"Director Liu, there is no problem here, it is not reflected on the black box, it should be normal, the helicopter's propeller hub may not be lubricated properly when taking off......" Liao Zhuojing said with a frown.

During the helicopter test flight, this slight small shock is normal.

They let the Z-7 fly for a short time, and they also let the Z-7 produce several prototypes for test flights.

"Yes, Director Liu, when I flew Zhi-7 in the past, I encountered a lot of this situation, and there was no problem." Huang Pingyang also frowned and said.

In the past, everyone discussed it together, and the plane also flew in the sky under the attention of many people, otherwise, it would not be enough to let the test pilot have many lives.

"Is there a problem, let's not talk about it for the time being, tell me, how many times did you encounter this slight vibration during the test flight?" Liu Yijiu shook his head, he wasn't sure, but he couldn't let go of any details.

Especially now when you can't find the problem.

In the past, Liao Zhuojing's team was engaged in a single rotor, but now they are engaged in double suspense, the helicopter is empty, and it fell off without loading anything, obviously, this situation is abnormal.

Moreover, this kind of vibration has already flown dozens of meters away before it appears, not at the beginning when it has just taken off, so it is even more prominent.

Whether it was caused by this small shock, Liu Yijiu didn't dare to guarantee, but he couldn't rule it out like others.

He is not an expert in helicopters, but only through his understanding of the structure of various old-fashioned equipment did he make Liao Zhuojing become the chief engineer without blushing. He became the chief designer himself. It is precisely for this reason that the helicopter is able to make its first flight now.

The time is too short. They didn't even notify the bigwigs above, and only after the first flight was successful would they report the test arrangements and progress of the project.

"About seven or eight seconds. I thought the propeller had fallen, but the sound of the propeller was still roaring, and the joystick was also very flexible, and the indicator light did not flicker without any flickering...... "Huang Pingyang said here with a depressed face.

It took so long to test fly and this was the first time it was encountered.

The Z-91 is much larger than the Z-7, and the helicopter maneuvers much better than the Z-7. Thanks to the extensive use of hydraulics, the operation is very light and flexible.

But it was not expected that the plane would fall without warning.

"How did you feel the plane falling? Didn't there be any vibration at all before it fell? "If the engine stops and the propeller stops, it can't stop completely in a matter of seconds.

"There was no vibration, the plane was falling, and I could feel it completely. Flying at level is different from descending. I didn't operate the descent at all......" Huang Pingyang replied helplessly.

He's in his forties, and this experience is still very good.

When the Z-5 sample came out, he served as a test pilot, although he did not fly a few times.

What is the situation and what is the problem that is causing it. As an experienced and excellent test pilot, it is completely possible to make an approximate judgment. They're half tech experts. If you don't know the equipment you use, you won't be able to maximize the performance of the equipment you use.

Liu Yijiu did not speak. Instead, he closed his eyes and imagined the situation when Huang Pingyang was flying.

He was not a test pilot. He couldn't and physically felt like driving, but he wanted to vomit when he sat up straight-5. All kinds of problems in the flight of the aircraft can be felt, but it is not as intuitive as the pilot.

I couldn't figure out what was going on, so I asked the managers and technicians again, and they were in the vicinity to observe, and the performance of the helicopter in the air, every movement, every second, was touching their heartbeats.

In the end, everyone told Liu Yijiu in unison that they didn't see anything abnormal.

The wreckage of the helicopter was on the ground, and perhaps it is not too appropriate to say that the wreckage was not disintegrated at all, because the plane fell from a height of more than 20 meters.

The huge body rolled over on its side on the gentle slope, like a truck after an overturn, perhaps because the forced landing was unsuccessful, after all, the whole system failed at the end.

The deformation is real in many places, even the bulletproof glass in front of the cockpit does not have any cracks. The only problem was the deformation of the tail sliver, and all the blades of the rotor were severely deformed.

Such a shape proves that the structural strength of their design is not too much of a problem.

"Have you analyzed the problem of rotor blades?" After checking the situation of the plane, Liu Yijiu asked Liao Zhuojing.

"The rotor blades were destroyed by the impact on the ground after we saw them fall......" Liao Zhuojing has always been in a bad mood.

If you can't find the problem, that's the biggest problem.

They would rather find a whole bunch of problems on this helicopter than find a problem like they are now.

"When the operating system failed, did you analyze what caused it?" Liu Yijiu continued to ask.

In that case, the operating system is clearly out of order.

