Chapter 103 The Jet Engine and the Dream of Flight
Edited by: Kanaa-senpai
”I didn’t say we’d go this far.”
”Now then, what’s a reaction propulsion system?” I began, tapping the side of a metal frame. “Simply put, it’s a machine that gains thrust by ejecting something in the opposite direction. That’s the easy version.”
The concept came from the jet engines of my previous life. Air gets drawn in by spinning fins, compressed, mixed with fuel, ignited, and blasted backward in a focused stream. The pushback drives the craft forward. By narrowing or widening the nozzle, you control the force, using the energy more efficiently.
Fuel doesn’t explode from burning alone—it needs air to ignite. Car fuel tanks don’t burst instantly in crashes because the vapor needs time to mix and ignite. Jet engines make use of that exact process, but controlling it is tricky. Get the mix wrong, and boom. So the balance between air and fuel needs delicate care.
”That’s the kind of function we’re aiming to build safely,” I said, scratching the back of my neck. “Any questions?”
Dahlia frowned. “If you mess up, wouldn’t that turn me into a pile of ash?”
”If I mess up, yeah, probably.” I smirked. “But with your defense, you’d end up with soot on your armor at worst.”
She didn’t look convinced.
”If we want a safer method, there’s another option,” I added.
”And that is?”
”Use wind magic instead of combustion. Treat the core—our ‘egg’—as the engine’s heart and blast high-level wind magic from it to get thrust.”
In terms of being eco-friendly, that would be better. It only consumes mana. But the problem is—such strong magic isn’t easy to use.
”Master, we Automaton Maidens can’t use magic,” Dahlia reminded me.
”I know. And no one around me can cast top-tier wind magic either.”
Even if I simplified beginner wind spells, without knowing how to amplify them, the thrust would be weak. If normal people can’t use it, a levitation stone would be more practical. Chef’s ‘Wagaga’ armor used something similar, but that was only possible thanks to Chef’s own stats and the armor’s quality. It’s unfinished tech—good for closing distance fast, nothing more, maybe reaching the speed of sound at best.
The goal was to create a jet engine for high-speed hit-and-run combat and eventually small passenger aircraft. A mana-core piston engine would likely be safer for the latter.
”That’s why I want to finish a jet engine fueled by liquefied mana stones and mount it for you, Dahlia,” I said.
It felt selfish, maybe hypocritical, but I wanted to give her the best tech to keep her safe. Her week-long journey home on foot could be done in a day, avoiding dangerous back roads.
”By the way, Master,” Dahlia asked suddenly, tilting her head, “if we put aside magic formulas and tried to gain thrust using only wind magic itself, what ideas would you have?”
I thought about it for a moment.
”Perhaps connect a mid-tier or higher wind spirit’s core stone directly to the ‘egg’. Feed mana from the egg into the stone to convert it into wind magic.”
In other words, use the spirit core’s conversion structure instead of a spell formula. If we analyzed one, we could replicate it, but I didn’t have any. Lower-ranked cores are found past the 45th dungeon floor.
The benefit is safety—almost no explosion risk compared to liquefied mana fuel. However, drawing too much mana could create a wind cannon effect.
”Why not take that route, Master? If it’s the 45th floor, I can guide you there,” Dahlia said.
”Relying on you for everything feels wrong,” I sighed. “I’m already depending on you against that Lich. Besides…”
It was partly stubborn pride, partly a Crafter’s ego.
”Don’t you want to see if flight is possible without magic?”
”…”
Dahlia blinked, then slowly smiled.
”Even though you’re still using mana stones?”
”With enough study, fossil fuels might work too,” I said. “That’s how it was in my previous world.”
She chuckled softly. “I like that answer.”
”Yeah, I know. I’m crafting for ‘romance’, right?”
”What’s wrong with that? Without dreams, practicality kills possibility.”
Her eyes glowed with humor and sincerity. Maybe Automaton Maidens loved magic devices because they turned dreams into reality.
