The prototype aircraft, built to give shape to Jin's idea, made a stable ascent into the air.
However, that stability was merely superficial. One could see Reiko utilizing exquisite control to suppress its pitching—the tendency to rotate up and down along its lateral axis.
"Hmm, as I thought, is it hard to handle?"
Having reached an altitude of about twenty meters, Reiko initiated a gentle turn.
"Oh, this part is stable."
Since the craft was symmetrical from left to right, it proved exceptionally resistant to rolling—the disturbance of rotating side to side along its longitudinal axis.
"Fumu. In that case, it'd probably be better to make it fore-and-aft symmetrical as well."
Jin muttered to himself as he observed the prototype's flight characteristics.
Reiko gradually tightened the radius of her turn from wide to narrow.
A fifty-meter radius became forty, then thirty-five, then thirty.
The prototype had a total wingspan of around ten meters. For a conventional aircraft relying purely on aerodynamic lift, executing a turn with such a tight radius would have been impossible.
The craft was now banked about twenty degrees to the right, continuing its turn.
"With this method, that's about the limit, huh."
A turning radius of roughly twenty meters was achievable.
"If we lean into its characteristics as a VTOL, though... Oh, exactly like that."
As if reading Jin's thoughts, Reiko demonstrated its VTOL capabilities by coming to a complete hover in midair before slowly changing its heading on the spot.
"Yeah, that's it. With that approach, it can change direction right where it is....All right."
Jin waved his hand, signaling Reiko to land.
The prototype touched down about ten meters away from him.
"Reiko, well done."
"Yes, Father."
"Thanks to that, I've spotted several issues."
Before tackling them, however, it was time for lunch.
"Jin-nii, food's ready."
Elsa had come out to call for him.
"Yeah, got it."
After instructing the Smith golems to carry the prototype back to the workshop, Jin followed Elsa toward the laboratory's dining hall.
Lunch that day consisted of sandwiches.
Ham, fresh vegetables, tuna salad, egg, ham cutlet, and more.
Once they finished eating, Elsa spoke up.
"How are things going? On my end, everything's smooth."
"Hmm... The first half was so-so. But I put together another prototype, and that one seems a lot more promising."
"I see. I'll come take a look later."
"Sure."
Quenching their thirst with citran juice, each went off to finish their remaining tasks.
Jin headed to the workshop, while Elsa made her way to the repository.
Standing before the prototype in the workshop, Jin smacked his right fist into his open left palm.
"Now then, let's fix this up a bit."
"Father, which parts will you be altering?" Reiko asked.
"Well, I'm thinking of making it fore-and-aft symmetrical as well."
Because the left and right sides were already symmetrical, it possessed excellent lateral balance.
Along its fore-and-aft axis, however, the balance was thrown off by the positioning of the cockpit and the propulsion system.
His plan was to correct that distribution properly.
"Let's bring the cockpit right over the center of gravity."
Furthermore, placing the propulsion systems beneath the left and right circular wings would make it even more stable.
Since the base concept was a Blow Floater, suspending the load beneath the circular wings naturally enhanced overall stability.
He made the front and rear circular wings identical in size and set them at equal distances from the center of gravity to keep everything balanced.
To put it in more technical terms, he was balancing the moments.
"All right, give it a try like this."
"Yes, Father."
They brought the modified prototype back out in front of the laboratory, and Reiko settled into the cockpit once more.
"Here I go."
Announcing her takeoff, Reiko engaged the Blow Engine.
The prototype ascended smoothly into the air.
"Oh, the stability looks great."
This time, without needing any active control compensations, the aircraft climbed vertically while maintaining a rock-steady posture.
Reiko entered a turn at an altitude of twenty meters.
As far as turning went, the performance remained as solid as before.
After completing a turn with a twenty-meter radius, Reiko moved on to vertical maneuverability tests.
"Oh, that's so much better."
Thanks to the balanced fore-and-aft configuration, gentle ascents and descents were remarkably steady.
"All right, Hope, we're taking the Eagle Unit 1 up."
"Yes, Master."
Observing from the ground was no longer enough, so Jin decided to monitor the flight from the sky.
"Jin-nii, let me come too."
Elsa arrived just in time. It seemed she had finished organizing her documents.
Since the Eagle Unit 1 seated six, accommodating her was no problem at all.
"Sure. Hop in, quick."
"Mm."
Carrying Jin, Elsa, and Hope, the Eagle Unit 1 took to the skies above Hourai Island, immediately moving to pursue the prototype.
"Reiko, we're heading out over Tatsumi Bay."
"Yes, Father."
Jin contacted Reiko through the communication function of his Fellowship Bracelet.
With that, the Smith golems maintaining the barrier on the ground were dismissed.
Cruising at roughly one hundred kilometers per hour, the two aircraft reached the airspace above Tatsumi Bay in the blink of an eye.
"All right, first up is the top-speed test. Try flying in a straight line."
"Understood."
The prototype surged forward, accelerating out toward the open sea with the Eagle Unit 1 trailing behind.
"Whoa, it's fast."
The Eagle Unit 1 had a top speed of two hundred kilometers per hour. Even at full throttle, the distance between it and the prototype steadily widened.
"Maximum speed is approximately two hundred and fifty kilometers per hour," Reiko reported.
"Got it. Next, test out its maneuverability....Just make sure not to push it to the absolute limit right away."
"Understood."
Jin held his breath, intently watching the prototype's every movement.