Chang Haonan was woken up by a burst of cheers.

He opened his eyes with some struggle and stared at the spinning ceiling fan on the ceiling for a second.

At this time, a voice shouted: "It's out!" ”

After sitting up, he found that not only Fang Zhen and Yao Mengna were standing in front of the computer, but even Du Yishan didn't know when he came here.

Unlike Yao Mengna and Fang Zhen, who were staring at the calculation results, Du Yishan was holding those pages of manuscript paper in his hand and had read them over and over again.

Compared with the two doctoral students, Du Yishan's theoretical foundation and experience are naturally more in place, so even if the above writing is a little sloppy, he still fully understands the content.

And at the age of seventy, he actually had a feeling of empowerment because of a few pages of scratch paper!

"Exquisite!"

Du Yishan flicked a few pieces of scratch paper with his left hand, and turned to look at Chang Haonan, who had already woken up.

"Xiao Chang, this modeling idea of yours is exquisite!"

"Based on the theory of small transonic disturbances, the influence of geometric nonlinear factors on the aerodynamic characteristics of a large aspect ratio wing is calculated by combining the nonlinear finite element and the nonlinear beam model, and the factors of the aerodynamic control surface in the wing structure are also taken into account in the modeling...... Not only flutter is a problem, but this idea can even be used to diverge and solve other design problems. ”

"From the Dewey-Hodges equation in 1974 to the present, twenty-two years later, another big step has finally been taken in the field of nonlinear flutter analysis, and it is still taken by us Chinese people!"

The rest of the lab watched in amazement.

In almost everyone's impression, Du Yishan will always be as stable as Mount Tai.

And now, with a few pieces of manuscript paper on his face full of excitement, he paced back and forth in the laboratory.

"Mr. Du, let's take a look at the simulation results first." In the end, it was Chang Haonan who reminded him that drew Du Yishan's attention back to the computer screen not far away.

One of the most important results of flutter analysis is the "flutter critical velocity", which ideally induces wing flutter once the aircraft reaches this speed, so the higher this number, the better, indicating that the wing is less prone to flutter.

However, the flutter critical velocity is not calculated directly, but the V-g and V-f plots must be drawn according to the calculation results before being judged.

And Fang Zhen and Yao Mengna have already started to do this.

……

A few minutes later.

"Teacher Du, junior brother, it's calculated."

Fang Zhen put the pencil on the table and stood up with a piece of paper, but his expression was a little dignified:

"Taking into account the nonlinear geometry, the flutter critical velocity is 157 m/s, which is 10 m/s higher than the British expert's estimate, but ......"

When the number 157m/s was said, I don't know if it was Chang Haonan's illusion, he always felt that the atmosphere in the laboratory suddenly froze for a moment.

"British experts?"

Chang Haonan noticed that Fang Zhen had just mentioned these four words.

Speaking of which, although he has solved the whole problem, because he has been working since he came in the morning, he is concerned about the technical problems related to the project, and he is completely ignorant of the ins and outs of the project itself.

In the previous life, Chang Haonan missed the insurance research, so he spent the first semester of his senior year preparing for the graduate school entrance examination, and his graduation project was also done with an unknown young teacher, so he didn't catch up with the opportunity to participate at all.

This experience in flutter analysis was later accumulated when he participated in a certain type of long-endurance UAV project.

"Oh, it's only the first day that junior brother has joined the group, so I shouldn't know about these things yet......"

In the end, Fang Zhen briefly introduced the situation of this project.

Since this is the first time that Huaxia has completely referred to international standards for aircraft design, and has directly used many subsystems of European and American companies, the 603 Institute has invited many foreign experts in related fields to be consultants, including a Briton Hawkint who is engaged in aeroelastic analysis.

When designing for the new passenger aircraft, the 603 Institute referred to the experience of the Y-7-100 aircraft and designed the wing that Chang Haonan is currently analyzing.

However, during the feasibility assessment, this advanced and high-performance wing design was rejected by Hawkint, because he calculated based on his own experience that the critical speed of flutter of this wing is only 147 m/s, or 530 km/h.

For an aircraft with a maximum cruise speed of 510 km/h, this is almost the equivalent of leaving no safety margin, and a slight dive of the aircraft can induce flutter.

Considering that the experience of Huaxia Aviation Industry in this area is almost 0, the first model to dock with the international is naturally to be safe.

Therefore, the 01 aircraft currently undergoing airworthiness tests are still installed with a set of wings with a relatively conservative design to ensure safety.

However, the designers of the 603 Institute are not reconciled, because according to the current design, the Y-7-200A has no advantage at all in the face of propeller regional airliners of the same level as ATR42/72.

With the same performance, why should someone else abandon a mature aircraft to buy your new model?

The only way is to take the cheap route.

However, cheap routes mean low profit margins, which in turn lead to a lack of funds to carry out subsequent upgrades to the aircraft, and eventually slow and slow to be left behind by those foreign counterparts.

Therefore, the 603 Institute still hopes to make some advantages in performance.

Only then did he hold on to the last glimmer of hope to find Du Yishan's research group.

"I see."

Chang Haonan, who had heard the whole ins and outs, suddenly realized that he really didn't know that there was such a story in later generations.

"I heard from the people at the 603 Institute that if the wing can be replaced, it can reduce the drag by about 5%, and combined with the weight reduction, the comprehensive fuel consumption can be reduced by almost 8%, which is already a huge attraction for airlines."

Fang Zhen looked at the calculation results in his hand and said with some regret.

"Although our calculation results are higher, they are equivalent to 565km/h, which is still not enough safety margin."

In China's current national standard CCAR25, it is required to retain at least 15% of the flutter critical velocity.

"Alas......" Yao Mengna rubbed her temples and sighed, but still raised her head and comforted Chang Haonan:

"Although this wing still proved to be unsatisfactory in the end, your method of nonlinear flutter analysis should still be fine, and when the time comes, we will find an opportunity to verify it on other models, and it will definitely be a good result."

"Wait......"

Chang Haonan felt a little speechless about the current situation - his performance was obviously not over yet, why did these people look like they had failed......

"Senior brother and sister, don't worry, this wing still has room to be saved."

Yao Mengna and Fang Zhen's eyes instantly looked at Chang Haonan.