The prototype's maneuverability far exceeded Jin's expectations.
While structurally incapable of inverted flight, it performed loops with ease.
Vertical ascents and descents posed no problem either.
It could even maintain a horizontal roll for short bursts.
"Father, compared to this morning's craft, the handling has improved dramatically."
"Looks like it....Alright, let's head back to the laboratory."
"Understood."
Deciding he had gathered plenty of data for a prototype run, Jin chose to return to the laboratory for the time being.
"Hmm, looks like the joints were a bit too weak for stunt maneuvers," Jin muttered as he inspected the craft.
"Naturally, after flying like that," Elsa said, having followed him into the workshop. Jin offered a wry smile and nodded.
"Fair enough. Blow Planes aren't meant for stunts in the first place."
It was even less suited for it than trying to drift a family car, Jin thought.
Still, the possibility of being forced into such maneuvers in an emergency was never zero. Jin set about strengthening the affected areas.
"If I double the overall structural strength, it should hold up even if we push the speed higher."
"Jin-nii, what's the concept behind this craft?"
"The Eagle Unit 1 was a personal passenger car. This one is a sports car."
Jin gave an analogy that meant little to the people of Planet Ars.
To Reiko and Elsa, however, it made perfect sense.
"In other words, you designed it with longer-distance flights in mind?"
"Exactly."
"Father, how does maneuverability factor into that?"
"Well... how should I put it?" Jin paused to consider how best to answer Reiko's question. "As speed increases, the reaction window to avoid hazards shrinks. So, improving the craft's responsiveness definitely serves a purpose... I think."
"I see. That makes sense."
"At the same time, I aimed to improve straight-line stability."
Stable during ordinary flight, yet nimble enough to pull off sharp evasive maneuvers when needed. That was Jin's goal.
"The Eagle Unit 1 was built for getting around within and around a town, but this prototype is intended for traveling from one town to another....At least, that's the official justification."
Here, Jin revealed his true motivation.
"Mostly, I just wanted to build it."
"......Mm, fair enough."
As a fellow craftsman, Elsa understood the urge to see just how far one could push a design, and she gave a quiet nod.
"And with that, the modifications are done. Reiko, take it out for another spin."
"Yes, Father."
The refined prototype performed with even greater finesse.
"Father, it has become much easier to handle!"
"Alright, bring it down for a landing."
After roughly fifteen minutes of test flights, Jin called for a brief intermission.
He inspected the prototype once it touched down in the laboratory courtyard. Finding no abnormalities anywhere on the craft, he turned to the others.
"Hope, you take the helm this time. Reiko, I'd like you to pilot the Eagle Unit 1."
"Understood."
"Yes, Father."
The two craft once again soared into the sky above Hourai Island.
Jin and Elsa boarded the Eagle Unit 1 under Reiko's control.
"Alright Hope, how does it feel?" Jin asked, transmitting via the manacam function of his Fellowship Bracelet.
"Yes, Master. It feels quite similar to the Eagle Unit 1. However, the rudder response here is much more direct."
"Good to hear."
The new feature Jin had implemented this time was variable handling characteristics based on speed and flight maneuvers.
During low-speed operations involving repeated turns, the controls were tuned to be agile and responsive; during high-speed, long-distance cruising, the sensitivity was dialed back for steadier control.
"Jin-nii, what happens if you need to take evasive action during long-distance flight?" Elsa asked after hearing his explanation.
"Rapid movement of the control stick immediately switches the handling profile, so dodging hazards shouldn't be an issue."
"What if someone makes a mistake?"
Elsa posed the question on the assumption that human error was inevitable.
"Blow Planes are naturally very stable to begin with. Even an abrupt attitude shift won't result in a total loss of control....Still, it'll be good practice to test those scenarios going forward."
"Mm."
While an operational mistake was virtually impossible for someone like Hope or Reiko, mathematically the chance was never absolute zero.
Because of that, Jin and Elsa wanted to build in every margin of safety possible.
After another landing, Jin made further adjustments before initiating another flight test.
Then came yet another landing and more fine-tuning.
"...Yeah, this ought to do it."
Jin had originally planned to board the craft himself for the final evaluation, but Elsa's objections won out, leading them to ride along via their Doppels instead.
Even so, they could fully appreciate the ride comfort.
"Mm, better than expected."
Elsa, who was also aboard via her Doppel, deemed the performance beyond reproach.
"It's not really a prototype anymore, is it?"
Having brought the craft back into the workshop for post-flight maintenance, Jin turned his thoughts to giving it a proper name.
"Mm, what will you call it?"
"At first, I was thinking of naming it 'Gemini'."
That would have worked back when it only had two circular wings on the left and right, but this completed design featured smaller circular wings at the front and back as well.
"Four wings... forming a cross... 'Southern Cross'."
The Southern Cross, or the constellation Crux. It was a famous constellation in Earth's Southern Hemisphere, visible south of the Tropic of Cancer.
Its four prominent stars traced the shape of a cross when connected, which gave the constellation its name.
It also served as a navigational landmark for locating the celestial South Pole.
Among astronomy enthusiasts, it was equally renowned for the dark nebula known as the Coalsack resting to its lower left.
Jin had only ever seen photographs of it, but he had always privately thought that it looked far more like a squid-type paper airplane than an actual cross.
As a side note, there was also a constellation called the Northern Cross, which served as an alternate name for Cygnus.
Regardless, Jin liked the ring of the name, and so he officially christened the new Blow Plane the 'Southern Cross'.