Back in 1978, I was admitted to Northwestern Polytechnical University.

Chapter 510 discusses the next generation of fighter jets.

The knock engine was indeed something Qin Liang used to fool the Americans when they first came over.

Over the years, the engine department has been developing this thing and it has been progressing smoothly. They already have engines for missiles, which Qin Liang knows. However, he has absolutely no idea that they already have engines for aircraft!

These two are not in the same league.

The thrust used in missiles is very small, only twenty or thirty kilonewtons is considered good, while the thrust required for fighter jet engines is over one hundred kilonewtons!
The combustion characteristics of a small engine are different from those of a large engine. It's not as simple as just scaling up; the internal fluid dynamics need to be recalculated and wind tunnel tests need to be conducted again.

Does our side still possess this technology?
Seeing Qin Liang's surprised look, Yang Wei introduced the situation again.

"After years of exploration, our engine system has shifted from detonation engine technology to stationary tilt detonation engine technology, which should be the most perfect technology for detonation engines."

When we first started researching, we focused on the technology of pulse detonation engines. The structure is very simple: a single-tube detonation combustion chamber with a narrow air intake. After the air and fuel mix, they undergo explosive combustion. As the shock wave propagates, it deflects the air intake, drawing in more air for re-ignition.

Such an engine will inevitably not be very powerful, since the front air intake must be very small. Therefore, to increase power, multi-pipe engine technology will be used. In order to be used at low speeds, it will be combined with a turbo engine to become a PDTE, which is a turbo-knock hybrid engine.

Northwestern Polytechnical University has conducted in-depth research on this engine. It has high technical feasibility and excellent performance. The drawback is that it needs to be ignited every time there is a knock.

Therefore, the rotary detonation engine was developed.

This engine is no longer a tube; instead, it contains an annular combustion chamber. With just one ignition, after the initial detonation wave is generated, it ignites the mixed combustion gases in the adjacent chamber, which then spread rapidly throughout the combustion chamber, creating a cyclical detonation process.

Another advantage of doing this is that the detonation frequency is very high, with hundreds of hertz being the entry level, and thousands or even tens of thousands of hertz being possible.

The faster the shock wave is generated, the greater the thrust will be, and the thrust-to-weight ratio will be very high!
However, this is not the best.

Even more powerful than that is the tilt detonation engine.

Previously, they could all be called normal detonation engines, which achieved stationary combustion of the detonation wave in the combustion chamber by changing the siphon conditions, while oblique detonation engines formed oblique detonation waves by introducing oblique shock wave inlets or central cones.

It has many advantages: the length of the combustion chamber can be shortened, which means the weight of the engine can be reduced; the stationary wave generated by combustion will not be easily blown away by the intake air, which can achieve higher flight speeds...

"Currently, our engine department is designing a slant knock engine with a diameter of about one meter and a length of about four meters, with a thrust of about two hundred kilonewtons..."

Qin Liang's eyes widened: What does this mean? Even if the engine's weight is the same as the existing turbofan engine, doubling the thrust means doubling the thrust-to-weight ratio. If it's 8 now, then the tilt detonation engine will be 16!

Moreover, this engine has a simple structure and is even lighter, so its thrust-to-weight ratio is likely to exceed 20!

This engine is absolutely incredible!
"What about self-respect?"

"The weight is still uncertain. The biggest problem is that the combustion temperature of this type of tilt-knock engine is much higher. The temperature in the combustion chamber should exceed 2,200 degrees Celsius. The protective materials should ideally be able to withstand temperatures of 3,000 degrees Celsius..."

If the weight of the protective materials cannot be determined, the weight of the engine cannot be determined either, and its own weight is completely unknown.

Qin Liang stood up excitedly and paced back and forth a few steps.

"The next step is to shift high-temperature resistant materials towards ceramic materials. Moreover, this type of engine does not require rotating parts; it can simply be designed as a patch that can be attached to the inner wall of the engine!"

The earliest turbine materials used were stainless steel, and for every 100 degrees of increase in thrust, the engine's thrust would increase by 20%. Therefore, materials experts began to tirelessly research new materials.

