Legendary Captain

Chapter 140 The God of Encyclopedias! (Please Subscribe!)

The first co-pilot remained silent, like a wooden statue. Qin Zongyang had only asked casually, not necessarily expecting an answer. Pilots aren't gods; aerodynamic configurations are inherently complex, and not everything can be explained clearly.

However, Xu Xian had his own thoughts and, after considering it for a moment, said, "I think it's still due to the plane's wake turbulence?"

Qin Zongyang's eyes lit up: "What do you mean?"

"Master, we should all know that airplane wakes are divided into slipstream, turbulence, jet stream, and wingtip vortex," Xu Xian said.

"Uh," Qin Zongyang touched his nose. Apart from wingtip vortices, he knew nothing about slip flow, turbulence, or jet flow. He was really curious where Xu Xian got all this strange knowledge from.

Xu Xian, oblivious to Qin Zongyang's expression, continued, "Slipstream is mainly found in propeller-driven aircraft, so let's leave that aside for now! Jet streams are the high-temperature, high-speed airflow generated by jet aircraft. Since we have turbofan engines, we basically don't have similar jet streams. In comparison, the turbulence generated by the lateral flow on the wing surface and the wingtip vortices have a greater impact. However, the aircraft's wake is still mainly composed of wingtip vortices."

Xu Xian seemed to transform into an encyclopedia, beginning to meticulously analyze the principles of airplane wake turbulence.

"In terms of aerodynamic configuration, since the pressure on the lower wing is higher than that on the upper wing, this pressure difference is lift. Due to this pressure difference, an upward-moving airflow is formed at the wingtip, creating a spiral airflow extending backward and downward from the wingtip," Xu Xian explained. "The direction of the wakes on both sides is outward and upward, inward and downward, with a width approximately twice the length of a wing and a thickness about the length of a wing. Due to its width, aircraft placed in the front wake are mostly subjected to downward impact."

This explains why, when Qin Zongyang attempted to increase speed by pushing the stick at low speeds, he unexpectedly discovered that the aircraft's rate of climb was much lower than expected, as if an invisible pressure was suppressing the aircraft.

"What about the wind shear after that?" Qin Zongyang asked.

After Qin Zongyang canceled the thrust reduction to escape the low-speed area, he encountered wind shear. Qin Zongyang wanted to know if this wind shear was caused by the aircraft's wake. Although this had nothing to do with his question, he simply wanted to get to the bottom of things, seeing Xu Xian's knowledgeable demeanor.

Of course, although wind shear occurred in this incident, it did not have much impact. What really caused the incident was the inexplicable rolling torque.

However, it would be a relief if we could also explain what wind shear is all about, since Qin Zongyang doesn't know the reason either.

"As for wind shear, I still think it should be an unstable region formed after the wake of the preceding aircraft spreads out. Once it's long enough for the wake to dissipate, the following aircraft won't encounter wind shear anymore," Xu Xian said.

Xu Xian meant that the wind shear they had just encountered was only a temporary and unstable area and would not persist. Wind shear formed by natural conditions, however, can usually last much longer as long as its source remains.

"You mean wind shear isn't a weather or terrain factor?" the first co-pilot asked.

Wind shear is a major threat to flight safety. Basically, every pilot must first understand how to recover from wind shear. This is a life-saving skill and is absolutely essential.

Furthermore, it is essential to understand as much as possible the working principles of forward-looking wind shear and reactive wind shear. This is because wind shear warnings and alerts differ depending on the situation, and pilots must be prepared to respond to the meanings of different wind shear warnings or alerts.

Another point is to understand the principles behind wind shear, so that pilots can know where wind shear is most likely to occur and thus effectively avoid it.

Of course, pilots aren't professionals; a general understanding of how wind shear is generated and its prone areas is sufficient. There's really no need to delve any deeper. After all, they're not aiming to become meteorologists.

"It shouldn't be! Topographically, although Dianyungang Airport has a high altitude, there aren't any particularly prominent mountains nearby, and the water area is also quite small. Although the building density in the vicinity is higher than before, apart from the newly built Xinfeng Building located at the intersection of Runway 21, there are basically no other high-rise buildings. From a topographical perspective, Dianyungang Airport's geographical location makes it difficult for it to experience wind shear. In the 'Domestic Airport Wind Shear Analysis Report' issued by the Civil Aviation Administration of China not long ago, Dianyungang Airport ranked extremely low among all airports in terms of the frequency of wind shear under non-severe weather conditions," Xu Xian said.

