Chapter Forty-Nine: Two More Diagrams Emerge

The combustion chamber tests had been in full swing for three days. Yang Hui shuttled back and forth between the test site and his own propulsion systems project group, barely finding time for anything else. As for Yang Yue’s work on the airframe design, Yang Hui simply couldn’t spare the time to get involved. Truth be told, he might manage when it came to aesthetics, but structural design was utterly beyond him; in his previous life as a test pilot, structural concerns were never his responsibility. The aviation industry was vast, and no one could possibly master every field.

There were, however, two pieces of good news. First, the testing center had pushed the combustion chamber to the point of normal failure, and all the relevant reports were being compiled—final results would be ready in three days. Second, Zhong Jianshe had completed the design for the centrifugal impeller. Yang Hui was now busy drafting the impeller’s drawings, while Zhong Jianshe? He was, quite understandably, fast asleep.

Zhong Jianshe had pulled several all-nighters to finish the design. Just last night, he hadn’t turned in until four in the morning, only to get up again at seven, dark circles under his eyes even more pronounced, and trudge back to work. Yang Hui quickly took over the design documents and urged Zhong to sleep at his desk. It didn’t look good, of course, but everyone in research knew how things were.

Zhong’s centrifugal compressor wheel was intriguing: a fully integrated, cast piece that appeared remarkably simple. But casting would be a challenge—the impeller’s complex curves made even model-making a laborious task, not to mention the uncertain yield of usable parts.

Micro turbojets, being turbine machinery, operated at extremely high speeds—anywhere from 100,000 to 200,000 revolutions per minute. At such velocities, the impeller’s thermal response during rotation was critical. Zhong had considered various structural approaches, ultimately relying on finite element analysis to determine the optimal configuration.

Yang Hui was astonished to see finite element analysis used here. This technique had only begun to develop rapidly in the 1970s and was still cutting-edge. Clearly, Zhong Jianshe had found a talented mentor at university. Even more surprising was that he’d managed to complete the analysis at all—he must have figured out a way to access a computer, as finite element calculations were impossible without one. Even with a computer, the process was challenging; the base’s computers were slow, and extracting meaningful results required real skill.

Regardless of how the finite element analysis was accomplished, the documentation proceeded with calculations for centrifugal force and high-temperature loads. Using material properties and projected heat exposure, he calculated tensile and strength limits, and precisely determined the clearances between impeller and casing.

The calculation process for each parameter was thoroughly recorded, a testament to the thought and effort poured into the design—many issues only revealed themselves after calculation, necessitating repeated revisions. The project group, fresh out of undergraduate studies, lacked experience and likely did much unnecessary work. After reviewing everything, Yang Hui made a few minor corrections but nothing critical.

With the design confirmed, Yang Hui turned to a skill he hadn’t exercised in years: mechanical drafting. In later years, computer-aided design had largely replaced hand-drawing; though some manual drafting persisted, it was rare, especially in aerospace where computer drawings were standard and printed directly. Paperless manufacturing was still a challenge, however.

Despite computers taking over, the fundamentals of drafting remained crucial, for the computer was only a tool—someone had to operate it. Yang Hui hadn’t forgotten the basics. He began with the border, title block, and normal lines, proceeding step by step. The process was anything but smooth; mistakes were frequent, the eraser left faint marks, and the completed drawing was so messy he was embarrassed to present it. In the end, he destroyed the failed attempt with the excuse of discarding it.

When Yang Hui returned, Zhong Jianshe had woken and was groggily reviewing his notes. Without access to the data, Yang Hui couldn’t continue drawing. After handing Zhong a fresh sheet of drafting paper, Yang Hui turned to his own assignment: the fuel supply system. Each member had been assigned two subsystems; his were the combustion chamber and fuel system.

The fuel system was relatively simple—a network of fuel lines. The main concern was fuel flow control, easily addressed with a couple of fuel valves and a propane valve, all likely available as standard parts. The only challenge was routing: a well-designed layout minimized bends, enhancing reliability.

After three days, Yang Hui’s fuel system design was nearly done. Though he wasn’t entirely satisfied with the final version, there was little choice—in 1983, electronic controls were out of the question. Mechanical control would suffice, even if it looked inelegant; for an engine destined for a model aircraft, a little ugliness could be forgiven.

Now, Yang Hui’s main concern was the model’s control system. Achieving ground control likely meant resorting to outdated vacuum tube circuitry, with uncertain response times. It certainly wouldn’t match the speed of transistorized systems, but there was nothing to be done except hope that military-grade equipment from the base would be reliable enough.

Burying himself in the finishing touches for the fuel system, Yang Hui found drafting pipe runs much simpler than complex machinery, and soon had the drawings ready. After a thorough check, he submitted them for review; only after all signatures were collected would the drawings be official and sent to the factory for prototyping.

The next morning, Yang Hui and Zhong Jianshe went to different factories to oversee parts production. Yang Hui returned early—his parts were just pipes, easily fabricated. Zhong, on the other hand, found progress far slower; the centrifugal impeller was another matter entirely, requiring casting, and it was uncertain how many usable pieces would result.

Clearly worried, Zhong Jianshe sat lost in thought about the impeller’s casting, neglecting even the design of his diffuser—unusual for someone so driven, and a sign of just how daunting the impeller’s manufacture was. Even the designer himself lacked confidence.

Two anxious days passed. On the third, Zhong Jianshe came to find Yang Hui, and together they headed out.

“Team Leader Yang, this afternoon the foundry has a casting run scheduled. They’ll use the leftover molten iron to cast our impellers—said they can do ten in total.”

They were lucky; the drawings had only been delivered at noon two days before, and now finished parts would be ready. Still, with only ten to be cast and this being the first attempt—given the complex curves—failure was quite possible. Yang Hui worried all the way there.

At the factory, they learned the main casting work was underway, so they hurried to the foundry. There was little for them to do but watch from a distance as the molten iron was poured into the molds.

Sure enough, by the time they arrived, the main casting was done, and a few workers were helping with their ten impellers. Within minutes, molten iron was flowing into the molds. The master who had agreed to help Zhong Jianshe came out to speak with them, leaving the cooling and grain refinement to a specialist—a delicate job best handled by an expert.

“Comrade Zhong Jianshe, just so you know, I made ten models—took a lot of effort. But we didn’t have much iron left, so we could only cast eight impellers.” The man’s booming voice carried from afar.

Only eight cast, which meant the odds of getting a usable piece were even lower. Yang Hui’s optimism faded further—he doubted any would turn out right.