Legendary Captain

Chapter 304 The Doomsday of Variable-Sweep Wings (Please Subscribe!)

"Doesn't this aircraft use an APU to start its engines?" Xu Xian remembered that many fighter jets still use APUs to help them start. Why doesn't the C-16 need one?

"APU? You mean auxiliary power unit? This aircraft doesn't have that. The CA18 fighter jet does use an APU for starting up, and the engine starting mechanism of that fighter jet is quite similar to that of your passenger plane." Ye Qing was very knowledgeable about the various types of fighter jets.

"CA18? There's an extra letter?" Xu Xian noticed that the current aircraft model was C16, while the fighter jet model Ye Qing had just mentioned was CA18, with an extra "A" in the model prefix.

"Oh, you mean this!" Ye Qing laughed. "The CA18 is also called the C/A18. To be precise, this fighter jet is not a simple fighter jet, but a fighter-attack aircraft, which also has some attack capabilities. However, we usually just call it C18, so it's not that accurate."

"Oh, oh!" Xu Xian nodded, feeling he had learned something new.

"Oh, what?! Here's the jet fuel starter switch I showed you earlier. Switch it to start mode, let's get started," Ye Qing urged. Time was of the essence, there was no time to dawdle. If they could figure out some of the ground start-up procedures within these two hours, then the trip would have been worthwhile.

Xu Xian wasn't the type to be coy. He located the jet fuel starter switch, paused for a moment, and then switched it to the start position.

At this moment, the plane began to emit a series of low rumbling sounds, as if a sleeping giant was gradually opening its sleepy eyes, and the energy accumulated within seemed about to burst forth.

"At this point, observe the engine tachometer. When the speed reaches 20%, turn the accelerator to idle. The accelerator is on your left, do you see it?" Ye Qing said to Xu Xian.

Inside this small cockpit, there are only two obvious levers: a control lever and a throttle lever. One is in the middle, and the other is on the left, making them easy to distinguish.

The starting mode of the jet fuel starter switch is somewhat similar to the function of the starter motor on a passenger plane. It first drives the engine to start running at a low speed. When the speed reaches a certain value, fuel is injected. Putting the throttle to the idle position will start the injection process.

The "idle speed position" mentioned by Ye Qing and the "slow speed position" that Xu Xian is more accustomed to using actually mean the same thing; they are just different in terms of personal preference.

As mentioned earlier, the throttle is divided into slow, medium, maximum, and first and second acceleration gears. Slow mode is the minimum throttle setting.

Ye Qing added, "Just floor the accelerator to a slow position, absolutely do not push it any higher. If you do, we'll both be in serious trouble."

When the maintenance crew agreed to Ye Qing's engine starting requirements, they specifically mentioned that the throttle must be limited to the idle position. This is because it's a hangar, not a test run area. If it were a test run area, the thrust limitation wouldn't be as significant.

Although Luohang Industrial's flight base is not officially part of the military establishment, it's not far off. In the military, discipline is paramount; if the rules are broken, problems will arise.

"I know, I can tell the difference between what's important and what's not." Xu Xian wasn't looking for trouble. He kept an eye on the row of mechanical gauges on the right side of the front, including the engine tachometer. Once the tachometer reading reached 20%, Xu Xian set the throttle to the slow position and started supplying fuel to the engine ignition.

At this moment, the engine speed continued to increase, and Ye Qing's reminder voice sounded: "When the speed reaches 60%, check the fuel flow rate to be between 700 and 1700 pounds per hour. The fuel flow meter is on the right side of the screen, see it?"

Ye Qing acted like a patient teacher this time, pointing out the location of each instrument to Xu Xian one by one.

With the screen display as a location point, Xu Xian was able to quickly find the fuel flow meter and report the value he could see at the time: "Nine hundred!"

"Then there's no problem. Now, see the row of gauges on the outside of the right-hand screen? The first one is the oil pressure gauge. The oil pressure should be greater than 15 pounds per square inch (PSI). Is that right?"

