how intensely the F404, P1120, and RB199 competed.

If finished medium-thrust engines were being sold, then there was certainly room to talk about small-thrust engines. Garrett was not a primary tier-one supplier in the U.S., so introducing this small-thrust commercial engine was a real possibility.

Shi Ping did not know what was running through Yang Hui’s mind, but he gave a firm reply. "Don't worry, I will study this engine carefully when I get back. If it truly is as good as you say, I will certainly recommend it to the institute. You seem very concerned about this—I assume you want to import it, right?"

Shi Ping hit the nail on the head. Yang Hui did not bother to hide it and admitted frankly, "Exactly. I am very optimistic about this engine. More importantly, I am optimistic about our new primary trainer, which is why I want to introduce it. Our domestic small-thrust engines are indeed not up to par at the moment."

Yang Hui’s candor pleased Shi Ping, who patted him on the shoulder before getting into his car and leaving. Watching Shi Ping depart, Yang Hui turned and walked back toward the base. As for whether the new primary trainer would actually use this engine, Yang Hui was not worried. In his previous life, the K-8 had chosen this engine from the start; in this life, there would certainly be no problems.