Why do we need to build C919 when we have Yun 20?

Finally, the domestic large aircraft C919 successfully made its first flight!

But the first flight is just the beginning. The so-called first flight is the first test flight, followed by the second, third and even the Nth test flight. Few people know that in the next In the next test flight, the large aircraft will face many more difficult challenges.

Today I push an old article, which records in detail the story of the ARJ21, also a domestically produced aircraft, and the details of the various test flights it went through after its first flight, "Tried the Danger." These experiences are likely to be carried out on the C919 in the future.

There is a high mountain 10 kilometers directly ahead, but the plane is still moving at a speed of 450 kilometers per hour. If it does not change its direction, it will only take 1 minute and 20 seconds for the plane to hit the mountain and be destroyed. People die.

The alarm sounded, 10 seconds, 9 seconds, 8 seconds... "Pull up! Pull out!" This behemoth made of steel suddenly raised its head and climbed steeply. In the last few seconds, the plane almost It passed the top of the mountain, and the closest distance to the mountain was only 30 meters. For an aircraft with a wingspan of less than 30 meters, this had reached its limit.

What a false alarm!

From the outside, this aircraft is no different from an ordinary passenger aircraft, but the test cabinet in the cabin still reveals that this is a prototype aircraft for test flights - China's first aircraft with independent intellectual property rights The civil regional passenger aircraft ARJ21 (the ARJ21 was tested first, followed by today’s large aircraft C919, editor’s note on May 5, 2017), and the only people on board were the test crew. The scene just now was them conducting a verification test flight of the terrain warning system.

Many people are familiar with test pilots, but the flight test engineers who stand behind them and silently direct experimental tasks and bear all potential risks alongside them rarely come into the public eye. Recently (someday in 2013, editor's note), a reporter from China Youth Daily visited the COMAC flight test center team stationed in the aviation city of Yanliang, Shaanxi Province, to experience this group and their work process up close.

Come on an unpredictable and risky journey

Exploring the most dangerous points in flight is an important task for these flight test engineers. Stall, 27-knot positive crosswind, engine shutdown, rudder jam, etc. These are dangers that people usually sound terrifying, as well as those small-probability events that only occur once in tens of thousands of flight hours in aviation history, but they are often encountered. faced and dealt with.

The first time Liu Lisu felt the nose of the aircraft "dropping", his face turned pale with fright, even though the flight test engineer had passed numerous "psychological tests" before.

Even if an ordinary civil aviation aircraft is close to stalling, if an alarm is heard, "the crew will be fined." But what Liu Lisu and his partner Zhang Dawei have to do is to turn off the stall protection system and let the aircraft enter. A natural stalling state "requires a sudden loss of lift of the aircraft." Zhang Dawei said.

To understand the stall, you must first understand "what makes the airplane float in the air." This seemingly simple question often misunderstands people. In the words of flight test engineer Wang Hucheng, "Many people think that the airplane floats in the air." It relies on the engine to fly in the air. This is only half true, because the engine only provides the forward thrust of the aircraft. "So what is the force that makes it float?

The engineering man in this team who loves animation made an interesting analogy, "The civilian aircraft we usually take is neither Tinker Bell nor Astro Boy. The former is a rotary-wing aircraft and the latter is a rocket." , are straight up and down traction and recoil forces, and the aircraft relies on lift."

Specifically, lift relies on the design of the aircraft wing itself, which causes the aircraft's wings to move up and down. The airflow velocity is different, and lift is generated through the pressure difference between the upper and lower airfoils. As the forward speed of the aircraft increases, the pressure difference between the bottom and top of the wings becomes larger and larger. When it reaches a certain level, the aircraft can be "lifted".

Just like what people usually see the pilot doing is to pull back the control stick, at this time the plane will "raise its head" and fly upward, but this is not to make the plane fly upward. The engine "sprays down" but instead increases the plane's angle of attack, increasing its lift.

However, when the elevation angle of the plane reaches a certain level, the airflow on the wing surface will separate and the plane will be bumpy. Liu Lisu on the plane felt as if "the whole plane stood up". He His back suddenly pressed against the seat.

Next, very quickly, the plane began to fall. It feels like "a person is holding you up, but suddenly, that hand is gone." If it is not corrected, it means that the aircraft will quickly enter a "spin" state from "stall" - just like a thrown paper airplane, flying in the air for a while and then spiraling downward. Viewed from above, the The tail circled back and forth, then fell freely, falling headlong until it hit the ground.

Tail spin is known as the "Valley of Death" in the field of military aircraft. Many military aircraft have fallen here and never "climbed" again.

