Test flight is one of the important ways of aircraft airworthiness verification.

Preventing the aircraft from stalling has always been a major technical problem in the design of civil aircraft, and it is also an important verification subject for C919 certification.

　　As the "national flight test team", the aviation industry test center is the main force to undertake the C919 stall test flight.

Let's get to know these flight test elites who have bravely braved the blue sky.

Du Yijie, flight test engineer of the C919 large passenger aircraft at the Aviation Industry Test Center:

This is the C919 aircraft in flight. Now we see these stainless steel cylinders with water in them. This is the water counterweight system, which adjusts the weight center of the aircraft.

There's an emergency exit here, and when something goes wrong with the plane, there's a small dynamite bag that will blow the door open.

This position is my job position. We can see a lot of monitoring pictures in this place, and we monitor the parameters of the aircraft in this place.

　　In this plane, which is only used for flight tests, the captain Zhao Peng and his colleagues are busy preparing for the stall test flight.

The water counterweight system, test cabinet, computer, dense test cables, several flight engineer seats, and the C919 aircraft used for the test flight are very different from the aircraft we usually fly.

　　Stall is a phenomenon in which the aircraft's angle of attack increases to a certain extent, which causes the aircraft's attitude to change rapidly, the flight altitude drops rapidly, or the aircraft vibrates excessively, and eventually causes the aircraft to lose control.

When the aircraft stalls, it will drop sharply. Within a dozen seconds, the drop height can be as little as one or two hundred meters, and as many as thousands of meters. Therefore, stalling is one of the test subjects that challenges the limit.

Zhao Peng, deputy director of the C919 large passenger aircraft test pilot of the Aviation Industry Test Flight Center:

This limit is mainly reflected in the real atmosphere. Maybe every second, if our unexpected roll and yaw occur in the early stage, if the recovery is not good, then It is easy to overload.

The aircraft body may crack, break or even disintegrate.

　　At the Aviation Industry Test Center, Captain Zhao Mingyu was called "Brother Stall" by his colleagues because he stalled the most times during the test flight of the ARJ21 aircraft; Captain Zhao Sheng was called "Brother Freeze" because he was good at flying and naturally icing.

And Zhao Peng, young test pilots call him "hexagonal warrior".

　　Zhao Peng, the "hexagonal warrior" in the eyes of my colleagues, is the chief test pilot of the ARJ21 aircraft and the test pilot of the C919 aircraft. million hours.

In 2007, Zhao Peng went to the United States for several months of study and training.

During his studies, his solid theoretical foundation and excellent driving skills attracted the attention of the head of the National Test Pilot School in the United States. Upon his recommendation, Zhao Peng became the first international test pilot in China to be recognized by the International Test Pilots Association.

　　These threads, which are attached to the wings, are one of the signals to check whether the plane has entered a stall.

They will move with the airflow. If the airflow is normal, the threads will float backwards; if the airflow is separated on the surface of the wing, the threads will fly or curl, which also means that the aircraft has entered a stall state.

Du Yijie, flight test engineer of the C919 large passenger aircraft at the Aviation Industry Test Center:

When the thread began to change, I told Zhao Yuan that the air flow was separated and the sound was very high.

After our plane stabilized, Captain Zhao Mingyu asked Zhao Yuan what Du Yijie said just now?

Zhao Yuan said that she saw that the air flow was separated, and I could feel Zhao Yuan's tone at the time. Seeing her making such a fuss, I felt that I had never seen the world.

　　Du Yijie, who "has never seen the world" in the stall test flight, graduated from Northwestern Polytechnical University with a master's degree in aeroengine in 2006. In 2013, he was sent by the Aviation Industry Test Flight Center to the French National Aeronautics and Astronautics Institute for more than one year.

Even in Europe, women who can become flight test engineers are rare.

Du Yijie, test flight engineer of C919 large passenger aircraft at the Aviation Industry Test Flight Center:

I feel very lucky, and I am very grateful that in 2019, I was 38 years old. I felt that I was very ordinary, and I was a middle-aged woman. The unit allowed me to do this things, give me credit, including the flight crew giving me this trust, giving me this kind of help.

　　The aircraft may roll after stalling. Excessive roll is very harmful to flight safety.

Therefore, a large roll test must be carried out before the stall test flight is carried out to verify the limit of the aircraft's roll recovery capability to cope with the extreme conditions that may occur in the stall test flight.