It's strange, but Yunnan Airport often experiences strong winds, yet wind shear is rare, which is quite odd.

"Domestic Airport Wind Shear Analysis Report?" Qin Zongyang was utterly speechless. "What is this? What kind of stuff do you read all day?"

Xu Xian: "Since you've decided to make a living this way, isn't it normal to study this kind of material a bit more?"

"But is it necessary to write all of this down?" Xia Qing asked.

She reads all sorts of books in her spare time, but reading them is one thing, and being able to accurately remember them is another.

Xu Xian laughed and said, "I'll probably remember some of it! But there will definitely be some slight discrepancies!"

"You call this 'remembering roughly'?" Qin Zongyang sighed. Xu Xian's brain circuits seemed to be somewhat different from his. His understanding of the word "roughly" also seemed to be slightly off.

"Fine, you can continue!" Qin Zongyang didn't want to feel intellectually suppressed anymore.

Xu Xian didn't dwell on his memory problem: "The terrain has little impact, so let's talk about meteorological factors. There was no severe convective weather just now, meaning there was no strong downdraft area of ​​thunderstorm clouds, nor a leading edge gust front of cumulonimbus clouds. Also, regarding frontal weather, there were no reports of cold fronts, warm fronts, or occluded fronts on the meteorological map, so they can basically be ruled out. In fact, radiation inversion type low-level jet stream weather is more consistent with the situation just now."

"Didn't you just say that wind shear is caused by wake dispersion and has nothing to do with natural factors? How come you're saying that radiation inversion-type low-level jet stream weather fits the description?" the first co-pilot said.

Qin Zongyang clicked his tongue: "You're just spouting nonsense when you have nothing to say!" Then, he turned to Xu Xian: "Tell me about the winter conditions and the calm winds on the ground?"

"That's right, radiation inversion layers are common in winter, and the wind speed in the lower layers is relatively low. In fact, near-shore areas may even experience calm winds due to topographic friction. In this situation, although the surface wind is calm, momentum accumulates in the upper layers, resulting in extremely high wind speeds. When crossing the boundary, wind shear is very likely to occur. It's very similar to the situation we just discussed!" Xu Xian explained.

"Then how were you able to rule out this factor?" Qin Zongyang asked.

Xu Xian paused for a moment, as if to stop speaking, before saying, "Firstly, although radiation inversions are common in winter, they actually strengthen at night and gradually disappear during the day. Our takeoff time is already in the afternoon, so logically, even if there was an inversion, it should have dissipated by now. Secondly, I don't think last night's weather was ideal for the formation of a radiation inversion."

"Last night, during pre-flight preparations, I checked the METAR report. Although we reported calm winds at takeoff, last night it was definitely a windy night. The report also indicated a cloudy sky, not a cloudless one," Xu Xian said. "Radiation inversions are formed by strong effective ground radiation. The air layer close to the ground is rapidly cooled, while the slightly higher air layers further away are less affected, resulting in the abnormal phenomenon of higher temperatures at the top and lower temperatures at the bottom. Therefore, the key to the formation of a radiation inversion lies in effective radiation and ground cooling."

"The presence of clouds weakens ground radiation, thus preventing the ground from cooling. Strong winds, on the other hand, enhance convection between vertical air layers, making it difficult for temperature separation to occur. Of course, windless conditions are also undesirable; without adequate wind, it's difficult for the cooling effect to spread to higher levels, which would compress the inversion layer to a negligible thickness. Therefore, cloudless and calm weather conditions are ideal for the formation of a radiation inversion layer, and last night's weather did not meet this requirement."

Xu Xian's series of analyses left Qin Zongyang speechless. He felt that his young apprentice was not a pilot, but a professional meteorologist.

Xia Qing chuckled and said, "Why do you seem more like a scholar?"

Being a pilot is a profession that emphasizes technique rather than theoretical analysis. Many pilots know this and how to handle things, but they don't understand the underlying principles.

This might seem like knowing the "how" but not the "why," but being able to do this already makes you a pretty good pilot. Not everyone is like Xu Xian.

"Scholar? That sounds much more high-end!" Xu Xian laughed.

"What exactly is the cause of the rolling torque?" Qin Zongyang asked.

Now let's get down to business!