In fact, all flight test engineers have participated in "spin" training when participating in training. Ling Ning recalled a detail. Before boarding the plane, the training teacher thrust the skydiving bag into his hand and said, "If something unexpected happens, just pull this bag." Then, "the teacher left." Ling Ning held this bag in his hand. The big guy I had only seen on TV was at a loss.

"You didn't even tell me where to pull, it was just for psychological comfort!" Ling Ning said.

However, civilian aircraft that are several times larger in size will not suffer this kind of "foolish luck", because once they fall in, they cannot "correct" them out. Therefore, every entry for test pilots is a very "psychologically stressful" challenge.

Although Liu Lisu once did a test flight in which he pulled up an airplane more than 20 meters above the ground, the danger level was that "in two or three seconds, the airplane will hit the ground." He still thinks stalling is more dangerous in comparison!

Today, he is the newest "stall brother" in the team because he "flew more than 120 stalls in one day". In Zhang Dawei's words, "Always looking down, looking up, looking down, looking up." ...It’s equivalent to riding a roller coaster more than 120 times a day, and you can imagine how uncomfortable it is.”

Experience the dangers

When Liu Lisu suffered from “bumps” in the sky. At the same time, Yin Xiangtao was experiencing a high-risk maneuver on the ground similar to "taking off with the tail of the aircraft." This flight test engineer, who had the longest boarding flight time in the entire team, only said one sentence when facing reporters. : "A little scared, maybe."

According to industry statistics, more than 90% of major flight accidents occur during takeoff or landing. A "McDonnell Douglas-82" passenger plane of Indonesian Lion Air overran the runway when landing at Solo Airport in Central Java Province, Indonesia, causing nearly 100 casualties.

No one dares to imagine what will happen if the ARJ21 in front of us, which can weigh up to 40 tons with nearly a hundred passengers, loses control of the brakes.

What Yin Xiangtao has to do is to minimize this possibility and verify that the aircraft is "still safe" in the most dangerous situation.

The reason why the tail of the aircraft is scraped to take off is to determine the minimum speed of the aircraft from the ground. From the outside, the plane is in a reclined position. To put it bluntly, it looks like most of the "butt" of the plane is rubbing on the ground. They added a "tail skid system" and a special metal material to the tail end of the aircraft. During the test flight, once the tail of the aircraft touches the ground, the sensor will immediately send a signal to the cockpit to remind the test pilot to pay attention.

After the plane started taxiing, sparks flew from the tail, and a thick layer of the steel plate more than 20 centimeters thick was scraped off. At this time, Yin Xiangtao in the cabin was still joking with the test pilot: " Dude, is your butt hot?"

People have never thought that the fuel tank on an airplane can be "exploded" by the sun? It wasn't until a TWA Boeing 747 exploded over Long Island, New York, in July 1996, killing 230 people, that people gradually became aware of this problem. From then on, any new passenger aircraft test flight must complete the hot climate fuel test flight.

Of course, ARJ21 is no exception.

Before taking off, what Wang Hucheng had to do was to "heat the oil in the tank" to 54.5°C, which was slightly higher than the scheduled 54°C to ensure that the temperature of the aviation fuel would not cool down quickly. The "flash point" of aircraft fuel is 38°C, which means that as long as an electric spark appears on the aircraft, it may cause an explosion. In addition, he had to take off immediately in this specially selected hot weather.

What still makes Luo Hailin sweat a cold sweat is the "single engine failure", that is, shutting down one of the two engines that was supposed to be turned on at the same time. Let's see how the aircraft performs under such conditions. Flight status. To put it bluntly, the purpose is to see if the plane can fly back to the airport "dragging the sick body" when encountering this unexpected situation.

The supplier provided Luo Hailin with a theoretical envelope. The speed and height within the envelope were safe. What he did was to verify its "authenticity". For example, when the aircraft flew to an altitude of 5,000 meters, a twin-engine aircraft would shut down one of the engines and then restart it to see if it could successfully restart at high altitude. If it could , which means that there is "no problem" in the theoretical range of the envelope.

The engine cannot be started under any conditions, especially at high altitudes. The higher the altitude, the thinner the oxygen, the less air the engine takes in, and the slower the turbine rotation speed. If the aircraft is below the It's just a big mountain. If the plane can't descend to "allow the engine temperature to rise or take in more air," it will most likely not start. This is similar to a car engine. For example, if it is too cold in winter, some car engines will not start.

The supplier said, "At an altitude of 5,000 meters, you can still restart the engine without lowering the altitude of the aircraft." What Luo Hailin had to do was fly to an altitude of 5,000 meters to verify that the engine was in this state. Can it be started?

