Rising: Ten Thousand Years Chapter 122: : angle of attack
After packing up the paragliders floating in the sea, the group hurriedly rowed ashore. X
As soon as I landed, I saw hundreds of people standing on the beach neatly and honestly.
"What's wrong?"
Liu Jinghong jumped off the boat and asked, saw Li Zhen and Qi Lianzi, and turned around quickly: "Mr. Lin, are you okay? Sigh, I tell you not to be impulsive, listen to Master Li and don't take risks rashly." .You just don’t listen.”
Lin Xiufeng said angrily: "What do you call me taking risks rashly? What kind of **** did you design?"
"Mr. Lin, this is wrong. You asked me to design it."
"When will I..." Lin Xiufeng said, seeing Li Zhen, realized in his heart that Liu Jinghong was throwing the blame. He kicked and collapsed on the spot: "Get out!"
A group of people stood there awkwardly, looking at Li Zhen whose face was sinking like water.
Li Zhen glanced at Lin Xiufeng who was trembling constantly, and sighed: "Old Lin, why are you following them to join in the fun?"
Lin Xiufeng blushed and remained silent for a long time.
Li Zhen sighed helplessly, glanced at the wreckage of the paraglider, and waved: "Assemble in the classroom."
“…”
Everyone watched Li Zhen leave first, looked at each other in blank dismay, and were a little uncertain.
Liu Jinghong sighed: "There is something wrong."
“…”
Along the way, Li Zhen kept thinking, it seems that it is really better to be blocked than to be sparse.
I can't stop this group of people at all, just like Fuxing University couldn't stop itself back then.
After thinking wildly for a while, Li Zhen went back to have breakfast and came to Kyushu Institute of Physics. In the physics academy, everyone had already arrived, and Lin Xiufeng was tremblingly drinking a bottle of hot soup. It was not lightly frozen.
"Do you know what's wrong?"
Li Zhen stunned everyone with his first sentence.
Liu Jinghong sighed: "I shouldn't have listened to Master Li's advice..."
"It's useless."
Liu Jinghong bowed his head: "I don't know."
"Bring me the drawing of the paraglider."
Someone sent over the blueprints, and Li Zhen took a look at them before throwing them away: "Who drew them?"
"I..." Liu Jinghong said with some shame.
Li Zhen looked at him, looked at him for a while, and said to everyone's surprise: "The thinking is correct. The direction is wrong, and there is a problem with the design. There are too many loopholes in it, and the paraglider is not how you came here."
'Wow' the crowd broke into a commotion.
This tone...is problematic.
All excited, are you going to explain the real thing?
"How did that happen?"
Someone asked a question.
Looking back, Li Zhen wrote down the four words gravity and lift on the blackboard.
"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 first understand this issue."
"First of all, there is an aerodynamic problem in the parachute. The pressure per unit area is proportional to the third power of the air flow velocity. Then when a parachute is opened, its area is fixed. During the falling process, we It can be understood as air blowing upward at the speed of your descent. That is to say, the wind resistance you encounter during your descent can be regarded as the wind blowing upward from below. This forms the lift.
The lift force received is related to the third power of the landing speed. When the parachute is first opened, the initial descent speed is fast, and the lift force received at the same speed will be greater. When the lifting force is greater than the weight of the human body + the weight of the parachute, the speed will slow down until the two sides reach a balance, so this is why when you jump down, there will be a sudden setback. "
“…”
Qin Enze suddenly slapped the table, but forgot that his hand was still in plaster, stood up gnashing his teeth in pain, and said a little excitedly:
"I understand. Is it because when I jumped down, the umbrella was not fully opened at that time. Then after fully opening, there was lift immediately, so there was such a setback?"
"Yes, you can say that."
Li Zhen also said: "The idea of paragliding is not a problem. In terms of aerodynamics, this kind of parachute with forward momentum is established."
Liu Jinghong stood up excitedly: "So, mine is right. But what's wrong?"
"The design direction is wrong. You just think about how to make it move forward, but you ignore a very important problem here. It is lift."
"There is a lift. The umbrella I designed is as big as it is."
"It has little to do with size. The shape is wrong. Your theoretical knowledge is not at home."
Li Zhen said seriously:
"The paraglider itself can have no power, but it is theoretically possible to fly. The reason why it fails is that your paraglider is not filled with air at all. It must be filled with air in order for it to work Just like a parachute, when you jump down, you can imagine a flat parachute or a concave parachute filled with air, which one will work.”
Everyone pondered for a while, but still couldn't get an answer.
Li Zhen also thought about it carefully, the conclusions he reached after his own research in the past two days, said:
"My idea is this: Since the paraglider will generate speed and lift during the flight in the air, and it must make its speed and lift far greater than its resistance. Therefore, in terms of structure, it must The inner layer of the canopy is provided with an air bag. Before the air is filled, the paraglider has no substantial edges and corners. Once the inner air bag is filled with air, the front edge of the paraglider will appear edges and corners. Like this, when the paraglider flies in the air, the relative airflow will be formed by The upper and lower surfaces of the wing divert the flow separately, the resistance is parallel to the opposing 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 comprehensive aerodynamics, you should understand this. "
Liu Jinghong patted his thigh: "Oh, I see. Mine is not equipped with airbags. Although I have a double-layered one, there is no airbag inside. It leaks air."
Li Zhen gave him a white look and continued:
"I think the length of the upper layer of the paraglider is different from that of the lower layer. 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 higher pressure will flow toward the side with lower pressure. Pushing on one side. When the air flows through the upper convex surface, the pressure becomes smaller due to the longer distance and the faster flow velocity. On the contrary, the air flowing through the lower concave surface increases the pressure due to the shorter distance and slower flow velocity, so the lower air pushes the airfoil upward. The pressure difference between the upper and lower layers is the total lift, which is the most basic flight principle.”
'Shushasha'
Everyone below began to take notes~IndoMTL.com~ Li Zhen continued: "The phenomenon that Mr. Lin experienced today should be called a stall."
"Stall?"
"Ms. Lin jumped off the cliff with a paraglider on his back today. The process of running up and landing is actually a relative movement with the air at a certain angle of attack, which generates aerodynamic force and makes him glide in the air for a short time. But he has to control the parachute again. Because the paraglider designed by Liu Jinghong is inherently unstable, it has a big problem. Therefore, when Mr. Lin flies at a certain angle of attack, the airflow flowing over the wing surface is smooth and tightly "sticking" flow over the upper surface.
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 at its rear, which will lead to a rapid increase in drag , and the lift force disappears, this phenomenon is called stall. After a stall, the control will deteriorate, and as the control gets worse, Liu Jinghong's paraglider has no device to limit the angle of attack at all, so it will fall down faster and faster, becoming a vertical landing.
Under sea wind conditions, the angle of attack has almost become a folded shape. So he started spinning wildly. Eventually fell into the sea. "
“…”
After listening to this explanation, everyone was speechless for a while.
There are so many reasons for this?
Lin Xiufeng looked at Liu Jinghong with even more resentment.
Liu Jinghong looked at Li Zhen speechlessly: "Since you know, Master Li, why didn't you tell me earlier."
Li Zhen gave him a blank look 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... rw