The row of gauges on the outside of the right-hand screen that Ye Qing mentioned is the same row of gauges from top to bottom that includes the engine tachometer. From top to bottom, there is the oil pressure gauge, the engine nozzle expansion status gauge, the engine tachometer, and below that, the engine turbofan inlet temperature gauge, also known as the FTIT gauge and the oil pressure A/B gauge.

After the engine has started, it is necessary to verify the values ​​of each instrument, each of which has its own limit standard.

"Yes, oil pressure 20, no problem." Xu Xian's gaze shifted downwards and fell upon a completely unfamiliar meter: "What's a NOZ POS meter?"

"The low oil pressure light illuminated when the engine oil pressure reading was below 10 pounds per square inch for more than 30 seconds. It's located on the right-eyebrow indicator light. The low pressure light will turn off once the engine oil pressure exceeds 20 pounds per square inch. The indicator lights on the right-eyebrow area display many different faults, so you need to pay close attention. As for NOZ POS, that's the engine nozzle expansion status indicator, or engine nozzle position indicator, showing the engine nozzle position," Ye Qing said. "The expansion reading should now be greater than 94%."

The engine nozzle displays NOZ, and its value is shown as a percentage.

The nozzles of fighter jet engines are not static, but rather convergent-divergent variable supersonic nozzles, also known as Laval nozzles.

It adjusts the critical cross-sectional area of ​​the nozzle based on the specific operating state of the engine and the discrete commands of the automatic regulator.

The working principle of an engine nozzle is that when the airflow velocity is below the speed of sound, the nozzle contracts to increase the airflow velocity and provide greater thrust. However, when the airflow exceeds the speed of sound, the nozzle diameter must expand to make the airflow velocity exceed the speed of sound.

Therefore, without afterburner, as thrust increases, the nozzle gradually decreases in size, reaching its smallest, conical shape at maximum throttle. Conversely, this means that at idle, the nozzle should be at its maximum expansion. If, at idle, the nozzle's expansion is less than 94%, then there is a problem with its operation.

"98%!" Xu Xian didn't really understand what these numerical limits meant. For example, what did it mean that the engine nozzle expansion needed to be greater than 94%, and why couldn't it be less than 94%?

However, beginners usually don't understand all the details at the beginning, otherwise the learning process would be very difficult.

Typically, beginners are bombarded with a large amount of knowledge, then they imitate experienced pilots, gradually understanding and integrating the knowledge they've been taught. When learning about passenger aircraft, instructors often made him memorize procedures, even though he didn't understand why they were necessary.

"After that, the engine tachometer will stabilize between 62 and 80. The engine tachometer is below the engine nozzle expansion status indicator; please verify that," Ye Qing continued.

When the engine is at idle, it will stabilize at a relatively balanced value. For example, in Xu Xianfei's 737, after starting and both engines are stable, N1 should be around 32 and N2 around 64. Therefore, for the C16 fighter jet at idle, it should stabilize between 62 and 80.

"The engine speed is 64."

Ye Qing continued, following Xu Xian's words: "Below is the engine turbofan inlet temperature gauge. It should be below 650℃. This is the engine's limit FTIT reading at idle. During engine startup, this value should not exceed 935℃, and during flight, the maximum can only be 980℃, with an error margin of plus or minus ten. Xu Xian, you must remember that the tachometer and engine turbofan inlet temperature gauge are used to indicate engine overheating and shutdown. Once the engine speed drops below idle or the engine turbofan inlet temperature gauge reading is below 1100℃ for more than two seconds, the engine light will illuminate, indicating a problem with engine operation."

Before Xu Xian could speak, Ye Qing continued to introduce the hydraulic gauge: "This is a hydraulic A/B gauge. The two pointers indicate the A system and the B system respectively. In slow mode, the value should be between 2900 and 3300 pounds per square inch. Once either value drops below 1000, the low hydraulic light will illuminate. It's the HYD PRESS light on the right eyebrow."

Ye Qing suddenly provided Xu Xian with a large amount of knowledge, and Xu Xian felt dizzy and lightheaded. He hadn't felt that kind of torment as a beginner in a long time.

