There is a facility called a wind tunnel.

Roughly speaking, it is a facility where <><>.

< indicates that the facility is isolated from the surroundings. The reason for this is to prevent damage to the surroundings and to regulate the flow of the wind, since strong winds are sometimes blown.

This <> is more important than one might think.

In reality, there may be few regular winds, but if the wind flow is disordered, the < in the experiment will be poor.

Usually, a scaled-down model is used for confirmation, but if a huge wind tunnel is used, a full-scale model of a car or a small airplane can be used for experiments.

Incidentally, there is also a method of conducting ship experiments using water or other liquids instead of wind (although it is not called a wind tunnel in such a case).

In general, fans are used for winds up to subsonic speeds, and compressed air is often used for winds above the speed of sound.

* * * * * * * * * *

<

"It is done, isn't it, Tester?

replied , the head of Onogoro Island's general management and magic brain.

The wind tunnel is as large as a large gymnasium and can test objects up to 20 meters in length and width and 10 meters in height.

The wind is generated by <, so experiments up to Mach 3 are possible.

The observer is protected by a , so it is possible to observe at close range, but normally the observer uses a special .

"The only thing we had to work on was the air circulation, but it seems to have worked."

<

In a closed space, the upwind side becomes negative pressure (lower atmospheric pressure) and the downwind side becomes positive pressure (higher atmospheric pressure) due to the blowing of wind.

To prevent this, an air inlet is provided on the downwind side, and the air is circulated to the upwind side and blown out, so that the wind tunnel can be operated more efficiently.

A similar method is also used in <, although the position of the air inlet is different. The position of the suction port is different. ...... (the details of which are omitted here).

"Now we can design and build a better performing aircraft."

Maricka muttered as she recalled the held the other day.

* * * * * *

Shu was the first to use the wind tunnel.

He had won the right to be the first to use the wind tunnel because he had made it to the finals.

"I can't wait to try it!"

Rubina is second, so she is participating in the experiment with Shu.

Rubina is the second one to participate in the experiment with Shu, partly because she wants to see with her own eyes what advice Jin has given her.

The two begin the experiment by observing from inside a special booth.

"Okay, here we go."

Shu sets up the <> in the wind tunnel and switches on the <>.

A weak breeze starts to blow.

The system increases the wind speed by pushing up a manual lever.

Shu slowly raised the lever.

Wind speed 5 meters......10 meters......15 5 meters......20 meters.......

The plane is still moving slightly.

Wind speed 30 meters......40 meters......5 0 meters......60 meters.......

At 70 meters, or about 250 kilometers per hour, the wingtips began to vibrate slightly.

"Well, in such a case, you can try ...... to see it through a modulation filter by irradiating a short wavelength light," he said.

In general, light with shorter wavelengths tends to be refracted more easily.

Therefore, there is a device that can observe the state of the air by irradiating electromagnetic waves of short wavelengths.

Not with the naked eye, but with a special optical device.

"Oh, there's a great vortex forming at the wingtips. ......"

Supercooling......When airplanes fly in an atmosphere containing water vapor that does not freeze even at sub-zero temperatures, airplane clouds can sometimes form at the wingtips.

This is thought to be the result of airflow turbulence at the wingtips (wingtip vortices or trailing vortices), which agitate the atmosphere and cause the supercooled water vapor to freeze.

"Jin-sama said that it might be a good idea to smash the wingtips or bend them upward."

"Mm. I think he said ......<> for the bending."

The vortexes that form mean that energy is being consumed, and by reducing the size of the vortexes, we can expect to increase fuel efficiency and speed.

The wind speed increased further, and when the wind speed exceeded 100 meters per hour, or 360 kilometers per hour, the horizontal tail fin began to experience slight vibration (flutter). "Oh, the main wing is fluttering," he said.

"Oh, it's because the airflow behind the wings is disrupted and the horizontal tail is in the middle of the disruption.

"Just like Jin-sama said."

"Yes. If we move it up or down another 50 or 60 centimeters, the problem will go away.

Eventually, Shu experimented with wind speeds of over 200 meters per hour, the equivalent of 800 kilometers per hour. Shu conducted the experiment.

"Well, I can see it clearly this way," he said.

Wind tunnels are very useful, aren't they?

"Yes, indeed. ...... Now let's experiment with Rubina's plane."

"Yeah, I'm looking forward to it."

* * * *

"Ah, ah, ah, ah......, great turbulence!"

Rubina's <> had a delta wing, and turbulence had been generated from the leading edge of the wing.

The <> is now catching the wind at a large elevation angle, and we are watching its behavior during takeoff.

"Uh, ......<>."

Rubina muttered in agreement as she looked at the guidebook on aerodynamics that the old man had compiled.

"......This is what is increasing the lift ....... I see."

Shu did the same.

This rudimentary knowledge of aerodynamics is based on what Jin learned in the process of model building, the academic books brought by Shuki Tsetsi from the original world, and the rules of thumb from countless experiments on Horai Island.

"Well, ...... the airflow around the vertical tail is not very favorable either."

Vertical tail wing located at the rear of the fuselage.

The vertical tail fin is located at the rear of the fuselage, and it was clearly seen to be subjected to the turbulence created by the canopy and other fuselage appendages.

The airflow in the lower half of the vertical tail is turbulent.

"You can see why it makes sense to have two vertical tails."

"Yeah. ...... I guess wind tunnel testing is still worthwhile."

Both Shu and Rubina were surprised that the shortcomings of the aircraft had become so clear in such a short time.

"It's much faster than building, flying, and improving ......."

"Absolutely."

I've been wanting to get my own wind tunnel," Shu said.

"I think I can make one for a one-tenth scale model by myself. ......"

"Jin-sama said that a model is different from a real aircraft, right?"

"Yes.

The theory of fluid dynamics in this area is difficult, and Jin does not fully understand it.

To put it in an extremely simplified manner, the atmosphere at one atmosphere pressure is than that of the actual model.

In other words, it is easier to float, but the resistance is greater.

To match these parameters, < is necessary, but this is a subject for engineering universities and above.

A word of caution.

"Once we have a rough idea with the small model, we can verify it with the full-scale model here in the wind tunnel, right?"

"That's what we'll do."

And if we keep repeating the experiment, we should be able to develop it into a theory someday.

"Yes, that's right."

Shu and Rubina thought that this might be their contribution to the world.