Special Forces: Class Reunion, I Parachute In A Tank

"I'll see what answer you can come up with!"

The lieutenant colonel snorted coldly, then looked straight at Ling Feng.

Ling Feng said directly: "Teacher, speaking verbally, I'm afraid they won't understand, can I go to the podium and write while speaking?"

"Can!"

The lieutenant colonel answered without hesitation.

"Thanks!!"

Ling Feng stepped out of his seat, and walked straight to the podium under the eyes of everyone.

Ling Feng faced all the students in the classroom, and said directly: "I think everyone should be more aware that at present, all supersonic aircraft use nothing less than three types of engines: turbojet, turbofan, and ramjet!"

"The principle of the thrust of these three engines is to turn the inhaled air into gas, and then eject it at a greater speed."

"Using this to obtain the reaction force of the jet. Everyone has studied dynamics, and they should all know that the momentum will inevitably increase when the air enters and exits."

"Let's give an example, if we subtract the undisturbed air momentum MDVO at the inlet and outlet from the air momentum M1V1 at the outlet, it must be the increase of momentum!"

"That is, this is the momentum the air has gained!"

While Ling Feng was talking, he had already picked up a pen and written the data on the blackboard.

The students in the classroom couldn't help but nodded slightly when they heard Ling Feng's words.

They all know these basic principles of knowledge.

Outside the classroom, several professors nodded when they heard this.

"This child should be fine. Being able to look at the problem from this level proves that he has seen the trap of this question." Wang Hai smiled.

Lin Yuan said: "Ling Feng is extremely thoughtful, it is impossible to hide this trap from him."

White-haired Professor Wu smiled at Lin Yuan: "No wonder you admire him so much. Indeed! It's a very rare genius to reach this level after just studying for a noon!

"Let's see what he said later. There is not only one trap in this question."

Lin Yuan and the others couldn't help but wry smiles when they heard this.

Inside the classroom.

Ling Feng continued: "Everyone should know that the impulse = the product of thrust F * action time S........."

Before Ling Feng finished speaking, Yan Tao in the audience said impatiently: "Can you just get to the point? What you said are all formulas in textbooks. Who doesn't know the people at the scene? You still need to come Make up lessons for us?"

Ling Feng glanced at him and said: "Since you know it well, I'm curious, why did you say such an answer just now without even thinking about it?"

Yan Tao snorted coldly: "I don't think what you said has any necessary connection with the topic."

"Whether there is any connection, you will know later."

Ling Feng didn't bother to explain anything to him, and continued: "Now, let me calculate a formula for everyone, and you will know how wrong this question is."

After speaking, Ling Feng quickly wrote on the blackboard.

F=M1/S*V1-MO/S*V......

Everyone quickly picked up their pens and quickly recorded the data given by Ling Feng.

And Ling Feng continued: "M1/S is the mass of air passing through the nozzle per unit time, which is the principle of "mass flow"."

"Similarly, MO/S is the "mass flow rate of inhaled air", and the inhaled and ejected air flow rates are equal, which is the law of conservation.

"Therefore, the thrust F is equal to the air mass flow rate M*the difference between the jet speed V1 and the flight speed V0!"

"This formula is a general thrust formula for propeller, turbojet, turbofan and ramjet engines under ideal conditions.

"If we follow the title, the jet speed is less than the flight speed, then the engine output is a negative number!"

"If this is the case, how can supersonic flight eject subsonic airflow and still maintain a state of constant flight? Not to mention whether it can continue to accelerate!"

Now, everyone finally understood.

It seems that this is the case!

Their previous thinking was fixed on the condition that there was nothing wrong with the topic.

And Ling Feng thinks from the level of the authenticity of the topic. After this calculation, it seems that it is really like what Ling Feng said, and the situation mentioned in the topic will not happen at all!

If so, did the teacher make a mistake?

Yan Tao was also a little blushing at this time, and suddenly, he didn't know how to refute.

On the contrary, the lieutenant colonel was on top, and said very calmly: "Perhaps, I didn't make it clear just now. Now, let me add."

"The plane I'm talking about is a rocket-engined X15.'

As soon as these words came out, Zhi Tao was immediately ignited with hope.

Everyone also turned their attention to Ling Feng again.

The rocket engine has its own fuel, and it also has an oxidant, which relies on the oxidant to support combustion, and does not need to absorb oxygen from the surrounding atmosphere

Therefore, it can work not only in the atmosphere, but also in the cosmic vacuum outside the atmosphere, which is impossible for any air jet engine.

If this is the case, this topic seems to be established!

But Ling Feng still said confidently: "If it is an X15 rocket engine, according to the calculation formula we mentioned earlier, because the mass flow rate of the inhaled air is 0, the thrust is equal to the mass flow rate M*jet speed ignited at the nozzle. V. Although the jet speed at this time has nothing to do with the flight speed."