"The wingtip vortices of an aircraft are all directed upwards on the outside and downwards on the inside. Due to the width of the wake of the aircraft in front, the aircraft behind is mostly only affected by the two downward airflows on the inside. However, for some reason, perhaps we deviated slightly from our flight path, or perhaps the inner vortex tightened due to a turn, but in any case, we left the centerline of the wake and were probably veering to the right. This caused our aircraft's right wing to catch the upward vortex from the outer right side of the aircraft in front, while our left wing encountered the downward vortex from the inner left side. With the left wing pointing downwards and the right wing pointing upwards, isn't that a left roll?" Xu Xian said.

Qin Zongyang clicked his tongue in amazement; Xu Xian had indeed explained it all. However, he still had some questions: "Then why wasn't the rolling torque large at first, but suddenly increased later?"

"Because of the altitude!" Xu Xiandao said.

"Altitude?" Qin Zongyang was confused.

Xu Xian: "Because the Airbus A380 has a much larger takeoff weight, its initial climb rate is not as high as our 737's. In other words, our climb trajectory should actually be higher than that of the Airbus A380. As a result, the wake turbulence we initially experienced was not very strong. This is why we only encountered turbulence in the initial stage. However, even though the impact of the wake turbulence was less, the overall climb rate was still suppressed by the downdraft. This caused our climb trajectory, which was originally higher than that of the Airbus A380, to gradually overlap with it, and the impact gradually increased. Then, as we went deeper into the wake turbulence, the turbulence intensified into wind shear. It's possible that the aircraft's trajectory underwent an unpredictable change during the wind shear, or some other unknown reason, but the aircraft changed from being solely affected by the downdraft to being affected by airflow from different directions on both wings, resulting in a left roll moment. At the same time, as our climb trajectory further overlapped with that of the Airbus A380, the roll moment further increased. This is why the roll moment kept increasing."

"Is there a problem with the bureau's documents?" the first co-pilot asked.

To be honest, the control measures were already implemented according to the standard intervals, yet they still experienced such strong wake turbulence. Doesn't that mean there's a problem with the intervals set by the authorities?

"Actually, it can't be said that the bureau's regulations are problematic!" Xu Xian corrected. "This situation can only be attributed to a combination of coincidences."

"After the Airbus A380 was launched, it was soon found to have excessive wake vortex issues because it continued to use the mature winglets from the previous models. Following that, the Airbus A380 PLUS was introduced. In addition to the redesigned cabin and the addition of seats, the biggest change was the modification of the winglets. The winglets of the Airbus A380 PLUS are larger, which can more effectively reduce wingtip vortices," Xu Xian said.

First officer: "You mean that Airbus A380 we just flew on was the initial model? You could even tell that?"

"All the improved Airbus A380s have the A380PLUS markings on the winglets, but the aircraft we just saw didn't. This is one of the few unmodified initial models. The winglets on the Airbus A380PLUS are not replaceable parts, meaning that the initial model Airbus A380 cannot be technically modified to have new winglets. This makes the wake of the initial model Airbus A380 much larger than that of the improved Airbus A380. At the time, only ten initial model Airbus A380s were delivered, and none of them involved domestic companies. I don't know if the Civil Aviation Administration of China (CAAC) considered that the very small number of initial model Airbus A380s rarely operated in China, so they didn't set a relatively conservative spacing standard. The spacing regulations issued by the CAAC seem to be based on the wake intensity of the Airbus A380PLUS. However, given the conservative style of the domestic CAAC, this should just be an accident. The stronger wake of the initial model and the lack of wind made it difficult for the wake to disperse, and the combination of these two factors led to today's situation," Xu Xian analyzed.

"Where did you hear about that Airbus A380PLUS thing?" Qin Zongyang asked.

Xu Xian: "I once flew on an Airbus A380PLUS abroad, and the magazines on the plane contained a detailed introduction to the Airbus A380PLUS by Airbus."

"So, you wrote it down?" Xia Qing asked.

Xu Xian nodded: "I've remembered most of it, but not all of it; I've forgotten some of it."

"Forgot something?" Qin Zongyang's lips twitched. Just today, he felt that he had been intellectually and completely outmatched by Xu Xian, and that his decades-long flying career had been wasted.

In comparison, Xia Qing felt that Xu Xian possessed a unique charm. There was no way around it; the distinctive aura Xu Xian had just exuded was simply too strong.

Qin Zongyang suddenly asked, "I'm saying, with that brain of yours, what can't you do? Isn't it a waste to be a pilot?"

The development of A380 was slightly modified due to the needs of the plot, so there's no need to worry too much about it.

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(End of this chapter)