After that, we began the actual crafting. A jet engine needs four steps: intake, compression, combustion, and exhaust. To draw and compress air, multiple fins—like fan blades—are arranged in sequence, each tightening the air further. The fuel-air mix burns in the chamber, expanding hot air and shooting directed exhaust out.
Simple in theory, but controlling it requires extreme precision. A single speck in the fins could cause an explosion—typical for engines. In my world, exhaust turbines powered a plane’s electricity. Trying that here might accidentally create a fusion drive—no thanks.
As I explained to Dahlia, I started forging the first fins. High-quality prototypes required mithril—two ingots per fin, fourteen total, linked in a cascade. Each blade had a specific angle for its compression stage. Dahlia calculated the angles using her magical processor and gave me the results. This let me craft them perfectly, matching our design.
It was the start of something that might just change the sky itself.
With the cascade of intake and compression fins complete, I moved on to the combustion chamber. To withstand explosions, I forged it with thick, even walls—five millimeters of solid mithril. My old master forged kettles with similar care; I aimed for her precision. I layered mithril ingots, hammered them flat, shaped the sheet into a cylinder, and fused the edges with my Crafting skill instead of welding. I made three identical chambers, each with a fuel injector and ignition system. To prevent disaster, I added intake and check valves—without them, burning air backflow could be catastrophic.
With the inner structure set, I assembled and tested the parts. Turning the turbine shaft by hand, I saw air flow smoothly into the combustion chamber. No leaks. Relief eased my shoulders. The exhaust spun the rear turbine as designed, powering the next intake. I skipped the generator turbine—it would’ve created an endless-motion nightmare. With my luck, Archangel would stab me before I finished explaining.
Next came the fuel injector. If the spray wasn’t exact, it wouldn’t ignite and would explode. I’d seen heat melt a mithril golem, and even reinforced metal would crumble if the mix was wrong. Using the 1:14.7 air-fuel ratio from my previous world, I tested with liquefied mana stone. I surrounded the bench with impact and heat barriers, then ignited the mixture.
The barrier shattered, and the bench cracked in half.
”…You’ve got to be kidding.”
”This could make an excellent bomb, Master,” Dahlia said calmly.
”Yeah, and the City Mayor will ban me for life. That barrier was Elingium-tier—it should hold unless pierced.”
”I see. Then it’s powerful enough for thrust-based flight,” she said with unnerving delight.
”Are you listening to me?”
The triple soundproof barriers contained the blast, but the roar still rang my ears. Dahlia seemed unfazed—her eyes sparkled with dangerous excitement.
After that, I spent hours finding the ideal ratio: 1:22.8—enough for full combustion without wasted mana residue. Even then, five-millimeter forged mithril barely survived the intense heat. Liquefied mana stone was terrifying.
”Master, the combustion chamber will melt like this,” Dahlia warned.
”I know. We’ll build it from something stronger.”
I forged one-millimeter adamantite plates—the best heat-resistant metal—and lined the chamber’s interior. A single millimeter of adamantite blocks eighty percent of a dragon’s breath. If I had more, I’d make the entire chamber from it, but this will do.
Testing again, the inner wall held firm. Success. I reforged the turbine shaft and fins from adamantite, melting down the old ones for reuse.
Next was the nozzle. It needed to expand and contract exhaust to control thrust. I forged the outer shell from mithril and the inner lining from adamantite—two layers for maximum endurance. Several interlocking plates allowed movement, and they shifted smoothly when tested. Perfect.
Finally, I built the outer casing—sleek, streamlined mithril for minimal air resistance. The prototype magic-powered reaction propulsion system—the “Proto Jet Engine”—was complete. Without fuel, it weighed under five kilograms.
”…It’s finished, Master,” Dahlia said softly.
”Yeah. A prototype, but a real jet engine all the same.”
The whole process took about two hours, including tests. Next time, I could make one in an hour.
”Shall we—”
”Time to make the second one.”
”…Excuse me?”
Dahlia froze, staring blankly. She’d seen the blueprints—she had to know.
”The flight unit uses twin engines—two side by side. We still need another.”
