Chapter 68 The courage to overthrow and start again (35)
Chang Haonan’s subconscious complaint just now naturally aroused a burst of curiosity.
"Dr. Chang has seen similar designs before?"
Someone came from the conference room and asked curiously.
"That's not true, I can only say that I have 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 is formed. ”
“But our J-8-2 has a conventional layout and a horizontal tail at the back. The advantages of this design cannot be fully utilized. Instead, the drag and dead weight are increased for no reason, and the effect is not good. It’s normal. No wonder Mr. Yang just said that the design is too complicated.”
After hearing this judgment, many people nodded in agreement.
When we cooperated with Dassault, it was in the mid-1980s. 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 the same. Blank, and by this time in 1996, everyone had some experience, so they could naturally see the problems with this plan.
Yang Fenghao stood up and came to two boxes containing information. He very 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 on the outside of the wing among the three-section slats, 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 just mentioned has not been solved."
Chang Haonan opened the thick document and saw the date of 1990 on it. It should be the improvement part that Yang Fenghata mentioned.
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 concerned about two main points: the length of the slats and the height of the slats. Location, but there is relatively little research on the "seam" that actually plays a role.
Of course, this is mainly because before the mid-1990s, there was really no condition to conduct too detailed research on complex flow fields. Everyone only knew the basic principles of slats and how they could improve low-speed maneuverability and high angle-of-attack performance. effect.
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 do this slat design!"
He closed the design document and returned it to its original position in the document box, then raised his head and looked at the person beside him Yang Fenghata:
“However, the conditions of our 601 Institute may not be enough.”
“The conditions of 601 Institute are not enough?”
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 problems in the slat design.”
Chang Haonan turned around and walked to the blackboard again The front, but this time he picked up a piece of chalk, and then turned the blackboard to the side that was not attached to anything:
"First, for multi-section airfoils with larger flap deflection angles, even if The Mach number of the flow is not high, and limited supersonic flow may occur on the upper surface of its leading edge. There is interference in the transonic zone and shock boundary layer. In other words, even if the slats will only activate at subsonic speeds, they will still Involving the most complex transonic flow field simulation ”
“The second is that the wake of the upstream wing section is often mixed with the boundary layer on the surface of the downstream wing section, and the resulting shear layer is a mixed boundary layer, without. Ready-made empirical formulas are available ”
"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."
Chang Haonan drew a classic three-section wing model of leading edge-main wing-trailing edge. Then start labeling 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, which we couldn't figure out when summing up our experience and lessons at that time."
Yang Fenghao was filled with emotions. He nodded. 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 most critical issues in the entire design in such a short period of time. 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 flaps, it may not be enough to just improve the former."
Chang Haonan drew a circle on the wing model he just drew. , continued:
“I plan to treat the two as a whole and conduct a more detailed integrated design, taking into account the trailing edge flap deflection angle, trailing edge flap chord length, and leading edge slat deflection. The five variables of angle, overlap amount, and slot width have completely overturned the entire plan.”
“In addition, after the design is completed, I am also planning to consider adding the trailing edge of the leading edge slat. A set of parallel leaf shanks serve as flow deflectors, directing the energy of the incoming flow near the airfoil of the wing, increasing the resistance to separation of the wall boundary layer and further inhibiting the occurrence of stalling. ”
“But this is the case. First of all, it is necessary to solve the Reynolds average N-S 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 the research institute can come forward. Apply to use 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 old.
It’s not because of the physical function, but...
The vigor that he had when he was young is missing.
According to his idea, since the No. 10 and No. 11 projects are already advancing rapidly, it is enough for the J-8-3 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 this aircraft in all aspects, which is essentially obsolete before it enters service.
To this end, no effort has been made to extensively change 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.
Behind this lies countless workloads, risks and responsibilities.
Yang Fenghata doesn’t like risks.
But this time, he was somewhat persuaded.
Besides, 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?"
(End of this chapter)