Horai Island is located in the middle of the sea to the east of the Laurentian Continent, where many humans live.

The Tropic of Cancer runs right above the island, and the climate is close to the subtropical zone.

< and .

Now, Jin is working on solving a big problem.

The problem is <>.

The problem is to solve the distance of about 1,300 kilometers from Kunlun Island to Loizart, the capital of the Shoro Empire.

"In short, 200 kilometers per hour.

Jin thought that if he could travel in six and a half hours, he would be able to go anywhere in the known world in a day.

"But that's a bit of a stretch with today's airships, isn't it ......?"

Even with wind-shielding wards and a force field generator, the speed limit is 150 kilometers per hour.

Anything higher than that is not strong enough for emergency situations such as wind gusts.

"Let's rebuild it."

Once Jin decided to do so, he acted quickly.

He asks Reiko to prepare materials, and asks the old man to send and to help him.

Erza is now back at her parents' house in Shoro.

The workshop was built behind the institute, and is a large workshop dedicated to this purpose.

"The total length should be 40 meters.

The same size as the current one and the same size as the large ships of the Shoro Empire and other countries.

Now we're going to make a rigid airship.

Rigid airships do not inflate their air sacs by internal air pressure (helium), but rather, they have a metal frame with an outer skin to hold multiple air sacs inside.

Although there are various advantages and disadvantages, Jin decided to use this method in order to increase the rigidity of the airframe.

The shape of the plane is an elongated droplet with a stabilizing wing attached at the rear. It looks almost the same as what we see in Japan today.

However, the inside is completely different.

"The frame is 64 light silver.

The frame is made as light and strong as possible.

Of course, the outer skin and the air sacs inside are made of GS (Grand Spider) P (resin).

The gondola is not suspended but attached to the frame. This reduces the upward visibility, but reduces swaying.

"Should we make it a 30-seater?"

Of course, it is impossible to accommodate 30 passengers with the size of this air sac.

With these specifications, the maximum number of passengers is four. However, for a certain purpose, Jin wanted to make it a 30-seater.

The difference is made up by the .

"Father, shouldn't we use <>?

Reiko questioned.

"Yes, that would be fine. I'm still having a hard time grasping the reality of <>. ......"

"What do you mean?"

Jin stopped his hand and explained.

"It's called gravity, but the mass also seems to be changing, and even if you increase the gravity, the downburst doesn't occur. ......

A downburst is a strong downdraft that usually occurs as a reaction to an updraft generated by a cumulonimbus cloud, etc. Jin here uses the word "downburst" in the sense of <>.

However, since all ordinary magic is an extension of the laws of physics, Jin is concerned about it.

"I guess the other thing is efficiency.

The Force Generator consumes less free magic element (ether) than gravity control magic.

This alone is a sufficient reason.

"I understand."

Reiko seemed to agree. Jin begins to assemble the magi machine.

"Father, what is it?"

It's a gyro.

"A gyro?"

The gyro Jin is referring to is a disk that rotates at high speed. Jin thinks of his old gyro-based spinning tops, which he used to own.

What exactly is Jin is building would be a .

Inside a sealed enclosure, a disk made of adamantite is rotated by wind magic. The principle is the same as that of a turbine, but since there is no need to extract power from outside, the consumption of free magic element (ether) is negligible.

The turbine is attached to the motor to suppress the oscillation of the motor.

Since a single gyrostabilizer does not suppress the motion around the axis of rotation, we solved this problem by turning two orthogonal disks, which are <> as a <>.

"The propulsor should be a jet propulsor (jet thruster)."

To keep the efficiency of the propulsion system even in the rain, he decided to use <> instead of <>.

"Father, is this the way for the cabin?"

He had asked Reiko to build a cabin for him.

"Yes, I like it."

The material used for the interior was not the usual 64LBE ...... titanium, but an aluminum alloy.

It is called super duralumin, which is made by adding copper and magnesium to aluminum. It is inferior in corrosion resistance, but it is safe for indoor use.

There are 20 folding chairs and 10 built-in chairs. The texture of both chairs is the same. The folding chairs do not have the cheapness of auxiliary seats.

The backrests of the chairs can be folded down to a full-flat position for sleeping.

A lightweight refrigerator and a microwave oven (also known as a ) were also provided for refreshments.

There was a warp gate at the back of the small warehouse, so that unloaded items could be taken out.

The inside of the gondola is completely airtight and air-conditioned, so it should be comfortable.

A warp gate for escape was also installed as a separate frame.

"Well done. Thank you, Reiko."

Reiko looks happy and offers to help Jin further.

"Father, what else should we do?"

"I'm already 90% done. I need you to do the test flight."

"Yes, sir."

These tests are always done by Reiko. If she asks another golem to do it, she gets depressed.

<

Reiko reports from the sky through the manacam.

<

"Oh, that will come after the final outfitting. For now, check the operation and balance."

.

Reiko flew over Horai Island for a while, and then came down slowly.

Using the force field generator, she landed at her original position without missing a beat.

Reiko gave a detailed report as soon as she landed.

"Father, the overall performance is excellent. The stability is better than before and the speed can be increased. I think it's also more comfortable."

"Yes, thank you. And the shortcomings?

Yes. Yes. The operability is a little less because of the emphasis on stability. Also, you can't see the top of the screen at all. ......"

Jin realized what Reiko had told him. As a result of seeking stability with the gyrostabilizer, the response to changes in attitude, such as changes in direction, had become sluggish.

"Oh, I see. ...... that's the problem."

Jin pondered. While the gyrostabilizers would reduce the sway, they would also create resistance when the airship tried to change direction.

"Wait, what?　We can just detach the gyrostabilizers when we want to change the direction of the airship. ......

Jin's idea is to fix the gyrostabilizer to the airship in three axes and release those axes as needed.

The three axes are, of course, X-axis (forward/backward), Y-axis (left/right), and Z-axis (up/down).

Swaying is nothing but rotational motion around each of these axes. A change of direction is also a rotation around any of these axes or a combination of them.

Generally, the motion around the left-right axis of the fuselage, or swinging the nose up and down, is called pitching, and the motion around the front-back axis of the fuselage, or tilting the plane to the right or left, is called rolling.

And the motion around the vertical axis of the fuselage, i.e., swinging the nose to the left or right, is called yawing.

Naturally, changing direction is also a combination of these axes, which means that the aircraft is less likely to sway = less likely to change direction.

"The gyrostabilizer should be moved near the center of gravity, and the fixed axis should be released in conjunction with the directional rudder.

For example, when you want to change the direction to the left or right, you can release the fixation on the Z-axis to make it easier to yaw.

This would require a tremendous amount of time, money, and mechanism to achieve with a mechanical device, but with magical engineering, it requires only a little effort.

It may be a little similar to the way that microcomputer-controlled devices can be modified by changing the program.

"To increase the speed, I think we can go 200 km if we put up a wind shield.

Reiko thinks for a moment before replying.

Reiko thinks for a moment and replies, "Yes, I think so. With that kind of stability, perhaps.

"And for the view directly above us, we should install a < instead of a periscope ......."

He decided to install an optical periscope, like a periscope on a submarine, that would allow him to look straight up, above the air sacs.

"You can control it remotely in case something goes wrong," he said.

It's an alternative to autopilot.

"Lastly, I will install the given to us by No. 700672. The marker should be Horai Island."

With this, he would be able to return to Horai Island in an instant in case of emergency.

Thus, Jin's second airship, named , was completed.

Just at the same time that Erza returned home from her parents' house.

Erza rolled her eyes when she saw the new airship.