Shivering.
But no matter how frightened they were, the loyal Grimalkyne guards wouldn't leave their Glavenus boss's side.
They just gripped their Nergigante spears a little tighter, guarding both sides of the tree hollow entrance.
Just like before, Asterion once again inhaled about ten cubic meters of air. The air sac, its inner walls lined with heat-resistant crystals, seemed to have become even tougher. If fully inflated, it should be able to hold even more air than the previous version.
Better to conduct the dragon energy mixing experiment first; the maximum air capacity test could wait.
It was a rather crude experiment. Following the previous steps, Asterion once again injected fire elemental energy into the air sac.
Boom!
It exploded, but this time it didn't blast into shredded meat like before. The explosion occurred inside the air sac. At that moment, the milky-white sac seemed to turn into a lantern, though not very translucent, only revealing a faint orange-red glow from within.
It lit up.
As expected of the heat-resistant crystals used by ordinary Glavenus to smelt ore, they were indeed reliable. They directly withstood the destructive force caused by fire elemental energy burning violently and releasing energy in such a confined environment.
He didn't try to add more fire elemental energy, nor did he dare to add more air. Asterion felt that if he dared to open the intake valve, the burning flames would definitely rush straight down the trachea into his lungs. Even if it didn't kill him, it would hurt like hell.
Patiently waiting for the fire inside the air sac to burn, Asterion wanted to see exactly how long this thing could burn, and whether the sac itself could withstand the prolonged high pressure and high temperature.
One minute, two minutes, thr— BOOM!!
Asterion was still silently counting, but before he even reached the four-minute mark, the second-generation air sac exploded. The expanding flames finally found space to release. The cramped nest was illuminated in an instant, the blinding light making it almost impossible to see.
At this moment, the small nest Asterion occupied felt like a burning furnace. Tongues of scorching fire sprayed out from the cave entrance, nearly burning the fur of the Grimalkyne guards standing on either side—uh, looks like they got singed.
"M-move back a bit further, meow!"
"It's so hot, meow!!"
Asterion heard the panicked voices of the Grimalkynes. The temperature of the burning fire inside the nest was bearable for him, though his exposed muscles and tissues, currently lacking protection on his chest, stung quite a bit.
He healed the wounds with life energy and regenerated a new air sac. However, Asterion didn't immediately start the next experiment. Instead, he recalled the sensation just before the explosion—starting from around the one-minute-thirty mark, he had already felt a sense of fullness from the surface of the air sac.
This sensation increased rapidly over time. By the eve of the explosion, there was a pain as if it had swollen to its limit and would burst at any moment.
Uh, Asterion had foreseen the explosion, but at that time, he didn't know what he could do to stop it, so he could only silently wait for it to blow.
Thinking about this, Asterion realized where the problem with the second-generation air sac lay—it lacked a release channel.
A very simple, very basic piece of middle school physics knowledge: thermal expansion.
The compressed air mixed with burning fire elemental energy would expand violently. Asterion had indeed inhaled only about ten cubic meters of air, but he had no idea what the volume became after violent combustion.
Uh, he only knew that his air sac was actually pretty awesome. It burned for that long without a pressure relief channel and withstood the violently expanding air for quite a while before bursting. In terms of strength, it seemed reliable enough.
Realizing where the problem was, the solution became clear, or at least there was a direction to solve it. Asterion began adding a new connecting pipe to the air sac, a duct leading directly to a heat vent beside a wing bone on his back.
He didn't connect all eight yet. Asterion lined this newly opened duct and the original heat vent with airtight heat-resistant crystals as well.
After confirming complete coverage, Asterion checked the accumulated life energy within his body. He discovered that evolving to this point had already consumed about half of it. He wondered if he could complete this evolution before the remainder was used up.
Experiment restarted. The process was no different from the second-generation air sac: inhale and compress air, mix in fire elemental energy, and feel the air begin to burn and expand.
Only when he felt a trace of pressure on the surface of the air sac did Asterion release the valve between the sac and the exhaust pipe—of course, it wasn't a metal valve, but a thick and powerful diaphragm muscle covered in a layer of heat-resistant crystals.
