Chapter 32 The result is out

Chang Haonan was awakened by a burst of cheers.

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

Then a voice shouted: "The results are out!"

After sitting up, he realized 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 closely at the calculation results, Du Yishan was holding the pages of manuscript paper in his hand and had read them over and over several times.

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

And at the age of seventy, he actually had a feeling of enlightenment because of these few pages of draft paper!

"Exquisite!"

Du Yishan flicked a few pieces of draft paper with his left hand, turned around and looked at Chang Haonan who had woken up.

"Xiao Chang, your modeling idea is so exquisite!"

"Based on the transonic small perturbation theory, the nonlinear finite element is combined with the nonlinear beam model to calculate the impact of geometric nonlinear factors on the aerodynamic characteristics of large aspect ratio wings, and the aircraft is also taken into consideration when modeling. The factors of the aerodynamic control surface in the wing structure... are not only flutter problems, but this idea can even be used to spread out to solve other design problems."

"Twenty-two years have passed since the Dewey-Hodges equation in 1974. Finally, another big step has been taken in the field of nonlinear flutter analysis, and it was taken by us Chinese!"

Others in the laboratory watched this scene in stunned silence.

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

But now, he was pacing back and forth in the laboratory with a few pieces of manuscript paper in his hands with excitement on his face.

"Teacher Du, let's take a look at the simulation results first." Finally, Chang Haonan reminded him, which brought 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 speed". Under ideal circumstances, once the aircraft reaches this speed, it will induce wing flutter. Therefore, the higher the data, the better, indicating that the wing is less likely to flutter. Vibrate.

However, the critical speed of flutter is not calculated directly. Instead, the Vg diagram and Vf diagram must be drawn based on the calculation results before making a judgment.

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

……

A few minutes later.

"Teacher Du, junior brother, we've figured it out."

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

"When considering nonlinear geometric factors, the critical speed of flutter is 157m/s, which is 10m/s higher than the data speculated by the British expert, but..."

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

"British expert?"

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

Speaking of which, although he had solved the entire problem, because he had been working since early in the morning, he was only focused on the technical issues related to the project and had no idea about the ins and outs of the project itself.

In his previous life, Chang Haonan spent the entire first semester of his senior year preparing for the postgraduate entrance examination because he missed the postgraduate entrance examination. His graduation project was also done with an unknown young teacher, so he missed the opportunity to participate.

These experiences related to flutter analysis were accumulated when he later participated in a certain long-endurance UAV project.

"Oh, junior brother, it's only your first day in the group, so you probably don't know these things yet..."

Finally, Fang Zhen gave a brief introduction to the project.

Since this is the first time that China has designed an aircraft in full reference to international standards, and directly used many subsystems from European and American companies, Institute 603 has invited many foreign experts in related fields as consultants, including an aeroelasticity expert. Analyzed by Englishman Hogent.

When designing new passenger aircraft, the 603 Research Institute referred to the experience of the Y7-100 aircraft and designed the wing that Chang Haonan and the others are currently analyzing.

However, during the feasibility evaluation process, this wing design with advanced concepts and excellent performance was rejected by Hogent, because based on his own experience, he calculated that the critical flutter speed of this wing is only 147m/s, which is 530km. /h.

For an aircraft with a maximum cruising speed of 510km/h, this is almost equivalent to leaving no safety margin. A slight dive of the aircraft may induce flutter.

Considering that China Aviation Industry has almost zero experience in this area, the first model to connect with the international market must naturally focus on safety.

Therefore, the 01 aircraft currently undergoing airworthiness testing is still equipped with a set of relatively conservatively designed wings to ensure safety.

但603所的设计人员却并不甘心，因为按照目前的设计，运7-200A面对ATR42/72等同级别的螺旋桨支线客机根本没有任何优势。

With the same performance, why would others abandon mature aircraft to buy your new model?

The only way is to go the cheap route.

However, the cheap route means low profit margins, and low profit margins will lead to a lack of funds for subsequent upgrades of the aircraft. In the end, it will be slow step by step, and it will be left behind by those foreign peers.

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

Only then did I find Du Yishan's research team with the last glimmer of hope.

"So that's it."

After hearing the whole story, Chang Haonan suddenly realized that in later generations, he really didn't know that such a story existed.

"I heard from people at the 603 Institute that if this wing can be replaced, it can achieve a drag reduction effect of about 5%. Combined with the reduced weight, the overall fuel consumption can be reduced by almost 8%. For airlines, This is already a huge attraction.”

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

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

China's current national standard CCAR25 requires that at least 15% of the flutter critical speed be retained.

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

"Although this wing was ultimately proven not to meet the requirements, your method of analyzing nonlinear flutter should still be fine. When the time comes, we will find opportunities to verify it on other models, and we will definitely get good results. "

"and many more……"

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...

"Brothers and sisters, don't worry, there is still room for saving this wing."

Yao Mengna and Fang Zhen looked at Chang Haonan instantly.