Nickel-based materials, directional alloys, single-crystal materials, and structures have evolved from solid to hollow film cooling and then to composite hollow, with temperatures continuously increasing. After the fourth generation of engines with a thrust-to-weight ratio of 10, ceramic materials are needed to further increase the turbine inlet temperature!
“Okay, then we’ll notify the Materials Science and Engineering Department to follow your route.” Yang Wei nodded.

Qin Liang decides what materials to use for the engine. He gives the direction, and we focus on research and development, which will make progress very quickly!
"By the way, what fuel will we use?" Qin Liang asked.

"We used liquid hydrogen in the design process before, but in order to make the engine more practical, our engine department is already developing one that uses aviation kerosene. This may result in lower combustion efficiency, but it is more practical."

Early knock engines used liquid hydrogen as fuel, which was inconvenient to use. Besides the problem of hydrogen embrittlement, it also required cryogenic storage. In contrast, aviation kerosene can be stored and transported normally, making it easier to use.

Its calorific value and other properties are certainly not as high as those of liquid hydrogen, but it is more convenient.

Qin Liang nodded: "Not bad, not bad!"

“Principal Qin, now that the engine problem is solved, the speed of our next generation of aircraft can be greatly improved. The faster the aircraft goes, the higher the friction temperature will be. Mach 2.5 is a critical threshold,” Old Song said.

Only laymen would boast about someone designing an airplane that is incredibly fast.

In fact, conventional fighter jets are around Mach 2. Even with an incredible engine or aerodynamic design, the maximum speed of an aircraft will be limited to Mach 2.5.

When you break the sound barrier, there is a terrible obstacle waiting ahead, and after reaching Mach 2.5, you will encounter the heat barrier!

When an aircraft moves through the air, it rubs against the air. The faster the speed, the higher the temperature generated by the friction.

When the Mach number is 2, the temperature of the head can already exceed 100 degrees Celsius. When the Mach number reaches 3, the surface temperature will increase to 350 degrees Celsius. At this temperature, the aluminum alloy will have already softened.

Therefore, aircraft capable of flying at Mach 3 must use other materials. The Blackbird uses titanium alloy, and the MiG-25 uses stainless steel. In short, these materials have strong high-temperature resistance.

Of course, these statements are limited. The parts that generate a lot of heat from friction are mainly the nose, the leading edge of the wing, and other parts that directly collide with the air. These parts are made of special materials.

Military enthusiasts can rave about how the MiG-25 is made of stainless steel. In reality, stainless steel is only used in areas that require high-temperature resistance; the entire airframe is not covered in stainless steel. Where aluminum alloy is required, it is still used.

Mach 2.5 is the limit for aluminum alloys; no aircraft made of pure aluminum alloys can fly above Mach 2.5.

Now, if we use a slant detonation engine, the flight speed will definitely exceed Mach 3, or even Mach 5!

It's important to know that pulse detonation can propel an aircraft to speeds of Mach 5 or higher, while the potential of oblique detonation is Mach 15 or higher!

At such high speeds, what materials should the aircraft be made of?
"Let's go with ceramics," Qin Liang suggested.

Currently, ceramics are already used in high-temperature resistant parts such as engine nozzles, so it seems not impossible that they will be used to cover the entire fuselage next.

"Compared to metal skin, ceramic has many advantages," Qin Liang explained. "First, it has very low electromagnetic wave reflection capability, and it can be integrated with the coating."

For modern fighter jets, stealth remains the primary and most important indicator. For fighter jets with metal skin, a stealth coating must be applied to the outside. However, if the skin is not smooth, it will not work. Therefore, putty is needed to level it, and countersunk rivets are used.

It's ceramic-based and can be completely integrated.

"At the same time, ceramic-based materials are resistant to high temperatures, not to mention Mach 3, Mach 5, or even Mach 10. Moreover, ceramics are harder and have stronger protective capabilities. If the warhead of an incoming missile is not powerful enough, it may not even be able to penetrate our skin."

