Emperor Chongzhen originally thought that something like a hot air balloon had no technical content at all, but it was just a bigger Kong Ming lantern.

But in fact, the hot air balloon that can be put into military use is by no means as simple as a Kong Ming lantern that has been magnified many times.

If you just let it lift it off, you don't think about what to do after liftoff, such as the length of time you stay in the air, you don't consider the weight of the materials you carry, and you don't consider the safety performance of manned lift-off and drifting in the wind, as well as direction control, then it's much simpler to do.

However, whether it is Li Tianjing, the sacrificial wine of the School of Engineering, or Song Yingxing, the second-in-command of the School of Engineering, they are extremely rigorous and meticulous scientists in this era.

Scholars like them either don't do it at all, and if they do, they must do it in every aspect of it to the best in order to go down in history.

It's no surprise that they have such an idea.

Because in the more than 200 years after the establishment of the Ming Dynasty, it was not that no one had engaged in the study of manned flights.

The famous story of Wanhu flying to the sky, which happened in the early days of the Ming Dynasty, is about an experiment in which a man called Wanhu Shidai used the thrust of a rocket to try to send himself into the air.

The man, known as Wan Hu, tied himself to a special chair surrounded by giant rockets, and then pulled several large kites in his hands like flying into the sky.

The results of this experiment were, of course, disastrous.

Some books record that the rockets tied around the chairs exploded shortly after they ignited, and the 10,000 households did not succeed in taking off at all.

Some accounts say that the 10,000 households lifted off into the air, and then after the rocket burned out, it lost power, fell and died, because the kite he was holding in his hand did not work.

There are many records about this incident, among which some people have verified that this Wanhu is just an official title that is false, and this person's real name is Tao Chengdao, and he is an old Taoist priest who has achieved great achievements in gunpowder production somewhere in Zhejiang.

However, no matter what, no matter whether this person is called Wanhu or Tao Chengdao, his flying experiment is a tragic event.

Now, Emperor Chongzhen's freshly baked engineering college, the first thing to focus on after its establishment is to carry out the experiment of manned flight, which is an arrangement that surprises them for Li Tianjing and Song Yingxing.

When the Ming Dynasty came to the Chongzhen period, the story of ten thousand households flying to the sky has passed for nearly two hundred years, even the scholars and doctors in some areas of the north have not heard of this seemingly extremely absurd thing, but Li Tianjing, Song Yingxing, who was born in Nanzhili and nearby areas, and several people in the engineering college who came into contact with Western studies earlier, have heard of it since childhood!

What is the emperor doing here? Is this to believe in the Tao and cultivate immortals, or is it just fun to be a plaything?!

In short, at first glance, when I saw these research tasks assigned to the Institute of Engineering by Emperor Chongzhen, whether it was Bi Maokang, the secretary of the Ministry of Engineering, or Xu Guangqi, the secretary of the Ministry of Rites, who participated in the matter, they were all a little dumbfounded.

As for Li Tianjing, the first priest of the School of Engineering, and Song Yingxing, the first director of the industry, they are even more inexplicable, incomprehensible, and have no way to start.

Fortunately, whether it is Xu Guangqi, Bi Maokang, or Li Tianjing, or Song Yingxing, they are not nerds who are stupid in reading.

It was not until the edicts written by Emperor Chongzhen himself were sent to the Institute of Engineering one after another, to Li Tianjing, Song Yingxing and others, and that they were given a Kong Ming lantern carefully sewn by the Da Nei Needlework Weaving and Dyeing Bureau, that these people finally decided on the direction, and also realized the unquestionable determination of Emperor Chongzhen.

Later generations all knew the basic principle of hot air balloon flight, but in the last years of the Ming Dynasty, even the most knowledgeable scientists stopped on this issue.

The reason for the rocket to take off is of course difficult for characters like Li Tianjing and Song Yingxing.

However, the story of Wanhu Feitian tells them that the biggest problem with the rocket is what to do after the gunpowder is exhausted.

If it is like Tao Chengdao back then, vainly thinking that after taking off, he will rely on a few kites in his hand to provide power, wouldn't it be like child's play?!

In addition, if you want to stay in the air longer, you have to use more gunpowder, but the weight becomes larger and it is more difficult to lift off.

The most important thing is that as long as the rocket uses gunpowder, then its gunpowder will always run out, and at that time, the higher it flies, the heavier it will fall?!

Therefore, from the very beginning they were in a predicament, and the tragedy of the flying of ten thousand households was in front of their eyes, how could they repeat the mistakes of the past?!

ruled out this choice, Li Tianjing, Song Yingxing and others could only choose the path of Kong Ming lantern.

After finding the right direction, no matter how far the road is, you are not afraid, because it is only a matter of time before you reach your destination.

Speaking of which, Kong Ming Lantern has a long history in China, especially after the "Romance of the Three Kingdoms" became popular in the last years of the Ming Dynasty, there are many people who know it.