To "test the dangers" for the public, there are thousands of subjects that "must be done" and thousands of test flights are required. Zhu Weidong told reporters, "The more detailed we are, the more complete the edges involved, and the safer the aircraft will be for the public during normal flight."

The choreographer behind the aerial stage play

It is easy for laymen to confuse flight test engineers with the engineers who design the aircraft and the test pilots who fly the aircraft.

Taking the former as an example, designers consider “making the system I design meet the airworthiness requirements”. Therefore, in order to achieve this goal, they pay more attention to the final data rather than the specific flight. process.

Flight test engineers not only need to obtain data to support verification, but also consider flight safety factors. After all, they themselves are "also in the sky."

Just a few days before the reporter's visit, Zhu Weidong had a disagreement with the designer during a test flight to verify the engine performance.

The designer's consideration was to let the aircraft fly levelly at a certain altitude and push the engine thrust to the maximum to verify whether it can reach a certain maximum power, but they ignored one point: " At maximum power, the aircraft is constantly accelerating, and there is a certain speed limit for aircraft flight, which is not feasible in actual operations."

Zhu Weidong gave a popular analogy: "This is like. When a car is driving on a highway, the speed limit is 120 mph. It is impossible to increase the speed from 100 mph to 200 mph all at once. You have to take your time. When the speed reaches 120 mph, you cannot accelerate any further, otherwise you will be speeding. ”

Don’t simply understand flight test engineers as engineers standing on the aircraft. During an outfield test flight to Dongying, flight test engineer Le Yafei drastically reduced the 18 task sheets to 8 sorties for execution.

Generally speaking, a task order is a sortie, and the cost of a sortie is 200,000. If measured from the perspective of cost savings, this is the value.

Le Yafei is the only female test flight engineer in this frontline team. She is responsible for the test flight of ARJ21-700 aircraft 103. This top student graduated from Fudan University has her head full of things. A series of test flight links including counter-signing of task orders, coordination of related tasks, flight monitoring, post-flight reviews, formulation of follow-up aircraft plans, preparation of sortie reports, etc.

However, it all boils down to the job of the flight test engineer, which is, in one sentence, "let the aircraft fly safely and test the certain performance it should have."

This morning, Le Yafei was wearing a blue overalls and holding a task list, ready to board the plane. This is the task list for the "mission" the afternoon before. All the test points that she and her aircraft will do today are written on this A4-sized paper. In the industry, flight test engineers refer to the standards used to test aircraft performance as "clauses" and "outlines." Simply put, when each clause on the syllabus is checked, the test flight of the aircraft can be called a qualified one. Finished.

However, the work done by the flight test engineer is more detailed, as detailed as "not only completing the task", but also clearly describing "how to complete each step of the task". Recording these details is the task list in her hand.

In fact, among international colleagues, flight test engineers are known as the soul of test flights. Test pilots perform the actions in the test flight mission list in the air, but how to do the actions and why they are done are determined by the test pilot. Engineers designed based on airworthiness clauses, aircraft body and system characteristics, and fully considered test flight safety and risk reduction factors.

In the United States, half of the test pilots are selected and trained from senior test flight engineers. Because these test pilots have a solid theoretical foundation in the early stage, after receiving flight skills training, they can usually become The best test pilot ever.

“If test pilots are compared to dancers in the air, then flight test engineers are the choreographers behind this aerial stage show.” Le Yafei said. And the task list in her hand is her script.

Out of the Mojave Desert and the Ostrich City

Since 2010, COMAC has selected 34 technicians four times to participate in the one-year professional flight test engineer training , the cost per person is about 3.5 million yuan. There are two locations, one is Oudtshoorn, the ostrich capital of South Africa, and the other is Mojave Air Base in California, USA.

"Escape from Amazon", when Wang Junjie heard about this "talent plan built with heavy investment" for the first time, the name of the movie popped into his mind. When he thought of the protagonist in the movie, he was... Under the extreme weather, he could not hold back his excitement while doing special movement training on the windy and rainy playground.

When Wang Junjie actually stood at the airport more than ten kilometers away from the city of Oudtshoorn, he saw that the airport runway was full of "weird" retired aircraft such as 707, 747, F4 Phantom, etc., and those with stickers on them. When he was flying low over the lake, "drawing big circles in the sky" and other "aviation performances" he had never seen before, he discovered that everything was not far from what he had imagined.

The harsh natural environment surrounds the seemingly glamorous airport. They found the best data observation point in the wilderness 600 meters away from the runway. However, that wilderness was full of submerged trees. Knee-high bushes, no roads to drive on, no place to sit and rest, no place to shelter from the scorching sun.

