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The flat white stones and interlocking bronzework that comprised bay 04 of the Old Sharlayan airship landing were covered in a variety of mobile workbenches and toolboxes; all dwarfed by the massive airship sitting on the pad with one of its large engines demounted and suspended off of a repurposed loading crane. Its armored metal housings sat neatly in a corner of the landing pad, covered by a light brown cloth tarp, leaving the internal workings of the lengthy thruster bare for repairs. Aydria’s torque wrench clicked as she finished replacing a bolt, put back into place at the perfect level of tightness.
She turned around to put the tool back, surprised to find a slight blue-haired hyuran girl staring at her. “Oh, um, hello,” she ventured. “You alright, kid?”
“That’s the Fulcrum , isn’t it? The Warrior of Light’s airship?” the brown-eyed child asked, not answering the question.
“Sure is; one of the fastest airships on the star!” Aydria replied proudly, passively glancing around for the child’s parents.
“So it’s all true, then?” the young girl said, amazed, “the stories that everyone tells about the Fulcrum outrunning Garlean airships with its specially designed engines?”
“One of a kind, yep! Shouldn’t you be in school or something?”
The girl waved the Warrior of Light off as though the very idea was preposterous. “They don’t teach anything interesting in school. How does it work?” they asked, walking over and plopping themselves on top of a toolbox as an impromptu seat, head promptly placed in upturned hands expectantly.
“The engine?” Aydria asked, amused by the child’s stubbornness.
“Yeah, how’s it work?”
“I, uh…I’m not really sure how I’d explain it in a way someone your age could understand, to be honest.”
The girl rolled her eyes. “My dads are both on the faculty of engineering, and I’m only a few years behind the famous Leveilleur twins on track for the fastest graduation from Studium. I can understand more than you think I can.”
“How old are you?”
“I’m 10. Can you answer the question?”
Aydria pulled a small cloth hanging off of a disconnected hose from the side of the engine and began to clean some of the black oil off her hands. “ Hey, C! ” she shouted over her shoulder, “ c’mere! I need you for something! ”
A whirring sound emanated from the far side of the ship, accompanied by the thudding metal steps colliding with the landing pad. C-V01, Aydria’s robotic companion, rounded the front of the ship and noisily walked up to the small miqo’te Warrior of Light and the barely smaller child.
“<Captain?>” it prompted, bright blue eye shining from the center of its steel-plated rectangular head that stared down at them from its towering nearly 7 fulm height.
“Pull up the engine schematics, would you? And put them on projection.”
The small girl stared wide-eyed up at the talking machine before her as it whirred and softly clunked, indexing internal file systems and then projecting a flickering blue hologram of the engine next to them into the air.
“Alright, so,” Aydria began, “basics first: how propulsion even works. You know what balloons are, right?”
“Of course.”
“Good. So, balloons, when you fill them up, they want to deflate again, unless you block the stem. If you unblock it, all the air you pushed into the balloon will escape out the hole, and when that happens, the side of the balloon opposite the hole has pressure put on it, which is what makes balloons go flying off if you fill one up and then let go. What makes the balloon go, that’s called thrust. Following so far?”
The girl nodded, visibly concentrating.
“Great. So, to the engine,” Aydria said, manipulating the model in the air and spinning it around so the rear of the engine was facing the girl. “Put really basically, this whole engine works on the same principle - make a pressure differential, and make it apply thrust this way,” she explained, running a finger along the model in the direction of the front.
“How does it do that?” asked the girl, impatient.
“I’m getting there, just hold on. C-V, cross section of the model please?” Aydria asked her metal friend. The model shifted, cutting the engine right down the center and baring the internal design. “Thanks. We’ll start right here at the front of the engine, in the air intake,” she said, spinning the model so it was facing the girl. “This part’s pretty straightforward, it does exactly what it’s called - takes in air for all the rest of the stages of the engine. It leads directly into the next stage, here, with all the rotors around that center turbine shaft, which is called the compressor. Now, you see how all the rotors get smaller and smaller with the walls of the engine?”
The girl nodded again.
“All those rotors are spinning really fast, like, thousands of times a second fast. They’re all pulling air in further and further up, and that air all has nowhere to go, so it gets packed in tighter together.”
“Compressed,” interrupted the girl.
“Yep, that’s why it’s called the compressor! Compressing all the air in the tighter space creates higher pressures and heats it up, so the pressure here, at the air intake, and the pressure here, at the back of the compressor,” Aydria said, illustrating with her fingers on the diagram in the air, “is 50 times lower.”
“So where’s all the compressed air go? Just slanting some walls like that isn’t going to make that thing fly,” the girl said incredulously, pointing at the Fulcrum sitting behind the Warrior of Light.
“You’re right, it wouldn’t - which is why the air from the compressor goes into the combustion chamber, here, where it mixes with injected fuel, which heats it up and burns some of the air. Now, here, the engine is getting a very specific amount of fuel, because if it’s not supplied in the right amounts to match with the air flowing through the combustor, it’ll leave excess fuel in there, which just generates a ton of soot, and we don’t want that to happen. That, and if it gets too much fuel, even if it all burns properly, the engine could overheat, and we don’t want that either.”