"Wait a minute, wait a minute, could you give me an instruction manual first? My brain isn't a computer, it's about to crash." Xu Xian indicated that he simply couldn't absorb such a huge amount of knowledge in a short time, even if it was based on the premise of not needing to understand it: "Give me an instruction manual, I'll go back and study it myself first, I think that should be more effective."

However, Ye Qing immediately rejected Xu Xian's suggestion: "You are not yet a formal member of the Luohang Industrial fleet. The fighter jet's operating manual is a restricted document and cannot be given to you."

"Is this still a restricted document?" Although Xu Xian thought this situation was normal, upon closer examination, even if an ordinary person could get their hands on a fighter jet's operating manual, it would only be something to look at for fun. Even if they studied the operating manual thoroughly, without a fighter jet to fly, it would only remain a pipe dream.

Ye Qing was quite displeased with Xu Xian's surprised tone: "Can't an operations manual be a restricted document? Some of your airline's manuals are controlled documents. What? Are you looking down on our military aviation?"

"No, no, hahaha!" Xu Xian quickly laughed it off, then tried to settle for second best: "Then speak a little slower, and I'll write it down. Writing it down by hand shouldn't be a problem, right?"

Xu Xian thought that since you wouldn't give me the instruction manual, I'll just write down what Ye Qing just said and review it later. A bad pen is worse than a good memory.

Moreover, Xu Xian had prepared a small notebook beforehand and was about to take it out.

Seeing Xu Xian's actions from behind, Ye Qing immediately stopped him, saying, "You are still an unofficial member of Luohang Industry. All text, pictures, and video records you have made here concerning Luohang Industry must be deleted. If discovered, the consequences will be unimaginable."

This is understandable, as the Los Angeles Aerospace Industries involves many confidential matters, and it is foreseeable that informal members would face restrictions in information gathering.

However, this made Xu Xian's face darken: "You mean I can't remember it?"

"Even if you write it down, destroy it on the spot. Don't waste your time," Ye Qing said.

"What are the next steps? Could you briefly describe them?" Xu Xian wanted to know the current progress of the ground preparations for a C-16 fighter jet.

"What about the next one?" Ye Qing thought for a moment: "The next one should be the main control switch, turning on the aircraft lights and brightening the main control panel. There are also the three quick tests on the main test panel: the pitot tube heating test switch, fire/overheat detection, and fault and indicator light tests. Then, start the airborne systems, such as the modular human computer power switch (MMC) and the hardpoint system power switches (ST and STA) on the avionics panel. Next, perform INS inertial navigation system laser gyroscope calibration, switch the communication and identification (C&I) system to the UFC position, the IFF system to the normal position, test the speed brakes, fire control radar, radar altimeter, secondary engine control mode, flight control system, and digital backup system."

"Wait, wait, Master, stop reading! It's giving me a headache!" Xu Xian was so dizzy from listening that he immediately told Ye Qing to stop. If Ye Qing continued, he was about to lose his mind.

"How can there be so many?" Xu Xian was truly impressed. He thought that fighter jets were only so big, so the preparation procedures shouldn't be more complicated than those for passenger planes. However, the reality was quite different from what he had imagined.

The main difference is that, in addition to the normal aircraft systems, fighter jets also have combat systems, including features such as fire control radar, hardpoint systems, and IFF (Identification Friend or Foe) systems, which are not equipped on passenger planes.

Xu Xian scratched his head: "How long would it take a seasoned fighter pilot to complete these procedures?"

"This preparation procedure? The whole thing takes about twenty minutes. Of course, in some emergency situations, we might omit some testing to cut the time in half," Ye Qing said. "How about that? It should take about the same amount of time as preparing your passenger plane. Your passenger plane's control knobs are much more sophisticated than a fighter jet's, yet you still know how to operate a passenger plane inside and out. You're still a beginner, so of course it's difficult. But once you get used to it and understand the underlying meaning of the procedure, it won't be hard at all. As they say, 'What's easy for someone who knows how is easy for someone who doesn't!'"

"It's not difficult to become proficient," Xu Xian sighed. "But how long will it take to reach that level?"