In order to obtain the best data, they had to be exposed to the scorching sun of more than 40 degrees Celsius and stay on standby at the observation point for at least five or six hours every day. When they successfully completed all the test tasks, the bush that originally had no road Cong has been forced out of a path.

Soon, Wang Junjie realized that "life can be changed through this special forces-like training."

In fact, the moment these people, including Wang Junjie, became the only training targets, their careers were no longer "in line" with what they had been before.

Since then, in the Chinese aviation industry, their business position has only one name - flight test engineer.

Just like what colleagues said about Le Yafei, without this training, this girl studying aircraft design might still be like other girls in their 20s working in Shanghai. In the design laboratory, I work from 9 to 5, and after get off work, I am used to living a leisurely life of shopping, singing karaoke, and playing board games.

She chose to rush to the Mojave Aviation Base, the U.S. National Test Pilot School, 40 kilometers north of Lancaster, California.

The first level is four major exams including "physical examination", "psychological test", "foreign language" and "theoretical basis". However, passing the physical examination of spinning in circles and standing upside down does not mean that she and her teammates will be able to "escape" the discomfort caused by real high-altitude flying in the real theoretical training and practical operations in the future.

It was an airport next to the desert, and the training teachers were basically the top pilots in the United States. Naturally, they had very strict requirements for their students.

The trainees have almost no weekends. Their lives are divided into three weeks. This method of division follows the rhythm of training. These three weeks are alternating theoretical classes, examinations, flights and reports. , usually there will be three to four different courses in the first week of theoretical classes, each course is equivalent to the content of a semester in college. After the study, there will be an exam, and in the next two weeks, the learned content will be directly applied to the test flight conditions. And during the actual flight, after completing the processing and analysis of all test flight data in the third week, oral and written reports will be formed.

In Ling Ning’s description, for the whole year they lived a life of “classes at 8 a.m. every day and classes at 6 p.m.”, “classes from Monday to Thursday, exams on Fridays”, “only one class every three weeks” Take two days off to catch up with the "China College Entrance Examination" day. The course is so difficult that even test pilots "who grew up listening to the native language" find it difficult.

As one of the few students in the entire team who graduated from an aviation major, Le Yafei finally graduated with an average score of 90. But not everyone is as lucky as she is. When Ling Ning saw that the first week's learning task was a thick English textbook on aerodynamics, this boy majoring in communications who was supposed to be engaged in 3G felt "overwhelmed". He really I can’t figure out how “aerodynamics alone, such a simple four words explain how an airplane flies.”

In order to find out the parameters of a certain engine, he spent a whole night searching more than 200 pages of Google to find it. After returning to the dormitory, Ling Ning made a simple dinner and spent the rest of the time "watching PPT and reviewing" and "reading and previewing".

At the same time, at Oudtshoorn Airport, Luo Hailin and Wang Junjie, who are still quasi-flight test engineers at the moment, have just spent half a year studying the course for more than 8 months. Although these two 30-year-old The young people who have not yet arrived are "studious" and "serious" that are different from the "local idle pilots", but they still show their timidity when facing the final test.

Give you an airplane and design a test flight plan! The school brought them to Johannesburg and asked him to use the simulator to complete specific tasks, but it was not until the first night that the students drew lots to know which type of aircraft they would fly.

“Totally confused!” He still has lingering fears when he recalls it. “There is a flight manual as thick as a fist, and it needs to be compressed into an A4 paper in one day!”

During the college entrance examination presentation, the school invited all the teachers who had taught them to be judges, "You are talking about the plan at the top, and the teacher below is asking you questions like nitpicking. This expression doesn't seem right, and that one doesn't seem right." There's something wrong, I should raise my arms to demonstrate better..."

Push everyone to the front desk! Luo Hailin recalled, "This is not only to exercise your expression skills, but also to let you know that you have to take on this responsibility and stand at the front desk, just like standing on an airplane. You must have the courage to support it all!"

Make a promise with life and use youth to fight in the sky

When the reporter visited, it happened to catch up with the birthday party of the test flight engineer on the ARJ21 aircraft "flight time exceeded 1,000 hours". Ma Fei, Five test flight engineers, Zhang Dawei, Le Yafei, Ling Ning, and Yin Xiangtao, who had "over 100 personal flight hours" received their award certificates and spoke in turn.

At that time, they didn’t have any “jianghu spirit” in their bodies. Their rosy faces and big red flowers on their chests made them look like middle school students who had just received the three-good student certificate.