Once this diaphragm muscle opened, the burning air inside the third-generation air sac suddenly had an outlet. The muscle tissue pipe visibly brightened. Asterion could clearly feel the heat traveling through his body, straight to that special wing bone—
Pssh!!!
With a sharp, high-frequency jet sound, Asterion bent the wing bone around to position it in front of his eyes. He saw a stream of bright yellow flame jetting out from the pore beneath the wing bone.
After traveling such a long distance, the temperature of the flame seemed to have dropped somewhat, but the tongue of fire was fierce. Even though Asterion hadn't deliberately created a special nozzle, it took on a sharp, tapered form.
The temperature was high, very high. Simply aiming this wing bone at the tree wall on the edge of the nest, Asterion watched the solidified tree sap melt rapidly, turn charred black in an incredibly short time, and burst into flames.
It could even ignite this fire-retardant tree sap?
Even though the flame wasn't roaring and extinguished itself in the subsequently secreted sap, Asterion was still very excited.
With this channel, the pressure on the air sac had an outlet. Asterion counted silently as before, but until the compressed air inside the sac was mostly exhausted, the fire elemental energy faded, and the flame went out, the third-generation air sac remained structurally intact. No explosion occurred.
When the last glint of fire inside the air sac vanished, Asterion finally breathed a sigh of relief. No explosion was a good thing.
Standing on the shoulders of giants felt great; just following the answer key got the job done.
After thinking for a moment, he curved his blade-tail and sliced the third-generation air sac in half vertically. Asterion wanted to observe the inner wall of the air sac after combustion.
The situation wasn't exactly good, but it wasn't bad either. The heat-resistant crystals hadn't completely melted; at least they hadn't turned into a molten glass-like solution that flowed out as soon as it was cut. This relieved Asterion.
For the moment, he really couldn't find a better substitute or fire-resistant material from the monsters he had eaten. As an apex Brute Wyvern, the materials on a Glavenus were just about the best available from monsters of this tier.
As expected of biological materials rigorously selected by nature over millions of years, they were reliable. By comparison, what Asterion was doing now was just a trial-and-error assembly, using whatever was at hand.
However, after careful observation, Asterion noticed that a slight melting phenomenon had indeed occurred on the surface of the heat-resistant crystals. The crystal surfaces near the inside had slightly fused together.
But perhaps due to the immense pressure during gas expansion, these melted crystals didn't drip. Instead, they were pressed evenly against the outer wall of the air sac, filling some of the gaps between the heat-resistant crystals, which actually protected the air sac on another level.
Except at the connection between the air sac and the exhaust channel. Even though Asterion had grown a thick diaphragm muscle there as a valve, when he opened the valve to vent, the melted crystal solution pressed against the inner wall flowed towards the exit under pressure, entering the heat vent pipe.
Solemnly slicing the connecting pipe open, Asterion saw that the outflowing solution was distributed in a scattered pattern within the pipe. Perhaps because the temperature at the inlet was still very high, combined with the expanded gas jetting out at high speed, the area where the air sac connected to the pipe was actually quite clean.
Instead, the parts entering Asterion's body, and even the heat vent pipe beneath the wing bone, showed signs of semi-solidified radial crystals. If the burning time had been a bit longer, they might have sprayed directly out of the vent holes.
Would it get clogged?
Asterion was a little worried. However, considering the speed of the high-pressure gas during expansion and the high temperature brought by the fire elemental energy, as long as he sprayed occasionally, Asterion felt it shouldn't get clogged.
What needed to be considered instead was the potential "chamber explosion" caused by the heat-resistant crystals inside the air sac melting and flowing away—but that was easy to solve. Asterion slapped his hip and thought of a way.
He just needed to continuously secrete heat-resistant crystals on the inner wall of the air sac, ensuring the secretion rate matched the ejection rate.
Asterion felt he was simply a genius.
Having found the initial path, he wouldn't even take a break. Asterion urged his life energy to continue the evolution.