The problem is that even if the operating system fails, the aircraft will have a runaway process in the air, and the pilot will be able to feel the problem. During the test flight, there were many technicians in the vicinity observing the situation.

Originally, a test flight plan was drawn up, and everything was strictly regulated for how much flight altitude and flight time it was.

The technicians who observed did not notice the problem at all.

"Remove the engine, and the hubs and propeller shafts. Other systems were carefully checked...... "Although I have searched it once, Liu Yijiu doesn't believe that he really can't find the problem."

As long as there is a problem, it can be identified.

There is no problem elsewhere, the operating system only began to fail in the process of the plane dropping, according to Liu Yijiu's memory, there is only one such situation - compressor!

It was caused by the kind of vibration reported by the test pilot.

In technical parlance, this phenomenon is called surge.

Surge is a very harmful, unstable operating condition of compressors on helicopters that supply a higher air boost ratio to the turboshaft engine.

When the compressor surges, the air flow, air pressure and speed will change suddenly, and even the air will flow backwards, which will cause serious mechanical damage to the engine, or turn off the engine combustion chamber and stop the ......

The plane falls down, and that's because the lift force is less than the gravity of the entire aircraft by the engine.

A rapid descent indicates that the lift suddenly becomes too much smaller......

The test flight of the aircraft, there is nothing on it, just the weight of the test pilot in the air, this situation occurs, it means that the rotor can not provide upward lift in an instant......

The biggest problem is the engine.

But even if there is a problem with the engine, it shouldn't go down so quickly.

This is one of the most puzzling questions.

Rao is Liu Yijiu has read countless materials and analyzed them countless times, but his head has been broken, and there is no way to figure out what is going on.

Even if the engine stops, the rotor does not stop instantaneously, but gradually decreases its speed under the drive of inertia. Unless in the process, the lift suddenly disappears.

Looking at the two sets of rotors on the plane, which had been completely deformed, Liu Yijiu frowned and became stunned.

In order to increase the stability of the helicopter and solve the problem that the Mi-24 will lose stability in the process of high-speed flight, Liu Yijiu used a coaxial twin-rotor on it, which is often referred to as a twin-rotor coaxial helicopter in the outside world, and the typical representative is the Soviet Union's Ka-26, Ka-226, Ka-50 and Ka-52.

The rotation direction of the two rotors is opposite, and their anti-torque can cancel each other, so there is no need to install a tail rotor, Liu Yijiu also added a tail rotor in order to improve maneuverability and make the helicopter more flexible. Although this kind of design is very strange for this era, Liu Yijiu understands that it takes time for some concepts to change.

He didn't want to explain, the pilot would find out during the flight.

The two sets of rotors rotate in opposite directions, while providing upward lift, which can fully allow the helicopter to have a greater take-off mass.

I kept thinking about it in my head, deducing it, simulating like a computer how the two sets of rotors would cancel out the upward lift force and keep spinning.

"Director Liu, otherwise, let's go back first, I'll let them check it again, and I won't let go of every screw......" Liao Zhuojing was really helpless.

I can't find a problem at all!

"Screws!" Hearing this, Liu Yijiu, who was in a daze, suddenly lit up his eyes.

"Have someone check it out...... No, I'll check it myself......" After Liu Yijiu finished speaking, he ran towards the helicopter that fell not far in front of him.

Above the helicopter, several crew members are preparing to disassemble the various parts of the helicopter.

Seeing Liu Yijiu running down while sliding, he fell twice in a row, and the staff who were heading to the helicopter couldn't help but hurriedly stop him.

"Look at the screws at the junction between the rotor and the propeller hub, and take ......it off," Liu Yijiu said to the personnel on the helicopter, despite the pain in his buttocks.

"What does this have to do with screws?" Liao Zhuojing smiled helplessly, he didn't understand Liu Yijiu's thinking pattern.

"It's on the screws! I'm sure the side where the screw joins the paddle is pretty badly damaged. The paddles are reversed! Liu Yijiu gritted his teeth and said.

"It's impossible, the two sets of rotors are the same...... Liao Zhuojing felt that Liu Yijiu's words didn't make the slightest sense. (To be continued.) )

PS: Now the gourd arms are weak, it is estimated that there have not been so many words for too long, and the state is not as good as before, and a recovery process is needed, so it may be so much tonight.

Brothers, go to sleep, don't wait, if you can still write a change, I'll send it tomorrow morning. Rest assured, the gourd is still in a state of madness.