The military-industrial scientific research system of the academic master.

Chapter 1329 Seeking Inspiration from Others’ Mistakes

Although it suffered a considerable impact during the disintegration and subsequent fall into the water, perhaps due to its location, the air intake fragment made of lightweight alloy did not show too much irreversible and bizarre deformation.

After scanning its appearance into the database, the technicians did not do much "rationalization" and basically restored its original appearance.

This is undoubtedly a huge benefit for subsequent analysis work——

Rational deductions certainly have sufficient theoretical basis to support them, but the problem is that the American design may not be as reasonable as imagined.

"Academician Chang, further analysis has proved that the reason why this object can float on the sea for a long time, in addition to its suitable shape, is that the interior of its wall is also designed to be a hollow structure."

Xing Muchun pointed at the 3D model of most of the air intake duct on the screen and introduced it to Chang Haonan:

"However, without further specific information, it is impossible to determine whether these spaces are used for coolant flow channels or are simply designed for weight reduction."

The latter leaned closer to the monitor and stared at the series of triangular cross-sectional shapes on the cutaway diagram for a while:

"It's unlikely to be the coolant..."

Chang Haonan shook his head:

"If the aircraft uses liquid cooling, it basically uses fuel directly as the heat exchange medium. Some water samples collected from the sea surface have been analyzed before. It is a mixture made of JP7 aviation fuel as the matrix, mixed with some flammable metals and metal oxide particles... The fluidity of the mixture itself is relatively poor. I am afraid that a special fuel circulation system is needed to maintain normal supply. It is hard to imagine that it will have to go through such a tortuous flow path again..."

This analysis was quite reasonable and well-founded. Xing Muchun did not express any objection, but only showed a slightly confused expression:

"But there is no evidence that the Americans have mastered the same plasma cooling technology as us... If no additional cooling methods are used, the aerodynamic heating of hypersonic flight alone is enough to cause the flying body to be stretched by several centimeters or even more due to thermal expansion and contraction..."

Chang Haonan was open-minded about this. After all, he only had a part of the wreckage in his hand. He couldn't focus on the technical details and had to focus on the key parts.

So just a simple answer:
"After all, the design speed of the X51A is only around Mach 6, so the aerodynamic heating is not particularly serious. If we can calculate the distribution of aerodynamic heat, we can still rely on structural design to withstand it... Anyway, don't think too much about it for now. Let the First Institute quickly manufacture a full-scale aerodynamic model according to this parameter and prepare it for the wind tunnel."

Xing Muchun immediately stood up, left the computer room and prepared to go back to the office to make a phone call.

Jiang Zonglin, who was in charge of the wind tunnel operation and had been sitting on the side without saying anything, also came over:
"There are many possibilities that may cause the test to fail. Which part do you plan to start the test from?"

Chang Haonan has already made plans for this issue in the past few days.

Therefore, I analyzed almost without thinking:

"From the flight parameters characterized by radar, the X51A maintained normal flight for about 143 seconds, reached a final speed of Mach 5.45 and maintained it for about 9 seconds, and then suddenly disintegrated almost without any signs...at least without any signs on the flight trajectory."

"This situation is unlikely to be a cumulative problem. It is more likely that the operating parameters of the scramjet engine were abnormal from the beginning. After accumulating to a critical point between Mach number 5.4 and 5.5, the working cycle was completely disrupted due to thermal congestion or sudden increase in shock wave train, which eventually induced structural damage."

"So, let's start with the gas heating and inlet overflow resistance corresponding to different characteristic Mach numbers. If this is the problem, we should be able to find the abnormality quickly..."

Jiang Zonglin stood up upon hearing this:
"Then I'll get ready right away!"

……

It should be said that Chang Haonan is quite lucky.

Although the most likely cause of the accident has been preliminarily analyzed, qualitative analysis and quantitative calculation are always two things that are completely different in difficulty.

Originally, he only planned to personally watch the entire testing process of the previous few days, so as to have a preliminary understanding of the design level of his American counterparts across the ocean, and then focus his main energy on the detailed design of the gliding waverider.