“That’s right, Principal Qin, you’re right, that’s one of the advantages of ceramics. But, aren’t ceramics a bit heavier?” one of the engineers present couldn’t help but ask.

"No, no, the idea that ceramics are heavy is just an illusion. The ceramic materials we are talking about are not all-ceramic, but ceramic-based materials, and their specific gravity is comparable to that of aluminum alloys."

Who says ceramics are always heavy? Ceramic-based skins aren't necessarily heavy!

Many people misuse concepts. Take phased array radar for example. Gallium nitride is already the best, and then there's silicon carbide, which is touted as even better, with a detection range of 1,000 kilometers. In reality, silicon carbide is just a substrate.

Old Song, beaming with pride, said, "Principal Qin, what you've said gives us confidence! With the aircraft skin and engine solved, we have the entire foundation for our next-generation fighter jet. All that's missing is the external structure. While the detonation engine can start from scratch, it's still..."

A ramjet engine cannot start from zero. Once it has speed, air will be forced into the intake port and the engine will continue to work. Generally speaking, the starting speed of a ramjet engine is above Mach 2.

The knock engine can start from zero, but the thrust is low at that point, so...

Qin Liang knew that Old Song was waiting here.

"Therefore, we need to use the three-print layout," Qin Liang explained.

Combining different engines together is too complicated; we might as well separate them! "Currently, our WS-15 engine is under development. This engine is already working on variable cycle technology, which can meet the conditions of Mach 2, or even below Mach 3. When the speed is higher, we will shut down the WS-15 and start our knock engine."

Three shots!

The WS-15 turbofan engine and a detonation engine were crammed into one aircraft!

The layout of this aircraft is absolutely unique in the world!
There are indeed three-engine passenger planes now, but three-engine fighters are very rare. The Soviet Yak-38 could barely be considered a three-engine configuration, with one main engine and two lift engines, but its layout was so unique that it doesn't count.

Our brand-new aircraft will be a unique three-engine fighter jet in the world!

"Principal Qin, please explain this to us in detail! Three engines, the air intake is a problem." Old Song said expectantly.

"The front still has the normal two-sided air intake layout, which can be placed under the leading edge strip, similar to our J-20. At the same time, we designed a third air intake on the fuselage. Anyway, after the detonation engine is turned on, there is no need for high-G maneuvers."

Air intake at the rear of the fuselage!

This is an air intake method that has been abandoned by aircraft designers worldwide!
The earliest air intake was in the nose, then the sides, and then the belly. The biggest drawback of the dorsal air intake is that the fuselage will block the air intake during climb.

The under-fuselage air intake is blocked during a dive, but gravity helps the aircraft accelerate during a dive, while climbing relies solely on its own power.

With the development of stealth technology, many unmanned aerial vehicles have adopted dorsal air intakes, the biggest advantage of which is high stealth capability. Especially when facing ground radar, this air intake has almost no risk of being exposed.

"Hmm, not bad, that's good!" Old Song nodded: "The three engines at the back are arranged in a straight line, which will make the fuselage more spacious, but... how should the wings be designed?"

In aircraft design, there is a very important concept called Mach angle.

Mach made significant contributions, so many things in aerodynamics are named after him.

For example, the ratio of flight speed to the speed of sound is called the Mach number, the cone of a shock wave is called the Mach cone, and the angle between this cone and the direction of the object's motion is called the Mach angle.

Mach angle is a very important concept. On an aircraft, the top of the plane and the two wingtips form an isosceles triangle, and half of the vertex angle of this triangle is the Mach angle of that aircraft model.

Take wings for example. Some people say that only swept wings can fly supersonic, but that's not necessarily true. The F-104 has straight wings, yet it can still fly supersonic because its fuselage is very long. The Mach angle formed by the wings and the nose meets the requirements for supersonic flight.

Of course, the F014's bizarre design resulted in poor flight performance, earning it the nickname "flying coffin," which is not entirely wrong.

Now... if we want our new aircraft to fly at speeds above Mach 5, then the shape design becomes crucial!

Qin Liang nodded: "Yes, it definitely can't have canards or horizontal tails, it can only use a tailless delta wing layout."

