129: Chapter 129 Hot air balloons are not easy to make!

"It can fly a distance of three thousand paces!"

"Your Majesty, please don't lie to us!"

Whether it was Cui Wenzi, Gongshu Chou, or the elderly men surrounding them, they all wore expressions that said, 'I'm not well-educated, so don't try to fool me.'

"Of course it's true."

Zhao Fusu said, "An emperor does not speak in jest!"

If this hot air balloon didn't fly high enough, he wouldn't have the motivation to spend money on its research and development.

If a hot air balloon flies to an altitude of three thousand meters and steel nails are dropped from it, ignoring air resistance, the terminal velocity would reach two hundred and forty-two meters per second!

Of course, in reality, air resistance would cause the iron nails to eventually reach a terminal velocity, but even considering air resistance, the falling speed of the nails would still be extremely fast, possessing immense kinetic energy.

The sharp tips of the iron nails ensure that the contact area is very small upon hitting a human body, making it easy for the nails to penetrate human tissue and cause fatal injuries.

During World War II, the Japanese devils once dropped iron nails from fighter planes, killing many Soviets.

Zhao Fusu's primary purpose for building hot air balloons was for reconnaissance.

By standing high, one can see far; especially when fighting on the grasslands, it would allow for the early detection of Xiongnu cavalry movements and the location of their main force's hiding spots.

The difficulty Central Plains dynasties had in dealing with grassland cavalry was not because the cavalry were particularly good fighters.

Rather, it was because the grassland cavalry moved fast; two legs couldn't keep up with four.

Once the grassland cavalry vanished into the depths of the plains, no one knew where they had gone.

This resulted in the Central Plains dynasties leading hundreds of thousands of troops into the grasslands only to 'check-in' and then retreat.

As soon as the Central Plains troops left, the grassland cavalry would return from the depths of the plains.

They were like sparrows stealing grain drying on a threshing floor; when you ran over, the sparrows would fly away in fright.

Once you left, they would come back.

When you approached again, they would fly away in advance.

At such times, reconnaissance aircraft were needed to scout the enemy's situation.

Zhao Fusu didn't have the means to produce reconnaissance planes yet, so he came up with hot air balloons.

Cui Wenzi frowned and said, "Flying so high... wouldn't that be very dangerous?"

For someone with a fear of heights, looking down from a height of ten meters would make their head spin and their legs go weak.

Looking down from an altitude of three thousand meters would be terrifying.

If one were to fall from three thousand meters, wouldn't they end up in pieces scattered everywhere?

Zhao Fusu smiled and said, "This hot air balloon is the safest aircraft in the world."

"It is essentially a giant parachute."

"Even if the hot air balloon runs out of fuel, it will descend slowly, and nothing bad will happen."

"Then how does it turn in the air?"

Gongshu Chou suddenly asked.

He hadn't noticed any measures for controlling the direction of the hot air balloon.

"There are."

Zhao Fusu said, "By controlling the size of the flame, you can control the altitude of the hot air balloon."

"The wind direction varies at different altitudes."

"By controlling the size of the flame to fly at different altitudes, we can utilize the wind directions there to change the flight path of the hot air balloon."

"What if the flame accidentally burns the fabric of the hot air balloon?"

Cui Wenzi raised another question.

The fabric could be coated with resin and paste to achieve an airtight seal.

But if the fire burned the fabric, the person would fall from a great height and end up in pieces scattered everywhere.

"Therefore, we must use fireproof materials to manufacture the hot air balloon."

Zhao Fusu said, "We can use asbestos to build the hot air balloon."

Asbestos is composed of fiber bundles, which in turn are made of long, thin fibers that can be separated from each other.

"This asbestos is what is known as fire-washed cloth."

"Oh, oh, oh!"

At first, Cui Wenzi and the others were confused, not knowing what asbestos was, but as soon as fire-washed cloth was mentioned, they immediately understood the concept.

During the Zhou Dynasty, people were already able to make fabrics from asbestos fibers; because they would become as white as new after being burned in a fire when soiled, they were called fire-washed cloth or fire-cleansed cloth.

"However, this asbestos is very dangerous and must not be touched directly!"

Zhao Fusu said with narrowed eyes.

Although asbestos has good thermal insulation and high fire resistance, it is extremely hazardous and is known as a Group 1 carcinogen.

This is mainly because asbestos fibers are extremely tiny, almost invisible to the naked eye.

When materials containing asbestos are processed, used, or damaged, asbestos fibers are released into the air.

After people inhale these tiny asbestos fibers, they deposit in the lungs, and long-term accumulation can lead to serious health problems.

The most common is asbestosis, a pulmonary fibrosis disease caused by long-term inhalation of asbestos fibers, which leads to a gradual decline in lung function and symptoms such as difficulty breathing and coughing.

The harm of asbestos to the human body is immense, but Zhao Fusu had no other choice.

He couldn't produce fireproof coatings yet, so he had to use asbestos.

All he could do was try his best to ensure that the workers coming into contact with asbestos took proper protective measures.

"How about it?"

Zhao Fusu asked, "Are you interested in researching hot air balloons?"

"As long as you are interested, I will set aside a specific area for the development of hot air balloons."

"Yes, yes, yes!"

"Naturally, we are."

Gongshu Chou said with an excited expression.

Their ancestors' purpose in researching flying machines was not to fly kites for children.

Gongshu Ban made wooden kites to spy on the deployment of Song City.

However, Gongshu Ban failed to create a kite capable of carrying a person, and Mozi dismissed his work as 'extravagant and useless ingenuity.'

For hundreds of years, the Gongshu Family has been synonymous with 'extravagant and useless ingenuity'; whenever they went out, they were ridiculed.

If the Gongshu Family could create a manned flying machine, they could wash away the shame of the past and let the world know that what they built was by no means 'extravagant and useless ingenuity'!

At this thought, the members of the Gongshu Family couldn't help but clench their fists.

They had to build this manned hot air balloon!

"Good, good, good!"

Zhao Fusu clapped his hands and laughed.

Seeing the Gongshu Family agree, he was in a great mood.

The members of the Gongshu Family were mostly inventors themselves and were very skilled with their hands.

Zhao Fusu was completely at ease leaving the research and development of the hot air balloon to them.

"I will have the people from the Great Qin Empire Academy of Sciences cooperate with you."

Zhao Fusu knew the difficulties in building a hot air balloon; one was the fuel storage tank.

The coke oven gas had to be purified, the moisture in the purified gas dried, and then it had to be compressed into steel gas tanks using a steam piston compressor.

The construction of the hot air balloon itself was also a major challenge.

Besides using asbestos for the balloon's envelope, a coating had to be applied to the exterior to prevent air leakage.

To speed up the descent, a pulley system needed to be installed at the top of the balloon to contract the top area and allow the hot air to escape when needed.

Hot air balloons were not easy to make!