The morning after our first night on Onogoro Island.

"Father, what are your plans for today?"

Reiko asked Jin as he finished rinsing his mouth and washing his face.

"Well, I'm going to build the small plane with the that I promised ......, and then I'm going back to Horai Island after watching the final game.

"Okay."

Before that, Jin was going to have a close-up look at Rubina and Shu's planes.

But first, breakfast.

This morning's menu was Japanese style.

Porridge, pickled ume plum, tsukudani of kombu seaweed, miso soup with fried bean curd and leek, fillets of mejika (salmon), and oshinko (Japanese pickles).

"Yes, this pickled plum is delicious."

"It's so sweet."

"The tsukudani tsukudani tastes good, too."

"It's well cooked."

Jin, Reiko, and Marikka had breakfast together. Reiko, however, did not eat, so I served her a refill and poured her some tea.

"Oh, it was delicious.

"Yes, it was delicious."

Jin and Marikka are drinking their after-meal brown rice tea with satisfaction.

"Let's go see Rubina and Shu's plane in a little while.

"Yes."

Both planes should be in the hangar at the airfield where the final match was held.

The second final starts at 9:00 a.m. It's 7:30 a.m. now. We don't have much time.

"Mr. Jin, Ms. Marikka, thank you for waiting."

Then Trichardt Randl, the caretaker, came in.

"Oh, we've been waiting for you. Let's go."

The trip to the warp gate is instantaneous.

"Ah, Mr. Jin, Ms. Marikka."

Welcome!"

Rubina and Shu greeted us at the warp gate of the airfield.

"Come on, take a look!　"Come on, take a look! And keep pointing out what's wrong!　If it can't be done today, it will be fixed by next time!"

Rubina is always so positive.

"That's what I'm good at."

"Ha-ha-ha."

We enter the hangar with this conversation. It seems that this hangar also serves as a simple maintenance dock.

"Oh!"

Jin is impressed by the spacious interior.

In the center of the hangar were two airplanes.

They are about 8 meters long. They are quite small.

Next to them stood the pilot's golem. He, too, was small, about the height of an elementary school student.

"What are the regulations this time?"

"The overall length and width must be no less than 7 meters and no more than 8 meters, and the overall height is not specified. Driven by a magical jet propulsion engine (Magijet engine). No more than two propulsion units. The pilot was Golem ......."

There are some detailed regulations, but Jin did not ask about them.

One of the regulations was that it had to be over 7 meters, which seemed to indicate that aerial combat was assumed.

"I see...and then aerial combat......... is a disadvantage if the target is large..."

The larger the target, the more likely it is to be hit.

"So, Jin-sama, what do you think?"

"Well, I'd say ...... Rubina's plane is an 85 and Shu's is an 80."

"That's a tough ......."

"That's a tough one. ......

"Oh, let me tell you, even my own creations don't get a perfect score of 100.　Even Reiko's body is only a 95. As a ...... girl, I'd give her 120 points, which is more than 100 points."

Jin's theory is that if you give a perfect score, progress and development will stop.

He wants to be a challenger forever. This is Jin's creed.

"......I see. So, 85 points is a pretty good score.

"Well, why is my score 5 points lower than yours?"

"Yes. Well, I'll explain it to you shortly.

Jin began his evaluation by looking at Shu's score.

"I deducted points for the position of the horizontal tail.

"What do you mean?"

"It is at the same height as the main wing when viewed from the front, right?"

"Yes . I was trying to reduce the aerodynamic drag as much as possible. ......"

"That's why the horizontal tail is not working so well. It's not very good, is it? ...... slightly, of course, but..."

Uh, yes.

"That's because the horizontal tail fins are in the air turbulence created by the wings."

The trailing edge of the wing generates turbulence, or air turbulence, which flows backward.

Jin explained that because the horizontal tail fin is in the turbulence, the horizontal tail fin ...... elevator is not as effective as it should be.

"I didn't know that. ......"

"I think I told someone about this before, during the model airplane competition. ...... I guess I wasn't thorough enough. ......"

Jin further explained that in such a case, it would be a good idea to conduct wind tunnel tests using a model airplane.

Wind tunnel tests are conducted by artificially creating a wind flow and making it seem as if the aircraft is flying, in order to investigate the occurrence of air resistance and other phenomena.

It is not limited to aircraft, but is also used in automobile body design.

"Wind tunnel testing. ...... I see."

"Trihart, can't we build one somewhere?"

Jin asked Trihardt, his sponsor, for advice.

"Yes, Jin-sama. I think it is possible. I'll make arrangements after this.

"Yes, please. I'll have the old man send the details to .

Thank you very much.

We have already conducted wind tunnel experiments on Horai Island. Using that data, we should be able to build a wind tunnel for testing on Onogoro Island soon.

"One more point to be deducted is that the upper angle of deflection is too large.

"I knew it."

Since the retrofoil itself has an upper-rear angle effect, if a similar upper-rear angle to that of a straight wing is applied, the wing becomes too resilient.

This, Jin thought, was the cause of the reduced mobility.

"I'm not going to go into too much detail about aerodynamics, because I'm an amateur at this myself," he said.

In fact, the aircraft that Jin had built was flying forcefully with an engine power that could be said to be excessive .......

"I think it would be good if you could fix that."

I understand.

Jin-sama, what about mine?

"Yes, the next one is Rubina's ."

Yes!

"I like the overall design. You did a great job.

"Thank you very much!

Jin himself is not good at design, so he appreciates Rubina's work in this respect.

"However, the actual delta wing aircraft has little lift at low speeds, right?

"Uh, yes."

The density of the air is sufficient to support an airplane the size of an origami airplane, but not so with an actual airplane.

A large angle of attack (the angle of the wings relative to the direction of flight) is required for takeoffs and landings.

"When I flew in the competition, it was a model, so even a plane that size, the <>, could get enough lift, but not the actual plane, right?"

"Yes. ...... yes. ......"

"I was a Golem pilot, so I was able to land the plane without a hitch.

If you were human, you'd fail to land about three times out of ten," Jin said.

"That's a point deduction."

"I understand. ....... But what should we do ......?"

"That's also something we'll have to experiment with in the wind tunnel, like changing the angle of the leading edge of the same delta wing, or changing the cross-sectional shape."

"I understand!"

Talking with the two, Jin became more and more eager to participate.

As promised, Jin, with Reiko and Marikka as his assistants, built three small airships with attached to them, so that they could broadcast the battle from the air.