"All rocket nozzles are Laval tubes. When the gas enters the throat, it will expand and decompress to reach the speed of sound."

"After leaving the throat, it will continue to expand until it exceeds the speed of sound!"

Everyone was stunned when they heard this. According to what you said, the plane can continue to accelerate!

If this is the case, isn't it an admission that the topic is correct, and what Yan Tao said is also correct?

Isn't this guy retorting?

How to say it, it becomes Yan Tao and the teacher's argument?

But the few professors outside seemed to know what Ling Feng was going to say later, and smiled at each other.

I saw that Ling Feng turned around slowly, looked at the lieutenant colonel, and asked: "Teacher, I would like to ask, you have been studying dynamics for so long, have you ever heard of the funny incident of rocket engines ejecting subsonic airflow? "

As soon as these words came out, all the students suddenly realized!

Game in game!

The teacher first confuses everyone with the topic.

Because the question was given by him, all students will not think it is wrong, and will answer according to his wrong question.

And the answer, of course, is wrong!

And when the mistake was pointed out, the teacher said that the rocket engine was used to make the problem valid again, but this establishment also has a trap, that is, the rocket engine cannot eject subsonic airflow!

joke!

If the rocket engine can't reach the supersonic airflow, then what kind of space will the rocket go to?

Can't even fly out of the atmosphere, okay?

So, ring after ring!

Confused students!

Now, everyone finally confirmed that this question was indeed wrong!

And Yan Tao followed the wrong question to answer the question, and the answer was even more wrong!

**t..........

At this time, the eyes of everyone looking at Ling Feng finally changed completely!

This guy actually saw through the trap of this topic from the very beginning!

According to what Ling Feng said, after listening to it, they realized that this question can be easily answered by using the basic knowledge of dynamics.

But obviously, the teacher does not want to test their basic knowledge, but to test their direction thinking ability!

Just like what Ling Feng said at the beginning, just because he is a teacher, is it true that what he said and the questions he wrote are completely correct?

The audience was silent.

Everyone looked at the lieutenant colonel.

The lieutenant colonel looked at Ling Feng, but the anger in his eyes had long since disappeared, and there was only strong praise in his eyes.

Finally, after a moment of silence, the lieutenant colonel said, "How did you find out?"

Ling Feng said directly: "When you haven't finished writing the topic, I can see it. This kind of brain teaser is like a sharp turn. It must be wrong to look at it with a fixed mindset. But when you change the angle, then It will be very clear."

Everyone was silent when they heard the words, with a strong sense of frustration in their hearts.

Ling Feng has never even studied dynamics, but just read the textbooks and materials casually, and he can fully understand the knowledge in it, and see through the authenticity of this question.

0

And they, from the very beginning, were led by the nose by the teacher, and finally even the most basic kinetic principles were completely forgotten.

"Not bad!"

Snapped!

Snapped!

Snapped!

The lieutenant colonel smiled and nodded, while applauding Ling Feng.

After being stunned for a moment, everyone started applauding one after another, full of admiration for Ling Feng.

Even Yan Tao is the same.

The lieutenant colonel said with a smile: "I have taught three classes of students, and in each class, I would ask them this question. However, no one has ever been able to see it."

"Of course, they made mistakes because they believed in my teaching ability and had unreserved trust in me. If it were a question posed by a student, I think they would be able to see the clue after a little thought."

"But you are different! You have questioned me from the very beginning. From this alone, it can be seen that you are either born with a questioning and innovative spirit, or you are a natural genius, and you have completely mastered it. The subject of dynamics! Therefore, you don’t like my lectures and content, because I can’t teach you anything. Right?”

Ling Feng looked at the lieutenant colonel slightly surprised.

I didn't expect this guy to be so wise and able to guess his own mind at once!

Indeed, the current him, with the help of the system, has basically completely mastered the dynamics.

What he has to do is to understand the current progress of Huaxia in this regard lol!

For the class taught by the lieutenant colonel, he felt as if he was listening to the teacher's addition and subtraction within ten in a primary school classroom!

Therefore, from the very beginning, he didn't take this class seriously, and naturally he didn't develop absolute trust in the lieutenant colonel like other students did.

Seeing that Ling Feng didn't answer, the lieutenant colonel knew he had guessed right, and asked curiously, "So, which one are you?"

Ling Feng smiled wryly, how could he answer this?

Tell you that my IQ is over 150?

Let me tell you, in fact, the dynamics knowledge in my mind exceeds the power technology field of any country in the present era?

Will you believe it?

Just when Ling Feng didn't know how to answer, the classroom door was suddenly pushed open.

Professor Wu and the others walked in slowly. .