Chapter 68 The courage to overturn and start over (35)

Chang Haonan's subconscious complaint just now naturally aroused a burst of curiosity.

"Dr. Chang has seen similar designs before?"

Someone from the conference room asked curiously.

"That's not true. It can only be regarded as a certain understanding." Chang Haonan quickly went back to make up for it:

"This three-stage slat is more suitable for use on French fighter jets with a tailless delta wing layout. It works together with the two-stage elevon on the trailing edge to guide the airflow between the wing root and the vertical tail. A vortex forms.”

"But our J-8-2 has a conventional layout, and there is a horizontal tail at the back. The advantages of this design cannot be used. Instead, the drag and dead weight are increased for no reason. It is normal for the effect to be poor. No wonder Mr. Yang just said This design is too complex.”

After hearing this judgment, many people nodded in agreement.

The cooperation with Dassault was in the mid-80s. At that time, the Chinese aviation industry could only be said to have just begun to try to truly "design" rather than just imitate a fighter jet. Many things were indeed blank, and in 1996 this year At least everyone has some experience by now, and can naturally see the problems with this plan.

Yang Fenghao stood up and came to two boxes containing information. He skillfully found a relatively new design document and handed it to Chang Haonan:

"The complexity is secondary. After the French withdrew, we also tried to make some improvements. We only retained the two sections of the three-section slats on the outside of the wing, and then changed the structure to an ordinary one-section, so that the dead weight was reduced. , but the interference problem between the ailerons and flaps mentioned just now has not been solved."

Chang Haonan opened the thick document. Judging from the date of 1990 on it, it should be the improvement mentioned by Yang Fenghao.

But at this time, he had basically made a judgment about the problem.

Although the application of leading edge slats has a long history, as a relatively simple and crude lift-increasing device, aircraft designers have long been focused on two main points: the length of the slats and the position of the slats. As for that slat There is relatively little research on the "seam" that actually plays a role.

Of course, this is mainly because before the mid-90s, there was really no condition to conduct too detailed research on complex flow fields. Everyone only knew the basic principles of slats and their effects on improving low-speed maneuverability and high angle-of-attack performance.

Another half hour passed, and Chang Haonan directly skipped the calculation design part, and finally found what he wanted in the final wind tunnel test data.

"Mr. Yang, I can make this slat design!"

He closed the design document and returned it to its original position in the data box, then raised his head and looked at Yang Fenghata beside him:

"However, I'm afraid it's not enough just based on the conditions of our 601 institute."

"The conditions of 601 Institute are not good?"

Liu Ming next to him could not help but widen his eyes.

"Yes, from the design document that Mr. Yang just took out, we can summarize several major issues in the slat design."

Chang Haonan turned around and walked to the blackboard again, but this time he picked up a piece of chalk and flipped the blackboard to the side with nothing on it:

"First, for multi-segment airfoils with large flap deflection angles, even if the incoming Mach number is not high, limited supersonic flow may appear on the upper surface of the leading edge, and there will be interference in the transonic zone and shock wave boundary layer. In other words, In other words, even if the slats will only activate at subsonic speeds, it will still involve the most complex transonic flow field simulation."

"The second is that the wake of the upstream wing section often mixes with the boundary layer on the surface of the downstream wing section. The resulting shear layer is a mixed boundary layer, and there is no ready-made empirical formula to use."

"The third and most fatal thing is that when the trailing edge flap deflects, a separation bubble will form at the trailing edge of the main wing. If the leading edge slat deflects at the same time, then the mixed boundary layer and flow separation will appear at the same time, and There is interference between the two lifting devices on the leading edge and the trailing edge."

While talking, Chang Haonan drew a classic three-section wing model of leading edge-main wing-trailing edge, and then began to mark the flow conditions involved in the upper surface of the wing when the two devices work together.

"That's true. Especially the third point you mentioned, Comrade Xiao Chang, was something we couldn't figure out when summarizing our experience and lessons at that time."

Yang Fenghao nodded with emotion. On the one hand, he remembered the difficulties he encountered when designing this leading edge slat. On the other hand, he was amazed that Chang Haonan could condense the entire design in such a short period of time. The most critical question.

Being able to find the main problems in complex real-life situations is already a very rare ability.

"So, since there is interference between the slats and the flaps, it may not be enough to just improve the former."

Chang Haonan drew a circle on the wing model he just drew and continued:

“I plan to treat the two as a whole and conduct a more detailed integrated design, taking into account the following five factors: trailing edge flap deflection angle, trailing edge flap chord length, leading edge slat deflection angle, overlap amount, and slot width. A variable, and the entire plan must be completely overturned.”

"In addition, after the design is completed, I am also planning to consider adding a set of parallel blades to the trailing edge of the leading edge slat as a flow deflector to guide the energy of the incoming flow into the vicinity of the wing surface and increase the wall boundary layer. The anti-separation ability further inhibits the occurrence of stall phenomenon.”

"But in this way, we need to solve the Reynolds average NS equation through numerical methods for CFD simulation. The calculation amount is very huge. It may take a long time to get the results just relying on the few workstations in the computing center, so I hope that by research Come forward and apply for the use of the supercomputer!"

At the conference table not far away, Yang Fenghao leaned on the back of his chair and looked at Chang Haonan, who was holding chalk and high-spirited.

For the first time, he felt that he might be getting old.

It's not because of how the body functions, but...

The vigor that I had when I was young is gone.

According to his idea, since the No. 8 and No. 3 projects are already advancing rapidly, it is enough for the J-- to only be responsible for the high-altitude and high-speed interception missions it is good at.

But Chang Haonan is obviously not satisfied with this.

He hopes to optimize all aspects of this aircraft, which is essentially obsolete before it enters service.

To this end, extensive changes were made to the existing wing design.

Knock it down and start over.

For designers in any field, it is quite courageous to dare to say these four words.

There's a lot of work, risk, and responsibility behind it.

Yang Fenghata doesn't like risks.

But this time, he was somewhat persuaded.

Moreover, from the first time he heard the name Chang Haonan to now, the other party has shown miraculous abilities many times, which is also an important bargaining chip that affects Yang Fenghata's judgment.

Of course, for such a serious and influential decision, you still have to ask questions clearly first.

"So what technical approach are you going to use to complete the integrated design of this slat-flap?"