He felt that even if he were a genius, when he could actually fly tomorrow, he would probably have to spend a lot of time on the ground, which made him feel a little regretful.

"You don't actually think that if I teach you for two hours today, you'll be able to go solo tomorrow, do you?" Ye Qing said speechlessly.

Xu Xian was a little disappointed: "Is it not going to work? When I was learning to drive a private pilot, I finished all the courses in one two-hour class and went solo the next day. Today, I reckon I can't even get the preparation done in two hours. I'm so sad."

Ye Qing's lips twitched a few times. Although he despised Xu Xian's Versailles-like behavior, he believed that Xu Xian had no reason to fool him on this matter.

"Shall we continue?" Ye Qing asked.

Xu Xian scratched his neck: "Let's continue."

Two hours flew by. When the two came down, Xu Xian felt like his head was about to explode. In those two short hours, he had been forcibly bombarded with a large amount of knowledge, and he was not allowed to take any notes. He could only rely on his brain to memorize it, which was really difficult for him.

"How much do you remember?" Ye Qing asked Xu Xian with a smile as the two walked out of the hangar.

Xu Xian said irritably, "What's the point of memorizing this? My head is spinning. I'll go back and go over it in my head myself. By the way, are there any places to stay around here? Hotels or something like that?"

Xu Xian looked around and saw how desolate the area was, and he was worried about where he would go that night.

"Stay here tonight. There's a guesthouse over here that caters to visitors. You can stay there," Ye Qing said. "Don't go out tonight unless you have something to do, to avoid getting questioned and causing a lot of trouble."

"I don't have the habit of going out for a stroll at night." After settling his accommodation, Xu Xian began to observe the planes on the tarmac. He had been in a hurry when he arrived and hadn't noticed the neatly arranged fighter jets on the tarmac.

Among the fighter jets, Xu Xian spotted one that stood out from the crowd. The wing sweep angle of this fighter jet was not straight and uniform; its outer wing was somewhat similar to a straight wing.

Xu Xian immediately became interested, grabbed Ye Qing, pointed at the fighter jet, and asked, "What kind of fighter jet is that? Is its wing sweep angle variable?"

"That's a C-14 fighter jet, a former main carrier-based aircraft, now quite rare. Its outer wings are variable, mainly to maintain maneuverability at subsonic speeds, and it has very strong firepower," Ye Qing said with a smile, as if he knew all kinds of aircraft like the back of his hand.

"Subsonic? Right, swept wings do have insufficient maneuverability at low speeds, no wonder the sweep angle of the outer wing needs to be changed." Xu Xian finally understood the working principle of this variable sweep wing.

Swept wing design is a very typical product of improving the high-speed performance of aircraft. As the saying goes, there are gains and losses. The improvement in high-speed performance often means insufficient maneuverability in low-speed environments. However, this variable sweep wing can reduce wing loading by changing the aircraft's sweep angle to achieve sufficient maneuverability in low-speed environments.

"Besides, the C16 you were just in has some connection with this C14," Ye Qing suddenly said.

Xu Xian's eyes lit up: "There's such an anecdote?"

"As you should know, the C-16 is a lower-spec version of the C-15. Actually, there were two design proposals for the lower-spec C-15 at the time. After the final selection, the C-16 design was chosen, while the rejected design was favored by the Navy. After modifications, it became the C-18, or CA-18 fighter-attack aircraft. Since the C-18 appeared, it has gradually replaced the C-14. Now, the Navy's main carrier-based aircraft is the C-18 series, and the C-14 is a thing of the past." Ye Qing said, looking at the C-14 fighter with a sigh: "It's a good aircraft, but unfortunately, the cost is too high. The wing box structure equipped with the variable-sweep wing is too complex, and the maintenance cost is also quite high. The total cost of one C-14 can be equivalent to two C-18s. Who can afford that? What a pity!"

Perhaps sensing the desolation of the C14 as it faded into the past, Xu Xian couldn't help but sigh, "I wonder if it will still have a place in the skies in the future."

(End of this chapter)