”You mean… we’re mounting two of these monsters?”
”Don’t you want to?”
Actually, including tail binders, the total would be four. Dahlia lowered her head, trembling—and then—
”Magnificent, Master!!”
It had been a while since I’d seen that reaction.
”To double the power of a perfect engine without compromise, to chase progress with such passion—truly a pioneer’s spirit! Even one unit could surpass the speed of sound! But with two—imagine the thrust! If your concept works and the barrier overcomes air resistance, we’ll break every speed record! We’ll be the fastest—untouchable even to our shadows!”
”Alright, calm down.”
It had been months—or maybe just two weeks—since I’d heard her full chanting rhythm. Hard to tell.
”And with this structure,” she continued, glowing, “the body floats with an antigravity spell and gains lift from a flight spell. The engines focus purely on thrust! Normally, jets need airflow to start, but this allows vertical takeoff—freedom to fly anytime, anywhere! My armor proves true freedom in this world!”
”Yeah, I get it, you’re happy. Please calm down?”
No use—she was in full chant mode, even activating her super-armor protocol.
”If you’re this hyped because you’re tired, maybe call it a night. Your brain’s swimming in happy chemicals.”
”No, Master. Let’s continue.”
”That was… fast,” I muttered. “You flipped the switch quickly.”
Still, her focus helped. We had more to do tonight.
We built the second engine and attached both to the connector unit, which doubled as a fuel tank. The design was inspired by an old real-robot anime from my previous life—the first hero machine’s booster pack. I added ports for extra fuel tanks for long-distance travel.
With the flight unit complete, it was time for the armor. Dahlia handed me her temporary suit, Alstroemeria, and I started removing the inner components. Her expression turned lonely, but when she remembered the new armor, her eyes shone again.
The wire anchor was built into the tail binder at the waist. The binder also held a small sub-engine and extra fuel tanks. The sub-engine was smaller and weaker than the twin main thrusters—for quick evasions or sharp turns during flight. Its flexible connectors allowed slight shifts, giving the unit fluid, balanced motion. With that, the rear waist module was complete.
The design was sleek and aerodynamic. I shaped the chest to cut through air cleanly, even without a wind-magic barrier. This gave Dahlia a slightly fuller chest shape, though underneath… flat as a board. Best not to comment.
I spared no materials this time. The outer armor was orichalcum and adamantite composite. My old master taught me that a katana with two parts orichalcum to one part adamantite reached ideal balance—and she was right. By weaving adamantite through orichalcum during forging, I boosted its strength nearly twofold. With Dahlia’s mind-link resonance, strength would rise another fifty percent. Perfect blade alloy, perfect armor.
To reduce drag, I gave the frame a slim silhouette. Still, I added retractable arm racks for her favorite sword—like the tonfa mount of a famous unicorn mobile warrior or a German ninja’s forearm blades. Not the most aerodynamic, but practicality beat style here. Dahlia needed to draw and fight instantly.
No skirt armor this time. From the front, the waist looked like a high-cut leotard, but protection came from inner muscle armor. I added a “Genbu” model internal structure—extra artificial muscle layers at every joint to increase power output.
Her legs ended in high-heeled feet with small nozzles releasing compressed air. They helped with balance, turns, and high-speed braking.
Finally, I added back connectors for the flight unit and storage bays on shoulders, arms, and calves for optional equipment. With that, the armor body was done.
Now it was my turn to add my answer—to Dahlia’s “romance.”
I fitted shoulder bays with attachable armor plating, extra boosters, and missile pods. I hadn’t given the main frame built-in artillery to keep it adaptable; modular weapons let it respond to any situation. This design became standard in later Arcane Armor models.
The main unit stayed affordable; optional gear cost extra. Some might call it greedy, but not everyone needed flight units or artillery. A modular setup let buyers avoid waste and tailor builds for specific missions.
Each arm carried two mana-focusing cannons, two rotating ballistic guns, and shields above them. The legs were the flight units. Think of offshoot mobile warriors from space-era side stories or the crimson kabuto from an old super-robot manga’s final charge. Yeah, that vibe.
