After collecting the paragliders floating in the sea, the group hurriedly rowed ashore.
As soon as we landed, we saw hundreds of people standing neatly and honestly on the beach.
"What's wrong?"
Liu Jinghong jumped off the boat and asked. When he saw Li Zhen and Qi Lengzi, he quickly turned around: "Mr. Lin, are you okay? Oh, I asked you not to be impulsive. Listen to Master Li and don't take risks rashly. You are Do not listen."
Lin Xiufeng said angrily: "What do you mean I take such a risk? What kind of bullshit did you design?"
"Teacher Lin, this is wrong. You asked me to design it."
"When did I..." Lin Xiufeng said, seeing Li Zhen, he realized that Liu Jinghong was passing the blame. He jumped on the spot and said, "Get out!"
A group of people stood there in disbelief, looking at Li Zhen, whose face was as dark as water.
Li Zhen glanced at Lin Xiufeng, who was trembling constantly, and sighed: "Mr. Lin, why are you following them to join in the fun?"
Lin Xiufeng blushed and said nothing for a long time.
Li Zhen sighed helplessly, looked at the wreckage of the paraglider, and waved his hand: "Assemble in the classroom."
“…”
Everyone looked at Li Zhen as he left first, looking at each other with some doubts in their hearts.
Liu Jinghong sighed: "It's a big deal."
“…”
Along the way, Li Zhen kept thinking, it seems that it is better to clear the road than to block it.
I couldn't stop this group of people at all, just like Fuxing University couldn't stop myself.
After thinking wildly for a while, Li Zhen went back to have breakfast and came to the Kyushu Institute of Physics. In the Institute of Physics, everyone was already here. Lin Xiufeng was trembling while holding a bottle of hot soup and drinking it. It was quite cold.
"Do you know what's wrong?"
Li Zhen's first words made everyone dumbfounded.
Liu Jinghong said: "I shouldn't have ignored Master Li's advice..."
"Don't talk nonsense."
Liu Jinghong lowered his head: "I don't know."
"Bring me the drawings of the paraglider."
Someone stupidly sent the drawing over. Li Zhen looked at it twice and threw it away: "Who drew it?"
"I..." Liu Jinghong said with some shame.
Li Zhen looked at him for a while, and said to everyone's surprise: "The idea is right. The direction is wrong, and there is a problem with the design. There are too many loopholes in it. This is not how you came to paraglider."
'Wow -' The crowd started to commotion.
There's something wrong with this tone...
Everyone is getting excited. Do you want to explain the real thing
"How did that happen?"
Someone asked.
Li Zhen looked back and wrote four words on the blackboard - gravity and lift.
"I have been thinking about the phenomenon of parachutes these days, and I have come to a conclusion. It is gravity and lift. You must understand this issue first."
"First of all, there is an aerodynamic problem with parachutes. The pressure per unit area is proportional to the cube of the air flow speed. Then when a parachute is opened, its area is fixed. The falling process can be understood as The air blows upward at the speed of your descent. In other words, the wind resistance you experience during your descent can be regarded as the wind blowing upward from below. This forms lift.
The lifting force received is related to the third power of the falling speed. When you first open the parachute, the descent speed is fast at the beginning, and the lift force you receive becomes greater as the speed increases. When the lifting force is greater than the weight of the human body + the weight of the parachute, the speed will slow down until both sides reach a balance, so this is why you will suddenly be frustrated when you jump down. "
“…”
Qin Enze slammed the table suddenly, but forgot that his hand was still in plaster. Gritting his teeth in pain, he stood up and said excitedly:
"I understand. Is it because when I jumped out, the parachute had not been fully opened at that time. Then after it was fully opened, lift appeared immediately, so there was such a setback?"
"Yes, you can say that."
Li Zhen added: "There is no problem with the idea of paragliding. In terms of aerodynamics, this kind of paraglider with forward power is established."
Liu Jinghong stood up excitedly: "So, I was right. But what was wrong with me?"
