Back in 1978, I was admitted to Northwestern Polytechnical University.

Chapter 7 The Unique Solution of Green's Function

Professor Liu, born in 1925, graduated from Nanjing University in 1950. He is a renowned expert in aerodynamics and flight mechanics in China. At Northwestern Polytechnical University, he both taught students and conducted research, with a wide range of research areas including aerodynamics, aeroelasticity, flight dynamics, and aircraft optimization design.

He not only studies it, but he is an expert in it, even capable of refuting the theories of foreign experts!

Now, he is the head of the aircraft engineering major in the Department of Aircraft Engineering at Northwestern Polytechnical University.

It was late at night. Professor Liu finished his workday, rubbed his eyes, and left his office.

As he pushed his 28-inch bicycle, intending to go home to sleep, he suddenly discovered that the lights were still on in the aircraft engineering laboratory!
It's past midnight, what are you still doing?
Professor Liu curiously put down his bicycle and walked over.

Pushing open the slightly ajar door, he heard the sound of planing wood. Looking closer, he saw an experienced carpenter making a wooden model with a plane. After a few strokes, an elderly professor nearby took out calipers and other tools to measure it. The two worked together seamlessly, clearly not for the first time.

"Old Sha? What are you doing here so late at night?"

"Make the model tonight, so it can catch the military transport plane to the wind tunnel at dawn."

This is a great opportunity! If we take the train, it will take a whole day, and it's not convenient to bring such a big guy on the train!
What model?

"The double delta wing is a key to solving the J-7's low-speed maneuverability and high angle-of-attack performance issues." Professor Sha said excitedly, "I've done preliminary calculations on paper, and it should greatly alleviate the J-7's problems. We'll have to test it in the wind tunnel to see the full extent. I've contacted them, and they're willing to provide me with several dozen hours of free time..."

Professor Liu looked at the design drawings. The leading edge of the wing was no longer a straight line, but had an angle in the middle. One wing and two sweep angles made it a double delta wing, but... could this really solve the problem?
"Old Sha, did you come up with this?"

"No, it was an idea from one of our freshmen. By the way, Lao Liu, how's your calculation and research on the Green's function method going?"

"I still firmly believe that Professor Hoss's conclusion is wrong! Green's function theory is rigorous and has a wide range of applications. The key point is that it requires little computation. We do not have advanced computers, so using Green's function to calculate the aerodynamics of aircraft is of great significance!"

"Alright, we can't persuade you, so we won't. Actually, everyone, including Director Luo, is only trying to persuade you because we're afraid that after years of research, you'll find it's wrong... Since you insist... So what if Western aerodynamics experts are wrong? They make mistakes too. Lao Liu, I support you!"

"Hmm, tell me about your wings!"

"it is good!"

It was past midnight when Professor Liu finally left with his bicycle. Back home, he tossed and turned, unable to sleep. He finally drifted off to sleep, only to have his alarm clock ring again.

It's six o'clock. I get up, wash my face, brush my teeth, eat breakfast, and then go to the office. Once he's committed to a project, he will never give it up!
dong dong!

"Come in!"

"Professor Liu, I have written a paper and would like to ask you to take a look at it."

"it is good."

Professor Liu put down his work, wiped his glasses, and then picked up the student's paper. The student, who hadn't taken the college entrance exam, might not be at the highest level, but his diligent and studious spirit was still worth encouraging.

Graduating from university requires a thesis, and this student, who started preparing early this summer, is commendable and deserves encouragement.

He seemed quite dissatisfied with the format, but he didn't say much and looked at the content first.

Analysis of Induced Drag in Subsonic High Angle-of-Attack Flight with Delta Wing Configuration?
Not bad, not bad. Using this as a graduation thesis is quite innovative. It must be because you went to Factory 132 and learned about the needs on the front line that you chose this research direction.

Wait a minute... Gaussian divergence theorem is used here? Aerospace engineering majors shouldn't be taught this theorem, right?
"Zhu Yongguang, you're quite impressive! You've actually taught yourself more complex aerodynamics, and you even know Gauss's divergence theorem!"

Zhu Yongguang was a little embarrassed: "Teacher, I only learned about this theorem last night. A freshman came to our dorm, and he's really amazing..." "Could his name be Qin Liang?"

"That's right, it's him, teacher...you know him too?"

Professor Liu's expression was complicated: "It really is him. Hmm, your thesis is good, it meets the graduation standard, but there are a few details to pay attention to. We'll correct them when we officially start writing the thesis. Zhao Ergang, what about you?"

Zhao Ergang stood awkwardly to the side: "Teacher, we're collaborating on a paper..."

"That definitely won't work. Each person has to write their own graduation thesis, so collaboration isn't an option. What are your thoughts?"

"If we can't cooperate, then I'll write... using Green's function to calculate the aeroelastic loads of a delta wing..."

Teng!
Professor Liu immediately stood up: "What did you say? How do you know about the Green's function?"

"Qin Liang..."

"Where is he? Take me there!"

Professor Liu knew, of course, that his student probably didn't even know what a Green's function was. His topic must have been introduced to him by Qin Liang—one through analysis, the other through calculation…

At this moment, he couldn't wait to meet this student.

Dormitory 13, Room 308.

Huh, huh...

The old-fashioned green train of that era rattled and clattered, and the journey took more than thirty hours! Along the way, the smells of sweat and cigarettes were unbearable for Qin Liang, making it difficult for him to sleep.

He finally arrived at his destination and entered university. He had just eaten his first meal at the school when he was drafted into the army. After returning, he helped give advice to two senior students on their papers. He was really exhausted.

In a daze, I heard a voice.

"Qin Liang, do you know about Green's function?"

"Green's function is used to solve non-homogeneous differential equations with initial or boundary conditions. It is an important tool in mathematical physics equations. What science student doesn't know it..." Qin Liang answered vaguely.

"Can we use aerodynamic numerical calculations?"

"Of course... There's this lousy foreign expert, some guy named Hoss, who published a flawed paper saying that the fundamental equations of the Green's function method in aerodynamic calculations don't have a unique solution. That's bullshit... This so-called aerodynamic expert, a brick in the ass... Authority? What a load of rubbish..."

"Great, then tell me in detail..."

A large hand grabbed Qin Liang's arm, causing him some pain. He opened his eyes and saw an elderly professor in his fifties with a thin face and a full head of white hair. His wise eyes were looking at him expectantly.

"Qin Liang, you're finally awake! This is Professor Liu, our teacher, who came specifically to see you."

"What?!" Qin Liang sat up abruptly. "Professor Liu?"

(End of this chapter)