Lastly, I added parts to prevent shoulder units from interfering with the wings, then mounted the twin engines. Two Elingium cannons went on top, completing the frame.
Control depended entirely on the pilot—definitely not beginner-friendly—but Dahlia could handle it. At max thrust, it could probably break free from gravity. Not that we’d ever need to.
”…Master, what is this?”
She stood staring at her new Arcane Armor, her voice caught between awe and disbelief. It hung from a reinforced hanger, too heavy for the standard frame. From my angle, I couldn’t see her face.
”I’m sorry, Dahlia,” I said. “I used your armor to test next-generation concepts. It has new weapon bays and test units for higher firepower. If it’s too much, we can remove them. Or, if they get in the way mid-battle, explosive bolts let you jettison them safely.”
Dahlia lowered her head, trembling. I sighed and covered my ears.
”Magnificent, Master!!”
Just as I thought. Dahlia adored prototypes and test models—pure engineering romance.
”Even base Arcane Armor achieves power and defense through its inner muscle frame and orichalcum-adamantite body,” she began, glowing with excitement. “Then you add the tail binder and sub-jets for agility, arm racks for swift melee, extra artificial muscles for power! Even if grabbed, foot thrusters tear free! No weaknesses! With this weaponry—overwhelming force! Defense and thrust in harmony! To strengthen under such weight——Master, your thinking is beyond normal limits!”
Well. She really liked it.
”The only issue,” I noted, “is that the added gear blocks the arm racks.”
”True,” Dahlia admitted, “but with shields included, that flaw is offset.”
She understood perfectly. That was a relief.
”Then, Master,” she said, eyes shining, “please name this armor and its equipment set.”
Ah. Right. I’d forgotten.
”…You name the armor, Dahlia.”
”Me?”
”Yeah. You’ll be the one using it. Pick something that feels right.”
The prototype’s code name was Gladiolus, but it had evolved far beyond that—no longer fitting for a mass-production tag.
”In that case,” she said softly, “I’ll call it Tritelia.”
Tritelia. The flower that means protection. Of course—she’d learned my naming pattern well.
”Good name,” I said.
Dahlia smiled—a full, radiant smile. Sometimes I forgot how beautiful she really was.
”Then, Master,” she said, voice bright with curiosity, “what will you name the new weapon system you built for it?”
Well, this was a problem. I’d just told Dahlia to name her armor, so there was no way I could dodge naming the weapon system myself. “Weapon Package” sounded fine to me—but she’d definitely frown at that. Still, I gave it a try.
”How about… Weapon Package?”
”That’s a little too plain, isn’t it?” Dahlia said thoughtfully. “I like simple names, but the Whirlwind division would probably prefer something more elegant.”
How does she always know what I’m thinking? I sighed.
”Then maybe… Fireworks?”
”Ah, so you plan to turn enemies into dirty fireworks, Master?”
”I did not say that.”
It was just a name I came up with because of the rising firepower—but somehow she managed to twist it into something terrifying.
”Very well,” she said brightly. “Then, I’ll take this ‘Tritelia Fireworks’ out for a test tomorrow.”
”Wait, test it where?”
There was no way she could run a full-power test inside Whirlwind HQ—it’d blow the walls apart. Even in the dungeon, she’d probably crash through stone with that much thrust.
”I’ll fly from this city to my hometown,” she explained. “With maintenance stops, I should be back within a day or two.”
”Maintenance—? Dahlia, I can’t come with you. I haven’t even made a teleport marker or a gate yet.”
Even if she called it maintenance, there was no one else who could perform it. And test-running an unverified build solo? That was begging for an explosion.
”It’s fine, Master,” she said, her voice steady. “I watched you build it. I can handle basic maintenance myself—though not at your level, of course. Besides, my Automaton Maiden abilities let me adjust for small errors on the fly.”
I had no counter to that. She wasn’t wrong, and I couldn’t exactly forbid her. Her travel permit from before should still be valid anyway.