As a result, just a few starts on the first day produced a set of eye-catching data...

"Are you sure... that the airflow entering the combustion chamber can exceed the speed of sound?"

Chang Haonan looked at the work cycle curve in front of him and asked the two people beside him doubtfully.

The question was so basic that the air in the wind tunnel control room fell silent for a moment.

"Of course..." Jiang Zonglin nodded:

"It is impossible to conduct a complete wind tunnel test on a single inlet compression surface, so we connected a standard tangential cone forebody and a standard equal-area-expansion type tandem combustion chamber. Theoretically, this can meet the minimum conditions for the start-up of the scramjet engine and simulate it to a speed slightly higher than Mach 5.5 when the disintegration occurs..."

As he described, he pulled up the wind tunnel operation log from his computer:

"It can be seen that near the speed corresponding to the critical point of disintegration, the thermal congestion disappears, the intensity of the shock wave train in the isolation section decreases, and the shock wave train in front of the combustion zone moves toward the entrance of the combustion chamber. The airflow in the combustion chamber must have reached supersonic speed."

Indeed, there seems to be no problem from the operating records.

"But these phenomena only indicate that the shock wave has reached supersonic speed at its exit. Due to the influence of the failure of the boundary layer to fully adhere, the situation in the combustion chamber may not be the same..."

"..."

Chang Haonan analyzed the situation to himself. His expression first became confused, then quickly became clear. He pointed to the work cycle in the report and said:

"You see, at the critical point, the working cycle in the combustion chamber is 0-3-4*-9*. The airflow compressed by the inlet duct is first heated to congestion in the equal area section, and then maintained at Ma=1 in the expansion duct until the fuel heat is completely released and the congestion disappears. It really meets the characteristics of the supersonic mode."

"But after crossing the critical point and reaching Mach 5.5, the working cycle in the combustion chamber becomes 0-3-3'-9'-9*. Moreover, the process from 3' to 9' is still an extreme case. The actual degree of expansion cannot reach the ideal value. That is, when the area section is heated to congestion, the heat of the fuel has not yet been completely released..."

In fact, when he finished the first half of the sentence, the other two had already noticed something was wrong.

"Is this a typical subsonic expansion process?"

Xing Muchun exclaimed.

Chang Haonan was also quite surprised by this conclusion, so he did not rush to draw conclusions, but went back and checked it again.

Finally, it was confirmed that there was nothing wrong with the analysis process just now.

"So, as the speed gradually approached Mach 5.5, the X51A's scramjet engine abnormally returned to its subramjet operating state, causing circulation abnormalities, thermal congestion to reappear and eventually leading to structural problems somewhere, and eventually disintegration..."

He made a preliminary guess about the whole process.

This is certainly not the root cause of the accident, but it is very close.

"If this is the case, it can explain why the aircraft was restricted by a Mach 5.5 speed wall for such a long time under the premise that the scramjet engine started normally."

Xing Muchun's tone gradually became confused:

"But it's so strange...how could this happen?"

"This is not something that can be inferred based on the shape of the air intake duct..."

Chang Haonan gently threw the report on the table:
"It's possible that the scramjet engine took a shortcut during its design, trying to obtain the highest possible isolation section pressure ratio through the transition mode. As a result, a small error caused the cycle stability to be insufficient, and it eventually left the scramjet state. It's also possible that the engine startup speed did not reach the preset value, causing problems at the beginning of the cycle. There's also the possibility..."

Before he could say the third possibility, his voice suddenly stopped.

"It's possible...what?"

Jiang Zonglin looked over with some curiosity.

"It does not matter."

Chang Haonan pulled the report back in front of him, picked up a pen from the side, and drew a few arrows on the cycle parameter curve graph:

"It suddenly occurred to me that if we reverse this process, that is, let the engine be in subsonic cycle mode at low speeds and enter supersonic cycle mode at high speeds, can we make the ramjet engine have both subsonic and scramjet characteristics?"

(End of this chapter)