Chapter 1601: Aerodynamic Stabilization, This Time It Was Finally Used

"Academician Chang! Chief Xing!" Yin Kaixian, the head of the Data Analysis Center, stood up from the main console and walked over quickly. "I was just about to contact you, but I didn't expect you to come faster than my phone call!"

Chang Haonan just nodded and looked directly at the huge display screen in front of the main console:

"what's the result?"

In fact, when he used this wind tunnel in Fucheng, Yin Kaixian had not even joined the Aviation Industry Corporation of China.

Although we have gradually moved away from the research and development of ordinary aircraft in recent years, we still have a basic idea of how long it takes for each wind tunnel to perform what task.

"Just finished!" Yin Kaixian led the two to the main console and couldn't help but admire, "Academician Chang, President Xing, the design of this 'Zou Yu' is really...superb!"

He pointed to the frozen 3D image of the model on the screen:

"Within such a compact volume, a low-drag design is achieved over a wide speed range from subsonic to hypersonic, while also taking into account the necessary internal space capacity..."

"..."

A whole set of compliments came out of his mouth, and I could hear that there was some flattery in it, but fortunately, there was substance to what he said.

"Director Yin, let's save the nice words for the celebration banquet." Chang Haonan raised his hand and gently but directly interrupted him, "We are here to find problems, so... let's just look at the three most important parts."

As a hypersonic aircraft, "Zou Yu" does not need to maneuver in medium and low speeds like conventional aircraft.

So you only need to focus on the three key parts: take-off and landing, transonic speed and maximum speed (about Ma=1.8).

If these ranges can be passed smoothly, there will be no problems in other speed ranges.

"I understand!" Yin Kaixian immediately stopped talking and his expression became serious.

He said no more and quickly operated the console.

Soon, three sets of aerodynamic data curves and corresponding flow field cloud maps were displayed side by side on the three screens in front of him.

"Please look." Yin Kaixian pointed at the screen. "These are the core aerodynamic data of the 'Zou Yu' in the three most typical flight conditions that test the design the most: take-off/landing state (Ma<0.3), transonic state (Ma=0.8~1.3), and ramjet engine subsonic mode start critical speed state (Ma>1.7)."

Chang Haonan and Xing Muchun took a step forward at the same time and leaned closer to the screen.

Of course, Yin Kaixian couldn't just sit there and let the two of them watch it slowly, so he quickly introduced:

"As I just said, when the waverider configuration deviates from its optimal design point, the matching degree of the flow field wave system will decrease, and the aerodynamic efficiency will inevitably decay. This is the law of physics."

“However, thanks to the extremely excellent lift matching design and the highly integrated layout of the forebody, air inlet and power cabin, the overall lift and lift-to-drag ratio in the critical speed section fully meet the requirements of autonomous takeoff, level flight acceleration and reaching the critical speed!”

"Moreover," he added, pointing to a set of thrust data, "with the improved turbojet 14, the power reserve is still sufficient. It will have no problem taking off and accelerating to Mach 1.7, and there will be about 7-8% redundancy left."

Single-digit percentage power redundancy is of course totally unacceptable for ordinary aircraft.

However, because hypersonic aircraft are equipped with two power units, the theoretical redundancy within the full speed range is generally only 3%-5%.

7-8 points are the result of Chang Haonan's hard work.

Chang Haonan nodded and then turned his gaze to the middle set of transonic data, especially the curve marked "lateral net stability derivative".

His expression immediately became solemn.

"The biggest risk point appears in the transonic section."

Yin Kaixian also added at the right time:

"In order to pursue hypersonic performance, the 'Zou Yu' adopts a small aspect ratio aerodynamic component design, which is of course necessary, but it also brings a side effect, that is, the design margin of the lateral and heading stabilizer is compressed very small."

Yin Kaixian enlarged the part of the curve representing the lateral net stability derivative.

Near Ma=1, the curve drops sharply and falls into a deep valley.

"Look here," he drew a circle with his laser pointer at the glaring valley, "near this speed point, the lateral net stability derivative drops sharply, indicating that the lateral stability of the aircraft itself has become very fragile."

His tone was filled with worry:

"It is impossible for the 'Zou Yu' to install a large tail or ventral fin to provide a strong restoring torque like a traditional aircraft. In this state, any tiny disturbance - a gust of wind, a little bit of uncoordinated control input - may cause oscillation in the rolling direction."

"Once the shock spreads, it is very likely to directly enter an uncontrollable rolling state, with disastrous consequences."

Xing Muchun’s brows were tightly furrowed.

He was a rocket scientist in his early years, and later jumped directly to high-speed aviation. However, he had some blind spots when it came to the aerodynamics in the atmosphere, especially at the transonic speed.

"Director Yin," Xing Muchun asked with a questioning tone and a hint of imperceptible anxiety, "Is there any way to improve it? For example, adding some small aerodynamic control surfaces to the trailing edge of the waverider body?"