”Fine,” I said at last, rubbing my temples. “Just get back safely, alright? You’re family too.”
”Yes, my Master.”
She smiled then—innocent, almost childlike.
After sending Dahlia back to her quarters, I stayed in the forge alone. Before me lay the adamantite Chef had entrusted to me. Time to craft the maguro-slicing knife she’d ordered. The deadline was tomorrow, but I didn’t want to risk running out of time later. Not that Chef would scold me if I missed it… more likely she’d sulk or cry, and I couldn’t stand that. I wanted her—and all the poster girls—to keep smiling.
So I followed the same old process, the same rhythm. As when I made my own tuna knife, I hummed quietly while I worked. Based on today’s experiments, I knew orichalcum-adamantite composite was ideal, but I only had pure adamantite now, so I focused on perfecting that.
Two hours passed before I set the hammer down. Longer than usual, but the result was worth it—better even than my own Shinguro. Even a single knife could show how far I’d come.
Using ebony from the Acting Head’s souvenir, I made the handle. The blade and grip both gleamed black—fitting for a tuna knife, I guess. Though, yeah… “all-black tuna blade” did sound ridiculous.
As always, I tried an Appraisal—but it bounced back, treating it as a different item from Shinguro. Figures.
Now, how to give it to Chef? She tended to appear at random… I could just wait until tomorrow.
(Who said you could go this far?)
A voice brushed against my mind. I turned—and of course, there she was. Chef, arms crossed, eyes narrowed, plush cat in hand. She really did love that thing.
”Perfect timing,” I said. “I was wondering how to hand this over.”
(If that were the case, you could’ve just shouted your love for me into the sky. I’d arrive at the speed of light.)
”Yeah, no. Not doing that, idiot.”
If Ethelena ever overheard that, I’d be strangled on the spot. And anyway, this was her commission; no way I’d summon an Archangel just to deliver it.
”Anyway, here. The maguro knife you ordered. Take a look.”
She accepted it with both hands, eyes focused on the blade’s dark gleam.
(…What is this Special Ability? Who told you to make it this overpowered?)
”It only works on seafood,” I said with a grin. “Pretty fun, right?”
(Well… a tool made to serve its purpose perfectly is a true tool, I suppose.)
She sighed—but the fact that she could read the Special Ability of a tuna knife that didn’t even exist in this world? That was peak Chef. Guess that’s what being part of the system gets you.
”At least give it a name,” I said.
(Then… since it’s a maguro knife, how about ‘Shinkuroso’?)
”Whoa, hold on! That sounds like some superdimensional fortress!”
For the record, so is a kind of Japanese cheese, not something you make from tuna. Still, she looked way too pleased with herself.
(One day early, but I’ll accept the delivery. You used the techniques your master taught you—I’ll score that high.)
”Yeah, I took extra care this time.”
When you inherit your master’s craft, you don’t slack. Translating katana forging into knife-making had its own challenges, but I was proud of what I’d made.
(Then, here’s your payment.)
”A weapon? That’s unusual for you.”
She handed me a longsword—a beautifully crafted one. Black sheath and hilt with golden accents, a blue gem gleaming at the guard.
(It will, in time, save you.)
”This sword? I don’t even use blades.”
(You won’t need to. It will help you just the same.)
So… one of my companions, then? But somehow, it didn’t feel right for any of them. If anything, it felt like something that belonged in Archangel’s hands.
”Alright,” I said finally. “I’ll hold onto it. If it’s meant to help me, I’ll trust it.”
(It’s your reward. But if you don’t like it, melt it down.)
”Not a chance,” I said firmly. “You made this for me. I’ll treasure it.”
She looked away, a faint sadness in her tone as she exhaled.
(…I see. Then take good care of it. Farewell.)
With a quick curtsey, she turned and left. I caught a glimpse of her ears—flushed red.
Tomorrow, the shop opens again. I should get some sleep.
Notes:
• Dahlia – The automaton.
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Edited by Kanaa-senpai.
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