"The design direction is wrong. You just thought about how to make it move forward, but you ignored that there is another very important problem here. That is lift."
"It has lift. It's as big as the umbrella I designed."
"It has nothing to do with size. The shape is wrong. You don't have enough theoretical knowledge."
Li Zhen said seriously:
"The paraglider itself can have no power, but it is theoretically true that it can fly. The reason why it fails is because your paraglider is not filled with air at all. It must be filled with air inside before it can be established. Just like It's like a parachute. When you jump down, you can try to think about which one will work, a flat parachute or a concave parachute filled with air."
Everyone pondered for a while, but still couldn't get an answer.
Li Zhen also carefully recalled the conclusions he had drawn from his own research in the past two days and said:
"My idea is this: since the paraglider will generate speed and lift when flying in the air, and its speed and lift must be far greater than its resistance. Therefore, in terms of structure, it must be inside the paraglider canopy The inner layer of the paraglider is equipped with an air bag. Before it is filled with air, the paraglider has no real edges and corners. Once the inner air bag is filled with air, the front edge of the paraglider will have edges and corners. In this way, when the paraglider flies in the air, the relative airflow will flow up and down the wing. The flow is diverted separately, the resistance is parallel to the opponent's wind force, and the weight is combined with the air above the wing, so that the paraglider can generate speed and move forward.
This has been said in fluid mechanics and combined with aerodynamics, you should understand this. "
Liu Jinghong slapped his thigh: "Oh, I know. Mine is not equipped with airbags. Although I have a double-layered one, there is no such thing as an airbag inside. It leaks air."
Li Zhen rolled his eyes at him and continued:
"I think the length of the upper and lower layers of the paraglider is different. When there is forward speed, the air flows through the upper and lower surfaces of the paraglider, and different pressure differences will be generated on the surfaces of different lengths. The side with greater pressure will push toward the side with lower pressure. . When the air flows through the convex surface of the upper layer, the pressure becomes smaller because the distance is longer and the flow speed is faster. On the contrary, the air flowing through the concave surface of the lower layer has a slower flow speed and the pressure becomes larger due to the short distance. Therefore, a lift force is generated where the air below pushes the wing surface upward. Up and down The pressure difference between layers is the total lift, which is the most basic principle of flight."
'sssssssss'
Everyone below began to take notes.
Li Zhen continued: "The phenomenon that Teacher Lin experienced today should be called stalling."
"Stalled?"
"Teacher Lin jumped off a cliff today with a paraglider on his back. The process of running up and landing is actually relative motion with the air at a certain angle of attack, which generates aerodynamic force and makes him glide in the air briefly. But he also has to control the angle of the paraglider to change direction. . Because the paraglider designed by Liu Jinghong is inherently unstable and has big problems. So when Teacher Lin flies at a certain angle of attack, the airflow flowing through the airfoil is smoothly "attached" to the upper surface. flow past.
When he further increases the angle of attack to a certain position, the airflow flowing close to the upper surface begins to separate from a certain position, thus generating an unstable vortex behind it, which causes the drag to increase rapidly and the lift to disappears, this phenomenon is called stalling. After stalling, the control will deteriorate. As the control becomes worse and worse, Liu Jinghong's paraglider has no device to limit the angle of attack, so it will fall downward faster and faster, becoming a vertical landing.
Under sea breeze conditions, the angle of attack has almost become a folded shape. So he started spinning like crazy. Eventually fell into the sea. "
“…”
Everyone was speechless after listening to this explanation.
Are there so many reasons for this
Lin Xiufeng looked at Liu Jinghong with a resentful expression.
Liu Jinghong looked at Li Zhen speechlessly: "Master Li, since you know, why didn't you tell me earlier?"
Li Zhen rolled his eyes at him and ignored him at all.
There is no way to answer the call. Because of these problems, it didn’t take long for Li Zhen himself to figure it out...
(End of chapter)