The previous tests were just small-scale attempts; now it was time to play for real.
Following the designated areas he had reserved in his body, he grew an air sac of the corresponding size. Unlike the first three generations, this time Asterion thickened the sac walls as much as possible and secreted a sufficiently thick layer of heat-resistant crystals on the inner wall.
However, he still didn't place it inside his body. Asterion didn't want this thing exploding inside him at all; even testing it in the nest right now made his heart pound with fear.
Inhaling air like a storm, mouthful after mouthful. For the first time, Asterion regretted arriving too late to eat the old Kushala Daora's Dragon Gem. If he had the ability to control storms right now, filling the air sac wouldn't be this exhausting.
A much larger and thicker air sac meant it could hold more air. As a vital organ for his future flight, Asterion used his toughest and most resilient muscles to construct it. He didn't plan to stop until he reached the limit and felt a slight pain.
He didn't know how long passed. Asterion felt so dizzy from inhaling that his tongue was lolling out. Finally, he felt a distended pain from the surface of the air sac, which meant its size had reached the limit.
Time for the next step.
Swallowing his saliva, Asterion narrowed his eyes and began injecting fire elemental energy into the air sac.
Theoretically speaking, air wasn't the best fuel. Jet fighters or rockets used aviation kerosene or liquid oxygen—propellants or oxidizers capable of providing high specific impulse to the engine. Only these could provide sufficient power.
But this world didn't adhere to science, at least not completely. Upon mixing with fire elemental energy, the air inside the sac burned and expanded explosively. Without waiting a second longer, Asterion opened the valve connected to the heat vent channel—
Pssh!!!
The forward-extending wing bone jerked violently in the opposite direction the instant the flame sprayed out. If Asterion hadn't urgently increased his strength to control it, this wing bone might have whipped around wildly under the force of the impact!
When high-pressure air expands suddenly, it performs work on the exterior. The high-speed expansion of gas molecules generates a reaction force, just like releasing the tail of a balloon—the compressed air pushes the balloon into reverse motion as it ejects.
But the thrust provided by this expansion was far from enough, at least not enough to lift Asterion's body, which was much heavier than a Valstrax, into the sky.
That was exactly why mixing fire elemental energy was necessary. When high-pressure gas mixes with fuel or energy and burns violently, it generates a high-pressure jet stream in an instant—this was the power Asterion wanted! Power far stronger than mechanical energy produced purely by pressure difference!!
This is the kind of propulsion used by jet fighters and rockets.
It hadn't been easy. He was so excited he even forgot to squint to protect his eyes from an explosion. Asterion constantly felt the thrust coming from the tip of the wing bone. It wasn't weak. Asterion tried relaxing his body, and the thrust drove the wing bone directly into the tree wall behind him.
However, this force didn't manage to pull Asterion's body; it only caused his shoulder to jerk back slightly.
That wasn't great.
His wyvern face fell. Asterion started chanting in his heart that this was only one wing bone, not all eight firing at once. Don't give up hope.
Overall, his attempt was a success. After the air inhaled this time was exhausted, Asterion sliced open the complete version of the air sac once again, getting a rough idea of the melting degree of the heat-resistant crystals inside and the sac's bearing capacity.
Although he wanted to continue experimenting until he verified a mature and reliable plan, the emptiness caused by the depletion of life energy in his body reminded Asterion that he couldn't do that—so he would just use this for now.
Sighing, Asterion began generating the air sac inside his body according to the final plan. He trimmed away the excess flesh tubes and finally regenerated the temporarily devolved shell and blade-scales on his chest to form a safety protection.
He patted his chest with his foreclaws. Hearing the crisp metallic sound of sharp claws colliding with blade-scales, Asterion suddenly felt like he had planted a bomb inside his body... Should he move the position of his heart and stomach further back in his body?
At least it would be safer.
No sooner said than done; life was important.
Once the air sac finished growing and he confirmed that it wouldn't affect his bodily functions during various movements, Asterion was ready to operate on his lungs.
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