Due to design advancements, the control laws of the C919 aircraft set protections, and under normal circumstances, the roll bank will not exceed 67 degrees.

But in a stall test flight, the crew needs to explore the boundaries of the aircraft's capabilities.

　　After analysis, the engineer believes that 90 degrees is a very representative critical slope. From 60 degrees to 70 degrees and 85 degrees, Zhao Peng began to gradually approach the limit of 90 degrees roll.

Zhao Peng, deputy director of the C919 large passenger aircraft test pilot of the Aviation Industry Test Flight Center:

Only during the test flight, in order to avoid the risk of stalling, do such maneuvers do, and it is impossible for a flight to make a 90-degree plane. Passengers can't stand it either.

We did 105 degrees and felt that the plane was still controllable and knew what to expect.

　　Before the C919 stall test flight, the roll gradient of the test design was 90 degrees, and the captain Zhao Peng finally flew out of 105 degrees.

In addition to the boldness of the captain, it also shows that the stability of the C919 is indeed very good.

There are a total of four C919 aircrafts tested by the Aviation Industry Test Flight Center, and they have undertaken different test flight subjects.

By January 19 this year, the stall test flight of the first C919 aircraft was successfully completed.

However, in order to obtain airworthiness certificates and obtain operational qualifications for large aircraft, a third aircraft with a more complete structure must be used for certification test flight, and the stall test flight is the highlight of it.

This is another new challenge for the C919 test flight team.

　　The stall parachute, which is guided by the launch of a small rocket and launched from the tail of the aircraft, is standard for stall test flights according to international practice.

Zhao Peng, deputy director of the C919 large passenger plane test pilot of the Aviation Industry Test Center:

It is necessary to put an umbrella at the tail to recover the plane from the state of rapid rolling and circling descent, and then the plane exits the dive. This is also the last way to save life.

　　After the C919 aircraft entered the flight test program approved by the Civil Aviation Administration of China, a debate plagued the entire flight test team.

When flying the first aircraft, in order to test flight safety, the Aviation Industry Test Center installed a stall parachute on the aircraft.

However, the CAAC approved the test flight task to be completed with a third aircraft. Should the third aircraft be equipped with a stall parachute?

If a stall parachute is installed, the progress of the entire project may be delayed for half a year.

If it is not installed, in case of a safety accident during the test flight, who will bear the responsibility?

Zhou Zhanting, chief flight test engineer of the C919 large passenger aircraft of the Aviation Industry Test Center:

There is an airbag in front of the car, do you think it should be installed?

Some people say that I have driven a car all my life, like the airbag has never been used, what am I doing with it?

If you don't install it, in case of this accident, it will be catastrophic for the model.

　　According to the task arrangement, the bureau has approved the test flight to be completed by September 2022 at the latest.

At this time, most of the flight test subjects approved by the bureau have not yet begun to fly.

Time waits for no one, and how to make a decision tests the wisdom and responsibility of decision makers.

Zhou Zhanting, chief flight test engineer of the C919 large passenger aircraft at the Aviation Industry Test Center:

If the aircraft has some unsafe characteristics, we must record the characteristics realistically and cannot fake it.

We are responsible for data and conclusions.

to stand the test of history.

In a few decades, everyone will think you did the right thing at the time.

　　The early planned test parameters of the C919 aircraft were around 50,000, but during the test flight, this number eventually increased to more than 90,000.

After each parameter is recorded, it must be analyzed and processed to find out its law.

It is precisely because of the solid data accumulation that, after a sufficient technical analysis, the flight test team and the design team reached an agreement that the stall parachute would not be installed during the stall test flight of the third aircraft.

　　On December 24, 2021, the Civil Aviation Administration of China's stall certification test flight kicked off. By January 19, 2022, a total of 148 stalls were entered in the 25-day test flight, and the test flight results reached the airworthiness standard.

As a member of China's first International Association of Test Pilots and a pilot who has been flying Boeing and Airbus for more than ten years, Zhao Peng is full of confidence in the future of the C919 aircraft.

Zhao Peng, deputy director of the C919 large passenger aircraft test aircraft of the Aviation Industry Test Flight Center:

If you introduce an aircraft among peers, whether it is good or not, the most typical language may be wonderful aircraft, so is it wonderful?

After we have obtained the certificate, we will soon be able to go all over the world.

At that time, when pilots from all over the world were operating our C919, they also said "wonderful" from their hearts. I think real power does not need more words.