Just two days ago, on the bus with reporters, Ling Ning, a man in his early 30s, was still describing how he was "inspired by his father who was a mechanic to join this team." ”, and six or seven model airplanes in his room.

The reasons they gave for “choosing to enter” or “choosing to stay” were very simple: “They just like it.”

Many of Le Yafei's college classmates "switched" to work in finance in investment banks, but she was the only one who came to an aircraft company with awe of "professionalism". She thought she liked airplanes enough, but when she met these engineering men, she discovered that “she didn’t even know that the Russian ‘Electric Ray’ without horizontal and vertical tails was the legendary sixth-generation fighter. ".

“Test pilots or flight test engineers generally have no hair, or very short hair.

"This is not consistent with the image of handsome pilots that people usually see in movies and TV dramas. At the scene, reporters also saw many test pilots with less hair or even hair loss. A very important reason is that the radiation is very large. "The hair loss is severe. "The flight test engineer even had a self-deprecating metaphor: "The less hair you have, the higher your flying skills will be."

And this group of young people didn't have much "worry" when talking about this topic. It’s more of a joke or a joke.

“I dreamed yesterday that I was bald. "These words come from Lai Peijun. At Yan Liang's test flight site, he is one of the few flight test engineers who has not been on the plane. The other one is Wang Junjie.

"I know why Prince William's hair is getting better every year. Young? I fly a lot! " Wang Junjie said.

Taking advantage of this topic, several male engineering students also took the opportunity to tease Le Yafei, the only female test flight engineer on the front line, "Although I usually feel that I don't have much hair, But once a barber shop owner told me that girls don’t have the baldness gene, and I felt relieved. ”

Before Le Yafei finished speaking, the boys threw insults at her, “There will be some, there will be”, “It’s true, women are not bald from the top of the head like men.” , I started taking it off from the front." "Don't comfort yourself, I've seen women with bald heads! ”

In the year when they gradually fell in love with the position of test flight engineer, there were many unknown bitterness behind almost everyone——

A brother went out for training At that time, the child had just been born, and he said that training abroad made me miss the birth of the child, and flying in the field made me miss the growth of the child.

Another brother originally got along very well with his girlfriend. , they broke up because they stayed with Fei for too long.

There are also two "appropriate" brothers who were single, but now they have no choice but to continue this state, "It's unrealistic. It's unrealistic." I still have to go back in a year or two. Isn't it a waste of time to search here? ”

This has a lot to do with the fact that they left their hometown and were stationed abroad. As Luo Hailin said, while training abroad, the COMAC Flight Test Center was established. In September 2012, he returned to Shanghai from abroad, but After the National Day, Luo Hailin quickly came to the aviation city of Yanliang, Xi'an. "On my last 'business trip' back to Shanghai, I realized that most of the people in the Shanghai base camp didn't know me. "

"There is the runway outside, and we hear planes flying around on the test field every day. We are flight test engineers. If we are not closest to the plane, what's the point? "Zhu Weidong said.

Although they are also on the front line, Wang Junjie and Lai Peijun's work is not in the sky, but in the monitoring hall on the ground. Test flight engineers are also needed here. They have to work with the design engineers through telemetry data and monitoring software in real time. Monitor various parameters of the aircraft to ensure the safe completion of the flight test mission.

In fact, apart from 11 of them, the remaining 23 are at the Shanghai headquarters. They are not idle either, they are compiling the C919 aircraft test flight outline.

They all know in their hearts that both those who are on the front line commanding the stage and those who are still behind the scenes as directors will be affected by their " As the first generation", he became a "pioneering pioneer in hardships". This is the words of Tan Xiangsheng, deputy director of the COMAC Flight Test Center and deputy captain of the Xi'an field test team.

There is no one in COMAC. Before the establishment of the company, this middle-aged man with a technical engineering background worked in another aviation company for nearly half his life before he could produce two models. He told reporters, “After experience, I realized that working on models and test flights is not suitable for young people. It's easy, it's a matter of 'giving your youth'. ”

34 young people with an average age of only 30 years old made a “deal” with youth: On this side, it is the youth of the young people who have accumulated 3823 hours of flying, and on the other side, it is the ARJ21 that has obtained 13 customers. 252 confirmed and intended orders, and the C919 has also received 400 orders from 16 domestic and foreign users.

“Make a promise with life and use your youth to fight for the sky. "Ma Fei said.

The text is comprehensively reported by China Youth Daily·China Youth Online, author: Qiu Chenhui. Pictures come from CCTV and COMAC Flight Test Center. WeChat editor: Qiu Chenhui.