The first is that without a pressure vessel to provide gas fuel, relying on firewood or charcoal to heat the air is not only inefficient, but also limited by the fuel, so it can't fly far. This is why the principle of hot air balloons was discovered very early in history, but hydrogen balloons were the first to be put into practical use. So Roland simply abandoned the combustion device and let Anna ignite and heat it.
The difficulty of the air bag lies in its airtightness, but for Roland, who has learned from the experience of his predecessors, this problem is easy to solve - using a laminated fabric. The outermost layer of the air bag is wear-resistant canvas, the middle is lined with beef intestine film, and the inner layer is lightweight gauze, so that it can be sewn together to prevent air leakage and not be afraid of birds pecking at it.
Roland propped open the bottom of the air bag and let Anna spray black fire, which was close to the temperature of ordinary flames, into it. The air bag slowly swelled up, looking like a wrinkled winter melon. Considering that the hot air balloon needed to carry two people into the air, the widest diameter of the air bag was five meters, using the intestinal membranes of twelve cows, and the sewing work took nearly a week. If he weren't a lord governing a territory, he might not be able to afford such a big toy.
"Does it fly by using the buoyancy provided by hot air?" Anna asked, "I remember you mentioned that hot air always rises."
"That's right, hot air rising and cold air sinking are common natural phenomena. Explaining it with particle theory, the hotter air molecules move more intensely and have a stronger ability to diffuse around, and the density decreases after the volume expands. For the surrounding air that has not changed, it is equivalent to becoming lighter, so it will rise."
After Roland finished explaining the principle, he found that in addition to Anna showing an "I see" expression, the other three were all blank, which made him sigh at the importance of talent.
When the air bag was fully inflated and floated upwards, the traction ropes were slowly straightened, Roland was the first to flip into the basket, and then took Anna, who was climbing in.
"I'm still a little worried," Nightingale said uneasily, "Why don't you let me go up and try it first."
"Trust me, nothing will happen," Roland smiled easily, "And even if there is an accident, there's Lightning."
"I'll catch them, don't worry." Lightning patted her chest.
"Me too, gu!" Maisie imitated Lightning's appearance and patted her chest.
With a burst of shaking, the hot air balloon pulled the basket away from the ground and gradually climbed upwards. Before long, the two had passed over the top of the castle, and the whole picture of the town was presented before them.
For Roland, this scene was not unfamiliar, after all, he had seen skyscrapers, but in Anna's eyes, it was a brand-new experience that was completely different from the past perspective. She leaned on the edge of the basket and peered out, one hand firmly grasping Roland's arm, appearing excited and nervous.
This was the first time Roland had seen her show such an expression. Perhaps people whose feet have never left the ground will have a slight fear of heights when they first fly into the sky.
After a while, the hemp rope used to tie the hot air balloon below the basket was pulled to its limit, and the ascent stopped. The hemp rope was about fifty meters long, which is the height of fifteen or sixteen floors in later generations. Roland had Anna reduce the heat, and the hot air balloon finally hovered in the air.
Lightning initially guarded the edge of the basket without leaving, and after seeing that the basket was stable, she felt relieved and started playing tag with Maisie around the hot air balloon.
From here, you can clearly see the castle roof, the town where construction is going on everywhere, the Chishui River flowing from west to east, and the green farmland along the river.
"How do you feel?"
Roland asked with a smile after Anna retracted her head.
"Thank you for the gift," she said excitedly, "I didn't expect I could fly so high."
"It can be even higher," Roland sat down against the wicker basket wall, "If the rope below is longer, it's no problem to fly ten times this distance, but the higher you go, the more complex the air currents are, and the harder it is to ensure safety. And this is just a primary aircraft. When piston engines are made in the future, ordinary people will be able to fly faster and higher than birds, and further on..." He looked up at the blue sky, "
People can even fly out of this world and travel to the boundless space."
"..." Anna held her breath, her eyes shining brightly, something was about to come out.
"I can't guarantee flying out of the world," Roland was amused by her appearance, "But making a piston engine so that ordinary people can fly like birds, I should be able to do it in my lifetime." In fact, with Anna, the processing capacity is no longer a bottleneck, and the current shortcoming lies in the material properties. Inferior pig iron can be used to make steam engines, wrought iron can be used to make cannons, and steel smelted with black fire can be used to make rotary guns without any problems, but internal combustion engines may require high-quality cast iron, cast steel, or aluminum. "Border Town can have its current appearance, all thanks to you, «Anna xiaojie»."
After hearing this sentence, Anna was stunned. After a long while, she leaned over and whispered, "My mother died in a fire, but not only did I not die in the smoke and flames, but I became a witch. For a long time, I thought it was my awakening that caused the fire, and I extremely hated being a witch. When I was locked in the prison, I thought that this might bring liberation, but you rescued me from the prison and taught me how to use my abilities... I didn't expect that fire, in addition to bringing destruction and pain, could have so many uses." Anna paused, "I should be very satisfied to meet you, but now I find that my thoughts have changed, and sometimes I feel suffocated and want more."
She climbed onto Roland's shoulder, "Even so, do you still want to hire me?"
Her lake-blue eyes sparkled, and her breath blew on his face, feeling a little itchy. Through the thin clothes, he could feel her soft body and her pounding heartbeat. Despite this, she did not avoid his gaze—when Nightingale was not around, she was always full of enthusiasm and initiative.
"There's someone outside..."
Before Roland could finish speaking, Anna had sealed his lips.
After separating, he took a light breath, "I want to hire you, always. Anna xiaojie."
"Yes."
This time, he took the initiative to lower his head and leaned close to her.
……
"Huh, wait," Maisie chased Lightning for a while, and suddenly stopped abruptly in the air, looking at the empty basket, "They're gone, gu!"
"Ah?" Lightning tilted her head and glanced, "They just sat down."
"Wouldn't that mean they can't see the scenery outside?"
"You can see the scenery anytime, but there aren't many opportunities like this."
"Opportunities?" Maisie shook her wings and landed on Lightning's shoulder, "Don't understand, gu, should we go see them, gu?"
"That won't do," Lightning put her arm around the pigeon, "This is a sacred ceremony that cannot be interrupted."
"Gu?"
"Anyway, you'll understand later. At this time, just pretend you didn't see it. This is what my father—the greatest explorer—told me." Lightning threw Maisie out and put her hands on her hips, "Now run quickly, it's my turn to chase you!"(。)