The next day, March 3.

Arnold will be a temporary lecturer at for about a week.

Jin decided to return to Horai Island.

On the way, he stops by the Kingdom of Selroa to tell them that Arnold will be a lecturer, and to hand them a report summarizing the past events.

"Well, Arnold, I'll see you later.

"Yes, thank you, Jin."

We can use the bracelets to contact each other if necessary, so that we can also go our separate ways.

Chel is with me so I don't have to worry.

"Thank you, Jin-dono, for everything you have done for us.

"Jin, see you again!　Come visit us sometime!

"Yeah, bye!"

Jin is seen off by Roar Eisker and the other members of the and Eira and the other members of the , and boards the .

Jin watches the float toward the morning sky,

"Someday, I'd like to build a plane that can fly faster than Jin-dono's .

Roar Aisker thought to himself.

* * * * *

The < with Jin on board arrives at Essiah, the capital of the Kingdom of Selroa, in one hour.

The familiar balloonists quickly gave way, and the plane was able to land easily.

"Welcome, Jin-dono!"

Prime Minister Dine greeted us.

"Arnold has been assigned as a temporary lecturer at Avalon, so I have brought a report on that and the past reports.

"Oh, thank you very much.

So I moved to the small conference room and submitted the report to Mr. Jin.

"I see......... you have done a lot in such a short period of time. That's what I'd expect from you, Jin-dono."

The Prime Minister skims through the report and closes it,

"You are a temporary lecturer, is that correct?

"That is correct. <

I see. Then shall we send some people from our country?

I think that would be a good idea.

A high-speed airship made in the Kingdom of Selroa can reach in about three hours.

There is also a way to connect with a transfer magic circle, but that has not been realized for security reasons.

Currently, the only routes that have a transfer system are between facilities related to <> (including the World Guard). (excluding Horai Island).

There is no law against it, but it is a self-imposed restriction.

(Ah, this time will be shortened if the Magi rocket engine (tentative name) is built.)

) It was Jin who had such hopes.

After a few more exchanges, Jin left the castle.

The Prime Minister and the King were both apparently very busy at the moment, and they did not want to be disturbed.

* * * *

The reason for ...... is just a front, but Jin was eager to study the < himself.

So he hurried back to Horai Island and hid himself in his workshop.

My assistant was Reiko as usual.

"First of all, let's make it as basic as ......, or rather as it was shown there. But at one-tenth the cost."

The engine uses explosive magic, so Jin is very careful.

"We'll use adamantite for the material, and make sure it's strong enough."

I understand. ......What kind of explosion magic do you use?"

"Well, ......, first of all, I'd use a ."

After deciding on the specifications, Jin and Reiko worked quickly and completed the prototype engine in about 30 minutes.

The engine consisted of a combustion chamber (?), an explosion chamber (?), and a jet. The engine consisted of a combustion chamber or rather an explosion chamber (?), a jet, a conductor for supplying mana to it, and the Magi Formula of <> engraved inside the explosion chamber.

The diameter of the jet port is 5 centimeters, and the total length is 15 centimeters.

It is fixed to the test bench in the workshop.

This test bench is used to measure the thrust of such a propulsion system, and is made of Magi-adamantite. It can withstand a thrust of up to approximately 10 tons.

A strong physical barrier (solid barrier) is deployed around it as a precaution, and the experiment is ready to begin.

The behavior of the robot will be recorded by the old man.

Reiko will take the place of the control core.

Reiko's processing power should be more than enough, Jin thought.

"Well then, <>"

In response to the magic key word (key word), the <> started to move.

"What?"

Red flames were shooting out of the jets.

The thrust gauge attached to the test bench read 200 kilograms.

"200 kilograms for something this big. That's amazing. ...... Reiko, can you stabilize it at 100 kilos?"

"Yes, father."

There was a time lag of about two seconds since this was the first time I had controlled it, but the thrust meter read almost steady at 100 kilometers.

"Good. Now I want you to increase the power little by little."

"Yes, father."

Under Reiko's control, the thrust begins to increase little by little.

The flames coming out of the jets begin to grow longer and longer. .......

"150 kilometers, 200 kilometers, 250 kilometers, 300 kilometers, 350 kilometers, 400 kilometers ......"

The jet flame is now about 50 cm long. The color has changed from red to yellow, indicating that the temperature has increased.

"500 km,550 km,600 km ...... Reiko, when it reaches 1000, keep it there."

"Yes, father."

The Magi rocket engine, which increased its output in an almost linear fashion, maintained a thrust of 1000 kilograms (equivalent to about 9800N). (This is equivalent to about 9800N.)

After holding for 10 minutes, Jin ordered an abrupt stop.

"<>"

The flame was extinguished at once, and the Magi rocket engine (tentative name) came to a standstill.

Jin immediately checked each part of the engine.

"The temperature is ...... 1100 degrees Celsius. That's still high."

The engine itself is adamantite, and the test bench is Magi-adamantite, so there is a margin for melting point, but Jin thought that heat countermeasures would be necessary if this engine was to be installed in a real machine such as a balloon or airship.

"The output is sufficient. Reiko, how about the controls?"

"Yes, father. I have tried small explosions at intervals of 0.2 seconds rather than medium explosions at intervals of 1 second, and the output is more stable, although it is more difficult to control.

"I see. ...... Mr. Elder, did you notice anything while you were looking at it?"

<

"That's for sure."

However, as for Jin, he remembers the image of a cartoon robot he saw when he was in the facility, which was flying in the sky while emitting flames from the rocket engine attached to its back.

I rather think that rockets are like that.

However, there is no doubt that heat will be a bottleneck for the widespread use of the rocket.

"Let's think about it again.

First is the phenomenon of <.

This time we used a <.

This is a magic that changes mana into sound, heat, light, and rapidly expanding gas.

The mana transformed into sound, heat, light, and gas disappears (or rather loses its physical properties) in a few seconds.

"From here, let's consider whether we can use magic with a little more efficiency.