“So, all the air is now blasted and super hot, and it’s gotta go somewhere,” Aydria continued, “so it leaves the combustion chamber and goes out through the turbine, where as you can probably see, it’s allowed to expand a little bit with the engine walls getting a little wider for a second in here. This very first stage of the turbine is getting all the hot air passed through it over and over again, so without something to cool it off, it’d get hot too, and get damaged - but we didn’t burn all the air from the compressor in the combustion chamber, so we pull some of that air, which is still cold enough, to keep it cool enough,” she said, drawing a line between the compressor and the turbine with her hands along the model. “You still with me?”
“I…think so,” the girl replied, brow furrowed deeply in concentration.
“Good. So, the turbine is made to spin from all the hot air hitting it over and over again, and this is the point where if I were to turn that on,” Aydria said, sticking a thumb over her shoulder at the demounted and stripped engine, “it would actually be starting. Because this turbine spinning is what drives the compressor, which makes everything go, spinning faster and faster. Anyway, I’m getting ahead of myself. Once the superheated air leaves the turbine, which I had to make from a special alloy just so it could even withstand the temperatures, it flows out as exhaust through the nozzle section, here,” she said, circling the slanted nozzle cross-section with her hands.
“Wait,” the girl said, stopping the Warrior of Light from continuing, “it’s slanted there at the end, in the nozzle, like the compressor. I thought you already got it hot, why do it again?”
“You remember the balloon?”
“Yeah, but-”
“You know how if you let only a little bit of air leave a balloon, it makes a really high pitched squeaking noise?”
“Yeah, but that doesn’t-”
“That’s because it’s going faster through the smaller hole. And so we’re doing the same thing here, and making the air a little hotter by re-compressing it slightly so that the thrust we get out the end is as high as we can get it.”
“Oh. What’re all those little things dotted around the inside of the nozzle, then?”
“Those are thrust augmentation afterburners; they can burn even more fuel after the turbine to make the air even hotter and make it flow even faster, but it makes the fuel efficiency of the engine absolutely plummet, so it’s only for short bursts of speed.”
“<You use it very often,>” C-V01 opined, breaking its silence on the lesson.
“C, I did not ask,” Aydria said, rolling her eyes.
“<I understand,>” the machine said, resuming its silent projection of the engine model.
“So, to summarize for you, I guess - air comes in the compressor, gets heated up, mixes in the combustor with fuel and burns to turn the turbine, then flows out as exhaust thrust,” the miqo’te said, crossing her arms over her coveralls.
“Hm. That’s a lot simpler than I thought it would be,” the girl said thoughtfully.
“I suppose it is, if I’m not bearing down into every single part. You can shut the projection, off, C.”
The blue light flickered as C-V01’s projection faded from midair.
“Say, kid, I don’t think you ever told me your name? You seem to know who I am, but…?”
“Hanna? Twelve above, there you are!” cried a man’s voice from the far side of the airship landing. “We’ve been looking all over for you!”
The girl sighed. “I’m fine, dad! The Warrior of Light was just giving me a lesson!” she called back. “Just go with it,” she said quietly to the miqo’te.
“A lesson from the Warrior of Light?! Young lady, I-” the man stopped as he approached, jacket askew from having run across Sharlayan looking for his daughter. “Oh, my, it really is you! I was about to chastise her for lying, but it’s really you! May I just say, Miss Fireheart, your designs are a marvel! I’ve long admired the Fulcrum just watching it from afar, but to meet you in person, well - it’s an honor!”
Aydria gave a small salute off her forehead with two fingers. “Well, glad to be appreciated, I suppose. Hanna here was an attentive learner; I gave them a short lesson on some mechanics.”
“<She mentioned that the Studium does, quote, ‘not teach anything interesting,’>” C-V01 shared unprompted, towering frame looking down on the trio.
“Don’t mind him,” Aydria quickly covered for Hanna, “he tends to just say anything that comes into his circuits.”
“Well, I’m sure any lesson you could give her would be interesting for her, coming from the Warrior of Light and all. So sorry to impose, I’m sure you have more important business to attend to,” the girl’s father said as way of farewell.
“Hey, wait, before you go,” Aydria interrupted, turning and rifling through a toolchest. When she turned back, she held in her hand a small hammer. “Take this. You’re a smart kid, Hanna - listen to your dads, and finish your school, and I’m sure you’ll make a fine engineer someday.”
The girl reached out and took the hammer in both hands, trying and failing to hide their obvious joy at recognition from the famed Warrior of Light and play it cool. “W-wow, um. Thank you!”
“Go on, now. You should get back to class,” Aydria said with a smile.
She watched as the girl and her father departed in the direction of the Studium, wondering what she must have been like when she was that age.
“<I will replace the hammer,>” C-V01 chimed in from behind her.
“...yeah,” Aydria said absentmindedly. “How’s the calibration coming on the dampers?”
“<Calibration was 87.74% complete before I was interrupted,>” C-V01 complained.
“Well, what’re you waiting for? I’ll need the dampers working before we can remount the engine,” Aydria said.
“<I understand,>” her robotic companion answered, turning and clankily walking back off towards the bow of the ship.
Aydria turned and picked up a screwdriver, thoughts drifting towards adventures and design upgrades as she set back to work piecing the engine back together.