This was one of the options selected when studying a completely tailless aircraft.

Yin Kaixian shook his head: "Boss Xing, we have tried to set up spoilers or small movable rudders on the trailing edge of the model."

He called up another set of comparative data charts:

"But before entering the waveriding state, the aerodynamic focus position of the hypersonic vehicle changes greatly, and these small aerodynamic surfaces cannot have a sufficient adaptation range. For reasons of strength and resistance, it is impossible to increase the number too much."

The analysis room fell silent for a moment.

In the workshop next door, the whistling sound produced by the wind tunnel test run could be faintly heard.

The glaring downward curve on the screen is like a cold needle.

Chang Haonan was listening quietly, his eyes fixed on the curve representing lateral stability, and there was not much expression on his face.

Just when the silence was about to solidify, he spoke, his voice still calm:

"Director Yin, please retrieve the detailed data of the transonic net stability derivative in the lateral and directional range. I want to see the original data, not the processed data."

Yin Kaixian was stunned for a moment.

But it still executes immediately:

"Okay, wait a minute."

Soon, an original curve with more subtle fluctuations replaced the previous smooth version and appeared in the center of the screen.

This time we can see that the lowest point of the concave shape appears near Ma=1.03, reaching a level of around -0.003.

For an aircraft with few aerodynamic control surfaces, this level is already dangerous.

Chang Haonan took a few steps closer, almost sticking to the screen, and carefully examined the shape and depth of the valley.

"Hmm..." He pondered for a moment, pointed at the curve, and issued an order that made Yin Kaixian even more confused: "Now, superimpose an additional stable increasing function on this curve. The value... Let's use our preliminary estimate first."

After hearing the instructions, Yin Kaixian subconsciously touched the keyboard, but was immediately surprised:

"Superposition stable increasing function?"

"But... this is the original data from the wind tunnel test?"

Xing Muchun also looked at him in confusion.

Chang Haonan turned around and his eyes fell on the conspicuous air intake design on the back of the "Zou Yu" model on the screen.

"Director Yin," he did not answer directly, but instead asked a question, "Do you know why we must design the air intake of the WP-14 on the back?"

Yin Kaixian was stunned again, and answered subconsciously: "Isn't it to... ensure the integrity and smoothness of the lifting surface on the lower surface of the waverider? To avoid opening holes in key areas that affect the hypersonic flow field?"

This is the most intuitive and conventional explanation, and was also the mainstream view during their previous internal discussions.

"That makes sense, but it's not the main reason." Chang Haonan shook his head slightly and explained, "The air intake of the WP-14 will be completely closed in hypersonic flight, and it will not destroy the integrity of the lower surface of the waverider."

He paused, glanced at Yin Kaixian, who was even more confused than before, and slowly revealed the answer:

"Its most critical role is actually to provide additional aerodynamic stability in the subsonic/transonic stage."

"Aerodynamic stabilization..." Yin Kaixian muttered and then came to his senses. "Does it mean that when the engine is working, the high-speed airflow produces an ejection effect?"

"That's right." Chang Haonan affirmed Xing Muchun's supplement, "This design can provide an additional, dynamic stability enhancement in the transonic section where the lateral stability is the weakest."

He pointed to the heart-wrenching trough curve on the screen.

Yin Kaixian was no longer confused, but he was still a little worried.

"However, current wind tunnel tests can only simulate static or quasi-static airflow. For this part with local active effects (engine operation), especially its dynamic response characteristics, the accuracy of wind tunnel simulation is not enough, or the cost is too high to bear..."

"That's right." Chang Haonan nodded. "So it's just an estimate, but it's better than staring at this naked curve... This is one of the backup plans we reserved during the design stage. Let's give it a try first."

Yin Kaixian sat back in front of the main console and began typing rapidly on the keyboard.

He called up the three-dimensional model of the "Zou Yu" dorsal air inlet structure and the estimated flow and velocity data of the WP-14 at transonic speed, and combined with aerodynamic formulas, began to build a mathematical model to simulate the stabilizing torque of this "active dorsal fin" under specific flight conditions.

Then, he ordered engineers to prepare a new round of wind tunnel tests.

The so-called "superimposing an additional stable increasing function" certainly does not mean directly modifying the finished product data.

Instead, you need to do a new set by changing the additional items.

Under the command of Yin Kaixian, the wind tunnel center became busy again.

Chang Haonan and Xing Muchun stood on both sides behind him, staring at the screen.

Time passed by minute by minute.

More than an hour later, Yin Kaixian breathed a sigh of relief and pressed the Enter key: "Alright! The model is built and the stabilization function is loaded! Now recalculate the net stability derivative curve after superposition!"

At the same time, a report came from the wind tunnel workshop indicating that the equipment inspection and model fixation had been completed.

Test and start again!