Not to mention Li Tianjing and Song Yingxing, who were well-known scientists in the late Ming Dynasty in later generations, even the ordinary people on the streets and alleys at that time could also say that they were the truth.

However, although there are many people who know what it is, there are not many people who really know why it is true.

The vast majority of people have seen it themselves, or made it themselves, so they know it's okay.

These are all lessons learned.

But if you really want to say that you can make a super-large Kong Ming lantern that can send people to the sky and bring hundreds of pounds of things to the sky, I'm afraid that ninety-nine and a half out of a hundred people can't do it.

Including people like Li Tianjing and Song Yingxing, the same is true.

The fuel needed for a Kong Ming lantern is very good, a candle is good, in addition, a butter lamp, a sheep fat lamp and even lard can also play a role.

But if you make a Kong Ming lantern that can send hundreds of catties into the sky and stay in the air for more than four hours, as the emperor requested, what fuel should be used to provide the flame?

Fortunately, Emperor Chongzhen gave this task to the most suitable person to study this matter in this era.

After Song Yingxing repeatedly experimented with the Kong Ming lantern carrying load and floating, he eliminated the fuel he originally envisioned one after another, and finally locked his eyes on the fierce fire oil.

The fierce fire oil that the wind does not blow and the rain does not extinguish is the best fuel to replace the grease lamp in the Kong Ming lantern.

After solving the problem of portable and long-lasting fuel, the Kong Ming lantern made by the School of Engineering began to grow in size, not only for longer and longer floating in the air, but also for the load during the experimental liftoff.

From the autumn of Chongzhen's third year to the end of Chongzhen's third year, after several months of experiments with experience, Song Yingxing and his own group of apprentices in the College of Engineering finally figured out the principle behind Kong Ming's lantern.

Therefore, in December of the third year of Chongzhen, there was no need for Emperor Chongzhen's reminder, and the hot air balloon made by Huangming Institute of Technology was no longer the shape of the traditional Kong Ming lantern, but was sewn into the droplet shape that was most conducive to its floating, and began to have the appearance of a hot air balloon in later generations.

The skeleton that supports the huge balloon inside has also been transformed from the bamboo and wood structure of the traditional Kong Ming lantern to a more slender but tougher copper tube.

The ball skin that wraps the skeleton on the outside and is used to seal it has also gradually transitioned from the rice paper, linen cloth and more solid cotton cloth originally used to make Kong Ming lanterns, and finally the use of cow and sheep leather with better sealing performance.

As a result, the cost of the College of Engineering's hot air balloons has risen rapidly, but its ability to float into the air has also made great progress.

In the first month of the fourth year of Chongzhen, Li Tianjing and Song Yingxing, the priest of the College of Engineering, who had already identified the direction and saw the dawn, canceled the New Year's holiday of the College of Engineering, and took a bunch of apprentices and cats in the experimental field of the College of Engineering, in full swing to make a balloon with a maximum diameter of up to two zhang, and a giant hot air balloon with a maximum diameter of more than three zhang after installing a hanging basket.

The purpose is to enable the School of Engineering to come up with a blockbuster achievement that the emperor has been looking forward to as soon as possible.

When the College of Engineering was first established, Emperor Chongzhen had to inquire about the research and experimental progress of the following hot air balloons every once in a while.

At that time, whether it was Li Tianjing or Song Yingxing, although the pressure was great, after all, it had just begun, and he had not yet found the right direction, and he was in the process of continuous trial and error.

Although the emperor was diligent, the sense of urgency was not so strong.

But when Emperor Chongzhen stopped caring and didn't bother to ask at all, these people in the engineering college began to be anxious from top to bottom.

The emperor spent so much money and invested so many resources that even the brass pipes that he was reluctant to use to make guns and cannons in the arsenal were allocated hundreds of kilograms, including the fierce fire oil with a small output, and it was given priority in unlimited quantities.

All of this is because the emperor attaches great importance to this project, and once the emperor does not produce convincing results for a long time, the emperor's interest is diverted, or he feels that it cannot be realized at all, then the engineering school will be finished.

On the 18th day of the first month of the fourth year of Chongzhen, the new giant hot air balloon "Wanhu" was completed, and the fixed-point ignition and liftoff experiment was carried out on the 19th day of the first month.

On the 22nd day of the first month of the fourth year of Chongzhen, in the experimental field of Tongzhou Huangming Institute of Technology, Song Yingxing asked people to tie a fat pig of more than 200 catties to their limbs and put it in the hanging basket of the "Wanhu", and once again carried out a fixed-point lift-off experiment.

It wasn't until the rope that connected to the ground was completely straightened that the "Wanhu" had to stop and continue to float.

More than two hours after the "Wanhu" was lifted off that day, the hot air balloon did not slowly land until the fierce fire oil in the hot air balloon was slowly exhausted.

When he landed, the big fat pig sent to the sky was tied in the hanging basket, and he was alive and well.