If you look at the J-36 of later generations, its aerodynamic layout is somewhat similar to that of the American space shuttle. To fly at hypersonic speeds, you have to lower the Mach angle, so you have to use this kind of wing. Of course, ours is different.

"Specifically, it belongs to the category of double-sweep delta waverider wing..."

This is a complicated matter, and it needs to be explained in detail!
So Qin Liang said, "Listen everyone, some people have already taken out their notebooks and started taking notes."

No one knew that the next generation of aircraft in the East was taking off right there at this dinner table!

Catching up is not enough, we must surpass!

Old Song's eyes shone brightly; he knew he had more work to do!

Generation after generation, over the years, we have caught up with the world's advanced levels very quickly!

The meal lasted until late at night, and they didn't go back to rest until dawn. When Qin Liang woke up, he found that even more people had arrived.

"Old Lin?"

"Well, you came over without even telling me! I only came after I heard about the report, and you were still sleeping when I got here!" Old Lin looked at Qin Liang, very dissatisfied.

"Mr. Lin, you are so busy..."

"What's there to argue about? What could be more important than our modern equipment?" Old Lin looked at Qin Liang: "Especially this fourth-generation fighter jet. This is just the beginning of our air force leading the world in equipment."

Third-generation fighter jets are already in mass production, but other countries already have them, even earlier than us. Only fourth-generation fighter jets are still lacking. We are all starting from the same point.

The Air Force certainly values ​​this equipment as well.

Hearing what Elder Lin said, Qin Liang could only nod: "Okay, okay, have you compiled the data from yesterday's gliding experiment? We should be doing gliding experiments for a while now, so Elder Lin, there's no point in you coming here."

High-speed taxiing is used to verify the rationality of the aerodynamic layout. This requires repeated taxiing and verification, which can often take several months. Now...

"Everything has been going on lately. The data analysis is complete, and it matches the design specifications perfectly. So tonight, we'll be preparing for the maiden flight."

"So fast?" Qin Liang's eyes widened.

"It's because we're using the most advanced computers. Yesterday's run data was all entered into the computer without any problems. It's exactly the same as the design specifications. Since that's the case, there's no need to do any more run experiments. It's a complete waste of time."

"Ok."

Running back and forth doesn't really make much sense. Since the data is confirmed to be the same as the theoretical value, let's fly.

The maiden flight was at night, which is quite a first!

At 8 p.m., Mr. Lin brought Qin Liang to the airport. At that time, the J-20 was already making preparations for takeoff.

The group checked again, even more carefully than before, for a full hour.

"Good, our aircraft has met the conditions for its maiden flight." Old Song finally breathed a sigh of relief.

"Lei Zi, are you ready?"

"Report, everything is ready!" Lei Qiang said. "I'm confident I can fly this plane back intact!"

"Okay, let's go!"

Lei Qiang stepped back into the cockpit, his attitude calm and his expression normal, showing no sign of tension.

Having flown so many different types of aircraft, what's there to be afraid of?

If we're talking about nervousness, the J-9's maiden flight might have made people nervous because they didn't know if the canard flight control system was perfect. But after the J-9's experience, the J-20 is already a mature product!

There's nothing to be nervous about!

With the roar of the engines filling the air, and under the watchful eyes of the crowd, Lei Qiang taxied the plane onto the runway and aligned it with the center line.

Release the brakes and coast!
The speed is getting faster and faster, lifting the front wheel, lifting the rear wheel!
The whole maneuver was completed in one smooth motion, and the plane was pulled up in less than 250 meters!
"Beautiful! This is a truly good aircraft!" Old Lin exclaimed excitedly.

"A good horse needs a good saddle. Our relevant departments are developing a new generation of long-range air-to-air missiles, which, when used in conjunction with this aircraft, will definitely play a significant role on the battlefield," Qin Liang said.

"Long-range air-to-air missile?"

"That's right, Elder Lin. This stealth aircraft is designed to hunt down high-value enemy targets, so its range must be long enough!"

(End of this chapter)