Chapter 61 Let’s take a test flight [Please read it! 】
In the front row of the conference table, Yang Fenghao and several other project team leaders gathered together to communicate quietly.
Before the August 3rd Project, the J-8B had conducted flight tests with 4 rounds of PL8 short-range air-to-air missiles.
According to the results at that time, the adverse impact of the missile on the rudder surface efficiency was within an acceptable range.
However, Aspad is a beyond-visual-range air-to-air missile with a large size and weight. This is the first time for China Aviation Industry to come into contact with design issues related to it.
As Chang Haonan said just now, aerodynamic analysis at high speed and high angle of attack is still based on experience.
Since I have never seen it before, I can’t say that I have any experience, let alone analyze it.
Similar to the situation at the time of the MA60, problems involving the rudder surface are difficult to resolve using the blow tunnel alone.
And if the flight test is carried out directly in one step according to Chang Haonan's calculation results, the risk is relatively high.
The safest way is of course to conduct a large number of test flights, starting from relatively mild flight conditions, and gradually approaching the theoretical position where the aileron reaction occurs, so as to maximize safety.
But in this case, the progress may be delayed by weeks or even months.
So several people discussed it for a while, but failed to come up with a solution that everyone thought was feasible.
In the area behind the conference room, the discussion became even more heated.
Many people even gathered around Chang Haonan, looking at the report he brought over.
In fact, what was just taken to the front and projected onto the screen through the projector was only the final conclusion he reached after highly condensing and summarizing it.
In order to reach this final conclusion, he analyzed many problems in the past day and a half, some to verify the accuracy of the algorithm, and others to provide data for the calculation of aileron efficiency.
These analyzes have no guiding significance for the already highly completed August 3rd Project, but for the designers around Chang Haonan, compared to the somewhat shocking conclusion just now, it is Content they are more familiar with has greater appeal.
“The calculation for this part is...the pressure difference between the upper and lower wings when the aileron deflects?”
A gray-haired engineer wearing thick glasses picked up a few pages of the report , after looking over it several times, he asked in a somewhat surprised tone.
“Yes, this is under the flight condition of Mach 0.6 speed and 10° angle of attack. When the ailerons are deflected up and down 3° and 5° respectively, the wingspan is 15%, 65% and 95%. Distribution of pressure difference between the upper and lower airfoils at three positions. ”
Chang Haonan raised his head and glanced at the content in the other person's hand, and smiled as if his plan had succeeded.
What the opponent was holding happened to be a wing pressure difference cloud map he made to show off his skills.
Originally, the computer output was just an ordinary line chart composed of discrete data points, but he spent about three hours plotting the data on the line chart on the cross-section of the wing.
For people who are used to seeing scatter data, seeing this kind of three-dimensional cloud image for the first time is no less shocking than the first time a human being sees a movie.
“This data is not much different from the results we obtained during previous test flights. Up and down deflection of the ailerons has the opposite effect. Downward deflection increases the lift and drag on the wing, and upward deflection reduces the wing. ”
A middle-aged female engineer nearby came over to take a look and commented: "And Dr. Chang's expression is very intuitive, especially it is easy to see the trend."
"Yes, this is also one of the advantages of our digital design and simulation." Chang Haonan nodded and replied:
"We can clearly see that the difference in lift on both sides of the wings causes the aircraft to produce Rolling motion, the different resistance of the wings on both sides will cause the aircraft to deflect and slip, and the side slip will produce a moment that offsets the aileron rolling effect, thereby reducing the aileron control efficiency.”
“When the speed and angle of attack are relatively low, mainly in the subsonic range, this drag is the main reason for weakening the aileron efficiency, but in general the impact is very small, and it can be reduced through differential ailerons. alleviate this problem.”
Chang Haonan said this, took out another page from the report in his hand and handed it over, and then continued:
"Once it enters the supersonic range, or flies at a high angle of attack, the wing will elastically deform. The torque generated will quickly increase and become the main factor affecting the efficiency of the aileron, which is what I said before."
"Look at this table, after considering the elasticity of the wing, the aileron is the main factor affecting the efficiency of the aileron. The wing should originally provide a clockwise rolling moment, but it is obvious from the calculation results that the bending moment of the left wing root is smaller than the right wing root bending moment. This shows that the aircraft in this state produces a counterclockwise roll around the roll axis. The torque of the rotation is that the aileron reaction occurs."
"..."
As Chang Haonan's explanation continued to deepen, he could even feel that the people around him were interested in digital design. Groups, and even attitudes toward digital design itself are changing at a speed visible to the naked eye.
The main reason is that the several simulation results that Chang Haonan produced in succession are consistent with the test flight results they obtained before, and the gap is not big.
This is real persuasion.
Many people still had dismissive or disdainful expressions when they first came over, but after listening to his explanation carefully, their expressions or eyes changed dramatically.
At this time, Yang Fenghata and others also ended the discussion and motioned everyone to return to their positions.
"Dr. Chang, now I really admire you."
After the crowd around Chang Haonan gradually dispersed, Lin Shikuan, who had just been squeezed outside, sat back down next to him with admiration on his face:
"The gray-haired old man just now is called Xu Jin. He I have always felt that our digital design team is a complete waste of project resources. Every time we hold such a meeting, they will target us intentionally or unintentionally. As a result, this time they only asked a question and then didn’t say a word.”
< br>“Old comrade, it’s understandable that you have concerns about new things, but as long as you can present strong enough facts, I believe anyone who pays attention to science can be convinced.”
Chang Haonan did not He raised his head and just answered while sorting out the report that was just messed up.
At this time Yang Fenghata in front of the conference room also spoke again:
"I think after the exchange and discussion just now, everyone should be able to see that the issues raised by Comrade Chang Haonan are worthy of our serious consideration, so our next focus is to verify the aileron reaction effect when bombs are loaded. "When will it appear?"
If Yang Fenghao had made such a decision twenty minutes ago, he might have encountered some objections, but after the report was circulated just now, everyone has different opinions. Chang Haonan's simulation calculation results are more or less trustworthy.
But as a result, the finalization of the design of the 83rd Project will inevitably be delayed.
However, just when everyone was worried about the progress of the project, Chang Haonan spoke again.
“I think the test flight verification work on aileron reversal can be divided into two stages. If it goes well, it should not delay too much progress.”
(End of this chapter)